TRENDS IN CHEMICAL CONCENTRATION IN SEDIMENT CORES FROM THREE LAKES IN NEW JERSEY 

AND ONE LAKE ON LONG ISLAND, NEW YORK

Water-Resources Investigations Report 02-4272

National Water-Quality Assessment Program

U.S. Department of the Interior

U.S. Geological Survey
TRENDS IN CHEMICAL CONCENTRATION IN SEDIMENT CORES FROM THREE LAKES IN NEW JERSEY 

AND ONE LAKE ON LONG ISLAND, NEW YORK

By Gary R. Long, Mark A. Ayers, Edward Callender, and Peter C. Van Metre

U.S. GEOLOGICAL SURVEY

Water-Resources Investigation Report 02-4272

West Trenton, New Jersey

2003
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

For additional information Copies of this report can be

write to: purchased from:

District Chief U.S. Geological Survey

U.S Geological Survey Branch of Information Services

Mountain View Office Park Box 25286

810 Bear Tavern Road Denver, CO 80225-0286

West Trenton, NJ 08628
CONTENTS

Page

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

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

Purpose and scope ............................................................................................................................ 2

Acknowledgments ............................................................................................................................ 3

Description of study area............................................................................................................................... 3

Clyde Potts Reservoir ....................................................................................................................... 3

Newbridge Pond ............................................................................................................................... 5

Orange Reservoir.............................................................................................................................. 5

Packanack Lake ................................................................................................................................ 5

Chemical constituents selected for analysis .................................................................................................. 5

Trace elements.................................................................................................................................. 5

Organochlorine compounds.............................................................................................................. 6

Polycyclic aromatic hydrocarbons.................................................................................................... 6

Collection, processing, analysis, and age dating of sediment cores .............................................................. 7

Collection, processing, and analysis................................................................................................. 7

Age dating......................................................................................................................................... 7

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

Occurrence of, and trends in, trace elements................................................................................................. 9

Arsenic.............................................................................................................................................. 9

Cadmium .......................................................................................................................................... 9

Chromium....................................................................................................................................... 12

Lead ................................................................................................................................................ 12

Mercury .......................................................................................................................................... 12

Nickel.............................................................................................................................................. 13

Zinc................................................................................................................................................. 13

Occurrence of, and trends in, hydrophobic organic compounds ................................................................. 13

Chlordane........................................................................................................................................ 13

Dieldrin........................................................................................................................................... 14

Total dichlorodiphenyl-trichloroethane .......................................................................................... 14

Total polychlorinated biphenyls ..................................................................................................... 16

Polycyclic aromatic hydrocarbons.................................................................................................. 16

Effect of watershed characteristics and regulatory action on constituent concentrations in sedment......... 16

Trace elements................................................................................................................................ 16

Organochlorine compounds............................................................................................................ 19

Polycyclic aromatic hydrocarbons.................................................................................................. 19

Summary and conclusions ........................................................................................................................... 20

References cited........................................................................................................................................... 22

ILLUSTRATIONS

Figure 1. Map showing location of the study lakes in New Jersey and on Long Island, New York........ 4

2-7. Graphs showing: 

2. Vertical distribution of trace elements in sediment cores from four study lakes .......... 11

3. Vertical distribution of organochlorine compounds in sediment cores from four 

study lakes................................................................................................................. 15

4. Vertical distribution of total polycyclic aromatic hyrocarbons (PAHs) in sediment 

cores from four study lakes....................................................................................... 15

5. Relation of log-transformed decadal lead concentrations in sediment cores to logtransformed decadal populaton of the municipalities adjacent to each study lake ... 18

6. Relation of log-transformed decadal zinc concentrations in sediment cores to logtransformed decadal populaton of the municipalities adjacent to each study lake ... 18

7. Population of municipalities adjacent to each of the four study lakes, 1930-90........... 18

iii
 TABLES

Table 1. Characteristics of watersheds for Clyde Potts Reservoir, Orange Reservoir, and

Packanack Lake in New Jersey and Newbridge Pond on Long Island, New York.................... 3

2. Statistically significant trends in concentrations of trace elements and hydrophobic

organic compounds in sediment cores from the four study lakes ............................................ 10

iv
CONVERSION FACTORS AND ABBREVIATIONS

Conversion Factors

Multiply By To obtain

Length

inch (in.) 25.4 millimeter

mile (mi) 1.609 kilometer

Area

square mile (mi2) 2.590 square kilometer (km2)

