U.S. Department of the Interior

U.S. Geological Survey

Circular 1406

Understanding Nutrients in the Chesapeake Bay Watershed 

and Implications for Management and Restoration—

the Eastern Shore
Cover. Selected landscapes on the Eastern Shore, clockwise from top: Chester River watershed, Choptank River watershed, 

Nanticoke River watershed, Pocomoke River watershed, and the Eastern Shore of Virginia. Aerial imagery from the National 

Agricultural Imagery Program, U.S. Department of Agriculture. Refer to figure 40.
Understanding Nutrients in the Chesapeake 

Bay Watershed and Implications for 

Management and Restoration—

the Eastern Shore

By Scott W. Ator and Judith M. Denver

Circular 1406

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Ator, S.W., and Denver, J.M., 2015, Understanding nutrients in the Chesapeake Bay watershed and implications for 

management and restoration—the Eastern Shore: U.S. Geological Survey Circular 1406, 72 p., 

http://dx.doi.org/10.3133/cir1406.

ISSN 1067-084X (print)

ISSN 2330-5703 (online)

ISBN 978-1-4113-3878-4
iii

Contents

Chapter 1. Overview of Major Findings..............................................................................................................1

The Importance of the Eastern Shore to Chesapeake Bay....................................................................1

Sources of Nitrogen and Phosphorus on the Eastern Shore.................................................................4

Movement of Nitrogen and Phosphorus From Application Areas on the 

Eastern Shore to Chesapeake Bay and Its Tributaries .............................................................5

Nitrogen and Phosphorus in Eastern Shore Groundwater and Surface Waters ...............................6

Understanding and Managing Nitrogen and Phosphorus on the Eastern Shore...............................8

Chapter 2. Chesapeake Bay and the Eastern Shore.........................................................................................9

Importance of the Eastern Shore to Water Quality in Chesapeake Bay..............................................9

Environmental Setting of the Eastern Shore of Chesapeake Bay.......................................................16

Land Use..............................................................................................................................................16

Geology and Soils ..............................................................................................................................18

Climate and Hydrology......................................................................................................................23

Chapter 3. Sources and Movement of Nitrogen and Phosphorus on the Eastern Shore.........................27

Sources of Nitrogen and Phosphorus......................................................................................................27

Movement of Nitrogen and Phosphorus from Source Areas to Surface Waters ............................29

Nitrogen...............................................................................................................................................29

Phosphorus .........................................................................................................................................36

Chapter 4. Nitrogen and Phosphorus in Groundwater and Surface Waters of the 

Eastern Shore..........................................................................................................................................37

Regional Groundwater Quality..................................................................................................................37

Regional Surface-Water Quality...............................................................................................................40

Water Quality in Tidal Estuaries................................................................................................................45

Nitrogen and Phosphorus in Major Eastern Shore Watersheds ........................................................45

Chester River Watershed .................................................................................................................48

Choptank River Watershed ..............................................................................................................50

Nanticoke River Watershed.............................................................................................................52

Pocomoke River Watershed ............................................................................................................54

Virginia Coastal Watersheds............................................................................................................56

Chapter 5. Understanding Nitrogen in Support of Water Resource Management 

on the Eastern Shore..............................................................................................................................59

Why are nitrogen concentrations elevated in Eastern Shore groundwater 

and streams?..................................................................................................................................59

Why are nitrogen concentrations in streams and groundwater on the 

Eastern Shore increasing? ..........................................................................................................59

What management practices might be most effective at reducing nitrogen 

concentrations?.............................................................................................................................60

How long will it take to see water-quality improvement and, in the meanwhile, 

how will we know if land-management or restoration practices are working? ................61

Chapter 6. Understanding Phosphorus in Support of Water Resource Management 

on the Eastern Shore..............................................................................................................................63

Why are phosphorus concentrations elevated in many agricultural soils 

on the Eastern Shore? ..................................................................................................................63

Why is phosphorus moving into streams and groundwater on the Eastern Shore? .......................63

Why is phosphorus continuing to increase in the Choptank River in recent years?.......................64

What management practices may be most effective at limiting phosphorus 

movement to Eastern Shore streams and groundwater?.......................................................64

How long will it take to see water-quality improvement and, in the meanwhile, 

how will we know if land-management and restoration practices are working? .............64

References Cited...................................................................................................................................................65
iv

Figures

1. Maps showing the Eastern Shore of Chesapeake Bay..........................................................2

2. Graphs showing nitrogen and phosphorus inputs to the Eastern Shore 

and yields from the Eastern Shore to Chesapeake Bay are substantially 

greater than in the remainder of the bay watershed..............................................................3

3. Graph showing nitrogen and phosphorus applications in fertilizer and 

poultry production increased substantially on the Delmarva Peninsula 

during the 20th century................................................................................................................4

4. Pie charts showing agriculture provides more than 90 percent of the 

nitrogen and phosphorus inputs to the Eastern Shore...........................................................4

5. Diagram showing idealized summary of hydrology and nutrient transport 

on the Eastern Shore in areas with oxic groundwater and well-drained soils..................5

6. Maps showing nitrogen and phosphorus concentrations in Eastern Shore 

streams commonly exceed concentrations that may adversely affect 

aquatic ecosystems .....................................................................................................................6

7. Graph showing nitrate concentrations have increased in the Choptank 

River since the 1960s....................................................................................................................7

8. Graph showing historical loads of dissolved nitrogen from streams on 

the Eastern Shore to Chesapeake Bay and predicted future loads under 

four different scenarios of nitrogen inputs to groundwater..................................................8

9. Maps showing estimated average annual nitrogen and phosphorus yields 

to tributaries of Chesapeake Bay.............................................................................................10

10. Graph showing estimated average annual yields of nitrogen and phosphorus 

to Chesapeake Bay from the Eastern Shore and the remainder of the 

Chesapeake Bay watershed.....................................................................................................11

11. Graph showing estimated annual inputs of nitrogen and phosphorus to 

the Eastern Shore and the remainder of the Chesapeake Bay watershed, 2002 ............11

12. Map showing the estimated probability of groundwater nitrate concentration 

exceeding 5 milligrams per liter as N in the Chesapeake Bay watershed .......................12

13. Graphs showing reductions of (A) nitrogen and (B) phosphorus from 

nonpoint sources in major watersheds of the Eastern Shore required 

to meet a 2010 Total Maximum Daily Load (TMDL) for the Chesapeake Bay 

established under the Clean Water Act..................................................................................13

14. Graphs showing annual streamflow and nitrogen and phosphorus loads 

delivered to Chesapeake Bay, 1990 through 2012.................................................................15

15. Graph showing a summary of selected ecological conditions in Chesapeake 

Bay, 1985 through 2012...............................................................................................................15

16. Map showing major land use and land cover on the Eastern Shore, 2001.......................17

17. Map showing landscape elevations on the Eastern Shore.................................................19

18. Map showing the average texture of surficial sediments on the Eastern Shore ............20

19. Map showing the sand content of Eastern Shore soils .......................................................21

20. Map showing soil drainage on the Eastern Shore................................................................22

21. Diagram showing conceptual hydrologic cycle and average annual water 

budget for the Eastern Shore....................................................................................................24

22. Map showing variable hydrogeomorphic conditions among different areas 

of the Eastern Shore...................................................................................................................25

23. Map showing the estimated age of groundwater contributing to streamflow 

on the Eastern Shore..................................................................................................................26

24. Pie charts showing annual inputs of nitrogen and phosphorus from various 

sources to the Eastern Shore ...................................................................................................28
v

25. Graph showing past poultry broiler production and fertilizer applications 

on the Delmarva Peninsula .......................................................................................................28

26. Graph showing average annual balance between inputs (primarily in 

fertilizer and manure) and outputs (primarily in harvested crops) of nitrogen 

and phosphorus on cropland on the Delmarva Peninsula in recent decades .................29

27. Diagram showing idealized summary of hydrology and nutrient transport 

on the Eastern Shore in areas with oxic groundwater and well-drained soils................31

28. Graph showing the importance of dissolved oxygen concentrations to nitrate 

concentrations in shallow groundwater on the Delmarva Peninsula, 2001 .....................31

29. Graph showing the relation of concentrations of nitrate, phosphorus, and 

suspended sediment to streamflow in Chesterville Branch, 1990–2012 ...........................32

30. Diagrams showing idealized summary of hydrologic conditions and the 

potential for denitrification in groundwater in various hydrogeologic 

settings on the Eastern Shore ..................................................................................................34

31. Map showing estimated probability of nitrate concentrations in shallow 

groundwater exceeding 1 milligram per liter as N in areas of the 

Delmarva Peninsula ...................................................................................................................38

32. Map showing summary of nitrate concentrations in shallow groundwater 

in selected agricultural areas of the United States ..............................................................39

33. Maps showing summary of nitrogen and phosphorus concentrations in 

selected streams draining primarily agricultural areas of the United States ..................39

34. Graph showing summary of nitrate concentrations in the surficial aquifer 

on the Delmarva Peninsula during 1988–90 and 2001–03 ....................................................40

35. Graphs showing concentrations of nitrogen compounds in streams and 

shallow groundwater on the Delmarva Peninsula, 2000–01................................................40

36. Maps showing estimated average-annual flow-weighted concentrations 

of nitrogen and phosphorus in Eastern Shore streams........................................................41

37. Graph showing seasonal variability in nitrate concentrations in the 

Pocomoke River, 1999–2001 ......................................................................................................42

38. Map showing ecological conditions in Eastern Shore tributaries to the 

Chesapeake Bay assessed by sampling communities of benthic aquatic 

organisms.....................................................................................................................................43

39. Graphs showing trends in (A) average nutrient yields during 1985 through 

2010 and 2001 through 2010, and (B) nitrate concentrations from the 

mid-1960s through 2013 in the Choptank River near Greensboro, Maryland ...................44

40. Maps showing a summary of selected landscapes on the Eastern Shore ......................46

41. Graphs showing estimated nitrogen and phosphorus inputs to the landscape 

from various sources, 2002, and average annual outputs in streamflow to 

Chesapeake Bay .........................................................................................................................47

42. Maps showing the Chester River watershed.........................................................................49

43. Maps showing the Choptank River watershed......................................................................51

44. Maps showing the Nanticoke River watershed....................................................................53

45. Maps showing the Pocomoke River watershed....................................................................55

46. Maps showing the Virginia Coastal watersheds...................................................................57

47. Graph showing changes in nitrate concentrations over time in groundwater 

beneath adjacent fields after the initiation of winter cover crops in 1988........................60

48. Graph showing use of cover crops on the Delmarva Peninsula, 1985–2011....................62

49. Graph showing forecasted nitrogen delivery from the Eastern Shore to 

Chesapeake Bay under selected potential management scenarios .................................62
vi

Multiply By To obtain

Length

centimeter (cm) 0.394 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

square kilometer (km2) 247.1 acre

square kilometer (km2) 0.3861 square mile (mi2)

hectare (ha) 2.471 acre

Flow rate

meter per day (m/d) 3.281 foot per day (ft/d)

Mass or Yield

kilogram (kg) 2.205 pound avoirdupois (lb)

megagram (Mg) 1.102 ton, short (2,000 lb)

megagram (Mg) 1,000 kilogram (kg)

kilograms per square kilometer 

(kg/km2) 0.0089 pounds per acre (lb/acre)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

 °F = (1.8 × °C) + 32

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) 

or micrograms per liter (μg/L). 

Conversion Factors and Datums


Understanding Nutrients in the Chesapeake Bay 

Watershed and Implications for Management 

and Restoration—the Eastern Shore

By Scott W. Ator and Judith M. Denver

Chapter 1. Overview of Major Findings

The Importance of the Eastern Shore to 

Chesapeake Bay

SEE CHAPTER 2

The Eastern Shore (fig. 1) includes only a small part of 

the Chesapeake Bay watershed, but contributes disproportionately large loads of the excess nitrogen and phosphorus 

that have contributed to ecological and economic degradation 

of the bay in recent decades. Chesapeake Bay is the largest 

estuary in the United States and a vital ecological and economic resource. The bay and its tributaries have been degraded 

in recent decades by excessive nitrogen and phosphorus in the 

water column, however, which cause harmful algal blooms 

and decreased water clarity, submerged aquatic vegetation, and 

dissolved oxygen. The disproportionately large nitrogen and 

phosphorus yields from the Eastern Shore to Chesapeake Bay 

are attributable to human land-use practices as well as natural 

hydrogeologic and soil conditions. Applications of nitrogen 

and phosphorus compounds to the Eastern Shore from human 

activities are intensive. Also, hydrogeologic and soil conditions promote the movement of these compounds from application areas on the landscape to groundwater and (or) surface 

waters, and the proximity of much of the Eastern Shore to tidal 

waters limits opportunities for natural removal of these compounds in the landscape. The Eastern Shore only includes 7 

percent of the Chesapeake Bay watershed, but receives nearly 

twice as much nitrogen and phosphorus applications (per area) 

as the remainder of the watershed and yields greater nitrogen 

and phosphorus, on average, to the bay (fig. 2).

Aerial view of Maryland’s Eastern Shore modified from the 

National Aeronautics and Space Administration (NASA) 

Terra satellite MODIS (Moderate Resolution Imaging 

Spectroradiometer) image of September 2011.

Chesapeake Bay Chesapeake Bay

Eastern Shore

Eastern Shore

ATLANTIC OCEAN

ATLANTIC

Potomacc

River

PENNSYLVVANIA

NEW JERSEY

MARYLAND

VIRGINIA

Washington,

D.C.

DELAWARE

Susquehanna

River

Susquehanna

River

N

Delaware Bay Delaware Bay

Chapter 1
2 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

38°

39°

76°

75°

Pennsylvania

Pennsylvania

Maryland

Virginia

Delaware

New Jersey

New York

New

Jersey

DE

Washington,

D.C.

Maryland

West

Virginia

Virginia

Chesapeake 

Bay

Delaware Bay

Delmarva

Peninsula

Chesapeake

Bay

watershed

Chesapeake Bay

watershed

boundary Eastern Shore

Eastern

Shore

ATLANTIC

OCEAN

ATLANTIC

OCEAN

CHESTER RIVER

WATERSHED

CHOPTANK

RIVER

WATERSHED

NANTICOKE

RIVER

WATERSHED

Delaware Bay

Delaware River

POCOMOKE RIVER

WATERSHED

VIRGINIA COASTAL 

WATERSHEDS

Chesapeake Ba

Agriculture y

Forest and swamp

Urban

Emergent wetland

Open water

EXPLANATION

Land cover

0 10 20 MILES

0 10 20 KILOMETERS

50 100MILES

0 50 100KILOMETERS

0

Base from U.S. Geological Survey,

1:2,000,000 DLG, Albers Equal Area

Conic Projection, NAD 83

Land-cover data from LaMotte, 2008a, b

N

N

Salisbury

Seaford

Cambridge

Chestertown

Easton

CHESTER RIVER Dover

WATERSHED

CHOPTANK

RIVER

WATERSHED

NANTICOKE

RIVER

WATERSHED

POCOMOKE RIVER

WATERSHED

VIRGINIA COASTAL 

WATERSHEDS

Eastern

Shore

Figure 1. The Eastern Shore of Chesapeake Bay. 

The Eastern Shore includes areas of the Chesapeake 

Bay watershed east of the bay on the Delmarva Peninsula.
Chapter 1. Overview of Major Findings 3

0

0

1

1

2

2

3

3

4

4

5

5

6

6

7

7

8

8

9

9

10 11

Nitrogen

Nitrogen

Phosphorus

Phosphorus

10

10

20

20

30

30

40

40

50

50

60

60

0 70

0

Eastern Shore

Rest of Chesapeake Bay watershed

Estimated average annual watershed inputs, in kilograms per hectare

(pounds per acre)

Estimated average annual delivered yield to Chesapeake Bay,

in kilograms per hectare

(pounds per acre)

[Estimated inputs from Bachman and others, 1998, Wieczorek and LaMotte, 2010a, b, c, d,

and Ator and others, 2011. Estimated yields from Ator and others, 2011.]

Figure 2. Nitrogen and phosphorus inputs to the Eastern Shore and yields from the 

Eastern Shore to Chesapeake Bay are substantially greater than in the remainder of 

the bay watershed.

Chapter 1
4 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

NITROGEN PHOSPHORUS

Fertilizer applications or (for nitrogen) direct fixation from

the atmosphere by crops (Wieczorek and LaMotte, 2010b).

Manure (Wieczorek and LaMotte, 2010c).

Atmospheric deposition (Wieczorek and LaMotte, 2010d).

Other, including point sources (U.S. Environmental Protection

Agency, 2009) and septic systems (Maizel and others, 1997).

SOURCE

INPUTS TO THE EASTERN SHORE

Figure 4. Agriculture provides more than 90 percent of the 

nitrogen and phosphorus inputs to the Eastern Shore. 

0

10

20

30

40

50

60

0

100

200

300

400

500

600

1910 1930 1950 1970 1990 2010

NITROGEN

PHOSPHORUS

0

10

20

30

Fertilizer applications, in millions of kilograms

Millions of broilers sold

[Broiler data are from U.S. Department of Agriculture, 2009. Estimates prior to 1950 are for total

chickens or broilers raised. Fertilizer inputs are from Alexander and Smith, 1990, Battaglin and

Goolsby, 1995, and Mid-Atlantic Water Program, 2012.]

Year Figure 3. Nitrogen and phosphorus 

applications in fertilizer and poultry 

production increased substantially on the 

Delmarva Peninsula during the 20th century.

Sources of Nitrogen and Phosphorus on the 

Eastern Shore

SEE CHAPTER 3

Agricultural operations contribute the vast majority 

of nitrogen and phosphorus to the landscape on the Eastern 

Shore. Land use in the area has been primarily agricultural for 

several hundred years. Nitrogen and phosphorus applications 

in support of agriculture increased substantially during the second half of the last century, however, but have since stabilized 

or decreased (fig. 3). More than 90 percent of nitrogen and 

phosphorus reaching the land in the Eastern Shore is applied 

as part of inorganic fertilizers or manure, or (for nitrogen) 

fixed directly from the atmosphere in cropland (fig. 4). Nonagricultural sources such as atmospheric deposition, septic 

systems, sewage treatment plants, or other urban sources 

are locally important in some areas, but 

provide less than 10 percent of nitrogen 

and phosphorus applications to the Eastern 

Shore, as a whole. Nitrogen and phosphorus applications to cropland on the Eastern 

Shore generally exceed the amount that is 

removed in crops during harvest, and agricultural applications therefore represent a 

net additional input of these compounds to 

the environment each year.
Chapter 1. Overview of Major Findings 5

Movement of Nitrogen and Phosphorus From 

Application Areas on the Eastern Shore to 

Chesapeake Bay and Its Tributaries

SEE CHAPTER 3

Once on the land surface, nitrogen and phosphorus movement to surface waters occurs primarily through the action 

of water. Nitrogen is primarily transported to surface waters 

through groundwater in the form of nitrate (fig. 5). Nitrate may 

be lost from the landscape to the atmosphere in groundwater 

SURFICIAL AQUIFER

EXPLANATION

Flow path or storage location

Hydrogeologic units

Estuary

Water table

Land surface

NONPOINT SOURCES

Nitrogen and phosphorus

GROUNDWATER FLOW

(Years) GROUNDWATER FLOW

(Years)

GROUNDWATER FLOW (Decades)

OVERLAND RUNOFF

(Days to decades)

ACCUMULATION IN

SOIL (Decades)

Stream

Submarine

groundwater

discharge

Flow path with natural water chemistry and

no anthropogenic nitrogen or phosphorus

Flow path with nitrate and any dissolved

phosphorus

Flow path with insoluble phosphorus and nitrogen

compounds (such as organic nitrogen)

Storage of insoluble phosphorus

Unsaturated zone above the water table Aquifer with oxic groundwater Confining unit

Figure 5. Idealized summary of hydrology and nutrient transport on the Eastern Shore in areas with oxic groundwater and 

well-drained soils. Nitrogen transport from the land surface to streams occurs primarily through groundwater in the form of 

nitrate, whereas phosphorus transport occurs primarily in overland runoff.

with limited dissolved oxygen, but natural hydrogeologic and 

soil conditions conducive to plentiful dissolved oxygen in 

groundwater are common in many areas of the Eastern Shore, 

and 70 percent of nitrogen in Eastern Shore streams travels 

to those streams through groundwater as nitrate. Phosphorus, 

conversely, is predominantly transported over the land in runoff attached to sediment (fig. 5). The pathways and amounts of 

these chemicals entering surface waters are controlled by the 

amounts that have been applied in excess of crop uptake, differing chemical and physical properties of nitrogen and phosphorus compounds, and by varying hydrologic, geochemical, 

and geologic environments in different areas.

