National Park Service

U.S. Department of the Interior

Natural Resource Stewardship and Science

Physical and Chemical Properties of Forest Soils

in the National Capital Region Network

Natural Resource Report NPS/NCRN/NRR—2020/2151
ON THIS PAGE

Soil profiles highlighting the diversity of horizons, color and texture found throughout the National Capital Region Network.

Photograph by: Daniel Colopietro 

ON THE COVER

The first author assessing soil profile characteristics in Catoctin Mountain Park.

Photograph by: Thomas Paradis
Physical and Chemical Properties of Forest Soils 

in the National Capital Region Network

Natural Resource Report NPS/NCRN/NRR—2020/2151

Matthew B. H. Bright,1 Ray R. Weil,1 Daniel Colopietro,

1

 and Bonnie Campbell2

1

University of Maryland 

Environmental Science & Technology Department 

1443 Animal Sciences Bldg 

College Park, MD 20742 

2

National Park Service 

National Capital Region Inventory and Monitoring Network

4598 MacArthur Blvd. NW 

Washington, DC 20007 

June 2020 

U.S. Department of the Interior 

National Park Service

Natural Resource Stewardship and Science 

Fort Collins, Colorado
ii

The National Park Service, Natural Resource Stewardship and Science office in Fort Collins, 

Colorado, publishes a range of reports that address natural resource topics. These reports are of 

interest and applicability to a broad audience in the National Park Service and others in natural 

resource management, including scientists, conservation and environmental constituencies, and the 

public. 

The Natural Resource Report Series is used to disseminate comprehensive information and analysis 

about natural resources and related topics concerning lands managed by the National Park Service. 

The series supports the advancement of science, informed decision-making, and the achievement of 

the National Park Service mission. The series also provides a forum for presenting more lengthy 

results that may not be accepted by publications with page limitations.

All manuscripts in the series receive the appropriate level of peer review to ensure that the 

information is scientifically credible, technically accurate, appropriately written for the intended 

audience, and designed and published in a professional manner. 

This report received formal peer review by subject-matter experts who were not directly involved in 

the collection, analysis, or reporting of the data, and whose background and expertise put them on par 

technically and scientifically with the authors of the information. 

Views, statements, findings, conclusions, recommendations, and data in this report do not necessarily 

reflect views and policies of the National Park Service, U.S. Department of the Interior. Mention of 

trade names or commercial products does not constitute endorsement or recommendation for use by 

the U.S. Government. 

This report is available in digital format from the NPS National Capital Region Network’s website

and the Natural Resource Publications Management website. If you have difficulty accessing 

information in this publication, particularly if using assistive technology, please email 

irma@nps.gov. 

Please cite this publication as:

Bright, M. B. H., R. R. Weil, D. Colopietro, and B. Campbell. 2020. Physical and chemical 

properties of forest soils in the National Capital Region Network. Natural Resource Report 

NPS/NCRN/NRR—2020/2151. National Park Service, Fort Collins, Colorado.

NPS 800/170921, June 2020
iii

Contents 

Page

Figures................................................................................................................................................... vi

Tables ................................................................................................................................................... vii

Appendices ........................................................................................................................................... vii

Executive Summary ............................................................................................................................viii

Acknowledgments .................................................................................................................................. x

List of Park Acronyms .......................................................................................................................... xi

Introduction ............................................................................................................................................ 1

Overview of the NCRN .................................................................................................................. 1

Importance of soils in the NCRN ................................................................................................... 3

NCRN soil monitoring objectives .................................................................................................. 3

Methods .................................................................................................................................................. 4

Field measurements: soil physical properties ................................................................................. 5

Bulk density (Db) ....................................................................................................................... 5

Infiltration and volumetric water content (θv) ........................................................................... 5

Soil penetration resistance......................................................................................................... 6

Aggregate stability..................................................................................................................... 7

Field measurements: soil profile description .................................................................................. 7

Field measurements: soil composite sampling ............................................................................... 7

Laboratory procedures .................................................................................................................... 7

Bulk density (Db) ....................................................................................................................... 7

Aggregate stability..................................................................................................................... 8

Chemical analyses..................................................................................................................... 8

Data analysis................................................................................................................................... 8

Results and Context ............................................................................................................................. 11

Soil physical properties ................................................................................................................ 11

Coarse fragments and clay percent .......................................................................................... 11
iv

Contents (continued)

Page

Bulk density (Db).....................................................................................................................13

Infiltration................................................................................................................................14

Volumetric Water Content (θv)................................................................................................16

Penetration resistance ..............................................................................................................17

Aggregate stability...................................................................................................................20

Soil chemical properties...............................................................................................................20

Total carbon and macronutrients.............................................................................................20

Micronutrients.........................................................................................................................23

pH, CEC, base saturation.........................................................................................................24

Contaminants overview...........................................................................................................27

Regression analysis ......................................................................................................................29

Statistical differences by horizon .................................................................................................30

Overview of soil classification, depths, and water tables in the NCRN.......................................33

Park Overviews ............................................................................................................................34

Antietam National Battlefield..................................................................................................34

Catoctin Mountain Park...........................................................................................................36

Chesapeake and Ohio National Historic Park .........................................................................38

George Washington Memorial Parkway .................................................................................40

Harpers Ferry National Historical Park...................................................................................42

Manassas National Battlefield Park.........................................................................................44

Monocacy National Battlefield Park .......................................................................................45

National Capital Parks-East.....................................................................................................47

Prince William Forest Park .....................................................................................................49

Rock Creek Park......................................................................................................................51

Wolf Trap National Park for the Performing Arts...................................................................52
v

Contents (continued)

Page

Discussion............................................................................................................................................55

NCRN soils data in the context of the I&M program ..................................................................55

NCRN soils data in the context of Eastern Deciduous Forests ....................................................55

NCRN soil patterns and ecological insights.................................................................................56

Future directions...........................................................................................................................58

Literature Cited ....................................................................................................................................60
vi

Figures

Page

Figure 1. Location of National Capital Region parks (highlighted in green) and 

physiographic regions within the NCRN. (Source: NPS NCRN website) ............................................2

Figure 2. Layout of vegetation plots. Soil samples were taken along three 15-m transects, 

radiating from the center of the plot.......................................................................................................5

Figure 3. Distribution of coarse fragments and clay percent by horizon in all parks of the 

NCRN. Errors bars represent standard error of the mean (S.E.M.) throughout all figures..................13

Figure 4. Db in the eleven parks of the NCRN. Parks that share the same letter are not 

statistically different.............................................................................................................................14

Figure 5. Unsaturated and saturated infiltration across the NCRN parks. Parks with 

values that are significantly different do not share the same letter over bars. .....................................16

Figure 6. θv pre and post-infiltration in the parks of the NCRN. Parks with values that are 

significantly different do not share the same letter over bars. .............................................................17

Figure 7. Penetration resistance showing a positive linear relationship with depth in the 

parks of the NCRN...............................................................................................................................18

Figure 8. Differences in penetration resistance between parks from 5 to 30 cm depth. 

Parks with values that are significantly different do not share the same letter over bars. ...................19

Figure 9. Distribution of total C and macronutrients (except Sulfur) by horizon in all 

parks of the NCRN...............................................................................................................................22

Figure 10. Distribution of micronutrients by horizon in all parks of the NCRN. ...............................24

Figure 11. Distribution of pH, CEC, and Base Saturation by horizon in all parks of the 

NCRN. .................................................................................................................................................26

Figure 12. Distribution of contaminants by horizon in all parks of the NCRN. .................................28

Figure 13. Regressions showing relationship between soil chemical variables in the 

NCRN. .................................................................................................................................................30

Figure 14. Total C, extractable P and K levels in the A composite and B horizons of the 

NCRN. Parks with values that are significantly different do not share the same letter next 

to their bar............................................................................................................................................32
vii

Tables

Page

Table 1. Parks and soil monitoring plots in the NCRN.........................................................................4

Table 2. Assorted soil profile characteristics from parks in the NCRN..............................................33

Table 3. Soil physical and chemical characteristics by horizon in ANTI. ..........................................35

Table 4. Soil physical and chemical characteristics in CATO. ...........................................................37

Table 5. Soil physical and chemical characteristics in CHOH............................................................40

Table 6. Soil physical and chemical characteristics in GWMP...........................................................41

Table 7. Soil physical and chemical characteristics in HAFE.............................................................43

Table 8. Soil physical and chemical characteristics in MANA...........................................................45

Table 9. Soil physical and chemical characteristics in MONO...........................................................46

Table 10. Soil physical and chemical characteristics in NACE. .........................................................48

Table 11. Soil physical and chemical characteristics in PRWI...........................................................50

Table 12. Soil physical and chemical characteristics in ROCR..........................................................52

Table 13. Soil physical and chemical characteristics in WOTR. ........................................................53

Appendices

Page

Appendix A..........................................................................................................................................64

Appendix B..........................................................................................................................................71

Appendix C..........................................................................................................................................77
viii

Executive Summary

Soils are the foundation of terrestrial ecosystems and affect all parts of the environment: water, 

atmosphere, animals, vegetation, and climate. To better understand soil function and the influence of 

soil morphology and nutrients on vegetation in urban and semi-urban forested ecosystems of the 

Mid-Atlantic, the National Capital Region Network (NCRN) collected a suite of soil physical and 

chemical data in the 426 permanent vegetation monitoring plots in 11 park units between 2007 and 

2017.

This report details the data collection methods and summarizes the soil physical and chemical data.

The objectives of the report are to:

1. Describe the physical and chemical characteristics of soils in the NCRN. 

2. Provide baseline soils data to aid park managers and future long-term soil monitoring in the 

NCRN.

3. Identify statistically significant differences among soil variables found at NCRN parks and

discuss the probable causes of these differences.

4. Highlight individual plots with outlier characteristics that might negatively affect ecosystem 

function or require further investigation.

5. Discuss future opportunities for soil monitoring and scientific studies in the NCRN.

At each of the 426 plots, a full soil profile description was made to a depth of 100 cm (when 

possible) consisting of: master and subordinate horizons, clay percentage, coarse fragments, colors, 

redoximorphic features, consistence, and soil structure. Measured soil physical variables were: 

aggregate stability, bulk density (Db), unsaturated and saturated infiltration, penetration resistance, 

and volumetric water content (θv). Soil chemical analyses were conducted on master horizons to a 

depth of 100 cm and on composite samples from the surface of the plot (O and A horizons) to 

account for intra-plot spatial variability. Analyzed soil chemical variables included: total carbon (C), 

total nitrogen (N), pH, cation exchange capacity (CEC), and extractable phosphorus (P), potassium 

(K), calcium (Ca), magnesium (Mg), manganese (Mn), iron (Fe), zinc (Zn), copper (Cu), 

molybdenum (Mo), cadmium (Cd), Chromium (Cr), and lead (Pb). The Methods section details data 

collection, inventory and analyses.

The Results section is divided into six subsections. ANOVAs were used to determine significant 

differences between variables by park, and the first subsection highlights the significant differences 

between physical characteristics while the second subsection focuses on chemical variables. The 

third subsection summarizes the results of a regression analysis that was conducted to determine the 

relationship between three master soil variables—C, pH, and clay percent—and all other chemical 

variables. The fourth subsection details significant chemical variable differences horizon by horizon 

among the parks. An overview of the NCRN’s soil series, relative soil depths, drainage and other 

horizon characteristics is presented in the fifth subsection. To assist NPS managers, the sixth and 

final subsection summarizes and inventories the soils in each of the region’s 11 parks including 
ix

individual plots with unique soils features and other outstanding soil characteristics within the 

context of the NCRN. 

Overall, the Results show a high diversity of soil types across the NCRN, including 85 soil series

from 4 soil orders. Ultisols dominate the region and are found in approximately 60% of plots

according to Web Soil Survey. Alfisols comprise 22% of the plots—mostly in the Ridge & Valley 

physiographic region. Inceptisols are found in many of the mountain plots (17% of the total), and six 

plots located near rivers or streams have Mollisols.

Physical characteristics also vary greatly. Rocky soils in Catoctin were typically very shallow, 

whereas soils of the National Capital Parks-East on the Coastal Plain were frequently quite deep. The 

subsoil (B horizon) of Harpers Ferry contained half the clay of subsoil in Antietam (16% compared 

to 32%). The physical characteristics affected soil physical measurements. For instance, mean 

infiltration rates in Antietam were one third of the mean rate in Catoctin, and the lowest Db values of 

the region were also observed at Catoctin. Manassas National Battlefield Park, with high amounts of 

clay, could also hold the greatest amount of water in the region. 

Chemical characteristics likewise differ significantly by park, with Prince William Forest Park 

having the lowest nutrient levels in the NCRN and the parks in the Blue Ridge and Ridge & Valley 

physiographic regions—Antietam, Catoctin, and Harpers Ferry—having the highest. Nutrient 

concentrations were far greater in the surface horizons (O and A) and decreased with depth. Very few 

soil contaminants were found in the NCRN, and overall the soils of the region are fertile.

The Discussion section highlights the importance of this report both within the context of the I&M 

program and also within the Mid-Atlantic region, and furthermore it highlights the report’s potential 

to act as a template for future NPS soil inventory efforts. It then presents important patterns and 

ecological insights gleaned from the data. Finally, it outlines four important areas for future research

that can be built off of the data in this report.

This report documents the first comprehensive assessment of soil chemical and physical 

characteristics in the NCRN. It provides valuable baseline data for future monitoring and advances 

our understanding of Mid-Atlantic forest ecology. Moreover, the soils data can be used in 

conjunction with vegetation data to guide forest management strategies and assess ecosystem health 

and services. Above all, this soils report furthers a key tenet of the NPS mission, “To guide park 

management using science.”
x

Acknowledgments

The authors wish to acknowledge the hard work and dedication of Gary Kaplan, Bernice Hwang, 

Shelley Porter, Elan Argulies, Kristen Felix, Melinda Householder, Jenna Smith, Christa Nye, Sarah 

Schmid, Paul Bickmore, Sarah Clark, Jennifer Keller, Nancy Khan, Christina Congedo, Christina 

Demariano, Ryan Adams, David Forgy, Tyler Witkowski, Shannon Beston, Adam Lee, Philip 

Schwartz, Cathy Wang, and Chris Palardy who, to varying degrees, collected soils data in the field 

and processed it in the Center for Urban Ecology lab from 2007 to 2017. We thank you for all the 

sweat shed, gnats swallowed, ticks picked, equipment carried, barberry endured, mosquito bites 

acquired, and poison ivy rashes suffered in the pursuit of quality soils data. In addition to the work of 

biological science technicians and interns, assorted members of the vegetation monitoring staff

routinely pitched in to help with field assays. Thanks go to Dr. Jason Lessl of the University of 

Georgia Soil, Plant, and Water Lab for explaining laboratory analyses. The Resource Managers 

across the NCRN provided valuable logistical help to coordinate sampling trips. Several reviewers 

provided valuable feedback on drafts of this manuscript, especially David K. Swanson of the NPS 

Arctic I&M Network; thank you. Finally, we are very grateful for the help, guidance, and 

encouragement of NCRN staff, including John Parrish, John Paul Schmit, Pat Campbell, Geoffrey 

Sanders, Liz Matthews, Leslie Frattaroli, Megan Nortrup, and Andrejs Brolis. Your advice, critical

reviews and comments on this report were invaluable. 
xi

List of Park Acronyms

ANTI: Antietam National Battlefield

CATO: Catoctin Mountain Park

CHOH: Chesapeake and Ohio National Historical Park

GWMP: George Washington Memorial Parkway

HAFE: Harpers Ferry National Historical Park

MANA: Manassas National Battlefield Park

MONO: Monocacy National Battlefield Park

NACE: National Capital Parks-East

PRWI: Prince William Forest Park

ROCR: Rock Creek Park

WOTR: Wolf Trap National Park for the Performing Arts
1

Introduction

Overview of the NCRN

The National Parks Omnibus Management Act of 1998 directed the National Park Service (NPS) to 

“undertake a program of inventory and monitoring of National Park System resources to establish 

baseline information and to provide information on the long-term trends in the condition of National 

Park System resources” (Fancy et al. 2009). With the enactment of that legislation, the Inventory and

Monitoring (I&M) Program was established to organize the nation’s approximately 270 parks into 32 

I&M networks based on geography and common natural resource characteristics. 

Among the 32 I&M networks, the National Capital Region Network (NCRN) is the smallest by area.

It consists of 11 park units situated predominantly in the Eastern Deciduous Forest ecosystem and 

spans 4 physiographic regions: Coastal Plain, Piedmont, Blue Ridge, and Valley & Ridge from east 

to west respectively (Figure 1). The underlying geology and topography are diverse. Parks situated 

on the Coastal Plain—NACE and a portion of PRWI—lie mostly at or near sea level and were 

primarily formed from sediments deposited by ancient seas and rivers that covered the area. Moving 

west, the Piedmont Plateau is sandwiched between the Coastal Plain and Blue Ridge and consists of 

metamorphic, igneous and sedimentary rocks punctuated by a fall line on its eastern edge. The Blue 

Ridge, which forms the easternmost edge of the Appalachian Mountains, is one of the oldest

mountain chains in the world. The geology of this region is predominantly ancient igneous and 

metamorphic rocks. At the western flank of the NCRN, the Ridge and Valley system encompasses 

the Great Appalachian Valley (Hagerstown and Shenandoah being local variants) and other smaller 

valleys formed from carbonate rocks that were eroded down to form low points between more 

resistant sedimentary rocks of the ridges.
2

Figure 1. Location of National Capital Region parks (highlighted in green) and physiographic regions 

within the NCRN. (Source: NPS NCRN website)

Annual precipitation in the region is approximately 1000 mm spread relatively evenly throughout the 

year, though the months of May through October generally experience greater precipitation. Monthly 

average air temperatures range from 0 to 23oC (January and July respectively).

Forests cover nearly three quarters of the area of the NCRN parks (Schmit et al 2012). Long-term 

forest monitoring plots in the NCRN have documented 81 tree species in the region, a large 

proportion of which are deciduous hardwoods such as tulip tree (Liriodendron tulipifera), red maple 

(Acer rubrum), American beech (Fagus grandifolia), and white oak (Quercus alba) (Schmit et al. 

2012). Virginia pine (Pinus virginiana) is the most common coniferous tree in the region. Tree 

density (the number of woody plants ≥10 cm diameter at breast height) averages 400 ha−1 across the 

region, with park averages ranging from 200 to 500 trees ha−1.

The small size of the NCRN belies its large environmental significance. The importance of the 

region’s parks arises from their location, ecology, and ecosystem services. At the center of the 6th

largest metropolitan area in the country—DC-VA-MD-WV—with a population of over 6.2 million 

(U.S. Census Bureau 2018), the NCRN provides important recreational opportunities to an urban 

population. Four of the NCRN’s 11 parks (GWMP, CHOH, ROCR, NACE) recorded over 1 million 

recreational visits in 2018, and GWMP was ranked the 7th most visited park in the nation with 7.3 

million visits (NPS Stats 2018). Ecologically, the NCRN sits squarely within the drainage basin of 

the country’s largest estuary—the Chesapeake Bay. Thus, forests in the region function as a water 

purification system for the Bay. Moreover, eastern deciduous forests in the Mid-Atlantic U.S. have 

been recognized for their high biodiversity and conservation importance (Olson and Dinerstein 2002; 
3

Miller et al. 2018). In addition, urban forests sequester significant amounts of carbon (C) and are 

important for climate change mitigation (Nowak and Crane 2002). Finally, urban forests perform

many other ancillary ecosystem services. For example, Long et al. (2019) recently showed that urban 

forest clusters in Raleigh, NC, similar to those found throughout the NCRN, helped protect 

neighboring trees in ornamental gardens from insect pests.

Importance of soils in the NCRN

By serving as a medium for plant growth, a habitat for microorganisms, a water-supply and 

purification system, an engineering medium, a modifier of the atmosphere, and a recycling system 

for nutrients and wastes (Weil and Brady 2017), soils are critical to the ecosystem services and 

ecology of the NCRN. Smith and Wilcock (2015) found that the sediment yields (a proxy for 

erosion) from forests in the Upper Patuxent watershed of MD were 28% of the yields from suburban 

landscapes and 35–64% of the yields from agricultural lands. Johnson and Richter (2010) described 

the important benefits of Mid-Atlantic forest soils for reducing the harmful effects of Pb and other 

heavy metals. Shen et al. (2016) discovered that soil pH in a Mid-Atlantic temperate forest in 

Virginia was an excellent predictor of invasive plant species. Szlavecz et al. (2011) studied the 

abundant earthworms in forest soils of the Piedmont plateau in MD, and found that they have 

significant ecological effects on leaf litter decay, soil fungi community dynamics, and even plant 

community selection (Szlavecz et al. 2011). Dixon et al. (1994) discovered that 64% of the total C in 

forest ecosystems of the contiguous U.S. was stored in the soil, whereas only 36% was contained in 

the vegetation, highlighting the carbon sequestration potential of forest soils in the Mid-Atlantic.

To measure the effect of soils on the forest ecosystems of the NCRN, the region began a soil 

inventory and monitoring program in 2007. The overarching goal was to integrate soils data with the 

existing vegetation, animal, and water monitoring programs to understand more completely 

ecosystem function. Accordingly, the NCRN developed protocols to measure soil chemical and 

physical properties across its 11 parks.

NCRN soil monitoring objectives

This report summarizes the soils data collected in the NCRN. The objectives are to: 

1. Inventory and describe the physical and chemical characteristics of forest soils in the NCRN. 

2. Provide baseline soils data to aid park managers and future forest soil monitoring in the 

NCRN.

3. Identify differences in forest soil variables between parks and the significance of these 

differences to overall soil quality and ecosystem function.

4. Highlight individual monitoring plots with outlier characteristic that might negatively affect 

ecosystem function or require further investigation.

5. Discuss future opportunities for soil monitoring in the NCRN.
4

Methods 

Soil monitoring was conducted at the long-term forest vegetation plots described in Schmit et al. 

(2012). In total, 426 plots were sampled across the 11 park units of the NCRN (Table 1), which 

represents a density of 1 plot for every 62 ha of parkland.

Table 1. Parks and soil monitoring plots in the NCRN.

Park Code State Physiographic Region

Number of 

Plots

Antietam NB* ANTI MD Valley and Ridge 13

Catoctin Mountain Park CATO MD Blue Ridge 46

Chesapeake & Ohio Canal 

NHP

CHOH DC/MD Coastal Plain/Piedmont/Valley and Ridge 67

George Washington Memorial 

Parkway

GWMP DC/VA Coastal Plain/Piedmont 28

Harpers Ferry NHP HAFE WV/MD Blue Ridge/Valley and Ridge 21

Manassas NB Park MANA VA Piedmont 19

Monocacy NB MONO MD Piedmont 15

National Capital Parks – East NACE DC/MD Coastal Plain 47

Prince William Forest Park PRWI VA Piedmont/Coastal Plain 145

Rock Creek Park ROCR DC Coastal Plain 19

Wolf Trap NP for the 

Performing Arts

WOTR VA Piedmont 6

* NB is a national battlefield; NHP is a National Historic Park; NP is a National Park.

Vegetation plots were laid out as a circle with a 15-m radius covering a total area of 707 m2. For soil 

sampling, three 15-m long transects radiated out from the center of each plot at 120°, 240°, and 360°

(Figure 2). In situ sampling efforts were divided into three components: 1) physical assays performed 

along the transects, 2) a soil profile description at the center of each plot, 3) a composite sample of O, 

A, and subsoil horizons taken from the top 15 cm of soil along the transects for soil chemical 

analyses. 
5

Figure 2. Layout of vegetation plots. Soil samples were taken along three 15-m transects, radiating from 

the center of the plot.

Field measurements: soil physical properties

Six physical measurements were performed at the 8-m mark (except for aggregate stability) along 

each of the three plot transects: bulk density (Db), unsaturated infiltration, saturated infiltration,

volumetric water content (θv), soil penetration resistance, and aggregate stability.

Bulk density (Db)

Bulk density (Db) was measured using a variation of the core method (Soil Survey Staff 2014a). In 

brief, loose leaves and duff were scraped off the top of the soil until the mineral soil was exposed.

