7 

Prepared in cooperation with the National Park Service and the Town of Bar Harbor, Maine

Changes in Nitrogen Loading to the Northeast Creek Estuary, 

Bar Harbor, Maine, 2000 to 2010

Open-File Report 2013–1256

U.S. Department of the Interior

U.S. Geological Survey
THIS PAGE INTENTIONALLY LEFT BLANK
Prepared in cooperation with the National Park Service and the Town of Bar Harbor, Maine

Changes in Nitrogen Loading to the Northeast Creek 

Estuary, Bar Harbor, Maine, 2000 to 2010

By Martha G. Nielsen

Open-File Report 2013–1256

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: 2013

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Suggested citation:

Nielsen, M.G., 2013, Changes in nitrogen loading to the Northeast Creek Estuary, Bar Harbor, Maine, 2000 to 2010: 

U.S. Geological Survey Open-File Report 2013–1256, 33 p., http://dx.doi.org/10.3133/ofr20131256.

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ISSN 2331-1258 (online)

ii
Contents

Acknowledgments ......................................................................................................................................................... vi

Abstract ......................................................................................................................................................................... 1

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

Northeast Creek Study Area ...................................................................................................................................... 2

Previous Investigations in the Northeast Creek Study Area....................................................................................... 4

Simulations Relating Loading Rates to Land Use .................................................................................................. 4

Application of Nutrient Export Simulation for Local Planning.................................................................................. 5

Purpose and Scope ................................................................................................................................................... 6

Field Study of Nitrogen Loading to Northeast Creek, 2010 Time Period ....................................................................... 7

Nitrogen Sampling and Streamflow Measurements, 2008–11 ................................................................................... 7

Water-Quality Sampling Procedures ...................................................................................................................... 7

Streamflow Measurements, 2008–11..................................................................................................................... 8

Nitrogen Constituent Concentrations in Northeast Creek Tributaries, 2008–11 ..................................................... 9

Fractions of Organic and Inorganic Nitrogen in Tributary Streams........................................................................11

Relations Between Constituent Concentrations and Streamflow...........................................................................13

Comparison of Total Nitrogen Concentrations in Northeast Creek Tributaries, 1999–2000 and 2008–11 ............15

Estimation of Nitrogen Loading to Northeast Creek, 2010 Time Period....................................................................16

Generation of Daily Mean Streamflow Values for Use in Load Estimation ............................................................16

Methods for Estimating Nitrogen Constituent Loads .............................................................................................17

Nitrogen Constituent Load Estimates for Northeast Creek Tributaries, 2010 Time Period....................................18

Northeast Creek Watershed Land-Use Change, 2000 to 2010, and Predicted Effect on Nitrogen Loading .................20

Decision Support System Predictions of Changes in Nitrogen Loading to Northeast Creek .....................................22

Changes in Estimated Total Nitrogen Loading to Northeast Creek, 2000 to 2010........................................................23

Changes in Total Nitrogen Loading Based on Sampling Data, 2000 to 2010 ...........................................................23

Factors Affecting Total Nitrogen Loads and Loading Rates ......................................................................................24

Changes in Nitrogen Load Predicted from Land-Use Data Compared to Estimated Changes Based on Field 

Studies in the Northeast Creek Watershed...................................................................................................................27

Summary and Conclusions...........................................................................................................................................28

References Cited..........................................................................................................................................................31

Figures

Figure 1. Map showing location of the Northeast Creek study area on Mount Desert Island, Bar Harbor, Maine........ 3

Figure 2. Hydrograph of daily mean streamflow at U.S. Geological Survey streamgage at Otter Creek, near Bar 

Harbor, Maine, May 2008 to September 2011, showing streamflow on days of sample collection for the 

Northeast Creek study...................................................................................................................................... 8

Figure 3. Boxplots summarizing distribution of nitrogen (N) constituent concentrations, Northeast Creek tributaries, 

2008–11...........................................................................................................................................................10

Figure 4. Graphs showing ratio of organic and inorganic nitrogen (N) to total N in samples from selected tributaries 

to Northeast Creek, Bar Harbor, Maine, 2008–11............................................................................................12

Figure 5. Graphs showing variation in total nitrogen concentration with stream discharge in tributaries to Northeast 

Creek, Bar Harbor, Maine, 2008–11................................................................................................................14

Figure 6. Bar graphs showing comparison of total nitrogen concentrations in samples from tributaries to Northeast 

Creek, Bar Harbor, Maine, 1999–2000 and 2008–11 (>, greater than). ..........................................................15

iii
Figure 7. Boxplot showing estimated average loading rates (yields) of total nitrogen (N) and nitrite+nitrate (N) for 

tributaries to Northeast Creek, Bar Harbor, Maine, with 95-percent confidence intervals, for the 2010 time 

period. (The 2010 time period includes samples from 2008–11.)....................................................................19

Figure 8. Map showing changes in land use in the Northeast Creek watershed from 2000 to 2010, Bar Harbor, 

Maine...............................................................................................................................................................21

Figure 9. Bar graph showing predicted annual loads of total nitrogen to Northeast Creek from selected tributaries 

for 2000 and 2010, from the decision-support system, determined from changes in land use, Bar Harbor, 

Maine...............................................................................................................................................................22

Figure 10. Boxplot showing estimated annual loads of total nitrogen from tributaries to Northeast Creek, 

determined from streamflow measurements and water-quality sampling, 2000 and 2010 time periods, Bar 

Harbor, Maine..................................................................................................................................................24

Figure 11. Hydrograph showing annual mean streamflow for period of record at U.S. Geological Survey streamflow 

gages on the Narraguagus River at Cherryfield and the Penobscot River at West Enfield, Maine, and the 

2000 and 2010 data-collection time periods. ...................................................................................................25

Figure 12. Graph showing cumulative distribution of annual mean streamflow at the U.S. Geological Survey 

streamflow gage at the Narraguagus River at Cherryfield, Maine, 1949–2010, and annual mean streamflow 

during the 1999–2000 and 2008–11 data-collection periods. ..........................................................................26

Figure 13. Boxplot showing estimated annual loads of total nitrogen from selected tributaries to Northeast Creek, 

determined from streamflow measurements and water-quality samples for the 2000 and 2010 time periods, 

and loads predicted by using the decision support system (DSS), 2000 and 2010, Bar Harbor, Maine. .........27

Tables

Table 1. Locations of water-quality sampling and streamflow measurements, 2008–11.............................................. 7

Table 2. Summary of streamflow and nitrogen-species concentrations for samples from Northeast Creek tributary 

monitoring sites, Bar Harbor, Maine, 2008–11. ................................................................................................ 9

Table 3. Summary of data used in the MOVE.1 estimation of daily mean streamflows at the Northeast Creek tributary 

sites, 2008–11.................................................................................................................................................17

Table 4. Load estimation model characteristics and estimated average annual loads and loading rates for Northeast 

Creek tributary sites, determined from sampling results, 2008–11..................................................................18

Table 5. Land-use changes in the Northeast Creek tributary watersheds, 2000 to 2010. ...........................................20

Table 6. Total nitrogen loads and yields estimated from streamflow and water-quality datasets for tributaries to 

Northeast Creek, 2000 and 2010 time periods. ...............................................................................................23

iv
Conversion Factors, Datum, and Abbreviations

SI to Inch/Pound

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

hectare (ha) 2.471 acre

square kilometer (km2) 247.1 acre

hectare (ha) 0.003861 square mile (mi2) 

square kilometer (km2) 0.3861 square mile (mi2)

Volume

liter (L) 0.2642 gallon (gal)

Flow rate

cubic foot per second (ft3/s) .02832 cubic meter per second (m3/s)

Mass

kilogram (kg) 2.205 pound avoirdupois (lb)

milligram (mg) 0.0003527 ounce (oz)

kilogram per hectare per year 

(kg/ha/yr)

.05710 pound per square mile per year 

(lb/mi2/yr)

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)

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

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

Abbreviations

ANP Acadia National Park

DSS decision support system

GIS geographic information system

NEC Northeast Creek

NPS National Park Service

USGS U.S. Geological Survey

v
Acknowledgments

Many individuals assisted in the successful completion of this project. The author would like to 

thank the private landowners on Mount Desert Island who generously allowed access to their properties 

for nutrient sampling. Glenn Guntenspergen and Hilary Neckles, U.S. Geological Survey (USGS) 

Patuxent Wildlife Center, were key investigators on earlier contributing work on nitrogen loading in 

Northeast Creek, together with Jason Rohweder of the USGS Upper Midwest Environmental Sciences 

Center. Staff of the National Park Service at Acadia National Park and the Town of Bar Harbor were 

helpful in evaluating the proposed work, and providing other support for the completion of the study. In 

particular, Karen Anderson and David Manski of the National Park Service provided technical support 

throughout this and the previous Northeast Creek studies.

vi
Changes in Nitrogen Loading to the Northeast Creek 

Estuary, Bar Harbor, Maine, 2000 to 2010

By Martha G. Nielsen

Abstract

Since 1999, the U.S. Geological Survey and the National Park Service have been monitoring 

land use and nitrogen loading in a 26.3-square-kilometer (10-square-mile) estuarine watershed at Acadia 

National Park, Mount Desert Island, Maine. The initial study linking land use and nitrogen loads

entering the Northeast Creek estuary was completed in 2000, and findings were used to develop 

simulations of nitrogen loading to the estuary, thereby helping to inform local land-use planning 

decisions. At that time, the amount of nitrogen entering the Northeast Creek estuary was relatively 

small, and no evidence of nutrient-related degradation was observed in the Ruppia-dominated estuarine 

ecosystem. A new round of water-quality monitoring and streamflow measurements was conducted to 

determine nitrogen loading from 2008 to 2011 as a means to evaluate the effects of increased rural 

residential housing within the watershed since 2000. On the basis of a 2.6-percent increase in 

residential-housing land use in the watershed from 2000 to 2010, simulations of nitrogen export 

predicted a 7-percent increase in nitrogen loading to Northeast Creek. The measurement-based loads

estimated for the Northeast Creek tributaries, however, increased much more than predicted, from 

1.89 kilograms per hectare per year (kg/ha/yr) in 2000 to 3.12 kg/ha/yr in the time period centered on 

2010—a 66-percent increase. This increase is likely primarily a result of the prevalence of much wetter 

conditions during the 2008–11 sampling period than during the earlier sampling period. In addition to 

increasing the physical transport of nitrogen in the watershed, wet climatic conditions have been shown 

in other studies to increase the rates of biotic and abiotic processes that control nitrogen export from 

northern-latitude forested watersheds. The new loading estimates, however, also support the possibility 

that some portion of the increase in nitrogen loading results from the observed land-use changes, and 

that the increase in residential housing has, in fact, contributed to the observed increase in nitrogen

loading.

