Prepared in cooperation with New York State Department of State

Water-Resources Investigations Report 02-4255

U.S. Department of the Interior

U.S. Geological Survey

Trends in Nitrogen Concentration and Nitrogen 

Loads Entering the South Shore Estuary Reserve from 

Streams and Ground-Water Discharge in Nassau and 

Suffolk Counties, Long Island, New York, 1952-97
Cover photograph: Narrow stretch of water in the South Shore 

Estuary Reserve where you can see across to the other side. The 

photo was taken from Smith Point Marina just west of Smith 

Point bridge. (Photograph by Jack Monti, Jr.; USGS)
i

Trends in Nitrogen Concentration and Nitrogen Loads 

Entering the South Shore Estuary Reserve from Streams 

and Ground-Water Discharge in Nassau and Suffolk 

Counties, Long Island, New York, 1952-97

By Jack Monti, Jr. and Michael P. Scorca

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 02-4255

Prepared in cooperation with 

NEW YORK STATE DEPARTMENT OF STATE 

Coram, New York

2003
ii

U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. Geological Survey

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes only 

and does not constitute endorsement by the U.S. Geological Survey.

______________________________________________________________________

For additional information Copies of this report may be

write to: purchased from:

U.S. Geological Survey U.S. Geological Survey

2045 Route 112, Bldg. 4 Branch of Information Services

Coram, NY 11727 Box 25286, Bldg. 810

Denver, CO 80225-0286
Contents iii

CONTENTS

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

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Purpose and scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Previous studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Physiography and hydrogeology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Ground-water system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Effects of urbanization on streamflow and ground water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Historic changes in base flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Effects of sanitary sewers, storm sewers, and recharge basins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Method and approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Stream data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Discharge data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Nitrogen-concentration data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Estimation of annual stream loads. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Ground-water data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Discharge data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Nitrogen-concentration data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Estimation of ground-water loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Factors affecting load calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Nitrogen concentrations in streams and ground water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Geographic trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Nassau County. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Suffolk County. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Seasonal trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Long-term trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Ground water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Geographic trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Temporal trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Trends with depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Nitrogen loads entering the South Shore Estuary Reserve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Annual stream loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Geographic trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Temporal trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Ground-water loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Shallow-ground-water system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Deep-ground-water system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Total nitrogen load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

References cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

FIGURES

1. Map showing location of study area and South Shore Estuary Reserve, Long Island, N.Y. . . . . . . . . . . . . . . . . . . . . . 3

2. Map showing locations of 13 selected streams that discharge to the South Shore Estuary Reserve from Nassau 

and Suffolk Counties, N.Y. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
iv Contents

3. Generalized section showing hydrogeologic units and generalized directions of ground-water flow on the north 

and south shores of Long Island, N.Y. (Modified from Nemickas and others, 1989, fig. 8). . . . . . . . . . . . . . . . . . . . 6

4. Map showing partial model grid and locations of upper layer (layer 1) constant-head cells representing the South 

Shore Estuary Reserve in the U.S. Geological Survey Long Island regional ground-water flow model . . . . . . . . . . 13

5. Vertical section showing model hydrogeologic geometry along column 50, constant-head cells in layer 1, and 

simulated shallow- and deep-ground-water discharge entering the South Shore Estuary Reserve (SSER) . . . . . . . . 14

6. Map showing locations of 192 wells on the south shore of Nassau and Suffolk Counties, N.Y. for which at least 

one sample was available with a calculated total nitrogen value during 1952-97. . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

7. Map showing location of the 1-mile-wide zone along the south shore of Nassau and Suffolk Counties, N.Y., and 

the five geographic areas into which it was divided for comparison of geographic trends in total nitrogen and 

nitrate concentrations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

8. Boxplots showing distribution of total nitrogen concentration in 13 selected streams on the south shore of 

Nassau and Suffolk Counties, N. Y., 1971-97.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

9. Boxplots showing distribution of nitrogen concentration for summer (April through September) and winter 

(October through March) during 1971-97 at 13 south shore streams in Nassau and Suffolk Counties, N.Y. . . . . . . 19

10. Graphs showing total nitrogen concentrations of 13 selected streams on the south shore of Nassau and Suffolk 

Counties, N.Y., 1971-97. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

11. Boxplots showing distribution of nitrogen concentration in streams on the south shore of Nassau and Suffolk 

Counties, N.Y. during selected time periods: A. In the nine streams in sewered areas. B. In the four streams in 

unsewered areas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

12. Boxplots showing distribution of total nitrogen concentrations in samples from streams and shallow wells, and 

nitrate concentrations in samples from deep wells in the five geographic areas within 1 mile of the south shore 

of Nassau and Suffolk Counties, N.Y., 1952-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

13. Boxplots showing distribution of nitrogen concentrations in samples from shallow wells in Areas A through E 

along south shore of Nassau and Suffolk Counties, N. Y., for four selected time periods . . . . . . . . . . . . . . . . . . . . . 25

14. Graphs showing annual mean discharge, mean nitrogen concentration, and mean nitrogen load calculated for 11 

selected south-shore streams that discharge to the South Shore Estuary Reserve from Nassau and Suffolk 

Counties, N.Y., 1972-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

15. Boxplots showing distribution of nitrogen load calculated in 11 selected streams on the south shore of Nassau and 

Suffolk Counties, N.Y. 1972-97. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

16. Bar chart showing combined nitrogen load from four streams in Nassau County and seven in Suffolk County, 

N.Y. that discharge to the South Shore Estuary Reserve during 1972-97. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Tables

1. Generalized description of principal hydrogeologic units underlying Long Island, N.Y. . . . . . . . . . . . . . . . . . . . . . . 7

2. Drainage area, period of record, mean discharge, and water-sampling data for the 13 selected streams that 

discharge to the South Shore Estuary Reserve, Long Island, N.Y. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3. Maximum, median, and minimum total nitrogen concentrations for the 13 selected streams that discharge to the South 

Shore Estuary Reserve from Nassau and Suffolk Counties, N.Y. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4. Simulated annual mean discharge from shallow and deep ground water to South Shore Estuary 

Reserve, Nassau and Suffolk Counties, N.Y., based on 1983 steady-state hydrologic conditions . . . . . . . . . . . . . . . 13

5. Time periods used in temporal-trend analysis of nitrogen concentrations in streams of Nassau and Suffolk 

Counties, N.Y., 1952-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

6. Number of samples collected from selected shallow and deep wells within 1 mile of the south shore of Nassau 

and Suffolk Counties, N.Y., and maximum, median, and minimum concentrations of nitrogen at shallow wells

and of nitrate at deep wells, 1952-97. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

7. Minimum, maximum, and median total nitrogen concentrations in shallow and deep ground water in Areas A 

through E of South Shore Estuary Reserve, Nassau and Suffolk Counties, N.Y., 1952-97. . . . . . . . . . . . . . . . . . . . . 23

8. Geographic grouping of the 13 selected streams that discharge to the South Shore Estuary Reserve, Long 

Island, N.Y. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

9. Estimated annual nitrogen loads entering the South Shore Estuary Reserve from 11 streams on the south shore 

of Long Island, N.Y., 1972-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Contents v

10. Median concentration and annual load of nitrogen entering the South Shore Estuary Reserve from shallow and 

deep ground water in Nassau and Suffolk Counties, N.Y., as calculated from concentrations at wells within 1 

mile of the shore, 1952-97. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

11. Total annual nitrogen load entering the South Shore Estuary Reserve from streams and ground water on the south 

shore of Long Island, N.Y., 1972-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATIONS

Multiply By To Obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

square mile (mi2) 2.59 square kilometer (km2)

Flow

foot per day (ft/d) 0.3048 meter per day (m/d)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

Mass

ton 907.2 kilogram (kg)

Chemical Concentration

milligrams per liter (mg/L)

Other Abbreviations Used

nitrogen (N)

kilograms per year (kg/yr) 

million gallons per year (Mgal/yr)

cubic meters per year (m3

/yr) 

year (yr)

second (s) 

less than (<)

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)--a 

geodetic datum derived from a general adjustment of the first-order level nets of the United States and Canada, 

formerly called Sea Level Datum of 1929.
This page has been left blank intentionally.
Abstract 1

Trends in Nitrogen Concentration and Nitrogen 

Loads Entering the South Shore Estuary Reserve 

from Streams and Ground-Water Discharge in 

Nassau and Suffolk Counties, Long Island, New 

York, 1952-97

By Jack Monti, Jr. and Michael P. Scorca

ABSTRACT

The 13 major south-shore streams in Nassau 

and Suffolk Counties, Long Island, New York 

with adequate long-term (1971-97) water-quality 

records, and 192 south-shore wells with 

sufficient water-quality data, were selected for 

analysis of geographic, seasonal, and long-term 

trends in nitrogen concentration. Annual total 

nitrogen loads transported to the South Shore 

Estuary Reserve (SSER) from 11 of these 

streams were calculated using long-term 

discharge records. Nitrogen loads from shallow 

and deep ground water also were calculated 

using simulated ground-water discharge of 

1968-83 hydrologic conditions.

Long-term declines in stream discharge 

occurred in East Meadow Brook, Bellmore Creek 

and Massapequa Creek in response to extensive 

sewering in Nassau County. The smallest longterm annual discharge to the SSER was from the 

westernmost stream, Pines Brook, which is in an 

area in which the water table has been lowered by 

sewers since 1952. The three largest average 

annual discharges to the SSER were from the 

Connetquot River, Carlls River, and Carmans 

River in Suffolk County; the discharges from each 

of these streams were at least twice those of the 

other streams considered in this study. 

Total nitrogen concentrations in streams show 

a geographic trend with a general eastward 

increase in median total nitrogen concentration in 

Nassau County and a decreasing trend from 

Massapequa Creek eastward into Suffolk County. 

Total nitrogen concentrations in streams generally 

are lowest during summer and highest in winter as 

a result of seasonal fluctuations in chemical 

reactions and biological activity. The greatest 

seasonal difference in median total nitrogen 

concentration was at Carlls River with values of 

3.4 and 4.2 mg/L (milligrams per liter) as N 

during summer (April through September) and 

winter (October through March), respectively. 

Streams affected by the completion of sewer 

districts show long-term (1971-97) trends of 

decreasing total nitrogen concentration and 

streams showing an increase in total nitrogen 

concentration are in unsewered areas with 

increased urbanization.

Discharges from shallow ground water (upper 

glacial aquifer) and deep ground water (upper part 

of Magothy aquifer) were simulated from a 

ground-water-flow model calibrated to steadystate (1968-83) conditions. Simulated discharges 

from shallow-ground-water system in Nassau 

County were 10,700 Mgal/yr (million gallons per 

year) or 40,500,000 m3/yr (cubic meters per year), 

and those from Suffolk County were 52,300 

Mgal/yr or 198,000,000 m3

/yr. Discharges from 

deep-ground-water system in Nassau County 

were 4,900 Mgal/yr or 18,500,000 m3

/yr, and 
2 Trends in Nitrogen Concentration and Nitrogen Loads Entering the South Shore Estuary Reserve from Streams 

and Ground-water Discharge in Nassau and Suffolk Counties, Long Island, New York, 1952-97

those in Suffolk County were 12,700 Mgal/yr or 

48,200,000 m3/yr. 

Ground-water concentrations of nitrogen 

decrease with depth and from west to east. The 

shallow ground water median nitrogen 

concentration for each county was determined 

using 1,155 samples collected at 167 shallow 

wells (125 feet deep or less) within 1 mile of the 

shore. The deep ground water median nitrate 

concentration (nitrate represented almost all of 

the total nitrogen) for each county was 

determined using 112 samples collected at 25

deep wells (greater than 125 feet deep) within 

1 mile of the shore. The median nitrogen 

concentration for the shallow and median nitrate 

concentration for the deep ground water in 

Nassau County were 3.85 and 0.15 mg/L as N, 

during 1952-97; the corresponding concentrations 

for Suffolk County were 1.74 and <0.10 (less than 

0.10) mg/L as N, during 1952-97.

Nitrogen loads discharged from streams to the 

SSER for each year during 1972-97 were 

calculated as the annual total nitrogen 

concentration multiplied by the annual discharge. 

These values were calculated only for the seven 

streams for which sufficient data were available. 

The largest long-term (1972-97) average annual 

nitrogen load from Carlls River was 104 ton/yr or 

94,300 kg/yr—about twice that of Connetquot 

River (54 ton/yr or 48,900 kg/yr) and over three 

times that of Carmans River (33 ton/yr or 29,900 

kg/yr). The smallest annual mean nitrogen load 

was from Pines Brook, which has the lowest 

annual mean discharge of all streams analyzed. 

The nitrogen load carried to the SSER by 

ground-water discharge in shallow-groundwater system in Nassau and Suffolk Counties 

was calculated as the simulated discharge for 

each county multiplied by the respective median 

nitrogen concentration, and loads from deepground-water system were calculated as the 

simulated discharge for each county multiplied 

by the respective median nitrate concentration. 

All discharges were obtained from the U.S. 

Geological Survey’s Long Island ground-waterflow model. The resultant nitrogen loads 

discharged to the SSER from shallow ground 

water were 172 ton/yr (156,000 kg/yr) from 

Nassau County and 380 ton/yr (345,000 kg/yr) 

from Suffolk County; equaling 552 ton/yr entering 

the SSER. Those from deep ground water were 

3 ton/yr (2,700 kg/yr) from Nassau County and 

<0.5 ton/yr (480 kg/yr) from Suffolk County; 

equaling about 3.5 ton/yr entering the SSER.

The sum of both stream loads and groundwater loads results in the total load to the SSER. 

The largest calculated total nitrogen load entering 

the SSER from both streams and ground water 

occurred in 1979 with a total load of 1,260 ton/yr 

(1,140,000 kg/yr). The smallest calculated 

nitrogen load entering the SSER occurred in 1995 

with a total load of 725 ton/yr (658,000 kg/yr).

INTRODUCTION

The South Shore Estuary Reserve (SSER) of Long 

Island, N.Y. is a series of shallow tidal bays enclosed 

by barrier islands and connected to the Atlantic Ocean 

by various inlets. The SSER extends about 80 mi 

(129 km) eastward from the Reynolds Channel in 

Nassau County to the eastern end of Shinnecock Bay 

in Suffolk County (fig. 1). The SSER’s shoals, 

mudflats, aquatic vegetation, and wetlands (tidal and 

freshwater) provide a rich habitat for fish and wildlife. 

The SSER is used for recreational activities such as 

swimming, boating, and fishing, as well as for 

commercial harvesting of shellfish. 

Freshwater entering the SSER from precipitation, 

streams, and ground water contains nitrogen in 

concentrations that vary temporally and spatially. 

Nitrogen is an essential nutrient for plant growth, but 

in excessive amounts it can give rise to algal blooms 

that consume oxygen when the algae die and 

decompose (Long Island Sound Study, 1998). The 

resulting low dissolved oxygen concentrations, known 

as hypoxia, can affect plant and animal populations 

adversely and is a growing concern in the SSER. 

Nitrogen enters the SSER from streams, ground water, 

atmospheric deposition (wetfall and dryfall), and the 

Atlantic Ocean. These sources can have elevated 

concentrations (above background levels) as a result of 

human activities and products, particularly sewage, 

and agricultural and domestic fertilizers.