Metal rings of a known volume were then driven into the ground until their top was level with the 

surface of the mineral soil. The ring was then carefully excavated, and the soil shaved off flush with 

the top and bottom of the ring. The soil and coarse gravel fragments inside each ring were then 

placed in a sealed plastic bag and taken back to the lab for further analysis (see laboratory procedures 

section for additional details). 

Infiltration and volumetric water content (θv)

A variation of the Natural Resources Conservation Service Infiltration Method was used to measure 

unsaturated and saturated infiltration (NRCS 1998). In brief, polyvinyl chloride (PVC) rings 15 cm in 

diameter and 15 cm high were pounded into the ground until 10 cm of the height of the ring were 

above ground and 5 cm were below ground. When present, loose leaf litter was removed from the 

surface of the soil on the inside and around the edges of the ring. Next, a two-pronged ECH2O EC-5 

capacitance moisture sensor (Decagon Devices, Pullman, WA) was inserted into the ground to 

measure θv (water volume/soil volume * 100) in the mineral soil (not O horizon) at 90o, 180o, 270o, 

and 360o around the edge of the ring. An average of the four measurements/ring was recorded as θv 

pre-infiltration (%). 

After that, a thin layer of plastic was placed on the inside of the infiltration ring making sure to cover 

the entire surface area of soil and ring walls. 1 L water was gently added to the inside of the ring
6

covered in plastic wrap. The plastic wrap was then quickly removed from under the 1-L of water 

exposing the entire soil surface area inside the ring to water at the same time. As soon as the water hit 

the soil surface, a stop watch was started and only stopped when all water infiltrated into the soil.

The time that it took for 1 L of water to fully enter the soil was entered into the following equation to 

calculate an unsaturated infiltration rate (cm hr−3):

UUUUUUUUUUUUUUUUUUUUUU ii iiiiii iiii (cccc h −3) = 1LL WW (1000cccc3) II RR RR AA (cccc2 ⁄ )

UUUUUUUUUUUUUUUUUUUUUU RR RR II TT ( )⁄3600

Saturated infiltration was measured within 5 minutes after unsaturated infiltration was completed. 

The same process that was used to measure unsaturated infiltration was repeated for saturated 

infiltration and the time that it took for 1 L of water to fully enter the soil a second time was recorded 

and used to calculate saturated infiltration (cm hr−3) using this equation:

SS ii iiiiii iiii (cccc h −3) = 1LL WW (1000cccc3) II RR RR AA (cccc2 ⁄ )

SS RR RR II TT ( )⁄3600

After infiltrations were completed, 30 minutes were allowed to elapse before the capacitance probe 

was used to take four readings on the inside of the ring where water infiltrated. The average of those 

readings was recorded as θv post-infiltration (%). 

Soil penetration resistance

For penetration resistance, the NCRN began its monitoring program using a FieldScout SC900

electronic soil compaction probe (Spectrum Technologies Inc., Aurora, IL) that recorded penetration 

resistance in kilopascals (kPa) every 5 cm from the soil surface to a depth of 35 cm as the probe was 

pushed into the soil. This meter was used to monitor approximately one quarter of the plots, and the 

measurement was conducted on the inside of the infiltration ring after θv post infiltration was

recorded.

For the rest of the plots, a variation of the cone penetrometer test and standard penetration test was 

used to determine penetration resistance in kilopascals (ASTM 1984, 1995). In summary, a drop 

hammer penetrometer was used to calculate penetration resistance at 5 cm intervals to 35 cm depth 

on the inside of infiltration ring after θv post infiltration was recorded. The drop hammer device 

consisted of a pole 165 cm tall with a pointed end for insertion into the ground. A cylindrical weight 

(2 kg) was manually slid along the pole from a fixed height in order to strike a peg to drive the pole 

into the ground. The number of times that the 2 kg cylindrical weight was dropped to drive the pole 5 

cm into the ground was recorded and used in conjunction with the height that 2 kg weight slid along 

the pole and the weight of the cylinder (2 kg) to determine penetration resistance in kPa using the 

following three equation sequence to calculate first work (joules), then force (newtons), then 

resistance (kPa):

WW WW (jj ) = nn h hii × gg gg × h h × ww h

FF ( ) = ww (jj )

pp ii ( )
7

PP ( ) = FF ( ) × 10

ππ( pp )2

Aggregate stability

At 4, 8, and 12 m along each transect, leaf litter and O horizon was removed from the soil surface 

before a trowel was used to gently remove a soil aggregate 0.5–1 cm in diameter from the top 5 cm 

of mineral soil surface (9 aggregates/plot). The aggregates were placed on a metal mesh screen 

attached to a small disk made from 1-cm PVC pipe. These screens were placed into tackle box for 

transport back to the Center for Urban Ecology. Aggregates were collected for approximately half of 

the plots in the NCRN because of the difficulty of transporting samples back to the lab without 

breaking them. 

Field measurements: soil profile description 

A bucket auger was used to excavate a soil core to a depth of 100 cm (when possible) within a 1-m 

radius of the center of each plot. The soil was laid out horizontally on a plastic sheet with ruler 

markings in centimeters corresponding to the depth of the sample. When bedrock was encountered 

less 100 cm from the soil surface, up to 3 more cores were excavated adjacent to the center of the 

plot, and the deepest core was used to complete a soil profile description. The description was carried 

out according to guidelines from the Natural Resources Conservation Service (NRCS, 2012) and

consisted of the master and subordinate horizon sequence with lower boundary depths, the textural 

class of each horizon and clay percentage (determined by feel), the predominant matrix color using 

the Munsell color scheme for each horizon, the presence and depth of redoximorphic (redox) features 

in a horizon (depletions and concentrations), and a visual estimation of coarse fragments (rock and 

mineral fragments >2 mm diameter). Approximately 75 g of soil was taken from each horizon, 

placed in a sealed plastic bag and transported back to the Center for Urban Ecology for further 

processing. 

Field measurements: soil composite sampling

At 4, 8, and 12 m from the center of the plot along each of the three 15-m long transects, a soil probe 

was used to collect a sample to a depth of 15 cm (9 probe points total/plot). The soil sample at each

probe point was then separated into O horizon, A horizon, and Subsoil horizon (defined here as any 

soil below the A horizon) components (when those horizons were present), and each fraction was 

placed into a separate container. This process was repeated at all 9 locations, and then a composite 

sample of O, A, and Subsoil horizons was made by thoroughly mixing the soil from the 9 probe 

points. The O, A, and subsoil composite samples were sealed in a plastic bag and transported to the 

Center for Urban Ecology for further processing. 

Laboratory procedures

Bulk density (Db)

Db samples were weighed fresh, and then the soil was passed through a 2 mm sieve. Any coarse 

fragments >2 mm in diameter that did not pass through the sieve were weighed. The sieved soil was 

then placed in a 105oC oven for 24 hours and re-weighed (weight dry soil). The volume of the coarse 
8

fragments in Db samples was calculated using the following equation which assumes a coarse 

fragment density of quartz—2.65 g cm−3 (the most common mineral in the NCRN):

VV cc (cccc3) = ww h cc ( )

DD cc (2.65 cccc−3)

Db was calculated accounting for the volume of coarse fragments in the Db rings according to this 

equation:

DDbb ( cccc−3) = ww h ( )

(cccc3) − cc (cccc3)

Aggregate stability

Aggregate stability was measured using a variation of the slake test (NRCS, 2019) and given a 

stability class rating of 1–6. Briefly, aggregates were air-dried at the lab before the mesh screen and

1-cm PVC apparatus that they rested on was submersed in distilled water for a total of 5 minutes.

Soil stability was rated as a function of the time that it took for the aggregate to disintegrate. If 50% 

of the aggregate disintegrated with 5 seconds after insertion in water, the aggregate was rated as a 1.

If 50% was gone between 5–30 seconds, the aggregate was a 2. At the end of 300 seconds (5 

minutes), if >50% was gone, the aggregate was a 3, but if 50–75% of the aggregate remained, the 

stability class was 4, and for 75–99% of the aggregate remaining after 5 minutes, the class was a 5.

Aggregates that showed no signs of disintegration within 5 minutes were classified as a 6.

Chemical analyses

Profile horizon samples and composite O, A, and Subsoil samples were air-dried on paper plates and 

passed through a 2-mm sieve before a subsample of 50–100 g was sent for chemical analyses to the

University of Georgia Agricultural and Environmental Services Laboratories (AESL) Soil, Plant, and 

Water lab (SPW). Total carbon (C) and total nitrogen (N) were measured by high temperature 

combustion at 13500C using an Elemental Combustion Analyzer, Model Vario Max (Langenselbold, 

Germany). The Mehlich-1 soil test extractant (Mehlich 1953) was used to extract plant 

macronutrients (P, K, Ca, Mg, Mn, and Zn), plant micronutrients (Fe, Zn, Cu, Mo), and soil 

contaminants (Cd, Cr, Pb). The Mehlich-1 extraction was followed by analysis on an Inductively 

Coupled Plasma Spectrograph (ICP). All extractable levels were expressed as mg element per 

kilogram soil (mg kg−1). Soil pH was measured on an automated analyzer with direct titration 

capabilities using a 1:1 soil:0.01 M CaCl2 suspension. An indirect measurement of cation exchange 

capacity (CEC) was determined by adding the milliequivalents of bases (Ca, Mg, K, and Na) present 

in the Mehlich-1 extract and the milliequivalents of exchangeable hydrogen as determined by direct 

titration with 0.023M Ca(OH)2 and the units were expressed as milliequivalents per 100 grams of soil

(Georgia Cooperative Extension 2008). The percent base saturation (BS) in the soil was calculated as 

the ratio of Ca, Mg, K, and Na to that of CEC. 

Data analysis

A thorough quality analysis/quality control (QA/QC) process was initiated for the NCRN soils 

dataset. Raw data were graphed and compared to ratios of known correlated soil physical and 

chemical variables to identify outliers and possible artifacts. Outliers or artifacts were excluded or 
9

corrected (if possible). Corrections were informed by field notes recorded at the time of data 

collection. 

For the analysis presented here, all data were grouped together and analyzed by park. Organizing 

physical and chemical properties by physiographic region, geology, or parent material (the material 

that the soil formed from) would undoubtedly have yielded more ecologically meaningful insights, 

but the rationale for choosing to categorize by park was based on the chief objective of the I&M 

Program—to guide park management using science. In addition, this report is primarily an inventory

of the soils in the NCRN, and parks served as a convenient framework to categorize the data. 

The NRCS Web Soil Survey (Web Soil Survey 2019) was used to determine the soil series at each 

plot using the GPS coordinates of the sampling site. When more than one possible soil series was 

present, the augered soil profile description was compared to the USDA’s Official Soil Series 

Descriptions (USDA 2019) to determine the most probable soil series. A list of soil series in the 

NCRN can be found in Appendix D. At the beginning of the “Park overviews” section, a general 

survey of important NCRN soil characteristics is given (Table 2): the number of soil series in each 

park, the relative depths of soils across the region, the presence or absence of three important soil 

horizons across the region (O, Bt, Bw), and the number of poorly drained soils. 

Kruskal-Wallis (non-parametric) ANOVAs were used to determine statistically significant 

differences (p<0.05) between parks for the soil physical properties: Db, infiltration rates, θv, 

penetration resistance, and aggregate stability. Dunn’s multiple comparisons post hoc test was 

performed to identify which park/s were significantly different. Plots where the FieldScout SC900 

was used to collect penetration resistance data were not double sampled with the drop hammer 

method, so a true comparison of the methods is impossible in this report. However, a T-test was used 

to determine if plots with penetration resistance values from the FieldScout SC900 were significantly 

different from plots with penetration resistance values using the drop hammer method. Finding no 

significant differences, data from both measurement methods were analyzed together. 

Descriptive statistics (mean ± standard deviation) were calculated for all chemical characteristics

(macronutrients, micronutrients, contaminants, pH, CEC, BS), clay content, and percentage of coarse 

fragment by master horizon (O, A, E, B, C) for each park and are shown in tabular form in the “Park 

Overviews” section. The distribution of these data (mean ± standard error of the mean {SEM}) 

throughout all parks of the NCRN are shown in figures in the “Soil physical properties” section (clay 

content and coarse fragments) and in the “Soil chemical properties” section (all other data).

To account for subordinate horizons with the same master horizon designation (e.g., Bt1, Bt2, Bt3 or 

Ap1, Ap2), a weighted average was used that accounted for the thickness of each of the subordinate 

horizons in relation to the thickness of the entire master horizon. For example, a profile description 

might contain a 13-cm thick Bt1 horizon, a 23-cm thick Bt2 horizon, and a 33-cm thick Bt3. The 

entire thickness of the B horizon, therefore, was 69 cm, and a weighting factor of 0.19 (13/69) was 

calculated for the Bt1, 0.33 for the Bt2, and 0.48 for the Bt3. These weighting factors were then 

multiplied by the quantitative chemical data for each of their respective horizons and then summed to 

give the weighted average of the entire B horizon. The “Horizon midpoint” designation in the “Park 
10

Overviews” data tables is the depth from the soil surface where the midpoint of the entire master 

horizon (the sum of the Bt1, Bt2, Bt3 to use the example above) occurred. 

Chemical data for the A horizon composite samples is shown separately (Composite A samples are 

referred to in in figures as “A comp,” and profile samples are “A prof.”). The rationale to analyze 

profile A and composite A samples distinctly was based on two reasons. First, the composite samples 

accounted for the spatial variability across the plot, whereas profile samples were taken from one 

point at the center of the plot. Second, composite sampling was confined to the top 15 cm of the soil

(i.e., If an A horizon continued deeper than 15 cm in the probe, nonetheless, only the portion of the A 

horizon from 0–15 cm was included in the sample.), but profile A samples could encompass an Ap 

horizon to a depth of 30+ cm. Thus, “A comp” samples more closely captured the surface A horizon 

development from the reforestation of plots under NPS management, and “A prof” samples 

contained a mixture of legacy A horizon from agriculture and more recent carbon accumulation from 

afforestation. Composite O horizon samples were sent for chemical analysis in lieu of profile O 

samples. The reason was that O horizons were typically 2 to 5 cm thick, and not enough sample 

could be obtained from the profile core. In addition, O horizons were sometimes present at certain 

transects in the plot but absent from the center point. The “Horizon midpoint” for O horizons was

recorded from the profile core, however, when “Horizon midpoint” is blank, it indicates that an O 

horizon was not present at the center of the plot. Subsoil composite samples were not analyzed. 

Regression analysis was used to evaluate relationships between soil properties. Total C, pH, and clay 

percent (often described as master variables because they affect so many other soil properties) were 

chosen as predictor variables for all other chemical variables.

Finally, Kruskal-Wallis ANOVAs were used to determine statistically significant differences 

(p<0.05) between parks for the chemical variables in each master horizon, e.g., significant 

differences between parks examining the O, A profile, A composite, E, B, and C horizons separately.

When significance was established, Dunn’s multiple comparisons post hoc test was employed to 

identify which park/s were significantly different.
11

Results and Context

Results are subdivided into six subsections: 1) Soil physical properties describes the coarse 

fragments, clay percent, bulk density (Db), bulk density hybrid (DbH), infiltrations, volumetric water 

content (θv), and penetration resistance; 2) Soil chemical properties covers macronutrients, 

micronutrients, pH, base saturation, cation exchange capacity, and contaminants; 3) Regression 

analysis outlines the results of a regression analysis examining the relationship between three master 

soil variables—C, pH, and clay percent—and all other chemical variables; 4) Statistical differences 

by horizon details significant chemical variable differences horizon by horizon among the parks; 5) 

NCRN overview summarizes the NCRN’s soil series, relative soil depths, drainage and other horizon 

characteristics; and 6) Park overviews presents a park-by-park analysis of horizon depths, clay 

content, coarse fragments, and chemical characteristics. All results are preceded by the definition of 

the measured property and a brief description of its relevance to natural resource monitoring and 

management within the NCRN. A complete list of soil terminology used in this report is found in 

Appendix A.

Soil physical properties

Coarse fragments and clay percent

Coarse fragments are solids >2 mm in diameter, while the fine earth fraction consists of soil particles 

<2 mm in diameter. Four types of coarse fragments are found in the NCRN, in order of their size 

from smallest to largest: 1) Gravel (GR) – Coarse fragments that are 2 to 75 mm along their greatest 

diameter; 2) Cobbles (CB) – Rounded coarse fragments that range from 75 to 250 mm along their 

greatest diameter; 3) Channers (CH) – Flattened coarse fragments that range from 75 to 250 mm 

along their greatest diameter; 4) Flags (FL) – Flattened large stones ranging from 150 to 380 mm 

along their greatest diameter. The abundance of coarse fragments in soils are a function of the parent 

material (e.g., soils formed from carbonate rocks will be very different from those formed from 

acidic shales.), topography (e.g. soils at the bottom of a mountain often have many coarse fragments 

that moved down hill), age (e.g., older soils frequently have fewer rocks because they have had time 

to break down into soil.), and climate (e.g., colder areas have slower chemical and biological reaction 

rates which means that coarse fragments often are more prevalent in colder environments). The 

relative abundance of coarse fragments does not necessarily have any effect on the fertility of the soil

or the ability to support vegetation. However, coarse fragments do typically alter water flow and 

water holding capacity in soils (see Infiltration section below). 

Soils are composed of three particle size classes all <2 mm in diameter: sand, silt, and clay (from 

largest to smallest, respectively). Clay particles have a diameter <0.002 mm. With an enormous 

surface area (a fixed mass of clay particles can have a surface area hundreds of thousands of times 

greater than the same mass of sand particles), the clay percentage has a very strong effect on many 

physical and chemical soil processes, including bulk density, penetration resistance, water infiltration 

and storage, carbon sequestration, and fertility. However, the chemical composition and morphology 

of clay particles can differ greatly, ranging from clays that hold an enormous quantity of plant 

nutrients to clays that are very low-charge and that have a low inherent fertility, depending on the 
12

parent material of the soil. Often clay soils in warmer, wetter regions (e.g., the NCRN) would be 

expected to have weathered, low-fertility clays.

Figure 3 shows the distribution of coarse fragments and clay throughout the profile from the A to C 

horizon. MONO contained the highest percentage of coarse fragments by volume (27, 65, and 38% 

in the A, E, and B horizons respectively), and MANA contained the lowest (2 and 4% in the A and B

horizons respectively). The other two parks with a predominance of mountain soils, CATO and 

HAFE, had the second and third highest coarse fragment percentages respectively in both A and B 

horizons. CHOH, GWMP, NACE, and PRWI (in addition to MANA) all contained ≤ 10% coarse 

fragments in their A and B horizons. There was a large amount of intra-park coarse fragment 

variation, and with the exception of MONO, HAFE, and CATO, the standard deviation in each park 

was greater than the mean (see data tables in Appendix B). Nevertheless, the ANOVAs showed that 

the differences between MONO, HAFE, CATO and the aforementioned parks with ≤ 10% coarse 

fragments were mostly statistically significant in the A and B horizons (Appendix C). MONO 

contained significantly more coarse fragments than PRWI in the E horizon and there were no 

differences between parks in the C horizon.

It should be noted that four parks—ANTI, CATO, GWMP, MANA—had no E horizons and 

consequently do not appear in Figure 3. Moreover, three parks—HAFE, ROCR, and WOTR—had 3

or fewer plots/park with an E horizon (HAFE had 3 plots; the other parks had 1). We therefore

decided to exclude them from statistical analyses and subsequent figures because too few replicates

generate a low power to detect statistical differences. Nevertheless, the E horizon average for HAFE

and values for ROCR and WOTR can be found in the data summary tables in Appendix B. There 

were also no C horizons in ANTI and HAFE, and 2 or fewer C horizons in CATO, MANA, MONO, 

and WOTR. Therefore, only CHOH, GWMP, NACE, PRWI, and ROCR’s C horizons are shown in 

Figure 3. (See Appendix B for the missing park values.)

From surface to base of the soil profile (A to C horizon), clay percentage trended the same way in all 

parks of the NCRN. The pattern was for a clay decrease from A to E horizon before increasing 

sharply from E to B and then tailing off from B to C horizon. Opposite of its coarse fragment 

percentages, MANA had the highest clay percentage of any park in the NCRN. It contained 23% clay 

in the A horizon and 33% in the B horizon. HAFE had the lowest clay percent: 11 and 16% in A and 

B horizons respectively. After MANA, PRWI and ANTI had the next highest clay percentages in 

their A and B horizons. ROCR was the only park other than HAFE to have <20% clay in its B 

horizon, and CATO had the second lowest clay percentage in its A horizons. The ANOVAs showed 

that the differences between MANA, PRWI and CATO and HAFE were statistically significant in 

the A horizon, and ANTI, PRWI, and MANA all had significantly more clay than HAFE and ROCR.
13

Figure 3. Distribution of coarse fragments and clay percent by horizon in all parks of the NCRN. Errors 

bars represent standard error of the mean (S.E.M.) throughout all figures.

Bulk density (Db)

Db is the dry weight of the soil fine earth fraction divided by the entire volume of that fine earth 

fraction (including pore spaces). Db differs from particle density (Dp) because Dp measures the dry 

weight of the fine earth fraction divided by the volume of fine earth fraction (without pore spaces).

Db can be used to calculate the pore space of the soil because soil scientists frequently assume a fixed 

particle density (Dp) of 2.65 g cm−3 for the soil solids (mainly quartz-based particles east of the 

Mississippi). So, percent pore space = 1 − Db/Dp. In addition, Db is an indirect measure of 

compaction. The higher the Db value, the fewer pores there are in that volume of soil and thus the 

more compacted the soil. Db values between 1.45 g cm−3 for clays and 1.85 g cm−3 in sandy soils will 

typically start to impede root growth and detrimentally affect plant growth (Weil and Brady 2017).

Db values across the NCRN were typical of uncultivated loamy A horizon forest soils (0.8 to 1.2 g 

cm−3), described in Weil and Brady (2017). This suggests that forest habitats of the NCRN parks are 

not experiencing excessive foot traffic or other forms of compaction. Moreover, it also indicates that 

soil C levels (which are generally inversely related to Db) are adequate to maintain lighter lowdensity soils in the NCRN.

All parks except WOTR had Db values <1.0 g cm−3 in the top 15 cm of the mineral soil (Figure 4).

The only park that was notably below typical Db mineral forest soils was CATO (0.49 g cm−3), which 

was significantly different from all other parks. The low values undoubtedly arose from the high 

levels of soil C (see figure in Soil chemical properties section) which promotes strong structure and 

numerous soil pores. HAFE, the only other park comprised of mountain soils, also had a lower Db

(0.75 g cm−3) than CHOH, MANA, and WOTR.
14

Figure 4. Db in the eleven parks of the NCRN. Parks that share the same letter are not statistically 

different. 

Infiltration

Unsaturated infiltration describes the rate at which water enters a soil, given that soil pores are not all 

filled with water (or in the case of this work, in soils that were not previously wetted by the soil 

tester). Saturated infiltration measures the rate water enters a soil that has been previously wetted and 

assumes, therefore, that all soil pores are filled with water. Saturated infiltration is a proxy for 

saturated hydraulic conductivity, when water flows through macropores (soil pores >0.08 mm in 

diameter).

The unsaturated infiltration rate at all plots was highly dependent on the soil moisture at the time of 

sampling. (Very dry plots would have very different infiltration rates than a plot with the same 

texture but higher moisture level.) Consequently, the purpose of the unsaturated infiltration was 

primarily to standardize moisture conditions across plots and ensure that all soil pores were filled 

with water before saturated infiltration could occur. The saturated infiltration rate is fundamentally a 

function of the size, abundance, and shape of the soil macropores which is dependent on soil texture, 

structure (strength of the soil aggregates), and coarse fragment content. Soils with high percentages 

of coarse fragments typically have faster infiltration rates (Chow et al. 2007), and soils with higher 
15

clay contents (all other factors held constant) have slower infiltration rates. Carbon content is related 

to soil structure, and soils with high total C typically have more pronounced aggregates, greater 

amounts of macrofauna (e.g., earthworms which create macropores), larger macropores, and thus 

faster infiltration rates all things being equal. 