Chapter 1
6 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Nitrogen and Phosphorus in Eastern Shore 

Groundwater and Surface Waters

SEE CHAPTER 4

On the Eastern Shore, nitrogen is common in groundwater and surface waters and phosphorus is common in surface 

waters at concentrations that are well above natural levels, and 

are among the highest in the Nation. Nitrogen and phosphorus 

commonly occur in streams at concentrations that may 

adversely affect aquatic ecosystems (fig. 6) and have increased 

Delaware River

ATLANTIC OCEAN

Delaware Bay

Chesapeake Bay

0 10 20 MILES

0 10 20 KILOMETERS

NITROGEN PHOSPHORUS

38°

39°

76°

75°

Pennsylvania

Maryland

Virginia

Delaware

POCOMOKE RIVER

WATERSHED

CHESTER RIVER

WATERSHED

CHOPTANK

RIVER

WATERSHED

NANTICOKE

RIVER

WATERSHED

VIRGINIA COASTAL 

WATERSHEDS

Chesapeake Bay

watershed

boundary

Eastern

Shore

N

Surface-water chemistry estimated

from Ator and others, 2011

Base from U.S. Geological Survey,

1:2,000,000 DLG, Albers Equal Area

Conic Projection, NAD 83

LE 0.031 (AQR)

GT 0.031 and LE 0.2

GT 0.2 and LE 0.3

GT 0.3 and LE 0.4

GT 0.4

EXPLANATION

Estimated average

annual flow-weighted

concentration during 2002,

in milligrams per liter

Estimated average

annual flow-weighted

concentration during 2002,

in milligrams per liter

LE 0.71 (AQR)

GT 0.71 and LE 2

GT 2 and LE 3

GT 3 and LE 5

GT 5

EXPLANATION

Delaware Bay

Delaware River

Chesapeake Bay

Pennsylvania

Maryland

Delaware

CHESTER RIVER

WATERSHED

CHOPTANK

RIVER

WATERSHED

NANTICOKE

RIVER

WATERSHED

POCOMOKE RIVER

WATERSHED

Chesapeake Bay

watershed

boundary

Eastern

Shore

ATLANTIC OCEAN

Virginia

VIRGINIA COASTAL 

WATERSHEDS

N

0 10 20 MILES

0 10 20 KILOMETERS

38°

39°

76°

75°

Base from U.S. Geological Survey,

1:2,000,000 DLG, Albers Equal Area

Conic Projection, NAD 83

Surface-water chemistry estimated

from Ator and others, 2011

Figure 6. Nitrogen and phosphorus concentrations in Eastern Shore streams commonly exceed concentrations that 

may adversely affect aquatic ecosystems. (AQR is the water-quality criteria recommended to protect aquatic organisms 

[U.S. Environmental Protection Agency, 2000]. GT = greater than; LE = less than or equal to.)
Chapter 1. Overview of Major Findings 7

in recent decades (fig. 7). Nitrate concentrations in the 

Choptank and Nanticoke Rivers have increased consistently 

since the mid-1960s (fig. 7), primarily due to increasing nitrate 

concentrations in groundwater discharge, the primary source 

of both water and nitrogen to those rivers. Nitrate concentrations in groundwater in the shallow surficial aquifer increased 

in parts of the aquifer between 1988 and 2001 in response 

to increased nitrogen applications in previous decades, and 

Figure 7. Nitrate concentrations have increased in the Choptank River since the 1960s. Nitrate, in milligrams per liter as N 4

3

Choptank River near Greensboro, Maryland

Spline smooth line 2

1

0

1970

[From U.S. Geological Survey, 2014. See also Moyer and others, 2012.]

1980 1990 2000 2010

Year

concentrations that may affect the suitability of the water for 

drinking are not uncommon. Differing nutrient concentrations in different areas are attributable to varying inputs from 

agriculture and other sources, as well as hydrogeologic, soil, 

and other natural conditions that affect the fate and movement 

of nitrogen compounds through the subsurface and phosphorus 

over the land surface.

Chapter 1

Great blue heron on the shores of the Choptank River. 

Photograph by Jane Thomas, Integration and Application 

Network, University of Maryland Center for Environmental 

Science (ian.umces.edu/imagelibrary/).

Osprey nesting in the Choptank River. Photograph by 

Ben Fertig, Integration and Application Network, University 

of Maryland Center for Environmental Science 

(ian.umces.edu/imagelibrary/).
8 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Understanding and Managing Nitrogen and 

Phosphorus on the Eastern Shore

SEE CHAPTERS 5 AND 6

Natural hydrogeologic and geochemical conditions promote the formation and movement of nitrate from the abundant (primarily agricultural) nitrogen sources on the Eastern 

Shore to groundwater, streams, and estuaries. Increasing 

nitrate concentrations over time largely reflect the increasing 

nitrogen applications in previous decades and the typically 

long time periods required for the movement of nitrate along 

groundwater flow paths to surface waters. Limiting the movement of nitrate to the water table could reduce concentrations 

relatively quickly in shallow groundwater, although many 

years or decades would be required before significant reductions occurred in deeper groundwater or receiving surface 

waters (fig. 8).

Applications of phosphorus to Eastern Shore farmland 

in recent decades have far exceeded the amounts necessary 

for crop growth, and consequently, phosphorus has increased 

in the environment. Unlike nitrate, phosphorus is relatively 

insoluble in water under most natural conditions, and excess 

phosphorus in the environment generally accumulates in 

agricultural soils rather than moving into groundwater. 

Reducing the accumulated phosphorus in Eastern Shore soils 

may be effective at limiting concentrations in streams and 

groundwater.

Figure 8. Historical loads of dissolved nitrogen from streams on the Eastern Shore 

to Chesapeake Bay and predicted future loads under four different scenarios of 

nitrogen inputs to groundwater. Because groundwater flow is generally very slow, the 

effects of reductions in nitrate concentrations reaching groundwater will not be fully 

realized in surface waters for many years. Even maintaining dissolved nitrogen loads 

from streams on the Eastern Shore to the bay at 2012 levels will require a 13-percent 

reduction in nitrogen loads to groundwater. Nitrogen load to the bay, in thousands of metric tons per year

8

7

6

5

4

3

2

1

0

1980 1990 2000

Year

2010 2020 2030 2040 2050

[From Sanford and Pope, 2013.]

EXPLANATION

Predicted future loads from

streams to Chesapeake Bay

0-percent

Reduction of

nitrogen load

to groundwater

The approximate 25-percent

reduction Total Maximum Daily Load

(TMDL) target proposed for the region

by the U.S. Environmental Protection Agency

in conjunction with local states 13-percent

40-percent

100-percent
Chapter 2. Chesapeake Bay and the Eastern Shore 9

Chapter 2. Chesapeake Bay and the 

Eastern Shore

Why is the Eastern Shore important to water quality in 

Chesapeake Bay? What are the ecological and management 

challenges facing Chesapeake Bay, and what are the environmental conditions in the Eastern Shore that contribute to 

these challenges?

The Eastern Shore includes only 7 percent of the 

Chesapeake Bay watershed, but contributes disproportionately 

large loads of the excess nitrogen and phosphorus that have 

contributed to ecological and economic degradation of the 

bay in recent decades. Sources of nitrogen and phosphorus 

compounds are abundant on the Eastern Shore, and hydrogeologic and soil conditions promote the movement from application areas on the landscape of nitrogen to groundwater and 

streams and phosphorus to streams that contribute to nearby 

tidal waters.

Importance of the Eastern Shore to Water 

Quality in Chesapeake Bay

Chesapeake Bay is the largest estuary in the United 

States and an important natural resource. As in many inland 

estuaries along the east coast of North America, however, 

excessive nitrogen and phosphorus in bay waters have contributed to ecological and economic degradation in recent 

decades (Kemp and others, 2005; Bricker and others, 2007; 

U.S. Environmental Protection Agency, 2011a) (see sidebar: 

“Water-Quality and Restoration Challenges in Chesapeake 

Bay”). The Eastern Shore, which includes the area of the 

Chesapeake Bay watershed east of the bay on the Delmarva 

Peninsula (fig. 1), is a relatively small part of the bay 

watershed, but contributes disproportionately large loads and 

yields of ecologically harmful excess nutrients (nitrogen and 

phosphorus) to the bay (see sidebar: “What are Stream Loads 

and Yields?”) (figs. 9, 10). 

The importance of the Eastern Shore to water quality in 

Chesapeake Bay is a result of a combination of natural conditions and human influences. Sources of nitrogen and phosphorus to the land surface, primarily from agricultural fertilizer 

and manure applications, are abundant on the Eastern Shore 

(fig. 11). Although the Eastern Shore includes only 7 percent 

of the land area in the bay watershed, it receives more than 

13 percent of the nitrogen and phosphorus applications in the 

form of fertilizer, manure, and (for nitrogen) direct fixation 

of atmospheric nitrogen by legume crops (Wieczorek and 

LaMotte, 2010b, c). Soils and surficial aquifer sediments are 

sandy and permeable over much of the area—conditions that 

promote the movement of nutrients from application areas to 

groundwater, streams, and tidal waters (Böhlke and Denver, 

1995; Denver and others, 2004; Ator, Denver, and Brayton, 

2005; Debrewer and others, 2007). In addition, the proximity of most areas of the Eastern Shore to tidal waters limits 

the opportunities for natural storage and mitigation of landapplied nutrients in upland landscapes and increases the likelihood of their delivery to the bay (Staver and Brinsfield, 2001).

 Abundant sources of nitrogen and phosphorus and 

natural conditions on the Eastern Shore contribute to concentrations of nitrate in groundwater (fig. 12) and yields 

of nitrogen and phosphorus in streams (figs. 9, 10) that are 

among the highest in the bay watershed. More than 10 percent 

of nonpoint nitrogen applications to the Eastern Shore move 

through groundwater to streams as nitrate, and groundwater 

contributes more nitrate to streams on the Eastern Shore than 

to streams in the entire remainder of the Atlantic Coastal Plain, 

from North Carolina through New Jersey, combined (Ator and 

Denver, 2012). Phosphorus transport from the land surface to 

streams also is more efficient in the Eastern Shore than in most 

other areas of the Chesapeake Bay watershed, possibly due to 

concentrated phosphorus in cropland soils related to excessive 

historical applications (Ator and others, 2011). Nearly a 

quarter and a third of phosphorus loads to the bay attributable 

to manure and fertilizer applications (respectively) are 

contributed from the Eastern Shore (Ator and others, 2011). 

Substantial nitrogen and phosphorus load reductions from the 

Eastern Shore will be required to meet water-quality standards 

designed to restore the bay (fig. 13) (see sidebar: “WaterQuality and Restoration Challenges in Chesapeake Bay”) 

(figs. 14, 15).

What are Stream Loads and Yields?

Chemical transport by streams and rivers is often measured and reported in terms of loads

or yields. A stream load is the total rate of transport of a 

particular chemical, or the amount of chemical transported past a particular point during a specified period of 

time. Stream loads are often reported in units of mass per 

time, such as kilograms per year (kg/yr). Stream loads are 

generally proportional to watershed area; streams draining larger watersheds generally carry greater loads than 

those draining smaller watersheds. To compare chemicals 

contributed by different landscapes to streams of different 

sizes, therefore, stream yield is often useful. Yield is computed as the load per watershed area, and is reported in 

units of mass per time per area, such as kilograms per year 

per square kilometer [(kg/yr)/km2].

Sources of nitrogen and phosphorus are abundant on the Eastern 

Shore, and natural conditions promote the movement of these 

contaminants to groundwater and streams in many areas. 

Consequently, levels of nitrate in groundwater and nitrogen and 

phosphorus in streams on the Eastern Shore are among the 

highest in the Chesapeake Bay watershed.

Chapter 2
10 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Figure 9. Estimated average annual nitrogen and phosphorus yields to tributaries of Chesapeake Bay. Yields to Eastern Shore 

streams are among the highest in the bay watershed. (GT = greater than; LE = less than or equal to.)

Estimated annual yield of

nitrogen to local streams,

in kilograms per hectare

(pounds per acre)

EXPLANATION

LE 2 (1.8)

GT 2 and LE 4 (3.6)

GT 4 and LE 8 (7.1)

GT 8 and LE 12 (10.7)

GT 12

Estimated annual yield of

phosphorus to local streams,

in kilograms per hectare

(pounds per acre)

EXPLANATION

LE 0.10 (0.09)

GT 0.1 and LE 0.15 (0.13)

GT 0.15 and LE 0.25 (0.22)

GT 0.25 and LE 0.50 (0.44)

GT 0.50

0 50 MILES

0 50 KILOMETERS

40°

42°

78°

76°

38°

CHESAPEAKE

BAY

A

TLANTIC OCEAN

N

New York

Pennsylvania

New

Jersey

New

Jersey

Delaware

Delaware

Washington

D.C.

Washington

D.C.

Maryland

West

Virginia

Virginia

Potomac River

Delmarva

Peninsula

0 50 MILES

0 50 KILOMETERS

40°

42°

78°

76°

38°

CHESAPEAKE

BAY

A

TLANTIC OCEAN

N

New York

Pennsylvania

Maryland

West

Virginia

Virginia

Potomac River

Delaware Ba

Delaware Bay

y

Delmarva

Peninsula

Base from U.S. Geological Survey,

1:2,000,000 DLG, Albers Equal Area

Conic Projection, NAD 83

Yield estimates from

Ator and others, 2011

Yield estimates from

Ator and others, 2011

Base from U.S. Geological Survey,

1:2,000,000 DLG, Albers Equal Area

Conic Projection, NAD 83

NITROGEN PHOSPHORUS

Chesapeake Bay

watershed

Chesapeake Bay

watershed
Chapter 2. Chesapeake Bay and the Eastern Shore 11

0

0

1

1

2

2

3

3

4

4

5

5

6

6

7

7

8

8

9

9

10 11

Nitrogen, total

Phosphorus, total

Applied in fertilizer

or fixed by crops

Applied in fertilizer

Applied in manure

Applied in manure

Estimated annual delivered yield to Chesapeake Bay,

in kilograms per hectare

(pounds per acre)

[Average yield estimates from Ator and others, 2011.]

From the Eastern Shore

From the rest of Chesapeake Bay watershed

Figure 10. Estimated average annual yields of nitrogen and phosphorus to 

Chesapeake Bay from the Eastern Shore and the remainder of the Chesapeake Bay 

watershed. Yields from the Eastern Shore are substantially larger than from the 

remainder of the watershed.

10

10

20

20

30

30

40

40

50

50

60

60

0 70

0

Nitrogen, total

Phosphorus, total

Applied in fertilizer

or fixed by crops

Applied in fertilizer

Applied in manure

Applied in manure

Estimated annual watershed inputs, in kilograms per hectare

(pounds per acre)

[Average inputs from Bachman and others, 1998, Wieczorek and LaMotte,

2010a, b, c, d, and Ator and others, 2011.]

Eastern Shore

Rest of Chesapeake Bay watershed

Figure 11. Estimated annual inputs of nitrogen and phosphorus to the Eastern 

Shore and the remainder of the Chesapeake Bay watershed, 2002. Inputs are 

more intensive (greater per unit area) on the Eastern Shore than in the 

remainder of the Chesapeake Bay watershed.

Chapter 2
12 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Chesapeake Bay

watershed

Delmarva

Peninsula

EXPLANATION

Likelihood (in percent) of nitrate

concentration exceeding

5 milligrams per liter as N

in shallow groundwater

LE 10

GT 10 and LE 20

GT 20 and LE 30

GT 30 and LE 40

GT 40 and LE 50

GT 50 and LE 60

GT 60 and LE 70

GT 70 and LE 80

GT 80 and LE 90

GT 90 and LE 100

40°

42°

78°

76°

38°

CHESAPEAKE BAY

A

TLANTIC OCEAN

N

New York

Pennsylvania

New

Jersey

Delaware

Washington

D.C.

Maryland

West

Virginia

Virginia

Potomac River

Delaware Bay

Delmarva

Peninsula

0 50 MILES

0 50 KILOMETERS

Base from U.S. Geological Survey,

1:2,000,000 DLG, Albers Equal Area

Conic Projection, NAD 83

Estimated groundwater quality

from Greene and others, 2005

Figure 12. The estimated probability of groundwater nitrate concentration exceeding 5 milligrams per liter as N in the 

Chesapeake Bay watershed. Some of the highest concentrations of nitrate in groundwater in the watershed occur in 

agricultural areas of the Eastern Shore. (GT = greater than; LE = less than or equal to.)
Chapter 2. Chesapeake Bay and the Eastern Shore 13

-1,000

-1,000

0

0

1,000

1,000

2,000

2,000

3,000

3,000

4,000

4,000

Agriculture

Urban or regulated stormwater runoff

Forest

Onsite septic systems

Wastewater and combined sewer

overflows (CSOs)

Atmospheric deposition directly

to tidal or nontidal waters

SOURCE SECTOR

-10

-10

0

0

20

20

60

60

80

80

100

100

120

120

140

140

160

160

180

180 200

40

40

Chester

Chester

Nanticoke

Nanticoke

Pocomoke

Pocomoke

Remainder of

Eastern Shore

Remainder of

Eastern Shore

Virginia

Virginia

Choptank

Choptank

Required reduction from 2009 baseline to 2025 target,

in metric tons per year

(tons per year)

A

B

EXPLANATION

[Required load reductions from Chesapeake Bay Program, 2014a.]

Figure 13. Reductions of (A) nitrogen and (B) phosphorus from nonpoint sources 

in major watersheds of the Eastern Shore required to meet a 2010 Total Maximum 

Daily Load (TMDL) for the Chesapeake Bay established under the Clean Water Act. 

Major watersheds are shown in figure 1. Where the reduction is negative, the 2009 

baseline load is lower than the 2025 target.

Chapter 2
14 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Water-Quality and Restoration Challenges in Chesapeake Bay

Chesapeake Bay extends for more than 300 kilometers (km) from its headwaters in northern Maryland to its mouth in southern Virginia, and has a 

surface area of more than 11,000 square kilometers (km2) (Langland and Cronin, 2003) 

(fig. 1). More than 240,000 km of tributary streams drain to the bay from a watershed 

that includes parts of Delaware, Maryland, New York, Pennsylvania, Virginia, West 

Virginia, and the District of Columbia. The bay is home to more than 3,700 different 

species of plants and animals (U.S. Environmental Protection Agency, 2008a) and 

supports commercial fisheries, tourism, international shipping, and other activities 

that are vital to the economy of the Mid-Atlantic region.

Chesapeake Bay and its nontidal tributaries have been degraded in recent 

decades by excessive nutrients (nitrogen and phosphorus) in the water column. 

Elevated concentrations of nutrients in the bay contribute to algal blooms and 

decreases in water clarity, submerged aquatic vegetation, and dissolved oxygen 

(Karlsen and others, 2000; Kemp and others, 2005; Fisher and others, 2006; Bricker 

and others, 2007; U.S. Environmental Protection Agency, 2008a). Algal production in 

temperate estuaries is often controlled primarily by nitrogen concentrations (Vitousek 

and others, 1997). Concentrations of both nitrogen and phosphorus may control 

ecological production and resulting impairments in Chesapeake Bay during different 

seasons, however, and phosphorus may be particularly important in the spring (Prasad 

and others, 2010). Impaired conditions have occurred periodically in Chesapeake Bay 

over the past 200 years, but have become particularly severe and frequent since 

the 1950s (Karlsen and others, 2000; Bratton and others, 2003; Kemp and others, 

2005). Under the authority of the Clean Water Act, Chesapeake Bay was listed as 

“impaired” in 2000 and a Total Maximum Daily Load (TMDL) was established for the 

bay in 2010 (U.S. Environmental Protection Agency, 2011b; Linker and others, 2013; 

Shenk and Linker, 2013). The TMDL represents a detailed nitrogen and phosphorus 

budget for the watershed, and includes mandatory quantitative load reductions 

for nitrogen and phosphorus from specific sources and specific geographic areas 

(fig. 13). 

Restoration efforts in the Chesapeake Bay watershed in recent decades 

have contributed to water-quality improvements but have been insufficient to 

meet ecological standards. Concentrations of nutrients in Chesapeake Bay are 

largely controlled by inputs from the bay watershed (Prasad and others, 2010), 

which are mainly controlled by natural variations in precipitation and streamflow 

over time (fig. 14). Changes in concentrations of nitrogen and phosphorus over 

time in streams when adjusted for such known effects of streamflow and season 

can be more indicative of the effects of changing sources, land management, 

or other human activities than changes associated with concentration alone 

(Langland and others, 2006). Such flow-adjusted concentrations have decreased 

substantially in many tributaries in recent decades, but continue to increase in 

others (Langland and others, 2006; Langland and others, 2013), particularly for 

nitrogen in areas like the Eastern Shore where nonpoint sources are important 

and groundwater is a major pathway for nitrogen transport (Hirsch and others, 

2010). In spite of improved water quality in many bay tributaries, only 38 percent of 

tidal waters in the bay system met dissolved oxygen standards during the summer 

months of 2008, 2009, and 2010, and during 2010, water-clarity and chlorophyll-a

goals were achieved in only 18 and 22 percent of tidal waters, respectively (fig. 15) 

(U.S. Environmental Protection Agency, 2011a). 
Chapter 2. Chesapeake Bay and the Eastern Shore 15

1990 1995 2000

Year

2005 2010

Nitrogen,

in thousands of metric tons

Phosphorus,

in thousands of metric tons

Average streamflow,

in billions of gallons per day

250

200

150

100

50

0

30

20

10

0

80

60

40

20

0

[Data from Chesapeake Bay Program, 2014b.]