Introduction

Estuaries within and around Acadia National Park (ANP) provide nursery, breeding, and forage 

grounds for many species of fish and wildlife, as well as unique recreational opportunities for the park’s 

visitors and local residents. These estuaries are threatened by potential contaminants from rapidly 

increasing residential development outside the park boundary. Nutrient loading to estuarine systems is 

one of the park’s most important resource-management challenges. The Water Resources Management 

Plan for ANP (Kahl and others, 2000) lists the maintenance of water quality to maintain ecosystem 

integrity as the highest water-resources priority for Park managers. The second largest of these estuaries, 

the Northeast Creek (NEC) estuary, is surrounded by privately owned rural residential land, which 

makes up most of the watershed of the estuary. In NEC, as well as in other estuaries in the park, the 

projected ecological response to nutrient enrichment (primarily nitrogen) is habitat degradation caused 

1
by the increased growth of algae and subsequent decline of submerged aquatic vegetation in the estuary 

(Kinney and Roman, 1998; Neckles and others, 2003).

Studies of nitrogen loading to the NEC estuary began in 1998, when the U.S. Geological Survey 

(USGS) and the National Park Service (NPS) began a cooperative project to quantify the water budget 

for Northeast Creek and determine nitrogen loadings from precipitation and surface-water sources 

(Nielsen, 2002b). The surface-water nitrogen loads measured during that study (conducted in 1999–

2000), hereafter referred to as the “2000 loads,” were used in conjunction with a land-use analysis of the 

watershed and in situ mesocosm experiments in the estuary to develop simulations of nitrogen export to 

the NEC estuary (Guntenspergen and others, 2005; Guntenspergen and others, 2009). The mesocosm 

experiments were conducted to determine the amount of nitrogen loading the estuary potentially could 

absorb before detrimental ecosystem change likely would occur (Neckles and others, 2003; 

Guntenspergen and others, 2009), and the simulations that were developed included information on the 

relative ecosystem health that would be expected from changes in land use, following changes in 

nitrogen loading. Local land managers were able to conduct these simulations using a geographic 

information system- (GIS) based decision-support system (Guntenspergen and others, 2009, p. 519–

520). 

Land-use changes in the NEC watershed since 2000 have raised questions about how much 

change has occurred in the nitrogen loading to the NEC estuary; how well the simulations predicted 

nitrogen loading changes; and whether the land-use-based predictions of nitrogen loading changes are 

sufficient for understanding loading variability and provide enough information to make planning 

decisions to protect the health of the ecosystem. The current study, undertaken in cooperation with NPS 

and the Town of Bar Harbor from 2008 to 2011, attempts to answer these questions so that NPS and the 

Town of Bar Harbor can continue working together to make science-based management decisions that 

minimize the adverse effects of development on the ecological health of the estuary and watershed.

Northeast Creek Study Area

The NEC estuary is a small tidal estuary located on the north side of Mount Desert Island in the 

Town of Bar Harbor, Maine (fig. 1). Northeast Creek flows into Thomas Bay; its outlet is constricted by 

a bridge and the remains of an old rock dam. The dam remains are at an elevation slightly below mean 

high tide. Sea water enters the estuary for a short period of time at the peak of each tidal cycle on most 

days of the lunar cycle. During neap tides and lower high tides, no saltwater enters the estuary. Water in 

the estuary is often highly stratified—freshwater from inflowing tributaries stays above the saltwater 

because of density differences. During large runoff events, the freshwater completely flushes the 

saltwater out of the estuary, only to be partly displaced again by saltwater at the next tidal maximum 

(unpublished data available at the U.S. Geological Survey office in Augusta, Maine). Because the 

saltwater stays at the bottom of the creek, the submerged vegetation consists primarily of salt-tolerant 

Ruppia maritima (widgeon grass) along most of its length.

2
3 

Figure 1. Map showing location of the Northeast Creek study area on Mount Desert Island, Bar Harbor, Maine. 
The estuary receives freshwater input from four perennial tributaries (from east to west with 

their watershed areas, Stony Brook (7.41 square kilometers (km2), Old Mill Brook (6.85 km2), French 

Hill Brook (1.30 km2

), and Aunt Betsey’s Brook (2.02 km2)); from three unnamed intermittent 

tributaries; and from unchannelized flow from upland and wetland areas adjacent to the estuary 

(6.58 km2) (fig. 1). The total watershed area is 26.25 km2. The topography of the watershed is quite 

varied—runoff from the smaller tributaries tends to be sluggish because of large areas of wetlands and 

relatively small topographic gradients, but runoff from Old Mill Brook is very rapid, as much of its

watershed is steep and very little soil covers the granitic bedrock of the area. Runoff from Stony Brook 

is slowed by a large wetland in the middle of the watershed and a pond (Hamilton Pond) a short distance 

upstream from where the tributary flows into Northeast Creek (fig. 1). Total topographic relief is 

221 meters (m). Average annual precipitation for the area (1981–2010) is 144 centimeters per year 

(cm/yr) (56.7 inches per year ) (National Oceanic and Atmospheric Association, 2013).

Previous Investigations in the Northeast Creek Study Area

The USGS has been conducting investigations in the NEC study area since 1998; these

investigations include studies of water quality and nitrogen cycling (Nielsen, 2002b; Culbertson and 

others, 2007; Nielsen and others, 2002; Nielsen and Kahl, 2007; Huntington and others, 2011; 

Huntington and others, 2012); watershed hydrogeology (Nielsen, 2002b); and the estuarine ecosystem 

(Neckles and others, 2003). The relation between land use and water quality has been of particular 

interest, because of the increasing residential construction in the watershed and concerns that nitrogen

input from that development could impair the relatively pristine condition of the estuary.

The first studies of nutrient export from the tributary watersheds to Northeast Creek during 

1999–2000 showed significant differences in nitrogen loading rates among the tributary watersheds, and 

indicated that one factor that may be responsible is the variation in land use across the watersheds

(Nielsen, 2002b; Nielsen and Kahl, 2007). The initial calculations of nitrogen loads to Northeast Creek 

were based on the results of sampling conducted from April 1999 to September 2000 (Nielsen, 2002b), 

and are referred to in this report as the “2000 loads.” Samples from the mouths of the four perennial 

tributaries were collected monthly along with instantaneous-streamflow measurements. A short-term 

continuous-streamflow gage located at an upstream site on Old Mill Brook was used to establish a local 

baseline to estimate daily streamflows at the monitoring sites and thereby to help estimate annual 

nitrogen loads to Northeast Creek. Additional details of this study are discussed farther on in this report.

The annual stream loads of a constituent can be divided by the watershed area of the stream to 

obtain an average annual load per unit area of watershed, also termed a “yield,” or loading rate. Loading 

rates for total nitrogen (as N) ranged from 1.3 kilograms per hectare per year (kg/ha/yr) in Aunt 

Betsey’s Brook to 2.7 kg/ha/yr in Stony Brook during 1999–2000 (Nielsen, 2002b). These yields were 

found to be much lower than yields from watersheds of eutrophic estuaries elsewhere on the East Coast.

However, these estimates were calculated on the basis of only 18 months of samples (not all of which 

were suitable for use in the estimates), and during a time period when precipitation during many months 

of the study was approximately half the long-term average (Nielsen, 2002b).

Simulations Relating Loading Rates to Land Use

After the field study of surface-water loads to the estuary was completed, work began to relate 

the loading rates to different land uses (Guntenspergen and others, 2009) and to determine how much 

nitrogen input the estuary could assimilate before undergoing changes indicative of degradation 

(Neckles and others, 2003). Land use in the watershed of Northeast Creek and other watersheds on 

Mount Desert Island was mapped by using color-infrared aerial photos from 1996 (scale 1:15,840)

4
(Nielsen and Kahl, 2007). The land-use delineations were then field-checked and adjusted to conditions 

observed on the ground in 2000. Each polygon in the land-use dataset was coded as one of six land-use 

types: forest; agriculture (primarily pasture and hay production); urban/suburban (houses and yards, 

roads and driveways, commercial properties, and other urban development); wetlands; open water; and 

quarry/bare rock/gravel pits.

The nitrogen export coefficients, as described by Guntenspergen and others (2009), represent

just the annual nitrogen yield from a unit area of a specific land use, whereas the total annual nitrogen 

yield, or loading rate, represents an average yield per unit area for an entire watershed or subwatershed

encompassing multiple land uses. In reality, the land uses in the NEC watershed are not entirely 

homogeneous, and some of the land-use categories, particularly the urban/suburban category, consist of 

a mixture of land uses related to the development of land for human habitation. Watershed areas having 

substantial numbers of houses, for example, may have older or newer housing stock (and septic-system 

technology) depending on their location and the history of development within the watershed, but they 

are all categorized the same in the NEC studies.

Nitrogen export coefficients for the calculation of loadings to the NEC estuary were based on 

previously published values and the estimated export of nitrogen (the 2000 loads) from the Northeast 

Creek watersheds plus one adjacent similarly sized watershed, and land-use characteristics in those 

watersheds in late 2000 (Guntenspergen and others, 2009). Nitrogen export coefficients (in kilograms 

per hectare per year) were derived by using a minimum-least-squares approach to parameter estimation, 

conditioned with ranges of values for those land uses published in other studies. The simulation of 

nitrogen export from watersheds based on land-use export coefficients, described by Guntenspergen and 

others (2009), provides a rough prediction of both the total nitrogen loading to the estuary on the basis 

of the proportions of the watershed within different land-use categories for any given time period for 

which land use is known, and an average loading rate, using a weighted average calculation.

In order to place predictions of nitrogen yields into an ecosystem-health context, Neckles and 

others (2003) conducted an in situ mesocosm study within the NEC estuary. Mesocosms are 

experimental enclosures situated in the natural environment that are small enough to control for 

variables to be studied but large enough to allow the natural ecosystem processes of interest to occur 

and be measured. The NEC mesocosms (each measuring 1 square meter) were constructed to mimic 

conditions in the estuary under varying levels of nitrogen loading, with four levels of nitrogen inputs 

studied. Each level was replicated with four mesocosms, plus two different sets of controls. This study 

identified a set of nitrogen loading thresholds at which the estuary would undergo changes in estuarine 

structure and function, moving toward a more eutrophic condition. The threshold for the transition 

between “healthy” and “degrading” was determined to be 2.2 kg/ha/yr for the entire watershed, and the 

threshold between “degrading” and “degraded” was 4.4 kg/ha/yr (Neckles and others, 2003). The 

simulations of nitrogen export conducted using a GIS-based decision-support system include 

comparisons of predicted nitrogen loading in NEC to these thresholds (Guntenspergen and others, 2009, 

p. 519–520).