In 1993, the Long Island South Shore Estuary 

Reserve Act established the SSER and called for the 

Reserve’s protection and prudent management. The 
3

5 10 MILES

0 5 10 KILOMETERS

0

NEW YORK

LONG ISLAND SOUND

SUFFOLK NASSAU

QUEENS

KINGS

WESTCHESTER

CONNECTICUT

ROCKLAND

ATLANTIC OCEAN

South Fork

North Fork

BRONX NEW YORK

NEW

JERSEY

RICHMOND

NEW YORK

Study Area

East River

New York 

Bay

Barrier Island

Reynolds Channel

SSER

Shinnecock

Bay

Regional 

Ground-Water Divide

Base modified from U.S. Geological Survey, 1:100,000

40 

45'

41 

41 

15'

74 73 30' 73 72 30' 72 o o o o o

o

o

o

SOUTH SHORE ESTUARY RESERVE 

EXPLANATION

STUDY AREA 

REGIONAL GROUND -WATER DIVIDE 

Act created a 23-member Council and charged it with 

preparation of a comprehensive management plan for 

the Reserve. The Council adopted the completed 

comprehensive management plan in April 2001. The 

plan identifies actions necessary to improve the 

Reserve’s water and living resources, public access, 

and the estuary-related economy.

As a part of the SSER study, the U.S. Geological 

Survey (USGS) began an investigation in 1998, in 

cooperation with the New York State Department of 

State (NYSDOS), to refine estimates of nitrogen 

loading (mass per year) to the SSER. The USGS 

combined ground- and surface-water-quality data from 

the USGS National Water Information System 

(NWIS) database with simulated ground-water 

discharge and with measured stream-discharge data to 

obtain estimates of nitrogen loading (mass per year) 

from the south shore streams and ground water to the 

SSER. Except for concentrations, data are presented in 

both English and metric units for the ease of use 

among the public and scientific readers.

Purpose and Scope

This report (1) describes the physiography and 

hydrogeology of the SSER study area and the methods 

of data compilation, (2) presents geographic, seasonal, 

and long-term (1971-97) trends of total nitrogen 

concentrations in the 13 major south-shore streams 

that discharge to the SSER, in Nassau and Suffolk 

Counties and geographic, temporal, and depth trends 

in shallow and deep ground water that discharge to the 

Figure 1. Location of study area and South Shore Estuary Reserve, Long Island, N.Y. 

Introduction
4 Trends in Nitrogen Concentration and Nitrogen Loads Entering the South Shore Estuary Reserve from Streams 

and Ground-water Discharge in Nassau and Suffolk Counties, Long Island, New York, 1952-97

south shore of these counties, and (3) presents the 

estimated annual mean nitrogen loads discharged from 

11 of these streams during 1972-97, and the estimated 

nitrogen loads discharged to the SSER from aquifers, 

as represented by data from 192 wells. The report also 

discusses the effects of urbanization and sewering on 

nitrogen loads entering the SSER.

Total nitrogen loads from stream- and groundwater discharge were calculated if both discharge and 

water-quality data were available. The SSER contains 

two areas for which nitrogen loads could not be 

calculated because discharge data were 

unavailable—the barrier islands and the South Fork. 

Discharge and nitrogen loads from these locations 

could be estimated through ground-water modeling 

but this was beyond the scope of the study.

Previous Studies

Various studies address the concentrations of 

nitrogen in ground water and surface water on Long 

Island, include Perlmutter and Koch (1975), Katz and 

others (1980), Ragone and others (1981), Bleifuss 

and others, (1998), and Scorca and Monti (2001). 

Water-quality differences between areas representing 

selected land uses on Long Island are reported by 

LeaMond and others (1992), Eckhardt and others 

(1989), Eckhardt and Stackelberg (1995), and 

Pearsall (1996). 

The Long Island Regional Planning Board (1978) 

gave preliminary estimates of nonpoint-source 

nitrogen loading from Long Island’s south shore to the 

SSER and provided a description of water-quality 

conditions in the SSER, indicating the amounts of 

contaminants from differing sources. Scorca and 

Monti (2001) calculated estimates of nitrogen loads 

entering the Long Island Sound from North-Shorestream and ground-water discharge, and compared 

nitrogen loads from areas characterized by differing 

land uses north of the regional ground-water divide.

Various studies have used other methods to 

compute loading to Chesapeake Bay and other 

coastal bays in Maryland and Virginia. Bachman and 

Phillips (1996) sampled base flow of streams from 

basins with differing characteristics on a seasonal 

basis and estimated the loads from calculated 

median instantaneous yields. Phillips and others 

(1999) evaluated nitrate loads from ground water in 

differing hydrogeomorphic regions and the residence 

time of ground water within the Chesapeake Bay 

watershed before it discharges to streams. Bachman 

and others (1998) related base-flow nitrate loads to 

hydrogeomorphic regions. Dillow and Greene 

(1999) estimated the nitrate loading to coastal bays 

of Maryland. 

Acknowledgments

Thanks are extended to Rodney McNeil, John 

Herring and Dennis Mildner of the NYSDOS for their 

assistance and cooperation during this project. Thanks 

also are extended to William McBrian of the Suffolk 

County Department of Public Works, Sanitation 

Engineering Division, and Ronald Green of the 

Suffolk County Management Information Services for 

providing maps that show the extent of sewered areas 

in Suffolk County, and to James Ennis of the Nassau 

County Department of Public Works, Division of 

Sanitation and Water Supply, for providing a map that 

shows the sewered areas in Nassau County. 

PHYSIOGRAPHY AND HYDROGEOLOGY

Long Island is bounded along its western shore by 

the East River and New York Bay, on the north by 

Long Island Sound, and on the east and south by the 

Atlantic Ocean (fig. 1). The eastern part of Long 

Island includes two large peninsulas that are referred 

to as the North and South Forks, which are poorly 

connected and have no effect on its shallow and deep 

ground water from the main body of Long Island. A 

detailed physiographic description of Long Island is 

presented by Franke and McClymonds (1972). 

The SSER study area (550 mi2) extends from the 

regional ground-water divide to the south shore of 

Nassau and Suffolk Counties (fig. 1); its western 

boundary is the Queens-Nassau County border, and 

its eastern boundary coincides with that of the USGS 

Long Island regional ground-water-flow model 

(Buxton and Smolensky, 1999). Kings and Queens 

Counties and the North and South Forks are 

excluded from analysis because either stream- or 

ground-water discharge enters a different estuary or, 

as is the case for the South Fork, the discharge data 

were not available. 

The south shore of Long Island is characterized 

by marshes and bays (fig. 2). Stream channels on the 

south shore generally are longer than those on the 

north shore because the main topographic drainage 
5

73o 30' 73o 72o 30'

42o

52'

30"

40o

45'

40o

37'

30"

Base modified from U.S. Geological Survey, 1:24,000

 Pines Brook STREAMFLOW-GAGING STATION AND NAME 

EXPLANATION

SEWER-DISTRICT BOUNDARY 

5 10 MILES

0 5 10 KILOMETERS

0

Regional Ground-Water Divide

NASSAU

COUNTY

QUEENS

COUNTY

SUFFOLK

COUNTY

ATLANTIC OCEAN

Sewer

District 2

Sewer

District 3

Southwest

Sewer District

Bellmore East Creek Meadow

Brook Massapequa Creek

Santapogue Creek

Carlls

River

Sampawams Creek

Penataquit Creek

Champlin Creek Connetquot River

Patchogue River Swan

River

Carmans

River

Pines

Brook

divide is north of the center of the island. The north 

shore consists of steep cliffs and narrow beaches; the 

southern part of the island is a gently sloping 

outwash plain.

Long Island is underlain by unconsolidated 

sediments of Late Cretaceous and Pleistocene age that 

were deposited on a southeastward-dipping bedrock 

surface. The hydrogeologic setting of Long Island has 

been described in detail by Suter and others (1949), 

Jensen and Soren (1971, 1974), and Smolensky and 

others (1989). A summary of the principal 

hydrogeologic units underlying the study area is given 

in table 1; a generalized north-south hydrogeologic 

section of the study area is given in figure 3.

The upper Pleistocene deposits, which form the 

uppermost principal geologic unit on Long Island, 

include glacial morainal sediments, till, outwash, and 

glaciolacustrine sediments that were deposited during 

the Wisconsinan glaciation of the Pleistocene series. 

This unit consists mostly of moderately to well-sorted 

sand and fine gravel, which is highly permeable in 

most places but locally contains fine-grained, poorly 

permeable layers of silt or clay. The saturated part of 

the upper Pleistocene deposits forms the upper glacial 

aquifer, which contains the water table throughout 

most of Long Island and is the source of base flow to 

streams. The effects of eustatic sea-level changes 

during the Pleistocene are shown by various lagoonal 

and shallow-bay clays along southern Long Island; the 

most prominent of these is the Gardiners Clay 

(Smolensky and others, 1989). 

Beneath the Pleistocene deposits is a sequence of 

Cretaceous-aged units overlying bedrock. The 

northern limits of the Cretaceous units are irregular 

and variable as a result of erosion by streams during 

the Tertiary period and Pleistocene series, and by 

glacial scour during the advances of the Pleistocene 

continental ice sheets; and the northern extent of these 

is onshore in some areas (Stumm, 2001). The southern 

extent of these units generally extend far offshore 

beneath the SSER and Atlantic Ocean. The Monmouth 

Group (Monmouth greensand) unconformably 

overlies the Matawan Group and Magothy Formation. 

The clay and silty sand material that forms the 

Monmouth Group was deposited by a transgressing 

sea. The Matawan Group and Magothy Formation, 

which forms the Magothy aquifer, is undifferentiated 

and is the main source of drinking-water supply on 

Long Island. Beneath the Magothy Formation is the 

Raritan Formation, which consists of an unnamed clay 

member (the Raritan confining unit) and the Lloyd 

Sand Member (Lloyd aquifer), which overlies 

bedrock. The Raritan confining unit confines water in 

the underlying Lloyd aquifer.

Figure 2. Locations of 13 selected streams that discharge to the South Shore Estuary Reserve from Nassau and Suffolk 

Counties, N.Y. 

Physiography and Hydrogeology
6 Trends in Nitrogen Concentration and Nitrogen Loads Entering the South Shore Estuary Reserve from Streams 

and Ground-water Discharge in Nassau and Suffolk Counties, Long Island, New York, 1952-97

Figure 3. Generalized section showing hydrogeologic units and generalized directions of ground-water flow on 

the north and south shores of Long Island, N.Y. (Modified from Nemickas and others, 1989, fig. 8.)

SEA

LEVEL

400

200

600

800

1,000

1,200

400

200

1,400

1,600

1,800

2,000

2,200

2,400

SALTWATER INTERFAC

? E

?

40

80

80

70

70

60

60

50

50

40

30

20

10

40 30 20

Long Island

Sound Atlantic Ocean

South

Shore

Estuary

Reserve

LLOYD

AQUIFER

RARITAN

 CONFINING 

 UNIT

MAGOTHY

AQUIFER

GARDINERS CLAY

UPPER GLACIAL AQUIFER

WATER

TABLE

REGIONAL GROUNDWATER DIVIDE

SALTY GROUND WATER

EQUIPOTENTIAL LINE, IN FEET

 ABOVE SEA LEVEL

INFERRED PATH OF GROUND-

 WATER FLOW

BEDROCK

EXPLANATION

Note: Position of the saltwater

 interface is estimated

Vertical scale greatly exaggerated

NORTH SOUTH

FEET

0 1 234

01 2 34

MILES

KILOMETERS

(Scale is approximate)

40

30

20

10
7

Table 1. Generalized description of principal hydrogeologic units underlying Long Island, N.Y.

[Modified from Jensen and Soren, 1971, table 1; Smolensky and others, 1989, table 1; and Scorca and others, 1995.

ft, feet; ft/d, feet per day] 

System Series Geologic unit

Hydrogeologic

unit Description and water-bearing character

QUATERNARY

PLEISTOCENE

Upper Pleistocene

deposits

Upper Pleistocene

deposits

Gardiners Clay

Upper glacial 

aquifer

20 - foot clay1

Gardiners Clay

1Not shown in figure 3.

Mainly brown and gray sand and gravel deposits of moderately 

high horizontal hydraulic conductivity (270 ft/d average for 

Long Island); may also include deposits of clayey till and 

lacustrine clay of low hydraulic conductivity. Local units are 

the south-shore aquifer and confining unit, and the Smithtown 

clay unit. A major aquifer.

Grayish-green clay, silt, and sand; generally underlain and 

overlain by outwash deposits. Unit has lower hydraulic 

conductivity than outwash deposits and tends to confine water 

in the underlying aquifer.

Green and gray clay, silt, clayey and silty sand, and some 

interbedded clayey and silty gravel. Unit has low vertical 

hydraulic conductivity (0.001 ft/d) and tends to confine water 

in the underlying aquifer.

CRETACEOUS

UPPER CRETACEOUS

Monmouth Group

Matawan Group and

Magothy Formation,

undifferentiated

Monmouth 

greensand1

Magothy aquifer

Interbedded marine deposits of dark gray, olive-green, dark 

greenish-gray and greenish-black glauconitic and lignitic 

clay, silt and clayey and silty sand. Unit has low vertical 

hydraulic conductivity and tends to confine water in the 

underlying aquifer.

Gray, white, and brownish-gray, poorly to well-sorted, fine-tocoarse sand of moderate horizontal hydraulic conductivity 

(50 ft/d). Contains much interstitial clay and silt, and lenses of 

clay of low hydraulic conductivity. Generally contains sand 

and gravel beds of low to high conductivity in basal 100 to 

200 ft.

A major aquifer.

Unnamed clay member of 

the Raritan Formation

Raritan confining 

unit

Gray, black, and multicolored clay and some silt and fine sand. 

Unit has low vertical hydraulic conductivity (0.001 ft/d) and 

confines water in the underlying aquifer.

Lloyd Sand Member 

of the Raritan Formation

Lloyd aquifer White and gray fine-to-coarse sand and gravel of moderate 

horizontal hydraulic conductivity (40 ft/d) and some clayey 

beds of low hydraulic conductivity.

PALEOZOIC and

PRECAMBRIAN

Undifferentiated 

crystalline bedrock Bedrock Mainly metamorphic rocks of low hydraulic conductivity; considered to be the base of the ground-water-flow system.

Physiography and Hydrogeology
8 Trends in Nitrogen Concentration and Nitrogen Loads Entering the South Shore Estuary Reserve from Streams 

and Ground-water Discharge in Nassau and Suffolk Counties, Long Island, New York, 1952-97

Streams

Streams in the highly permeable glacial outwash 

deposits on the south shore of Nassau and Suffolk 

Counties are broad, straight, and shallow and 

generally follow the courses established by meltwater 

channels during glacial retreat (fig. 2). More than 100 

stream channels, typically less than 5 mi long, flow to 

the tide water that surrounds Long Island (Buxton and 

Smolensky, 1999). Stream discharge consist of two 

distinct components—base flow and stormflow or 

direct runoff. Base flow is the discharge from ground 

water that intercepts the stream channel; stormflow is 

the discharge caused by precipitation that falls on the 

stream or is redirected to the stream through storm 

runoff drains. Streams on Long Island function as 

ground-water drains; small changes in ground-water 

levels may cause large changes in stream discharge 

(Spinello and Simmons, 1992). Water that enters the 

ground-water system on Long Island either discharges 

to stream channels, is pumped by wells, or discharges 

to the tidal waters as ground-water discharge. 