In the NCRN, infiltration is especially important to monitor because of the number and duration of 

high rainfall events in the area. The opposite of infiltration is runoff, which can lead to erosion, 

eutrophication in the Chesapeake Bay, loss of vegetation, and infrastructure damage potentially 

costing parks millions of dollars in cleanup and repair fees. 

Unsaturated infiltration was 156% faster (averaged across all parks) than saturated infiltration (282 v. 

126 cm hr

−1 respectively). Though unsaturated infiltration is dependent on soil moisture at the time of 

measurement, there was a positive linear relationship between the two infiltrations (r=0.91).

Relatively slow saturated infiltrations were preceded by slow unsaturated infiltrations (Figure 5).

CATO had a significantly faster saturated infiltration rate (266 cm hr−1) than all other parks except 

for PRWI and WOTR. (It should be noted that WOTR, with its small number of samples brought

down the statistical power to detect significant differences.) WOTR, MANA, ANTI, GWMP, and 

HAFE were all characterized by particularly slow saturated infiltrations of <100 cm hr−1, which were 

approximately three times slower than CATO’s. The fast infiltration rates in CATO can be explained 

both by the high levels of soil C (see figure in Soil chemical properties section) which create 

macropores, the shallowness of the soils (Table 2), and the high numbers of large rocks in the soil.

Chow et al. (2007) found that larger pore sizes were more prevalent in soils with 30% coarse 

fragments than with no coarse fragments and consequently, that water flowed through the stony soils 

much faster than through the soils without stones. In contrast, parks such as ANTI and MANA had 

the least amount of coarse fragments (Figure 3) and the highest clay percentages in the region which 

undoubtedly contributed to their slower infiltration rates.
16

Figure 5. Unsaturated and saturated infiltration across the NCRN parks. Parks with values that are 

significantly different do not share the same letter over bars.

Volumetric Water Content (θv)

Volumetric water content (θv) measures the volume of water in a specific volume of soil (expressed 

as the percent of a volume of soil that is occupied by water). Like infiltration, θv is a function of the 

size, shape, and abundance of soil pores. Unlike infiltration, many of the factors that increase the 

abundance of macropores and thus infiltration rate, have the inverse effect on θv. For example, water 

is held more tightly (i.e., does not flow through the soil) in small micropores (pores <0.08 mm in 

diameter) with a lower matric potential. Soil textures with higher percentages of clay, therefore, have 

a higher percentage of micropores and thus higher water content, all other factors remaining constant.

Plants take up water according to energy status (potentials), and two soils that have the same θv can 

have very different potentials based on their texture. Thus, θv is not ipso facto an indicator of whether 

plants are well watered. However, θv is very useful for understanding the water holding capacity of 

NCRN soils—i.e., the potential of the region’s soils to serve as a sponge after heavy rainfall events.

Moreover, θv is important for gauging how quickly water might be released to vegetation after 

infiltration events have occurred.

Averaged across all parks, θv post-infiltration was 44% greater than θv pre-infiltration (29 compared 

to 20%, respectively; Figure 6). Like unsaturated and saturated infiltration, θv pre and post infiltration 

shared a positive linear relationship (r=0.74). Parks with relatively lower θv pre-infiltration had lower

θv post-infiltration. However, the magnitude of the difference between parks was much less for θv

than for infiltration. Only a 6% gap in θv separated the park with the lowest post-infiltration values

(PRWI with a 26% θv average) from the park with the highest (MANA with 31%). Similarly, 7% θv

separated PRWI from MANA’s pre-infiltration rates (17 and 24% respectively). CHOH, MANA, and 
17

ROCR were statistically greater than CATO and ROCR pre-infiltration. Post-infiltration, only 

MANA was significantly greater than HAFE, and CHOH, 

Post-infiltration values at MANA and NACE were significantly greater than PRWI. MANA has 

much more clay in its soils than PRWI, and NACE has fewer coarse fragments which undoubtedly 

contributed to the differences. All other parks were not statistically different.

Figure 6. θv pre and post-infiltration in the parks of the NCRN. Parks with values that are significantly 

different do not share the same letter over bars.

Penetration resistance

Penetration resistance, measured in kilopascals (kPa), is a measure of the ease of penetrating the soil 

with a narrow rod capped by a cone-shaped head. This test is an indirect measure of soil compaction 

and can indicate how quickly water can enter a soil or the corollary—whether water might run off the 

surface and cause erosion—or whether plant root growth will be impeded. High-clay soils with

tighter bonds between particles are typically more resistant to penetration than sandy soils. In the 

NCRN, clay percentages typically increased from the A to B horizon which likely drove the observed

increases in penetration resistance with depth (Figure 7). However, coarse fragments also impede 

penetration, and soils with a preponderance of coarse fragments can increase resistance. With its 

positive effect on soil structure, carbon content is inversely related to penetration resistance. 
18

Figure 7. Penetration resistance showing a positive linear relationship with depth in the parks of the 

NCRN. 

Across the NCRN, penetration resistance increased linearly with depth (r=0.99) from 5 to 35 cm 

below the soil surface (Figure 7). Near the surface at 5 cm depth, the region’s average penetration 

resistance was 397 kPa, and at 35 cm depth it was 1814 kPa. MANA, MONO, or WOTR had the 

greatest penetration resistance from 5 to 30 cm depth, and HAFE also had relatively high values in 

the top 15 cm (Figure 8). MANA and MONO had the highest clay and coarse fragment percentages, 

respectively, which likely is responsible for their higher penetration resistances. ROCR or CATO had 

the least penetration resistance throughout the profile, and ANTI and NACE also had low resistance 

values in the top 15 cm. Though CATO had large amounts of coarse fragments, its fragments were 

generally large stones with many large pores between the rocks. Thus, the probe was able to 

penetrate easily between rocks into large pores spaces. ANOVAs showed that MANA typically had 

statistically greater penetration resistance than CATO, CHOH, NACE and ROCR. (Again the 

hypothesis is that this is caused by the high clay contents at MANA.) Moreover, in the top 20 cm 

NACE, and ROCR had significantly less penetration resistance than GWMP, HAFE and MANA, and 

from 15 cm down, CATO had less resistance than MANA, MONO, and PRWI.
19

Figure 8. Differences in penetration resistance between parks from 5 to 30 cm depth. Parks with values 

that are significantly different do not share the same letter over bars.
20

Aggregate stability

Aggregate stability is an important test of the cohesion of an aggregate (a mass of soil particles held 

together in a cohesive shape) from the surface of the soil. If the aggregate falls apart quickly after 

being placed in water, it is poorly cohesive. Aggregate stability is an important measure of erosion 

resistance. When soils have strong aggregates, they do not erode easily. Aggregate formation is 

typically heavily influenced by soil C content and the turnover of organic matter. In addition, 

aggregates can be broken up as a result of human or mechanical traffic disturbing the soil surface.

Thus, aggregate stability can indicate park managers about specific areas of a forest that might be

enduring a heavy volume of foot traffic, or that have low organic matter inputs, or be subject to some 

other stressor. 

Aggregate stability values were not significantly different between parks (data not shown). The park 

averages were between 5.6 and 6.0 (6 being the highest value possible for this parameter). For 

aggregate stability descriptive statistics by park unit, see Appendix B, table B13. ANTI had the 

largest amount of variation between plots (an average aggregate stability of 5.6 ± a standard 

deviation of 1), whereas all of WOTR’s plots contained aggregate stability values of 6. The following 

9 plots had aggregate stabilities <3 indicating that the aggregates slaked (fell apart) very quickly 

when immersed in water: NACE-0304, CHOH-1148, NACE-0621, ANTI-0207, CATO-0035, 

ROCR-0186, CHOH-1148, MONO-0061, and PRWI-0707. These plots should undergo further 

scrutiny to determine if human traffic or other causes are endangering the overall soil health in those 

plots. 

Soil chemical properties

Total carbon and macronutrients

Total carbon (C) is a measure of the grams of C per gram of soil on a dry weight basis. Carbon is 

critical to the functioning of soils. Structurally, it helps soil aggregate; it increases pore space and 

water content thus reducing compaction; it is a fuel for microorganisms; it increases the cycling of 

nutrients; it is the backbone of many large organic molecules that other elements can attach to. 

Macronutrients are chemical elements that plants need in large quantities for proper growth. There 

are six inorganic macronutrients: N, P, K, Ca, Mg, and S.

Figure 9 shows the distribution of total C and macronutrients (except S) by horizon. One park, 

WOTR, had no O horizons in any of their plots and consequently O horizon data do not appear in the 

figure. Moreover, four parks—ANTI, MANA, MONO, ROCR—had two or fewer plots/park with an

O horizon (MONO had 2 plots; all the rest had one.). We therefore decided to exclude O horizon data 

for these parks’ statistical analyses and subsequent figures because of low power to detect 

differences. Nevertheless, their values can be found in the data summary tables in Appendix C. The E 

and C horizons were excluded from analyses, and the reasons for their exclusions can be found in the 

section describing coarse fragments and clay percent. 

Macronutrient concentrations generally decreased with depth throughout parks of the NCRN 

(Figure 9) which is common in forest soils (Johnson and Lindberg 1992; Weil and Brady 2017). Four 

clear exceptions were found: P and Mg were highest in CHOH’s C horizon; MONO’s P 

concentration in the E horizon was greater than other horizons; and Mg concentration in MANA’s B 
21

horizon was higher than other horizons. The aberrations in CHOH and MONO can be explained by 

one outlier plot with extremely high nutrient concentrations in each of those parks (discussed in more 

detail in the CHOH and MONO park overview sections), whereas MANA’s increasing Mg with 

depth is attributable to the particular parent materials from which those soils formed (further 

discussion in the MANA park overview section).

Averaged across all parks, total C in the O horizon (30.5%) was 5.5 times greater than total C in the 

A horizon composite samples (5.5%). The magnitude of the decrease in total C between the A 

composite and B horizon samples was even greater than from O to A. The B horizons had 7 times 

less total C (0.79%) than the A composites (5.5%). The NCRN average total C in the C horizons was 

0.48%. Interestingly, total C in the A profile horizons (3.7%) was 32% less than in the A composite

horizons. For all macronutrients except P, the A profile samples contained 25–31% less of the 

nutrient than the A composite samples. This suggests that in the surface horizons even a slight 

change in depth can have a measurable impact on soil chemistry. 

Total N was distributed very similarly to total C. The O, A composite, A profile, E, B, and C

horizons contained 1.28, 0.30, 0.22, 0.06, 0.06, and 0.03% total N respectively. Extractable K, Mg, 

and Ca did not experience a decrease by depth to the same proportion as total C and N. However, 

there was at least a threefold drop in extractable K from O to A and another threefold drop from A to 

B horizon. There was also a threefold drop in Ca from A composite to B. Mg increased slightly from 

the B to C horizon (126 to 162 mg kg−1 respectively). K, Mg, and Ca all decreased from the A 

composite to E horizon and then increased from E to B horizon. The proportionate increase from E to 

B was small for K and Ca but especially large for Mg where there was 156 mg kg−1 in the A 

composite horizon, 48 mg kg−1 in the E horizon and 126 mg kg−1 in the B horizon. Extractable P was 

the only macronutrient that was quite low compared to the other macronutrients, and throughout the 

mineral horizons (A comp, A prof, B, E, C), P did not fluctuate much (12, 12, 7, 13, 18 mg kg−1

respectively). 
22

Figure 9. Distribution of total C and macronutrients (except Sulfur) by horizon in all parks of the NCRN.
23

Micronutrients

Micronutrients are chemical elements necessary for plant growth but in smaller quantities than the 

macronutrients. Micronutrients include: Cu, Fe, Mn, Zn, B, and Cl. 

Throughout the NCRN parks, extractable Mn and Zn followed the same horizon-by-horizon trend as 

most of the macronutrients, decreasing with depth from O to C (Figure 10). Like total C, there was

3.4 and 3.3 times more Mn and Zn respectively in the O horizons compared to the A composites. Mn

further decreased by a factor of 3.9 from the A composite (69 mg kg−1) to the B horizon (19 mg kg−1)

and Zn by a factor of 2.2. Exchangeable Fe also decreased from top of the profile to the bottom, but 

the magnitude of the decrease was less than with Mn and Zn. The levels of Exchangeable Cu were

low and fairly homogenous from top to bottom of the profile: 8.1, 4.0, 4.4, 3.7, 4.7, and 9.2 mg kg−1

in the O, A composite, A profile, E, B, and C horizons respectively. The higher level of extractable 

Cu in the C horizon is primarily attributable to one plot in PRWI with 321 mg kg−1 (discussed further 

in the PRWI Park Overview section).
24

Figure 10. Distribution of micronutrients by horizon in all parks of the NCRN.

pH, CEC, base saturation

Soil pH measures the negative logarithm of the hydrogen (H) ion activity. It is considered a master 

soil variable because it controls so many facets of nutrient and contaminant availability and thus 

whether these elements are available for plant or other organism uptake. CEC measures the total of 

exchangeable cations (e.g., K+

, Na+, Ca2+) that a soil can absorb. Base saturation (BS) measures the 

percent of the CEC occupied by base (non-acid) cations: Ca, Mg, K, and Na. Since most cations are 

also plant nutrients, generally higher CEC and BS values indicate higher fertility and sometimes BS 

is used as a proxy for soil fertility.
25

pH varied widely among parks. PRWI had the lowest pH values of any park from the A composite to 

C horizon (Figure 11) ranging from 4.1 to 4.3. WOTR also had consistently low pH values 

throughout the profile. On the opposite end of the spectrum, ANTI and HAFE had pH values ≥ 5.8 

from A composite to B horizons. In all parks except PRWI, the O horizon was more acidic than the 

A. At NACE the change was dramatic: an increase from an O horizon pH of 3.2 to an A horizon pH 

of 5.4. On average, however, the O horizon was 0.7 units more acidic than the A composite horizon 

below it. In addition to the among-park variation, there was also substantial variation among horizons

within some parks. For example, the pH values for the O, A composite, A profile, E, B, and C 

horizons at NACE were 3.2, 5.4, 6.0, 4.0, 6.1, and 5.6 respectively. The pH values at MONO by 

horizon from O to C were 4.4, 5.2, 5.3, 6.1, 5.0, and 4.0. 

Base saturation closely mirrored pH. PRWI had the lowest base saturation from the A composite to C 

horizon. WOTR, ROCR, and NACE also had relatively low base saturations. ANTI had the highest 

base saturation, and CHOH and MANA also had relatively high base saturations (>60%) from the A 

composite to C horizon.

CEC followed a pattern similar to total C and most of the macronutrients from the surface to base of 

the profile. Averaged across all parks, CEC in the O horizon was 4.6 times greater than CEC in the A 

composite horizon and decreased again by nearly half from A composite to B horizon. CATO and 

ANTI had the highest A composite CEC in the NCRN (22 and 20 meq 100g−1 respectively), and 

WOTR and PRWI had the lowest CEC (5.8 and 8.2 meq 100g−1 respectively). In the B and C 

horizons, there was little inter-park variation in CEC with values ranging from 6 to 12 meq 100g−1 in 

the B horizon and from 4 to 10 meq 100g−1 in the C horizon.

As discussed in the Methods section, CEC and base saturation measurements in this report are

merely an approximation of the true value and thus underestimate true base saturation. These 

measurements are also not the methods used by the Natural Resources Conservation Service to 

classify soil series. Based upon Soil Taxonomy (Soil Survey Staff 2014b), these lower base 

saturation values indicate that there are fewer Ultisols in the NCRN than Web Soil Survey predicts 

(Web Soil Survey 2019). In the “Overview of soil classification, depths, water tables in the NCRN” 

section, the soil series presented throughout the region are those found on Web Soil Survey.
26

Figure 11. Distribution of pH, CEC, and Base Saturation by horizon in all parks of the NCRN.
27

Contaminants overview

Contaminants are operationally defined in this report as any soil elements that cause damage to plant 

growth or other soil organisms, or that could jeopardize human health if ingested through water or 

directly from soils. Contaminants are often heavy metals (e.g., Pb, Cr, Cd). Typical sources of these 

contaminants in the NCRN are automobile exhaust, industrial processes, and coal-fired power 

generation. The EPA has developed soil screening levels for these contaminants (EPA 2019) which 

are considered safe thresholds for residential uses and can be used for comparison with these soil 

data.

Soil contaminants, Cr and Cd, had low exchangeable levels throughout the region (Figure 12), 

though individual plots in ANTI and CHOH contained relatively higher amounts of both metals (see 

additional discussion in the ANTI and CHOH sections.). Many of the Cd and Cr levels in the B and 

C horizons were below detection limit, but in all horizons where levels were detectable the values 

were predominantly <1 mg kg−1. NACE had 4 times more extractable Pb in its O horizon than the 

regional average (20 mg kg−1 compared to 4.8 mg kg−1) and nearly 3 times more Pb in its A 

composite horizon (10 mg kg−1) than the region (3.7 mg kg−1). In addition, the three other parks 

nearest to Washington, D.C., and with high proportions of vehicle and human use (ROCR, WOTR, 

and GWMP), also had higher relative amounts of Pb in the A composite and A profile.
28

Figure 12. Distribution of contaminants by horizon in all parks of the NCRN.
29

Regression analysis 

The regression analysis examined total C, pH, and clay percent as predictor variables for all chemical 

variables and showed a strong positive relationship between total C and total N (R2 =0.91), and a 

positive relationship between total C and CEC (R2 = 0.70), total C and K (R2 =0.68), and pH and 

base saturation (R2 =0.80)(Figure 13). At a pH of approximately 6.0, base saturation plateaued at 

100%, and the linear relationship would have been much stronger if the samples with only a pH <6.0 

were analyzed. In addition to examining all horizon samples combined, the regression analysis was 

performed horizon by horizon. However, this did not yield more significant relationships. 

Surprisingly, clay percentage was not a good predictor for any chemical variable. With its large 

surface area, clay typically holds a lot of charge (CEC). Frequently, clay, CEC and the abundance of 

macronutrients attached to the CEC are all positively related. The lack of relationship between clay 

and nutrients in the NCRN is undoubtedly a result of low-activity, weathered clays that do not have 

the charge-holding capacity of younger, high CEC clays. In addition, some of the absence of positive 

relationship is undoubtedly because measuring clay percentage by hand using multiple field 

technicians was imprecise (or too often incorrect) and masked the true effect of clay on soil 

chemistry in the NCRN.
30

Figure 13. Regressions showing relationship between soil chemical variables in the NCRN. 

Statistical differences by horizon

ANOVAs were used to detect significant differences among parks, horizon by horizon. A general

pattern emerged from this analysis. A park with nutrient concentrations in the uppermost A horizon 

composite that were the highest or lowest in the region and statistically different from multiple other 

parks would often have the same highest or lowest statistically significant difference in the lower 

horizons. Figure 14 illustrates this pattern for total C in CATO. The A horizon composite levels in 

that park were statistically higher than 8 other parks in the network, and the B horizon levels were

statistically higher than 5 other parks. Similarly, Figure 14 shows that PRWI had an A horizon 
31

extractable P level that was significantly lower than 7 other NCRN parks. In the B horizon, PRWI’s 

extractable P was still significantly lower than 6 other parks. ANTI’s extractable Ca in the A horizon 

composite was significantly greater than extractable Ca in GWMP, NACE, and PRWI. ANTI’s B 

horizon extractable Ca was also significantly greater than GWMP, NACE, and PRWI (Figure 14). 

Appendix C gives the tables of P values that were used to find significant differences among parks 

for each horizon using the post hoc Dunn’s multiple comparison test when the ANOVA had a P 

value ≤0.05.

For the O horizon, the ANOVA showed no significant differences between parks for K, Mg, Fe, or 

Cu. Total C, total N, extractable P, Ca, and Zn were all significantly higher in CATO than PRWI.

HAFE contained significantly higher extractable P than PRWI and significantly higher extractable 

Ca than NACE and PRWI. Mn in CATO was significantly higher than NACE.

In the A composite horizon, the differences for total C, extractable P and Ca can be seen in Figure 

14. Total N followed the same pattern as total C and PRWI had significantly or near significantly 

(P<0.1) lower levels than all parks except MANA, ROCR, and WOTR. ANTI’s extractable K levels 

were significantly greater than most other parks and NACE and PRWI had significantly lower levels 

than most other parks. 

The A horizon profile samples had similar statistical differences to the A composite horizon. The 

ANOVA showed no significant differences between the depth of the horizon midpoint from which 

all chemical samples were taken. Thus, the data indicates that the A horizon profile chemical samples 

were all taken from around the same depth in the profile (12 cm was the NCRN average midpoint for 

the A horizon.).

There was no significant difference in E horizon chemistry for extractable Mg, Mn, CEC, Fe, or Cu.

clay percentage between parks. There was also no significant difference in clay content or depth of 

the horizon midpoint (25 cm was the NCRN average midpoint for the E horizon.).

The most variation among parks occurred in the B horizon, and all physical and chemical variables 

contained significant differences. CATO’s B horizon midpoint was significantly shallower in the 

profile (36 ± 16 cm) than CHOH, MANA, NACE, and PRWI. HAFE’s midpoint (35 ± 15 cm) was 

significantly shallower than CHOH, NACE, and PRWI. All other horizons parks were not 

statistically different. For the rest of the chemical and physical differences, see Appendix C. 

Extractable P, K, Mg, Mn, and Zn in the C horizon were not significantly different in the NCRN

plots. Horizon midpoints were also not statistically significant, though GWMP was nearly

significantly (P<0.1) shallower in the profile (54 cm depth) than PRWI (84 cm depth). For all other 

significance levels see Appendix C.
32

Figure 14. Total C, extractable P and K levels in the A composite and B horizons of the NCRN. Parks 

with values that are significantly different do not share the same letter next to their bar.
33

Overview of soil classification, depths, and water tables in the NCRN

There are 85 total soil series represented in the NCRN parks (Table 2) according to Web Soil Survey 

(Web Soil Survey 2019). A soil series is the most specific unit of soil taxonomy, akin to a species in 

the plant and animal kingdoms (Soil Survey Staff 2014b) (discussed further in Appendices A and D).

Some series are well represented in multiple parks, whereas others are found in only one park.

Approximately one quarter of the NCRN’s soils are shallow (<50 cm deep), one quarter are

moderately deep (50–100 cm deep), and one half are at least 100 cm deep based on the depth that 

samplers were able to auger before hitting bedrock or an impenetrable zone. (In this survey, fragipans 

and other restrictive layers were inconsistently identified by field technicians, but based on 

descriptive evidence as well as NRCS soil mapping, some of the shallow soils can be attributed to 

fragipans.) Two thirds of plots contained a Bt horizon—a horizon with a heavy accumulation of 

illuviated clay indicating well weathered, old soils that belong to the Ultisols or Alfisols soil order 

(see definition in Appendix A), and another 21% of soils contained a Bw horizon most often

associated with profiles that have had insufficient time or improper climate conditions (e.g., too cold 

and insufficient rain) to form a Bt horizon. A little over a quarter of the region’s soils have an O 

horizon (an organic layer covering the soil surface), which are frequently associated with forest soils 

(see Discussion). Finally, 17% of the region’s soils were poorly or somewhat poorly drained, 

indicating that they experience saturated soil conditions (all soil pores are filled with water) in the top 

100cm of soil for at least three to four weeks of the year, during periods of high microbial activity 

(e.g., in the warm months of spring and summer). This means that the high-water table could be 

within 100 cm of the soil surface all winter and also for three to four weeks in the spring. Poorly 

drained soils have a water table within the top 50 cm of the soil surface and somewhat poorly drained 

within 50 to 100 cm of the soil surface. 

Table 2. Assorted soil profile characteristics from parks in the NCRN.

Park

Number 

of 

Profiles

Number 

of Soil 

Series

Profiles 

0–50 cm 

deep

Profiles 

50–100 

cm deep

Profiles 

≥ 100 cm 

deep

Profiles 

w/ O 

horizons

Profiles 

w/ Bt 

horizons

Profiles 

w/ Bw 

horizons

Poorly or 

somewhat 

poorly 

drained 

soils

ANTI 13 5 1 7 5 1 11 1 0

CATO 46 10 28 14 4 16 25 9 1

CHOH 67 30 20 15 30 4 31 25 6

GWMP 28 11 4 8 16 4 19 6 6

HAFE 21 10 14 5 2 5 6 8 1

MANA 19 6 1 7 10 2 13 5 11

MONO 15 6 9 4 3 0 4 4 1

NACE 47 18 7 13 28 14 37 10 16

* NOTE there are 85 distinct soil series in the NCRN. However, 33 soil series are seen in multiple parks. If those 

that were counted in multiple parks were summed, the result would be 118 soil series. 
34

Table 2 (continued). Assorted soil profile characteristics from parks in the NCRN.