Application of Nutrient Export Simulation for Local Planning

The Bar Harbor comprehensive land-use plan, adopted in 2007 (Town of Bar Harbor, 2007),

directs the town to use the simulations of nitrogen export to help guide land-use decisions in the 

Northeast Creek watershed. The Town of Bar Harbor’s planning department is committed to 

considering the simulation results in planning decisions (Town of Bar Harbor, 2007). From 2000 to

2008, the number of houses in the NEC watershed increased by 40 percent, resulting in a likely increase

in the nitrogen load to the estuary. Simulation of nitrogen export from watersheds with coefficients 

5
based on 2007 land-use data indicated that the recent land-use changes might already be resulting in 

yields that approach the lower threshold identified in the mesocosm study—in other words, levels that 

would cause an increase in nutrient enrichment and possible degradation of the estuary (Karen 

Anderson, Acadia National Park, written commun., 2008). 

Use of these simulations has been successful in motivating the community to consider the effects 

of land-use change on water quality. However, the fact that the simulation of nitrogen loads to the 

estuary by use of export coefficients based on land use is a simplification of the processes operating on 

the landscape (it considers only the type of land use in each parcel within the watershed and no other 

factors, such as distance to streams or other water bodies, or variability in hydrologic conditions from 

year to year) contributes to uncertainty in the predictions relating land-use change for a specific time 

period to estuarine nitrogen input and potential ecosystem impacts. This uncertainty points to several

critical areas of concern that require scientific inquiry to support the local land-use-planning community

in making effective decisions for the health of the ecosystem: How has the nitrogen loading to the NEC

estuary changed since the first round of sampling in 1999–2000? Is simulation of nitrogen export from 

watersheds based on land use and export coefficients a sufficient tool for understanding recent and 

future changes in loading? What other factors contribute to variability in loading?

These questions prompted the current collaboration among the USGS, the NPS, and the Town of 

Bar Harbor to address the following points: (1) What is the rate of nitrogen loading to the NEC estuary 

after 10 years of land-use change? (2) Has loading changed since the 2000 load study? (3) How do the 

updated loads compare to the predictions from the simulations using land use from 2010? (4) Are 

simulations based on export coefficients still useful for making planning decisions? (5) What factors 

other than land-use changes should be considered to improve understanding of potential future changes 

in loading?

Purpose and Scope

This report presents the results of a study that was undertaken to evaluate current nitrogen loads 

to the Northeast Creek estuary as of 2010; to evaluate the simulations, based on land-use coefficients of 

nitrogen export, used to help make decisions about land management in the estuary watershed; and to 

better understand variability in nitrogen input to the estuary. Results of sampling for nitrogen in 

tributary streams to the NEC estuary from 2008 to 2011 is described and summarized. The nitrogen 

concentrations are compared to concentrations measured during an earlier nutrient loading study (1999–

2000) in NEC. Annual nitrogen loading estimates for the 2010 time period, based on the 2008–11

sampling, are presented. The report also documents land-use changes following almost 10 years of rural 

residential development in the tributary watershed after the initial nitrogen loading estimates were done 

in 2000. The simulation of nitrogen loading to NEC in 2010 using export coefficients, based on these 

land-use changes, is presented. The changes in nitrogen loading between two sampling periods (2000 

and 2010) are presented and compared to the simulations based on land-use changes. Factors such as 

climatic variability are discussed as possible additional variables to take into consideration in future 

predictions of nitrogen inputs to NEC.

6
Field Study of Nitrogen Loading to Northeast Creek, 2010 Time Period

The 1999–2000 study of nutrient loading in tributaries of NEC (Nielsen, 2002b) established a

baseline for the amount of nitrogen entering the NEC estuary (referred to as the “2000 loads” in this 

report) from its four tributaries. In the current study, a second round of nitrogen loading estimates was 

made for these tributaries, with water-quality sampling and streamflow measurements starting in two 

streams in July 2008, and in the remainder of the streams in April 2010. Sampling continued in all 

streams through November 2011. After sampling was completed, the annual nitrogen loads were 

estimated using the LOADEST program developed by the USGS. The load estimates include all 

sampled months from 2008 to 2011, representing a period roughly centered on 2010. These estimates 

are referred to as the “2010 loads” in this report, and represent an annual average for the whole 

sampling period. The 2010 loads are compared with the 2000 loads, which similarly represent an annual 

average for the period from April 1999 to September 2000 (Nielsen, 2002b).

Nitrogen Sampling and Streamflow Measurements, 2008–11

Water-quality samples were collected at the same sites for the 2008–11 study as for the 1999–

2000 study, with one additional site on Stony Brook, upstream from a large pond (Hamilton Pond, 

fig. 1), for a total of five sampling sites (table 1). Instantaneous streamflow was measured during sample 

collection at all sites using standard USGS methods (Carter and Davidian, 1968; Rantz and others, 

1982).

Table 1. Locations of water-quality sampling and streamflow measurements, 2008–11.

[km2, square kilometers; USGS, U.S. Geological Survey]

Site name USGS station 

number

Drainage area, 

in hectares

Drainage area, 

in km2 Samples collected for:

Old Mill Brook 01022805 685 6.85 This study, 2008–11

Upper Stony Brook 01022809 669 6.69 This study, 2008–11

Lower Stony Brook 01022810 741 7.41 This study, 2008–11

Aunt Betsey’s Brook 01022815 202 2.02 Huntington and others (2011), 

2008–09; this study, 2010–11

French Hill Brook 01022807 130 1.30 Huntington and others (2011), 

2008–09; this study, 2010–11

Water-Quality Sampling Procedures

Following the methodology used in the 1999–2000 study (Nielsen, 2002b), water-quality 

samples were collected monthly at five sites on four tributary streams in the NEC watershed (table 1), in 

two phases. A filtered sample (.45-micron filter size) and an unfiltered (preserved) sample were 

collected and analyzed for total nitrogen (as N), nitrite plus nitrate (as N), ammonia (as N), and total

phosphorus. Organic nitrogen concentration was calculated from measured values of other nitrogen 

constituents. Samples were kept on ice and analyzed at the USGS National Water Quality Laboratory in 

Lakewood, Colorado, within 5 days of sample collection. Additional sampling and analysis details can 

be found in Nielsen (2002b).

7
Samples were collected on a monthly schedule. The first phase of the sampling, from July 2008 

to July 2009, included Old Mill Brook and the Upper and Lower Stony Brook sites. Wintertime samples 

were not collected during that sampling phase. The second phase of the sampling, from April 2010 to 

November 2011, added the Aunt Betsey’s Brook and French Hill Brook sites. Samples were collected 

monthly year-round during the second sampling phase. A total of 28 samples were collected at the sites 

that were sampled during both phases, and 20 samples were collected at the two sites that were sampled 

only during the second phase (table 1). In a separate study, additional monthly samples were collected 

from Aunt Betsey’s Brook and French Hill Brook in 2008–09 (Huntington and others, 2011), but 

streamflow was not measured. Water-quality data from those samples (11 per site; table 1) are included 

in the discussion below, but were not used for load estimation because of the lack of concurrent 

streamflow data. 

Streamflow Measurements, 2008–11

The sampling events during the study period covered a wide range of streamflows. Low flows 

were generally observed during July and August of 2010 and 2011. High flows were measured during 

April 2009 and December 2010. An evaluation of the daily mean streamflows at the USGS gaging 

station at Otter Creek near Bar Harbor (station number 01022840), located 7 kilometers (km) southeast 

of the study area, during the study period and on days on which samples were collected at NEC

tributaries (fig. 2) indicates that instantaneous streamflows measured during the sampling events were

representative of the range of streamflows during the entire study period, and captured high, average,

and low flows. 

Figure 2. Hydrograph of daily mean streamflow at U.S. Geological Survey streamgage at Otter Creek, near Bar 

Harbor, Maine, May 2008 to September 2011, showing streamflow on days of sample collection for the 

Northeast Creek study. 

8 
Nitrogen Constituent Concentrations in Northeast Creek Tributaries, 2008–11

Nitrogen concentrations, both inorganic and total N, varied in both time and space, but were 

generally low, with most total N concentrations less than 1 milligram per liter (mg/L). Concentrations of 

inorganic N species (ammonia-N (NH4-N) and nitrite plus nitrate-N (NO2+NO3-N)) in samples 

collected from 2008 to 2011 ranged from 0.0014 to 0.7 mg/L and from 0.003 to 0.17 mg/L, respectively

(table 2). Total N concentrations ranged from 0.09 to 1.4 mg/L (filtered) and from 0.08 to 1.49 mg/L 

(unfiltered). Concentrations of organic N, which was not analyzed for but was determined as a 

calculated value, ranged from below detection (0.2 mg/L) to 1.3 mg/L. Concentrations of NH4-N and 

NO2+NO3-N were frequently below the detection limit, which ranged from 0.0014 to 0.02 mg/L and 

from 0.0014 to 0.016 mg/L, respectively. In Old Mill Brook, which was anomalously low in inorganic 

N species, concentrations of NH4-N and NO2+NO3-N were below detection in 79 and 71 percent of the 

samples, respectively. In other tributaries, the percentage of samples with concentrations of inorganic N 

species below detection ranged from 3 to 32 percent of all samples.

Table 2. Summary of streamflow and nitrogen-species concentrations for samples from Northeast Creek tributary 

monitoring sites, Bar Harbor, Maine, 2008–11.

[Available separately at http://pubs.usgs.gov/of/2013/1256/]

Nitrogen concentrations also varied by tributary (fig. 3). Overall, Old Mill Brook had the lowest 

concentrations of all the nitrogen species, with medians of 0.24 mg/L of total N (filtered), 0.008 mg/L of

NO2+NO3-N, 0.01 mg/L of NH4-N, and 0.24 mg/L of organic N. The Upper Stony Brook site had the 

highest concentrations of almost all the nitrogen species, with medians of 0.59 mg/L of total N 

(filtered), 0.013 mg/L of NO2+NO3-N, 0.014 mg/L of NH4-N, and 0.56 mg/L of organic N.