Ground-Water System

Precipitation is the sole source of freshwater 

recharge to Nassau and Suffolk Counties. In 

undeveloped areas of Long Island, about 50 percent of 

the precipitation that falls is lost through 

evapotranspiration and direct runoff to streams; the 

other 50 percent infiltrates the soils and enters the 

ground-water system (Aronson and Seaburn, 1974; 

Franke and McClymonds, 1972). In urban areas the 

infiltration is decreased considerably by paved 

surfaces, as explained later. The hydrologic cycle on 

Long Island is discussed at length in Franke and 

McClymonds (1972), which includes an islandwide 

water budget. 

The Long Island ground-water system consists of 

two major components—the shallow-flow or shallowground-water system, which is associated with 

streams, and the regional-flow or deep-ground-water 

system. Precipitation entering the shallow-flow system 

(mainly the upper glacial aquifer) flows seaward and 

discharges directly to tidewater as shallow-groundwater discharge, or, if it falls within the contributing 

area of a stream, it seeps into the stream channel to 

become base flow. Water that enters the shallow-flow 

system north of the regional ground-water divide 

flows northward, and water that infiltrates south of the 

divide flows southward (fig. 3). Ground water that 

enters the flow system in the area just south of the 

regional ground-water divide moves downward 

through the upper glacial aquifer into the underlying 

Magothy and Lloyd aquifers, where it moves laterally 

southward, then upward to the SSER and Atlantic 

Ocean as deep-ground-water discharge; unless it is 

withdrawn from the aquifers by pumping wells. The 

flowpaths that ground water follows through the 

aquifer system, and the traveltime, also are affected by 

the hydraulic properties of the hydrogeologic units 

and by stresses, as well as those imposed by 

urbanization such as pumping.

Franke and Cohen (1972) and Buxton and Modica 

(1992) used cross-sectional (2-dimensional) groundwater-flow models to estimate the ground-water age. 

They estimated that ground water in the southern part 

of Long Island takes less than 100 years to move 

through most of the shallow-flow system and 

discharge along the south shore, although water that 

reaches the deepest parts of the shallow-flow system 

can take more than 400 years to reach the south shore. 

Human activities, such as pumping, can decrease this 

time, however. The ground-water age was not 

evaluated as part of this study because it would have 

required particle-tracking analysis, which was 

beyond the scope of the study.

Effects of Urbanization on Streamflow and 

Ground Water 

Continuous eastward development on Long Island 

throughout the 20th century has decreased the base 

flow of streams and increased the amount of 

stormflow. Factors that have contributed to this change 

are (1) ground-water pumping for water supply, (2) 

disposal of wastewater to sanitary sewers rather than 

to underground septic systems that return the water to 

the upper glacial aquifer, (3) construction of 

impervious surfaces, such as roads and parking lots, 

that produce storm runoff and prevent the infiltration 

of precipitation, and (4) construction of storm sewers 

that route storm runoff to streams. These practices 

have lowered ground-water levels substantially, even 

where artificial recharge basins mitigate the loss of 

stormwater (Franke, 1968; Sulam, 1979). 
9

Historic Changes in Base Flow

Ground water as base flow provided the main 

component of streamflow in Long Island streams 

under natural (pre-development) conditions. Base flow 

accounted for about 95 percent of annual streamflow 

(Franke and McClymonds, 1972); only about 5 

percent was derived from direct runoff, which 

consisted of precipitation falling directly on stream 

surfaces and overland runoff flowing into stream 

channels. Stream channels in some urban areas have 

been modified from their natural condition by culverts 

and storm sewers, which divert runoff from 

impervious surfaces to the stream and, thereby, 

increase the runoff component of total streamflow and 

decrease the base-flow component. 

Effect of Sanitary Sewers, Storm Sewers, and 

Recharge Basins

The continuous discharge of cesspool and septictank effluent to ground water in heavily developed 

parts of Nassau and Suffolk Counties eventually 

contaminated the upper glacial aquifer with nitrogen 

and other constituents. To prevent further aquifer 

contamination, sanitary-sewer and sewage-treatment 

systems were constructed to discharge treated 

wastewater to south-shore bays within the SSER and 

the Atlantic Ocean. The discharge of treated 

wastewater from sewage-treatment plants to offshore 

surface-water bodies rather than to the ground-water 

system has improved the ground-water quality but 

results in the removal of a large volume of water from 

the ground-water system (Spinello and Simmons, 

1992). This loss of water in sewered areas, particularly 

along the south shore of Nassau County, has caused 

water-table declines, decreased the base flow of 

streams, and decreased the rates of shoreline and 

subsea discharge (Franke, 1968; Pluhowski and 

Spinello, 1978; Reilly and others, 1983). The effects 

of sewer systems on surface-water and ground-water 

quality have been documented by Perlmutter and Koch 

(1972), Ku and Sulam (1979), Katz and others (1980) 

and Ragone and others (1981).

The conversion of land underlain by permeable 

soils to impervious surfaces (such as streets, 

sidewalks, and parking lots) that prevent infiltration of 

precipitation to the water table creates large volumes 

of street runoff, which flows into storm-sewer systems 

that discharge to nearby streams and tidewater or to 

artificial-recharge basins. Stormwater disposal 

through storm sewers that flow to streams and 

tidewater have three main hydrologic consequences: 

(1) stormwater does not replenish the ground-water 

system, (2) peak stream discharges during individual 

storms are larger and more variable than in 

undeveloped areas (Seaburn, 1969), and (3) the ratio 

of surface runoff to base flow in streams that receive 

street runoff has increased sharply (Spinello and 

Simmons, 1992). Storm runoff in many parts of Long 

Island is directed to artificial-recharge basins, which 

facilitate the infiltration of water to the ground-water 

system and mitigate undesirable changes in 

streamflow patterns. Ku and others (1992) estimated 

that ground-water recharge in areas with artificialrecharge basins is about 10 percent greater than in 

areas without them, which helps to maintain groundwater levels and stream base flow.

Previous investigators (Pluhowski and Spinello, 

1978; Spinello and Simmons, 1992) quantified the 

ratios of streamflow components (base flow and storm 

runoff) in selected streams on the south shore of 

Nassau County and southwestern Suffolk County. 

These ratios have been altered substantially in some 

locations by the diversion of stormwater to streams 

and by the reduction in base flow that has resulted 

from sanitary sewering. Results of hydrograph 

separation show that during 1976-85 the annual base 

flow of streams in heavily urbanized Nassau County 

averaged from 14 percent in western Nassau County to 

79 percent in eastern Nassau County; and from 88 

percent in western Suffolk County to 96 percent in an 

unsewered area of Suffolk County (Spinello and 

Simmons, 1992). These results indicate that the 

installation of sanitary sewers is one of the major 

causes of base-flow declines. The most extreme 

example is at Valley Stream, in southwestern Nassau 

County (fig. 2), in which all of the streamflow was 

derived from storm runoff, and none from base flow, 

for most of the time during 1976-85 (Spinello and 

Simmons, 1992). 

METHOD AND APPROACH

The methods described in this report are similar to 

those used in a previous estimation of nitrogen loads 

entering Long Island Sound (Scorca and Monti, 2001). 

The data consisted of stream discharges and nitrogen 

concentrations, and ground-water discharges from 

shallow- and deep-flow system and nitrogen 

concentrations. Stream-discharge data were obtained 

from stage-recording devices and ground-water 

Method and Approach
10 Trends in Nitrogen Concentration and Nitrogen Loads Entering the South Shore Estuary Reserve from Streams 

and Ground-water Discharge in Nassau and Suffolk Counties, Long Island, New York, 1952-97

discharges were obtained from the Long Island 

regional flow model (Buxton and Smolensky, 1999). 

Stream and ground-water nitrogen-concentration data 

were obtained from the NWIS database. The nitrogenconcentration data were grouped temporally and 

spatially for trends analyses.

Many samples represented in this data base have 

no stored value for total nitrogen. In the absence of a 

total nitrogen value, the concentrations of the four 

individual N components (nitrate, nitrite, ammonia, 

and organic nitrogen) were summed to obtain a total 

nitrogen value. The individual N-components 

concentrations (in mg/L as N) can represent either 

filtered or unfiltered methods. Unfiltered individual N 

values represent unfiltered raw samples, and filtered 

individual N values represent filtered samples. In the 

absence of an unfiltered N value for a given 

component, the filtered N value was used, if available. 

The minimum, median, and maximum total nitrogen 

values for groups of samples were calculated (table 3 

and table 6). Samples for which individual Ncomponents values were insufficient to provide a total 

nitrogen value were omitted from further analysis. 

Nitrogen loads from streams were calculated as 

the annual discharge multiplied by the annual nitrogen 

concentration. Nitrogen loads from shallow and deep 

ground-water systems were calculated as the median 

nitrogen and nitrate concentrations, respectively, 

multiplied by the simulated ground-water discharge 

from the respective county and aquifer.

The SSER contains two areas for which entering 

nitrogen loads could not be calculated because 

discharge data were unavailable—the barrier islands 

and the South Fork. Discharge and nitrogen loads 

from these locations could be estimated through 

ground-water modeling but this was beyond the scope 

of the study.

Stream Data 

Thirteen major streams along the south shore 

were selected for the study. The stream-discharge 

data used in this study were collected at stagerecording stations; stream nitrogen-concentration data 

collected at these stations were obtained from the 

NWIS database. 

The streams were, from west to east, Pines Brook, 

East Meadow Brook, Bellmore Creek, Massapequa 

Creek, Santapogue Creek, Carlls River, Sampawams 

Creek, Penataquit Creek, Champlin Creek, 

Connetquot River, Patchogue River, Swan River, and 

Carmans River (fig. 2). The first four streams are in 

Nassau County; the other nine are in western or central 

Suffolk County. All 13 streams originally were 

equipped with stage-recording devices, referred herein 

as continuous-recording stations; but by 2002, only 

five stations remain active—Carlls River, Sampawams 

Creek, Connetquot River, Swan River, and Carmans 

River. Continuous-recording stations generally have 

long records of discharge with concurrent waterquality data, allowing the calculation of loads for that 

time period. Two of the 13 streams—Santapogue 

Creek and Champlin Creek—do not have concurrent 

discharge and water-quality records; therefore, loads 

for these streams could not be calculated.

Discharge Data

Summary statistics of the discharge data and 

water-quality samples for the 13 streams are given in 

table 2. Connetquot River has two continuousrecording stations, herein referred to as Connetquot 

River base station and Connetquot River 

supplementary station. The discharge data from the 

two stations are summed in table 2; water-quality 

sample data are presented separately (table 2).

The discharge indicate that Connetquot River 

provided the largest discharge to the SSER (38.5 ft3

/s 

for water years1

 1944-2000) even though Carmans 

River has the largest drainage area to its continuousrecording station on the south shore (71 mi2

). The 

recorded discharge increases appreciably along a 

stream’s course because the streams contributing area 

increases moving downstream—the closer the location 

of measurement is to the stream’s mouth, the greater 

the discharge. The continuous-recording station at 

Carmans River is farther from the mouth than at 

Connetquot River and Carlls River; thus, the Carmans 

River discharge at that location is less than that of 

Connetquot River and Carlls River (fig. 2). Partialrecord discharge sites are points along a stream 

channel at which instantaneous measurements are 

taken. Data collected over 2.5 mi downstream from the 

continuous-recording station at a partial-record site on 

Carmans River (gaging-station number 01305040) 

indicate that this stream provides the largest discharge 

of all streams to the SSER (63 ft3

/s for water years 

1

A water year extends from October 1 of the preceding year 

through September 30 of the named year. 
11

1972-98). The discharge rate at the partial-record 

station on Carmans River is 2.6 times greater than the 

discharge at the continuous-recording station. If 

nitrogen concentrations were assumed to be equal at 

both stations then the load could be extrapolated to be 

2.6 times greater than those calculated for Carmans 

River. Water-quality data were not obtained at this 

partial-record-discharge station, however; therefore, 

no nitrogen load could be calculated.

Nitrogen-Concentration Data

The NWIS database contains water-quality data 

for samples collected from the 13 selected streams 

during 1966-97 (table 3); but only samples 

collected after 1971 contain sufficient nitrogen 

information for calculation of a total nitrogen value; 

hence, the concentrations given in table 3 represent 

only 1971-97. The following sections describe the 

overall geographic, seasonal and long-term trends 

of total nitrogen concentration observed in southshore streams.

Geographical, seasonal, and long-term (1971-97) 

trends in total nitrogen concentrations in each stream 

were evaluated from graphs of chemical 

concentrations in water samples plotted as a function 

of time and in boxplots (Chambers and others, 1983). 

Examination of discharge-related trends in base flow 

and storm runoff was beyond the scope of this study 

because stormflow water-quality data were 

unavailable. It is assumed that most samples were 

collected under base-flow conditions, although some 

samples reflect effects of storm runoff. 

Estimation of Annual Stream Loads

Annual nitrogen loads for the 13 selected streams 

for 1972-97 were calculated as the mean stream 

discharge for each calendar year multiplied by the 

mean total nitrogen concentration for that year; thus, 

the annual values presented herein for discharges and 

total nitrogen concentrations in streams represent 

calendar years rather than water years. Annual values 

were calculated for both stations on the Connetquot 

River. This method of computation does not fully 

Table 2. Drainage area, period of record, mean discharge, and water-sampling data for the 13 selected streams that 

discharge to the South Shore Estuary Reserve, Long Island, N.Y.

[Discharge data from Spinello and others (1997, 1998, 2001). mi2, square miles; ft3/s, cubic feet per second. Locations are shown 

in fig. 2.] 

Station name

Station 

number

Drainage area 

(mi2)

Discharge records Water-quality records

 Period

of

record

Mean 

discharge 

(ft3/s)

Total 

number of 

samples

Date of

first 

sample

Date of 

last 

sample

Pines Brook at Malverne 01311000 10.0 1937-1999

3.45 81 5/5/66 2/27/96

East Meadow Brook at Freeport 01310500 31.0 1937-2000 12.70 157 4/22/66 8/26/96

Bellmore Creek at Bellmore 01310000 17.0 1937-2000 8.78 102 4/22/66 5/22/96

Massapequa Creek at Massapequa01309500 38.0

1937-2000

9.77 156 5/11/66 6/16/97

Santapogue Creek at Lindenhurst01309000 7.0

1945-1969

4.16 120 5/4/66 1/30/97

Carlls River at Babylon 01308500 35.0 1945-2000 26.00 134 5/4/66 6/17/97

Sampawams Creek at Babylon 01308000 23.0 1945-2000 9.68 125 5/4/66 6/17/97

Penataquit Creek at Bay Shore 01307500 5.0 1945-1976 6.31 122 5/6/66 8/19/96

Champlin Creek at Islip 01307000 6.5 1945-1969 7.05 116 10/17/65 8/19/96

Connetquot River near Oakdale 01306500 24.0 1944-2000 38.50 1

1Base-station data and supplementary-station data combined for mean discharge value

 1272

2Samples collected at base station

5/6/66 8/19/96

 703

3Samples collected at supplementary station

2/14/67 6/17/97

Patchogue River at Patchogue 01306000 13.5 1948-1969, 

1974-1976 

20.40 109 5/6/66 8/12/96

Swan River at East Patchogue 01305500 8.6 1947-2000 12.30 114 5/11/66 6/18/96

Carmans River at Yaphank 01305000 71.0 1942-2000 24.00 311 5/11/66 6/18/97

Method and Approach
12 Trends in Nitrogen Concentration and Nitrogen Loads Entering the South Shore Estuary Reserve from Streams 

and Ground-water Discharge in Nassau and Suffolk Counties, Long Island, New York, 1952-97

account for effects of seasonal fluctuations, datacollection location, or discharge-related effects and, 

therefore, provides only a general estimate of annual 

streamflow load that may be lower than the actual 

load. For example, concentrations typically decrease 

during a storm through dilution, even though the 

increasing discharge might result in an increased load. 