Mass

pound, avoirdupois (lb) 0.4536 kilogram (kg)

Abbreviation

Abbreviated water-quality unit used in report: μg/g, micrograms per gram

v
FOREWORD

The U.S. Geological Survey (USGS) is 

committed to serve the Nation with accurate and 

timely scientific information that helps enhance 

and protect the overall quality of life, and facilitates effective management of water, biological, 

energy, and mineral resources. Information on the 

quality of the Nation’s water resources is of critical 

interest to the USGS because it is so integrally 

linked to the long-term availability of water that is 

clean and safe for drinking and recreation and that 

is suitable for industry, irrigation, and habitat for 

fish and wildlife. Escalating population growth and 

increasing demands for the multiple water uses 

make water availability, now measured in terms of 

quantity and quality, even more critical to the longterm sustainability of our communities and ecosystems.

The USGS implemented the National WaterQuality Assessment (NAWQA) Program to 

support national, regional, and local information 

needs and decisions related to water-quality management and policy. Shaped by and coordinated 

with ongoing efforts of other Federal, State, and 

local agencies, the NAWQA Program is designed 

to answer: What is the condition of our Nation’s 

streams and ground water? How are the conditions 

changing over time? How do natural features and 

human activities affect the quality of streams and 

ground water, and where are those effects most 

pronounced? By combining information on water 

chemistry, physical characteristics, stream habitat, 

and aquatic life, the NAWQA Program aims to 

provide science-based insights for current and 

emerging water issues. NAWQA results can contribute to informed decisions that result in practical 

and effective water-resource management and 

strategies that protect and restore water quality.

Since 1991, the NAWQA Program has implemented interdisciplinary assessments in more than 

50 of the Nation’s most important river basins and 

aquifers, referred to as Study Units. Collectively, 

these Study Units account for more than 60 percent 

of the overall water use and population served by 

public water supply, and are representative of the 

Nation’s major hydrologic landscapes, priority 

ecological resources, and agricultural, urban, and 

natural sources of contamination.

Each assessment is guided by a nationally 

consistent study design and methods of sampling 

and analysis. The assessments thereby build local 

knowledge about water-quality issues and trends in 

a particular stream or aquifer while providing an 

understanding of how and why water quality varies 

regionally and nationally. The consistent, multiscale approach helps to determine if certain types 

of water-quality issues are isolated or pervasive, 

and allows direct comparisons of how human 

activities and natural processes affect water quality 

and ecological health in the Nation’s diverse geographic and environmental settings. Comprehensive assessments on pesticides, nutrients, volatile 

organic compounds, trace metals, and aquatic 

ecology are developed at the national scale through 

comparative analysis of the Study-Unit findings.

The USGS places high value on the communication and dissemination of credible, timely, and 

relevant science so that the most recent and 

available knowledge about water resources can be 

applied in management and policy decisions. We 

hope this NAWQA publication will provide you 

the needed insights and information to meet your 

needs, and thereby foster increased awareness and 

involvement in the protection and restoration of 

our Nation’s waters.

The NAWQA Program recognizes that a 

national assessment by a single program cannot 

address all water-resource issues of interest. 

External coordination at all levels is critical for a 

fully integrated understanding of watersheds and 

for cost-effective management, regulation, and 

conservation of our Nation’s water resources. The 

Program, therefore, depends extensively on the 

advice, cooperation, and information from other 

Federal, State, interstate, Tribal, and local 

agencies, non-government organizations, industry, 

academia, and other stakeholder groups. The assistance and suggestions of all are greatly appreciated.

Robert M. Hirsch

Associate Director for Water

vi


1

ABSTRACT

Sediment cores were extracted from three 

lakes in northeastern New Jersey and one lake on 

western Long Island, New York, as part of the U.S. 

Geological Survey National Water-Quality 

Assessment Program. Sediment layers were dated 

by use of cesium-137 (137Cs), copper, lead, or 

dichlorodiphenyl-trichloroethane (DDT) profiles. 

Sediment layers were analyzed for seven selected 

trace elements, including arsenic, cadmium, 

chromium, lead, mercury, nickel, and zinc, and five 

hydrophobic organochlorine compounds, including 

chlordane, dieldrin, total DDT, total 

polychlorinated biphenyls (PCBs), and total 

polycyclic aromatic hydrocarbons (PAHs). 