Park

Number 

of 

Profiles

Number 

of Soil 

Series

Profiles 

0–50 cm 

deep

Profiles 

50–100 

cm deep

Profiles 

≥ 100 cm 

deep

Profiles 

w/ O 

horizons

Profiles 

w/ Bt 

horizons

Profiles 

w/ Bw

horizons

Poorly or 

somewhat 

poorly 

drained 

soils

PRWI 145 16 19 40 88 64 121 15 25

ROCR 19 4 1 4 14 3 9 4 3

WOTR 6 2 2 3 1 1 4 0 0

Total 426 85* 106 120 201 114 280 87 70

* NOTE there are 85 distinct soil series in the NCRN. However, 33 soil series are seen in multiple parks. If those 

that were counted in multiple parks were summed, the result would be 118 soil series.

Park Overviews

Antietam National Battlefield

ANTI is located in the Hagerstown Valley, part of the Great Appalachian Valley of the Ridge and 

Valley physiographic province in Washington County, Maryland. The geology of the Hagerstown 

Valley is predominantly carbonate rocks, and Antietam Creek, a tributary of the Potomac River, runs 

through the park. 

There are thirteen long-term vegetation monitoring plots in ANTI (Table 3). The soils of these plots

uniformly belonged to the Alfisols soil order. These are soils that have a high percentage of clay in 

the B horizon and are typically quite fertile containing higher amounts of cations, which are useful 

for plant growth. Five soil series are present in ANTI’s plots: Carbo, Duffield, Hagerstown, Ryder, 

and Swanpond. Hagerstown was the most prevalent series in the park found in five plots, and 

Duffield was the series in three plots. (For a list of all soil series in the NCRN, their parent materials,

and landscape positions see Appendix D.)

A unique characteristic of ANTI soils is that they were all formed from the same parent material—

residual limestone rocks. All other parks in the region contained at least two different parent 

materials and rock types. As a result limestone parent material, pH and base saturation levels in 

ANTI were consistently high throughout the profile with averages ≥ 5.7 and 69 respectively (Table 

3). The pH and base saturation values in ANTI were either the highest or among the highest of any 

park in the region.

Extractable Ca and Mg levels in the A composite horizon were higher than any other park of the 

NCRN, and in the B horizon they were the second highest levels. This is attributable to the CaCO3

and MgCO3 comprising the limestone parent material. The parent material also affected K levels,

which were significantly higher than most other parks in the region. Interestingly, extractable Fe was 

significantly lower than all other parks in the region except HAFE (another park in the Ridge and 

Valley Province). Soil pH exerts a strong influence on extractable Fe levels. At high pH values, Fe is 

not as available for plant uptake which is why blueberries (which require high amounts of Fe) grow 
35

better in acidic soils. It follows, therefore, that ANTI soils with a higher pH would also have low 

levels of extractable Fe.

One plot, ANTI-0200, had outlier high values of extractable Cd (28 mg kg−1) and Cr (3 mg kg−1) in 

the B horizon. For context, the plot with the next highest level of Cd had 0.06 mg kg−1. pH in the B 

horizon (which has a controlling effect on Cd and Cr) was 3.98 which suggests that a localized 

change in parent material might be responsible for the extremely high values. Moreover, the 

technicians were not able to dig below 68 cm which also indicates that perhaps a change of parent 

material at the base of the horizon caused the high Cd and Cr. However, the A profile horizon pH 

was 5.77, nearly 100 times greater than in the B horizon which also could indicate that there is some 

form of metal object (perhaps of historical or archaeological interest) buried in the soil that is causing 

the low pH and high levels of extractable Cd and Cr. We suggest further inquiry.

Clay values were some of the highest in the region which is typical of limestone residual soils in the 

Hagerstown Valley. However, only five of the twelve plots were able to be excavated down to 100 

cm, which suggests shallow soils across the park. There were no E or C horizons in any plots. The 

absence of E horizons is due to high clay and non-acid (base cations) levels in the soil. The lack of C 

horizons indicates an abrupt change from clay to limestone bedrock and little transitional weathering 

of that bedrock.

Table 3. Soil physical and chemical characteristics ± standard deviation by horizon in ANTI.

Soil Variables O horizon⁑ A horizon composite A horizon profile B horizon

n 1 12 9 13

Horizon midpoint n.a. n.a. 11 ± 6 49 ± 12

Clay n.a. n.a. 17 ± 7 32 ± 15

Coarse fragments n.a. n.a. 7 ± 11 23 ± 31

pH 5.7 6.0 6.2 5.8

CEC 20 ± n.a. 20 ± 8.7 13 ± 5.1 9.4 ± 4.7

BS 94 ± n.a. 90 ± 7.5 85 ± 8.8 69 ± 27

Total C n.a. 5.0 ± 2.2 3.3 ± 1.6 0.6 ± 0.3

Total N n.a. 0.39 ± 0.17 0.30 ± 0.16 0.07 ± 0.05

P 37 ± n.a. 23 ± 21 13 ± 8.8 9.2 ± 8.5

K 500 ± n.a. 270 ± 82 200 ± 92 94 ± 32

Ca 2670 ± n.a. 2750 ± 1340 1670 ± 737 787 ± 275

⁑ If horizons are not shown in a table (i.e., no E or C horizon in this table), it signifies that those horizons were 

not present throughout the park. 

§ b.d.l. stands for below detection limit.
36

Table 3 (continued). Soil physical and chemical characteristics ± standard deviation by horizon in ANTI.

Soil Variables O horizon⁑ A horizon composite A horizon profile B horizon

Mg 450 ± n.a. 350 ± 210 230 ± 160 170 ± 75

Na 35 ± n.a. 13 ± 7.3 10 ± 1.8 11 ± 6.2

Mn 80 ± n.a. 52 ± 26 45 ± 18 16 ± 13

Fe 22 ± n.a. 8.5 ± 4.7 10 ± 3.1 12 ± 6.5

Cu 12 ± n.a. 1.8 ± 1.4 2.5 ± 2.1 3.9 ± 3.1

Zn 21 ± n.a. 6.2 ± 3.7 4.7 ± 3.5 2.7 ± 2.6

Ni 2 ± n.a. 0.8 ± 0.2 0.8 ± 0.3 0.8 ± 0.5

Mo b.d.l.§ 0.03 ± 0.06 0.02 ± 0.05 0.1 ± 0.3

Pb 2.5 ± n.a. 0.7 ± 0.4 0.5 ± 0.4 0.5 ± 0.5

Cd b.d.l. 0.24 ± 0.47 0.07 ± 0.06 2.2 ± 7.5

Cr b.d.l. 0.05 ± 0.08 0.05 ± 0.08 0.3 ± 0.7

⁑ If horizons are not shown in a table (i.e., no E or C horizon in this table), it signifies that those horizons were 

not present throughout the park. 

§ b.d.l. stands for below detection limit.

Catoctin Mountain Park

CATO is the only park in the NCRN entirely within the Blue Ridge physiographic region. The soils 

in this park are all located either on a mountain summit or side slope (many of them with a high

percentage grade). In total, 46 long-term vegetation monitoring plots in CATO were sampled for soil.

Ten soil series are found in those plots: Airmont, Bagtown, Edgemont, Highfield, Myersville, 

Ravenrock, Rohrersville, Stumptown, Thurmont, and Zion. Ravenrock is the predominant series in 

CATO, located in ten plots, and Highfield was the primary series in seven plots. Bagtown, 

Stumptown, Thurmont, and Zion were all found in only one plot. 

CATO’s soils are mostly shallow to very shallow over bedrock. For two thirds of the plots (25 total), 

the field technicians could only excavate to 50 cm below the surface. Moreover, only four plots have 

profile descriptions to a depth of 100 cm. The shallow soils are due to a number of factors, chief 

among them the underlying geology of very hard metamorphic and some igneous rocks. The climate 

is also cooler than other areas of the Mid-Atlantic (primarily due to elevation), and weathering occurs 

more slowly. Because of the steep mountain slopes, the soils of CATO are naturally prone to erosion.

The two major classes of parent materials in the park are colluvium (parent materials that have 

moved downslope by gravity) and residuum. The rocks which the soils formed from are primarily 

metarhyolite, schist, metabasalt, greenstone, and quartz phyllite. Boulders are evident throughout the 

park on the surface of the soil.
37

Eighty-two percent of the soils in CATO belong to the Alfisol soil order and the other eighteen 

percent to the Ultisols, which are more weathered than alfisols and have a lower percentage of base

cations and typically a lower pH. Though CATO’s soils were shallow, 68% of its plots contained an 

O horizon, making it the park with the highest percentage of plots with O horizons in the NCRN.

PRWI was second highest, but only 28% of its plots had an O horizon. There were no delineated E 

horizons in CATO, and only one C horizon. 

Physical characteristics showed that the soils of CATO are in good health, providing important 

ecosystem services—water infiltration, storage and filtration, a porous medium excellent for root 

growth, and a habitat for soil fauna. Db was lower in CATO than all other parks in the region, and 

infiltration was the most rapid. The average porosity of a CATO soil (the percentage of pore space in 

the soil matrix) was very high due to the very high levels of soil C. (Because soil C was so high a 

particle density {Dp} of 2.65 g cm−3 could not be assumed and thus used to calculate porosity, 

however, infiltration rates suggest abundant macropores.) Penetration resistance was quite low 

compared to other parks in the region.

The chemical variables in the park (Table 4) were also some of the highest in the region (typically in 

the top third of parks in the NCRN). Total C and Total N were the highest among other parks in the 

surface mineral horizons, and the other extractable macro and micronutrients (except for Fe and Cu)

were also high. Contaminants were very low compared to EPA screening levels. 

Table 4. Soil physical and chemical characteristics in CATO.

Soil Variables O horizon A horizon composite A horizon profile B horizon C horizon

n 26 37 30 31 1

Horizon midpoint 3.8 ± 2.7 n.a. 10 ± 6 36 ± 16 38 ± n.a.

Clay n.a. n.a. 14 ± 4 30 ± 20 26 ± n.a.

Coarse fragments n.a. n.a. 24 ± 23 23 ± 7.3 85 ± n.a.

pH 5.0 5.3 5.1 4.9 4.4 ± n.a.

CEC 55 ± 14 22 ± 7.8 19 ± 13 9.0 ± 3.3 6 ± n.a.

BS 44 ± 29 57 ± 30 41 ± 31 31 ± 27 17 ± n.a.

Total C 33 ± 7.1 9.9 ± 3.4 8.7 ± 5.0 2.1 ± 1.8 1.4 ± n.a.

Total N 1.6 ± 0.29 0.59 ± 0.18 0.50 ± 0.27 0.12 ± 0.09 0.09 ± n.a.

P 51 ± 24 16 ± 13 17 ± 18 4.8 ± 2.7 5.1 ± n.a.

K 420 ± 140 130 ± 51 120 ± 75 49 ± 23 40 ± n.a.

Ca 3410 ± 2760 1990 ± 1510 1100 ± 1210 361 ± 330 138 ± n.a.

Mg 470 ± 300 250 ± 220 150 ± 150 82 ± 78 20 ± n.a.
38

Table 4 (continued). Soil physical and chemical characteristics in CATO.

Soil Variables O horizon A horizon composite A horizon profile B horizon C horizon

Na 83 ± 69 30 ± 28 25 ± 23 22 ± 22 8.8 ± n.a.

Mn 300 ± 240 120 ± 120 92 ± 130 26 ± 19 18 ± n.a.

Fe 75 ± 55 60 ± 70 82 ± 91 44 ± 40 13 ± n.a.

Cu 6.0 ± 7.4 3.2 ± 3.4 3.3 ± 3.5 2.9 ± 2.6 3.8 ± n.a.

Zn 38 ± 28 14 ± 9.7 9.9 ± 8.5 3.2 ± 2.9 2.8 ± n.a.

Ni 2.6 ± 1.2 1.8 ± 0.78 1.6 ± 0.88 1.6 ± 2.0 0.5 ± n.a.

Mo 0.1 ± 0.1 0.2 ± 0.4 0.2 ± 0.5 0.1 ± 0.2 b.d.l.

Pb 3.9 ± 4.7 2.7 ± 3.6 3.5 ± 3.9 1.0 ± 1.5 0.34 ± n.a.

Cd 0.4 ± 0.4 0.2 ± 0.09 0.3 ± 0.3 0.3 ± 1.4 0.03 ± n.a.

Cr 0.1 ± 0.2 0.1 ± 0.2 0.2 ± 0.2 0.1 ± 0.1 0.02 ± n.a.

Chesapeake and Ohio National Historic Park

The Chesapeake and Ohio canal begins in Washington, D.C. and parallels the Potomac river west 

and north for approximately 180 miles. It is the only park in the region that spans all four

physiographic provinces. Consequently, the soils in this park are quite diverse. There are 30 soil 

series in CHOH, scattered across 67 permanent vegetation monitoring plots: Airmont, Allegheny, 

Atkins, Beltsville, Berks, Bigpool, Blocktown, Bownmansville, Brinklow, Codorus, Combs, 

Downsville, Elk, Funkstown, Gilpin, Glenelg, Hagerstown, Hatboro, Hazel, Huntington, Lindside, 

Melvin, Monogahela, Nollville, Opequon, Penn, Pope, Ryder, Swanpond, Talladega, and Trego (see 

Appendix D for descriptions of the series). Sixteen of the 30 soil series are found in only one plot.

Lindside and Downsville were the most ubiquitous soils in the region and comprised the dominant 

series at CHOH, found in eight and six plots respectively.

Most of the CHOH plots are located either on the historical Potomac River floodplain or an ancient 

stream terrace from the days when the river was much wider. Other plots are periodically flooded by 

rising waters in the canal itself. As a result, CHOH is the NCRN’s park with the highest proportion

of plots with younger soils in the Inceptisol order (38% of plots), which contain weakly developed 

Bw horizons. These horizons have not had enough time for clay to move down from the surface and

settle in the Bt horizon, generating the increase in clay with depth and the pronounced structure 

found in Alfisols and Ultisols. CHOH is also the only park in the region with soils in the order 

Mollisols (6 plots total) which have thick, dark A horizons and a high amount of organic C and base 

saturation. These soils can be found where flooding and saturated conditions simultaneously 

introduce and prevent the decomposition of organic material. The rest of the soils in CHOH were 

Alfisols (23%) or Ultisols (29%).

Predictably, the parent materials in the park were also quite diverse. Alluvium (parent materials 

deposited by rivers or moving water) comprised 58% of the plots. The rest of the plots had an 
39

assortment of colluvium, residuum, and two plots within or close to Washington D.C. possibly 

contained old coastal plain sediments. The mineral fraction of the parent materials was composed of 

both acidic and basic (carbonate) rocks. Shale, siltstone, sandstone, schist, quartzite, and limestone 

were the primary rocks in the parent material. Nearly 10% of plots would be classified as poorly or 

somewhat poorly drained (meaning they contained saturated soil conditions for at least a few 

consecutive weeks of the growing season in the upper 50 cm of the soil profile).

The soil physical conditions were close to the average for the region. The clay percentages were in 

the middle of the parks. However, infiltration rates were in the top third for the NCRN.

Soil chemical values (Table 5) showed that the soils of CHOH were quite fertile. CEC and Base 

saturation values were some of the highest in the region. This is almost certainly due to the sediment 

deposition from Potomac River flooding events which replenish the surface of the soil with nutrients.

Total C and extractable P, Ca, and Mg were also very high.

Plot CHOH-0262 was an outlier for extractable P, containing 299, 546, and 397 mg kg−1 in the A, B, 

C horizons respectively (the B horizon P average for CHOH was 20 mg kg−1). Extractable Mg was 

also extremely high in CHOH-0262 ranging from 1480 to 2080 mg kg−1 through the profile. The high 

levels throughout the profile suggest that there was a smelter on the site or perhaps something that 

produced a heavy amount of wood ash or manure. CHOH-1350 also had unusually high extractable P 

values (162 and 172 mg kg−1) in the A and B horizons respectively. CHOH-0380 contained 16.2 mg 

kg extractable Cd in the A horizon and 23.0 mg kg−1 in the B horizon which suggests that there was 

some form of human activity on the site that contributed to these outlier values throughout the 

profile. Likewise CHOH-0026 contained 7.9 mg kg−1 Cd in the A horizon and 7.0 mg kg−1 in the B 

horizon. Both CHOH-0380 and CHOH-0026 contain different soil series which further supports the 

hypothesis that the high Cd levels are caused by human activity. We suggest further inquiry into the 

history of all of these outlier plots. 
40

Table 5. Soil physical and chemical characteristics in CHOH.

Soil Variables O horizon

A horizon 

composite

A horizon 

profile E horizon B horizon C horizon

n 7 65 50 4 57 4

Horizon midpoint n.a. n.a. 15 ± 12 24 ± 6.7 50 ± 20 50 ± 37

Clay n.a. n.a. 17 ± 7 12 ± 6.5 25 ± 10 9.8 ± 5.9

Coarse fragments n.a. n.a. 8 ± 12 22 ± 34 10 ± 18 21 ± 14

pH 4.5 5.9 6.0 6.4 5.9 5.9

CEC 78 ± 56 17 ± 8.6 14 ± 8.7 8.8 ± 3.9 9.4 ± 3.9 10 ± 5.4

BS 39 ± 30 78 ± 23 72 ± 26 85 ± 16 55 ± 31 77 ± 15

Total C 33 ± 7.7 4.9 ± 2.9 3.9 ± 3.4 1.9 ± 0.6 1.1 ± 1.1 1.1 ± 0.4

Total N 1.3 ± 0.5 0.30 ± 0.12 0.23 ± 0.14 0.1 ± 0.05 0.08 ± 0.05 0.1 ± 0.02

P 57 ± 38 15 ± 11 20 ± 46 18 ± 13 20 ± 74 110 ± 170

K 370 ± 160 130 ± 88 100 ± 54 37 ± 16 47 ± 26 63 ± 11

Ca 2200 ± 1820 2190 ± 1580 1630 ± 1490 963 ± 824 803 ± 699 940 ± 277

Mg 280 ± 150 200 ± 150 180 ± 280 85 ± 53 140 ± 270 440 ± 600

Na 84 ± 72 22 ± 20 21 ± 21 18 ± 7.4 21 ± 26 19 ± 5.1

Mn 180 ± 140 59 ± 32 49 ± 28 30 ± 21 27 ± 22 18 ± 7.0

Fe 91 ± 41 44 ± 44 41 ± 26 57 ± 24 28 ± 17 28 ± 8.8

Cu 3.8 ± 3.1 3.8 ± 3.5 4.4 ± 4.3 4.1 ± 3.1 4.7 ± 5.1 0.9 ± 0.5

Zn 25 ± 13 12 ± 15 9.3 ± 7.0 12 ± 10 5.8 ± 11 2.0 ± 1.2

Ni 2.4 ± 0.6 2.0 ± 1.3 2.2 ± 1.8 3.6 ± 2.9 2.0 ± 1.5 2.5 ± 1.5

Mo 0.1 ± 0.4 0.05 ± 0.09 0.07 ± 0.2 b.d.l. 0.1 ± 0.2 0.1 ± 0.04

Pb 3.2 ± 3.9 1.1 ± 1.3 1.4 ± 2.9 0.5 ± 0.3 0.7 ± 0.8 0.6 ± 0.05

Cd 0.2 ± 0.1 0.5 ± 2 0.8 ± 3 0.1 ± 0.1 0.6 ± 3.1 0.07 ± 0.04

Cr 0.02 ± 0.06 0.1 ± 0.1 0.1 ± 0.1 0.1 ± 0.1 0.1 ± 0.1 0.04 ± 0.04

George Washington Memorial Parkway

The GWMP follows the Virginia side of the Potomac River from George Washington’s home, Mount 

Vernon, to Great Falls Park, north of the I-495 Capital Beltway (a distance of approximately 30 

miles). The parkway crosses both the eastern edge of the Piedmont Plateau and the western edge of 

the Coastal Plain, though >70% of its 28 long-term vegetation monitoring plots are in the Piedmont 

Region. There are 11 soils series in GWMP: Baile, Blocktown, Brinklow, Elkton, Fluvaquents, 

Glenelg, Hatboro, Mattapex, Meadowville, Rhodhiss, and Sassafras. Glenelg was the most prevalent 

series in the park found in 11 (39%) of the plots.
41

Many of the plots in GWMP are close to the Potomac River, but unlike CHOH, the soils in only 5 

plots (18% of the total) were formed from alluvial parent materials. This is due to the fact that tall 

bluffs rise steeply from the Virginia side of the river, in the section from D.C. to the Beltway. Many

of the vegetation monitoring plots are located on the summit or slopes of those bluffs. Consequently, 

a majority of soils in the GWMP are formed from metamorphic residual rocks, predominantly schist, 

quartzite, and phyllite. Four of the plots on the Coastal Plain are underlain by ancient marine 

sediments. 

Eighty nine percent of the soils in GWMP are Ultisols. Two plots have Inceptisols, and one plot has a 

soil that classifies as an Entisols making it one of only two parks with this soil order (NACE also has 

two plots with Entisols).

There were no physical or chemical outliers in GWMP soils (Table 6). It was a park with few 

statistically significant differences from the other parks in the NCRN. This suggests two things: first,

that GWMP’s soils are fairly uniform (e.g., 89% are Ultisols formed from the same type of parent 

material and having a similar landscape position.) and second, that the soils in GWMP could be 

considered the central concept of an NCRN soil, or soils that most “typify” the region.

Table 6. Soil physical and chemical characteristics in GWMP.

Soil Variables O horizon

A horizon 

composite

A horizon 

profile B horizon C horizon

n 7 28 20 23 4

Horizon midpoint 2 ± n.a. n.a. 12 ± 7 52 ± 14 54 ± 15

Clay n.a. n.a. 16 ± 7 24 ± 9.6 9.0 ± 4.1

Coarse fragments n.a. n.a. 3 ± 5 7 ± 13 34 ± 36

pH n.a. 5.6 5.5 6.1 5.1

CEC n.a. 14 ± 10 11 ± 4.3 9.3 ± 3.3 4.2 ± 1.0

BS n.a. 60 ± 29 47 ± 34 48 ± 34 47 ± 37

Total C 29 ± 6.7 5.6 ± 3.0 2.9 ± 1.1 0.6 ± 0.3 0.5 ± 0.2

Total N 1.3 ± 0.17 0.30 ± 0.12 0.18 ± 0.087 0.05 ± 0.02 0.04 ± 0.02

P 54 ± 18 14 ± 15 16 ± 25 5.6 ± 4.9 32 ± 28

K 410 ± 87 120 ± 49 82 ± 40 54 ± 22 33 ± 17

Ca 1830 ± 1210 1070 ± 1850 765 ± 899 361 ± 442 245 ± 200

Mg 360 ± 190 160 ± 120 130 ± 114 130 ± 150 38 ± 24
42

Table 6 (continued). Soil physical and chemical characteristics in GWMP.