Brown and others (1997) and Stockar (1994) observed 

changes in the concentrations of selected constituents 

during storms at the headwaters of East Meadow 

Brook (fig. 2) and often found the concentrations to be 

lower than those in base flow. 

Ground-Water Data 

Simulated ground-water discharges and nitrogen 

concentrations were used to calculate loads discharged 

to the SSER from the shallow and deep ground water 

in Nassau and Suffolk Counties. Wells less than 125 ft 

deep were used to characterize shallow ground water; 

wells from 126 to 300 ft deep were used to 

characterize deep ground water.

Discharge Data

Shallow- and deep-ground-water discharges were 

calculated separately because shallow ground water is 

more likely than deep ground water to reflect the 

effects of land use and the chemical concentrations of 

ground water that discharges to the SSER. The 

discharges from both depths were generated by the 

USGS Long Island regional ground-water-flow model 

for a steady-state simulation of 1968-83 (Buxton and 

Smolensky, 1999). 

The Long Island regional model was developed 

during the 1980’s using MODFLOW, a threedimensional finite-difference model (McDonald and 

Harbaugh, 1988) that was designed for assessment of 

the Long Island aquifer system and estimation of the 

effects of proposed water-management strategies. Four 

model layers were used to represent three major 

aquifers; the intervening confining units are 

represented implicitly. The model grid extends as far 

east as the ground-water-flow systems of the North 

and South Forks. The effects of the North and South 

Fork ground-water-flow systems on ground water in 

the main body of Long Island are negligible.

Discharge to the SSER from the shallow and deep 

ground water used in this study is represented in the 

model by flow into constant-head cells in the 

uppermost model layer along the south shore of 

Nassau and Suffolk Counties (fig. 4). Horizontal 

discharge into constant-head cells in the uppermost 

layer represents shallow ground water, that is younger 

Table 3. Maximum, median, and minimum total nitrogen concentrations for the 13 selected streams that discharge to the

South Shore Estuary Reserve from Nassau and Suffolk Counties, N.Y. 

[Concentrations are in milligrams per liter. Stream locations are shown in fig. 2.] 

Station name

Number of 

samples

Total nitrogen concentration1

1Values reported as less than the detection limit were included in the statistical analyses as half the detection limit.

Maximum Median Minimum

Pines Brook at Malverne 68 6.58 3.01 .4

East Meadow Brook at Freeport 120 15.9 3.92 .63

Bellmore Creek at Bellmore 83 21.5 5.7 .69

Massapequa Creek at Massapequa 123 16.1 7.4 .71

Santapogue Creek at Lindenhurst 99 15.3 4.4 .71

Carlls River at Babylon 113 6.51 3.83 1.01

Sampawams Creek at Babylon 102 9.6 4.36 .36

Penataquit Creek at Bay Shore 101 6.55 4.33 1.08

Champlin Creek at Islip 97 9.92 3.32 1.68

Connetquot River near Oakdale (Base) 108 2.9 1.82 .84

Connetquot River near Oakdale (Supplementary) 52 4.3 2.18 .89

Patchogue River at Patchogue 97 4.23 2.83 1.33

Swan River at East Patchogue 97 3.91 1.92 1.05

Carmans River at Yaphank 241 8.3 1.25 .53
13

and more likely to be affected by contamination from 

human activities than deep ground water. Deepground-water discharge is simulated by vertical flow 

into constant-head cells in the uppermost model layer 

representing the discharge from the upper part of the 

Magothy aquifer (layer 2) into the SSER (fig. 5).

Simulated discharges that flow horizontally 

(shallow-ground-water discharge) into selected 

constant-head cells from Nassau County totaled 

10,700 Mgal/yr (40,500,000 m3

/yr), and those from 

Suffolk County totaled 52,300 Mgal/yr (198,000,000 

m3

/yr) (table 4). The shallow-ground-water discharge 

represents about 78 percent of the ground water 

discharged from the south shore to the SSER. 

Simulated deep-ground-water discharges totaled 

4,900 Mgal/yr (18,500,000 m3/yr) from Nassau 

County and 12,700 Mgal/yr (48,200,000 m3/yr) from 

Suffolk County (table 4). Deep-ground-water 

discharge represents about 22 percent of the ground 

water discharged from the south shore to the SSER.

Nitrogen-Concentration Data

The NWIS database contains water-quality data 

for 192 wells within a 1-mi-wide zone along the 

southern coastline of the study area; 121 wells are in 

Nassau County, and 71 in Suffolk County (fig. 6). The 

data analysis included 1,267 samples collected during 

1952-97—1,155 from 167 shallow wells (0-125 ft in 

depth) and 112 from 25 deep wells (126-300 ft in 

depth). The shallow-well data were used to determine 

42o

52'

30"

40o

45'

40o

37'

30"

73o 30' 73o 72o 30'

Column 50

5 10 MILES

0 5 10 KILOMETERS

0

QUEENS

COUNTY

SUFFOLK

COUNTY

Regional GroundWater Divide

ATLANTIC OCEAN

CONSTANT-HEAD CELLS

EXPLANATION

MODEL CELLS 

Base modified from U.S. Geological Survey, 1:62,500

NASSAU

COUNTY

Figure 4. Partial model grid and locations of upper layer (layer 1) constant-head cells representing the South Shore Estuary 

Reserve in the U.S. Geological Survey Long Island regional ground-water flow model. (Vertical section of column 50 is shown 

in fig. 5.)

Table 4. Simulated annual mean discharge from shallow and deep ground water to South Shore 

Estuary Reserve, Nassau and Suffolk Counties, N.Y., based on 1983 steady-state hydrologic conditions

[Mgal/yr, million gallons per year; m3/yr, cubic meters per year] 

County

Shallow-ground-water discharge Deep-ground-water discharge

Mgal/yr m3/yr Percent of total Mgal/yr m3/yr Percent of total

Nassau 10,700 40,500,000 13 4,900 18,500,000 6

Suffolk 52,300 198,000,000 65 12,700 48,200,000 16

Total 63,000 238,500,000 78 17,600 66,700,000 22

Method and Approach
14 Trends in Nitrogen Concentration and Nitrogen Loads Entering the South Shore Estuary Reserve from Streams 

and Ground-water Discharge in Nassau and Suffolk Counties, Long Island, New York, 1952-97

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33

ROW

-2000

-1500

-1000

-500

Constant-head

cells Constant-head

cells

Shallow-ground-water discharge

Deep-ground-water discharge

SEA

LEVEL

EXPLANATION

UPPER GLACIAL AQUIFER

MAGOTHY AQUIFER

LLOYD AQUIFER

CONFINING UNIT- Gardiners Clay and Raritan

confining unit

MODEL LAYERS AT 

REPRESENTATIVE ROW

Layer 1

Layer 2

Layer 3

Layer 4

Confining unit

SSER

Vertical scale greatly exaggerated

100

Bottom of model

FEET

N S

Figure 5. Vertical section showing model hydrogeologic geometry along column 50, constant-head cells in layer 1, 

and simulated shallow- and deep-ground-water discharge entering the South Shore Estuary Reserve (SSER). 

(Location of column 50 is shown in fig. 4.)
15

73o 30' 73o 72o 30'

42o

52'

30"

40o

45'

40o

37'

30"

Base modified from U.S. Geological Survey, 1:62,500

5 10 MILES

0 5 10 KILOMETERS

0

NASSAU

COUNTY

QUEENS

COUNTY

SUFFOLK

COUNTY

Regional Ground-Water Divide

Sewer

District 2

Sewer

District 3 Southwest

Sewer District

1-MILE ZONE

ATLANTIC OCEAN

Well location

EXPLANATION

the median total nitrogen concentrations in the upper 

glacial aquifer, and the deep-well samples were used 

to determine median nitrate concentration (rather than 

as total nitrogen concentrations because the ammonia, 

organic-nitrogen, and nitrite components in the great 

majority of samples were so small that nitrate 

represented almost all of the total nitrogen) in the deep 

ground water (upper part of the Magothy aquifer) for 

Nassau and Suffolk Counties.

A geographic information system (GIS) was used 

to delineate the 1-mi-wide zone along the south shore 

(fig. 7). Ground water within this zone includes that 

which discharges directly into the SSER by horizontal 

and vertical flow. Median total nitrogen concentrations 

for each county were calculated from water-quality 

data collected (during 1952-97) at 192 wells selected 

within the 1-mi-wide zone. Five geographic areas 

within this zone also were delineated by a GIS and 

were used to spatially group wells and sample data 

(fig. 7). Three of the geographic areas (A,B, and C) 

are in sewered areas and two (D and E) are in 

unsewered areas. The geographic, temporal, and depth 

trends in total nitrogen concentrations in each 

geographic area are depicted in boxplots, as discussed 

later in the report.

Estimation of Ground-Water Loads

Nitrogen loads entering the SSER from ground 

water on Long Island’s south shore were calculated as 

groundwater discharges from each county (generated 

by the model) multiplied by the median total nitrogen 

concentration for that county. The loads from shallow 

ground water were calculated as the median total 

nitrogen concentrations for Nassau and Suffolk 

Counties, multiplied by the shallow-ground-water 

discharges for each county; the loads from the deep 

ground water were calculated as the median nitrate 

concentrations—rather than as total nitrogen 

concentrations—multiplied by the deep-ground-water 

discharges for each county.

Factors Affecting Load Calculations

The nitrogen loads to the SSER from both groundwater and stream discharge that are calculated in this 

report will assist with estuary budget calculations. As 

with any data analysis, the data quality and approach 

that are used in this analysis to estimate loads are 

affected by various factors.

 Although the nitrogen data represents all 

available data in the USGS database over the last 50 

years, they reflect changes in data collection, and 

sampling and analytical techniques that have occurred 

over that time. The historical data were collected for 

purposes other than this study and were obtained at 

sites not related to this investigation. Wells have been 

installed and abandoned over time for many different 

Figure 6. Locations of 192 wells on the south shore of Nassau and Suffolk Counties, N.Y., for which at least one sample was 

available with a calculated total nitrogen value during 1952-97.

Method and Approach
16 Trends in Nitrogen Concentration and Nitrogen Loads Entering the South Shore Estuary Reserve from Streams 

and Ground-water Discharge in Nassau and Suffolk Counties, Long Island, New York, 1952-97

5 10 MILES

0 5 10 KILOMETERS

0

73o 30' 73o 72o 30'

42o

52'

30"

40o

45'

40o

37'

30"

NASSAU

COUNTY

QUEENS

COUNTY

Regional Ground-Water Divide

SUFFOLK

COUNTY

Sewer

District 2

Sewer

District 3 Southwest

Sewer District

Base modified from U.S. Geological Survey, 1:62,500

ATLANTIC O

1-MILE ZONE CEAN

A

B

C

D

E

reasons, which could include water-quality or 

-quantity problems, damage to the well, changes in 

data-collections network, changes in ownership. In 

addition, sampling frequency differs widely from site 

to site and through time.

 Generally, on Long Island, stream discharge 

increases with distance downstream; therefore, if the 

concentration of nitrogen in the stream were to remain 

the same along the length of the stream channel, then 

the load that would reach the SSER should be greater 

than the load calculated at upstream sites. The 

continuous-gaging stations at most streams were 

installed at the furthest downstream non-tidal site, but 

could be further upstream as a result of access 

limitations. Thus, the load of a stream at its mouth, 

where it reaches the SSER, could be larger than the 

calculated values presented in this report. 

 Although over 100 streams discharge to the 

SSER, stream loads were calculated for 11 major 

streams with continuous-record discharge stations 

and water-quality records. The large majority of the 

approximately 90 remaining streams are smaller and 

have lower discharges than the gaged streams, but 

the loads from these streams are not accounted for in 

this study. 

 The Long Island regional model was developed 

for a different purpose than the objective of this study. 

The simulated ground-water discharges used in the 

model were based on 1968-83 hydrologic conditions, 

which was a period of long-term average and relatively 

stable hydrologic conditions as compared to other 

periods. In order to simulate changes in hydrologic 

conditions, the inputs to the regional model could be 

changed and the resulting changes in the simulated 

ground-water discharges could be determined.

In addition, only 20 streams that discharge to the 

SSER were represented in the Long Island regional 

model. The discharge from the other (approximately 

80) south-shore streams, which were not quantified in 

the model, were included effectively in the simulated 

shallow-ground-water discharge.

NITROGEN CONCENTRATIONS IN 

STREAMS AND GROUND WATER

Estimating nitrogen loads to the SSER requires 

both a flux and a concentration to calculate a load. The 

changes that have occurred along the south shore of 

Long Island such as waste management and urban 

growth have certain effects on the inputs used to 

calculate load. This section describes the trends in 

nitrogen concentrations in streams and ground water 

with focus on changes in waste management and 

urban development.

Streams

Trends in nitrogen concentrations (geographic, 

seasonal and long-term (1971-97)) are discussed in the 

following sections. They are presented here to give the 

reader an understanding of how concentrations varied 

under different flow conditions.

Figure 7. Location of the 1-mile-wide zone along the south shore of Nassau and Suffolk Counties, N.Y., and the five 

geographic areas (A-E) into which it was divided for comparison of geographic trends in total nitrogen and nitrate 

concentrations.
17

PinesBrookEast MeadowBrookBellmoreCreekMassapequaCreekSantapogueCreekCarllsRiverSampawamsCreekPenataquitCreekChamplinCreekConnetquotRiverPatchogueCreekSwanRiverCarmansRiver

10 15 20 25

TOTAL NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER AS N

NASSAU COUNTY SUFFOLK COUNTY

SEWERED AREA UNSEWERED AREA

0 5

n = 68

n = 120

n = 83

n = 123

n = 99

n = 113

n = 102

n = 101

n = 97

n = 160n = 97n = 97

n = 241

x

x

x

x

x

x

x

x

o

x

x

x

o

x

x

x

o

x

x

xx

x

o

x

o

o

o

x

x

x x

xxxx

o

n=30 Number of values 

EXPLANATION 

x

x

x

o

o

o

Upper quartile (75th percentile)

Median (50th percentile)

Lower quartile (25th percentile)

Data value(s) exceeding

upper quartile plus 3 times

the interquartile range

Data value(s) exceeding upper

quartile plus1.5 times the

interquartile range but less than

the upper quartile plus 3 times

the interquartile range 

Largest data values less than or

equal to the upper quartile plus

1.5 times the interquartile range

Smallest data values greater than

or equal to the upper quartile

minus 1.5 times the interquartile 

range

Geographic Trends

The geographic distribution of total nitrogen data 

collected during 1971-97 is presented in boxplots 

(fig. 8). Nitrogen data for both stations at Connetquot 

River were combined. The boxplots indicate a general 

eastward increase in median total nitrogen 

concentration in Nassau County streams, and a 

decreasing trend from Massapequa Creek eastward 

into Suffolk County. Patchogue River, in Suffolk 

County deviated slightly from this decreasing trend.