1990

Middle year of 3-year assessment period

1995 2000 2005 2010

Percent of tidal water area achieving standards

based on dissolved oxygen, water clarity,

and chlorophyll-a 100

80

60

40

20

0

[Data from Chesapeake Bay Program, 2014c.]

Figure 14. Annual streamflow and 

nitrogen and phosphorus loads 

delivered to Chesapeake Bay, 1990 

through 2012. Loads of nitrogen and 

phosphorus reaching the bay from 

the watershed in any given year 

are controlled mainly by natural 

variation in precipitation and 

streamflow.

Figure 15. A summary of 

selected ecological conditions in 

Chesapeake Bay, 1985 through 

2012. Although water quality in the 

bay varies substantially from year 

to year, ecological standards for 

dissolved oxygen, water clarity, and 

chlorophyll-a have not been attained 

in even half of tidal waters since the 

mid-1980s.

Chapter 2
16 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Environmental Setting of the Eastern Shore of 

Chesapeake Bay

The Eastern Shore includes 11,200 square kilometers 

(km2) of the Chesapeake Bay watershed east of the bay on the 

Delmarva Peninsula (fig. 1). The area includes parts of western 

Delaware and eastern Maryland and Virginia. The combination 

of hydrogeologic, soil, and climatic conditions on the Eastern 

Shore supports intensive agriculture, but also promotes the 

movement of nutrients from nonpoint sources (such as agricultural manure and fertilizer applications) from the land surface 

to groundwater, streams, and adjacent tidal waters of the bay.

Land Use

The Eastern Shore is predominantly rural and has been 

primarily agricultural for several hundred years (Allen, 2009) 

(fig. 16). Only 3 percent of the Eastern Shore is urban, including small towns such as Easton, Cambridge, and Salisbury, 

Maryland, and Seaford, Delaware. Historically, the area was 

almost entirely forested, although nearly all of the original forests had been cleared by the middle of the 18th century within 

150 years of European settlement (Allen, 2009). In 2001, 

49 percent of the Eastern Shore was used for agriculture, 

whereas 39 percent was regrown forests or wetlands 

(Wieczorek and LaMotte, 2010a). Many of the remaining 

forested areas occur in small isolated patches or in wetlands 

along streams; many of the original wetland marshes have 

been drained for cultivation or urban development (Allen, 

2009).

Agriculture is an important economic resource on the 

Eastern Shore (fig. 16). Most agricultural land is used for row 

crops, primarily corn and soybeans for poultry feed, although 

plant nurseries, dairy farms, and other operations are present 

in some areas (Staver and Brinsfield, 2001; Denver and others, 

2004). In 2012, more than 550 million broiler chickens were 

produced on the Delmarva Peninsula (U.S. Department of 

Agriculture, 2014). 
Chapter 2. Chesapeake Bay and the Eastern Shore 17

Figure 16. Major land use and land cover on the Eastern Shore, 2001. Agriculture, primarily corn and soybean production 

for poultry feed, is the predominant land use.

38°

39°

76°

75°

Pennsylvania

Maryland

Virginia

Delaware

New Jersey

Chesapeake Bay

watershed

boundary

Eastern

Shore

ATLANTIC

OCEAN

CHESTER RIVER

WATERSHED

CHOPTANK

RIVER

WATERSHED

NANTICOKE

RIVER

WATERSHED

Delaware Bay

Delaware River

POCOMOKE RIVER

WATERSHED

VIRGINIA COASTAL 

WATERSHEDS

Chesapeake Bay

Agriculture

Forest and swamp

Urban

Emergent wetland

Open water

EXPLANATION

Land cover

0 10 20 MILES

0 10 20 KILOMETERS

Base from U.S. Geological Survey,

1:2,000,000 DLG, Albers Equal Area

Conic Projection, NAD 83

Land-cover data from LaMotte, 2008a, b

N

Chester

Nanticoke

Pocomoke

Remainder of

Eastern Shore

Virginia

0

Percent of area

20 40 60 80 100

Choptank

Salisbury

Seaford

Cambridge

Chestertown

Easton

Dover

Chapter 2
18 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Geology and Soils

The Eastern Shore is entirely within the Atlantic Coastal 

Plain, a relatively flat area that slopes gently from higher elevations in the Piedmont Physiographic Province to the north 

and west toward sea level at the Atlantic Coast (Fenneman and 

Johnson, 1946). The Eastern Shore landscape is particularly 

flat and low-lying, even more so than in other areas of the 

Coastal Plain to the west of the bay and to the north in New 

Jersey (fig. 17). The area is underlain by several thousand 

meters of unconsolidated sediments that vary laterally and 

vertically in texture and composition from relatively impermeable silt and clay to extremely permeable sand and gravel 

(Meng and Harsh, 1988; Mixon and others, 1989; Vroblesky 

and Fleck, 1991; Ator, Denver, Krantz, and others, 2005). The 

central core of the Delmarva Peninsula along the watershed 

divide is underlain at the surface by up to 30 or 40 meters (m) 

of generally coarse, permeable, and well-weathered (primarily 

quartz) sediment; younger surficial and near-surface sediments 

along the coast of the bay are typically finer in texture and less 

permeable (fig. 18). Soils on the Eastern Shore are generally 

sandy and permeable, but also vary in composition along 

with the underlying geologic parent material (fig. 19), and are 

poorly drained in many areas regardless of permeability due to 

the typically flat landscape (fig. 20).
Chapter 2. Chesapeake Bay and the Eastern Shore 19

Figure 17. Landscape elevations on the Eastern Shore. The Delmarva Peninsula (including the Eastern Shore) is generally 

more flat and low-lying than surrounding areas of the Coastal Plain such as southern New Jersey and the Western Shore. 

(GT = greater than; LE = less than or equal to.)

Chapter 2

Eastern

Shore

Western

Shore

Delaware Bay

Delaware River

Chesapeake Bay

CHESTER RIVER

WATERSHED

CHOPTANK

RIVER

WATERSHED

NANTICOKE

RIVER

WATERSHED

POCOMOKE RIVER

WATERSHED

VIRGINIA COASTAL 

WATERSHEDS

ATLANTIC OCEAN

0 10 20 MILES

0 10 20 KILOMETERS

38°

39°

76°

75°

Pennsylvania

New Jersey

Maryland

Virginia

Delaware Chesapeake Bay

watershed

boundary

N

Base from U.S. Geological Survey,

1:2,000,000 DLG, Albers Equal Area

Conic Projection, NAD 83

Data from the National Elevation

Dataset, Gesch and others, 2009

EXPLANATION

Elevation, in meters

LE 2

GT2 and LE 4

GT 4 and LE 6

GT 6 and LE 8

GT 8 and LE 10

GT 10 and LE 12

GT 12 and LE 14

GT 14 and LE 16

GT 16 and LE 18

GT 18 and LE 20

GT 20 and LE 22

GT 22 and LE 24

GT 24 and LE 26

GT 26 and LE 28

GT 28 and LE 30

GT 30 and LE 40

GT 40 and LE 50

GT 50 and LE 100

GT 100

Chester

Nanticoke

Pocomoke

Remainder of

Eastern Shore

Virginia

0

Mean altitude, in meters

5 10 15

Choptank
20 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Figure 18. The average texture of surficial sediments on the Eastern Shore. Most near-surface sediments are 

relatively coarse and permeable sand or gravel, particularly in the central core of the Delmarva Peninsula.

Eastern

Shore

Delaware Bay

Delaware River

Chesapeake Bay

CHESTER RIVER

WATERSHED

CHOPTANK

RIVER

WATERSHED

NANTICOKE

RIVER

WATERSHED

POCOMOKE RIVER

WATERSHED

VIRGINIA

COASTAL WATERSHEDS

ATLANTIC OCEAN

0 10 20 MILES

0 10 20 KILOMETERS

38°

39°

76°

75°

Pennsylvania

New Jersey

Maryland

Virginia

Delaware Chesapeake Bay

watershed

boundary

N

Base from U.S. Geological Survey,

1:2,000,000 DLG, Albers Equal Area

Conic Projection, NAD 83

Geologic data from Ator, Denver,

Krantz, and others, 2005

Silt or clay

Mixed texture

Mixed, with peat

Sand or gravel

EXPLANATION

Average sediment texture

Chester

Nanticoke

Pocomoke

Remainder of

Eastern Shore

Virginia

0

Percent of area

20 40 60 80 100

Choptank
Chapter 2. Chesapeake Bay and the Eastern Shore 21

Eastern

Shore

Delaware Bay

Delaware River

Chesapeake Bay

CHESTER RIVER

WATERSHED

CHOPTANK

RIVER

WATERSHED

NANTICOKE

RIVER

WATERSHED

POCOMOKE RIVER

WATERSHED

VIRGINIA

COASTAL WATERSHEDS

ATLANTIC OCEAN

0 10 20 MILES

0 10 20 KILOMETERS

38°

39°

76°

75°

Pennsylvania

New Jersey

Maryland

Virginia

Delaware Chesapeake Bay

watershed

boundary

N

Base from U.S. Geological Survey,

1:2,000,000 DLG, Albers Equal Area

Conic Projection, NAD 83

Soil data from Wolock, 1997

EXPLANATION

Mean soil sand content,

in percent

LE 20

GT 20 and LE 40

GT 40 and LE 60

GT 60 and LE 80

GT 80

Chester

Nanticoke

Pocomoke

Remainder of

Eastern Shore

Virginia

0

Mean percent sand in soil

10 20 30 40 50 60 70

Choptank

Figure 19. The sand content of Eastern Shore soils. Soils on the Eastern Shore are predominantly sandy, reflecting 

the texture of the underlying surficial sediments. (GT = greater than; LE = less than or equal to.)

Chapter 2
22 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Figure 20. Soil drainage on the Eastern Shore. Drainage varies from well-drained to very poorly drained because of 

differences in geomorphology and soil texture. In spite of the generally coarse, sandy texture, soils in many areas are 

poorly drained due to the typically flat landscape.

EXPLANATION

Soil drainage

Excessive

Well

Moderate

Poor

Very poor

Eastern

Shore

Delaware Bay

Delaware River

Chesapeake Bay

CHESTER RIVER

WATERSHED

CHOPTANK

RIVER

WATERSHED

NANTICOKE

RIVER

WATERSHED

POCOMOKE RIVER

WATERSHED

VIRGINIA

COASTAL WATERSHEDS

ATLANTIC OCEAN

0 10 20 MILES

0 10 20 KILOMETERS

38°

39°

76°

75°

Pennsylvania

New Jersey

Maryland

Virginia

Delaware Chesapeake Bay

watershed

boundary

N

Base from U.S. Geological Survey,

1:2,000,000 DLG, Albers Equal Area

Conic Projection, NAD 83

Soil data from Wolock, 1997

Chester

Nanticoke

Pocomoke

Remainder of

Eastern Shore

Virginia

Excessive

Mean soil drainage

Very poor

Choptank
Chapter 2. Chesapeake Bay and the Eastern Shore 23

and Reay, 2002). Consequently, several decades are often 

required for water to move from infiltration areas at the water 

table along groundwater flow paths to discharge areas in local 

streams, although water may discharge to streams from short, 

near-stream, flow paths within less than a year (figs. 21, 23) 

(Dunkle and others, 1993; Böhlke and Denver, 1995; Staver, 

2010; Sanford and others, 2012). Most groundwater discharges 

to nontidal streams and rivers; a small fraction of groundwater 

(less than 2 percent) discharges directly from the peninsula to 

tidal waters in areas at or below sea level (Sanford and others, 

2012).

More than half of the groundwater discharging to 

streams on the peninsula takes more than 13 years to move 

along groundwater flow paths from the water table to stream 

discharge areas. In contrast, in areas of the Chesapeake Bay 

watershed underlain by consolidated bedrock, less than 15 

percent of groundwater discharging to streams is that old 

(Sanford and Pope, 2013). A small fraction (2 to 3 percent) of 

groundwater flows to confined aquifers that are present several 

hundred meters below the land surface. The age of groundwater in these aquifers can be centuries or older. 

Climate and Hydrology

Hydrologic conditions on the Eastern Shore reflect the 

humid and temperate climate, a relatively flat landscape, and 

the texture and composition of soils and near-surface sediments. Annual precipitation on the Delmarva Peninsula averages around 112 centimeters (cm) (44 inches), the majority of 

which returns to the atmosphere through evaporation or transpiration by plants (fig. 21). The remaining water drains from 

the landscape through a network of nontidal streams and rivers 

or (in near-coastal areas) directly to tidal waters. Overland 

runoff of precipitation and occasional snowmelt contributes 

a small part (generally less than 25 percent in most areas) 

of streamflow on the peninsula. The majority of streamflow 

is generated by water that infiltrates through the soil to the 

water table and flows through groundwater to discharge areas 

in streams (Cushing and others, 1973; Hancock and Brayton, 

2006; Sanford and others, 2012). The relative importance of 

groundwater flow and overland runoff to streamflow generation among different areas of the Eastern Shore reflects variations in topography (fig. 17), land-surface drainage 

(figs. 20, 22), and underlying soil (fig. 19) and geologic 

(fig. 18) conditions.

Most groundwater flows to nearby streams through the 

uppermost few meters of a shallow, surficial unconfined aquifer system that is generally less than 30 m thick (Sanford and 

others, 2012). The length and orientation of flow paths vary 

across the peninsula (fig. 21). Groundwater generally flows 

very slowly, often less than 1 meter per day (m/d) (Robinson 

About one-third (35 percent) of the precipitation on the Eastern 

Shore drains from the landscape in streamflow to Chesapeake 

Bay. The majority of this water travels from upland landscapes to 

streams very slowly through groundwater over a period of multiple 

years or even decades.

Chapter 2
24 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Surficial water-table aquifer Wetland

INPUT TO THE

LANDSCAPE

TRANSPORT

TO STREAMS

LOSSES FROM

THE LANDSCAPE

Groundwater flow

West East

Land

surface

Vertical scale greatly exaggerated

[Hydrologic cross section modified from Shedlock and others, 2007. Average annual water budget generalized from Cushing and others, 1973;

Hancock and Brayton, 2006; Sanford and others, 2012.]

Not to scale

CONFINING UNIT

UNCONFINED AQUIFER

CONFINED

AQUIFER

CONFINED

AQUIFER CONFINING UNIT

CONFINING UNIT

Chesapeake Bay

Stream

Stream

Coastal Bays

Atlantic Ocean

PRECIPITATION

(112 CENTIMETERS) EVAPOTRANSPIRATION

(65 PERCENT)

STREAMFLOW

(35 PERCENT)

OVERLAND

(10 PERCENT)

GROUNDWATER

FLOW

(25 PERCENT)

Figure 21. Conceptual hydrologic cycle and average annual water budget for the Eastern Shore. Most precipitation 

(65 percent) returns directly to the atmosphere through evaporation or transpiration by plants. The remaining water drains from 

the landscape in streamflow, most of which reaches streams through groundwater.
Chapter 2. Chesapeake Bay and the Eastern Shore 25

Eastern

Shore

Delaware Bay

Delaware River

Chesapeake Bay

CHESTER RIVER

WATERSHED

CHOPTANK

RIVER

WATERSHED

NANTICOKE

RIVER

WATERSHED

POCOMOKE RIVER

WATERSHED

VIRGINIA

COASTAL WATERSHEDS

ATLANTIC OCEAN

0 10 20 MILES

0 10 20 KILOMETERS

38°

39°

76°

75°

Pennsylvania

New Jersey

Maryland

Virginia

Delaware Chesapeake Bay

watershed

boundary

N

Base from U.S. Geological Survey,

1:2,000,000 DLG, Albers Equal Area

Conic Projection, NAD 83

Hydrogeomorphic regions by

Bachman and others, 1998

Coastal Plain Upland: Located along

the major drainage divides in areas

with low relief and shallowly incised

stream valleys. Poorly drained forested

areas containing wetlands are interspersed

with moderately well- to well-drained

agricultural areas. Depressional wetlands

are common in the northern part of the area.

The water table is generally within 3 meters

of the land surface and ditching to lower the

water table and promote drainage is common.

Poor drainage is generally related to shallow

stream incision and high water table, rather

than to fine-grained sediments.

Coastal Plain Dissected Upland:

Area is relatively flat to gently rolling with

predominantly well-drained soils underlain by

sandy deposits. Stream channels are incised

and the depth to water ranges from 3 to 10

meters below land surface. Most upland areas

are used for agriculture with wooded areas

generally confined to the incised sides of

narrow riparian zones and flood plains.

Coastal Plain Lowlands and Valleys:

Located in lowlands underlain by generally

fine-grained estuarine deposits in the tidal

areas adjacent to the bay and in major river

valleys. Area is very flat and poorly drained

with the water table generally less than

3 meters below land surface. Wetlands, such

as coastal marshes and broad riparian swamps

along tidal rivers, are common. Parts of this

area have been extensively ditched to lower

the water table.

Hydrogeomorphic regions

EXPLANATION

Figure 22. Variable hydrogeomorphic conditions among different areas of the Eastern Shore. Although mostly 

flat and low-lying, important differences in topography and drainage among different areas of the Eastern Shore 

contribute to variable land use and water quality.

Chapter 2
26 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Eastern

Shore

Delaware Bay

Delaware River

Chesapeake Bay

CHESTER RIVER

WATERSHED

CHOPTANK

RIVER

WATERSHED

NANTICOKE

RIVER

WATERSHED

POCOMOKE RIVER

WATERSHED

VIRGINIA

COASTAL WATERSHEDS

ATLANTIC OCEAN

0 10 20 MILES

0 10 20 KILOMETERS

38°

39°

76°

75°

Pennsylvania

New Jersey

Maryland

Virginia

Delaware Chesapeake Bay

watershed

boundary

N

Base from U.S. Geological Survey,

1:2,000,000 DLG, Albers Equal Area

Conic Projection, NAD 83

Estimated groundwater age from

Sanford and others, 2012

EXPLANATION

Age of groundwater,

in years

LE 10

GT 10 and LE 20

GT 20 and LE 50

GT 50

Chester

Nanticoke

Pocomoke

0 20 40 60 80 100

Percent of area

Choptank

Figure 23. Estimated age of groundwater contributing to streamflow on the Eastern Shore. Most water flows along 

groundwater flow paths to local streams within a few decades, although much longer time periods are required for 

water recharging the water table along watershed divides. (GT = greater than; LE = less than or equal to.)
Chapter 3. Sources and Movement of Nitrogen and Phosphorus on the Eastern Shore 27

Chapter 3. Sources and Movement 

of Nitrogen and Phosphorus on the 

Eastern Shore

Where do the nutrients, nitrogen and phosphorus, on the 

Eastern Shore originate, and how do these nutrients move 

from upland source areas to surface waters and Chesapeake 

Bay? 

Fertilizer and manure applied as part of agricultural 

operations are by far the predominant sources of nitrogen 

and phosphorus to the landscape on the Eastern Shore. Once 

on the land surface, nitrogen and phosphorus movement to 

surface waters occurs primarily through the action of water. 

Nitrogen is primarily transported to surface waters through 

groundwater in the form of nitrate. Conversely, phosphorus 

is predominantly transported over the land in runoff attached 

to sediment. The pathways and amounts of these chemicals 

entering surface waters are controlled by the amounts that 

have been applied in excess of crop uptake, differing chemical 

and physical properties of nitrogen and phosphorus compounds, and by varying hydrologic, geochemical, and geologic 

environments. 

Sources of Nitrogen and Phosphorus

Agricultural sources supply the majority of nitrogen 

and phosphorus inputs to the land surface, groundwater, and 

nontidal streams on the Eastern Shore (fig. 24) (Staver and 

Brinsfield, 2001; Fisher and others, 2006; Whitall and others, 

2010; Ator and others, 2011). More than half (53 percent) of 

the nitrogen reaching the Eastern Shore landscape is applied 

in inorganic fertilizers or fixed directly from the atmosphere in 

cropland; an additional 37 percent is contributed by manure. 

Less than 10 percent of nitrogen applied to the Eastern Shore 

is contributed by non-agricultural sources, including atmospheric deposition, septic systems, and urban sources 

(fig. 24) (Debrewer and others, 2007; Ator and others, 2011). 

Phosphorus sources to the landscape on the Eastern Shore are 

similarly almost exclusively from agricultural applications of 

fertilizers (44 percent) and manure (56 percent) (fig. 24). In 

the Chesapeake Bay watershed as a whole, livestock produce 

36 billion kilograms (kg) of manure annually, approximately 

10 times the mass produced by the watershed’s human population (Kleinman and others, 2012). Much of the livestock is 

concentrated in poultry production on the Eastern Shore. 

Although nonpoint sources provide the majority of nutrients 

to the land surface and nontidal streams on the Eastern Shore, 

some point sources discharge directly to tidal waters and may 

be the predominant source of phosphorus locally to parts of 

some sub-estuaries of the bay (Boynton and others, 1995; 

Whitall and others, 2010).