Soil Variables O horizon

A horizon 

composite

A horizon 

profile B horizon C horizon

Na 95 ± 110 30 ± 23 23 ± 15 33 ± 44 13 ± 3.9

Mn 260 ± 190 84 ± 71 45 ± 29 24 ± 19 18 ± 13

Fe 120 ± 47 86 ± 61 87 ± 81 46 ± 58 67 ± 49

Cu 11 ± 20 4.0 ± 5.2 4.6 ± 7.9 6.1 ± 9.5 3.4 ± 4.1

Zn 28 ± 16 7.4 ± 6.2 6.0 ± 6.7 3.8 ± 4.3 2.3 ± 1.8

Ni 4.2 ± 0.52 1.8 ± 0.78 1.5 ± 0.91 1.7 ± 1.1 3.2 ± 2.7

Mo 0.3 ± 0.4 0.1 ± 0.2 0.1 ± 0.2 0.1 ± 0.1 0.1 ± 0.1

Pb 4.1 ± 2.8 4.1 ± 3.6 4.0 ± 2.9 1.6 ± 2.1 0.8 ± 0.5

Cd 0.5 ± 0.7 0.7 ± 3 0.1 ± 0.1 0.2 ± 0.5 0.1 ± 0.1

Cr 0.3 ± 0.4 0.2 ± 0.2 0.2 ± 0.1 0.1 ± 0.1 0.1 ± 0.1

Harpers Ferry National Historical Park

HAFE sits at the confluence of the Shenandoah and Potomac Rivers and the intersection of the Blue 

Ridge and Ridge and Valley physiographic provinces. Its 21 long-term vegetation monitoring plots 

are mostly scattered on the mountains surrounding the historic town, though at least one is on the 

Potomac River floodplain.

The majority of plots are underlain by residual and colluvial metamorphosed slate, phyllite, schist, 

quartzite, and greenstone. However, 4 of its plots sit atop sedimentary sandstone, and one consists of 

limestone residuum.

Roughly two thirds of the plots are characterized by the soil order Ultisols and the other one third are 

Inceptisols. Ten soil series are present in HAFE’s plots: Airmont, Bagtown, Catoctin, Dekalb, Hazel, 

Lindside, Purcellville, Stumptown, Weverton, and Whiteford. Bagtown was the most prevalent (5 

plots), and Whiteford was the second most prevalent (4 plots).

Soil physical and chemical characteristics of HAFE (Table 7) were similar to those of CATO. This is 

not surprising, given the two parks share similar soil series. The soil profiles in HAFE were some of 

the shallowest in the NCRN. A profile deeper than 50 cm could only be excavated in one third (7) of 

the plots, and a 100 cm deep profile was only achievable in 2 plots. From profile surface to base, 

HAFE had the lowest clay percent of any park in the NCRN. Like CATO, it was characterized by a

high coarse fragment percentage. HAFE’s Db values were the second lowest in the region behind 

CATO, and its total C values in the mineral surface (A) horizons were the second highest in the 

region behind CATO. Total N in HAFE and CATO were either the highest or second highest of all 

parks. 
43

pH levels were all ≥ 5.9 (among the highest in the region). Most of the other extractable 

macronutrients were very high in HAFE’s soils (in the top third of values for the NCRN parks)

probably because they have not had enough time to weather out of the soil. The level of extractable

micronutrients, Mn and Zn, were similarly high. The nutrient data indicates that the soils are in very 

good health and able to support vigorous plant growth. However, like CATO, the levels of Fe and Cu 

were some of the lowest in the region. As discussed with ANTI, the high pH levels probably limited 

the extractable Fe present in HAFE soils. Extractable Cd and Cr levels in the O horizon were higher 

than in any other park, but the absolute values of those contaminants was still <1 mg kg−1. 

Table 7. Soil physical and chemical characteristics in HAFE.

Soil Variables O horizon

A horizon 

composite

A horizon 

profile E horizon B horizon

n 4 21 18 3 17

Horizon midpoint n.a. n.a. 9 ± 5 18 ± 7.2 35 ± 15

Clay n.a. n.a. 11 ± 4 12 ± 4.2 16 ± 8.3

Coarse fragments n.a. n.a. 18 ± 15 38 ± 27 25 ± 18

pH n.a. 6.0 5.9 6.8 6.0

CEC n.a. 18 ± 7.4 16 ± 14 8.9 ± 5.1 6.4 ± 2.7

BS n.a. 64 ± 24 54 ± 34 52 ± 36 37 ± 31

Total C 28 ± 3.6 7.7 ± 3.5 5.4 ± 3.7 1.4 ± 0.2 1.1 ± 0.7

Total N 1.5 ± 0.23 0.46 ± 0.21 0.34 ± 0.25 0.1 ± 0.01 0.07 ± 0.05

P 79 ± 44 18 ± 14 15 ± 18 23 ± 25 11 ± 14

K 510 ± 33 160 ± 92 130 ± 100 28 ± 12 57 ± 41

Ca 4790 ± 2800 1990 ± 1670 1680 ± 2470 1140 ± 1310 396 ± 482

Mg 500 ± 200 230 ± 170 180 ± 160 120 ± 100 64 ± 52

Na 45 ± 7.8 16 ± 6.3 17 ± 10 8.4 ± 2.8 14 ± 7.7

Mn 290 ± 150 72 ± 51 53 ± 58 17 ± 7.5 16 ± 16

Fe 45 ± 26 46 ± 48 45 ± 46 24 ± 5.7 28 ± 19

Cu 1.6 ± 1.0 1.6 ± 1.1 1.2 ± 1.5 1.7 ± 1.0 1.3 ± 1.4

Zn 28 ± 9.2 10 ± 7.0 8.0 ± 7.5 5.5 ± 3.2 2.2 ± 1.4

Ni 2.4 ± 1.2 1 ± 0.3 1 ± 0.6 0.6 ± 0.2 1.7 ± 1.8

Mo 0.3 ± 0.5 0.06 ± 0.2 0.06 ± 0.2 b.d.l. 0.04 ± 0.1

Pb 2.6 ± 1.6 2 ± 2 1.8 ± 1.5 0.6 ± 0.3 0.7 ± 0.4

Cd 0.6 ± 0.3 0.2 ± 0.2 0.3 ± 0.4 0.1 ± 0.03 0.2 ± 0.5

Cr 0.4 ± 0.9 0.08 ± 0.2 0.08 ± 0.2 0.01 ± 0.02 0.04 ± 0.1
44

Manassas National Battlefield Park

MANA is located squarely in the center of the Piedmont region of Northern Virginia. Unlike the 

other parks of the Piedmont, however, the geology of MANA is unique in the NCRN. The park 

occupies an ancient lowland basin which was filled with silt and clay from the eroding Blue Ridge 

mountains. These clasts lithified into siltstones and shales which comprise the parent material of

many of the MANA soils. Approximately 80% of the 19 total long-term vegetation monitoring plots

in the park are composed of ancient alluvial shale and siltstone soil parent materials. The other 

MANA plots are underlain by parent materials of residual igneous diabase which formed when 

magma rose to the surface between the cracks of the overlying continental crust which was thin from 

the separation of Africa from Eastern North America.

Alfisols are the soil order found in 15 of the 19 plots. The other plots have Inceptisols formed from 

recent shale and siltstone alluvium carried by Bull Run—the biggest stream in the park. Six soil 

series are present at MANA: Aden, Albano, Bermudian, Dulles, Haymarket, and Manassas. Albano 

is the prevalent series found in 10 plots 

Overall, MANA soils were characterized by heavy clay—the highest percentage of any park in the 

NCRN. On the opposite end of the spectrum, it had the lowest percentage of coarse fragments. The 

high clay is a function of the clay/siltstone parent materials and a warm wet climate suitable for the 

weathering of rocks into soil. The high clay in MANA affected all aspects of park’s soil physical and 

chemical properties. 

Db values were greater in MANA than in all other parks except WOTR, and its infiltration rates were 

the second slowest in the region behind WOTR. MANA had the highest penetration resistance in the 

NCRN, but it also had the highest volumetric water content. Both of these properties are attributable 

to the high clay soil texture which leads to the formation of many micropores able to hold a 

significant amount of water. Not surprisingly, MANA also had the highest proportion of poorly 

drained soils in the NCRN. 58% of plots contained a soil with reduced redoximorphic conditions in 

the upper 50 cm of the soil profile. 

Superlatives also characterized two chemical properties of MANA soils (Table 8). Extractable Mn 

and Mg levels were the highest or nearly the highest in the region in certain soil horizons. However, 

a lot of variation accompanied the high Mg and Mn values which suggests that there is a stark 

difference between Mg and Mn background levels in the diabase and siltstone parent materials in the 

park. Most of the other soil chemical characteristics were near the regional average for all parks and 

pH was between 5.1 and 5.5 throughout the profile. 
45

Table 8. Soil physical and chemical characteristics in MANA.

Soil Variables O horizon

A horizon 

composite

A horizon 

profile B horizon C horizon

n 1 19 17 18 1

Horizon midpoint n.a. n.a. 10 ± 6 55 ± 3 68 ± n.a.

Clay n.a. n.a. 23 ± 8 33 ± 13 32 ± n.a.

Coarse fragments n.a. n.a. 2 ± 5 4 ± 8 0 ± n.a.

pH n.a. 5.1 5.2 5.5 4.8 ± n.a.

CEC n.a. 13 ± 4.6 11 ± 3.8 12 ± 3.7 14 ± n.a.

BS n.a. 61 ± 27 61 ± 27 61 ± 21 88 ± n.a.

Total C 29 ± n.a. 4.4 ± 2.1 2.6 ± 1.2 0.55 ± 0.32 0.77 ± n.a.

Total N 1.0 ± n.a. 0.28 ± 0.13 0.17 ± 0.09 0.06 ± 0.05 0.04 ± n.a.

P 66 ± n.a. 9.8 ± 4.3 7.9 ± 3.8 4.6 ± 3.7 4.0 ± n.a.

K 390 ± n.a. 100 ± 52 68 ± 31 38 ± 21 29 ± n.a.

Ca 1960 ± n.a. 1310 ± 807 991 ± 662 692 ± 487 989 ± n.a.

Mg 300 ± n.a. 240 ± 160 220 ± 220 390 ± 250 800 ± n.a.

Na 59 ± n.a. 36 ± 30 35 ± 33 60 ± 53 41 ± n.a.

Mn 610 ± n.a. 130 ± 71 89 ± 83 24 ± 23 16 ± n.a.

Fe 63 ± n.a. 79 ± 90 74 ± 110 28 ± 14 33 ± n.a.

Cu 1.1 ± n.a. 3.8 ± 5.0 5.9 ± 9.3 9.3 ± 22.1 1.0 ± n.a.

Zn 27 ± n.a. 5.7 ± 3.0 5.3 ± 5.1 3.4 ± 5.2 1.6 ± n.a.

Ni 3.2 ± n.a. 1 ± 1 1 ± 0.6 1 ± 0.7 2 ± n.a.

Mo b.d.l. 0.1 ± 0.2 0.06 ± 0.1 0.06 ± 0.1 b.d.l.

Pb 2 ± n.a. 1 ± 1 1 ± 2 0.5 ± 0.4 0.2 ± n.a.

Cd 0.5 ± n.a. 0.1 ± 0.1 0.2 ± 0.5 0.2 ± 0.4 b.d.l.

Cr b.d.l. 0.2 ± 0.2 0.1 ± 0.1 0.1 ± 0.1 b.d.l.

Monocacy National Battlefield Park

Like MANA, MONO is found in the center of the Piedmont on the Maryland side of the Potomac 

River. Though some limestone is present in the park, the predominant soil parent material is 

metamorphosed slate, phyllite and schist. Of the soils in MONO’s 15 long-term vegetation plots, 14 

were formed from metamorphic residuum (either slate, phyllite or schist). One soil had alluvial 

parent materials located in a plot on the Monocacy floodplain, and one soil had a limestone parent 

material.
46

Three quarters of the park’s soils are Ultisols, but there were also three Inceptisols, and one Alfisol.

The park has 6 soil series: Baile, Cardiff, Comus, Glenelg, Hagerstown and Whiteford. More than 

half the soils (9 plots total) are from the Whiteford series.

MONO soils were rocky. They contained the highest percentage of coarse fragments in the NCRN, 

and consequently only 3 profiles were excavated to 100 cm depth. The coarse fragments undoubtedly 

affected penetration resistance which was higher than any other park in the region below 15 cm.

Other physical characteristics in MONO were average for the region. 

Though soils were rocky, the chemical data suggests that they are fairly fertile (Table 9). Total C, 

total N, extractable P and K were in the top third of soils in the NCRN. Extractable Ca was also 

above the regional average. The pH from A composite to B horizon ranged from 5.0 to 6.1, and soil 

contaminants were very low.

One plot, MONO-0044, contained 190 mg kg−1 extractable P in the E horizon (29 cm depth) when 

the other 3 plots with E horizons contained a maximum of 7 mg kg−1. The soil in MONO-0044 was 

only able to be excavated to 37 cm, and the extractable P in the A composite horizon was 70 mg kg−1

when the park average for that horizon was 21 ± 15 standard deviation. The pH of the plot was also 

≥6.4 which suggests that there is an unusual parent material in that plot which is affecting the soil 

properties of the entire profile. An alternative explanation is that perhaps there was an influx of wood 

ash or manure. We suggest further inquiry into the reasons for the abnormally high P values in 

MONO-0044. 

Table 9. Soil physical and chemical characteristics in MONO.

Soil Variables O horizon

A horizon 

composite

A horizon 

profile E horizon B horizon C horizon

n 2 16 14 4 13 2

Horizon midpoint 11 ± n.a. n.a. 12 ± 7 23 ± 5.4 44 ± 17 61 ± 10

Clay n.a. n.a. 15 ± 6 10 ± 4.3 22 ± 7.6 25 ± 13

Coarse fragments n.a. n.a. 27 ± 18 65 ± 22 38 ± 25 57 ± 13

pH 4.4 5.2 5.3 6.1 5.0 4.0

CEC 36 ± 2.2 19 ± 6.8 12 ± 6.2 9.1 ± 2.6 8.2 ± 3.3 7.2 ± 2.5

BS 87 ± 14 63 ± 23 53 ± 25 42 ± 37 42 ± 26 22 ± 11

Total C 24 ± 0.59 6.9 ± 3.8 4.5 ± 3.2 0.74 ± 0.26 1.4 ± 2.0 1.1 ± 0.6

Total N 1.6 ± 0.11 0.41 ± 0.15 0.29 ± 0.18 0.06 ± 0.02 0.09 ± 0.09 0.08 ± 0.03

P 92 ± 42 21 ± 15 15 ± 6.3 52 ± 80 7.1 ± 4.8 5.2 ± 1.7

K 450 ± 22 180 ± 62 120 ± 61 73 ± 36 62 ± 25 52 ± 17

Ca 5160 ± 551 1910 ± 1030 1080 ± 609 811 ± 1030 460 ± 303 161 ± 57.2
47

Table 9 (continued). Soil physical and chemical characteristics in MONO.

Soil Variables O horizon

A horizon 

composite

A horizon 

profile E horizon B horizon C horizon

Mg 520 ± 59 190 ± 74 120 ± 68 41 ± 27 64 ± 31 40 ± 7.0

Na 26 ± 3.5 23 ± 23 24 ± 34 9.3 ± 3.1 20 ± 24 14 ± 5.7

Mn 170 ± 77 71 ± 36 45 ± 15 22 ± 12 21 ± 14 10 ± 1.9

Fe 20 ± 13 57 ± 54 55 ± 32 23 ± 5.0 37 ± 29 21 ± 3.6

Cu 0.48 ± 0.10 6.1 ± 6.8 7.2 ± 5.5 9.6 ± 6.3 6.5 ± 5.3 4.6 ± 2.8

Zn 22 ± 1.5 10 ± 4.8 8.4 ± 4.8 7.8 ± 4.3 4.1 ± 2.6 2.1 ± 0.7

Ni 1.8 ± 0.52 1.3 ± 0.41 1.3 ± 0.83 0.8 ± 0.4 1.4 ± 1.3 1.9 ± 1.3

Mo 0.5 ± 0.01 0.06 ± 0.1 0.08 ± 0.1 b.d.l. 0.1 ± 0.1 0.08 ± 0.08

Pb 2.9 ± 0.84 1.9 ± 1.5 1.7 ± 1.5 0.8 ± 0.4 1.0 ± 1.0 1.3 ± 0.6

Cd 0.4 ± 0.06 0.4 ± 0.8 0.1 ± 0.1 0.03 ± 0.03 0.1 ± 0.1 0.1 ± 0.04

Cr 0.8 ± 0.01 0.1 ± 0.2 0.1 ± 0.1 b.d.l. 0.1 ± 0.1 0.04 ± 0.01

National Capital Parks-East

NACE is composed of a series of parks that form a modified semicircle from north to south around 

the eastern edge of DC and which continue to parallel the Potomac and Anacostia Rivers into

southeastern Maryland. It is the only park unit in the NCRN located entirely on the Coastal Plain.

With the exception of a handful of plots on the Potomac River floodplain, the parent materials found 

in NACE are entirely ancient marine sediments deposited millions of years ago when seas covered 

most of Eastern Maryland. A total of 47 long-term vegetation monitoring plots were established in 

the park. Ultisols are the primary soil order in 81% of those plots. In the rest of the plots which are 

located on the floodplain, 2 soils are Entisols and 7 are Inceptisols.

Eighteen soil series are present in NACE: Chillum, Christiana, Croom, Dodon, Downer, Elkton, 

Fallsington, Fluvaquents, Hammonton, Hatboro, Howell, Ingleside, Muirkirk, Potobac, Sassafras, 

Udorthents, Wist, and Woodstown. Christiana is the most prevalent series in the park found in 25% 

of the plots. Potomac is the second most prevalent found in 13% of the plots.

The soils of NACE are some of the deepest in the NCRN and contain very few coarse fragments

(Table 10). Marine sediment parent materials vary widely in texture from almost pure sand to clay

which explains why clay percent ranged from 4 to 67% in NACE.

Soil physical values in NACE were mostly in the middle two thirds of NCRN park values.

Penetration resistance in the top 15 cm was some of the lowest in the region, and all other values 

suggested the soils were adequately performing their intended ecosystem services.
48

Essential plant nutrient levels were often in the lower third of NCRN park values. This was true for 

most of the macronutrients: total N, extractable K, Ca, Mg, and for the micronutrient Mn. On the 

other hand, NACE’s extractable Fe levels were the highest in the NCRN. Sandy parent materials and 

those with naturally low fertility are probably responsible for a large amount of the relatively poor 

nutrient status in NACE, compared to other parks and agricultural soils in the region.

Extractable Pb levels were higher in NACE than in any other park in the region. The fact that Pb

levels are highest in the surface layers and decline throughout the profile suggests two things: first, 

that the levels are likely not tied to the parent material but rather come from automobile exhaust. (See 

Discussion Section.), and second, that Pb isn’t leaching down throughout the soil profile. However,

the levels are still well below the U.S. EPA residential soil screening level of 400 mg kg−1.

Nevertheless, these levels should be monitored in the future to determine if changes occur. 

Table 10. Soil physical and chemical characteristics in NACE.

Soil Variables O horizon

A horizon 

composite

A horizon 

profile E horizon B horizon C horizon

n 11 48 37 5 47 4

Horizon midpoint 3.0 ± 2.0 n.a. 14 ± 7 32 ± 8.9 55 ± 18 86 ± 22

Clay n.a. n.a. 16 ± 6 7.4 ± 3.1 24 ± 10 14 ± 9.3

Coarse fragments n.a. n.a. 5 ± 9 11 ± 15 9 ± 16 4 ± 7

pH 3.2 5.4 6.0 4.0 6.1 5.6

CEC 100 ± 31 14 ± 7.1 12 ± 8.8 4.2 ± 2.1 8.9 ± 5.4 6.5 ± 2.7

BS 11 ± 6.4 42 ± 31 39 ± 31 15 ± 12 31 ± 31 52 ± 33

Total C 32 ± 7.3 4.8 ± 2.6 3.1 ± 2.5 0.68 ± 0.38 0.72 ± 0.78 0.33 ± 0.20

Total N 1.3 ± 0.39 0.27 ± 0.15 0.18 ± 0.11 0.03 ± 0.02 0.06 ± 0.07 0.04 ± 0.02

P 40 ± 15 11 ± 11 10 ± 12 8.8 ± 7.4 7.4 ± 12 17 ± 25

K 320 ± 150 85 ± 54 59 ± 45 18 ± 7.3 39 ± 33 64 ± 66

Ca 996 ± 587 844 ± 916 707 ± 919 57.3 ± 42.2 435 ± 922 589 ± 389

Mg 330 ± 130 110 ± 85 73 ± 65 17 ± 13 80 ± 130 100 ± 95

Na 90 ± 61 29 ± 32 22 ± 15 6.8 ± 3.2 23 ± 17 20 ± 8.5

Mn 98 ± 58 52 ± 49 41 ± 50 13 ± 8.5 13 ± 16 7.8 ± 5.2

Fe 180 ± 300 99 ± 160 110 ± 200 50 ± 22 63 ± 160 27 ± 19

Cu 6.5 ± 7.5 4.6 ± 4.1 7.6 ± 18 1.8 ± 1.2 5.8 ± 7.3 2.7 ± 0.9

Zn 29 ± 15 11 ± 17 11 ± 23 1.8 ± 1.4 7.1 ± 23 1.3 ± 0.5

Ni 4.7 ± 1.7 1.7 ± 1.1 2 ± 1 0.8 ± 0.8 1.5 ± 1.6 1.6 ± 1.1
49

Table 10 (continued). Soil physical and chemical characteristics in NACE.

Soil Variables O horizon

A horizon 

composite

A horizon 

profile E horizon B horizon C horizon

Mo 0.02 ± 0.05 0.02 ± 0.07 0.02 ± 0.08 b.d.l. 0.02 ± 0.05 b.d.l.

Pb 20 ± 11 10 ± 9.4 7.5 ± 9.5 3.5 ± 2.7 3.0 ± 8.9 0.5 ± 0.3

Cd 0.2 ± 0.2 0.2 ± 0.3 0.1 ± 0.3 0.04 ± 0.07 0.06 ± 0.1 0.03 ± 0.02

Cr 0.02 ± 0.05 0.07 ± 0.08 0.08 ± 0.08 0.05 ± 0.03 0.1 ± 0.1 0.1 ± 0.1

Prince William Forest Park

PRWI straddles the boundary between the Piedmont and the Coastal Plain at the southern end of the 

NCRN. The majority of its 5,089 ha however, are squarely in the Piedmont making it the largest 

protected Piedmont forest ecosystem in the United States. Pyrite mining played an important role in 

PRWI, and much of the park’s land area was homesteaded or farmed into the 1930s. The forest 

ecosystem encompasses most of the watershed for Quantico Creek which meanders through the park.

With 145 long-term vegetation monitoring plots, PRWI is the second largest park in the NCRN. The

soils in those plots can be divided into two classes: those formed on the Piedmont (90%) and those 

formed on the Coastal Plain (10%). Most of the Piedmont soils were formed from metamorphosed 

residuum: primarily gneiss and schist with some mafic rocks and quartzite scattered throughout.

Micaceous minerals are common in the Piedmont soils. The Coastal plain soils were formed from 

Coastal Plain sediments. Some ancient and recent alluvial parent materials are also present in 

PRWI’s plots. The recent materials are found on the floodplain adjacent to Quantico Creek.

Greater than 85% of the soils in PRWI plots are Ultisols. Inceptisols located on the floodplain 

comprise 7% of the plots, and a few Alfisols also exist in PRWI. Coastal Plain soil series found in the 

park are: Bourne, Dumfries, Neabsco, and Quantico. The Inceptisols all belong to one soil series, 

Hatboro. The Piedmont soil series from most to least prevalent in PRWI plots are: Meadowville (35 

plots), Buckhall (22 plots), Elsinboro (22 plots), Glenelg (17 plots), Appling (7 plots), Orenda (4 

plots), Spriggs (4 plots), Worsham (4 plots), and Ashlar, Baile, Occoquan with with ≤3 plots each. It 

is surprising that only 16 soils series are found in a park with 147 long-term plots. That fact gives 

PRWI the distinction of having the highest plot:soil series ratio in the NCRN. 