Nassau County

The trend in Nassau County is due primarily to the 

effects of sewer systems. Nassau County generally 

was a rural community with a population of 400,000 

before World War II but grew into a highly 

suburbanized community with a population of 

1,400,000 by 1970 (Sulam and Ku, 1977). Sewering of 

residential communities, Sewer District 2 (SD2) in 

southwestern Nassau County (fig. 2) began in 1952, 

and sewer hookups continued until the 70-mi2

 system 

was completed in 1964. Sewering of residential 

communities, Sewer District 3 (SD3) in southeastern 

Nassau County (fig. 2) began in 1974 and sewer 

hookups continued until the 105-mi2

 system was 

completed in 1988. Both systems took 12 to 14 years 

to complete, but the start of wastewater treatment in 

SD2 preceded that in SD3 by 20 years. The stream 

data analyzed in this investigation start in 1971, which 

is about 20 years after SD2 started treating wastewater 

and just before SD3 began treatment.

The ground-water-contributing area to Pines 

Brook, the westernmost stream, is within SD2; that of 

East Meadow Brook is within both sewer districts, and 

those of Bellmore and Massapequa Creeks are within 

SD3. As expected, the boxplots (fig. 8) show less 

variability in the total nitrogen distribution at Pines 

Brook than at East Meadow Brook, Bellmore Creek or 

Massapequa Creek because the only change in 

Figure 8. Distribution of total nitrogen concentration in 13 selected streams on the south shore of Nassau and Suffolk 

Counties, N.Y., 1971-97.

Nitrogen Concentrations in Streams and Ground Water
18 Trends in Nitrogen Concentration and Nitrogen Loads Entering the South Shore Estuary Reserve from Streams 

and Ground-water Discharge in Nassau and Suffolk Counties, Long Island, New York, 1952-97

sewering in Nassau County during the period 

represented (1971-97) was in SD3 (fig. 8). Many of 

the early samples from East Meadow Brook, Bellmore 

Creek, and Massapequa Creek had high total nitrogen 

concentrations; these most likely are a reflection of 

background conditions before sewering. The median 

total calculated nitrogen concentration for Pines 

Brook, East Meadow Brook, Bellmore Creek and 

Massapequa Creek during 1971-97 are 3.0, 3.9, 5.7, 

and 7.4 mg/L as N, respectively; this eastward increase 

reflects the later completion of sewering in SD3.

Suffolk County

The trend in Suffolk County is most likely related 

to the pattern of eastward urban growth on Long 

Island. The sewer district in southwestern Suffolk 

County, locally called the Southwest Sewer District 

(SWSD), started treating wastewater in residential 

communities in 1982 (fig. 2) and was completed in 

1989. This service area contains five 

streams—Santapogue Creek, Carlls River, 

Sampawams Creek, Penataquit Creek and Champlin 

Creek. The northern part of drainage areas of Carlls 

River and Sampawams Creek (35 and 23 mi2

, 

respectively) probably are outside the SWSD service 

area and intercept water from unsewered areas. The 

median total nitrogen concentration of these five 

streams (Santapogue Creek, Carlls River, Sampawams 

Creek, Penataquit Creek, and Champlin Creek) during 

1971-97 are similar— 4.4, 3.8, 4.4, 4.3, and 3.3 mg/L 

as N, respectively (fig. 8). 

The village of Patchogue, east of SWSD, provides 

sewage treatment for some of its residents, but all 

other parts of Suffolk County beyond SWSD are 

served by residential septic systems. Ground water 

beneath densely populated areas in eastern Suffolk, as 

in Nassau and western Suffolk Counties, is 

characterized by elevated (above background levels) 

total nitrogen concentrations. The streams that drain 

these unsewered areas are Connetquot, Patchogue, 

Swan, and Carmans Rivers. The median (1971-97) 

total nitrogen concentrations for the two Connetquot 

River stations and Swan River is about 2 mg/L as N. 

Patchogue River, has the highest median total nitrogen 

concentration of the four streams is 2.8 mg/L as N; the 

probable cause for the higher concentration is the 

community was developed by the 1950’s and urban 

growth continued within the stream’s drainage area. 

Carmans River had the lowest median total nitrogen 

concentration of all 13 streams analyzed (1.25 mg/L as 

N, during 1971-97).

Seasonal Trends

Concentrations of total nitrogen in streamwater 

samples during 1971-97 were divided into two 

groups—summer and winter—for each stream. The 

summer group included samples collected from April 

through September, and the winter group consisted of 

samples collected from October through March. Data 

collected at the two Connetquot River stations were 

grouped as one site. The seasonal differences in 

nitrogen concentration in each stream are depicted in 

boxplots (fig. 9). 

Seasonal fluctuations in total nitrogen 

concentrations are caused by chemical reactions and 

biological activity in the streams. Summer values are 

lower than winter values as a result of biological 

uptake of N during the growing season. Although most 

samples probably were collected during normal flow 

conditions, some samples might show effects of storm 

runoff, which can contain nitrogen from fertilizers or 

animal wastes (Brown and others, 1997). The median 

concentrations for winter are higher than those for 

summer in all streams, but the difference is small and 

is difficult to discern in some of the boxplots (fig. 9). 

The greatest seasonal difference in median total 

nitrogen concentration was at Carlls River with values 

of 3.4 and 4.2 mg/L as N during summer (April 

through September) and winter (October through 

March), respectively.

Long-Term Trends

The eight streams whose total nitrogen 

concentration have been lowered by the completion of 

sewer districts (Pines Brook, East Meadow Brook, 

Bellmore Creek, Massapequa Creek, Santapogue 

Creek, Carlls River, Sampawams Creek and 

Penataquit Creek) show clear long-term trends of 

decreasing total nitrogen concentration since 1971 

(fig. 10). A quantitative comparison with pre-sewer 

conditions was not possible because no data from 

before 1972 were available, but Sulam and Ku (1977) 

analyzed nitrate trends during 1910-75 using two 

abandoned infiltration galleries—one near 

Massapequa Creek, and the other near Bellmore 

Creek. The results indicate that nitrate concentrations 

increased during 1910-40 and 1941-60, but decreased 

during 1961-75. The decreasing trend may reflect the 
19

Pines Brook

Summer Winter

n = 33

n = 35

x

x

x

x 0

1

2

3

4

5

6

7

8

East Meadow Brook

Summer Winter

n = 61

n = 59 x

x

o

x

0

5

10

15

20

Bellmore Creek

Summer Winter

n = 42

n = 40

x

0

5

10

15

20

25

Massapequa Creek

Summer Winter

n = 64

n = 59

0

5

10

15

20

Santapogue Creek

Summer Winter

n = 50

n = 49

xx

o

0

5

10

15

20

Carlls River

Summer Winter

n = 59

n = 54

x

x

1

2

3

4

5

6

7

8

Sampawams Creek

Summer Winter

n = 50

n = 52

o

x

x

0

2

4

6

8

10

12

Champlin Creek

Summer Winter

n = 53

n = 44

o

o

x

x

o

x

0

2

4

6

8

10

12

Penataquit Creek

Summer Winter

n = 51

n = 50 x

o

x

x

1 o

2

3

4

5

6

7

8

Swan River

Summer Winter

n = 48

x n = 49 xx

o

1

2

3

4

Carmans River

Summer Winter

n = 131

n = 110

x

xx x

x

o

0

2

4

6

8

10

Patchogue River

Summer Winter

n = 48 n = 49

1

2

3

4

5

Connetquot River (Combined)

Summer Winter

n = 86

n = 74

x

x

0

1

2

3

4

5

NASSAU COUNTY STREAMS SUFFOLK COUNTY STREAMS 

TOTAL NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER AS N

n=30 Number of values 

EXPLANATION 

x

x

x

o

o

o

Upper quartile (75th percentile)

Median (50th percentile)

Lower quartile (25th percentile)

Data value(s) exceeding upper quartile plus

3 times the interquartile range

Data value(s) exceeding upper quartile plus

1.5 times the interquartile range but less 

than the upper quartile plus 3 times the 

interquartile range 

Largest data values less than or equal to the 

upper quartile plus 1.5 times the interquartile range

Smallest data values greater than or equal to the 

upper quartile minus 1.5 times the interquartile 

range

Figure 9. Distribution of nitrogen 

concentration for summer (April 

through September) and winter 

(October through March) during 

1971-97 at 13 south shore streams 

in Nassau and Suffolk Counties, 

N.Y. (Locations are shown in fig. 2.) 

Nitrogen Concentrations in Streams and Ground Water
20 Trends in Nitrogen Concentration and Nitrogen Loads Entering the South Shore Estuary Reserve from Streams 

and Ground-water Discharge in Nassau and Suffolk Counties, Long Island, New York, 1952-97

0

2

4

0

2

4

6

0

2

4

6

0

2

4

6

8

10

12

14

0

2

4

6

8

10

12

14

0

2

4

6

8

10

12

14

0

2

4

6

8

0

2

4

6

8

10

0

2

4

0

2

0

2

4

6

0

2

0

2

4

6

8

10

Patchogue River

TOTAL NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER

Carlls River

70 75 80 90 95 85

Year

97

Pines Brook

70 75 80 85 90 95

Year

97

East Meadow Brook

15.9

Bellmore Creek 21.50

Massapequa Creek

16.06

Sampawams Creek 9.60

70 75 80 85 90 95

Year

97

Champlin Creek

Base station Connetquot River

Supplementary station

Swan River

Penataquit Creek

Carmans River 8.30

70 75 80 85 90 95

Year

97

Santapogue Creek 15.30

Figure 10. Total nitrogen concentrations of 13 selected streams on the south shore of Nassau and Suffolk Counties, 

N.Y., 1971-97. (Locations are shown in fig. 2.)
21

decreasing rate of population growth or the effect of 

increased recharge after the drought of 1962-66. 

Four of the streams that were unaffected by 

sewers—Connetquot River, Patchogue River, Swan 

River, and Carmans River— show an increase in 

total nitrogen concentration since 1972, probably as 

a result of eastward urbanization over time. The 

Champlin Creek data show no discernible longterm trends, even though the station is in SWSD. 

The change that probably had the greatest 

effect on nitrogen concentrations in Long Island 

ground water was the installation of sewers. This 

period of change was divided into six phases, 

described in table 5. The stream data were grouped 

accordingly for comparison of nitrogen 

concentration in streams in the sewered areas with 

those in the unsewered areas. The first two time 

periods were omitted because only the stream data 

collected after 1971 contain sufficient nitrogen 

information for calculation of a total nitrogen 

concentration. The distribution of nitrogen in each 

time period for streams in sewered and unsewered 

areas is depicted in boxplots of figure 11.

Ground Water

The 167 shallow wells within 1 mi of the south 

shore provided 1,662 samples, of which 1,155 had 

sufficient information for calculation of total nitrogen 

concentration (table 6A). The 25 deep wells within 

1 mi of the shore provided 193 samples, of which 112 

had values of total nitrate concentration. 

The median total nitrogen concentration for 408 

samples collected at 104 shallow wells in Nassau 

County (during 1952-97) was 3.85 mg/L as N; values 

ranged from 0.008 mg/L to 40.1 mg/L as N; the 

median total nitrogen concentration for 747 samples 

collected at 63 shallow wells in Suffolk County 

(during 1952-97) was 1.74 mg/L as N; the values 

ranged from <0.01 mg/L as N to 21.6 mg/L as N 

(table 6B). 

The median nitrate concentration for 58 samples 

collected at 17 deep wells in Nassau County (during 

1952-97) was 0.15 mg/L as N; values ranged from 

<0.01 mg/L to 12.61 mg/L as N; the corresponding 

concentration for Suffolk County was <0.10 mg/L as 

N; values ranged from <0.01 mg/L to 4.93 mg/L as N 

(table 6B). The nitrogen concentrations, although 

based on sparse data, were sufficient for a rough 

computation of spatial, temporal, and depth trends.

Geographic Trends 

The water-quality data from the 192 wells were 

grouped into five geographic areas (fig. 7). Area A is 

SD2, area B is SD3, area C is SWSD, area D is east of 

SWSD and west of Carmans River, and area E is east 

of Carmans River. Summary statistics for shallow and 

deep wells within the five areas are given in table 7. 

The distribution of total nitrogen data collected from 

streams, shallow wells and deep wells during 1952-97 

are presented in boxplots (fig. 12). The boxplots 

indicate an eastward increase in median total nitrogen 

concentrations in shallow-wells in Nassau County 

(from Area A to Area B), and a decreasing trend 

eastward into Suffolk County (from Area C through 

Area E), similar to the geographic trends observed in 

the stream data. The deep-well data in figure 12 

indicate uniformly low concentrations except in the 

easternmost area (Area E), where the median nitrate 

concentration exceeded 3 mg/L as N. Eleven of the 16 

samples with nitrate concentrations greater than 

3 mg/L as N were from a single well in Area E and, 

thus, probably are not a true representation of the deep 

ground water within that area, but rather a site-specific 

occurrence. More data collection would be needed to 

confirm this conclusion, however.

Temporal Trends

The shallow-well data that were grouped into 

geographic areas A through E were regrouped to 

Table 5. Time periods used in temporal-trend analysis 

of nitrogen concentrations in streams of Nassau and 

Suffolk Counties, N.Y., 1952-97.

[SD2, SD3, Nassau County Sewer Districts 2 and 3, respectively; 

SWSD, Southwest Sewer District. Locations are shown in fig. 2.] 

Time 

period

Calendar 

years Description

1 pre-1952 Most of Nassau County and all of Suffolk County 

unsewered

2 1952-64 SD2 began treating wastewater; final sewer 

hookups completed in 1964

3 1965-73 Pre-SD3 period; SD2 in operation 

4 1974-81 Pre-SSD period. SSD began treating wastewater; 

final sewer hookups completed in 1988. 

5 1982-88 SSD began treating wastewater; SD33 completed 

in 1988.