Concentrations of some constituents (except NO2+NO3-N and NH4-N) were higher in samples from 

Upper Stony Brook than in those from Lower Stony Brook, indicating that processes in Hamilton Pond, 

such as nitrification and mineralization, may be converting organic N to inorganic forms, and 

denitrification may be reducing the total amount of N exiting the pond.

9
10

Figure 3. Boxplots summarizing distribution of nitrogen (N) constituent concentrations, Northeast Creek 

tributaries, 2008–11.
Other researchers investigating N export from relatively undisturbed watersheds in northern 

latitude forests also have found significant natural variability in concentrations over time and among 

adjacent watersheds (Creed and Beall, 2009; Creed and Band, 1998; Lovett and others, 2002; Willard 

and others, 1997; and Andersson and Lepistö, 2000). Factors known to affect the magnitude and 

variability of N concentrations include soil composition (Lovett and others, 2002), topography (Creed 

and Band, 1998), hydrogeology and its effects on stream generation (Schiff and others, 2002), and 

possibly forest disturbance history (Goodale and others, 2000), although the importance of forest 

disturbance has been disputed (Lovett and others, 2002).

Fractions of Organic and Inorganic Nitrogen in Tributary Streams

Organic and inorganic forms of nitrogen function differently in aquatic environments, and 

information on the relative amounts of these constituents is useful in evaluating possible sources and 

potential effects on ecosystem health. The ratio of organic N:inorganic N was estimated for each set of

samples from three tributaries (fig. 4). Because concentrations of the inorganic species were frequently

below the detection limit, a value of half the detection limit was used for each nondetected value in this 

estimation. The ratio of organic N:inorganic N ranged from a high of 95:5 to a low of 73:27. A seasonal 

pattern can be identified in the data, as seen in a graph of the ratio of organic N:inorganic N plotted over 

time for the three tributaries (fig. 4). The percentage of total N in the organic form is highest during the 

warmer months for most of the samples. This pattern is especially noticeable in the samples from Old 

Mill Brook and Upper Stony Brook. During the colder months, the amount of inorganic N increases 

substantially. Creed and Beall (2009) suggest that topographic depressions and flat areas in watersheds 

can transform inorganic N (particularly NO3) to organic N, primarily through microbially mediated 

reactions.

11
12

Figure 4. Graphs showing ratio of organic and inorganic nitrogen (N) to total N in samples from selected 

tributaries to Northeast Creek, Bar Harbor, Maine, 2008–11.
The percentages of inorganic N are generally higher in samples from Aunt Betsey’s Brook than 

in those from the other two tributaries (as is the magnitude of inorganic N) (fig. 3), and the seasonal 

pattern is less pronounced (fig. 4). The topographic setting of Aunt Betsey’s Brook is not substantially 

different from the other watersheds, so natural topographic differences do not appear to account for the 

differences in proportions of nitrogen constituents in this watershed. The differences could be a 

reflection of the fact that the Aunt Betsey’s Brook watershed has a larger percentage of urban or 

suburban land use (with residential construction and associated septic systems), and that the septic 

systems employ older technology than much of the newer construction in the Old Mill Brook watershed.

NH4-N concentrations are higher in Aunt Betsey’s Brook than in the other tributaries, and NO2+NO3-N 

concentrations are substantially higher than in Old Mill Brook (fig. 3). Both NH4 and NO2+NO3 are 

produced from septic systems.

Relations Between Constituent Concentrations and Streamflow

The relation between nitrogen concentrations and streamflow is slightly different for each of the 

tributaries. Old Mill Brook and Upper Stony Brook both exhibit a decrease in total N concentration with 

increasing streamflow (fig. 5). The lowest flows in Old Mill Brook (less than about 2 cubic feet per 

second (ft3/s)) are associated with total N concentrations in the range of 0.3 to 0.8 mg/L (fig. 5), and 

those in higher flows (up to about 40 ft3/s) range from less than 0.1 to about 0.6 mg/L. In Upper Stony 

Brook, the lowest flows (less than about 1 ft3/s) are associated with concentrations of total N in the 

range of 1.0 to 1.5 mg/L, whereas those in higher flows (up to about 10 ft3/s) range from 0.2 to 

0.8 mg/L. The highest flows for both streams are associated with some of the lowest measured total N 

concentrations. This pattern of decreasing concentration with increasing streamflow also is observed, to 

a lesser degree, in French Hill Brook. Dilution of higher concentration base flow with lower

concentration storm runoff could explain the observed relation. The relation between flow and total N 

concentration for Lower Stony Brook and Aunt Betsey’s Brook is less clear, although the highest flows 

are associated with lower concentrations than the lower flows. Because the Lower Stony Brook site is 

just downstream from a surface-water body (Hamilton Pond), mixing within the pond would be 

expected to dampen any chemical signal in water entering the pond from upstream during high-flow 

events. The reason for the absence of a relation between flow and concentration in Aunt Betsey’s Brook 

is not readily apparent. The number of sampling events is small for all the tributaries, however, and 

additional water-quality samples and streamflow measurements may be necessary to identify a 

concentration–streamflow relation that yields more information about processes in the tributary 

watersheds.

13
14

Figure 5. Graphs showing variation in total nitrogen concentration with stream discharge in tributaries to 

Northeast Creek, Bar Harbor, Maine, 2008–11.
Comparison of Total Nitrogen Concentrations in Northeast Creek Tributaries, 1999–2000 and 2008–11

The concentrations of total N (unfiltered) in water samples from the four tributaries sampled in 

the 1999–2000 study were compared to the concentrations in samples collected at the same sites during 

the 2008–11 study (fig. 6). Upper Stony Brook was not included in the comparison because it was not 

sampled in the first study. Overall, the concentrations of total N do not appear different between the two 

studies. Nonparametric two-sample t-tests showed no significant differences (at an α of 0.05) between 

the two datasets for any of the tributaries. The highest measured concentrations in Aunt Betsey’s Brook 

and French Hill Brook were higher in the more recent study, indicating a possible long-term trend 

toward higher concentrations in those tributaries, but the opposite result was observed in Old Mill 

Brook and Lower Stony Brook, where the highest concentrations were measured in the earlier study.

However, naturally high variability in total N concentrations over time is to be expected, regardless of 

whether there is any long-term trend in the data.

15

Figure 6. Bar graphs showing comparison of total nitrogen concentrations in samples from tributaries to 

Northeast Creek, Bar Harbor, Maine, 1999–2000 and 2008–11 (>, greater than). 
Estimation of Nitrogen Loading to Northeast Creek, 2010 Time Period

Loads in the tributary streams to Northeast Creek were estimated in the same manner as those

estimated for the 1999–2000 study (Nielsen, 2002b). The LOADEST program requires a continuous 

record of daily mean streamflow values for the estimation period, and a time series of paired constituent 

concentrations and instantaneous streamflows, with a minimum number of concentration values above 

the detection limit.

The loads estimated with the LOADEST software were based on a dataset of continuous daily 

mean streamflows derived from instantaneous streamflow measurements made during the field study, 

using techniques described in this report, and on analytical results for water-quality samples collected 

during the field study. These load estimates are hereafter referred to as “estimated loads” or “measured 

loads” to distinguish these field-based estimates from the estimates predicted from simulation of 

nitrogen export from watersheds based on land use and export coefficients, described by Guntenspergen 

and others (2009), and referred to as “predicted loads” in this report. Technically, constituent loads are 

not “measured” instream, but the estimates are based on instream field measurements and analyses of 

instream water quality.

Generation of Daily Mean Streamflow Values for Use in Load Estimation

The daily mean streamflow datasets required for load estimation were developed for each 

tributary stream by using the MOVE.1 technique (Hirsch, 1982) and the instantaneous streamflow 

measurements from 2008–11, similarly to those developed for the 1999–2000 study (Nielsen, 2002b).

This technique uses log-transformed instantaneous-streamflow data from the tributary streams paired 

with continuous daily mean flows for an index stream to develop equations that predict continuous daily 

mean flows for the tributary streams, with statistical distributions similar to those expected if the daily 

streamflows actually had been measured (Helsel and Hirsch, 1992).

The USGS streamflow gage at Otter Creek in Bar Harbor (station 01022840) was used as the 

index gage for all of the daily mean streamflow estimations for the 2008–11 study. Very low flows and 

zero-flow values in the measured tributary streams present problems with this method, as all the 

calculations are done in log space, so the days with zero or near-zero flow were omitted from the 

development of the streamflow estimation equations. Each site had either 18, 26, or 28 pairs of flows 

with which to develop the equations (table 3). The R2 values describing the correlation between the 

instantaneous discharges at the Northeast Creek tributary sites and the daily mean flows at the Otter 

Creek index site (in log space) ranged from 0.67 (at the Lower Stony Brook site) to 0.88 (at the Aunt 

Betsey’s Brook site) (table 3). Values at the Lower Stony Brook site were lagged 1 day compared to 

those at the Otter Creek site because of storage in Hamilton Pond upstream. Daily mean flows were 

estimated for each site between the start and end dates of streamflow data collection (table 3).

16
Table 3. Summary of data used in the MOVE.1 estimation of daily mean streamflows at the Northeast Creek 

tributary sites, 2008–11.

[R2, correlation coefficient squared; USGS, U.S. Geological Survey]

Site name

(USGS station 

number)

Start date End date

Number 

of nonzero 

streamflow 

measurements

R2 relating 

instantaneous 

measurements to 

index site 

daily mean 

flows

Tributary 

site 

streamflow 

mean 

(log)

Tributary 

site 

streamflow 

standard 

deviation 

(log)

Index site 

streamflow 

mean 

(log)

Index site 

streamflow 

standard 

deviation 

(log)

Old Mill 

Brook 

(01022805)

7/30/2008 11/3/2011 26 0.82 0.66549 0.60901 0.52120 0.61693

Upper Stony 

Brook 

(01022809)

7/30/2008 11/3/2011 28 0.77 0.26524 0.76561 0.43750 0.58435

Lower Stony 

Brook 

(01022810)

7/30/2008 11/3/2011 28 0.67 0.38344 0.69074 0.40547 0.58442

Aunt Betsey’s 

Brook 

(01022815)

4/28/2010 11/3/2011 18 0.88 -0.01000 0.76802 0.72241 0.67445

French Hill 

Brook 

(01022817)

4/28/2010 11/3/2011 18 0.79 0.03687 0.71000 0.67847 0.64363

Methods for Estimating Nitrogen Constituent Loads

The LOADEST program (Runkel and others, 2004) was utilized to develop regression equations 

relating constituent concentration to daily mean streamflow for NO2+NO3-N and total N for each 

tributary stream. LOADEST can evaluate up to nine potential models for the estimation of loads to 

determine which model best fits the data for each dataset. The models include various combinations of 

explanatory variables, including the natural log of streamflow, the square of the natural log of 

streamflow, decimal time, and sine and cosine terms to address seasonal variability.