Fertilizer applications and poultry production on the 

Eastern Shore have increased substantially in recent decades 

(fig. 25) and nitrogen and phosphorus applications to cropland typically exceed the amounts removed in crops during 

harvest (fig. 26). Although land use on the Delmarva Peninsula 

has been primarily agricultural for several hundred years 

(Allen, 2009), applications of nitrogen in fertilizer increased 

from less than 10 million kg/yr in 1950 to around 60 million 

kg/yr in 1980 (fig. 25) (Alexander and Smith, 1990; Battaglin 

and Goolsby, 1995; Mid-Atlantic Water Program, 2012). 

Applications of phosphorus in fertilizer similarly increased 

during that period, but have since decreased. Poultry production on the Delmarva Peninsula has also increased in recent 

decades from less than 4 million broilers in 1919 to nearly 600 

million by 2007 (fig. 25) (U.S. Department of Agriculture, 

2009). Applications of nitrogen and phosphorus from these 

sources to croplands on the Eastern Shore have exceeded crop 

needs since at least the 1980s (fig. 26) (Mid-Atlantic Water 

Program, 2012).

Agriculture contributes more than 90 percent of the nitrogen and 

phosphorus to the Eastern Shore.

Although agriculture has been a primary land use on the Eastern 

Shore for several centuries, poultry production and applications of 

nitrogen fertilizer increased substantially during the latter half of 

the 20th century.

Applications of nitrogen and phosphorus to cropland on the 

Eastern Shore typically exceed amounts that are incorporated into 

crop growth and removed at harvest.

Chapter 3
28 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

NITROGEN

40,700

(53%)

6,480

(44%)

5,560 (7%)

1,650 (2%) 82 (1%)

28,300

(37%)

8,320

(56%)

PHOSPHORUS

Fertilizer applications or (for nitrogen) direct fixation from

the atmosphere by crops (Wieczorek and LaMotte, 2010b).

Manure (Wieczorek and LaMotte, 2010c).

Atmospheric deposition (Wieczorek and LaMotte, 2010d).

Other, including point sources (U.S. Environmental Protection

Agency, 2009) and septic systems (Maizel and others, 1997).

SOURCE

INPUTS, IN THOUSAND KILOGRAMS PER YEAR

(PERCENT OF TOTAL)

Figure 24. Annual inputs of nitrogen and phosphorus from various sources to the Eastern Shore. 

Agriculture provides more than 90 percent of both nitrogen and phosphorus applications.

0

10

20

30

40

50

60

0

100

200

300

400

500

600

1910 1930 1950 1970 1990 2010

NITROGEN

PHOSPHORUS

0

10

20

30

Fertilizer applications, in millions of kilograms

Millions of broilers sold

[Broiler data are from U.S. Department of Agriculture, 2009. Estimates prior to 1950 are for total

chickens or broilers raised. Fertilizer inputs are from Alexander and Smith, 1990, Battaglin and

Goolsby, 1995, and Mid-Atlantic Water Program, 2012.]

Year

Figure 25. Past poultry broiler production and fertilizer applications on the Delmarva Peninsula. Broiler production has increased 

consistently and substantially since the early part of the 20th century. Nutrient applications to cropland on the Peninsula similarly 

increased between the 1950s and 1980s, but have decreased or remained relatively consistent since that time.
Chapter 3. Sources and Movement of Nitrogen and Phosphorus on the Eastern Shore 29

1930 1940 1950

0

10

20

30

40

50

60

70

80

90 100

90

80

70

60

50

40

30

20

10

0

1960 1970

Year

[Balances were computed from estimates of Mid-Atlantic Water Program, 2012.]

1980 1990 2000 2010

Average nitrogen or phosphorus balance

on cropland, in kilograms per hectare

(pounds per acre)

Positive values indicate nitrogen or phosphorus inputs

in fertilizer and manure exceed removal in crops

At zero, nutrient inputs to cropland exactly

equal nutrients removed in crops.

Area of Delmarva

Peninsula

Phosphorus

Nitrogen EXPLANATION

Delaware

Maryland

Virginia

Figure 26. Average annual balance between inputs (primarily in fertilizer and manure) 

and outputs (primarily in harvested crops) of nitrogen and phosphorus on cropland on 

the Delmarva Peninsula in recent decades. Nitrogen and phosphorus applications to 

cropland have consistently exceeded removal during harvest, leaving excess nutrients 

available in the environment for transport to groundwater and (or) streams.

Movement of Nitrogen and Phosphorus from 

Source Areas to Surface Waters

Nitrogen and phosphorus compounds move from upland 

source areas to streams and groundwater on the Eastern 

Shore primarily through the action of water. Pathways most 

important to nutrient transport in different areas therefore 

depend primarily on local hydrologic and geologic conditions 

that control water movement, including the slope of the 

land surface and the texture, thickness, and permeability of 

soils and geologic sediments. Also important are chemical 

and physical properties of different compounds and local 

geochemical conditions, since they control the solubility of 

nitrogen or phosphorus compounds in water and the likelihood 

of their persistence in water or transformation to other forms 

(Dubrovsky and others, 2010).

Nitrogen and phosphorus occur in a variety of forms in 

streams and groundwater. Nitrogen in chemical fertilizers and 

atmospheric deposition generally reaches the land in inorganic 

forms such as ammonia (NH3), ammonium (NH4

+

), or nitrate 

(NO3

-

), whereas nitrogen in animal wastes (such as poultry 

manure) and septic effluent often occur in ammonium or 

organic compounds. Much of the applied nitrogen is converted 

in the soil to nitrate, which remains stable in groundwater as 

long as dissolved oxygen is present, and is the most common 

form of nitrogen in groundwater and streams of the Eastern 

Shore (Denver and others, 2004; Ator, Denver, and Brayton, 

2005; Debrewer and others, 2007) and elsewhere (Dubrovsky 

and others, 2010). Phosphorus is less soluble than nitrate and 

commonly occurs in solid form bound to soils or sediment 

particles, although some phosphorus may dissolve in streams 

or groundwater in the form of phosphate (PO4

3-) (Dubrovsky 

and others, 2010).

Nitrogen

Nitrogen moves from source areas on the landscape to 

surface waters of the Eastern Shore primarily through groundwater in the form of nitrate (Böhlke and Denver, 1995; Ator, 

Denver, and Brayton, 2005; Ator and Denver, 2012). Because 

nitrate is very soluble, it dissolves easily in rainfall or other 

water as it infiltrates through the soil toward the water table. 

Once below the water table, nitrate similarly moves slowly 

with groundwater to withdrawal wells or to discharge areas 

in surface waters (fig. 27). Although nitrate remains stable 

for long time periods in groundwater containing abundant 

dissolved oxygen, it is converted to nitrogen gas and lost from 

groundwater (through a process called “denitrification”) where 

dissolved oxygen is lacking. On the Eastern Shore, hydrogeologic conditions controlling the effectiveness of denitrification 

in groundwater are quite variable from place to place; groundwater generally contains more nitrate in areas with abundant 

Chapter 3
30 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

dissolved oxygen than in areas where oxygen is limited 

(Debrewer and others, 2007) (fig. 28), and denitrification 

removes minimal nitrogen from groundwater discharging to 

some Eastern Shore streams but substantial nitrogen in others 

(see sidebar: “Nitrate Removal Through Denitrification, and 

Limitations Caused by Local Hydrogeology”). Hydrogeologic 

conditions in many areas are conducive to nitrate transport 

from groundwater to streams, however, and 70 percent of the 

nitrogen load from Eastern Shore streams to Chesapeake Bay 

reaches streams as nitrate through groundwater (Domagalski 

and others, 2008; Ator and Denver, 2012). Hydrogeologic 

conditions in aquifer discharge areas and the resulting interactions between groundwater and surface waters are complex 

and variable among and within individual streams, and nitrate 

contributions from groundwater may occur through diffuse or 

spatially concentrated seepage through the streambed or along 

flood-plain seeps (Domagalski and others, 2008; Knee and 

Jordan, 2013). 

Groundwater discharge contributes nitrate directly to tidal 

estuaries adjacent to the Delmarva Peninsula through submarine groundwater discharge (Reay and others, 1992; Gallagher 

and others, 1996; Speiran, 1996; Staver and Brinsfield, 1996; 

Bratton and others, 2004) as well as to nontidal tributary 

streams (fig. 27). Less than 10 percent of freshwater from the 

Eastern Shore reaches the bay directly through submarine 

groundwater discharge (Hussain and others, 1999; Sanford and 

others, 2012); most freshwater flow to Chesapeake Bay occurs 

through nontidal tributary streams. Groundwater discharge of 

nitrate directly to coastal bays along the Atlantic margin of the 

Delmarva Peninsula is similarly much smaller than groundwater discharge of nitrate to nontidal tributaries (Dillow and 

Greene, 1999), although the relative importance of such 

discharge to Chesapeake Bay is unknown. Nitrate contributions from submarine groundwater discharge may be limited 

by anoxic conditions in estuarine sediments (Bratton and 

others, 2004; Bratton and others, 2009) and—as in nontidal 

streams—likely vary with variable hydrogeologic conditions 

over different areas (Speiran, 1996; Krantz and others, 2004; 

Manheim and others, 2004; Knee and Jordan, 2013). Direct 

discharge of nitrate from groundwater to tidal creeks is 

limited by fine-grained organic-rich sediments and associated 

anoxic conditions in the northern part of the Eastern Shore in 

Virginia, for example, but promoted by coarser organic-poor 

sediments to the south (Speiran, 1996).

Nitrogen in organic compounds or other forms also 

moves to surface waters over the land surface during overland 

runoff following precipitation, and may constitute a substantial 

part of in-stream nitrogen loads during such periods, particularly in the spring following fertilizer and manure applications, 

but before major crop growth. Groundwater discharge as base 

flow provides the majority of streamflow on the Eastern Shore, 

however, and nitrate from groundwater discharge constitutes 

the majority of nitrogen in nontidal streams (Ator and Denver, 

2012). Nitrate concentrations often decrease in streams during 

high-flow periods, as relatively high concentrations contributed from groundwater discharge are diluted by overland 

runoff containing lower nitrate concentrations (fig. 29). 

Nitrate in surface waters on the Eastern Shore represents 

a mixture of nitrogen contributed to the land surface in 

the upstream watershed over a variety of time periods. 

Groundwater generally flows very slowly, and nitrate concentrations in groundwater therefore reflect application rates and 

other influences during previous periods when the water actually infiltrated from the land surface to the water table. Nitrate 

moving through the soil to the water table close to streams and 

other discharge areas may flow along short groundwater flow 

paths to streams within a few years. However, several years or 

decades are typically required for nitrate movement through 

the surficial aquifer from source areas to streams (fig. 23), and 

even greater time periods are often required for flow along 

longer flow paths from watershed uplands (fig. 27) (Dunkle 

and others, 1993; Böhlke and Denver, 1995; Lindsey and 

others, 2003; Debrewer and others, 2007; Sanford and Pope, 

2007; Denver and others, 2010). Groundwater discharge to 

streams therefore represents a mixture of flow paths of differing ages from throughout the stream watershed (fig. 27), and 

nitrate in streams during base flow is a mixture of nitrogen 

applied during many different time periods (Lindsey and others, 2003; Sanford and others, 2012). 

Nitrogen moves from source areas on the landscape to streams 

and tidal waters of the Eastern Shore primarily as nitrate through 

groundwater.
Chapter 3. Sources and Movement of Nitrogen and Phosphorus on the Eastern Shore 31

SURFICIAL AQUIFER

EXPLANATION

Flow path or storage location

Hydrogeologic units

Estuary

Water table

Land surface

NONPOINT SOURCES

Nitrogen and phosphorus

GROUNDWATER FLOW

(Years) GROUNDWATER FLOW

(Years)

GROUNDWATER FLOW (Decades)

OVERLAND RUNOFF

(Days to decades)

ACCUMULATION IN

SOIL (Decades)

Stream

Submarine

groundwater

discharge

Flow path with natural water chemistry and

no anthropogenic nitrogen or phosphorus

Flow path with nitrate and any dissolved

phosphorus

Flow path with insoluble phosphorus and nitrogen

compounds (such as organic nitrogen)

Storage of insoluble phosphorus

Unsaturated zone above the water table Aquifer with oxic groundwater Confining unit

Figure 27. Idealized summary of hydrology and nutrient transport on the Eastern Shore in areas with oxic groundwater and 

well-drained soils. Nitrogen transport from the land surface to streams occurs primarily through groundwater in the form of 

nitrate, whereas phosphorus transport occurs primarily in overland runoff.

Figure 28. The importance of dissolved oxygen 

concentrations to nitrate concentrations in shallow 

groundwater on the Delmarva Peninsula, 2001. Nitrate 

concentrations are typically much higher in groundwater 

containing abundant dissolved oxygen than in 

groundwater where dissolved oxygen is low (less than 1 

milligram per liter).

Nitrate, in milligrams per liter as N

Dissolved oxygen, in milligrams per liter

EXPLANATION 20

16

12

8

17

27

27

4

0

Less than or equal to 1

[From Debrewer and others, 2007.]

Greater than 1

75th

percentile

Number of

samples

25th

percentile

Median

Chapter 3
32 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Figure 29. Relation of concentrations of nitrate, phosphorus, and suspended sediment 

to streamflow in Chesterville Branch, 1990–2012. Decreasing nitrate concentrations 

but increasing phosphorus and sediment concentrations during periods of increased 

streamflow indicate that different mechanisms are primarily responsible for the 

transport of these contaminants to Chesterville Branch. Nitrate moves to Chesterville 

Branch primarily through groundwater, and concentrations are highest during low-flow 

periods when streamflow is primarily contributed by groundwater discharge. Sediment 

and phosphorus, conversely, are lowest during low flow and move to Chesterville 

Branch primarily through overland runoff during high-flow periods.

Suspended sediment

EXPLANATION

Phosphorus

Nitrate (as Nitrogen)

Phosphorus or sediment concentration,

in milligrams per liter

Streamflow, in cubic feet per second

[From Ator, Denver, and Brayton, 2005.]

Nitrate concentration, in milligrams per liter as N

100

10

1

0.1

0.01

10,000

1,000

100

10

1

0.1

0.01

0.001

1 10 100 1,000 10,000

Chesterville Branch near Crumpton, Maryland
Chapter 3. Sources and Movement of Nitrogen and Phosphorus on the Eastern Shore 33

Nitrate Removal Through Denitrification, and Limitations 

Caused by Local Hydrogeology 

Nitrogen is transported as nitrate through groundwater to streams with minimal losses in water with abundant dissolved oxygen, but 

can be lost in substantial quantities to the atmosphere in anoxic areas (fig. 

30). Precipitation generally contains abundant dissolved oxygen from the 

atmosphere as it infiltrates through the soil to the water table. Where soils 

and aquifer sediments contain little organic material (as in many areas of the 

Eastern Shore), water remains oxic (retains dissolved oxygen) and nitrate 

remains stable for long time periods as the water infiltrates to the water 

table and moves along groundwater flow paths to streams and coastal estuaries. In organic-rich soil and aquifer sediments, however, dissolved oxygen 

is consumed and anoxic conditions develop as naturally occurring bacteria 

consume the organic matter. In such geochemical environments, nitrate 

becomes unstable and is lost to nitrogen gas through denitrification, an 

important process for removing nitrate from terrestrial ecosystems worldwide (Howarth and others, 1996). 

Denitrification may substantially reduce nitrogen delivery to streams 

in some areas of the Eastern Shore, but has limited effect on nitrogen 

loads in streams in other areas where groundwater flow largely bypasses 

anoxic conditions. Denitrification has been observed in many different settings on the Eastern Shore, including at or near the land surface in soils 

of depressional (Denver and others, 2014) and riverine (Jordan and others, 2007) wetlands, along groundwater flow paths (Böhlke and Denver, 

1995; Denver and others, 2010), in riparian flood plains (Duff and others, 2008; Puckett and others, 2008), and in coastal swamps and marshes 

(Speiran, 1996). The importance of denitrification to overall nitrogen 

delivery to individual streams, however, depends on the local hydrogeology, particularly the orientation of groundwater flow paths and the 

extent to which groundwater containing nitrate encounters anoxic conditions prior to discharging to streams (Denver and others, 2014). Nitrate 

in groundwater is most likely to encounter anoxic conditions conducive to denitrification where the surficial aquifer is particularly thin 

(figs. 30-1b, 30-1c, 30-4). The surficial aquifer in many areas of the Eastern 

Shore is relatively thick, however, and anoxic conditions associated with 

wetlands on the land surface in such areas often do not extend through the 

entire thickness of the aquifer (fig. 30-2a) or have been truncated by artificial 

ditching or channelization (fig. 30-3). In such areas, oxic groundwater carries nitrate to streams beneath forested stream buffers (fig. 30-1a) or denitrifying conditions at the land surface (fig. 30-2a). Nitrate concentrations are 

generally much higher in streams in areas where these conditions are common (such as the Eastern Shore) than in other areas of the Atlantic Coastal 

Plain (such as, for example, the Western Shore) where the surficial aquifer 

is typically much thinner (Vroblesky and Fleck, 1991; Ator, Denver, Krantz, 

and others, 2005; Ator and Denver, 2012). Groundwater also carries nitrate 

directly to estuaries where sediments are coarse-grained with low organic 

matter (Speiran, 1996), similar to the setting in fig. 30-1a.

Chapter 3
34 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

38°

39°

76°

75°

Pennsylvania

Maryland

Virginia

Delaware

New Jersey

Chesapeake Bay

watershed

boundary

ATLANTIC

OCEAN

Delaware Bay

Delaware River

Chesapeake Bay

0 10 20 MILES

0 10 20 KILOMETERS

Base from U.S. Geological Survey,

1:2,000,000 DLG, Albers Equal Area

Conic Projection, NAD 83

Land-cover data from LaMotte, 2008a, b

N

CHESTER RIVER

WATERSHED

CHOPTANK

RIVER

WATERSHED

NANTICOKE

RIVER

WATERSHED

POCOMOKE RIVER

WATERSHED

POCOMOKE RIVER

WATERSHED

VIRGINIA'S EASTERN SHORE VIRGINIA'S EASTERN SHORE

Eastern

Shore

Eastern

Shore

1

2

3

4

Streams or wetlands

Forest

EXPLANATION

Selected natural features

1 A

B

C

The surficial aquifer in the Chesterville Branch watershed contains

dissolved oxygen in most areas, and groundwater carries nitrate at

relatively high concentrations to Chesterville Branch.

In the Morgan Creek watershed, nitrate is lost from groundwater to

denitrification near the base of the aquifer and in near-stream sediments,

and as groundwater that discharges at a seepage face flows across the

flood plain.

Chesterville Branch Morgan Creek

Morgan Creek

Nitrate moves with groundwater to stream

Denitrification occurs along flow paths at the base

of the aquifer and in near-stream sediment

Denitrification occurs in flood plains

Seepage

face

Böhlke and Denver, 1995; Bachman and others, 2002; Ator, Denver, and

Brayton, 2005; Hancock and Brayton, 2006; Domagalski and others, 2008;

Denver and others, 2010.

Figure 30. Idealized summary of hydrologic conditions and the potential for denitrification in groundwater in various 

hydrogeologic settings on the Eastern Shore. Denitrification has been observed in many different settings on the Eastern Shore, 

but the effectiveness of denitrification in limiting nitrogen transport through groundwater to streams varies substantially with 

varying hydrogeologic conditions. 
Chapter 3. Sources and Movement of Nitrogen and Phosphorus on the Eastern Shore 35

2

3

A B

Nitrate is lost in anoxic groundwater beneath depressional wetlands in the upper part of the Choptank River watershed. The lateral and vertical

extent of anoxic groundwater may be limited, however, and groundwater containing dissolved oxygen and nitrate may pass beneath these

wetlands to discharge areas in streams. (Denver and others, 2014.)

Streams and rivers of the Nanticoke watershed have been channelized to lower the water

table. Because of this, much of the groundwater containing nitrate discharges directly through

the sandy streambed and bypasses anoxic flood-plain sediments. (Clune and Denver, 2012.)

EXPLANATION

Aquifer with oxic groundwater

Aquifer with anoxic groundwater

Confining unit

Water table

Containing nitrate

Nitrate removed by denitrification

Likely never contained nitrate

Hydrogeologic units

Groundwater flow paths

Wetland

Nitrate moves with

groundwater at depth

Nitrate moves with

groundwater to ditches

Denitrification occurs in

deeper groundwater

Denitrification occurs along

flow path beneath wetland

Denitrification occurs along

flow path beneath wetland

Wetland

Ditch

Nanticoke River

Pocomoke River

Perennial

stream

Field ditches

Ditch

4

Short flow paths often carry nitrate through shallow groundwater to ditches in farm fields in the Pocomoke River watershed;

denitrification occurs along longer flow paths contributing to larger streams and the river. (Phillips and Donnelly, 2003;

Ator, Denver, and Brayton, 2005; Denver and others, 2010; McCoy, Sigrist, and others, 2010.)