6 1988-97 All three sewer districts completed

Nitrogen Concentrations in Streams and Ground Water
22 Trends in Nitrogen Concentration and Nitrogen Loads Entering the South Shore Estuary Reserve from Streams 

and Ground-water Discharge in Nassau and Suffolk Counties, Long Island, New York, 1952-97

Pines Brook

x

x

1989-97 1965-73 1974-81 1982-88

NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

n = 4

n = 28

n = 10 n = 26

0

1

2

3

4

5

6

7

8 East Meadow Brook

10

15

20

n = 20

n = 52

n = 19

n = 29

x

o

o

xx

x

x

o

1989-97 1965-731974-811982-88

0

5

Bellmore Creek

10

15

20

25

x

x

x

o

o

x

1989-97 1965-73 1974-811982-88

n = 7 n = 32

n = 17

n = 27

0

5

Massapequa Creek

10

15

20

x

o

x

1989-97 1965-731974-811982-88

NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

0

5

n = 21

n = 55

n = 18

n = 29

Santapogue Creek

0

10

15

20

n = 10

n = 32

n = 26

n = 31

x

x

1989-97 1965-731974-811982-88

5

Carlls River

x

1989-97 1965-73 1974-811982-88

1

2

3

4

5

6

7

8

Sampawams Creek

n = 12

n = 32

n = 26

n = 32

x

x

o

x

x

o

x

1989-97 1965-731974-811982-88

NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

0

2

4

6

8

10

12 Penataquit Creek 8

n = 11

n = 32

n = 26

n = 32

x

x

x

o

x

1989-97 1965-731974-811982-88

1

2

3

4

5

6

7

Champlin Creek

x

x

o

o

o

x

1989-97 1965-73 1974-811982-88

0

2

4

6

8

10

12

A. STREAMS IN SEWERED AREAS

Connetquot River

(supplementary 0130495)

o

x

1989-97 1965-731974-811982-88

NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

n = 9

n = 14

n = 2

n = 27

5

4

3

2

1

0

Connetquot River

(base 0130499)

0.5

1.0

1.5

2.0

2.5

3.0

3.5

x

1989-97 1965-731974-811982-88

n = 9

n = 32

n = 27

n = 40

Patchogue River

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

1989-97 1965-73 1974-811982-88

n = 8

n = 31

n = 27 n = 31

Swan River

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

x

o

1989-97 1965-731974-811982-88

NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

n = 7

n = 32

n = 26

n = 32

Carmans River

x x

x

x

x

o

1989-97 1965-731974-811982-88

0

2

4

6

8

10

n = 22 n = 83

n = 60

n = 76

B. STREAMS IN UNSEWERED AREAS

n=30 Number of values 

EXPLANATION 

x

x

x

o

o

o

Upper quartile (75th percentile)

Median (50th percentile)

Lower quartile (25th percentile)

Data value(s) exceeding upper quartile plus

3 times the interquartile range

Data value(s) exceeding upper quartile plus

1.5 times the interquartile range but less 

than the upper quartile plus 3 times the 

interquartile range 

Largest data values less than or equal to the 

upper quartile plus 1.5 times the interquartile range

Smallest data values greater than or equal to the 

upper quartile minus 1.5 times the interquartile 

range

n=9

n=32

n=27

n=45

n=8

n=33

n=26 n=30

Figure 11. Distribution of nitrogen concentration in streams on the south shore of Nassau and Suffolk Counties, N.Y. 

during selected time periods: A. In the nine streams in sewered areas. B. In the four streams in unsewered areas. 

(Time periods are defined in table 5; locations are shown in fig. 2.)
23

represent changes that have occurred over time. The 

factor that seems to have the greatest effect on groundwater quality along the south shore, as in the long-term 

trend analysis for the streams, was the implementation 

of sewering. Initially, the six time periods listed in

table 5 were chosen but two periods—pre-1952 and 

1989-97—lacked data. Therefore, the pre-1952 period 

was omitted and the data for 1989-97 were merged 

with data collected during 1982-88; thus, the last time 

period was 1982-97. The results are presented in 

boxplots (fig. 13).

The boxplots for Area A (SD2) show little change 

in median nitrogen concentration over time probably 

because this area has been sewered since 1952, and 

most of the data were collected after 1965 (fig. 13). 

The median nitrogen concentrations for periods 1 

through 4 are 2.70, 3.60, 3.02, and 3.95 mg/L as N, 

respectively. Note that only four samples were used to 

calculate the median nitrogen concentration in time 

period 1; therefore, the boxplot is not comparable with 

the others.

The boxplots for Area B (SD3) indicate no change 

in median nitrogen concentrations from period 1 to 

period 2 (median values are 1.26 and 1.55 mg/L as N, 

Table 6. Number of samples collected from selected shallow and deep wells within 1 mile of the south shore of Nassau and 

Suffolk Counties, N.Y., and maximum, median, and minimum concentrations of nitrogen at shallow wells and of nitrate at 

deep wells, 1952-97.

[Shallow-well depth 0-125 feet; deep-well depth 126−300 feet; mg/L as N, milligrams per liter as nitrogen; <, less than; Min, minimum; Med., median; 

Max., maximum]

* Most samples do not have values for organic nitrogen

A. Number of wells and samples

Shallow ground water Deep ground water

Nassau Suffolk Total Nassau Suffolk Total

Number of wells with water-quality data 104 63 167 17 8 25

Number of samples used to calculate

total nitrogen load

408 747* 1155 58 54 112

B. Nitrogen and nitrate concentration, in mg/L as N:

Total Nitrogen Total Nitrate

Min. Med. Max. Min. Med. Max.

Nassau County .008 3.85 40.1 <.01 .15 12.61 

Suffolk County <.01 1.74 21.6 <.01 <.01 4.93

Table 7. Minimum, maximum, and median total nitrogen 

concentrations in shallow and deep ground water in 

Areas A through E of South Shore Estuary Reserve, 

Nassau and Suffolk Counties, N.Y., 1952-97. 

[Concentrations are in milligrams per liter; <, less than. Locations 

are shown in fig. 2]

Geographic 

area

Total nitrogen 

concentration Number 

of 

samples

Number 

of 

Min Median Max wells

Shallow wells (depth 0-125 feet)

A .102 3.31 17.81 220 57

B .008 5.40 40.1 188 47

C <.01 2.25 21.60 53 10

D <.01 2.36 19.06 457 33

E .022 1.03 21.04 237 20

Deep wells (depth 126-300 feet)

A <.01 .14 2.14 40 10

B <.01 .17 12.61 18 7

C .10 .10 .40 7 1

D <.01 <.05 .20 31 4

E .24 3.63 4.93 16 3

Nitrogen Concentrations in Streams and Ground Water
24 Trends in Nitrogen Concentration and Nitrogen Loads Entering the South Shore Estuary Reserve from Streams 

and Ground-water Discharge in Nassau and Suffolk Counties, Long Island, New York, 1952-97

0

10

20

30

40

50

n =188

n = 220

n = 40

n = 206

n = 188

n = 18

n = 512

n = 53

n = 7

n = 354

n = 457

n = 31

n = 241

n = 237

n = 16

StreamShallowDeep Stream Shallow Deep Stream Shallow Deep Stream Shallow Deep Stream ShallowDeep

AREA A AREA B AREA C AREA D AREA E

TOTAL NITROGEN AND NITRATE CONCENTRATION, IN MILLIGRAMS PER LITER

x

xx

x

o

o

o

x

x

x

x

x

x

o

o

ox

o

x

x

x

x

x

x

o

o

o

x

o

x

xxx

x

x

x

x

o

oooo

xx

x

x

o

x

xx

x

x

x

xxx

x

x

x

x

xx

x

x

x

x

x

x

x

x

x

x

x

x

x

o

oo

o

o

o

o

ox

xxxx

o

x

xx

x

x

oo

o

o

o

o

n=30 Number of values 

EXPLANATION 

x

x

x

o

o

o

Upper quartile (75th percentile)

Median (50th percentile)

Lower quartile (25th percentile)

Data value(s) exceeding upper quartile plus

3 times the interquartile range

Data value(s) exceeding upper quartile plus

1.5 times the interquartile range but less 

than the upper quartile plus 3 times the 

interquartile range 

Largest data values less than or equal to the 

upper quartile plus 1.5 times the interquartile range

Smallest data values greater than or equal to the 

upper quartile minus 1.5 times the interquartile 

range

respectively) (fig. 13). An increase is indicated in 

period 3 (median nitrogen concentration of 7.00 mg/L 

as N) and a small decrease in period 4 (median 

nitrogen concentration of 6.20 mg/L as N). Wastewater 

has been treated in Area B since 1974, but this increase 

occurs in 1974-81, probably because water with high 

nitrogen concentrations north of the 1-mi-wide zone 

was entering the zone at this time. Katz and others 

(1980) mapped the areal distribution of median 

nitrate-N concentrations in the upper glacial aquifer 

during 1972-76, and Perlmutter and Koch (1972) 

mapped the nitrate concentration in the upper glacial 

aquifer in Nassau County during 1966-70; both 

investigations indicate higher concentrations of nitrate 

north of the 1-mi-wide zone. Buxton and Modica 

(1992) estimated that velocities range from less than 

1 ft/d to 2 ft/d, under steady-state conditions, in the 

upper glacial aquifer; thus, water moving at the faster 

rate of 2 ft/d would take more than 7 years to travel 

1 mile. Therefore, the water north of the 1-mi zone, 

with high nitrate values, probably was entering the 

1-mi zone during period 3 causing the increase from 

period 2 to period 3. Another reason for the high 

nitrate concentrations may be increased fertilizer use; 

Porter (1980) indicated two principal sources of 

nitrogen are human waste and fertilized turf. Sewering 

removes the human wastewater contribution, but the N 

contribution from fertilizers remains. This contribution 

Figure 12. Distribution of total nitrogen concentrations in samples from streams and shallow wells, and nitrate 

concentrations in samples from deep wells in the five geographic areas within 1 mile of the south shore of Nassau 

and Suffolk Counties, N.Y., 1952-97. (Locations are shown in figs. 6 and 7.)
25

Area A (Sewer District 2)

1952-64 1965-73 1974-81 1982-97

10

15

20

x

x

x

x

o

x

x x

NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

0

5

n = 4

n = 53

n = 119

n = 45

Area B (Sewer District 3)

n = 31

n = 34

n = 96

n = 27

x

x

o

x

x

x

o

o

o

1952-64 1965-73 1974-81 1982-97

NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

0

10

20

30

40

50

Area D (Unsewered West of Carmans River)

o

o

o

x

x

xxx

x

xx

x

x

x

x

x

x

o

o

o

o

o

o x

x

x

1952-64 1965-73 1974-81 1982-97

NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

0

5

10

15

20

25

n = 2

n = 55

n = 222

n = 178

Area C (Southwest Sewer District)

10

15

20

25

o

o

o

o

1952-64 1965-73 1974-81 1982-97

NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

5

0

n = 1

n = 18

n = 16

n = 18

Area E (Unsewered area East of Carmans River)

10

15

20

25

n = 151

n = 77

o

xx

x

xx

x

x

o

o

o

o

x

o

1952-64 1965-73 1974-81 1982-97

NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

n = 9

n = 0

5

0

n=30 Number of values 

EXPLANATION 

x

x

x

o

o

o

Upper quartile (75th percentile)

Median (50th percentile)

Lower quartile (25th percentile)

Data value(s) exceeding upper quartile plus

3 times the interquartile range

Data value(s) exceeding upper quartile plus

1.5 times the interquartile range but less 

than the upper quartile plus 3 times the 

interquartile range 

Largest data values less than or equal to the 

upper quartile plus 1.5 times the interquartile range

Smallest data values greater than or equal to the 

upper quartile minus 1.5 times the interquartile 

range

Figure 13. Distribution of nitrogen concentrations in samples from shallow wells in Areas A through E along south shore 

of Nassau and Suffolk Counties, N.Y, for four selected time periods. (Locations are shown in figs. 6 and 7.)

Nitrogen Concentrations in Streams and Ground Water
26 Trends in Nitrogen Concentration and Nitrogen Loads Entering the South Shore Estuary Reserve from Streams 

and Ground-water Discharge in Nassau and Suffolk Counties, Long Island, New York, 1952-97

may account for the observed increase from period 2 

to period 3. Solute-transport modeling might be used 

to investigate the occurrence of high nitrogen water. 

This modeling is beyond the scope of this study.

The boxplots for Area C (SWSD) show little 

change in median nitrogen concentration from periods 

1 through 3 (median values are 3.40, 2.95, and 

2.76 mg/L as N, respectively) (Note that period 1 only 

has one sample). The median nitrogen concentration 

decreased to 0.86 mg/L as N in period 4, possibly in 

response to sewering, which started in 1982.

The boxplots for Areas D and E show increasing 

median nitrogen concentrations over time (fig. 13). 

The median nitrogen concentrations in Area D from 

periods 1 through 4 are 0.64, 1.18, 2.50, and 

2.69 mg/L as N, respectively (Note that period 1 only 

has one sample). In Area E, no samples were available 

for period 1 but median nitrogen concentrations for 

periods 2 through 4 are 0.93, 0.94, and 1.19 mg/L as 

N, respectively. This small increasing trend probably 

is the result of urban growth; the Long Island regional 

planning board recorded a population increase in 

Suffolk County from around 276,000 in 1950 to 

1.3 million in 1990.

Trends with Depth

Nitrogen concentrations generally decrease with 

depth below land surface, and water in the upper part 

of the Magothy aquifer contains less nitrogen than the 

overlying upper glacial aquifer. Median nitrate 

concentrations in samples taken in 1989 from parts of 

the Magothy aquifer that were unaffected by human 

activities were less than 0.3 mg/L as N (Pearsall, 

1996). Pumping in some developed areas can draw 

high nitrogen waters from the shallow part of the 

ground-water system into deeper parts (Eckhardt and 

Pearsall, 1989). Median nitrate concentrations in 

samples from deep wells (depth was based on travel 

time more than 100 years along a vertical flow path) 

in selected areas near the regional ground-water 

divide from June 1987 through September 1988 were 

3.55 mg/L as N in SD2, 2.36 mg/L as N in SD3, and 

0.60 mg/L in unsewered areas (Stackelberg, 1995). 

These elevated concentrations in the deep ground 

water of sewered areas are attributed to the drawdown 

of shallow ground water that has been affected by 

human activities. 

The geographic areas that were used to group the 

well data also were applied to the stream water-quality 

data for comparison with the corresponding shallowand deep-well data to discern trends with depth (fig. 

12). The streams whose data were used for each area 

are listed in table 8. 

The boxplots indicate that the median nitrogen 

concentration decreases with depth, except in Area E, 

as explained earlier. Stream median nitrogen 

concentration also are similar or slightly higher than, 

the shallow-well median nitrogen concentration for 

each geographic area (fig. 12). The plots also show a 

wider variability in shallow-well data than in stream 

data, although this might be attributed to differences in 

periods of records of water-quality samples.

NITROGEN LOADS ENTERING THE 

SOUTH SHORE ESTUARY RESERVE 

The nitrogen loads discharged from streams to the 

SSER for each year during 1972-97 were calculated as 

the annual mean total nitrogen concentration 

multiplied by the annual mean discharge. These values 

were calculated only for the seven streams for which 

sufficient data were available (East Meadow Brook, 

Bellmore Creek, Massapequa Creek, Carlls River, 

Sampawams River, Swan River, and Carmans River). 

Discharge data collection on Santapogue and 

Champlin Creeks was discontinued in water year 

1969; therefore, these streams were omitted from the 

1972-97 load calculations. 

The nitrogen load carried to the SSER by the 

shallow-ground-water system (upper glacial aquifer) 

was calculated as the model-generated discharge 

multiplied by the median total nitrogen concentrations 

for Nassau and Suffolk Counties at 167 shallow wells 

(125 ft deep or less) within 1 mi of the shore. The 

Table 8. Geographic grouping of the 13 selected streams 

that discharge to the South Shore Estuary Reserve,

Long Island, N.Y.

[Stream locations are shown in fig. 2; geographic-area locations 

are shown in fig. 7.] 