The program utilized the adjusted maximum likelihood estimation (AMLE) method to select and 

test model coefficients, using the Akaike Information Criterion (AIC) and the Schwartz Posterior 

Probability Criterion (SPCC) to evaluate the various possible models (Runkle and others, 2004). The 

AMLE method reduces bias when censored data (concentrations below the detection limit) are present. 

Once the “best” model was selected by the LOADEST program, it was applied to the daily streamflow 

dataset for each stream to determine total, seasonal, and annual loads.

A new version of the load estimation software (LOADEST) became available between the two 

studies, which primarily affected the calculation of the 95-percent confidence intervals on the load 

estimates. The LOADEST output from the 2000 loading estimates provided a measure of the standard 

error of the prediction, which was used to calculate 95-percent confidence intervals on the estimates for 

the earlier time period. The LOADEST output from the 2010 loading estimates provided the 95-percent 

confidence intervals on the estimates directly.

17
Nitrogen Constituent Load Estimates for Northeast Creek Tributaries, 2010 Time Period

Loads of total N and NO2+NO3-N were estimated for the Northeast Creek tributaries by using all 

available data for each site. Consequently, loads for Aunt Betsey’s Brook and French Hill Brook were 

estimated by using data for 2010–11, whereas load estimates for the other sites were estimated by using

data for 2008–11 (table 2). The number of censored values in the NH4-N data exceeded the threshold for 

load estimation in LOADEST. Consequently, NH4-N loads and organic nitrogen loads could not be 

estimated. The LOADEST program produced estimates of mean daily loads in kilograms per day on an 

annual basis, with upper and lower 95-percent confidence intervals. Multiplying the mean annual daily 

load by 365 gave estimates of average annual loads for each of the sites. The annual loads represent 

averages for the years used in the estimation, rather than annual loads for specific years. Seasonal 

estimates were also produced, but were not the focus of this study, as the decision support system (DSS)

uses the annual loading rate in its output.

Either 20 or 28 uncensored concentration values were used in the load estimation models for 

total N for the five sites (table 4), and from 8 to 24 uncensored values were used for NO2+NO3-N. Old 

Mill Brook had only eight uncensored values for NO2+NO3-N, resulting in a high level of uncertainty

for this estimate, with an R2 of zero and very high residual variance (table 4). The sites with a greater 

number of uncensored values had higher R2 values and lower residual variances but, in general, the 

regression results for the NO2+NO3-N load estimates were much more uncertain than those for the total 

N load estimates, which had R2 values as high as 0.92 and very low residual variances.

Table 4. Load estimation model characteristics and estimated average annual loads and loading rates for 

Northeast Creek tributary sites, determined from sampling results, 2008–11.

Number of 

observations

Number of 

uncensored 

observations R2

Residual 

variance

Mean 

daily 

load

95-

percent 

lower CI

95-

percent 

upper CI

Standard 

error

Old Mill Brook 28 28 0.69 0.0928 4.33 3.69 5.06 0.34 1,580 2.3

Aunt Betsey's Brook 20 20 0.73 0.0645 1.06 0.88 1.27 0.09 387 1.9

Upper Stony Brook 28 28 0.92 0.0285 6.76 5.67 8.00 0.59 2,470 3.7

Lower Stony Brook 28 28 0.60 0.0496 8.56 7.16 10.2 0.74 3,120 4.2

French Hill Brook 20 20 0.65 0.1184 1.03 0.82 1.28 0.11 376 2.9

Old Mill Brook 28 8 0.00 2.227 0.26 0.06 0.73 0.17 95 0.14

Aunt Betsey's Brook 20 19 0.49 0.2288 0.090 0.070 0.130 0.010 33 0.16

Upper Stony Brook 28 20 0.70 0.5085 0.52 0.22 1.07 0.22 190 0.28

Lower Stony Brook 28 24 0.72 0.3141 0.41 0.2 0.74 0.14 150 0.2

French Hill Brook 20 12 0.43 0.6768 0.036 0.020 0.058 0.009 13 0.1

[CI, confidence interval; kg, kilograms; kg/d, kilograms per day; kg/ha/yr, kilograms per hectare per year; R2

, correlation 

coefficient squared; N, nitrogen]

Nitrite + Nitrate as N

Monitoring watershed and 

constituent

Concentration regression results Estimated daily mean load, in kg/d

Annual 

load, kg

Total N

Annual 

loading 

rate, 

kg/ha/yr

18
Mean daily loads for total N ranged from 1.03 kilograms per day (kg/d) in French Hill Brook to 

8.56 kg/d in Stony Brook (at the lower site) (table 4). Average annual loads for total N ranged from 

376 kilograms per year (kg/yr) in French Hill Brook to 3,210 kg/yr in Stony Brook (lower site). Annual 

estimated loads for NO2+NO3-N ranged from 13 kg/yr in French Hill Brook to 190 kg/yr at the Upper 

Stony Brook site. Chemical transformations in Hamilton Pond may be responsible for the lower 

estimated NO2+NO3-N load downstream (150 kg/yr) at the Lower Stony Brook site; however, because 

the confidence intervals for the upstream and downstream load estimates for Stony Brook overlap, 

additional data would be necessary to confirm the effects of Hamilton Pond. When annual loads are 

divided by drainage area to adjust for tributary size, the annual loading rates for total N, in kilograms 

per hectare per year, for the sites vary considerably (fig. 7, table 4), from 1.9 kilograms per hectare per 

year (kg/ha/yr) in Aunt Betsey’s Brook to 4.2 kg/ha/yr in Lower Stony Brook. For all tributaries 

combined, the average annual loading rate was 3.1 kg/ha/yr. 

The 95-percent confidence intervals for the total N estimates range from ± 15 to 24 percent of 

the estimated load. Because concentrations of NO2+NO3-N nitrogen generally have greater variability

than those of total N, with a larger number of censored values, the 95-percent confidence intervals for

the NO2+NO3-N load estimates represent a much greater percentage of the estimated loads, ranging 

from ± 22 to 180 percent. 

Figure 7. Boxplot showing estimated average loading rates (yields) of total nitrogen (N) and nitrite+nitrate (N) for 

tributaries to Northeast Creek, Bar Harbor, Maine, with 95-percent confidence intervals, for the 2010 time 

period. (The 2010 time period includes samples from 2008–11.) 

Loading rates for total N in the Northeast Creek tributary watersheds are similar to those in other 

small, northern latitude forested watersheds. Total N export rates from small undeveloped watersheds in 

the Algoma Highlands of southern Ontario, at the eastern end of Lake Superior, ranged from 3.65 to 

6.79 kg/ha/yr (Creed and Beall, 2009). Nitrate-N export from nine watersheds in the mid-Appalachians 

of the U.S. (West Virginia, Maryland, and Pennsylvania) ranged from 0.04 to 7.88 kg/ha/yr (Willard 

and others, 1997). In Finland, export of nitrate-N plus organic N from six small forested watersheds 

ranged from 1.29 to 2.2 kg/ha/yr (Andersson and Lepistö, 2000). 

19
Northeast Creek Watershed Land-Use Change, 2000 to 2010, and Predicted 

Effect on Nitrogen Loading

The GIS-based simulation tool or decision support system (DSS) used by the National Park 

Service and the Town of Bar Harbor to predict nitrogen loading applies nitrogen export coefficients to 

each land-use polygon in the spatial land-use data (Guntenspergen and others, 2009). This method can 

best be considered as a way to evaluate potential changes in average conditions over time. Data from the 

Town of Bar Harbor’s Assessing Department (unpublished data on file at the office of the Town of Bar 

Harbor, Bar Harbor, Maine) showed an increase in the number of rural houses in the watersheds of more 

than 40 percent from 2000 to 2008, when the first part of this study began. By using updated aerial 

photos available from online databases, comparisons can be made between the land use at the time that 

the DSS was developed (2000) and 2010. A new land-use GIS data layer was developed from 2010 

aerial imagery, by using the same mapping techniques as those used in the 2000 land-use delineation 

that formed the basis of the DSS. The same land-use categories (forest, wetlands, urban/suburban

(residential), agriculture, open water, and quarry/open rock/gravel pits) were used to ensure 

compatibility with the earlier mapping. The 2000 land-use data layer was used as a starting point for 

delineating changes.

Comparing the new (2010) land-use distribution with the old (2000) shows that although there 

was a fairly large increase in the number of residential units in the watershed, only 2.6 percent of the 

watershed (68 hectares) changed land-use categories (fig. 8). The land-use change was fairly evenly 

distributed throughout the NEC watershed, and none of the tributary watersheds monitored for the 

loading study had a substantially different percentage of land-use change (table 5). Almost all of the 

changes were from the forest or agriculture category to urban/suburban.

Table 5. Land-use changes in the Northeast Creek tributary watersheds, 2000 to 2010.

Subwatershed Total area, 

in hectares

Number of hectares of 

land-use change

Percent

change

Aunt Betsey’s Brook 202 7.6 3.7

French Hill Brook 130 3.8 2.9

Old Mill Brook 685 18.2 2.7

Stony Brook 741 15.4 2.1

Unmonitored uplands 559 23.1 3.4

20
21

Figure 8. Map showing changes in land use in the Northeast Creek watershed from 2000 to 2010, Bar Harbor, 

Maine. 
Decision Support System Predictions of Changes in Nitrogen Loading to Northeast Creek

Simulations were run with the 2000 land-use distribution and the updated 2010 land-use 

distribution to determine the changes in nitrogen export that would be predicted from the 2.6-percent 

land-use change that occurred during that 10-year time period. The export coefficients for land-use 

categories used in the DSS simulations were determined by using previously published ranges of values 

and a minimum least squares best-fit optimization approach based on land use and nitrogen loading 

calculations for five watersheds on Mount Desert Island in 1999–2000 (Guntenspergen and others, 

2009). Total N export coefficients for agriculture, forest, urban/suburban (residential), and wetlands 

land-use types were derived to be 4.7, 1.5, 6.9, and -0.1 kg/ha/yr, respectively. Two land-use types had

export coefficients of zero: open water and quarry/open rock/gravel pits. More detailed descriptions of 

the land-use types and determination of the export coefficients can be found in Guntenspergen and 

others (2009) and Rohweder and others (2004). 