Figure 30. Idealized summary of hydrologic conditions and the potential for denitrification in groundwater in various 

hydrogeologic settings on the Eastern Shore. Denitrification has been observed in many different settings on the Eastern Shore, 

but the effectiveness of denitrification in limiting nitrogen transport through groundwater to streams varies substantially with 

varying hydrogeologic conditions.—Continued 

Chapter 3
36 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Phosphorus

Phosphorus moves from source areas on the land surface 

to streams on the Eastern Shore primarily in overland runoff. 

Phosphorus is much less soluble in water than nitrate, particularly where dissolved oxygen is abundant. Phosphorus 

compounds therefore generally remain bound to soils and sediment in particulate form rather than moving to groundwater in 

dissolved form, although phosphorus may dissolve in groundwater in anoxic areas. Consequently, phosphorus transport to 

streams occurs primarily during high-flow periods following 

precipitation when erosion and overland runoff may mobilize 

and carry soil, sediment, and attached phosphorus to streams 

(figs. 27, 29) (Denver and others, 2004; Ator, Denver, and 

Brayton, 2005). Unlike nitrate concentrations, phosphorus and 

sediment concentrations are often greatest in streams during high-flow periods (fig. 29). Although shallow slopes and 

permeable soils and sediments typical of much of the Eastern 

Shore suggest soil erosion and related phosphorus transport to 

streams may be relatively minor, the transport of phosphorus 

from upland sources to streams is greater in the Coastal Plain 

than in other areas of the Chesapeake Bay watershed (Ator and 

others, 2011). Phosphorus from manure applications in excess 

of crop needs has been accumulating in Eastern Shore soils 

for decades (fig. 26), and such soils may carry greater phosphorus to streams during runoff periods than in the past and be 

less likely to sequester newly applied phosphorus (Heckrath 

and others, 1995; Staver and Brinsfield, 2001). Agricultural 

management practices (such as no-till cropping) that increase 

phosphorus at the land surface may also increase dissolved 

phosphorus in runoff (Staver and Brinsfield, 1995).

Phosphorus is much less soluble in water than nitrate, and 

consequently moves from source areas on the landscape to 

streams and tidal waters on the Eastern Shore primarily in solid 

(particulate) form over the land surface rather than through 

groundwater.
Chapter 4. Nitrogen and Phosphorus in Groundwater and Surface Waters of the Eastern Shore 37

Chapter 4. Nitrogen and Phosphorus in 

Groundwater and Surface Waters of 

the Eastern Shore

How high are concentrations of nitrogen and phosphorus 

in groundwater, streams, and estuaries on the Eastern Shore?

On the Eastern Shore, nitrogen is common in groundwater 

and surface waters and phosphorus is common in surface 

waters at concentrations that are well above natural levels, 

and are among the highest in the Nation. Differing concentrations in different areas are attributable to varying inputs from 

agriculture and other sources, as well as hydrogeologic, soil, 

and other natural conditions that affect the fate and movement 

of nitrogen compounds through the subsurface and phosphorus over the land surface.

Regional Groundwater Quality

Nitrate occurs in groundwater in many areas of the 

unconfined surficial aquifer on the Eastern Shore, typically 

at concentrations far greater than would be expected under 

natural conditions (see sidebar: “Natural Water Quality”), and 

often at concentrations high enough to affect the suitability 

of the water for human consumption (Hamilton and others, 

1993; Ferrari, 2001; Debrewer and others, 2007) (fig. 31). The 

presence of nitrate at concentrations indicative of human contamination has been reported in different parts of the aquifer 

since at least the early 1970s (fig. 31) (Cushing and others, 

1973; Bachman, 1984; Denver, 1986) (see sidebar: “Eastern 

Shore Water Quality in a National Context”) (figs. 32, 33). 

In the early 2000s, nitrate concentrations at various depths in 

the surficial aquifer on the Delmarva Peninsula had a median 

concentration above 5 milligrams per liter (mg/L as N), even 

in relatively deep parts of the aquifer commonly used for public supplies (Ferrari, 2001; Debrewer and others, 2007). More 

time is generally required for groundwater to move to greater 

depths, and the occurrence of nitrate from human sources at 

similar concentrations at various depths within the aquifer 

reflects the long history of agricultural nitrogen application 

on the Eastern Shore (figs. 25, 26). Concentrations in about 

one-third of samples from shallow groundwater in agricultural areas and from deeper groundwater commonly used for 

domestic supply in the early 2000s exceeded 10 mg/L, the 

Federal drinking-water standard (Maximum Contaminant 

Level) for nitrate in public water supplies (Debrewer and 

others, 2007). Consumption of water containing nitrate at 

concentrations greater than 10 mg/L can cause health problems, particularly in infants (U.S. Environmental Protection 

Agency, 2004), and prolonged consumption of nitrate at even 

lower concentrations in drinking water may be related to the 

development of certain types of cancer (Aschebrook-Kilfoy 

and others, 2012). 

Nitrate concentrations in groundwater in different areas 

of the Eastern Shore are related to the distribution of sources 

and natural soil and geochemical conditions affecting nitrate 

fate and transport (Debrewer and others, 2007; Ator, 2008). 

Concentrations are generally highest near agricultural areas, 

although horizontal groundwater flow may carry nitrate to 

Nitrate occurs in groundwater in many areas of the Eastern 

Shore at concentrations well above what might be expected 

under natural conditions, and concentrations that may affect the 

suitability of groundwater for drinking water are not uncommon.

Natural Water Quality

Natural water (water that has not been chemically influenced by human activities) in aquifers and streams on the Eastern Shore is typically dilute and acidic with 

few dissolved chemicals. Rainfall on the peninsula is generally acidic with very low concentrations of dissolved chemicals. The surficial aquifer on the Eastern Shore (particularly 

in the central part of the peninsula) is composed of quartz-rich sediments that are relatively 

insoluble and therefore include few natural minerals that may dissolve in infiltrating rainwater (Denver, 1989; Knobel and others, 1998; Ator and others, 2000). Natural groundwater 

in the aquifer is therefore typically similarly dilute and acidic, as is water in local streams, 

which receive the majority of their flow from groundwater discharge. Younger sediments 

common in coastal areas are generally finer-textured and contain a greater variety of minerals and more organic matter, however, and natural groundwater and streams in such 

areas often contain a greater variety of dissolved compounds contributed from these materials (Tesoriero and others, 2004; Ator, 2008). Nitrate from natural sources such as leaf litter 

and other vegetation rarely exceeds 0.4 mg/L in groundwater or 0.6 mg/L in streams on the 

Eastern Shore (Hamilton and others, 1993; Clark and others, 2000).

Chapter 4
38 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

groundwater beneath other land uses, as well (fig. 27). Nitrate 

concentrations are significantly higher in oxic groundwater 

where any nitrate that is formed in the soil zone and transported to groundwater is persistent (see Chapter 3). These 

conditions generally occur in areas with good soil drainage 

and permeable soils and sandy aquifer sediments that promote 

oxic conditions, such as in much of the central core of the 

Delmarva Peninsula (fig. 31). In contrast, concentrations of 

nitrate are typically low in areas with anoxic aquifer conditions where denitrification is common (see Chapter 3), such as 

those that generally occur in wetlands and in low-lying areas 

along Chesapeake Bay and its tidal tributaries (Bachman and 

others, 1998; Shedlock and others, 1999; Debrewer and others, 

2007).

Nitrate concentrations have increased in groundwater in 

parts of the surficial aquifer in recent decades. Nitrate concentrations in oxic groundwater on the Delmarva Peninsula 

increased by an average of about 2 mg/L between the late 

1980s and the early 2000s at depths in the surficial aquifer 

typically used for domestic supplies (fig. 34), although no such 

changes occurred during that period in shallower groundwater 

(Debrewer and others, 2007, 2008). The increase in nitrate 

concentrations in groundwater over that period is likely a 

result of increasing nitrate leaching to groundwater from 

increasing fertilizer and poultry manure nitrogen applications 

to the landscape during previous decades when groundwater 

sampled during 1988 and 2001 moved from the land surface to 

the water table (figs. 25, 26).

Concentrations of ammonia, organic nitrogen, and phosphorus compounds in groundwater on the Eastern Shore are 

generally much lower than concentrations of nitrate and generally do not exceed 0.2 mg/L (Debrewer and others, 2007). 

Although concentrations of these compounds may be elevated 

in poorly drained anoxic areas (Debrewer and others, 2008), 

ammonium concentrations are still typically relatively low 

compared to nitrate concentrations in groundwater because 

ammonium is preferentially adsorbed on certain clay minerals 

that are present in the soil (Denver, 1986). Once these ions are 

fixed in the soil, they are not likely to be removed. Phosphorus 

also is present in fertilizers, manure, and human sewage, but 

is fixed by silicate clays and oxides of iron, aluminum, and 

manganese in the soil zone and aquifer sediments and generally not dissolved in groundwater (Denver, 1986). 

Figure 31. Estimated probability of nitrate concentrations in 

shallow groundwater exceeding 1 milligram per liter as N in areas 

of the Delmarva Peninsula. Nitrate concentrations often exceed 

estimated natural levels (less than 0.4 milligrams per liter) in 

groundwater in many areas of the Eastern Shore, particularly in 

the central core of the Delmarva Peninsula. (GT = greater than; 

LE = less than or equal to.)

Eastern

Shore

Delaware Bay

Delaware River

Chesapeake Bay

CHESTER RIVER

WATERSHED

CHOPTANK

RIVER

WATERSHED

NANTICOKE

RIVER

WATERSHED

POCOMOKE RIVER

WATERSHED

VIRGINIA

COASTAL WATERSHEDS

ATLANTIC OCEAN

0 10 20 MILES

0 10 20 KILOMETERS

38°

39°

76°

75°

Pennsylvania

New Jersey

Maryland

Virginia

Delaware Chesapeake Bay

watershed

boundary

N

Base from U.S. Geological Survey,

1:2,000,000 DLG, Albers Equal Area

Conic Projection, NAD 83

Estimated groundwater quality

from Greene and others, 2005

EXPLANATION

Likelihood (in percent) of nitrate concentration exceeding

1 milligram per liter as N in shallow groundwater

LE 20

GT 20 and LE 40

GT 40 and LE 60

GT 60 and LE 80

GT 80 and LE 100
Chapter 4. Nitrogen and Phosphorus in Groundwater and Surface Waters of the Eastern Shore 39

Median concentration of nitrate, in milligrams per liter as N.

Each circle represents a groundwater study.

Background concentration

Average annual total nitrogen input, in pounds per acre,

by county, for 1995–98. Inputs are from fertilizer, manure,

and the atmosphere.

Highest (greater than 5 milligrams per liter as N)

Bold outline indicates median values greater than

background concentration (2 milligrams per liter as N)

Greater than 25

6 to 25

Less than 6

[From Denver and others, 2004.]

Medium (0.4 to 5 milligrams per liter as N)

Lowest (less than 0.4 milligrams per liter as N)

Delmarva

Peninsula

Nitrate concentrations in shallow groundwater

(Agricultural areas)

[From Denver and others, 2004.]

Total nitrogen in streams, 1993–2001

(Agricultural areas)

Total phosphorus in streams, 1993–2001

(Agricultural areas)

Mean annual concentration,

in milligrams per liter Nitrogen input,

in pounds per acre

Phosphorus input,

in pounds per acre

Less than 6

6 to 25

Greater than 25

Less than 2

2 to 5

Greater than 5

Less than 0.6

0.6 to 3

Greater than 3

Less than 0.05

0.05 to 0.3

Greater than 0.3

Mean annual concentration,

in milligrams per liter

Delmarva

Peninsula

Delmarva

Peninsula

Eastern Shore Water Quality in a National Context

Nutrient concentrations in streams and shallow groundwater in parts of the Eastern Shore are among the highest in the Nation (Denver and others, 2004). Nitrogen and phosphorus sources are abundant on the 

Eastern Shore, and hydrologic, geologic, and soil conditions in many areas are particularly suitable for the persistence of these compounds in the environment and their movement to streams and shallow groundwater (see 

Chapter 3). Consequently, nitrate concentrations in groundwater (fig. 32) and nitrogen and phosphorus concentrations in selected streams (fig. 33) in agricultural areas are among the highest observed in similar settings across the 

United States.

Figure 32. Summary of nitrate concentrations in shallow groundwater in selected agricultural areas of the United States. 

Nitrate concentrations in shallow groundwater underlying agricultural areas on the Eastern Shore are among the highest 

observed in agricultural areas of the Nation.

Figure 33. Summary of nitrogen and phosphorus concentrations in selected streams draining primarily agricultural areas of 

the United States. Nitrogen and phosphorus concentrations in streams in agricultural areas on the Eastern Shore are among 

the highest in the Nation.

Chapter 4
40 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Figure 34. Summary of nitrate 

concentrations in the surficial aquifer on 

the Delmarva Peninsula during 1988–90 

and 2001–03. Nitrate concentrations 

increased between the late 1980s and 

early 2000s at depths typically used for 

domestic supply.

90th

percentile

Number of

samples

10th

percentile

Median

Maximum

Contaminant

Level

(MCL)

Nitrate, in milligrams per liter as N 20

10 11

15

0

1988–90

Years

2001–03

[Modified from Debrewer and others, 2007.

See also Debrewer and others, 2008.]

Regional Surface-Water Quality

Nitrate concentrations in freshwater streams on the 

Eastern Shore are typically lower than in nearby groundwater 

(fig. 35), although concentrations of phosphorus and other 

nitrogen compounds (ammonium and organic nitrogen) are 

generally higher in streams than in groundwater (Shedlock 

and others, 1999; Denver and others, 2004; Ator, Denver, and 

Brayton, 2005). During base-flow conditions, streams are a 

mixture of groundwater contributed from multiple flow paths 

reflecting a variety of land uses and human impacts over time 

(figs. 21, 27). The highest nitrate concentrations entering 

streams with groundwater are therefore often diluted by mixing with water from other flow paths that have lower nitrate 

concentrations. These flow paths may have originated beneath 

forests where nitrogen was not applied, contain water that 

comes from older flow paths where nitrate concentrations are 

low, or come from parts of the aquifer system that are anoxic. 

Biological processes also may consume nitrate in streams, 

particularly during the growing season. Because phosphorus 

and other nitrogen compounds are typically less soluble 

than nitrate and most commonly transported with sediment, 

however, they often occur at much higher concentrations in 

streams than in groundwater, particularly during high-flow 

periods when streamflow is dominated by overland runoff 

(fig. 29) (Shedlock and others, 1999; Denver and others, 2004; 

Ator, Denver, and Brayton, 2005).

Nitrate concentrations in Eastern Shore streams reflect 

a combination of the abundance of agricultural and other 

nitrogen sources, hydrogeologic conditions that often promote 

nitrate formation and transport from the land surface, and the 

resulting elevated nitrate typical of shallow groundwater. The 

vast majority (over 90 percent) of headwater streams on the 

Delmarva Peninsula contained nitrate at concentrations greater 

than natural levels (see sidebar: “Natural Water Quality”) 

during base flow in the winter and spring of 2000, and about 

half contained nitrate exceeding 3 mg/L (fig. 35) (Denver 

and others, 2004; Ator and Denver, 2012). Similar base-flow 

nitrate concentrations were observed in Eastern Shore streams 

during the early 1990s (Bachman and Phillips, 1996). Nitrate 

concentrations in larger streams draining primarily agricultural 

areas are also typically greater than would be expected under 

natural conditions (see sidebar: “Eastern Shore Water Quality 

in a National Context”), but lower than in headwater streams 

draining exclusively agricultural areas (fig. 36) (Ator, Denver, 

and Brayton, 2005; Langland and others, 2013). Nitrate 

Figure 35. Concentrations of nitrogen compounds in streams 

and shallow groundwater on the Delmarva Peninsula, 2000–01. 

Nitrate concentrations are often higher in shallow groundwater 

than in receiving streams, but ammonia plus organic nitrogen 

concentrations are generally higher in streams.

[From Denver and others, 2004.]

Groundwater 29

Median

Minimum

Maximum

Number of samples

Streams

EXPLANATION

23

29

23

Nitrate concentration,

in milligrams per liter as N

Ammonia plus organic nitrogen

concentration,

in milligrams per liter

30 29

29

23

23

20

10

0

10

1

0.1

0.01

Concentrations of nitrate in Eastern Shore streams are generally 

lower than concentrations in contributing groundwater, but 

concentrations of phosphorus and other nitrogen compounds 

are often higher in streams. Both nitrogen and phosphorus occur 

in Eastern Shore streams at concentrations that may adversely 

affect aquatic ecosystems. 
Chapter 4. Nitrogen and Phosphorus in Groundwater and Surface Waters of the Eastern Shore 41

Delaware River

ATLANTIC OCEAN

Delaware Bay

Chesapeake Bay

0 10 20 MILES

0 10 20 KILOMETERS

NITROGEN PHOSPHORUS

38°

39°

76°

75°

Pennsylvania

Maryland

Virginia

Delaware

POCOMOKE RIVER

WATERSHED

CHESTER RIVER

WATERSHED

CHOPTANK

RIVER

WATERSHED

NANTICOKE

RIVER

WATERSHED

VIRGINIA COASTAL 

WATERSHEDS

Chesapeake Bay

watershed

boundary

Eastern

Shore

N

Estimated stream-water quality

from Ator and others, 2011

Base from U.S. Geological Survey,

1:2,000,000 DLG, Albers Equal Area

Conic Projection, NAD 83

Estimated average

annual flow-weighted

concentration during 2002,

in milligrams per liter

LE 0.71 (AQR)

GT 0.71 and LE 2

GT 2 and LE 3

GT 3 and LE 5

GT 5

EXPLANATION

Delaware Bay

Delaware River

Chesapeake Bay

Pennsylvania

Maryland

Delaware

CHESTER RIVER

WATERSHED

CHOPTANK

RIVER

WATERSHED

NANTICOKE

RIVER

WATERSHED

POCOMOKE RIVER

WATERSHED

Chesapeake Bay

watershed

boundary

Eastern

Shore

ATLANTIC OCEAN

Virginia

VIRGINIA COASTAL 

WATERSHEDS

N

0 10 20 MILES

0 10 20 KILOMETERS

38°

39°

76°

75°

Base from U.S. Geological Survey,

1:2,000,000 DLG, Albers Equal Area

Conic Projection, NAD 83

Surface-water chemistry estimated

from Ator and others, 2011

LE 0.031 (AQR)

GT 0.031 and LE 0.2

GT 0.2 and LE 0.3

GT 0.3 and LE 0.4

GT 0.4

EXPLANATION

Estimated average

annual flow-weighted

concentration during 2002,

in milligrams per liter

Figure 36. Estimated average-annual flow-weighted concentrations of nitrogen and phosphorus in Eastern Shore 

streams. Concentrations of nitrogen and phosphorus in streams of the Eastern Shore generally exceed natural levels. 

(AQR is the water-quality criteria recommended to protect aquatic organisms [U.S. Environmental Protection Agency, 

2000]. GT = greater than; LE = less than or equal to.)

Chapter 4
42 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

concentrations in Eastern Shore streams often vary seasonally; 

concentrations are generally greatest in the winter months 

when groundwater discharge is greatest and uptake by aquatic 

plants is minimal, and lowest in the late summer when such 

conditions are reversed (fig. 37) (Denver and others, 2004; 

Ator, Denver, and Brayton, 2005). 

Phosphorus, ammonia, and organic nitrogen are generally 

present along with nitrate in Eastern Shore streams, however, 

like in groundwater, typically at much lower concentrations. 

Phosphorus concentrations in streams draining undeveloped 

watersheds are generally less than 0.02 mg/L and rarely 

exceed 0.1 mg/L (Clark and others, 2000). Concentrations of 

phosphorus in Eastern Shore streams during base-flow conditions are generally well below 0.1 mg/L, but can be much 

higher (as high as 3 or 4 mg/L) during high-flow periods 

(fig. 29), or in poorly drained areas with abundant organic 

matter and low dissolved oxygen (fig. 36) (Denver and others, 

2004; Ator, Denver, and Brayton, 2005) (see sidebar: “Eastern 

Shore Water Quality in a National Context”). Concentrations 

of ammonia plus organic nitrogen in Eastern Shore streams 

during base-flow conditions are typically well below 1.0 mg/L 

(fig. 35), but—like phosphorus—can increase substantially 

during high-flow periods (Clark and others, 2000; Ator, 

Denver, and Brayton, 2005). 

Nitrogen and phosphorus in stream water contribute 

to excessive algal growth and other ecological deterioration 

of freshwater streams on much of the Eastern Shore. 

Concentrations of nitrogen greater than 0.71 mg/L and (or) 

phosphorus greater than 0.031 mg/L in streams of the eastern 

Coastal Plain may cause excessive plant growth and other 

conditions detrimental to aquatic organisms, and these concentrations have been recommended as criteria to protect aquatic 

communities (U.S. Environmental Protection Agency, 2000). 