The low soil series diversity was reflected in the relatively low variation in physical and chemical 

characteristics between plots within the park. Like MANA, PRWI was in the highest third of parks 

for clay percent and the lowest third for coarse fragments. Db and penetration resistance were in the 

middle third of parks. Interestingly, infiltration rates were the second fastest in the NCRN, and θv pre 

and post infiltration were the lowest values in the region (post infiltration θv was significantly lower 

than 5 other parks). This indicates that PRWI’s soils drain quickly, but also do not hold as much 

water in the surface as the other parks in the region. The predominantly loamy soil textures are 

probably responsible for the fast drainage and low water holding capacity.
50

Nearly all soil chemical values (Table 11) in all horizons were in the lowest third of NCRN park

averages, and frequently the chemical property was the lowest in the region. PRWI’s soils were quite 

acidic with pH values between 4.1 and 4.3 from surface to base of the profile. Base saturation 

(frequently used as an overall index of fertility, e.g., Perles et al. 2014) values were the lowest in the 

region. All parks in the NCRN, except WOTR, had at least double the extractable Ca of PRWI in the 

A composite horizon, and ANTI had close to an order of magnitude greater extractable Ca in the top 

mineral horizon. Levels of Total C, Total N, extractable P, K, and Mg also ranged from lowest to 

third lowest park values in the region. Only extractable Fe and Cu levels were in the highest third of 

parks. This is expected due to the underlying geology where pyrite (FeS2) is a prominent mineral.

One plot, PRWI-0537, contained 321 mg kg−1 extractable Cu in the C horizon making it an outlier 

among other PRWI plots. Copper deposits in sedimentary rocks can be found throughout Prince 

William County, Virginia, and the high levels in the bottom of the PRWI-0537 soil profile suggest 

that there might be a localized high ore deposit directly underneath this plot.

Table 11. Soil physical and chemical characteristics in PRWI.

Soil Variables O horizon

A horizon 

composite

A horizon 

profile E horizon B horizon C horizon

n 40 147 118 15 146 18

Horizon midpoint 2.0 ± 0.82 n.a. 11 ± 5 22 ± 9.4 52 ± 14 84 ± 14

Clay n.a. n.a. 19 ± 7 11 ± 3.9 27 ± 9.0 15 ± 11

Coarse fragments n.a. n.a. 7 ± 11 8 ± 14 8 ± 15 10 ± 20

pH 4.2 4.1 4.2 4.1 4.2 4.3

CEC 57 ± 25 12 ± 7.9 8.2 ± 5.1 6.4 ± 3.0 10 ± 5.0 8.0 ± 4.9

BS 23 ± 18 22 ± 18 20 ± 18 14 ± 11 20 ± 18 35 ± 19

Total C 28 ± 5.4 4.6 ± 2.9 2.6 ± 1.4 1.0 ± 0.5 0.5 ± 0.3 0.21 ± 0.19

Total N 1.0 ± 0.2 0.20 ± 0.12 0.12 ± 0.07 0.05 ± 0.03 0.03 ± 0.02 0.01 ± 0.01

P 33 ± 12 7.0 ± 4.4 5.1 ± 4.1 1.9 ± 0.9 2.6 ± 2.6 3.8 ± 2.2

K 420 ± 170 93 ± 60 63 ± 32 40 ± 25 44 ± 24 41 ± 18

Ca 1210 ± 1210 323 ± 393 161 ± 225 75.3 ± 74.8 122 ± 168 129 ± 185

Mg 350 ± 280 90 ± 89 57 ± 77 37 ± 59 120 ± 120 170 ± 130

Na 43 ± 30 18 ± 13 16 ± 10 12 ± 7.8 16 ± 10 17 ± 8.4

Mn 220 ± 160 58 ± 59 34 ± 32 18 ± 9.1 11 ± 12 16 ± 18

Fe 83 ± 40 81 ± 46 69 ± 59 40 ± 33 25 ± 52 18 ± 19

Cu 11 ± 14 4.3 ± 4.5 3.6 ± 4.9 3.4 ± 2.1 4.3 ± 17 19 ± 73

Zn 23 ± 18 5.8 ± 5.5 3.7 ± 5.3 2.2 ± 1.0 2.6 ± 7.1 6.3 ± 21
51

Table 11 (continued). Soil physical and chemical characteristics in PRWI.

Soil Variables O horizon

A horizon 

composite

A horizon 

profile E horizon B horizon C horizon

Ni 3 ± 1 1 ± 0.9 0.8 ± 0.5 0.5 ± 0.4 1.1 ± 1.0 1.3 ± 1.1

Mo 0.1 ± 0.3 0.04 ± 0.1 0.06 ± 0.2 b.d.l. 0.04 ± 0.08 0.04 ± 0.05

Pb 2.1 ± 1.3 3.0 ± 1.7 2.5 ± 1.9 1.8 ± 1.0 1.1 ± 0.6 0.5 ± 0.3

Cd 0.2 ± 0.3 0.09 ± 0.2 0.1 ± 0.5 0.1 ± 0.1 0.03 ± 0.05 0.03 ± 0.04

Cr 0.1 ± 0.2 0.09 ± 0.08 0.1 ± 0.1 0.1 ± 0.1 0.06 ± 0.07 0.1 ± 0.1

Rock Creek Park

ROCR is the third oldest national park in the United States (established in 1890), and the only park in 

the NCRN entirely within the bounds of Washington, D.C. It is also the only park that could be 

classified as an urban forest located entirely within the boundaries of a city. The park has long been 

an oasis for and destination for city dwellers and hosts heavy vehicle and pedestrian traffic on a daily 

basis. 

Like PRWI, ROCR also straddles the border of the Piedmont and Coastal Plain, but resides mainly in 

the Piedmont. Rolling hills are the backbone of the park, and often they rise steeply from the banks 

of Rock Creek. The geology and soil parent materials in the 19 long-term vegetation monitoring plots 

are primarily residual metamorphic gneiss and schist with a high amount of micaceous minerals.

These materials are found in 14 plots. Marine sediments from the Coastal Plain comprise the 

predominant parent material in 5 plots.

Four soil series are present in ROCR. Brandywine (5 plots), Manor (5 plots), and Glenelg (4 plots)

are the series with metamorphic residuum parent materials. The Coastal Plain soils are all from the 

Sassafras series.

Horizon mean clay contents in ROCR were some of the lowest in the NCRN. The penetration 

resistance in the park was also the lowest in the region for the top 15 cm of the profile and the second 

lowest in the region from 20 to 30 cm. All other physical property averages were in the middle third 

of the region’s parks.

ROCR was also in the middle third of park averages for almost every extractable plant nutrient

(Table 12). Like GWMP, ROCR’s soils could also be considered a “typical” soil of the region. It 

should be noted, however, that total C and total N in the B horizon were lower than 2/3 of the other 

parks. Behind NACE, Pb was also the second highest in the region in the mineral surface horizon, 

likely due to leaded gasoline used in pre-1990 vehicle traffic (see discussion in the NACE section).
52

Table 12. Soil physical and chemical characteristics in ROCR.

Soil Variables O horizon

A horizon 

composite

A horizon 

profile E horizon B horizon C horizon

n 1 19 15 1 18 7

Horizon midpoint n.a. n.a. 12 ± 7 49 ± n.a. 51 ± 8.8 73 ± 29

Clay n.a. n.a. 16 ± 7 3 ± n.a. 17 ± 9.3 6.9 ± 3.3

Coarse fragments n.a. n.a. 9 ± 16 10 ± n.a. 10 ± 14 28 ± 29

pH n.a. 5.7 5.8 4.2 ± n.a. 4.7 4.4

CEC n.a. 13 ± 6.2 13 ± 11 5.4 ± n.a. 8.5 ± 3.3 6.3 ± 3.1

BS n.a. 46 ± 28 43 ± 30 8 ± n.a. 31 ± 25 39 ± 25

Total C 35 ± n.a. 4.7 ± 2.3 4.1 ± 3.7 0.56 ± n.a. 0.42 ± 0.26 0.69 ± 1.4

Total N 1.5 ± n.a. 0.26 ± 0.12 0.29 ± 0.39 0.04 ± n.a. 0.04 ± 0.03 0.03 ± 0.05

P 75 ± n.a. 13 ± 17 14 ± 22 5.3 ± n.a. 5.8 ± 5.6 5.1 ± 2.5

K 650 ± n.a. 120 ± 51 100 ± 71 41 ± n.a. 60 ± 21 56 ± 26

Ca 1360 ± n.a. 958 ± 908 895 ± 1390 39.3 ± n.a. 303 ± 330 180 ± 104

Mg 300 ± n.a. 160 ± 100 170 ± 260 12 ± n.a. 120 ± 129 99 ± 49.7

Na 74 ± n.a. 21 ± 11 20 ± 13 6.9 ± n.a. 17 ± 8.4 13 ± 4.7

Mn 160 ± n.a. 66 ± 41 75 ± 70 14 ± n.a. 22 ± 21 12 ± 5.6

Fe 94 ± n.a. 59 ± 50 64 ± 77 22 ± n.a. 36 ± 77 27 ± 38

Cu 1.9 ± n.a. 3.2 ± 3.1 4.5 ± 6.3 1.2 ± n.a. 3.5 ± 2.9 0.6 ± 0.4

Zn 24 ± n.a. 7.3 ± 4.5 8.5 ± 11 1.0 ± n.a. 3.6 ± 4.2 1.5 ± 0.8

Ni 4.1 ± n.a. 1.9 ± 1.8 1.6 ± 0.8 0.7 ± n.a. 1.6 ± 1.2 1.5 ± 1.0

Mo b.d.l. b.d.l. b.d.l. b.d.l. 0.02 ± 0.06 0.01 ± 0.02

Pb 11 ± n.a. 7.9 ± 7.2 4.5 ± 3.6 1.1 ± n.a. 1.5 ± 1.2 2.3 ± 4.0

Cd 0.3 ± n.a. 0.1 ± 0.08 0.06 ± 0.06 b.d.l. 0.2 ± 0.3 0.05 ± 0.06

Cr 0.1 ± n.a. 0.09 ± 0.08 0.1 ± 0.1 0.1 ± n.a. 0.1 ± 0.2 0.06 ± 0.05

Wolf Trap National Park for the Performing Arts

At 43 ha, WOTR is the smallest national park in the NCRN. It is located in the Piedmont region, and

a stream, Wolf Trap Run, cuts through the park.

There are only six long-term vegetation monitoring plots in WOTR. Glenelg, which is comprised of 

schist residuum parent materials, is the predominant soil series in 5 plots. The Codorus soil series 

formed from schist and quartzite alluvium is found in the 1 plot located on Wolf Trap Run’s 

floodplain. This soil is classified as an Inceptisol and the other 5 soils in the park are Ultisols.
53

WOTR’s soils had the highest Db in the NCRN. Moreover, they also had the slowest infiltration 

rates. The penetration resistance values are also some of the highest in the region. These data suggest 

that the park struggles with compacted soils. This could increase the risk to vegetation health and 

also the erosion potential in the park leading to stream degradation. We suggest that these factors be 

monitored to prevent undue damage from compaction.

The soil chemistry and fertility patterns in WOTR (Table 13) were very similar to those in PRWI.

WOTR soils are quite acidic with a pH between 4.1 and 4.6 in all horizons. In the A and B horizons, 

Total C was the lowest in the region. For Total N and the extractable macronutrients, WOTR’s levels 

were either the lowest or second-to-lowest (behind PRWI) among the parks in the region. Extractable

Mn and Zn values were also low. Only extractable Fe and Cu were above average in the region. Cu 

was the highest in the NCRN in the A and B horizons and extractable Fe was in the highest third of 

parks in the A composite horizon.

The combination of poor physical and chemical characteristics in WOTR should monitored to ensure 

that they do not interfere with ecosystem function in the park.

Table 13. Soil physical and chemical characteristics in WOTR.

Soil Variables

A horizon 

composite

A horizon 

profile E horizon B horizon C horizon

n 6 4 1 4 2

Horizon midpoint n.a. 8 ± 3 42 ± n.a. 47 ± 14 70 ± 11

Clay n.a. 16 ± 6 8 ± n.a. 27 ± 5.1 8.9 ± 1.1

Coarse fragments n.a. 6 ± 9 50 ± n.a. 10 ± 10 30 ± 10

pH 4.6 4.2 4.6 ± n.a. 4.1 4.2

CEC 9.0 ± 4.1 5.8 ± 1.2 4.1 ± n.a. 6.0 ± 0.3 4.3 ± 0.6

BS 38 ± 29 36 ± 20 32 ± n.a. 22 ± 7.8 24 ± 0.9

Total C 3.7 ± 1.0 2.5 ± 0.26 1.0 ± n.a. 0.38 ± 0.04 0.13 ± 0.003

Total N 0.20 ± 0.05 0.16 ± 0.02 0.06 ± n.a. 0.04 ± 0.01 0.02 ± 0.0

P 6.2 ± 1.7 5.1 ± 0.7 1.4 ± n.a. 2.5 ± 0.2 2.1 ± 0.14

K 74 ± 22 56 ± 9.5 52 ± n.a. 34 ± 8.8 25 ± 6.9

Ca 428 ± 346 286 ± 190 137 ± n.a. 138 ± 80.1 101 ± 14.2

Mg 73 ± 60 52 ± 26 50 ± n.a. 49 ± 11.3 47 ± 4.4

Na 20 ± 17 21 ± 19 16 ± n.a. 18 ± 12.1 12 ± 1.8

Mn 38 ± 27 38 ± 15 26 ± n.a. 8.0 ± 3.4 16 ± 7.2

Fe 99 ± 66 53 ± 16 30 ± n.a. 20 ± 6.9 12 ± 2.0
54

Table 13 (continued). Soil physical and chemical characteristics in WOTR.

Soil Variables

A horizon 

composite

A horizon 

profile E horizon B horizon C horizon

Cu 7.6 ± 3.3 7.1 ± 2.5 2.1 ± n.a. 9.6 ± 7.7 2.3 ± 0.65

Zn 6.1 ± 2.2 5.9 ± 3.1 1.1 ± n.a. 3.8 ± 3.2 1.4 ± 0.2

Ni 1 ± 0.2 0.6 ± 0.1 0.7 ± n.a. 0.4 ± 0.1 0.3 ± 0.02

Mo b.d.l. 0.03 ± 0.06 b.d.l. b.d.l. b.d.l.

Pb 6.4 ± 5.0 6.5 ± 5.4 1.6 ± n.a. 1.6 ± 0.4 1.0 ± 0.5

Cd 0.5 ± 1.2 0.09 ± 0.07 b.d.l. 0.04 ± 0.03 0.1 ± 0.0006

Cr 0.03 ± 0.04 0.03 ± 0.02 0.07 ± n.a. 0.01 ± 0.01 b.d.l.
55

Discussion

NCRN soils data in the context of the I&M program

Soil Resources is one of the twelve basic Natural Resource Inventories identified by NPS to help 

park managers “understand and manage park natural resources.” (NPS 2019a). However, a search of

each I&M website for all 32 networks (accessed 26 May 2019) reveals that over half (including 

NCRN) have either not yet collected or not yet published their own field-derived soil dataset. Six

networks have a Soil Resources Inventory (SRI) from the National Cooperative Soil Survey 

(NCSS)—a joint effort of the United States Department of Agriculture and other Federal agencies, 

State agencies including the Agricultural Experiment Stations, and local agencies; it is unclear 

whether those six networks plan to instate their own monitoring program. Moreover, only 91 of

greather than 400 NPS units monitor “soil functions and dynamics” which includes soil nutrients, 

biological soil crust communities, and soil aggregate stability (Fancy and Bennetts 2012).

Of the published soils reports from I&M networks, this is the first to examine such an extensive suite 

of physical and chemical properties. I&M networks typically report on aggregate stability, 

compaction, and bulk density, but to the best of our knowledge, no networks have measured 

infiltration or penetration resistance. In addition, for soil chemical variables, most networks restricted 

themselves to total C, total N, pH, CEC and BS, and no network has published the breadth of macro 

or micronutrient data recorded in this report. Some networks focus on ecosystem-specific soil 

measurements important to their region, e.g., biological soil crust cover in the Chihuahuan Desert, 

electrical conductivity (EC) in Sonoran Desert, or soil surface elevation in South Florida/Caribbean

(McIntyre and Studd 2013; Pan et al. 2015; Whelan and Smith 2006), but none has combined 

chemical and physical measurements with a soil profile description to a depth of 100 cm.

Furthermore, NCRN collected data from 426 plots, whereas typically networks collected many fewer 

samples. Only Eastern Rivers and Mountains Network (ERMN) with 348 plots came close to the 

number of plots in the NCRN (Perles et al. 2014). This report, therefore, is novel within the context 

of the national I&M program not only for the number of soil variables measured, but also for the

sheer volume of data collected. It was the intent of the NCRN to inventory as many soil variables as 

possible in anticipation of discovering new and meaningful insights into the Eastern Deciduous 

Forest Ecosystem function (air, water, flora, fauna).

NCRN soils data in the context of Eastern Deciduous Forests

Relatively few forest soil studies have been conducted in the Mid-Atlantic region. None measures the 

entire suite of chemical and physical variables covered in this report and to the best of our knowledge 

only one (McGarvey et al. 2015) covers the 4 physiographic provinces that the NCRN surveyed.

Consequently, in addition to its value within the NPS I&M Program, this report represents an 

important, unique and extensive survey of Mid-Atlantic forest soil chemical and physical properties.

To date, forest soil research in the Mid-Atlantic has primarily been conducted at two locations: the 

Smithsonian Environmental Research Center (SERC) on the Coastal Plain in Anne Arundel County, 

MD (see McGarvey et al. 2015; Szlavecz et al. 2011; Yesolinis et al. 2016) and the Fernow

Experimental Forest on the Allegheny Plateau in Tucker County, WV (see Adams et al. 1997;
56

Gilliam et al. 1994, 2001). Those studies targeted specific components of forest soil ecosystems, 

(e.g., earthworm dynamics, historical land use, carbon storage, and nitrogen saturation). This report, 

however, serves three critical purposes for the Mid-Atlantic region: 1) it fills a void in the literature 

by answering a sometimes overlooked but fundamental ecological question, “What is there?”; 2) it

lays a solid foundation for many future ecological studies; 3) it provides easily accessible soil 

physical and chemical data, horizon by horizon, to depths not frequently sampled. 

NCRN soil patterns and ecological insights

The NCRN soils data reveals several important ecological patterns and insights. The first is that

contrary to expectations based on the urban nature of the region, there are relatively few heavy metal 

contaminants (Cd, Cr, and Pb). It is not surprising that NACE and ROCR had the highest levels of 

Pb, given that these parks are situated in urban centers in close proximity to roads with heavy vehicle 

traffic. This suggests that pre-1970s leaded gasoline is primarily responsible for soil Pb and further 

attested to by the fact that Pb concentrations declined with depth (Erel et al. 1997). However, even

the highest levels of extractable soil Pb are an order of magnitude below the EPA soil screening level 

of 400 mg kg−1—the recommended limit for safe residential use (EPA, 2019). Nonetheless, it must 

be noted that the screening levels are developed for total levels of contaminants (i.e., the weight 

contaminant/weight soil) not extracted levels of Pb. Thus, those specific plots with noted high levels 

of Pb, Cd or Cr in the “Park overviews” section, might warrant further testing for total contaminant 

levels to determine if soil levels are considered safe for accidental ingestion. Future monitoring 

should also determine whether Pb moves deeper in the soil profile over time as Johnson and Richter 

(2010) found in other forest soils of the Mid-Atlantic.

Another insight is that parent materials appear to have the greatest effect on soil chemical variables

throughout the region. Though important variables such as landscape position, elevation, slope 

aspect, and the effect of soil micro- and macro-organisms were not characterized in this study, and 

thus we cannot determine their relative effect on soil chemistry (For an example of this approach, see

Perles et al. 2014.), the data point to a strong parent material effect. This finding is attested to by the 

fact that a park with the highest levels of a nutrient in its upper horizons compared to other parks’ 

upper horizons, typically had the highest or nearly highest level of that nutrient in its lower horizons

compared to other parks’ lower horizons. The same phenomenon held true for parks with the lowest 

levels of nutrients in all horizons. The parks typically maintained their relative level of nutrients 

compared to other parks throughout the entire profile. For example, ANTI and MANA had the 

highest levels of extractable K and Mn respectively in their A and B horizons of any park in the 

region. PRWI and NACE had the lowest levels of Mg in their A and B horizons throughout the 

region. Since ANTI in the Appalachian Valley is largely underlain by a parent material not found in 

many of the other parks—limestone. MANA is underlain by rocks high in Mn, and PRWI and NACE 

are largely formed from acidic, quartzite parent materials. This suggests that parent materials are

responsible for the observed patterns.

Interestingly, the homogeneity of relative nutrients throughout the profile also suggests that though 

parks are often defined by political boundaries, this delineation appears to be an ecologically 

significant grouping mechanism for NCRN soils. Soils within a park boundary typically have similar 
57

parent materials. This is a fruitful area for future study. It also suggests that because parent materials 

have such a strong effect on relative nutrient levels throughout the profile, future sampling events for 

plant available nutrients can focus on the soil surface. Surface values can be used to estimate 

nutrients lower in the profile based on the magnitude of decrease or increase from upper to lower 

horizons. 

The vertical distribution of nutrients in the soil profile revealed another important NCRN pattern.

Most soil properties are strongly linked to horizon and more soil studies should focus on the soil 

horizon concept of sampling. Moreover, the highest levels of both macro and micronutrients were 

found in the O horizon, underlain by high nutrient levels in the A composite horizon, and a frequent

noticeable decrease in nutrients between A composite and A horizon samples. This suggests that 

nutrient levels change very rapidly in the top 30 cm of the soil surface (the typical maximum depth of 

cumulative A horizons). It further suggests that sampling by horizon and by arbitrary depth (e.g., 15 

cm as was used for composite sampling) tell different ecological stories, and that both are important

when considering ecology and landscape trends. If depth and horizon are not both taken into account, 

the sampling will be fraught with the possibility of seriously over or underestimating nutrients. 

Though the scientific literature points to higher concentrations of nutrients in the surface than in 

lower forest soil horizons (see summaries in Johnson and Lindberg 1992; Weil and Brady 2017), the

very high surficial levels of a broad suite of nutrients suggests that nutrient cycling from organic 

material—specifically the decay of leaf, twig and root litter—is the driver of vegetative growth in the 

region. Further studies are needed to confirm this hypothesis in the NCRN. Moreover, because 

NCRN nutrient distribution below the A horizon decreased slightly with depth but was overall fairly 

homogenous, these data further suggest that future sampling activities that correlate vegetation 

growth and soil properties should focus on the surface horizons. However, since we found noticeable 

differences between composite (surficial) and profile A samples (usually from deeper in the horizon) 

more research is needed to determine the very specific changes that occur with depth in the top 30 

cm of a forest soil. 

Surprisingly, only a little over quarter of NCRN plots have an O horizon. This raises several 

intriguing ecological questions: why do so few plots have O horizons? What factors in the region 

lead to robust O horizons? Is vegetative growth retarded by the lack of an O horizon? In a study

conducted at SERC in MD, soil properties were measured in virgin (uncut) forests and those that 

were converted from agricultural use 50–70 years ago or 120–150 years ago (Yesilonis et al. 2016). 

The authors found that the most prominent difference between the treatments was the presence or 

absence of a well-developed O horizon. The uncut forests had a thick O horizon, the 120–150-year 

old forests had a small or nonexistent O horizon, and the 50–70-year old forests had absolutely no O 

horizons. This indicates that many of the soils in the NCRN have not had enough time to develop O 

horizons and offers another fruitful opportunity for future studies. Yesilonis et al also found that soils 

in uncut stands were significantly more acidic than the older secondary forests, which in turn were 

significantly more acidic than the younger secondary forests. The uncut forests had higher soil C and 

lower bulk density compared to the other two treatments. This suggests that time is a very important

controlling factor for forest soil dynamics in the region, and also that NCRN soils could continue to 
58

sequester carbon over multiple century timescales. It also highlights the need for continued 

monitoring to track these changes. 

Future directions

Throughout the Discussion section, we have identified areas for fruitful future studies. This section 

highlights the gaps and limitations of this data set and recommends four major objectives for future 

studies.

Soil formation is a function of five independent factors which work in tandem to determine soil 

properties observed in the field: climate, parent material, time, relief, and organisms (Jenny 1941).

Data on the last formation factor, organisms, is entirely missing from this data set, and thus presents 

a major gap in the NCRN soil survey. Though aggregate stability is heavily influenced by 

microorganisms, there are no direct measures of this very important component of soil science.

Moreover, soil biology is at the center of nutrient cycling, ecosystem function, and soil health;

biological properties should be assessed and integrated with chemical and physical measurements.