For the entire NEC watershed, predicted load for total N increased from 5,210 kg/yr in the 2000 

time period (1.98 kg/ha/hr) to 5,560 kg/yr in the 2010 time period (2.12 kg/ha/yr), a 7-percent increase.

The spatially averaged predicted total N yields for 2010 for all tributary watersheds (monitored or 

unmonitored) in the NEC watershed, including all land-use types, ranged from 2.03 to 3.76 kg/ha/yr. 

The highest yield was for a tributary with a very small watershed (28 ha) near Stony Brook and Old Mill 

Brook (not sampled during the loading study; see fig. 1) that is mostly residential (urban/suburban) land 

use mixed with agriculture and forest. The lowest total N yields were for the larger tributary watersheds, 

such as Old Mill Brook, that are largely forested and wetland areas. Predicted increases in total N load 

for the tributary watersheds that were monitored for nitrogen loading are illustrated in figure 9. 

Individually, the predicted increases in total N load in the tributary watersheds ranged from 5.6 percent 

in Stony Brook to 8.6 percent in Aunt Betsey’s Brook. 

Figure 9. Bar graph showing predicted annual loads of total nitrogen to Northeast Creek from selected tributaries

for 2000 and 2010, from the decision-support system, determined from changes in land use, Bar Harbor, 

Maine. 

22
The DSS tool not only provides the predicted total N loading rates from the various watersheds 

in the study area, but also compares them to thresholds that can be used to put the loads in an ecological 

context. The threshold for the transition between “healthy” and “degrading” is 2.2 kg/ha/yr for the entire 

watershed, and the threshold between “degrading” and “degraded” is 4.4 kg/ha/yr (Neckles and others, 

2003). In 2000, the loading rate predicted by use of the DSS was 1.98 kg/ha/yr, and in 2010, the 

prediction was 2.12 kg/ha/yr. It should be noted that these thresholds were determined specifically for 

the NEC estuary, based on in-estuary experiments (Neckles and others, 2003). In the process for 

deriving the thresholds, it is also assumed that the loading rate during the growing season, when the 

experiments were conducted, is the same as the year-round average loading rate.

Changes in Estimated Total Nitrogen Loading to Northeast Creek, 2000 to 2010

The main focus of this study was to evaluate the loading results from the 2010 time period, 

based on a field study of streamflow measurements and water-quality sampling, and compare the results 

to both those for the 2000 time period and the predictions from the DSS. Because the same 

methodology was used for the 2010 time period (sampling during 2008–11) as in the original study 

(2000 time period, with sampling during 1999–2000), it was possible to make a direct comparison of 

nitrogen loading between the two time periods. One small change from the original study (Nielsen, 

2002b) was the redelineation of the drainage basins used for the calculation of the loading rate. The 

original watershed delineations were based on the topographic map contours, but the watersheds were 

redelineated on the basis of stereo orthophotograph pairs in 2001. Before comparing the two loading 

estimates, the 2000 loads were recomputed to reflect the adjusted watershed areas.

Changes in Total Nitrogen Loading Based on Sampling Data, 2000 to 2010

The average loading rates and total average annual load increased for all the tributaries sampled

in both the 2000 and 2010 studies (table 6). Although the measured concentrations of nitrogen in 

samples collected during the two time periods were not significantly different statistically, the total 

loads estimated for the 2010 study were much higher than those estimated for the 2000 study (fig. 10).

In all but the French Hill Brook tributary, where loads increased 16 percent, the 2010 loads were from

68 to 84 percent higher than the earlier loads. For the four tributaries combined, the load was 66 percent 

higher during the 2010 study. The average loading rates for three of the four tributaries for the 2010 

time period are above the threshold that would move the Northeast Creek estuary from a “healthy” 

condition to a “degrading” condition, as is the 2010 loading rate for all tributaries combined (table 6).

Table 6. Total nitrogen loads and yields estimated from streamflow and water-quality datasets for tributaries to 

Northeast Creek, 2000 and 2010 time periods. 

[kg/ha/yr, kilograms per hectare per year; kg/yr, kilograms per year; --, no data]

Watershed

Average loading rate, 

in kg/ha/yr

Average annual load, 

in kg/yr

2000 2010 2000 2010

Aunt Betsey’s Brook 1.1 1.9 210 387

French Hill Brook 2.5 2.9 324 376

Old Mill Brook 1.4 2.3 938 1,580

Upper Stony Brook -- 3.7 -- 2,470

Lower Stony Brook 2.5 4.2 1,830 3,120

All tributaries combined 1.9 3.1 3,300 5,460

23
Figure 10. Boxplot showing estimated annual loads of total nitrogen from tributaries to Northeast Creek, 

determined from streamflow measurements and water-quality sampling, 2000 and 2010 time periods, Bar 

Harbor, Maine. 

Factors Affecting Total Nitrogen Loads and Loading Rates

A number of different factors may be responsible for the observed increases in total N loading 

from 2000 to 2010. As is indicated by the land-use-based simulations, changes in land use can cause 

changes in loading, particularly if, over time, land uses that export less nitrogen are converted to uses 

that export more nitrogen. Changes in point sources (as separate from distributed land-use export from 

nonpoint sources) may increase or reduce loads if population increases or if improved technologies are 

implemented.

Other factors that can cause changes in loading include changes in climate and streamflow

patterns. As calculated in the LOADEST program, load is a product of concentration and flow, and the 

LOADEST program estimates loads by using the observed flows for the period of the estimation (flow 

is typically the first term in the load estimation equation, and derivatives of flow may appear in other 

terms in the equation for a given stream). If the climatic conditions during the two different, relatively 

short-term study periods were significantly different, the loading estimates would also differ.

independent of other potential causes. 

One way to evaluate the climatic conditions during the two study periods is to examine longterm streamflow records for a nearby streamflow gage, and determine where the streamflow during the 

two study periods falls with respect to long-term regional averages. The record of annual mean 

streamflow, encompassing both data-collection periods (1999–2000 and 2008–11), was evaluated for 

two long-term USGS gages in eastern Maine, the Narraguagus River at Cherryfield and the Penobscot 

River at West Enfield (fig. 11). The annual mean streamflow in both rivers was about average during 

the earlier study (about 450 ft3

/s for the Narraguagus River and 12,500 ft3/s for the Penobscot River), 

but appears from the graph to have been slightly above average during the second study (about 550–

600 ft3/s for the Narraguagus River and 15,000 ft3/s for the Penobscot River). A graph of cumulative 

flow distribution for annual mean streamflow at the Narraguagus River at Cherryfield, with annual 

24
records dating back to 1949, illustrates where the years of data collection for the two studies fall within 

that long-term context (fig. 12). The annual mean streamflow at the Narraguagus River in 1999 and 

2000 fell at approximately the 35th and 55th percentiles, respectively, of the total distribution. In other 

words, flow during these years was near the median flow. The annual mean streamflow for the second 

data-collection period (2008–11) was more varied, with flows falling at the 45th, 83rd, 87th, and 97th 

percentiles (fig. 12). Regional streamflow conditions during the second data-collection period were, for 

3 of the 4 years, much above normal. 

Figure 11. Hydrograph showing annual mean streamflow for period of record at U.S. Geological Survey streamflow 

gages on the Narraguagus River at Cherryfield and the Penobscot River at West Enfield, Maine, and the 2000 

and 2010 data-collection time periods. 

25
26

Figure 12. Graph showing cumulative distribution of annual mean streamflow at the U.S. Geological Survey 

streamflow gage at the Narraguagus River at Cherryfield, Maine, 1949–2010, and annual mean streamflow 

during the 1999–2000 and 2008–11 data-collection periods.

If the supply of N in the watersheds of NEC was finite, the amount of runoff would not produce 

a large change in loading, as the additional water would dilute the source and the total load would 

remain constant. Therefore, if N loading does increase with increasing runoff, there must be some factor 

or factors that could cause variation in N supply with climatic variability.

Researchers investigating temporal variability in N export from forested watersheds have found 

that N loading rates do, indeed, correlate with streamflow conditions. Andersson and Lepistö (2000) 

found that annual runoff was the single most significant factor in explaining variability in N yields. 

Other recent long-term studies of natural variability in loading rates have identified several 

hydrologically mediated processes that affect loading. Dry conditions and low soil-moisture levels are 

known to suppress microbial activity, and therefore also nitrogen transformations and export (Willard 

and others, 1997). Temperature-related effects on microbial activity were also cited as a factor in the 

variability of N export (Andersson and Lepistö, 2000). Topographically modulated hydrologic 

flushing—in other words, residence time of water in the soil column, which is in turn a function of both 

topography and rainfall patterns—has been identified as a major explanatory variable in N export 

(Creed and Beall, 2009). It is likely, therefore, that much of the observed increase in load in the NEC 

study area is linked to increased streamflow during the second data-collection time period.

The effect of atmospheric deposition on N loading may relate to spatial variation in atmospheric 

deposition over large distances, but the effect has not been observed everywhere. A USGS study of 

small undeveloped watersheds across the United States found that wet deposition of nitrate correlated 

well to nitrate yields in the eastern part of the country (Clark and others, 2000), but other studies have 
not found a strong link between atmospheric deposition and nitrogen yields (Andersson and Lepistö, 

2000; Willard and others, 1997; Lovett and others, 2002). Other factors that have been linked to the 

spatial variability of N export include the ratio of carbon to nitrogen in soils and possibly forest type or 

disturbance history (Lovett and others, 2002; Andersson and Lepistö, 2000). 

Changes in Nitrogen Load Predicted from Land-Use Data Compared to

Estimated Changes Based on Field Studies in the Northeast Creek Watershed

The results of the two field-based N loading studies and the predictions for the 2000 and 2010 

time periods from the DSS were compared in order to evaluate the effectiveness of the DSS (fig. 13). 

Overall, the magnitude of predicted change from the DSS from 2000 to 2010 is well exceeded by the 

magnitude of the estimated change in load based on the field study. This result indicates that the DSS 

may not be well suited to predicting N loading for a very specific time period, especially for one (such 

as 2010) that deviated substantially from “average” climatic conditions. The DSS uses land use as the 

only explanatory variable and, consequently, other factors that affect transport from the landscape are 

not incorporated in the predictions. 

Figure 13. Boxplot showing estimated annual loads of total nitrogen from selected tributaries to Northeast Creek, 

determined from streamflow measurements and water-quality samples for the 2000 and 2010 time periods, and 

loads predicted by using the decision support system (DSS), 2000 and 2010, Bar Harbor, Maine. 