Nitrate concentrations, alone, commonly exceed 0.71 mg/L 

in Eastern Shore streams (fig. 35), and phosphorus concentrations greater than 0.031 mg/L are not unusual (fig. 36) (Clark 

and others, 2000; Ator, Denver, and Brayton, 2005). Although 

the growth and decay of algae and aquatic plants and resulting 

oxygen depletion depend on the availability of light and other 

habitat conditions as well as water quality, such conditions in 

Eastern Shore streams are apparently generally not limited by 

the availability of nutrients. Overall, the structure and composition of communities of benthic aquatic organisms in Eastern 

Shore streams are typically fair, poor, or very poor (fig. 38) 

(Chesapeake Bay Program, 2012).

Nutrient concentrations in Eastern Shore streams are 

increasing, particularly where nonpoint sources are important 

and groundwater is a dominant pathway for nutrient transport. 

Nitrate concentrations in the Choptank and Nanticoke Rivers 

have increased consistently since the mid-1960s (fig. 39), 

primarily due to increasing nitrate concentrations in groundwater discharge (fig. 34), the predominant source of water 

and nitrate to those rivers (Hirsch and others, 2010; Robert 

Hirsch, USGS, written commun., 2013). Similarly, total 

nitrogen and phosphorus have increased since the mid-1980s 

in the Choptank River, in spite of the restoration of streamside 

buffers to forest in much of the Choptank watershed since the 

1990s (Sutton and others, 2010) (fig. 39). Suspended-sediment 

yields in the Choptank River have generally increased since 

2001, but on average, have decreased since 1985 (Moyer and 

others, 2012). Phosphorus transport to streams occurs primarily in particulate form attached to sediment, and increasing 

phosphorus concentrations during a period of decreasing sediment concentrations (possibly due to forested buffer restoration) suggests that dissolved phosphorus transport may be 

increasing and (or) that average concentrations of particulate 

phosphorus on sediment particles moving to the Choptank 

River are increasing.

Figure 37. Seasonal variability in nitrate concentrations in 

the Pocomoke River, 1999–2001. Nitrate concentrations reflect 

greater shallow groundwater discharge and lesser biotic 

activity in the cooler months and reversed conditions during 

the warmer months. Nitrate concentration, in milligrams per liter as N

5

4

3

2

1

0

Jan Feb Mar Apr May

[From Denver and others, 2004.]

Month

Jun Jul Aug Sep Oct Nov Dec
Chapter 4. Nitrogen and Phosphorus in Groundwater and Surface Waters of the Eastern Shore 43

Good

Fair

Poor

Very poor

Eastern

Shore

Delaware Bay

Delaware River

Chesapeake Bay

CHESTER RIVER

WATERSHED

CHOPTANK

RIVER

WATERSHED

NANTICOKE

RIVER

WATERSHED

POCOMOKE RIVER

WATERSHED

VIRGINIA

COASTAL WATERSHEDS

ATLANTIC OCEAN

0 10 20 MILES

0 10 20 KILOMETERS

38°

39°

76°

75°

Pennsylvania

New Jersey

Maryland

Virginia

Delaware Chesapeake Bay

watershed

boundary

N

Base from U.S. Geological Survey,

1:2,000,000 DLG, Albers Equal Area

Conic Projection, NAD 83

Data from Chesapeake Bay

Program, 2012

EXPLANATION

Health of freshwater

ecosystems, 2000–10,

based on communities

of benthic aquatic

organisms

Figure 38. Ecological conditions in Eastern Shore tributaries to the Chesapeake 

Bay assessed by sampling communities of benthic aquatic organisms. Ecological 

conditions in Eastern Shore streams are generally fair, poor, or very poor.

Chapter 4
44 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Suspended

sediment

Choptank River near Greensboro, Maryland

Nitrate concentration,

in milligrams per liter as N

Average change in flow-adjusted yield in the Choptank River

near Greensboro, Maryland, in percent per year

[From Moyer and others, 2012.]

[From U.S. Geological Survey, 2014.]

Orthophosphorus

Nitrogen

Yield decreased

1985–2010

EXPLANATION

2001–2010

Yield increased

Nitrate

Phosphorus

-4

4

3

2

1

0 1970 1980

Year

1990 2000 2010

-3 -2 -1 0 1 2 3 4

A

B

Spline smooth line

Figure 39. Trends in (A) average nutrient yields during 1985 through 2010 and 

2001 through 2010, and (B) nitrate concentrations from the mid-1960s through 2013 

in the Choptank River near Greensboro, Maryland. Nutrient concentrations have 

generally increased in the river over recent decades.
Chapter 4. Nitrogen and Phosphorus in Groundwater and Surface Waters of the Eastern Shore 45

Water Quality in Tidal Estuaries

Degraded ecological conditions in tidal reaches of 

major streams draining the Eastern Shore reflect high inputs 

of nitrogen and phosphorus from contributing watersheds. 

Eutrophic conditions in Chesapeake Bay may be controlled 

by either nitrogen or phosphorus inputs during different 

seasons (Prasad and others, 2010), and include excessive algal 

growth and related decreases in dissolved oxygen, submerged 

aquatic vegetation, and habitat for benthic organisms (Bricker 

and others, 2007; McCoy, Spotts, and others, 2010; U.S. 

Environmental Protection Agency, 2011a). Water quality and 

benthic habitat in Eastern Shore sub-estuaries to Chesapeake 

Bay are often similarly fair or poor (Fisher and others, 2006; 

U.S. Environmental Protection Agency, 2008b); eutrophic 

conditions (particularly chlorophyll-a levels), for example, 

were high or moderately high in tidal reaches of the Chester 

and Choptank Rivers and in Tangier and Pocomoke Sounds 

during 2004, and worsened in the Chester and Choptank 

River estuaries between 1999 and 2004 (Bricker and others, 

2007). Dissolved oxygen levels in deeper waters in the 

Choptank River estuary decreased between 1984 and 2004, 

and approached minimum water-quality standards during wet 

years (Fisher and others, 2006). 

Nitrogen and Phosphorus in Major Eastern 

Shore Watersheds 

Locally variable land use, associated nutrient inputs, and 

hydrogeologic, soil, and other natural conditions contribute 

to similarly variable nitrogen and phosphorus concentrations 

in streams and groundwater in different parts of the Eastern 

Shore and resulting differences in nutrient contributions to 

Chesapeake Bay. Local differences in natural drainage and 

other hydrologic conditions are reflected in differing rural 

landscapes among major Eastern Shore watersheds within 

the broader agricultural setting (fig. 40). These differences 

are related to variations in natural conditions (see Chapter 2) 

and contribute to variable inputs and transport of nitrogen and 

phosphorus to tidal waters (fig. 41). Some areas have similar 

landscape characteristics (such as, for example, forested riparian wetlands) but different subsurface conditions that affect 

the potential for denitrification in groundwater (see sidebar: 

“Nitrate Removal Through Denitrification, and Limitations 

Caused by Local Hydrogeology”). Phosphorus transport from 

areas receiving similar inputs also varies substantially with 

variable soil conditions that affect phosphorus retention on the 

landscape or movement to streams. Local studies in different 

areas of the Eastern Shore (see following sections) illustrate 

the importance of these differences to predominant pathways 

of nutrient transport in different areas, and results from these 

studies can be extrapolated to understanding nutrient transport 

in other parts of the Eastern Shore and the wider Coastal Plain 

region where relevant physical conditions are similar. 

Chapter 4
46 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

38°

39°

76°

75°

Pennsylvania

Maryland

Virginia

Delaware

New Jersey

Chesapeake Bay

watershed

boundary

ATLANTIC

OCEAN

Delaware Bay

Delaware River

Chesapeake Bay

0 10 20 MILES

0 10 20 KILOMETERS

Base from U.S. Geological

Survey, 1:2,000,000 DLG,

Albers Equal Area Conic

Projection, NAD 83

Land-cover data from LaMotte, 2008a, b.

Aerial imagery from the National

Agricultural Imagery Program,

U.S. Department of Agriculture.

N

CHESTER RIVER

WATERSHED

CHOPTANK

RIVER

WATERSHED

NANTICOKE

RIVER

WATERSHED

POCOMOKE RIVER

WATERSHED

VIRGINIA'S EASTERN SHORE 'S EASTERN SHORE

Eastern

Shore

Eastern

Shore

Streams or wetlands

Forest

EXPLANATION

Selected natural features

Well-drained soils, incised stream channels,

and extensive areas of agricultural production

in parts of the Chester River watershed lead to

high concentrations of nitrate in groundwater

transported to streams and overland transport

of phosphorus.

Poor surface drainage and depressional wetlands

interspersed in forested and agricultural areas in

the headwaters of the Choptank River watershed

limit concentrations of nitrogen and phosphorus in

groundwater transported to streams.

The very flat landscape of the Pocomoke River

watershed requires extensive ditching in fields and

channelization of streams to lower the water table

and allow for crop production. The field ditches are

generally not buffered and provide short flow paths

for nutrient movement into streams.

Low topographic relief, channelized streams,

extensive agriculture over sandy soils, and a thick

permeable surficial aquifer limit overland runoff

and phosphorus transport, but lead to high

concentrations of nitrate in groundwater and

streams in parts of the Nanticoke River watershed.

The Eastern Shore of Virginia is narrow and

dissected by numerous tidal creeks and inlets.

Groundwater discharge and overland runoff

directly to tidal waters are the major pathways for

nutrient transport. Poor drainage and extensive

wetlands limit nutrient transport in the north, but

well-drained soils and sandy aquifer sediments

directly adjacent to tidal waters promote nutrient

transport to surface water further south.

Figure 40. A summary of selected landscapes on the Eastern Shore. Variable landscapes and hydrogeology affect the inputs and 

transport of nutrients among major Eastern Shore watersheds.
Chapter 4. Nitrogen and Phosphorus in Groundwater and Surface Waters of the Eastern Shore 47

Figure 41. Estimated nitrogen and phosphorus inputs to the landscape from various 

sources, 2002, and average annual outputs in streamflow to Chesapeake Bay. Nutrient 

outputs vary among major Eastern Shore watersheds and generally represent less 

than 25 percent of inputs.

0 10 20 30 40 50 60 70 80 90 100

0

0

2

2

4

4

6

6

Average annual input to the landscape or yield to Chesapeake Bay,

in kilograms per hectare

(pounds per acre)

8

8

10

10

12

12

14

14

16

16 18

Atmospheric

Fertilizer or fixation

Manure

Urban

Point sources

SOURCE

S: Inputs to the watershed landscape (U.S. Environmental

Protection Agency, 2009; Wieczorek and LaMotte, 2010a;

2010b; 2010c; 2010d; Ator and others, 2011). Inputs from

urban areas are estimated inputs reaching stream channels.

L: Output from the watershed carried in streams to Chesapeake

Bay (Ator and others, 2011).

18

16

14

11

23

percent of total inputs carried in streams to Chesapeake Bay

12

8.8

4.4

7.0

7.3

0 10 20 30 40 50 60 70 80 90

Pocomoke

Pocomoke

Chester

Chester

Choptank

Choptank

Nanticoke

Nanticoke

Virginia

Virginia

S

S

S

S

S

S

S

S

S

S

L

L

L

L

L

L

L

L

L

L

Nitrogen

Phosphorus

Chapter 4
48 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Chester River Watershed

Natural soil and hydrogeologic conditions promote the 

movement of nutrients from the land surface to surface waters 

in much of the Chester River watershed, although a thin surficial aquifer limits nitrogen movement through groundwater 

in some areas. The watershed includes 760 km2 of the upper 

Eastern Shore (fig. 42). Agriculture, mostly the production of 

corn, soybeans and small grains, covers about 60 percent of 

the watershed and contributes 87 percent of the nitrogen load 

and 95 percent of the phosphorus load from the watershed 

to Chesapeake Bay. Agriculture in the watershed is typically 

underlain by well-drained sandy soils (see Chapter 2) that 

promote the formation of nitrate and its movement to shallow 

groundwater (see Chapter 3) (fig. 30-1). Concentrations of 

nitrate in these areas are consequently often between 10 

and 20 mg/L in groundwater (Domagalski and others, 2008; 

Denver and others, 2010) and greater than 3 mg/L in streams 

(Böhlke and Denver, 1995; Bachman and others, 2002; Ator, 

Denver, and Brayton, 2005; Domagalski and others, 2008). 

Nitrate is the major form of nitrogen in streams, as would be 

expected if most nitrogen transport to streams occurs through 

groundwater (Domagalski and others, 2008). Phosphorus 

concentrations in groundwater are generally less than 0.1 mg/L 

(Bachman and others, 2002) but can be much higher in 

streams during periods of overland flow following storms 

when surface transport of nutrients occurs (fig. 29) (Ator, 

Denver, and Brayton, 2005). 

Nitrate concentrations in streams in the Chester River 

watershed are typically lower than in contributing groundwater, and reflect variability in land use and the thickness 

of the surficial aquifer. The general lack of human inputs in 

the forested eastern headwaters is reflected in surface-water 

nitrate concentrations that rarely exceed 1 mg/L (fig. 36) 

and average nitrogen and phosphorus yields that are among 

the lowest in the watershed (fig. 42). In agricultural areas, 

however, the thickness of the surficial aquifer varies and is 

a primary control on the movement of nitrate from groundwater to local streams (Böhlke and Denver, 1995; Bachman 

and others, 2002; Ator, Denver, and Brayton, 2005; Denver 

and others, 2010) (fig. 30-1) (see sidebar: “Nitrate Removal 

Through Denitrification, and Limitations Caused by Local 

Hydrogeology”). The surficial aquifer is relatively thick (up to 

30 m) beneath Chesterville Branch, a tributary in the northern 

part of the watershed, and much of the nitrate in groundwater 

discharges with minimal losses to streams (fig. 30-1a). Nitrate 

concentrations in Chesterville Branch during base flow have 

been measured between 8 and 10 mg/L. In watersheds of the 

Morgan Creek and the Corsica River tributaries, however, 

some streams have incised completely through the surficial 

aquifer into an underlying fine-grained deposit, and much of 

the discharging groundwater is forced through shallow anoxic 

sediments (fig. 30-1b) or through seeps to the flood plain, 

where denitrification can occur (Hancock and Brayton, 2006) 

(see Chapter 3) (fig. 30-1c). Nitrate concentrations in these 

streams during base flow are consequently generally lower 

than in Chesterville Branch, but still around 5 mg/L (Böhlke 

and Denver, 1995; Bachman and others, 2002; Ator, Denver, 

and Brayton, 2005; McCarthy and Capel, 2009; Denver and 

others, 2010).

Phosphorous is transported to streams in the Chester 

River watershed from agricultural areas primarily with 

water and sediment during periods of overland runoff. 

Concentrations of phosphorus in streams are generally higher 

than in groundwater, and during runoff periods can approach 

1 mg/L (fig. 29). Phosphorus yields from the Chester River 

watershed are highest where the potential for runoff carrying 

phosphorus-laden sediment from agricultural fields is greatest, 

such as where land-surface slopes are steepest.

Natural conditions in the Chester River watershed 

promote the relatively efficient transport of nutrients from 

application areas to Chesapeake Bay. On average, nutrient 

yields from the Chester River watershed to Chesapeake Bay 

are very similar to or greater than those from the Choptank 

and Nanticoke Rivers, in spite of lower average inputs 

(fig. 41). Particularly efficient nitrogen transport is facilitated 

by the generally thick and permeable surficial aquifer; 

phosphorus transport within the watershed is facilitated by 

average land slope and relief in the Chester River watershed 

that is generally greater than in watersheds further south (see 

Chapter 2). Reductions of 380 metric tons of nitrogen and 19 

metric tons of phosphorus per year will be required to meet the 

TMDL for the Chesapeake Bay in this watershed (fig. 13). The 

majority of these reductions will be required from agriculture, 

the largest local source of nutrients (fig. 41).

Chester River just east of Chestertown, Maryland. 

Photograph by Jane Thomas, Integration and Application 

Network, University of Maryland Center for Environmental 

Science (ian.umces.edu/imagelibrary/).
Chapter 4. Nitrogen and Phosphorus in Groundwater and Surface Waters of the Eastern Shore 49

Chester

Chester

River

Chesapeake Bay

Chesapeake Bay

River

Chestertown

Denton

CHESTER

RIVER

WATERSHED

CHESTER

RIVER

WATERSHED

NITROGEN PHOSPHORUS

Land cover from LaMotte, 2008a, b

Estimated nutrient yields

from Ator and others, 2011

Estimated nutrient yields

from Ator and others, 2011

Land cover

EXPLANATION

Estimated annual yield to local streams,

in kilograms per hectare

(pounds per acre)

LE 2 (1.8)

GT 2 and LE 3 (2.7)

GT 3 and LE 4 (3.6)

GT 4 and LE 5 (4.4)

GT 5 and LE 7 (6.2)

GT 7 and LE 10 (8.8)

GT 10 and LE 14 (12)

GT 14 and LE 17 (15)

GT 17 and LE 22 (20)

GT 22

LE 0.05 (0.04)

GT 0.05 and LE 0.1 (0.09)

GT 0.1 and LE 0.2 (0.18)

GT 0.2 and LE 0.3 (0.27)

GT 0.3 and LE 0.5 (0.44)

GT 0.5 and LE 0.8 (0.71)

GT 0.8 and LE 1 (0.88)

GT 1 and LE 1.5 (1.3)

GT 1.5 and LE 2 (1.8)

GT 2

NITROGEN PHOSPHORUS

Agriculture

Urban

Forest

Wetland

Open water

Nutrient point

source

Chester

River

Chesapeake Bay

CHESTER

RIVER

WATERSHED

213

301

50 404

301

Figure 42. The Chester River watershed. The watershed is located on the upper Eastern Shore and is primarily agricultural. 

Nutrient yields from the land surface to streams are generally lower in the forested eastern headwaters than in the remainder of the 

watershed, which is predominantly agricultural. (GT = greater than; LE = less than or equal to.)

Chapter 4
50 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Choptank River Watershed

Anoxic groundwater around current and former wetlands 

limits nitrogen movement through groundwater in parts of 

the Choptank River watershed, although natural conditions 

promote nitrate transport through groundwater to streams in 

other areas. Agriculture covers about 60 percent of the land 

in the Choptank River watershed (fig. 43) and contributes 

more than 80 percent of the load of nitrogen and phosphorus 

from the watershed to Chesapeake Bay (fig. 41). A large part 

of the headwaters, however (particularly in the east above 

Greensboro, Maryland), includes poorly drained uplands (see 

Chapter 2) where agriculture is interspersed with large tracts 

of forested wetlands. Streams in this area are generally low 

gradient and channelized, and artificial ditches lower the water 

table beneath depressional wetlands in agricultural fields. In 

other areas of the watershed (such as around the Tuckahoe 

Creek tributary to the west), however, better drainage and 

greater stream incision are common, ditching is less prevalent, 

and agricultural tracts are generally larger. Nitrate in oxic 

groundwater commonly exceeds 20 mg/L beneath agricultural 

fields with well-drained soils, but is less than 1 mg/L in 

poorly drained forested areas with minimal nitrogen inputs 

and around current and former wetlands where groundwater 

is typically anoxic (Staver, 2010; Denver and others, 2014) 

(see sidebar: “Nitrate Removal Through Denitrification, and 

Limitations Caused by Local Hydrogeology”). 

As in most areas of the Eastern Shore, groundwater 

provides the majority of nitrate to streams in the Choptank 

River watershed (Knee and Jordan, 2013), and concentrations 

in individual streams reflect concentrations in local contributing groundwater. Nitrate concentrations in small streams in 

predominantly poorly drained and forested sub-watersheds 

are generally less than 0.5 mg/L (McCarty and others, 2008; 

Denver and others, 2014). In agricultural areas, concentrations 

during base flow are generally higher in well-drained parts 

of the Tuckahoe Creek watershed (often 4 to 5 mg/L) than in 

more poorly drained areas of the Choptank River watershed 

farther east (about 2 mg/L) (McCarty and others, 2008). 

Nitrate concentrations in the Choptank River have increased 

consistently since the 1960s, primarily due to increasing 

nitrate concentrations in groundwater discharging to the river 

(fig. 39) (Fisher and others, 2006; Hirsch and others, 2010).

Phosphorus concentrations in the Choptank River generally range from less than 0.01 mg/L during base flow to about 

0.2 mg/L during higher flow (Sprague and others, 2000). 

Concentrations of phosphorus have increased over time in the 

river, in spite of decreasing concentrations of suspended sediment (Fisher and others, 2006; Langland and others, 2013). 

Increasing concentrations of phosphorus in the river during 

a period of decreasing sediment concentrations suggests 

increasing dissolved phosphorus transport in the watershed or 

increasing average phosphorus content on suspended sediment. These conditions may be related to increasing phosphorus saturation in watershed soils and resulting decreasing soil 

retention of applied phosphorus (Ator and others, 2011).