Geographic

area Streams

A Pines Brook, East Meadow Brook

B Bellmore Creek, Massapequa Creek

C Santapogue Creek, Carlls River, Sampawams Creek, 

Penataquit Creek, and Champlin Creek

D Connetquot River, Patchogue River, and Swan River

E Carmans River
27

nitrogen load from the deep-ground-water system 

(upper part of Magothy aquifer) to the SSER were 

calculated as the simulated discharge multiplied by the 

median nitrate concentrations (nitrate represented 

almost all of the total nitrogen) for Nassau and Suffolk 

Counties at 25 deep wells (greater than 125 feet deep) 

within 1 mi of the shore. 

Annual Stream Loads

The nitrogen loads discharging to the SSER from 

streams during 1972-97 varied with fluctuations in 

total nitrogen concentrations and stream discharge 

(fig. 14). The large variations mainly are a result of the 

implementation of sewer systems, fluctuations in 

recharge from precipitation and urban growth. The 

nitrogen loads entering the SSER from streams are 

summarized in table 9.

Geographic Trends 

The three westernmost streams except Pines 

Brook (East Meadow Brook, Bellmore Creek, and 

Massapequa Creek) show a wide variation in annual 

nitrogen load throughout 1972-97 (table 9) and is 

visible in the boxplots shown in figure 15. The loads 

for all four streams ranged from 1.65 to 184 ton/yr 

(1,500 to 165,000 kg/yr). The smallest loads for these 

four streams occurred in 1995, a year characterized by 

low annual precipitation and low stream discharge. 

Pines Brook (the westernmost stream) had the smallest 

range in annual nitrogen load (1.97 - 15.8 ton/yr; 1780 

- 14,300 kg/yr), and had the lowest discharge of all 

streams, it also had the smallest annual mean nitrogen 

load. Carlls River had the largest long-term (1972-97) 

average annual mean nitrogen load (104 ton/yr; 

94,300 kg/yr), with a range of 36.3 to 184 ton/yr 

(32,900 to 167,000 kg/yr) (fig. 15). The annual mean 

nitrogen load from Carlls River was over three times 

that of Carmans River (33 ton/yr or 30,000 kg/yr) and 

twice that of Connetquot River (54 ton/yr or 

49,000 kg/yr); however, from 1972 to 1987 only a 

portion of the load from Connetquot River was 

calculated (table 9).

Temporal Trends 

Nitrogen loads from streams entering the SSER 

were evaluated for two periods—1972-84 and 1985-

97. A median load for each stream was calculated for 

each period from the 1972-97 load calculations in 

table 9; Penataquit Creek and Patchogue Creek were 

omitted because no loads were calculated for 1985-97. 

The results indicate that the sewered residential areas 

in Nassau County had a large reduction in estimated 

nitrogen loads. The four streams in this area (Pines 

Brook, East Meadow Brook, Bellmore Creek, and 

Massapequa Creek) produced about 220 ton/year 

(200,000 kg/yr) before 1985 and 43 ton/year 

(39,000 kg/yr) after 1985—an 80 percent decrease in 

nitrogen load. The two streams in the SWSD (Carlls 

River, and Sampawams Creek) together produced 

about 175 ton/yr (159,000 kg/yr) before 1985 and 

98 ton/yr (88,900 kg/yr) after 1985—a 40-percent 

decrease. The streams in the unsewered areas in 

Suffolk County (Connetquot River, Swan River, and 

Carmans River) produced about 129 ton/yr 

(117,000 kg/yr) during 1972-84 and 139 ton/yr 

(126,000 kg/yr) during 1985-97—a long-term increase 

of about 7 percent.

The stream nitrogen loads discharged to the SSER 

in each year from 1972 through 1997 (from table 9) 

were summed for each county and graphed in figure 

16 to show each counties annual stream load. The 

loads from both stations at Connetquot River were 

combined, however, from 1972 through 1987 the 

combined value is missing a calculated load from one 

or both stations, also Penataquit Creek and Patchogue 

River only have 4 and 2 years of calculated load, 

respectively; therefore, the loads calculated in Suffolk 

County streams is smaller than the actual load. The 

combined stream load discharged to the SSER from 11 

streams ranged from 169 ton/yr (153,000 kg/yr) in 

1995 to 705 ton/yr (640,000 kg/yr) in 1979; however, 

note that values for the Penataquit and Patchogue 

Rivers are missing for both years, and the value for 

Connetquot base station in 1979 is missing (fig. 16). 

This range in stream loads is in addition to the loads 

transported by ground-water discharge

Ground-Water Loads

The nitrogen load entering the SSER from aquifers 

was calculated as simulated ground-water discharges 

multiplied by the median total nitrogen concentrations 

calculated from data from the selected wells represented 

in the NWIS database. The numbers of shallow and 

deep wells, and samples are summarized by well depth 

and county in table 6; the concentrations and loads are 

summarized by county and depth in table 10. 

Nitrogen Loads Entering the South Shore Estuary Reserve
28 Trends in Nitrogen Concentration and Nitrogen Loads Entering the South Shore Estuary Reserve from Streams 

and Ground-water Discharge in Nassau and Suffolk Counties, Long Island, New York, 1952-97

Table 9. Estimated annual nitrogen loads entering the South Shore Estuary Reserve from 11 streams on the

south shore of Long Island, N.Y., 1972-97. 

[Discharge measurement on Santapogue and Champlin Creeks ceased in 1969; therefore, these streams are omitted.

ton/yr, tons per year; kg/yr, kilograms per year. Dashes indicate no samples collected. Locations are shown in fig. 2.]

Year

Pines Brook

East Meadow 

Brook Bellmore Creek

Massapequa 

Creek Carlls River

Sampawams 

River

ton/yr kg/yr ton/yr kg/yr ton/yr kg/yr ton/yr kg/yr ton/yr kg/yr ton/yr kg/yr

1972 3.18 2,880 57.6 52,300 -- -- 119 108,000 111 101,000 55.8 50,600

1973 7.93 7,190 93.9 85,200 83.8 76,000 182 165,000 134 122,000 52.2 47,400

1974 5.91 5,360 40.0 36,300 58.0 52,600 74.1 67,200 110 99,800 55.4 50,300

1975 10.1 9,170 76.0 68,900 65.6 59,500 123 112,000 121 110,000 87.2 79,100

1976 6.74 6,120 71.3 64,700 38.2 34,700 89.5 81,200 116 105,000 33.6 30,500

1977 6.72 6,090 47.5 43,000 62.2 56,400 101 92,000 114 103,000 32.9 29,800

1978 9.89 8,970 85.6 77,700 69.8 63,300 118 107,000 184 167,000 56.1 50,900

1979 14.1 12,800 150 136,000 65.6 59,500 155 141,000 156 142,000 63.4 57,500

1980 7.59 6,890 57.3 52,000 34.9 31,700 83.4 75,700 119 108,000 47.5 43,100

1981 2.70 2,450 16.6 15,100 16.2 14,700 34.6 31,400 91.4 82,900 41.2 37,400

1982 1.97 1,780 18.0 16,300 13.8 12,500 45.9 41,600 92.4 83,800 39.4 35,700

1983 3.51 3,180 82.6 74,900 44.2 40,100 85.2 77,300 129 117,000 55.2 50,100

1984 15.7 14,200 76.2 69,100 41.9 38,000 92.9 84,300 161 146,000 69.9 63,500

1985 -- -- 12.8 11,600 13.2 12,000 23.6 21,400 78.9 71,600 37.4 33,900

1986 -- -- 10.5 9,560 9.34 8,470 20.0 18,100 74.1 67,200 31.2 28,300

1987 1.99 1,800 13.6 12,300 8.22 7,460 20.9 19,000 80.7 73,200 35.9 32,600

1988 -- -- 3.79 3,440 4.27 3,870 22.7 20,600 62.7 56,900 21.1 19,100

1989 9.14 8,300 30.5 27,700 12.4 11,200 33.5 30,400 131 119,000 56.5 51,300

1990 8.48 7,690 34.6 31,400 16.8 15,200 38.9 35,300 154 140,000 55.6 50,400

1991 7.22 6,550 16.7 15,100 11.0 9,940 26.4 23,900 98.8 89,600 33.4 30,300

1992 4.90 4,440 5.07 4,600 6.73 6,100 14.1 12,800 74.0 67,100 22.9 20,800

1993 4.39 3,990 6.97 6,320 5.69 5,160 15.3 13,900 69.0 62,600 24.9 22,600

1994 7.32 6,640 6.36 5,770 4.60 4,170 12.2 11,100 65.0 59,000 24.0 21,800

1995 2.90 2,630 1.66 1,500 2.00 1,810 5.25 4,760 36.2 32,800 13.2 12,000

1996 9.60 8,710 7.62 6,910 5.82 5,280 10.4 9,410 60.9 55,200 24.1 21,900

1997 -- -- -- -- -- -- 10.1 9,130 72.2 65,500 2.45 2,220

Penataquit Connetquot River stations Patchogue Carmans

Year

Creek Base Supplementary River Swan River River

ton/yr kg/yr ton/yr kg/yr ton/yr kg/yr ton/yr kg/yr ton/yr kg/yr ton/yr kg/yr

1972 33.9 30,800 -- -- 10.9 9,900 -- -- 23.4 21,200 27.1 24,600

1973 38.9 35,300 -- -- 17.3 15,700 29.9 27,100 20.9 19,000 32.3 29,300

1974 19.4 17,600 -- -- 26.2 23,800 32.1 29,100 20.1 18,200 27.5 24,900

1975 29.2 26,500 -- -- 24.8 22,500 -- -- 17.8 16,100 24.3 22,000

1976 -- -- -- -- 27.3 24,800 -- -- 22.4 20,300 26.3 23,900

1977 -- -- -- -- -- -- -- -- 19.6 17,800 25.9 23,500

1978 -- -- -- -- 26.9 24,400 -- -- 27.1 24,600 31.1 28,200

1979 -- -- -- -- 27.6 25,000 -- -- 30.3 27,500 43.3 39,300

1980 -- -- 53.4 48,400 -- -- -- -- 23.2 21,000 32.6 29,600

1981 -- -- 38.7 35,100 -- -- -- -- 17.5 15,900 22.3 20,200

1982 -- -- 32.8 29,800 -- -- -- -- 20.7 18,800 47.7 43,300

1983 -- -- 49.1 44,500 -- -- -- -- 27.3 24,800 35.7 32,400

1984 -- -- 60.4 54,800 -- -- -- -- 45.3 41,100 55.2 50,100

1985 -- -- 40.3 36,600 -- -- -- -- 20.5 18,600 33.2 30,100

1986 -- -- 37.8 34,300 -- -- -- -- 19.7 17,900 25.9 23,500

1987 -- -- 42.8 38,800 -- -- -- -- 22.2 20,100 27.7 25,100

1988 -- -- 26.0 23,600 21.7 19,700 -- -- 16.8 15,200 25.0 22,700

1989 -- -- 42.8 38,800 40.5 36,700 -- -- 27.6 25,000 39.4 35,700

1990 -- -- 60.2 54,600 73.8 67,000 -- -- 33.8 30,700 52.2 47,400

1991 -- -- 49.0 44,500 61.5 55,800 -- -- 29.7 26,900 44.3 40,200

1992 -- -- 45.3 41,100 39.9 36,200 -- -- 23.8 21,600 28.0 25,400

1993 -- -- 39.1 35,500 40.8 37,000 -- -- 24.9 22,600 33.8 30,700

1994 -- -- 45.4 41,200 43.9 39,800 -- -- 25.0 22,700 34.8 31,600

1995 -- -- 33.5 30,400 34.0 30,800 -- -- 19.2 17,400 20.8 18,900

1996 -- -- 36.8 33,400 47.1 42,700 -- -- 25.6 23,200 24.7 22,400

1997 -- -- -- -- 53.2 48,300 -- -- 29.7 26,900 31.1 28,200
29

Pines Brook East Meadow Brook

MEAN ANNUAL DISCHARGE, IN CUBIC FEET PER SECOND

MEAN ANNUAL LOAD, IN KILOGRAMS PER YEAR 

MEAN ANNUAL NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER

0

2

6

10

14

18

22

1970 1975 1980 1985 1990 1995

Year

0

20,000

60,000

100,000

140,000

0

1

2

3

4

5

6

7

8

2000

missing data

missing data

missing data

missing data

MEAN ANNUAL DISCHARGE, IN CUBIC FEET PER SECOND

0

1

2

3

4

5

1970 1975 1980 1985 1990 1995

Year

0

5,000

10,000

15,000

MEAN ANNUAL LOAD, IN KILOGRAMS PER YEAR 

0

1

2

3

4

5

MEAN ANNUAL NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER

2000

missing

data missing data

missing data missing

data

0

2

4

6

8

Bellmore Creek

1970 1975 1980 1985 1990 1995

Year

0

20,000

40,000

60,000

80,000

0

2

4

6

8

10

MEAN ANNUAL LOAD, IN KILOGRAMS PER YEAR 

MEAN ANNUAL NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER

MEAN ANNUAL DISCHARGE, IN CUBIC FEET PER SECOND

missing data

missing data

missing data

missing data

2000

0

4

8

12

16

20

Massapequa Creek

1970 1975 1980 1985 1990 1995

Year

0 20,000

60,000

100,000

140,000

180,000

0

2

4

6

8

10

MEAN ANNUAL LOAD, IN KILOGRAMS PER YEAR 

MEAN ANNUAL NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER

MEAN ANNUAL DISCHARGE, IN CUBIC FEET PER SECOND

missing

data

missing

data

missing data

missing data

2000

MEAN ANNUAL LOAD, IN KILOGRAMS PER YEAR MEAN ANNUAL LOAD, IN KILOGRAMS PER YEAR 

MEAN ANNUAL NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER

MEAN ANNUAL DISCHARGE, IN CUBIC FEET PER SECOND

0

4

8

12

16

Sampawams River

1970 1975 1980 1985 1990 1995

Year

0

20,000

40,000

60,000

80,000

0

1

2

3

4

5

6

7

missing data

missing data

missing data

missing data

2000

0

8

16

24

32

Carlls River

1970 1975 1980 1985 1990 1995

Year

0 20,000

60,000

100,000

140,000

180,000

0

1

2

3

4

5

6

MEAN ANNUAL NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER

MEAN ANNUAL DISCHARGE, IN CUBIC FEET PER SECOND

missing data

missing data

missing data

missing data

2000

Figure 14. Annual mean discharge, mean nitrogen concentration, and mean nitrogen load calculated for 11 selected 

south-shore streams that discharge to the South Shore Estuary Reserve from Nassau and Suffolk Counties, N.Y., 

1972-97. (Locations are shown in fig. 2.)