Recommended soil biology tests include active carbon, soil respiration, soil proteins, and potentially 

mineralizable nitrogen (Islam and Weil 2000; Moebius-Clune et al. 2016).

Other I&M networks on the East Coast (ERMN and Appalachian Highlands Network) focused soil

monitoring efforts on sulfur (S) and nitrogen (N) pollution (Perles et al. 2014; Sullivan et al. 2011).

Sulfur was not evaluated in this study, nor did we attempt to determine N saturation. However,

according to a report published by the Appalachian Highlands Network that evaluated the sensitivity 

of I&M parks to acidification and S and N pollution from the atmosphere, the NCRN ranked 2nd

among the country’s 32 regions in the Pollutant Exposure category (Sullivan et al. 2011). This high 

ranking undoubtedly stems from the NCRN’s proximity to urban and industrial centers. We 

recommend that future monitoring efforts assess S levels as well as nitrate fluxes to determine 

whether the NCRN’s soils are at risk from these potential pollutants. 

Future studies are also needed to determine not only the pool of extractable nutrients in the NCRN at 

single point in time (assessed in this study) but also their fluxes and how these fluxes are affecting 

vegetation growth. It remains a challenge to measure the flux of nutrients into the soil pool from 

decaying organic material (leaves, twigs, rotting wood) and inorganic mineral sources and out of the 

pool through plant uptake or leaching, and whether these nutrients are limiting vegetation growth.

Nevertheless these biogeochemical studies are vital to understanding healthy ecosystem function

(Fisher and Binkley 2000). 

The soil C data in this study can be used to assess soil C stocks (megagrams of C per unit area to a 

depth of 100 cm) in the NCRN (i.e., how much carbon is sequestered in the region’s soils). This 

computation is a very important part of quantifying the impact that these urban forests can have on

mitigating CO2 emissions. Lal (2005) found that temperate forest soils contain 69% more C than the 

vegetation (100 compared to 59 Pg) which attests to the importance of forest soils for long-term CO2

reduction strategies. Moreover, Yesilonis et al. (2016) discovered that the soil C in 120–150-year old 

secondary forests at SERC in MD was significantly greater than in the 50–70-year old stands.

McGarvey et al. (2015) likewise found that total C density was 30% higher in old growth forests than 
59

in secondary forests. These studies suggest that the value of the NCRN forest soils for combating 

climate change will only increase. 

Many other scientifically important questions can be addressed with this data, including: do 

differences in nutrient concentrations among parks have any significance for ecosystem function? Do 

low pH values across the region reduce fine roots (a pattern observed by McNulty et al. (2007) and

Vanguelova et al. (2007), and caused by high aluminum and depletion of calcium and magnesium)?

In sum, the soils data collected in this report lay a solid foundation for future monitoring activities

and shed light on the condition of NCRN soils. It is the sincere hope of the authors that this report 

will aid other I&M networks in their soil monitoring efforts and will advance the science of forest 

ecology in the Mid-Atlantic region.
60

Literature Cited 

ASTM. 1984. Designation D 1586-84 Standard test method for penetration test and split-barrel 

sampling of soils. American Society for Testing and Materials: Annual Book of Standards Vol. 

4.08 Soil and Rock (I): D 420-D-4914. 

ASTM. 1995. Designation D 5778-95 Standard test method for performing electronic friction cone 

and piezocone penetration testing of soils. American Society for Testing and Materials: Annual 

Book of Standards Vol. 4.08 Soil and Rock (II): D 4943. 

Adams, M. B., T. R. Angradi, and J. N. Kochenderfer. 1997. Stream water and soil solution 

responses to 5 years of nitrogen and sulfur additions at the Fernow Experimental Forest, West 

Virginia. Forest Ecology and Management 95(1):79–91.

Chow, T. L., H. W. Rees, J. O. Monteith, P. Toner, and J. Lavoie. 2007. Effects of coarse fragment 

content on soil physical properties, soil erosion and potato production. Canadian Journal of Soil 

Science 87:565–577. 

Dixon, R.K., S. Brown, R. A. Houghton, A. M. Solomon, M. C. Trexler, and J. Wisniewski. 1994. 

Carbon pools and flux of global forest ecosystems. Science 263: 185–190.

EPA, 2019. Regional screening levels (RSLs) – user’s guide. Available at: 

https://www.epa.gov/risk/regional-screening-levels-rsls-users-guide#lead (Accessed 28 May 

2019).

Erel, Y., A. Veron, and L. Halicz. 1997. Tracing the transport of anthropogenic lead in the 

atmosphere and in soils using isotopic ratios. Geochimica et Cosmochimica Acta 61(21):4495–

4505. 

Fancy, S. G., J. E. Gross, and S. L. Carter. 2009. Monitoring the condition of natural resources in US 

national parks. Environmental Monitoring Assessment 151:161–174.

Fancy, S. G. and R. E. Bennetts. 2012. Institutionalizing an effective long-term monitoring program 

in the US National Park Service. Pages 481–497 in Gitzen et al. (editors). Design and Analysis of 

Long-term Ecological Monitoring Studies. Published by Cambridge University Press. The 

original book chapter is available from Cambridge University Press. 

Fisher, R. F. and D. Binkley. 2000. Ecology and management of forest soils. 3rd ed. John Wiley & 

Sons, New York, NY. 

Georgia Cooperative Extension. 2008. Soil test handbook for Georgia. University of Georgia. Kissel 

and Sonon (editors). Special Bulletin 62. 

Gilliam, F. S., N. L. Turrill, S. D. Aulick, D. K. Evans, and M. B. Adams. 1994. Herbaceous layer

and soil response to experimental acidification in a central Appalachian hardwood forest. Journal 

of Environmental Quality 23:835–844. 
61

Gilliam, F. S., B. M. Yurish, and M. B. Adams. 2001. Temporal and spatial variation of nitrogen 

transformations in nitrogen-saturate soils of central Appalachian hardwood forest. Canadian 

Journal of Forest Research 31(10):1768–1785. 

Islam, K.R., and R. R. Weil. 2000. Soil quality indicator properties in mi-Atlantic soils as influenced 

by conservation management. Journal of Soil and Water Conservation 55(1):69–78. 

Jenny, H. 1941. Factors of Soil Formation: A System of Quantitative Pedology. McGraw-Hill. 

Johnson, D. W., and S. E. Lindberg. 1992. Atmospheric deposition and forest nutrient cycling. 

Springer-Verlag, New York.

Johnson, A. H., and S. L. Richter. 2010. Organic-horizon lead, copper, and zinc contents of MidAtlantic forest soils, 1978–2004. Soil Science Society of America Journal 74(3):1001–1009.

Lal, R. 2005. Forest soils and carbon sequestration. Forest Ecology and Management 220:242–258. 

Long, L.C., V. D’Amico, and S.D. Frank. 2019. Urban forest fragments buffer trees from warming 

and pests. Science of the Total Environment 658:1523–1530.

McGarvey, J. C., J. R. Thompson, H. E. Epstein, and H. H. Shugart Jr. 2015. Carbon storage in oldgrowth forests of the Mid-Atlantic: toward better understanding of eastern forest carbon sink. 

Ecology 96:311–317. 

McIntyre, C. L. and S. E. Studd. 2013. Terrestrial vegetation and soils monitoring at Fort Davis 

National Historic Site: status report. Natural Resource Technical Report NPS/CHDN/NRTR—

2013/753. National Park Service, Fort Collins, Colorado.

McNulty, S. G., E. C. Cohen, J. A. Moore Myners, T. J. Sullivan, and H. Li. 2007. Estimates of 

critical acid loads and exceedances for forest soils across the conterminous United States: air 

pollution and vegetation effects research in national parks and natural areas: implications for 

science, policy and management. Environmental Pollution 149(3):281–292. 

Miller, K. M., B. J. McGill, B. R. Mitchell, J. Comiskey, F. W. Dieffenbach, E. R. Matthews, S. J. 

Perles, J. P. Schmit, and A. S. Weed. 2018. Eastern national parks protect greater tree species 

diversity than unprotected matrix forests. Forest Ecology and Management 414:74–84.

Moebius-Clune, B. N., D. J. Moebius-Clune, B.K. Gugino, O.J. Idowu, R. R. Schindelbeck, A. J. 

Ristow, H. M. van Es, J. E. Thies, H.A. Shayler, m.B. McBride, K. S. M. Kurtz, D. W. Wolfe 

and G. S. Abawi, 2016. Comprehensive Assessment of Soil Health – The Cornell Framework, 

Edition 3.2, Cornell University, Geneva, NY. 

NRCS. 1998. Soil Quality Test Kit Guide: Soil Quality Institute. U.S. Department of Agriculture.

NRCS. 2012. Field Book for Describing and Sampling Soils, version 3.0. National Soil Survey 

Center. U.S. Department of Agriculture.
62

NRCS. 2019. Slake Test Method. Available at: 

https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_051287.pdf (accessed 25 

April 2019). 

Nowak, D. J., and D. E. Crane. 2002. Carbon storage and sequestration by urban trees in the USA. 

Environmental Pollution 116:381–389. 

NPS Stats. 2018. Annual Park Ranking Report for Recreation Visits in: 2018. Available at: 

https://irma.nps.gov/Stats/SSRSReports/National%20Reports/Annual%20Park%20Ranking%20

Report%20(1979%20-%20Last%20Calendar%20Year) (accessed 20 April 2019).

NPS. 2019. Natural Resource Inventories. Available at: https://www.nps.gov/im/inventories.htm

(accessed 26 May 2019). 

Pan, J. J., D. Craig, D. Robinson, D. A. Soukup, L. A. Starcevich, N. Tallent, and R. Truitt. 2015. 

Integrated upland protocol of the Mojave Desert Network: Volume 1, protocol narrative. Natural 

Resource Report NPS/MOJN/NRR—2015/1010. National Park Service, Fort Collins, Colorado. 

Perles, S. J., D. R. Manning, K. Callahan, and M. R. Marshall. 2014. Condition of soils in Eastern 

Rivers and Mountains Network parks. National Resource Technical Report. 

NPS/ERMN/NRTR—2014/891. National Park Service, Fort Collins, Colorado. 

Olson, D.M., and E. Dinerstein. 2002. The Global 200: Priority ecoregion for global conservation. 

Annals of the Missouri Botanical Garden 89: 199–224.

Schmit, J. P., J. Parrish, and J. P. Campbell. 2012. National Capital Region Network: 2006–2009

forest vegetation status report. Natural Resource Technical Report NPS/NCRN/NRTR—

2012/570. National Park Service, Fort Collins, Colorado.

Shen, X., N. A. Bourg, W. J. McShea, and B. L. Turner. 2016. Long-term effects of white-tailed deer 

exclusion on the invasion of exotic plants: a case study in a Mid-Atlantic temperate forest. PLoS 

ONE 11(3):1–16. 

Smith, S. M. C., and P. R. Wilcock. 2015. Upland sediment supply and its relation to watershed 

sediment delivery in the contemporary mid-Atlantic Piedmont (U.S.A.). Geomorphology 

232:33–46.

Soil Survey Staff. 2014a. Soil Survey Field and Laboratory Methods Manual. Soil Survey 

Investigations Report No. 51, Version 2.0. Burt and Soil Survey Staff (ed.). U.S. Department of 

Agriculture, Natural Resources Conservation Service. 

Soil Survey Staff. 2014b. Keys to soil taxonomy 12th ed. U.S. Department of Agriculture, Natural 

Resources Conservation Service. 

Sullivan, T.J., G. T. McPherson, T. C. McDonnell, S. D. Mackey, and D. Moore. 2011. Evaluation of 

the sensitivity of inventory and monitoring national parks to acidification effects from 
63

atmospheric sulfur and nitrogen deposition: Appalachian Highlands Network (APHN). Natural 

Resource Report NPS/NRPC/ARD/NRR—2011/350. National Park Service, Denver, Colorado.

Szlavecz, K., M. McCormick, L. Xia, J. Saunders, T. Morcol, D. Whigham, T. Filley, and C. Csuzdi. 

2011. Ecosystem effects of non-native earthworms in Mid-Atlantic deciduous forests. Biological 

Invasions 13: 1165–1182.

U.S. Census Bureau. 2018. New Census Bureau population estimates show Dallas-Fort WorthArlington has largest growth in United States. Available at: 

https://www.census.gov/newsroom/press-releases/2018/popest-metro-county.html (accessed 20 

April 2019).

USDA. 2019. Official soil series descriptions. Available at: 

https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/survey/geo/?cid=nrcs142p2_053587

(accessed May 2019).

Vanguelova, E., S. Nortcliff, A. Moffat, and F. Kennedy. 2007. Short-term effects of manipulated 

increase in acid deposition on soil, soil solution chemistry and fine roots in Scots pine (Pinus 

sylvestris) stand on a podzol. Plant and Soil 294(1):41–54. 

Web Soil Survey. 2019. United States Department of Agriculture. Available at: 

https://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm (accessed May 2019).

Weil, R. R., and N. C. Brady. 2017. The nature and properties of soils. 15th ed. Pearson, Columbus, 

OH.

Whelan, K. R. T., and T. J. Smith III. 2006. Hurricane Wilma benefits mangrove forests at 

Everglades National Park. NPS Natural Resource Year In Review—2006. Available at: 

https://irma.nps.gov/DataStore/DownloadFile/564261 (accessed 27 May 2019).

Yesilonis, I., K. Szlavecz, R. Pouyat, D. Whigham, and L. Xia. 2016. Historical land use and stand 

age effects on forest soil properties in the Mid-Atlantic US. Forest Ecology and Management 

370: 83–92.
64

Appendix A

Definition of Soil Terminology

This appendix contains definitions of terms used in this report and general vocabulary germane to 

soil science. The definitions presented here are summaries from Weil and Brady (2017) and Soil 

Taxonomy (Soil Survey Staff 2014b). When abbreviations were used for workbook soil terms, the 

abbreviation is given in parentheses after the soil term, e.g., “cobbles” (CB). The definitions of 

certain soil properties are nested within the overarching term. For example, specific horizon 

designations (O, A, E, B, C, R) are explained nested underneath the word “Horizons.” Any general 

soil terminology used in this report is also defined, and every effort was made to give examples and 

explain terms within the context of the NCRN. Terms appear in alphabetical order unless otherwise 

noted.

Definitions

Aggregate stability – An important test of the cohesion of an aggregate (a mass of soil particles held 

together in a cohesive shape) from the surface of the soil. Aggregate stability is measured on a scale 

from 1 to 6 (least to most cohesive respectively) when it is immersed in water. If the aggregate slakes 

(falls apart) quickly after being placed in water, it is poorly cohesive. Aggregate stability is very 

responsive to human management, and typically is closely related to soil carbon content and 

inversely related to compaction. 

Base Saturation – The percent of the CEC occupied by base (non-acid) cations: Ca, Mg, K, and Na. 

It is sometimes used as a proxy for fertility.

Boundary description – Profile descriptions note the base of each horizon. However, horizons 

transitions are typically not defined by clear lines but rather change more gradually over a certain 

depth. The boundary descriptions (abrupt {A}, clear {C}, gradual {G}, diffuse {D}) describe the 

relative definition of the boundary from a strong, easily distinguished boundary to a boundary that 

shows a lot of variation respectively.

Bulk density (Db) – The dry weight of the fine earth fraction of soil divided by the entire volume 

that the fine earth fraction occupies (including pore spaces). Db can be used to calculate the pore 

space of the soil because soil scientists frequently assume a fixed particle density (Dp) of 2.65 g cm−3

for the soil solids (mainly quartz-based particles east of the Mississippi). Percent pore space = 1 −

Db/Dp. 

CEC – The cation exchange capacity (CEC) of a soil measures the total amount of exchangeable 

cations (Ca, Mg, K, Na) present in an acid soil extractant (Mehlich 1) in addition to exchangeable H 

(determined by titration with 0.023 M Ca(OH)2) and expressed as milliequivalents per 100 g soil.

CEC typically increases with clay and organic carbon content, but is also heavily influenced by the 

mineralogy of the clay particles.
65

Class – The three main categories of rock—sedimentary, metamorphic, or igneous—that characterize 

the PM rocks in a profile. If the PM was marine sediments or if the predominant rock/s was not 

discernable from Web Soil Survey, then this category was left blank.

Clay percent – Clay particles have a diameter <0.002 mm in diameter. With an enormous surface 

area (a fixed mass of clay particles can have a surface area hundreds of thousands of times greater 

than the same mass of sand particles) the clay percentage has a very strong effect (greater than that of 

sand and silt) on many physical and chemical soil processes such as the bulk density, penetration 

resistance, water infiltration and storage, carbon storage, etc.

Coarse fragments – Solids larger >2 mm in diameter within the soil profile. These are not 

considered part of the fine earth fraction (soil particles <2 mm in diameter) and thus do not factor 

into a determination of soil textural class. Four types of coarse fragments are found in the NCRN in 

order of their size from smallest to largest:

● Gravel (GR) – Coarse fragments that are 2 to 75 mm along their greatest diameter.

● Cobbles (CB) – Rounded coarse fragments that range from 75 to 250 mm along their greatest 

diameter.

● Channers (CH) – Flattened coarse fragments that range from 75 to 250 mm along their 

greatest diameter.

● Flags (FL) – Flattened large stones ranging from 150 to 380 mm along their greatest diameter.

Color (Hue, Value, Chroma) – Soil color is determined using the Munsell Color system with a hue, 

value and chroma (e.g., 10YR 4/6). Hue (the first symbol in a Munsell scheme—the “10YR” in the 

previous example) corresponds with the wavelength of light reflected off the soil. Value indicates 

how light or dark the soil sample is. The lower the value, the darker the color, and soil samples with 

values ≤3 are typically found in A or O horizons where organic carbon darkens the soil. The last 

number in the Munsell color designation, chroma, shows the saturation or brightness of the color.

High chromas indicate well oxidized conditions. High values (≥4) and low chromas (≤2) indicate 

gleyed, reducing conditions when water saturates the profile for a significant period of time, and 

microorganisms reduce iron from its ferric to ferrous state causing it to become soluble and move to 

another part of the soil profile, leaving the uncoated mineral particles which appear colorless or gray 

to human eyes.

Consistency – The ease with which a soil aggregate ruptures when crushed between thumb and 

forefinger. 

Contaminants – The extractable levels of 3 soil contaminants (Cd, Cr, Pb) most often associated 

with industrial or residential use were measured. High levels of these contaminants could 

detrimentally affect biological function for living organisms.

Gravimetric water content (θg) – A measure of the weight of water per weight of dry soil sample.

This is measured by taking a soil sample, sieving out particles > than the fine earth fraction, weighing 
66

the sample fresh, then drying the sample for 24 hours at 105oC before weighing the sample dry. θg = 

(weight fresh sample – weight dry sample)/weight dry sample.

Horizons (Master Horizons) – Soil layers of varying thickness that run roughly parallel to the soil 

surface and occur due to soil-forming processes (losses, additions, translocations, transformations).

As naturally occurring bodies in an ecosystem, soils are divided into and described according to the 

sequence of their horizons from the soil surface down to the parent material from which the soil 

formed. Every horizon consists of a master variable, either an O, A, E, B, or C (called the master 

horizons) denoted by a capital letter. The following descriptions of the master horizons appear in the 

order that these horizons would be found in a typical profile sequence from the soil surface to 

bedrock.

● O horizons are typically found at the soil surface in forest environments (and wetland 

environments where decomposition occurs slowly) when the soil is covered by a blanket of 

leaves (often described as the duff layer). Forested O horizons are directly underneath the layer 

of loose leaves and consist of predominantly organic materials (decomposing leaves forest 

debris) usually mixed with some mineral material. These horizons frequently increase water 

infiltration helping reduce erosion and are an important source of carbon and nutrients for soil 

micoorganisms and forest vegetation.

● A horizons are the topmost predominantly mineral layers near the soil surface that contain a 

high amount of organic matter and are therefore usually dark in color. In lay terms, an A 

horizon roughly corresponds with the term “topsoil” and have high fertility, high root density, 

and high numbers of soil microorganisms. 

● E horizons are characterized by losses (eluviation) of soil materials—clay, Fe and Al oxides, 

nutrients, organic matter—and typically are found beneath an A horizon in acidic forested soils 

where materials leach through the E to the lower horizons. E horizons are usually lighter in 

color than the overlying horizons and are not accompanied by a subordinate horizon 

designation.

● B horizons are commonly associated with the term, “subsoil.” They are layers typically 

characterized by accumulation (illuviation) of soil materials from the horizons above—clay, 

salts, iron, sulfates, carbonates, nutrients—that settle out beneath the O, A, and E horizon. B 

horizons must have a subordinate horizon designation next to them. 

● C horizons are the bottommost layers of the soil profile which have been little affected by the 

soil forming processes that shaped the horizons above it. Often they resemble the parent 

material from which they formed and therefore consist of a large volume of rock or sand, 

whatever the original parent material was. 

● R signifies bedrock and is not technically classified as soil, i.e., there are no physical or 

chemical descriptions.

Infiltration – Water entering the surface of the soil. In the NCRN, infiltration was performed on all 

soils without prior wetting (unsaturated), and then a second infiltration was performed (saturated) 
67

after the first meaning that the soil was fully moistened with the same amount of water at all sites 

prior to the saturated infiltration.

Lithologic discontinuity – These are zones in a soil profile that represent a change in the parent 

materials from which the soil formed. For example, alluvial soil materials are frequently deposited on 

top of residuum. The interface of the two differing soil materials is the lithologic discontinuity, and 

there can be multiple discontinuities in a soil profile. 

Nutrients – There are 14 essential nutrients that plants take up from the soil (meaning that without 

them a plant will not survive). Six of these nutrients (N, P, K, Ca, Mg, S) are referred to as 

macronutrients because plants use a relatively large amount of them (they make up >0.1% of the 

plant dry mass), and the others are considered micronutrients. The NCRN dataset includes the 

extractable levels (extracted using a strong acid solution) but not the total amount (with the exception 

of N) of 5 macronutrients (excluding S) and 7 micronutrients (Cl, Cu, Fe, Mn, Mo, Ni, Zn). In 

general, higher extractable levels of each nutrient (especially the macronutrients) indicates a healthier 

soil.

Order – The most general category of Soil Taxonomy, orders are primarily distinguished by the 

presence of specific diagnostic horizons. There are 12 soil orders in the world and five in the NCRN:

● Alfisol – These soils usually form under broad-leafed forests and in some grasslands. Like 

Ultisols, the Alfisols contain illuviated clay but are less weathered than the Ultisols, less acidic, 

and typically quite fertile for plant growth.

● Entisol – Soils that contain very little profile development. These soils do not have a B horizon 

because the environment is too extreme (e.g., insufficient water and cold temperatures) for 

them to form or because new parent materials or other disturbances are constantly resetting the 

soil forming processes. Often these soils are found in the mountains or directly next to a river 

where constant flooding changes the soil profile.

● Inceptisol – These are young soils (from the Latin inceptus) that have not had a lot of time for 

soil forming processes to delineate strong horizons. They therefore do not have many 

diagnostic features like a high presence of illuviated clay. Often Inceptisols will be found on a 

stream terrace or at the base of an eroded hill where an influx of parent materials in the not-toodistant past reset the soil forming clock. 

● Mollisol – Soils with a thick surface horizon containing a high amount of organic carbon. They 

typically are found under grasslands where root turnover leads to a large influx of soil organic 

carbon but can also be found near rivers or in wetlands where a lack of oxygen impedes 

organic matter decomposition. 

● Ultisol – Highly weathered soils that formed in forests of the humid tropics and subtropics.

They contain illuviated (moved down from the horizons above) clay, are found throughout the 

southeast U.S., and are more acidic and typically less fertile than Alfisols. 
68

Parent Material (PM) – The material from which a soil formed. The NCRN contains a diverse array 

of PMs: 

● Alluvium – Water-deposited PM from a river or stream. Alluvium can be transported and

deposited many miles from its original source and often produce highly fertile soils. Frequently 

alluvial materials are high in silt which is readily transported by water. 

● Colluvium – Gravity-deposited PM (rocks, sand, etc) that is typically found in valleys or 

downslope from the summit of a hill or mountain. 

● Marine and sandy sediments – PM deposited by ancient seas on top of the Coastal Plain. 