Hydrogeologic and landscape conditions that are more 

conducive to anoxic conditions and denitrification (particularly in the headwaters) promote slightly less efficient nutrient 

transport from the Choptank River watershed than from the 

Chester River watershed. In spite of more intensive inputs 

of fertilizer and manure in the Choptank River watershed, 

average yields of nitrogen and phosphorus to Chesapeake Bay 

are very similar to those from the Chester River watershed 

(fig. 41). Reductions of approximately 210 metric tons of 

nitrogen and 46 metric tons of phosphorus per year will be 

required in the Choptank River watershed to meet the 2010 

TMDL for the Chesapeake Bay (fig. 13).

Choptank River watershed flooded farm field, June 2006.

Photograph by Jane Thomas, Integration and Application 

Network, University of Maryland Center for Environmental 

Science (ian.umces.edu/imagelibrary/).
Chapter 4. Nitrogen and Phosphorus in Groundwater and Surface Waters of the Eastern Shore 51

Figure 43. The Choptank River watershed. The watershed covers 1,800 square kilometers from its headwaters in Kent County, 

Delaware to its tidal estuary near Cambridge, Maryland. As in the Chester River watershed, nutrient yields are generally lower in 

the forested eastern headwaters where wetlands are common than in the remainder of the watershed where agriculture and welldrained soils are more common. (GT = greater than; LE = less than or equal to.)

Land cover

EXPLANATION

Estimated annual yield to local streams,

in kilograms per hectare

(pounds per acre)

LE 2 (1.8)

GT 2 and LE 3 (2.7)

GT 3 and LE 4 (3.6)

GT 4 and LE 5 (4.4)

GT 5 and LE 7 (6.2)

GT 7 and LE 10 (8.8)

GT 10 and LE 14 (12)

GT 14 and LE 17 (15)

GT 17 and LE 22 (20)

GT 22

LE 0.05 (0.04)

GT 0.05 and LE 0.1 (0.09)

GT 0.1 and LE 0.2 (0.18)

GT 0.2 and LE 0.3 (0.27)

GT 0.3 and LE 0.5 (0.44)

GT 0.5 and LE 0.8 (0.71)

GT 0.8 and LE 1 (0.88)

GT 1 and LE 1.5 (1.3)

GT 1.5 and LE 2 (1.8)

GT 2

NITROGEN PHOSPHORUS

Agriculture

Urban

Forest

Wetland

Open water

Nutrient point

source

Easton

Cambridge

Denton

Greensboro

Dover

CHOPTANK

RIVER

WATERSHED

CHOPTANK

RIVER

WATERSHED

CHOPTANK

RIVER

WATERSHED

Choptank

River

Chesapeake Bay

NITROGEN PHOSPHORUS

Land cover from LaMotte, 2008a, b

Estimated nutrient yields

from Ator and others, 2011

Estimated nutrient yields

from Ator and others, 2011

Federalsburg

50

50

404

50 328

213

313

Chapter 4
52 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Nanticoke River Watershed

Water quality in the Nanticoke River watershed reflects 

locally variable land use and hydrologic conditions. Most 

of the Nanticoke River watershed is in the low-relief upland 

characteristic of much of the central Delmarva Peninsula (see 

Chapter 2). Incision of nontidal streams is generally limited 

but channelization and artificial ditches are common (fig. 40). 

Where successful in areas of well-drained sandy soils and 

a thick (up to 30 m) surficial aquifer, artificial drainage has 

lowered the water table in support of agriculture, which covers 

about 41 percent of the Nanticoke River watershed (fig. 44), 

and includes intensive poultry production. Forest and wetlands 

cover much of the remainder of the watershed, particularly in 

the eastern headwaters where drainage has been less successful. Agriculture contributes 85 percent of the nitrogen load 

and 92 percent of the phosphorus load from the watershed to 

Chesapeake Bay (fig. 41). In agricultural areas, nitrate concentrations in groundwater commonly exceed 10 mg/L (Clune 

and Denver, 2012) and concentrations in headwater streams 

and ditches are similarly elevated (Andres and others, 2007; 

Clune and Denver, 2012). Nitrate concentrations in forested 

areas rarely exceed 1 mg/L. Average yields of nitrogen and 

phosphorus are greatest in the central part of the watershed 

where agriculture is concentrated, and relatively low in the 

poorly drained forested headwaters and in riparian wetlands 

near major stream channels (fig. 44). In the main stem of the 

Nanticoke River, nitrate concentrations range from around 3 

to 5 mg/L and phosphorus concentrations range from less than 

0.1 during base flow to about 0.5 mg/L during storms (Andres 

and others, 2007). As in the Choptank River, nitrate concentrations in the Nanticoke River have increased consistently since 

the 1960s due to increases in nitrate in discharging groundwater (Robert Hirsch, USGS, written commun., 2013). 

Although nutrient applications in the Nanticoke River 

watershed (particularly manure) are greater, on average, than 

in the Chester, Choptank, or Pocomoke River watersheds, 

transport to streams is generally less efficient, especially for 

phosphorus (fig. 41). The generally flat landscape, extremely 

permeable soils beneath agricultural areas, and forested riparian zones along most of the Nanticoke River likely limit runoff 

and associated phosphorus transport in many parts of the 

watershed. Potential reduction of nitrate transport in riparian 

areas, however, is limited by channelization, that has disconnected much of the stream network from riparian wetlands and 

the thick surficial aquifer, which allows much of the nitrate in 

groundwater to bypass the riparian zone and discharge directly 

through sandy streambed sediments (see sidebar: “Nitrate 

Removal Through Denitrification, and Limitations Caused by 

Local Hydrogeology”) (fig. 30-3) (Clune and Denver, 2012). 

The Nanticoke River watershed is larger with greater overall 

inputs than the other major watersheds (fig. 41), and a greater 

reduction in nitrogen (940 metric tons) and phosphorus 

(48 metric tons) is required to meet the Chesapeake Bay 

TMDL (fig. 13). 

Poultry farming in the Nanticoke River watershed.

Photograph by Jane Thomas, Integration and Application 

Network, University of Maryland Center for Environmental 

Science (ian.umces.edu/imagelibrary/).
Chapter 4. Nitrogen and Phosphorus in Groundwater and Surface Waters of the Eastern Shore 53

!

Seaford

NANTICOKE

RIVER

WATERSHED

NANTICOKE

RIVER

WATERSHED

NITROGEN PHOSPHORUS

Estimated nutrient yields

from Ator and others, 2011

Estimated nutrient yields

from Ator and others, 2011

Land cover from LaMotte, 2008a, b

NANTICOKE

RIVER

WATERSHED

Nanticoke

River

NANTICOKE

RIVER

WATERSHED

Salisbury

Land cover

EXPLANATION

Estimated annual yield to local streams,

in kilograms per hectare

(pounds per acre)

LE 2 (1.8)

GT 2 and LE 3 (2.7)

GT 3 and LE 4 (3.6)

GT 4 and LE 5 (4.4)

GT 5 and LE 7 (6.2)

GT 7 and LE 10 (8.8)

GT 10 and LE 14 (12)

GT 14 and LE 17 (15)

GT 17 and LE 22 (20)

GT22

LE 0.05 (0.04)

GT 0.05 and LE 0.1 (0.09)

GT 0.1 and LE 0.2 (0.18)

GT 0.2 and LE 0.3 (0.27)

GT 0.3 and LE 0.5 (0.44)

GT 0.5 and LE 0.8 (0.71)

GT 0.8 and LE 1 (0.88)

GT 1 and LE 1.5 (1.3)

GT 1.5 and LE 2 (1.8)

GT 2

NITROGEN PHOSPHORUS

Agriculture

Urban

Forest

Wetland

Open water

Nutrient point

source

Federalsburg 13

50

13

13

50

50

404

404

13

Figure 44. The Nanticoke River watershed. The watershed is the largest of the major watersheds on the Eastern Shore, covering 

about 2,120 square kilometers. Nutrient yields to streams are generally greatest in the central part of the watershed where 

agriculture is concentrated. (GT = greater than; LE = less than or equal to.)

Chapter 4
54 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Pocomoke River Watershed

Water quality in the Pocomoke River watershed reflects 

particularly poor natural drainage and complex natural and 

human-impacted groundwater hydrology in the upstream 

watershed. Unlike the other major watersheds on the Eastern 

Shore, the Pocomoke River watershed is extremely flat, 

low-lying, and poorly drained with large tracts of forested 

wetlands (fig. 45). Soils in many areas are sandy, however, 

and have been effectively drained to support crop production 

with nearly 2,000 km of artificial ditching (Bricker and others, 

2003). The Pocomoke River channel and its major tributaries 

also have been straightened and channelized, although extensive riparian wetlands remain (fig. 40). Poultry production 

is widespread in agricultural areas and manure applications 

constitute most of the nitrogen and phosphorus inputs to the 

landscape (fig. 41). Agriculture contributes more than 80 

percent of the nitrogen and 90 percent of the phosphorus load 

from the watershed to Chesapeake Bay (fig. 41).

Water quality in the Pocomoke River watershed reflects 

a complex shallow groundwater-flow system (see sidebar: 

“Nitrate Removal Through Denitrification, and Limitations 

Caused by Local Hydrogeology”) (fig. 30-4). Nitrate is lost 

over time to denitrification in groundwater in a thin (generally 

3- to 6-m thick) shallow surficial aquifer, but has been 

measured at concentrations as high as 60 mg/L (Phillips and 

Donnelly, 2003). Nitrate is generally undetectable, however, 

in an underlying anoxic aquifer (Ator, Denver, and Brayton, 

2005; Denver and others, 2010). When the water table is high, 

short flow paths to drainage ditches in the shallow aquifer 

contribute an important source of flow and relatively rapid 

transport of nitrate to local surface waters (Ator, Denver, 

and Brayton, 2005; McCoy, Sigrist, and others, 2010). When 

ditches are dry or stagnant during drier periods, however, 

longer flow paths in the deeper aquifer maintain base flow in 

streams. Concentrations of nitrate as high as 15 mg/L have 

been measured in headwaters ditches and decrease downstream as more denitrified water from the surficial aquifer 

and deeper water from the underlying aquifer discharges to 

streams. Concentrations of nitrate in the main stem of the 

Pocomoke River range from less than 1 mg/L to about 5 mg/L 

with a median of about 2 mg/L (Ator, Denver, and Brayton, 

2005). 

Concentrations of total phosphorus in the Pocomoke 

River are generally below 0.2 mg/L during base flow but 

increase to over 1 mg/L during stormflow. Phosphorus 

attached to soil particles is mobilized by bank erosion in the 

field ditches or suspended bed load in streams (Ator, Denver, 

and Brayton, 2005). Soil-bound phosphorus from excessive 

historical applications represents a continuing source of phosphorus to surface waters and therefore greatly complicates 

management efforts to restore water quality (McCoy, Sigrist, 

and others, 2010). Another potential source of phosphorus in 

the Pocomoke River system is groundwater discharge from the 

deeper anoxic aquifer where concentrations of dissolved phosphorus greater than 0.6 mg/L have been measured (Shedlock 

and others, 1999). This phosphorus is bound to iron particles 

that form in the flood plains and can dissolve in anoxic conditions (Bricker and others, 2003).

In spite of relatively high rates of applied nitrogen and 

phosphorus in the Pocomoke River watershed, average yields 

to the bay are generally lower than from other major watersheds (fig. 41). The required nitrogen and phosphorus load 

reductions as part of the Chesapeake Bay TMDL are smaller 

than in the Chester, Choptank, Nanticoke, or Virginia Coastal 

watersheds, at about 63 metric tons and 8 metric tons per year, 

respectively (fig. 13).

Pocomoke River. Photograph by Ben Fertig, Integration and 

Application Network, University of Maryland Center for 

Environmental Science (ian.umces.edu/imagelibrary/).
Chapter 4. Nitrogen and Phosphorus in Groundwater and Surface Waters of the Eastern Shore 55

Figure 45. The Pocomoke River watershed. The watershed covers about 1,225 square kilometers and land use is predominantly 

forested with wetlands. Nutrient yields from the land surface to streams are generally lower than in other major watersheds, 

particularly where agriculture is interspersed with poorly drained soils and wetlands. (GT = greater than; LE = less than or equal to.)

Land cover

EXPLANATION

Estimated annual yield to local streams,

in kilograms per hectare

(pounds per acre)

LE 2 (1.8)

GT 2 and LE 3 (2.7)

GT 3 and LE 4 (3.6)

GT 4 and LE 5 (4.4)

GT 5 and LE 7 (6.2)

GT 7 and LE 10 (8.8)

GT 10 and LE 14 (12)

GT 14 and LE 17 (15)

GT 17 and LE 22 (20)

GT 22

LE 0.05 (0.04)

GT 0.05 and LE 0.1 (0.09)

GT 0.1 and LE 0.2 (0.18)

GT 0.2 and LE 0.3 (0.27)

GT 0.3 and LE 0.5 (0.44)

GT 0.5 and LE 0.8 (0.71)

GT 0.8 and LE 1 (0.88)

GT 1 and LE 1.5 (1.3)

GT 1.5 and LE 2 (1.8)

GT 2

NITROGEN PHOSPHORUS

Agriculture

Urban

Forest

Wetland

Open water

Nutrient point

source

1

Snow Hill

Pocomoke

City

Salisbury

Chincoteague

NITROGEN PHOSPHORUS

Estimated nutrient yields

from Ator and others, 2011

Estimated nutrient yields

from Ator and others, 2011

Pocomoke

River

Chincoteague Bay

Chincoteague BayChincoteague Bay

Land cover from LaMotte, 2008a, b

POCOMOKE

RIVER

WATERSHED

POCOMOKE

RIVER

WATERSHED

POCOMOKE

RIVER

WATERSHED

Berlin

13

113

113

12

90

50

13

113

Chapter 4
56 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Virginia Coastal Watersheds

The Delmarva Peninsula in Virginia is a narrow spit of 

land that runs generally from north to south (fig. 46), and 

streams in the Virginia Coastal watersheds on the Eastern 

Shore flow generally to the west over relatively short distances 

from a well-drained upland near the watershed divide in the 

east to tidal waters of Chesapeake Bay in the west. The average land-surface elevation is only about 5 m (fig. 17). Coastal 

lowlands along Chesapeake Bay are generally poorly drained 

with forests and wetlands in the north but include excessively well-drained sandier soils in the south (figs. 19, 20). 

Agriculture (including the production of corn, soybeans, small 

grains, poultry, and vegetables) and rural residential development is therefore confined to uplands near the drainage divide 

in the north, but extend from the drainage divide to the shore 

of the bay, often with no fringing wetlands, in the south (fig. 

46). Variable drainage conditions and the resulting land use 

are reflected in in-stream nitrogen yields that are generally 

greater in the south than in the north; phosphorus yields are 

greatest in agricultural areas near the drainage divide (fig. 46). 

Agricultural sources provide 79 percent of the nitrogen load 

and 81 percent of the phosphorus load from the watersheds 

to Chesapeake Bay (fig. 41). A reduction of 270 metric tons 

of nitrogen and 10 metric tons of phosphorus, annually, will 

be required from the Virginia Coastal watersheds to meet the 

TMDL for Chesapeake Bay; unlike in other major watersheds, 

the majority of nitrogen reduction from this area will be 

required from wastewater treatment or combined sewer overflows (fig. 13). 

Nitrate concentrations in streams and groundwater of 

the Virginia Coastal watersheds reflect variable land use and 

hydrogeologic conditions, as in other areas of the Eastern 

Shore. Concentrations in groundwater beneath agricultural 

fields commonly exceed 10 mg/L where sandy soils and dissolved oxygen are abundant, but are less than 1 mg/L in areas 

with fine-grained organic-rich soils where dissolved oxygen 

is lacking (Speiran, 1996) (see sidebar: “Nitrate Removal 

Through Denitrification, and Limitations Caused by Local 

Hydrogeology”). Groundwater discharge carries nitrate 

directly to tidal waters through coarse-textured sediments, 

even beneath forested buffers with fine-textured sediments 

along the shoreline. In areas with fine-textured sediments, 

however, nitrate in groundwater is generally removed through 

denitrification prior to discharge (Speiran, 1996). On average, 

nearly one-quarter (23 percent) of nitrogen applied to upland 

landscapes in the Virginia Coastal watersheds is carried in 

streamflow to Chesapeake Bay; nitrogen transport from this 

area is generally more efficient than from other major watersheds (fig. 41), possibly because relatively short transport 

distances from upland source areas to tidal waters (particularly 

in the south) limit opportunities for nitrogen loss or sequestration in uplands. Phosphorus delivery from upland source 

areas in the Virginia Coastal watersheds to Chesapeake Bay is 

similar to other parts of the Eastern Shore with similarly flat 

landscapes, such as the adjacent Pocomoke River watershed 

(fig. 45). 

The Eastern Shore of Virginia. Photograph by Ben Fertig, 

Integration and Application Network, University of Maryland 

Center for Environmental Science (ian.umces.edu/

imagelibrary/).
Chapter 4. Nitrogen and Phosphorus in Groundwater and Surface Waters of the Eastern Shore 57

Land cover

EXPLANATION

Estimated annual yield to local streams,

in kilograms per hectare

(pounds per acre)

LE 2 (1.8)

GT 2 and LE 3 (2.7)

GT 3 and LE 4 (3.6)

GT 4 and LE 5 (4.4)

GT 5 and LE 7 (6.2)

GT 7 and LE 10 (8.8)

GT 10 and LE 14 (12)

GT 14 and LE 17 (15)

GT 17 and LE 22 (20)

GT 22

LE 0.05 (0.04)

GT 0.05 and LE 0.1 (0.09)

GT 0.1 and LE 0.2 (0.18)

GT 0.2 and LE 0.3 (0.27)

GT 0.3 and LE 0.5 (0.44)

GT 0.5 and LE 0.8 (0.71)

GT 0.8 and LE 1 (0.88)

GT 1 and LE 1.5 (1.3)

GT 1.5 and LE 2 (1.8)

GT 2

NITROGEN PHOSPHORUS VIRGINIA COASTAL WATERSHEDS

VIRGINIA COASTAL WATERSHEDS

NITROGEN PHOSPHORUS

Estimated nutrient yields

from Ator and others, 2011

Estimated nutrient yields

from Ator and others, 2011

Land cover from LaMotte, 2008a, b

Chesapeake Bay

Chesapeake Bay

ATLANTIC OCEAN

ATLANTIC OCEAN

ATLANTIC OCEAN

Chesapeake Bay

Chesapeake

Bay

watershed

boundary

Chesapeake

Bay

watershed

boundary

Chesapeake

Bay

watershed

boundary

VIRGINIA COASTAL WATERSHEDS

VIRGINIA COASTAL WATERSHEDS

Agriculture

Urban

Forest

Wetland

Open water

13

Figure 46. The Virginia Coastal watersheds. These watersheds are generally small, and streams and groundwater flow over 

relatively short distances before discharging to tidal waters. Average nitrogen yields from the watersheds vary from north 

to south with similar changes in land use and drainage characteristics; phosphorus yields are generally highest near the 

watershed divide in the east. (GT = greater than; LE = less than or equal to.)

Chapter 4
58 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Mouth of the Corsica River flowing into the Chester River, Eastern Shore of Maryland. 

Photograph by Ben Longstaff, Integration and Application Network, University of Maryland 

Center for Environmental Science (ian.umces.edu/imagelibrary/).

Wye River near Bryantown, Maryland. Photograph by Jane Thomas, Integration and 

Application Network, University of Maryland Center for Environmental Science (ian.umces.

edu/imagelibrary/).
Chapter 5. Understanding Nitrogen in Support of Water Resource Management on the Eastern Shore 59

Chapter 5. Understanding Nitrogen 

in Support of Water Resource 

Management on the Eastern Shore

Why are nitrogen concentrations elevated in Eastern 

Shore groundwater and streams, and why are they continuing to increase? What management practices might reduce 

nitrogen concentrations and how much time will this take?

Natural hydrogeologic and geochemical conditions promote the formation and movement of nitrate from the abundant 

(primarily agricultural) nitrogen sources on the Eastern Shore 

to groundwater, streams, and estuaries. Increasing nitrate 

concentrations over time largely reflect increasing nitrogen 

applications in previous decades. Limiting the movement of 

nitrate to the water table could reduce concentrations very 

quickly in shallow groundwater, although many years or 

decades would be required before significant reductions occur 

in deeper groundwater or receiving surface waters.

Why are nitrogen concentrations elevated in 

Eastern Shore groundwater and streams?

Widespread and abundant nitrogen sources and natural 

soil and aquifer conditions conducive to the transport and stability of nitrate in the environment are responsible for elevated 

nitrate concentrations in groundwater and surface waters on 

the Eastern Shore. The application of manure and fertilizers 

to agricultural areas is the predominant source of nitrogen 

to the landscape on the Eastern Shore (see Chapter 3), and 

agriculture occurs widely throughout the area (see Chapter 2). 