27
Despite the magnitude of the differences between predicted and measured loads (the estimates 

based on field data), the DSS predictions fell within the 95-percent confidence intervals of the measured 

2010 loads in two of the four tributaries, and represent to some degree the average measured loads for 

the two time periods in those two watersheds. The use of land-use-based export coefficients, although 

imperfect, is reasonable in some of the watersheds. The measured loads in Aunt Betsey’s Brook were 

slightly lower than those predicted from the DSS. In Lower Stony Brook, however, the 2010 measured 

loads exceeded predicted loads by about a factor of two. Several possible explanations for this exist. The 

six land-use categories represented in the DSS may not sufficiently represent the actual variability in the 

landscape; some categories may be more heterogeneous than homogeneous, and categories may be too 

generalized, with respect to the magnitude of nitrogen sources. The climate-based variability seen in the 

other watersheds may, because of soil types or slope characteristics, be enhanced in Stony Brook, or the 

increased rainfall may have increased export from the urban/suburban land-use category more in that 

watershed than in others. Differences in the proximity of development to streams and monitoring 

locations may also be a factor; equal percentages of a given land use in two watersheds do not 

necessarily result in equal transport rates of nitrogen to streams. The measurement data, although 

providing the most realistic assessment of instream conditions determining nitrogen loads, could be 

improved by the addition of continuous streamflow monitoring at one or more locations in the 

watershed, year-round water-quality sampling in the tributaries, and monitoring of the water quality in 

the estuary itself.

Based on the sampling from the 2010 time period, it would be unwise to ignore the predictions 

of the DSS that increases in total nitrogen loads are likely to occur as land use shifts from undeveloped, 

primarily forested land to more urbanized land, and that some change in long-term nitrogen loading may 

already have occurred. However, the increases in annual loading of total nitrogen may result in large 

part from variability in streamflow—that is, above-average streamflow during much of the 2010 

sampling period. The differences in streamflow conditions between the two time periods make 

interpretation and comparison of the specific loading values (as predicted by the DSS) difficult. The

DSS may be performing as intended in predicting the change in loading resulting from land-use change.

Similarly, it would be difficult to firmly conclude that the current loads, on a long-term basis, are 

now exceeding the ecosystem-health threshold established for Northeast Creek, pushing the estuary into 

the “degrading” category, even though the combined loading rate for the monitored tributary watersheds 

was 3.1 kg/ha/yr (the threshold value is 2.2 kg/ha/yr). The length of time needed for the estuary to begin

to degrade once conditions have in fact crossed that threshold also is unknown. However, it cannot be 

ruled out that conditions are, in fact, degrading as land is converted from forested and agricultural uses 

to rural homes and house lots. The lack of any monitoring within the estuary itself reduces the ability to 

draw definite conclusions about the ecological condition of the estuary at the present time (2012).

Summary and Conclusions

This study of nitrogen (N) loading in the tributaries of the Northeast Creek (NEC) estuary was 

begun in 2008 and continued until 2011, and was conducted by the U.S. Geological Survey (USGS) in 

cooperation with the National Park Service and Acadia National Park (ANP) and the Town of Bar

Harbor, Maine. The study builds on an earlier USGS study of nitrogen loads conducted from 1999 to 

2000.

The objectives of this report are to (1) present recent (2010) nitrogen concentrations and loads, 

and to document changes in nitrogen loading to Northeast Creek from 2000 to 2010; (2) evaluate the 

effects of increased amounts of rural residential housing within the watershed since 2000, by using load 

estimates based on the streamflow measurements and water-quality analyses (referred to here as 

28
“measured loads”), as well as predictions from the land-use-based simulations by use of export 

coefficients (referred to here as “predicted loads”); (3) evaluate the effectiveness of the decision support 

system (DSS) in predicting nitrogen loads; and (4) improve understanding of the variability in nitrogen 

loading, and the factors that contribute to that variability.

Stream samples for nitrogen species were collected approximately monthly and concurrent 

instantaneous streamflow measurements were made in four tributaries to the NEC estuary. Samples 

were analyzed for total nitrogen, ammonia-nitrogen (NH4-N), and nitrite-plus-nitrate-N (NO2+NO3-N), 

and organic nitrogen was calculated from measured values of other nitrogen constituents. Loads were 

estimated using the LOADEST software developed by the USGS, and total annual loads and loading 

rates were calculated, with 95-percent confidence intervals on the estimates, for the period generally 

centered around 2010, which are referred to as “the 2010 loads.” The 2010 load estimates represent an 

annual average for the sampling period 2008 to 2011. The 2010 loads were compared to those 

determined in the earlier USGS study by using the same methods used to estimate loads on the basis of 

sampling in 1999–2000, which are referred to as “the 2000 loads.”

The concentrations of inorganic N species (NH4-N and NO2+NO3-N) in samples from 2008 to 

2011 ranged from 0.0014 to 0.7 milligrams per liter (mg/L) of NH4-N and from 0.003 to 0.17 mg/L of 

NO2+NO3-N. Total N concentrations ranged from 0.09 to 1.4 mg/L (filtered) and from 0.08 to 

1.49 mg/L (unfiltered). Old Mill Brook had the lowest concentrations for all the nitrogen species and the 

Upper Stony Brook site had the highest concentrations of almost all the nitrogen species. Samples from 

Upper Stony Brook had higher concentrations than those from the Lower Stony Brook site for some 

constituents (except NO2+NO3-N and NH4-N), indicating that processes in Hamilton Pond, such as 

nitrification and mineralization, may be converting organic N to inorganic forms, and denitrification 

may be reducing the total amount of N exiting the pond.

The concentrations of total N (unfiltered) in water samples from the four tributaries sampled in 

the 1999–2000 study were compared to the concentrations at those same sites during the 2008–11 study.

Overall, the concentrations of total N do not appear different between the two studies. Nonparametric 

two-sample t-tests found no significant differences (at an α of 0.05) between the two datasets for each 

tributary.

LOADEST was used to develop regression equations relating constituent concentration to daily 

mean streamflow for NO2+NO3-N and total N for each tributary stream (NH4-N loads and organic 

nitrogen loads could not be estimated because of the large number of censored values in the NH4-N 

dataset). The daily mean streamflow datasets required for load estimation were developed by using the 

MOVE.1 technique for each tributary stream, and using the USGS streamflow gage at Otter Creek as 

the index gage for all of the daily mean streamflow estimations for the 2008–11 study.

Average annual loads for total N ranged from 376 kg/yr in French Hill Brook to 3,120 kg/yr at 

the Lower Stony Brook site. Annual estimated loads for NO2+NO3-N ranged from 13 kg/yr in French 

Hill Brook to 190 kg/yr at the Upper Stony Brook site. Chemical transformations in Hamilton Pond may 

be responsible for the lower estimated NO2+NO3-N load downstream at the Lower Stony Brook site, 

150 kg/yr. Adjusting for watershed size, the annual loading rates from the different sites vary 

considerably, from 1.9 kilograms per hectare per year (kg/ha/yr) in Aunt Betsey’s Brook to 4.2 kg/ha/yr 

at the Lower Stony Brook site. For the NEC tributary watersheds combined, the loading rate for the 

2010 time period was 3.1 kg/ha/yr.

The 95-percent confidence intervals for the total N estimates range from ± 15 to 24 percent of 

the estimated load. Because concentrations of NO2+NO3-N generally have greater variability than those 

of total nitrogen, with a larger number of censored values, the 95-percent confidence intervals for the 

NO2+NO3-N load estimates represent a much greater percentage of the estimated loads, ranging from

29
± 22 to 180 percent. A simulation tool or DSS has been used for several years by Acadia National Park 

and the Town of Bar Harbor and to conduct simulations of total nitrogen loads in the Northeast Creek 

watershed. The DSS uses land use and nitrogen export coefficients to predict how increases in rural 

housing developments and other land-use changes could be affecting the ecological health of the 

Northeast Creek estuary. On the basis of a 2.6-percent change in the land-use distribution from 2000 to 

2010, the DSS predicted that the nitrogen loading to the estuary would increase by 7 percent. The 

predicted loading rate for 2010, averaged over the tributary watersheds, was 2.12 kg/ha/yr. This loading 

rate is just below the threshold of 2.2 kg/ha/yr identified as the level at which local estuaries may 

undergo a transition from a “healthy” to a “degrading” condition.

The changes in nitrogen loading to the estuary based on sampling, however, show a much 

greater increase than predicted by the DSS. The 2010 loading rates based on the sampling showed an 

overall increase from 1.9 ( in 2000) to 3.1 (in 2010) kg/ha/yr for the NEC tributaries (a 66-percent 

increase over the 2000 loads). This value is well above the 2.2-kg/ha/yr threshold for continued estuary 

health. The average loading rates and total average annual load increased for all the tributaries sampled 

in both the 2000 and 2010 studies. Although the measured concentrations of nitrogen sampled during 

the two time periods were not significantly different statistically, the total loads estimated for the 2010 

study were much higher than those estimated for the 2000 study. In all but the French Hill Brook 

tributary, where loads increased 16 percent, the 2010 loads were between 68 and 84 percent higher than 

the earlier loads.

The final goal of the study was to determine what factors, other than land use, that contribute to 

changes in nitrogen loading. Previous research by other investigators on natural variability in nitrogen 

export from northern-latitude forested watersheds has identified a number of factors that relate to the 

natural interannual variability in N export, the primary ones being variations in climate—specifically 

rainfall, streamflow (sometimes evaluated as runoff in other studies), and temperature. These climatic 

variables have been shown to relate to biotic and abiotic processes in soils that control N export, such as 

microbial activity, mineralization, and nitrification, as well as direct transport. The climatic conditions 

in the study area during the 2008–11 time period, when most of the sampling for this loading study was 

conducted, were overall much wetter than normal. Streamflow in one gaged river in the same part of the 

state was in the upper 83rd, 87th, and 97th percentiles of the long-term record of flow (going back to 

1949) during 3 of the 4 sampling years. In contrast, climatic conditions during the 2000 loading study 

were very close to average for this part of Maine, indicating that a part of the increase in measured total 

N loading could be a result of the wetter climatic conditions during the second study and may not be 

related to a long-term trend caused by changes in land use. The measurement data, although providing 

the most realistic assessment of instream conditions determining nitrogen loads, could be improved by 

the addition of continuous streamflow monitoring at one or more locations in the watershed, and yearround water-quality sampling.

Although climatic conditions could be responsible for much of the increase in measured total N 

loading to the NEC estuary beyond the DSS-predicted loads, the available data do not allow for 

partitioning the increase into specific amounts from different causes. A conservative approach would be 

to assume that the DSS is correct in predicting that the change in land use that occurred between 2000 

and 2010 likely contributed to some of the observed increase in total N loading from the NEC 

tributaries.