These materials are texturally diverse from very sandy to very clayey.

● Residuum – the bedrock that underlies a soil formed in place, i.e., residual PM is frequently 

found in upland areas where other wind, water, or gravity-deposited PMs have not been 

deposited overtop of the underlying bedrock.

Penetration resistance – A measure of the ease of penetrating the soil (in kPa) with a narrow rod 

capped by a cone-shaped head. This test is an indirect measure of soil compaction and can indicate 

how quickly water can enter a soil or the corollary—whether water might run off the surface causing 

erosion—or whether plant root growth will be impeded. 

pH – The negative log of the hydrogen ion activity in the soil solution. This master variable controls 

many soil chemical and biological processes, especially the availability of plant nutrients for uptake 

and whether Al might be toxic to plant growth. Very acid soils or basic soils typically impede 

vegetative growth. pH was measured using a CaCl2 solution.

Profile – The sequence of horizons described from the soil surface to bedrock or whatever depth is

excavated. 

Region – Describes the physiographic province (Coastal Plain, Piedmont Plateau, Blue Ridge, or 

Ridge & Valley) where the soil plot is located. If the plot was located on a floodplain or stream 

terrace (regardless of province), then “stream terrace” or “floodplain” were noted in this category. 

The rationale is that a floodplain or stream terrace would have a greater effect on the nature of the 

sample than the physiographic region.

Rock – Refers to the predominant rock/s that comprise the PM. If the PM was marine sediments or if 

the predominant rock/s was not discernable from Web Soil Survey, then this category was left blank.

Series – The most specific category of the Soil Taxonomy system that identifies a soil based on 

specific diagnostic features localized to a certain geographic location (e.g., Myersville). There are 

over 23,000 soil series in the U.S. Each one can be likened to a species in the animal kingdom having 

all the characteristics that distinguish it from other soil series with sufficient geographic distribution 

to merit its own unique series classification.

Soil Taxonomy – The system of soil classification developed by the United States Department of 

Agriculture (USDA) in conjunction with the National Cooperative Soil Survey (NCSS) and used in 

the U.S. and other countries to group soils according to measurable, diagnostic properties (e.g., clay 
69

content and chemical characteristics). There are six levels of soil taxonomy (from general to specific 

respectively): order, suborder, great group, subgroup, family, series.

Structure (type, size, grade) – Typically, soil particles clump together to form aggregates or peds 

based on the texture, carbon content, climate, etc., but in some very sandy conditions or in soils with 

lots of Na, the mineral particles stay in a loose non-aggregated condition. Soil texture describes the 

arrangement of the soil particles; the structure type designates the predominant shape of the peds; the 

size indicates how small or large the peds are (from very fine to very coarse); the grade indicates how 

distinct the structure is within the horizon (1 through 3 from not distinct to very distinct). Structure 

types within the NCRN are:

● Granular (GR) – spheroidal condition typically found in the surface A horizons where high 

carbon contents, plant roots, and macro and microfauna combine to form this structure. 

● Platy (PL) – Stacked structure into pancake-like sheets. This structure is often a result of 

compacted conditions near the surface of the soil. 

● Prismatic (PR) – Knife-like structure units where length of the ped is greater than width. 

Often found in horizons with a fragipan (Bx). 

● Subangular or Angular Blocky (SBK or ABK respectively) – The most common structure 

of illuviated clay (Bt) horizons. This structure is cube shaped but greater in width than length.

Subangular blocks have more round edges. 

Subordinate horizon designations – These lower case letters are placed after the capitalized master 

horizons and detail the specific nature or a predominant characteristic of the master horizon (e.g., Bt).

For example, the “t” subscript following a “B” master horizon indicates the presence of silicate clays 

in the B horizon. Subordinate horizon designations (with a few exceptions) are specific to particular 

master horizons. For example, the “p” subscript (denoting a plowed horizon) is only found after the 

A master horizon found at the surface of the soil profile. Multiple subordinate horizon designations 

may be combined after a master horizon (e.g., Btg). Subordinate horizon designations found in the 

NCRN are:

● b – Indicates that the horizon is buried underneath other layers and most often seen with A 

horizons (The b subordinate horizon typically occurs in zones that are flooded by rivers or 

streams). 

● c – Indicates the presence of concretions or nodules (minerals or elements e.g., iron, that have 

moved down into the profile and solidified as little masses within the profile). 

● g – Most often found next to a B horizon but can also be present with an A or C horizon, the g 

signifies gleying (gray colors) conditions when high water tables or saturation is present for a 

long enough duration to enable microorganisms to reduce ferric iron to its ferrous condition 

after which it leaves the profile.

● i, e, a – O horizons must be accompanied by a lower case subscript: either an “i, e, or a” which 

stand for fibric, hemic, or sapric respectively and denote the state of decomposition of the 

organic material from least to most decomposed respectively.
70

● p – In the NCRN, A horizons frequently have a “p” subscript next to them which denotes that 

the A horizon bears visible signs of being plowed at one time in history.

● r – This subordinate horizon is used only after the C horizon and represents saprolite or 

bedrock that is decaying in place. 

● ss – Stands for “slickensides.” This condition occurs in soils with a large amount of 

shrink/swell clays. When the soil is wet, the prismatic soil peds swell and as the soil dries out, 

the peds shrink causing them to slide against each other polishing the faces of the prisms and 

causing them to appear glossy and smooth.

● t – Used next to a B horizon denoting an argillic horizon or the accumulation of illuviated 

silicate clays moved down from the horizons above. 

● u – Indicates the presence of human-transported materials. 

● w – Denotes a cambic (or weak) horizon that has not had a lot of time for soil forming 

processes to occur and thus does not have many distinguishing strong morphological 

characteristics. The “w” is used with a B master horizon.

● x – Indicates the presence of a fragipan (a dense silica-cemented horizon that impedes root 

growth and water flow) or fragic conditions. 

Subsoil – Any soil beneath the A horizon which could include E, B, or C horizons. Subsoil typically 

connotes B horizon material, however, in the NCRN composite samples, the term represents 

anything beneath the A horizon. 

Texture – The distribution of mineral particles in the fine earth fraction (particles <2 mm in 

diameter) into three main size classes: 1) sand (2 to 0.05 mm diameter), 2) silt (0.05 to 0.002 mm 

diameter), 3) clay (<0.002 mm diameter). The relative proportions of sand, silt, and clay determine 

the soil texture which influences the surface area of the soil medium. Because the surface of soil 

particles is the site of water and gas adsorption, nutrient exchange for plants, carbon molecule 

attachment for C sequestration, and many other biogeochemical reactions, soil texture has an 

outsized effect on most soil processes. 

Textural class – Based on the texture (percentage of sand, silt, clay in a soil sample which add up to 

100) the soil textural class (e.g., silt loam, sandy loam, sandy clay loam) can be determined by 

examining the soil textural triangle chart. There are twelve textural classes with a defined percentage 

of sand, silt, clay. 

Transition horizons – Transition horizons contain properties of two master horizons and are denoted 

by combining the two appropriate capitalized letters (e.g., AB); the dominant horizon is always listed 

first. 

Volumetric water content (θv) – The volume of water in a specific volume of soil (expressed as the 

percent of a volume of soil occupied by water). Measured using a capacitance probe. 
71

Appendix B

Tables with Summary Statistics for All Physical Data

Table B1. Summary statistics for bulk density (Db) in parks of the NCRN.

Park n Bulk Density (Db)* stdev (σ) Std error

ANTI 38 0.87 0.17 0.03

CATO 117 0.49 0.24 0.02

CHOH 187 0.90 0.23 0.02

GWMP 82 0.82 0.23 0.03

HAFE 59 0.75 0.21 0.03

MANA 50 0.96 0.16 0.03

MONO 46 0.83 0.31 0.05

NACE 140 0.83 0.30 0.03

PRWI 425 0.82 0.27 0.01

ROCR 49 0.80 0.19 0.03

WOTR 16 1.01 0.26 0.06

* Db units are in g cm−3

Table B2. Summary statistics for unsaturated infiltration in parks of the NCRN.

Park n

Unsaturated infiltration

(cm hr−1) stdev (σ) Std error

ANTI 39 237 286 46

CATO 103 497 634 62

CHOH 158 326 594 47

GWMP 77 227 172 20

HAFE 32 232 181 32

MANA 49 220 287 41

MONO 51 254 247 35

NACE 143 297 420 35

PRWI 383 388 414 21

ROCR 53 302 355 49

WOTR 16 123 109 27
72

Table B3. Summary statistics for saturated infiltration in parks of the NCRN.

Park n Saturated Infiltration (cm hr−1) stdev (σ) Std error

ANTI 36 79 109 18

CATO 102 266 346 34

CHOH 146 150 352 29

GWMP 67 86 69 8

HAFE 32 91 83 15

MANA 47 77 98 14

MONO 51 101 116 16

NACE 137 152 250 21

PRWI 361 184 183 10

ROCR 51 129 172 24

WOTR 10 69 82 26

Table B4. Summary statistics for volumetric water content (Ɵv) pre-infiltration in parks of the NCRN.

Park n

Volumetric Water (Ɵv) preinfiltration* stdev (σ) Std error

ANTI 31 20.0 12.3 2.2

CATO 99 17.8 13.6 1.4

CHOH 169 22.4 11.3 0.9

GWMP 72 19.8 10.4 1.2

HAFE 53 17.2 9.6 1.3

MANA 54 24.0 10.9 1.5

MONO 49 18.7 10.9 1.6

NACE 139 20.4 11.6 1.0

PRWI 390 16.8 9.5 0.5

ROCR 54 23.5 10.1 1.4

WOTR 15 17.3 7.1 1.8

* Ɵv units are percent
73

Table B5. Summary statistics for volumetric water content (Ɵv) post-infiltration in parks of the NCRN.

Park n

Volumetric Water (Ɵv) postinfiltration (%) stdev (σ) Std error

ANTI 31 29.6 14.7 2.6

CATO 98 28.4 14.5 1.5

CHOH 161 30.0 9.8 0.8

GWMP 67 27.3 9.9 1.2

HAFE 48 25.7 11.2 1.6

MANA 51 31.5 9.5 1.3

MONO 46 27.1 7.9 1.2

NACE 134 30.6 8.7 0.7

PRWI 383 25.6 9.6 0.5

ROCR 50 28.4 8.0 1.1

WOTR 13 29.3 5.3 1.5

Table B6. Summary statistics for penetration resistance at 5-cm soil depth in parks of the NCRN.

Park n 5 cm penetration resistance (kPa) stdev (σ) Std error

ANTI 33 253 188 33

CATO 113 358 455 43

CHOH 186 365 374 27

GWMP 57 403 316 42

HAFE 54 568 590 80

MANA 43 561 559 85

MONO 48 315 305 44

NACE 106 268 225 22

PRWI 371 469 597 31

ROCR 45 224 222 33

WOTR 16 580 632 158
74

Table B7. Summary statistics for penetration resistance at 10-cm soil depth in parks of the NCRN.

Park n

10 cm penetration resistance 

(kPa) stdev (σ) Std error

ANTI 33 535 322 56

CATO 108 651 728 70

CHOH 182 609 575 43

GWMP 57 761 684 91

HAFE 48 1183 1200 173

MANA 43 1288 1192 182

MONO 48 809 614 89

NACE 105 546 578 56

PRWI 371 901 868 45

ROCR 43 488 745 114

WOTR 16 905 609 152

Table B8. Summary statistics for penetration resistance at 15-cm soil depth in parks of the NCRN.

Park n

15 cm penetration resistance 

(kPa) stdev (σ) Std error

ANTI 32 879 605 107

CATO 95 711 757 78

CHOH 175 823 846 64

GWMP 54 928 817 111

HAFE 40 1371 1271 201

MANA 42 1713 1258 194

MONO 44 1357 1055 159

NACE 104 743 598 59

PRWI 344 1096 922 50

ROCR 41 637 661 103

WOTR 15 1008 558 144
75

Table B9. Summary statistics for penetration resistance at 20-cm soil depth in parks of the NCRN.

Park n

20 cm penetration resistance 

(kPa) stdev (σ) Std error

ANTI 31 1008 674 121

CATO 90 805 873 92

CHOH 163 992 954 75

GWMP 47 965 804 117

HAFE 28 996 831 157

MANA 38 1697 1047 170

MONO 38 1721 1247 202

NACE 100 997 814 81

PRWI 328 1298 1020 56

ROCR 39 866 781 125

WOTR 14 1397 625 167

Table B10. Summary statistics for penetration resistance at 25-cm soil depth in parks of the NCRN.

Park n

25 cm penetration resistance 

(kPa) stdev (σ) Std error

ANTI 28 1142 717 136

CATO 78 916 929 105

CHOH 149 1199 1162 95

GWMP 45 1344 1164 174

HAFE 23 1244 1049 219

MANA 35 1793 1038 175

MONO 30 2089 1092 199

NACE 97 1381 1156 117

PRWI 306 1471 1092 62

ROCR 38 1105 1057 171

WOTR 12 1643 821 237
76

Table B11. Summary statistics for penetration resistance at 30-cm soil depth in parks of the NCRN.

Park n

30 cm penetration resistance 

(kPa) stdev (σ) Std error

ANTI 26 1681 1732 340

CATO 67 998 1004 123

CHOH 141 1518 1513 127

GWMP 44 1680 1295 195

HAFE 20 1508 1344 301

MANA 34 1958 1081 185

MONO 22 2023 1048 223

NACE 91 1808 1533 161

PRWI 288 1756 1310 77

ROCR 33 1199 1134 197

WOTR 11 1948 1020 308

Table B12. Summary statistics for aggregate stability in parks of the NCRN.

Park n aggregate stability (1–6) stdev (σ) Std error

ANTI 27 5.6 1.0 0.2

CATO 138 5.7 0.8 0.1

CHOH 166 5.6 0.7 0.1

GWMP 72 5.8 0.6 0.1

HAFE 57 5.8 0.6 0.1

MANA 57 5.6 0.7 0.1

MONO 42 5.8 0.6 0.1

NACE 107 5.7 0.7 0.1

PRWI 354 5.9 0.4 0.0

ROCR 42 5.7 0.9 0.1

WOTR 12 6.0 0.0 0.0
77

Appendix C

Soil Series in the NCRN

Here we present an alphabetical list of the 85 soil series in the NCRN compiled from Web Soil 

Survey (Web Soil Survey 2019). After each soil series name, we present a short description of the 

parent material the series is formed from and frequently the landscape position. All description come 

from the Official Soil Series Descriptions (USDA 2019).

1. Aden: Stream terraces of the Piedmont Plateau. Alluvial materials from the Triassic area. 

Quartz and siltsone fragments. 

2. Airmont: Mountain drainageways and backslopes of the Northern Blue Ridge. Colluvial 

materials from schist, quartzite, phyllite.

3. Albano: Head of drainage ways. Alluvium over residuum. Residuum is sandstone, shale, 

siltstone, argillite of Triassic age. 

4. Allegheny: Alluvium in variable areas.

5. Appling: Side slopes of the Piedmont Uplands. Very deep soils formed from felsic igneous 

and metamorphic residuum. 

6. Ashlar: Piedmont. Residuum weathered from felsic igneous and metamorphic rocks. 

Excessively drained. 

7. Atkins: Acid alluvium on flooplains. 

8. Bagtown series: Colluvial materials on mountain back slopes, footslopes and benches in the 

Blue Ridge Province. 

9. Baile: Piedmont. Alluvium over residuum. Residuum is acid crystalline rocks of mica schist 

and granitized schist and gneiss. 

10. Beltsville: Silty eolian sediments over fluviomarine deposits on the Coastal Plain.

11. Berks: Residuum weathered from shale, siltstone, fine-grained sandstone. The dominant clay 

minerals are illite, vermiculite and interstratified vermiculite chlorite. Small amounts of 

kaolinite are present.

12. Bermudian: Recent alluvium from sedimentary rocks (sandstone, shale) on floodplains.

13. Bigpool: Alluvium derived from sedimentary rocks along major rivers. 

14. Blocktown: Piedmont, shallow well drained soils formed from metamorphic phyllite and 

schist.

15. Bourne: Coastal plain upland soils formed in stratified marine and fluvial deposits.

16. Bowmansville: Recent alluvial soils formed from weathered dolerite or basalt. On 

floodplains. Lots of stratified sand and gravel. 

17. Brandywine: Piedmont upland soils formed from residuum from gneiss and related Cambrian 

and Precambrian rocks often on steep side slopes >15%.

18. Brinklow: Ridges and sideslopes of the Piedmont plateau. Formed from schist and phyllite. 
78

19. Buckhall: Very deep, well drained soils of the Piedmont Plateau formed from weathered 

gneiss and schist.

20. Carbo: Found in the Ridge & Valley formed from limestone bedrock. 

21. Cardiff: Deep, well drained soils of the Piedmont formed from quartzitic slate, phyllite, and 

other fine-grained rock. Often contain lots of channers. 

22. Chillum: Silty eolian materials underlain by marine sediments on the Coastal Plain. 

23. Christiana: Clayey fluviomarine sediments on the Coastal Plain. 

24. Codorus: Recently deposited alluvial deposits containing medium to large quantities of mica 

derived from schist, gneiss, phyllite, and other metamorphic rocks. 

25. Combs: Mollisols on floodplains and terrace treads formed from alluvium chiefly from 

colluvial soils that weathered from sandstone, siltstone, shale, and occasionally limestone. 

26. Croom: Coastal Plain soils formed from gravelly fluvial deposits. Loamy-skeletal.

27. Dekalb: Soils found on slopes and ridges formed from acid sandstones. 

28. Dodon: Coastal Plain soils formed from loamy marine sediments of Miocene age containing 

diatomaceous earth and very fine sand. 

29. Downer: Coastal Plain soils formed from loamy fluviomarine sediments. 

30. Downsville: Formed from old alluvium on high stream terraces from sandstone, shale, 

limestone. These are paleudults. 

31. Duffield: Very deep, well drained soils formed from residual limestone bedrock. 

32. Dumfries: Very deep soils on narrow ridges and sideslopes formed from feldspathic sandy 

sediments. 

33. Edgemont: Very deep residual soils from quartzitic rocks and schist. 

34. Elk: Alluvial mixed parent materials made from mixed sandstone, limestone, shale on stream 

terraces. 

35. Elkton: Low-lying uplands and lowland soils formed from silty eolian material underlain by 

marine sediments. Poorly drained endoaquults. Ancient floodplains.

36. Elsinboro: Can be on piedmont or coastal plain. Heavy mica throughout the profile. Loamy 

mica bearing alluvium. Stream terraces. 

37. Fairfax: Fluvial materials on the surface over residual schist and gneiss on Piedmont uplands. 

38. Fallsington: Coastal Plain Soils formed from fluviomarine sediments. 

39. Funkstown: Colluvium and alluvium washed down from surrounding uplands that covers 

underlaying limestone residuum. These soils occupy upland draws and head slope positions. 

40. Glenelg: Soils of the Piedmont and Blue Ridge formed in residuum weathered from 

micaceous schist. 

41. Hagerstown: Deep limestone residuum soils in the valley bottoms of the Ridge & Valley. 

42. Hammonton: Coastal Plain Soils formed from fluviomarine sediments. 
79

43. Hatboro: Soils on floodplains formed from alluvium derived from metamorphic schist, 

gneiss, and other crystalline rocks.

44. Haymarket: Residual soils from diabase and basalt. Triassic rocks.

45. Hazel: Piedmont residual soils on slopes. Sandstone and phyllite.

46. Highfield: Soils on mountain crests, slopes and intermountain valleys. Formed from 

metamorphosized igneous rocks. 

47. Howell: Deep well drained soils in marine sediments with detectable amounts of 

diatomaceous earth and/or glauconite.

48. Huntington: River valley soils on floodplains. Alluvium from sedimentary rocks. 

49. Ingleside: Coastal Plain soils from alluvial and marine sediments. 

50. Lenni: Poorly drained depressional soils formed from clayey fluviomarine sediments. 

51. Lindside: Floodplain soils formed from calcareous or limestone alluvium. 

52. Manassas: Colluvium and residuum in the Piedmont from Shale, Siltstone and conglomerate.

53. Manor: Piedmont soils formed from residual micaceous schist. 

54. Mattapex: Soils formed in silty eolian over fluviomarine sediments on the Coastal Plain. 

55. Meadowville: “Undulating to rolling uplands of the Piedmont Plateau around the head of 

drainageways, in saddles or depressions. Formed in acidic and basic rock material washed 

down from higher slopes.” 

56. Melvin: Alluvium from shale, sandstone, limestone and sedimentary rocks on floodplains.

57. Monogahela: Old alluvium from acid sandstone and shale on stream terraces and toeslopes.

58. Muikirk: Coastal Plain soils formed in a thin sandy mantle overlying old Cretaceous clays. 

59. Myersville: Blue Ridge Mountain soils formed from basic crystalline rocks such as 

greenstone. 

60. Neabsco: Coastal plain soils formed from stratified marine and fluvial sediments

61. Nollville: Formed on convex upland ridges in residuum from limestone and limy shale. 

62. Occoquan: Formed on summits, shoulders and sideslopes of narrow ridges in the northern 

part of the Piedmont Plateau. Underlain by schist and gneiss.

63. Opequon: Limestone uplands on summits, shoulders, backslopes. 

64. Orenda: Piedmont residual soils formed from basic metamorphic rocks—hornblende schist 

and hornblende gneiss. 

65. Penn: Red shale, siltstone and sandstone (but non calcareous) soils of uplands. 

66. Pope: Alluvium from sandstone, siltstone, shale on floodplains.

67. Potobac: Loamy and sandy fluvial sediments of the Coastal Plain. 

68. Purcelville: Residual soils formed from various kinds of schists in the Blue Ridge Uplands. 
80 

69. Quantico: Stratified marine and fluvial sediments of the northern coastal plain. Lots of 

feldspathic sands. 

70. Ravenrock: Colluvium from metamorphic metabasalt and metarhyolite on the backslopes and 

footslopes of the Blue Ridege. Typically rocky. 

71. Rhodhiss: Piedmont soils formed from felsic crystalline residuum. 

72. Rohrersville: Soils on the lower footslopes in the Blue Ridge and along drainage courses 

formed in local colluvial and alluvial material over residuum from metabasalt and 

metaandesite. 

73. Ryder: Residuum weathered from thin bedded limestone. 

74. Sassafras: Coastal Plain fluviomarine sediment soils. 

75. Spriggs: Piedmont soils but weathered from mafic rocks. 

76. Stumptown: Colluvium/Residuum from quartzite, muscovite schist, phyliite on ridges and 

sideslopes of the Blue Ridge. 

77. Swanpond: In the limestone valleys, these are formed from very old (from the Cambrian and 

Ordovician periods) limestone and have vertic properties (even slickensides). 

78. Talladega: Soils on the summits and sideslopes of the Blue Ridge and Ridge and Valley 

regions formed from metamorphic rocks. 

79. Thurmont: Formed in metamorphic colluvium on footslopes, colluvial fans, benches and 

stream terraces in the Blue Ridge. 

80. Trego: Formed in alluvial fans and colluvial footslopes out of alluvial metamorphic 

materials. 

81. Weverton: Soils formed from residual or colluvial muscovite schist, phyllite, quartzite in the 

Blue Ridge. 

82. Wist: Coastal Plain soils formed from glauconitic-bearing fluviomarine sediments. 

83. Woodstown: Coastal Plain soils formed from sandy marine and old alluvial sediments. 

84. Worsham: Soils of the Piedmont formed from alluvium formed from granite, gneiss, schist. 

Poorly drained soils at the heads of drains and base of slopes. 

85. Zion: Soils on the Piedmont uplands (summits, shoulders, backslopes) formed from mafic 

rocks (hornblende schist, gabbro, diorite, diabase, or dacite). 

The Department of the Interior protects and manages the nation’s natural resources and cultural heritage; provides scientific 

and other information about those resources; and honors its special responsibilities to American Indians, Alaska Natives, and 

affiliated Island Communities.

NPS 800/170921, June 2020
National Park Service

U.S. Department of the Interior

Natural Resource Stewardship and Science

1201 Oakridge Drive, Suite 150

Fort Collins, CO 80525

EXPERIENCE YOUR AMERICA TM