The average intensity of nitrogen applications to the landscape 

on the Eastern Shore is consequently much higher than in the 

remainder of the Chesapeake Bay watershed (fig. 11). Some 

of the nitrogen that is applied, but not used, by crops or other 

plants moves directly over the land surface to streams with 

storm runoff, but the majority is converted to nitrate in the 

soil and moves through the ground with infiltrating precipitation to groundwater (Ator and Denver, 2012). Natural soil and 

aquifer conditions in much of the Eastern Shore (particularly 

in the areas most suitable for agriculture) ensure that nitrate is 

generally stable for long periods and is not typically lost to the 

atmosphere through denitrification or to other environmental 

processes. Also, nitrate is very soluble and moves easily with 

groundwater to withdrawal wells or to discharge areas in surface waters (see Chapter 3). As a result, nitrate concentrations 

in streams and groundwater on the Eastern Shore are among 

the highest in the Chesapeake Bay watershed (figs. 9, 12) and 

the entire United States (figs. 32, 33).

Why are nitrogen concentrations in streams and 

groundwater on the Eastern Shore increasing?

Increasing nitrogen concentrations in groundwater and 

streams on the Eastern Shore reflect increasing nitrogen applications in previous decades. Nitrate concentrations in groundwater in parts of the surficial aquifer on the Eastern Shore 

have increased in recent decades (fig. 34), in spite of relatively 

constant nitrogen applications during the same period (fig. 25) 

(Debrewer and others, 2007, 2008). Nitrogen concentrations in 

selected streams on the Eastern Shore have similarly increased 

recently (fig. 39), primarily due to increasing nitrate in contributing groundwater (Hirsch and others, 2010). Because 

most nitrogen movement to streams on the Eastern Shore 

occurs in the form of nitrate through groundwater (fig. 27) 

(Ator and Denver, 2012), and groundwater flow is very slow 

(fig. 23) (Dunkle and others, 1993; Sanford and others, 2012), 

several years or decades are often required before the effects 

of changes in nitrogen application rates, land-management, or 

other practices are fully reflected in streams and groundwater 

chemistry. Increasing nitrate in groundwater on the Eastern 

Shore between 1988 and 2001 was the result of increasing 

nitrogen applications through the 1970s (fig. 25) (Debrewer 

and others, 2007, 2008). 

Comprehensive information about land management 

could support a more thorough understanding of changes over 

time in nitrogen concentrations in groundwater and streams 

on the Eastern Shore. Certain land-management practices may 

substantially reduce nitrogen movement from upland source 

areas to groundwater and streams and have been increasingly 

used on the Eastern Shore in recent years for that purpose 

(see following sections). Changes over time in water quality 

are often gradual, however, and can be difficult to detect and 

(especially) to explain. Although available regional summaries 

of management practices over counties or large watersheds 

can be useful for comparison to similarly broad spatial patterns in water quality, more detailed information about the 

nature, extent, and location of such practices would support 

a more thorough understanding of their importance to waterquality trends.

Most nitrogen moves from landscape application areas to Eastern 

Shore streams through groundwater very slowly over a period 

of multiple years or decades. Consequently, changes over time 

that are observed in Eastern Shore streams reflect increasing or 

relatively high nitrogen applications in past decades.

Chapter 5
60 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

What management practices might be most 

effective at reducing nitrogen concentrations?

Managing agriculture and other human activities on the 

landscape to limit the movement of nitrogen from source areas 

to surface waters typically involves limiting nitrogen applications and (or) modifications to increase the effectiveness of 

natural nitrogen removal. Management practices designed to 

limit runoff and soil losses (such as riparian buffers, contour 

tillage, or manure or fertilizer injection) also may be effective 

at limiting the movement of nitrogen in particulate form from 

the land surface to surface waters (Staver and Brinsfield, 

2010a). Nitrogen, however, moves from the landscape to 

streams on the Eastern Shore primarily through groundwater 

in the form of nitrate (Ator and Denver, 2012). Such practices 

may limit nitrate transport through groundwater in certain 

hydrogeologic settings (Böhlke and Denver, 1995; Lowrance 

and others, 1997; Puckett, 2004; Puckett and others, 2008), 

but may be relatively ineffective for reducing nitrogen transport in other areas and may actually promote the movement 

of nitrogen retained on fields to groundwater. Winter cover 

crops can sequester excess soil nitrogen in vegetation and 

thereby limit losses to groundwater (Staver and Brinsfield, 

1998; Hively and others, 2009; McCoy, Spotts, and others, 

2010; Staver and Brinsfield, 2010a, b) (fig. 47). When not 

needed, limiting manure applications on fields for crops may 

limit nutrient losses over the land surface and to groundwater 

(Staver and Brinsfield, 2001); the State of Delaware plans to 

prohibit winter manure applications and relocate manure to 

nutrient poor areas as part of efforts to limit nutrient losses to 

the bay (Kleinman and others, 2012). Wetland restoration and 

controlled-drainage structures have been used to retain water 

on the landscape and increase the likelihood of nitrogen losses 

through denitrification (Sadeghi and others, 2008).

Various conditions and processes limit the effectiveness 

of management practices for reducing nitrogen transport from 

the land surface to surface waters. Nitrate may be reduced to 

nitrogen gas in anoxic riparian areas, but often passes beneath 

riparian zones to discharge areas in streams (Böhlke and 

Denver, 1995; Denver and others, 2010). Variable hydrogeologic conditions on the Eastern Shore contribute to variable 

nutrient retention in riparian buffers; nitrate losses may be 

substantial where a thin surficial aquifer restricts groundwater 

to shallow flow paths, but minimal where a thicker surficial 

aquifer permits deeper groundwater flow (Lowrance and 

others, 1997; Ator, Denver, Krantz, and others, 2005). 

Restoration of streamside buffer areas to grass or forest in 

the Choptank River watershed failed to decrease base-flow 

nitrogen concentrations in streams between 1986 and 2006, 

although this may be attributable to coincident increasing 

nitrogen applications or to insufficient buffer width, age, or 

extent (Sutton and others, 2010). Nitrogen losses in riparian 

zones also depend upon the types and amounts of available 

carbon, such as from leaf litter and other plants (McCarty and 

others, 2007). The effectiveness of cover crops at reducing 

nitrogen losses to groundwater varies with the species of cover 

crop and previous crop, the method and date of planting, soil 

types, and precipitation (Ritter and others, 1998; Hively and 

others, 2009; Staver and Brinsfield, 2010a). Nitrogen removal 

in artificial ditches varies with ditch management, including 

ponding to retain water on the landscape during certain 

periods and dredging frequency (Sadeghi and others, 2008; 

Shigaki and others, 2009). 

With any management technique that is used, significant 

differences between nitrogen and phosphorus requirements 

for plant growth, content in animal manure commonly applied 

to cropland on the Eastern Shore, and chemical and physical 

properties controlling environmental fate and transport, 

substantially complicate the design of 

management practices that would be 

effective for both nutrients (Staver and 

Brinsfield, 2001). Removal of manure 

and the use of chemical fertilizers to 

customize applications to crop needs 

can substantially reduce nutrient applications to crops in excess of plant needs 

(McCoy, Sigrist, and others, 2010). 

Nitrate concentration,

in milligrams per liter as N 30

20

10

0

1986 1988 1990

Year

[Data from K. Staver, University of Maryland, written commun., January 30, 2014.

Modified from Staver and Brinsfield, 1998 and Staver and Brinsfield, 2010a.]

1992 1994 1996 1998

No winter

cover crops

Use of rye winter

cover crops

Conventional till

No till Figure 47. Changes in nitrate 

concentrations over time in groundwater 

beneath adjacent fields after the 

initiation of winter cover crops in 1988. 

Groundwater nitrate concentrations 

decreased after use of cover crops began.

Local hydrologic and geologic conditions specific to different 

areas substantially affect the movement of nitrogen from uplands 

to streams, and therefore, the effectiveness of management 

practices intended to limit nitrogen in streams.
Chapter 5. Understanding Nitrogen in Support of Water Resource Management on the Eastern Shore 61

more quickly, although larger streams that receive water from 

longer flow paths may require much more time.

Decades will likely be required before the effects of management practices at the land surface are reflected in decreasing nitrogen contributed to the Chesapeake Bay from streams 

on the Delmarva Peninsula. Nutrient management practices 

have reduced nitrogen losses from the land surface to streams 

since the 1970s (Sanford and Pope, 2013), and the use of 

cover crops that may specifically limit nitrogen movement to 

the water table has increased on the peninsula in recent years 

(fig. 48). Because groundwater flow is very slow, however, 

much of the nitrogen from previous decades remains in the 

groundwater system and will continue to discharge to streams 

in future years. For this reason, even stable fertilizer and 

manure applications at average 2007–12 levels will result in 

continuously increasing nitrogen in streams in future decades, 

and an estimated 13-percent reduction in such applications 

would be required simply to maintain in-stream nitrogen 

at current levels (fig. 49). Even a 40-percent reduction of 

nitrogen at the water table would be insufficient to reduce 

annual nitrogen loads from the peninsula to Chesapeake Bay 

to an estimated 5,000 metric tons, the U.S. Environmental 

Protection Agency (EPA) target for bay restoration, within the 

next 35 years (fig. 49). If nitrogen movement to the water table 

were to stop completely, the restoration goal would likely be 

met by 2020, but as much as 2,500 metric tons of nitrogen 

would continue to discharge annually from groundwater to 

Delmarva streams through at least 2050 (fig. 49) (Sanford and 

Pope, 2013).

How long will it take to see water-quality 

improvement and, in the meanwhile, how will 

we know if land-management or restoration 

practices are working?

Significant time periods often pass before management 

practices produce the desired effects on local waters, these 

effects are propagated downstream, and receiving waters 

respond to these effects (Meals and others, 2010). The effects 

of landscape management practices designed to reduce 

nitrogen pollution in Eastern Shore streams will require 

years to become fully realized in surface waters, but would 

likely become apparent more quickly in shallow groundwater 

beneath nitrogen application areas. If precision applications, 

cover crops, or other management practices are effective in 

reducing nitrogen leaching from the land surface to the water 

table, such reductions should be evident very quickly with 

reduced nitrate concentrations in shallow groundwater and 

water of the overlying unsaturated zone (fig. 47). If these 

reductions are sustained over time, lower nitrate concentrations will continue to move slowly along groundwater flow 

paths as water from previous years with higher nitrate concentrations moves out of the system to streams. Eventually, nitrate 

concentrations in streams will begin to decrease with increasing discharge of groundwater with reduced nitrate concentrations. In general, small streams receive water from primarily 

shorter groundwater flow paths and will therefore improve 

Chapter 5

Decades will be required before nitrogen currently in Eastern 

Shore groundwater moves through to local streams and the 

effects of any current land-management practices on surfacewater quality are fully realized.
62 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore Nitrogen load to the bay, in thousands of metric tons per year

8

7

6

5

4

3

2

1

0

1980 1990 2000

YEAR

2010 2020 2030 2040 2050

[From Sanford and Pope, 2013.]

EXPLANATION

Predicted future loads from

streams to Chesapeake Bay

0-percent

Reduction of

nitrogen load

to groundwater

13-percent

40-percent

100-percent

The approximate 25-percent

reduction Total Maximum Daily Load

(TMDL) target proposed for the region

by the U.S. Environmental Protection Agency

in conjunction with local states

Figure 49. Forecasted nitrogen delivery from the Eastern Shore to Chesapeake 

Bay under selected potential management scenarios. Even if loads of nitrogen 

to groundwater on the Eastern Shore are substantially reduced in future years, 

groundwater will continue to discharge nitrate from applications in previous years to 

Chesapeake Bay tributaries. Cover crops, in thousands of hectares (thousands of acres)

150

100

50

0

1980

Year

[Data from M. Johnston, Chesapeake Bay Program,

written commun., March 14, 2013.]

1990 2000 2010 2020

400

300

200

100

0

Figure 48. Use of cover crops on the Delmarva Peninsula, 1985–2011. Use of cover 

crops has increased substantially in recent years.
Chapter 6. Understanding Phosphorus in Support of Water Resource Management on the Eastern Shore 63

Chapter 6. Understanding Phosphorus 

in Support of Water Resource 

Management on the Eastern Shore

Why are phosphorus concentrations elevated in 

sediment and water resources on the Eastern Shore and 

(in some areas) increasing? What can be done to reduce 

phosphorus concentrations in the environment and how long 

might that take?

Applications of phosphorus (in livestock manure and 

fertilizer) to Eastern Shore farmland in recent decades have far 

exceeded the amounts necessary for crop growth, and phosphorus has consequently increased in the environment. Unlike 

nitrate, phosphorus is relatively insoluble in water under most 

natural conditions, and excess phosphorus in the environment 

generally accumulates in agricultural soils rather than moving 

into groundwater.

 Why are phosphorus concentrations elevated in 

many agricultural soils on the Eastern Shore?

Phosphorus has accumulated in agricultural soils in 

parts of the Eastern Shore at levels far in excess of agricultural needs (Staver and Brinsfield, 2001; Leytem and others, 

2003). Although phosphorus applications in fertilizer have 

decreased in recent decades (fig. 25), farming practices on the 

Eastern Shore since the latter half of the 20th century have 

generally involved importing phosphorus in fertilizer and (or) 

applying phosphorus in manure in greater amounts than what 

is removed in agricultural products (fig. 26). Nutrient management plans for crops often involve limiting the transport of 

nutrients to water resources by limiting application to crop 

uptake requirements (Staver and Brinsfield, 2001). Livestock 

(primarily chickens) on the Eastern Shore produce more than 

8 million kg of phosphorus in manure annually (Wieczorek 

and LaMotte, 2010c), most of which is spread on croplands. 

The crop needs for nitrogen and phosphorus generally differ 

from their relative content in poultry manure, however, and 

applying manure sufficient to meet crop nitrogen needs 

often results in a threefold or fourfold over-application 

of phosphorus (Staver and Brinsfield, 2001). Phosphorus 

application in fertilizer (fig. 25) and excess over crop needs 

(fig. 26) have decreased since the latter half of the 20th 

century; however, applications of phosphorus in fertilizer and 

manure to cropland on the Eastern Shore in Maryland and 

Delaware in 2007 remained approximately 5 and 10 kilograms 

per hectare (respectively) greater than crop needs (fig. 26) 

(Mid-Atlantic Water Program, 2012). Because phosphorus 

compounds are relatively insoluble in water, applied phosphorus in excess of crop needs generally attaches to and accumulates in soils rather than moving to groundwater. 

Why is phosphorus moving into streams and 

groundwater on the Eastern Shore?

Continuing accumulation of excess phosphorus in Eastern 

Shore soils likely promotes the movement of phosphorus 

into local streams and groundwater. Phosphorus concentrations in groundwater on the Eastern Shore are typically below 

0.1 mg/L, but may be higher in areas with anoxic conditions 

where phosphorus is more soluble (Denver and others, 2004; 

Debrewer and others, 2007). Phosphorus concentrations in 

streams during base flow are similarly generally below 0.1 

mg/L, but are often as high as 3 or 4 mg/L during storms 

(Denver and others, 2004; Ator, Denver, and Brayton, 2005). 

Mean annual phosphorus concentrations in the Pocomoke 

River are among the highest in the Nation (Denver and others, 

2004). Phosphorus is much less soluble than nitrate and typically attaches to solid particles such as soil or sediment grains 

rather than dissolve in water. Soils can only hold a limited 

amount of phosphorus, however, and as phosphorus accumulates at higher and higher concentrations, newly applied 

phosphorus becomes less likely to attach to the soils and more 

likely to move into groundwater (Staver and Brinsfield, 2001; 

Maguire and Sims, 2002; Leytem and Sims, 2005; Domagalski 

and Johnson, 2011). Also, erosion during and following storm 

events often carries soil, sediment, and attached phosphorus 

directly to streams in overland runoff. Phosphorus transport 

from source areas on the land surface to streams is more 

efficient in the Coastal Plain (particularly the Eastern Shore) 

than in other areas of the Chesapeake Bay watershed, possibly 

because of historically excessive phosphorus applications to 

cropland and resulting greater movement to groundwater or in 

overland runoff (Ator and others, 2011).

Phosphorus compounds are relatively insoluble and tend 

to accumulate in particulate matter (such as soils) in areas 

of application. Phosphorus applications in excess of crop 

requirements over a number of years have resulted in elevated 

phosphorus levels in certain cropland soils.

Increasing phosphorus accumulation in Eastern Shore soils 

may make newly applied phosphorus more likely to move into 

groundwater and streams.

Chapter 6
64 Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore

Why is phosphorus continuing to increase in the 

Choptank River in recent years?

In the Choptank River, the largest nontidal Chesapeake 

Bay tributary on the Eastern Shore, phosphorus concentrations 

increased significantly between 1985 and 2008, coincident 

with a significant decrease in suspended-sediment concentrations (Moyer and others, 2012). Because phosphorus movement into and through surface waters generally occurs in solid 

form attached to soils and other sediment particles, trends in 

phosphorus concentrations often mimic those in suspended 

sediment. Increasing phosphorus in the river in recent decades 

in spite of decreasing sediment concentrations suggests that 

individual sediment grains in the river carry (on average) 

greater particulate phosphorus than in the past, and (or) 

that phosphorus transport to the river in the dissolved phase 

may be increasing. Although the particular reason for recent 

phosphorus trends in the river remains unclear, either or both 

of these conditions could be a result of increasing phosphorus 

saturation in cropland soils in the Choptank River watershed. 

As with nitrogen (see Chapter 5), more detailed information 

about the nature and location of land-management practices 

intended to limit the movement of phosphorus from agricultural areas to water resources could support a more thorough 

evaluation of changes over time in phosphorus concentrations 

in Eastern Shore streams.

What management practices may be most 

effective at limiting phosphorus movement to 

Eastern Shore streams and groundwater?

Land-management practices designed to limit the movement of phosphorus from upland application areas to surface 

waters often involve limiting soil erosion. Phosphorus compounds are relatively insoluble and typically remain bound 

to soil particles when applied in excess of crop or other plant 

needs. Riparian buffers, contour tillage, conservation tillage, 

and other land-management practices designed to minimize 

soil erosion are therefore often similarly effective at limiting 

phosphorus transport (Staver and Brinsfield, 2001). The 

effectiveness of these practices typically varies significantly 

among different sites and conditions (Sharpley and others, 

2002; Sutton and others, 2010), however, and may be limited 

in flat areas such as the Eastern Shore, where erosion is 

unlikely (Staver and Brinsfield, 2010a). Phosphorus has been 

applied to Eastern Shore crops at rates much higher than crop 

requirements since at least the 1930s (fig. 26), however, and 

Eastern Shore soils may have a reduced capacity to absorb 

additional phosphorus (Ator and others, 2011). In addition, 

phosphorus retention at the land surface resulting from practices such as conservation tillage may increase the transport 

of phosphorus in dissolved form (Staver and Brinsfield, 2001; 

Sharpley and others, 2002). Phosphorus transport increased 

following no-till practices on one farm in the Wye River 

watershed in the 1990s because reduced transport of particulate phosphorus was more than offset by increased transport 

of dissolved phosphorus (Staver and Brinsfield, 2010a). 

Reducing the reservoir of phosphorus in cropland soils may 

be effective at reducing phosphorus concentrations in Eastern 

Shore streams and groundwater. Removing phosphorus from 

the soil can be accomplished by nutrient management practices to ensure that new applications of phosphorus are smaller 

than phosphorus removal at harvest (Jarvie and others, 2013). 

How long will it take to see water-quality 

improvement and, in the meanwhile, how will 

we know if land-management and restoration 

practices are working?

Several years or decades may be required before effects 

of land-management practices are fully realized in surfacewater phosphorus concentrations on the Eastern Shore. 

Reducing phosphorus applications below crop requirements 

should reduce phosphorus levels in cropland soils, although 

such reductions will occur slowly in areas where excessive 

soil phosphorus from previous applications greatly exceeded 

the annual uptake requirements of crops (McCollum, 1991). 

Riparian buffers, conservation tillage, and other land-management practices intended to limit erosion or sediment transport 

should be similarly effective at limiting the movement of sediment-associated phosphorus to streams (Staver and Brinsfield, 

2001). Such practices may increase the storage of phosphorus 

in upland landscapes, however, which may require years or 

decades to move to stream channels (Jarvie and others, 2013). 

Once sediment and associated phosphorus reaches streams, 

delivery to downstream tidal waters may be similarly delayed 

as sediment is deposited within stream channels and transported only intermittently during high-flow periods (Jarvie and 

others, 2013). Due to the relatively minor role of groundwater 

in phosphorus transport, long time periods typically required 

for groundwater flow should be minimally important to phosphorus changes over time in streams. 
References Cited 65

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Prepared by USGS West Trenton Publishing Service Center.

Edited by Valerie M. Gaine.

Graphics and layout by Timothy W. Auer.

For additional information, contact:

Director, MD-DE-DC Water Science Center

U.S. Geological Survey

5522 Research Park Drive

Baltimore, MD 21228

or visit our Web site at:

http://md.water.usgs.gov
Ator, S.W., and Denver, J.M.—Understanding Nutrients in the Chesapeake Bay Watershed and Implications for Management and Restoration—the Eastern Shore—Circular 1406

ISSN 1067-084X (print)

ISSN 2330-5703 (online)

http://dx.doi.org/10.3133/cir1406 Printed on recycled paper