As long as forested areas in the NEC watershed continue to be converted to roads, driveways, 

and house lots, a shift toward higher N loading to the estuary will likely continue. If land uses that 

contribute a greater amount of total N are converted to land uses that contribute less, the loading from 

those parcels could decrease. The urban/suburban land-use category is itself quite heterogeneous, as it is 

30
comprised of lawns, houses with septic systems (of various ages), roads, driveways, and commercial 

areas (which may or may not also have septic systems). If any of those specific uses within the 

urban/suburban category were to reduce their N export, that could also act to mitigate the effect of 

converting additional forested land use to residential land use.

Future efforts to enhance the DSS could include a more in-depth analysis of the urban/suburban 

land-use category, including the possibility of dividing it into two categories based on the age of and 

(or) the septic technology used for rural residential housing. Any upgrades to the DSS tool will need to 

be undertaken with consideration of the power of the available data to support the calibration of 

additional variables or to recalibrate the land-use coefficients with the same or redefined land-use 

categories.

The DSS tool in use by Acadia National Park and the Town of Bar Harbor likely will continue to 

be useful in testing alternative development patterns, up to and including build-out scenarios, or in 

testing any community-wide targeted actions to reduce N export from specific land-use categories.

However, results of this study indicate that the tool has limitations in predicting loading from a specific 

time period, at least in part because interannual hydrologic variability is not incorporated. Although the 

DSS was originally designed as a software tool using ArcViewTM, which is no longer a supported GIS 

software package, the calculations it performs can be recreated with modern GIS software for continued 

future use, or for refinement of its functions.

Because no current monitoring program provides any information about trends in actual 

estuarine ecological condition, the increase in N loading from 2000 to 2010 cannot be compared to any

changes in the observed health of the estuary.

The 2008–11 field investigation of nitrogen loading has contributed to the understanding of

variability of total N loading to NEC, and to the evaluation of the possibilities and limitations of landuse-based computer predictions of loads. Evaluations of spatial and temporal variability in measured 

nitrogen concentrations and loads indicate that long-term monitoring of this important ecological habitat

is essential for understanding natural variability in nitrogen loads, temporal trends in concentrations and 

loads, the effects of streamflow variability, and the effects of changing land use and other factors that 

affect estuarine health. Ongoing monitoring needs that will support local managers in their efforts 

include continuous streamflow measurements and water-quality monitoring in freshwater tributaries to 

support load estimation and trend analysis, and coordinated monitoring of conditions in the estuary that 

determine estuarine health. Reliable and timely data and related interpretations will continue to provide 

the kind of information that can lead to effective collaboration among local governments, ANP, and 

other interested organizations to protect the NEC ecosystem.

References Cited

Andersson, L., and Lepistö, A., 2000, Annual variability of nitrogen concentrations and export from 

forested catchments: A consequence of climatic variability, sampling strategies, or human 

interference?: Boreal Environment Research, v. 5, p. 221–233.

Carter, R.W., and Davidian, J., 1968, General procedure for gaging streams: U.S. Geological Survey 

Techniques of Water-Resources Investigations, book 3, chap. A6, 13 p.

Clark, G.M., Mueller, D.K., and Mast, M.A., 2000, Nutrient concentrations and yields in undeveloped 

stream basins of the United States: Journal of the American Water Resources Association, v. 36, 

no. 4, p. 849–860.

Creed, I.F., and Band, L.E., 1998, Export of nitrogen from catchments within a temperate forest: 

Evidence for a unifying mechanism regulated by variable source area dynamics: Water Resources 

Research, v. 34, no. 11, p. 3,105–3,120.

31
Creed, I.F., and Beall, F.D., 2009, Distributed topographic indicators for predicting nitrogen export 

from headwater catchments: Water Resources Research, v. 45, p. W10407.

Culbertson, C.W., Huntington, T.G., and Caldwell, J.M., 2007, Nutrient enrichment in estuaries from 

discharge of shallow ground water, Mt. Desert Island, Maine: U.S. Geological Survey Scientific 

Investigations Report 2007–5188, 34 p.

Goodale, C.L., Aber, J.D., and McDowell, W.H., 2000, The long-term effects of disturbance on organic 

and inorganic nitrogen export in the White Mountains, New Hampshire: Ecosystems, v. 3, p. 433–

450.

Guntenspergen, G.R., Baldwin. A.H., Hogan, D.M., Neckles, H.A., and Nielsen, M.G., 2009, Valuing 

urban wetlands—modification, preservation, and restoration, in McDonnell, M.J., Breuste, Jurgen, 

and Hahs, A.K., eds., Ecology of cities and towns—a comparative approach: New York, Cambridge 

University Press, chap. 29, p. 503–520.

Guntenspergen, G.R., Neckles, H.A., Kopp, B., Nielsen, M.G., and Rohweder, J., 2005, Modeling 

estuarine response to changing land use in a coastal watershed: Mt. Desert Island, Maine: 26th 

Meeting of the Society of Wetland Scientists, Charleston, South Carolina, June 5–10, 2005.

Helsel, D.R., and Hirsch, R.M., 1992, Statistical methods in water resources: Amsterdam, the 

Netherlands, Elsevier Science Publishers, 522 p.

Hirsch, R.M., 1982, A comparison of four streamflow record extension techniques: Water Resources 

Research, v. 18, no. 4, p. 1,081–1,088.

Huntington, T.G., Culbertson, C.W., and Duff, J.H., 2011, Denitrification rates in marsh soils and 

hydrologic and water quality data for Northeast Creek and Bass Harbor Marsh watersheds, Mount 

Desert Island, Maine: U.S. Geological Survey Open-File Report 2011–1252, 30 p.

Huntington, T.G., Culbertson, C.W., and Duff, J.H., 2012, Ambient and potential denitrification rates in 

marsh soils of Northeast Creek and Bass Harbor Marsh watersheds, Mount Desert Island, Maine: U.S. 

Geological Survey Scientific Investigations Report 2012–5166, 40 p.

Kahl, S., Manski, D., Flora, M., and Houtman, N., 2000, Water Resources Management Plan, Acadia 

National Park, Mount Desert Island, Maine: National Park Service, Bar Harbor, Maine, April 2000, 

5 sections [variously paged].

Kinney, E. H., and Roman, C.T., 1998, Response of primary producers to nutrient enrichment in a 

shallow estuary: Marine Ecology Progress Series, v. 163, p. 89–98.

Lovett, G.M., Weathers, K.C., and Arthur, M.A., 2002, Control of nitrogen loss from forested 

watersheds by soil carbon: Nitrogen ratio and tree species composition: Ecosystems, v. 5, p. 712–718.

Neckles, H.A., Kopp, B.S., Nielsen, M.G., and Guntenspergen, G.R., 2003, Autotrophic responses to 

nutrient loadings in a Ruppia-dominated estuary: Current status and future projections: Abstracts of 

the 17th Biennial Conference of the Estuarine Research Federation, September 14–18, 2003, Seattle, 

Wash.

Nielsen, M.G., 2002a, Estimated quantity of water in fractured bedrock units on Mt. Desert Island, and 

estimated ground-water use, recharge, and dilution of nitrogen in septic waste in the Bar Harbor area, 

Maine: U.S. Geological Survey Open-File Report 02–435, 45 p.

Nielsen, M.G., 2002b, Water budget for and nitrogen loads to Northeast Creek, Bar Harbor, Maine: U.S. 

Geological Survey Water-Resources Investigations Report 02–4000, 32 p. 

Nielsen, M.G., Caldwell, J.M., Culbertson, C.W., and Handley, Michael, 2002, Hydrologic data 

collected in small watersheds on Mount Desert Island, Maine, 1999–2000: U.S. Geological Survey 

Open-File Report 02–416, 47 p.

Nielsen, M.G., and Kahl, S.K., 2007, Nutrient export from watersheds on Mt. Desert Island, Maine, as a 

function of land use and fire history: Environmental Monitoring and Assessment, v. 126, p. 81–96.

32
National Oceanic and Atmospheric Association, National Climatic Data Center, 2013, Annual/seasonal 

normals data for Bar Harbor-Acadia National Park climate station, 1981–2010: accessed January 16, 

2013, at http://www.ncdc.noaa.gov/cdo-web/datasets/NORMAL_ANN/locations/ZIP:04609/detail.

Rantz, S.E., and others, 1982, Measurement and computation of streamflow: U.S. Geological Survey 

Water-Supply Paper 2175, 2 v., 631 p.

Rohweder, J.J., Fox, T.J., Guntenspergen, G.R., Nielsen, M.G., and Neckles, H.A., 2004, Acadia 

National Park nutrient load and estuarine response decision support system—user's manual: 

unpublished final report for the National Park Service, Acadia National Park, 74 p.

Runkel, R.L., Crawford, C.G., and Cohn, T.A., 2004, Load Estimator (LOADEST): A Fortran program 

for estimating constituent loads in streams and rivers: U.S. Geological Survey Techniques and 

Methods, book 4, chap. A5, 69 p.

Schiff, S.L., Devito, K.J., Elgood, R.J., McCrindle, P.M., Spoelstra, J., and Dillon, P., 2002, Two 

adjacent forested catchments: Dramatically different NO3

- export: Water Resources Research, v. 38, 

no. 12, p. 1,292.

Town of Bar Harbor, 2007, Comprehensive Plan Update, Bar Harbor, Maine, June 2007: Town of Bar 

Harbor, Maine, 2007, 5 sections [variously paged], 8 app., accessed November 13, 2012, at

http://www.barharbormaine.gov/document/0001/1411.pdf.

Willard, K.W.J., DeWalle, D.R., Edwards, P.J., and Schnabel, R.R., 1997, Indicators of nitrate export 

from forested watersheds of the mid-Appalachians, United States of America: Global Biochemical 

Cycles, v. 11, no 4, p. 649–656.

33
Prepared by the Pembroke and West Trenton Publishing 

Service Centers.

For more information concerning this report, contact:

Office Chief

U.S. Geological Survey

New England Water Science Center

Maine Office

196 Whitten Road

Augusta, ME 04330

dc_me@usgs.gov

or visit our Web site at:

http://me.water.usgs.gov
Nielsen—Changes in Nitrogen Loading to the Northeast Creek Estuary, Bar Harbor, Maine, 2000 to 2010—Open-File Report 2013–1256 

ISSN 2331-1258 (online) 

http://dx.doi.org/10.3133/ofr20131256