Nitrogen Loads Entering the South Shore Estuary Reserve
30 Trends in Nitrogen Concentration and Nitrogen Loads Entering the South Shore Estuary Reserve from Streams 

and Ground-water Discharge in Nassau and Suffolk Counties, Long Island, New York, 1952-97

MEAN ANNUAL LOAD, IN KILOGRAMS PER YEAR 

MEAN ANNUAL NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER

MEAN ANNUAL DISCHARGE, IN CUBIC FEET PER SECOND

MEAN ANNUAL LOAD, IN KILOGRAMS PER YEAR 

MEAN ANNUAL NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER

MEAN ANNUAL DISCHARGE, IN CUBIC FEET PER SECOND

0

8

16

24

32

Connetquot River- Base Station

1970 1975 1980 1985 1990 1995

Year

0

20,000

40,000

60,000

0

1

2

3

missing data

missing data

missing data

missing data

2000

0

2

4

6

8

10

Penataquit Creek

1970 1975 1980 1985 1990 1995

Year

0

20,000

40,000

0

1

2

3

4

5

missing data

missing data

missing

data

2000

missing

data

MEAN ANNUAL LOAD, IN KILOGRAMS PER YEAR 

MEAN ANNUAL NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER

MEAN ANNUAL DISCHARGE, IN CUBIC FEET PER SECOND

MEAN ANNUAL LOAD, IN KILOGRAMS PER YEAR 

MEAN ANNUAL NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER

MEAN ANNUAL DISCHARGE, IN CUBIC FEET PER SECOND

0

4

8

12

16

20

Patchogue River

1970 1975 1980 1985 1990 1995

Year

0

20,000

40,000

0

1

2

3

4

missing data missing data

missing data missing data

2000

0

4

8

12

16

20

24

Connetquot River- Supplementary Station

1970 1975 1980 1985 1990 1995

Year

0

20,000

40,000

60,000

80,000

0

1

2

3

missing data missing data

missing data missing data

missing data

missing data

missing data

missing

data

2000

Carmans River

Year

MEAN ANNUAL LOAD, IN KILOGRAMS PER YEAR 

0

8

16

24

32

40

1970 1975 1980 1985 1990 1995

0

20,000

40,000

60,000

0

1

2

3

MEAN ANNUAL LOAD, IN KILOGRAMS PER YEAR 

MEAN ANNUAL NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER

MEAN ANNUAL DISCHARGE, IN CUBIC FEET PER SECOND

missing

data

missing data

missing data

missing data

2000

0

4

8

12

16

20

Swan River

0

20,000

40,000

60,000

0

1

2

3

MEAN ANNUAL NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER

MEAN ANNUAL DISCHARGE, IN CUBIC FEET PER SECOND

missing data

missing data

missing data

missing data

1970 1975 1980 1985 1990 1995

Year

2000

Figure 14. (continued) Annual mean discharge, mean nitrogen concentration and mean nitrogen load calculated for 

11 selected south-shore streams that discharge to the South Shore Estuary Reserve from Nassau and Suffolk 

Counties, N.Y., 1972-97. (Locations are shown in fig. 2.)
31

Table 10. Median concentration and annual load of nitrogen entering the South Shore Estuary Reserve from 

shallow and deep ground water in Nassau and Suffolk Counties, N.Y., as calculated from concentrations 

at wells within 1 mile of the shore, 1952-97.

[Based on simulated discharge of 1983 steady-state conditions. mg/L, milligrams per liter; ton/yr, tons per year; 

kg/yr, kilograms per year; <, less than.]

Shallow ground water (as total nitrogen) Deep ground water (as total nitrate)

Median concentration

for wells 

(mg/L as N)

Annual load from 

ground water

Median concentration

for wells 

(mg/L as N)

Annual load from ground water

ton/yr kg/yr ton/yr kg/yr 

Nassau County 3.85 172 156,000 0.15 3.0 2,700

Suffolk County 1.74 380 345,000 <0.01 <0.5 <480

Total 552 501,000 <3.5 <3,180

Figure 15. Distribution of nitrogen load calculated in 11 selected streams on the south shore of Nassau and 

Suffolk Counties, N.Y., 1972-97. (Locations are shown in fig.2.)

0

50

100

150

200

250

n = 22

n = 25

n = 24

n = 26 n = 26

n = 26

n = 4

n = 25

n = 2

n = 26

n = 26

x

xx

PinesBrookEast MeadowBrookBellmoreCreekMassapequaCreekCarllsRiverSampawamsCreekPenataquitCreekConnetquotRiverPatchogueCreekSwanRiverCarmansRiver

NITROGEN LOAD, IN TONS PER YEAR

n=30 Number of values 

EXPLANATION 

x

x

x

o

o

o

Upper quartile (75th percentile)

Median (50th percentile)

Lower quartile (25th percentile)

Data value(s) exceeding upper quartile plus

3 times the interquartile range

Data value(s) exceeding upper quartile plus

1.5 times the interquartile range but less 

than the upper quartile plus 3 times the 

interquartile range 

Largest data values less than or equal to the 

upper quartile plus 1.5 times the interquartile range

Smallest data values greater than or equal to the 

upper quartile minus 1.5 times the interquartile 

range

Nitrogen Loads Entering the South Shore Estuary Reserve
32 Trends in Nitrogen Concentration and Nitrogen Loads Entering the South Shore Estuary Reserve from Streams 

and Ground-water Discharge in Nassau and Suffolk Counties, Long Island, New York, 1952-97

Shallow-Ground-Water System

The median nitrogen concentration for samples 

from the 104 shallow wells in Nassau County was 

3.85 mg/L as N; values ranged from 0.008 mg/L to 

40.1 mg/L as N, during 1952-97 (table 6). The median 

concentration for the 63 shallow wells in Suffolk 

County was 1.74 mg/L as N; the values ranged from 

<0.1 mg/L as N to 21.6 mg/L as N, during 1952-97. 

Multiplying the simulated shallow-ground-water 

discharges by the shallow well median total nitrogen 

concentrations of 3.85 and 1.74 mg/L as N for Nassau 

and Suffolk Counties, respectively, gave nitrogen 

loads of 172 and 380 ton/yr or 156,000 and 

345,000 kg/yr; equaling 552 ton/yr (501,000 kg/yr) 

entering the SSER from the shallow-ground-water 

system (table 10). 

Deep-Ground-Water System

The median nitrate concentration for the 17 deep 

wells in Nassau County was 0.15 mg/L as N, and the 

range was from <0.01 to 12.61 mg/L as N, during 

1952-97. The median concentration for the eight deep 

wells in Suffolk County was <0.01 mg/L as N, and the 

range was from <0.01 to 4.93 mg/L as N, during 1952-

97. Multiplying the simulated deep-ground-water 

discharges by the respective median total nitrogen 

concentrations of 0.15 and <0.01 mg/L as N for Nassau 

and Suffolk Counties, respectively, gave total nitrate 

loads of 3.0 and <0.5 ton/yr or 2,700 and 480 kg/yr; 

equaling about 3.5 ton/yr (3,180 kg/yr) entering the 

SSER from the deep-ground-water system (table 10). 

Total Nitrogen Load

The total nitrogen loads entering the SSER is the 

sum of both the stream loads and ground-water loads. 

It only was possible to calculate annual loads from 11 

selected streams with the available data. These loads 

varied geographically, and temporally. The groundwater loads calculated are annual loads; however, the 

load is a constant value (556 ton/yr; 504,000 kg/yr) 

because water-quality data were sparse and discharge 

data were simulated under steady-state hydrologic 

conditions. The ground-water load is the sum of the 

shallow-ground-water system nitrogen load 

(552 ton/yr; 501,000 kg/yr) and deep-ground-water 

system nitrate load (3.5 ton/yr; 3,180 kg/yr). The 

surface-water load and the total load to the SSER 

(surface- water plus ground-water load) for each year 

(1972-97) is summarized in table 11.

The largest calculated total nitrogen load entering 

the SSER occurred in 1979 with a total load of 

1,260 ton/yr (1,140,000 kg/yr). The smallest 

0

200

400

600

800

CALCULATED TOTAL NITROGEN LOAD, IN TONS

72

73

74

75

76

77

78

79

80 88

87

86

85

84

83

82

81 89

90

91

92

93

94

97

96

95

YEAR

SUFFOLK COUNTY

NASSAU COUNTY

MISSING DATA

Pines Brook (Nassau) 1985-86, 1988 and 1997

East Meadow Brook (Nassau) 1997

Bellmore Creek (Nassau) 1972 and 1997

Penataquit Creek (Suffolk) 1976-97

Connetquot River Base (Suffolk) 1972-79 and 1997

Connetquot River Supplementary (Suffolk) 1977 and 1980-87

Patchogue River (Suffolk) 1972 and 1975-1997 

EXPLANATION

Figure 16. Combined nitrogen load from four streams in Nassau County and seven in Suffolk County, N.Y. that 

discharge to the South Shore Estuary Reserve during 1972-97.
33

calculated nitrogen load entering the SSER occurred 

in 1995 with a total load of 725 ton/yr (658,000 kg/yr). 

This range in load is an estimate based on the available 

data; the actual load to the SSER is higher because of 

various factors discussed in previous sections. These 

factors should be considered when calculating the 

SSER nitrogen load budget.

SUMMARY

The South Shore Estuary Reserve (SSER) of Long 

Island, N.Y. is a series of shallow tidal bays that 

provide a rich habitat for fish and wildlife. High 

nitrogen concentrations and resulting low dissolved 

oxygen concentrations (hypoxia) is a concern in the 

SSER. The U.S. Geological Survey, in cooperation 

with the New York State Department of State 

(NYSDOS), began an investigation in 1998 to refine 

estimates of nitrogen loading to the SSER.

Analyses of total nitrogen concentrations in the 13 

streams that discharge from Nassau and Suffolk 

Counties, N.Y. from the SSER indicate a general 

eastward increase from Pines Brook (the westernmost 

stream) to Massapequa Creek in Nassau County, and a 

decrease from Massapequa Creek to Carmans River 

(the easternmost stream) in Suffolk County. Patchogue 

River deviated slightly from this decreasing trend. 

Eight of the streams (Pines Brook, East Meadow 

Brook, Bellmore Creek, Massapequa Creek, 

Santapogue Creek, Carlls River, Sampawams Creek, 

and Penataquit Creek) showed apparent decreasing 

trends in total nitrogen concentration during 1971-97, 

whereas four streams (Connetquot River, Patchogue 

River, Swan River, and Carmans River) showed longterm (1971-97) increasing trends. No long-term trends 

were discernible from Champlin Creek data.

Seasonal fluctuations in total nitrogen 

concentrations in the streams result from chemical 

reactions and biological activity within the stream 

systems. In all 13 selected streams, the median 

nitrogen concentration in winter (October through 

March) were higher than in summer (April 

through September) during 1971-97; but the 

difference is small. Carlls River had the largest 

difference in median nitrogen concentration 

between winter and summer.

The estimated annual nitrogen load discharged to 

the SSER from 11 of the 13 streams (Santapogue and 

Champlin Creeks were omitted because discharge data 

were not available during 1972-97) for 1972-97 was 

calculated as the annual mean total nitrogen 

concentration for each stream multiplied by its 

annual mean discharge. The combined annual 

nitrogen load from these 11 streams during 1972-97 

ranged from 169 ton/yr (153,000 kg/yr) in 1995 to 

705 ton/yr (640,000 kg/yr) in 1979. Carlls River had 

the highest mean annual nitrogen load (104 ton/yr; 

94,300 kg/yr) during this period and a wide range of 

values (36.3 to 184 ton/yr; 32,900 to 167,000 kg/yr). 

Pines Brook had the smallest range in annual 

nitrogen load (1.97 to 15.8 ton/yr; 1,780 to 

14,300 kg/yr) and coincides with the lowest discharge 

of all selected streams.

Geographic trends of total nitrogen concentrations 

in shallow wells (0-125 ft deep) grouped into five 

geographic areas within 1 mi of the south shore were 

similar to that of the stream nitrogen concentration—a 

Table 11. Total annual nitrogen load entering the 

South Shore Estuary Reserve from streams and 

ground water on the south shore of Long Island, 

N.Y., 1972-97.

[Total load is the sum of combined stream load and ground 

water load; missing stream loads explained in fig. 16; bar graph 

of combined stream load shown in fig. 16. ton/yr, tons per year; 

kg/yr, kilograms per year.] 

Year

Combined 

Stream Load Total Load

ton/yr kg/yr ton/yr kg/yr

1972 442 401,000 998 905,000

1973 664 602,000 1,220 1,110,000

1974 467 424,000 1,023 928,000

1975 611 554,000 1,170 1,060,000

1976 431 391,000 987 895,000

1977 410 372,000 966 876,000

1978 608 552,000 1,160 1,050,000

1979 705 640,000 1,260 1,140,000

1980 459 416,000 1,020 925,000

1981 281 255,000 837 759,000

1982 312 283,000 868 787,000

1983 512 464,000 1,070 971,000

1984 619 562,000 1,180 1,070,000

1985 260 236,000 816 740,000

1986 229 208,000 785 712,000

1987 254 230,000 810 735,000

1988 204 185,000 760 689,000

1989 424 385,000 980 889,000

1990 528 479,000 1,080 980,000

1991 378 343,000 934 847,000

1992 265 240,000 821 745,000

1993 265 240,000 821 745,000

1994 269 244,000 825 748,000

1995 169 153,000 725 658,000

1996 253 230,000 809 734,000

1997 199 181,000 755 685,000

Summary
34 Trends in Nitrogen Concentration and Nitrogen Loads Entering the South Shore Estuary Reserve from Streams 

and Ground-water Discharge in Nassau and Suffolk Counties, Long Island, New York, 1952-97

general eastward increase in Nassau County followed 

by a eastward decrease in Suffolk County. The 

streams and the shallow wells within each geographic 

area had similar median nitrogen concentrations. Total 

nitrogen concentrations in ground water generally 

decrease with depth. Water in the upper part of the 

Magothy aquifer have a lower median nitrate value 

than the median nitrogen value of the overlying upper 

glacial aquifer.

The nitrogen load entering the SSER from 

shallow-ground-water and deep-ground-water system 

was calculated as the horizontal and vertical groundwater discharges generated by the USGS Long Island 

regional-ground-water-flow model multiplied by the 

median total nitrogen concentrations calculated from 

data from selected wells represented in the USGS 

NWIS database. Simulated shallow-ground-water 

discharge from Nassau County totaled 10,700 Mgal/yr 

(40,500,000 m3

/yr), and that from Suffolk County 

totalled 52,300 Mgal/yr (198,000,000 m3

/yr). Median 

total nitrogen concentrations for the two counties were 

3.85 and 1.74 mg/L as N, respectively. The resultant 

nitrogen load from shallow-ground-water discharge 

was 172 ton/yr (156,000 kg/yr) in Nassau County, and 

380 ton/yr (345,000 kg/yr) from Suffolk County; 

equaling 552 ton/yr entering the SSER.

Simulated deep-ground-water discharge to the 

SSER from Nassau County totaled 4,900 Mgal/yr 

(18,500,000 m3

/yr), and that from Suffolk County 

totaled 12,700 Mgal/yr (48,200,000 m3

/yr). The 

median nitrate concentrations for the two counties 

were 0.15 and <0.01 mg/L as N, respectively. The 

resultant nitrogen load from deep-ground-water 

discharge was 3 ton/yr (2,700 kg/yr) in Nassau 

County, and <0.5 ton/yr (480 kg/yr) in Suffolk 

County; equaling about 3.5 ton/yr entering the SSER.

The sum of both stream loads and ground-water 

loads results in the total load to the SSER. The largest 

calculated total nitrogen load entering the SSER from 

both streams and ground water occurred in 1979 with 

a total load of 1,260 ton/yr (1,140,000 kg/yr). The 

smallest calculated nitrogen load entering the SSER 

occurred in 1995 with a total load of 725 ton/yr 

(658,000 kg/yr). 

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