All seven trace elements were detected 

throughout the cores from all four lakes. 

Concentrations of all elements, except arsenic, 

were elevated in the three cores from lakes within 

urbanized watersheds (Packanack Lake, Orange 

Reservoir, and Newbridge Pond) relative to the 

concentrations in the lake core collected below the 

largely forested, reference watershed (Clyde Potts 

Reservoir). Results of trend analyses indicate that 

concentrations of all trace elements, with the 

exception of arsenic and lead, were relatively 

constant throughout the core from the minimally 

urbanized Clyde Potts Reservoir. In urban lakes, 

significant upward trends in concentrations from 

deeper to shallower sediments were observed 

either to peak concentrations or throughout the 

core for all elements, with the exception of 

chromium at all lakes and arsenic and nickel at 

Orange Reservoir. This finding indicates that 

changes in population and land use in the 

urbanized watersheds over the period of 

sedimentary record have contributed to upward 

trends in trace-element concentrations. Although 

downward trends in concentrations were observed 

for some trace elements in the years after their 

concentrations peaked, concentrations of all trace 

elements in urban lake cores were higher in the 

most recently deposited sediments than at the base 

of each respective core.

Lead concentrations over time were highly 

correlated with the population in the vicinity of the 

lake until the concentration peak in sediment 

deposited in the mid-1970’s. Concentrations of 

lead in lake sediment appear to be closely related to 

the use of leaded gasoline because lead 

concentrations generally decreased after the use of 

leaded gasoline was phased-out in the mid-1970’s. 

Zinc concentrations were highly correlated with 

population over the entire length of the core. In 

general, zinc concentrations increased in the three 

urbanized watersheds, probably in response to 

increasing population and vehicular use. This 

trend was not evident at Clyde Potts Reservoir, 

however, where vehicular traffic in the watershed 

is minimal.

Detectable concentrations of chlordane, 

total DDT, and total PCBs were present in cores 

from all lakes; however, dieldrin was detected only 

in the Newbridge Pond and Packanack Lake cores. 

Concentrations generally were higher in cores from 

the urbanized Newbridge Pond and Orange 

Reservoir watersheds than in those from the 

minimally urbanized Clyde Potts Reservoir 

watershed. With the exception of chlordane in the 

Clyde Potts and Orange Reservoir cores, 

concentrations of the four organochlorine 

compounds had significant downward trends from 

peak concentrations to recently deposited sediment 

or non-significant trends throughout the core. On 

the basis of these findings and as a result of 

regulatory actions prohibiting the production and 

use of these compounds, downward trends in 

sedimentary concentrations are expected to 

continue; however, the persistence of these 

TRENDS IN CHEMICAL CONCENTRATION IN SEDIMENT 

CORES FROM THREE LAKES IN NEW JERSEY AND ONE 

LAKE ON LONG ISLAND, NEW YORK

By Gary R. Long, Mark A. Ayers, Edward Callender, and Peter C. Van Metre 
2

compounds indicates that a substantial amount of 

time may be required to purge them from the 

watersheds. 

Concentrations of PAHs in sediment 

generally increased with population growth and 

urbanization, probably as a result of increased 

fossil-fuel combustion (gasoline and home-heating 

fuels and other uses (roads and parking lots paved 

with asphalt) associated with increased urban 

development and vehicular traffic. This finding is 

supported by low concentrations of PAHs in 

Packanack Lake sediments in the 1930’s, before 

the watershed was urbanized and when 

automobiles were comparatively rare. As vehicular 

use and urbanization increase in these watersheds, 

the general increase of PAH concentrations in lake 

sediments can be expected to continue. 

Data from this study indicate that changes 

in population, land use, and chemical use in the 

urbanized watersheds over the period of 

sedimentary record have contributed to upward 

trends in concentrations of trace elements and 

hydrophobic organic compounds. Although 

downward trends were observed for some 

constituents in the years after their concentrations 

peaked, concentrations of most constituents in 

urban lake cores were higher in the most recently 

deposited sediments than at the base of each 

respective core and in the reference lake cores. 

Similar trends in concentrations of these 

constituents have been observed in sediment cores 

from other urban lakes across the United States.

INTRODUCTION

A main objective of the U.S. Geological 

Survey (USGS) National Water Quality 

Assessment Program (NAWQA) is to define trends 

(or lack of trends) in the quality of the Nation’s 

water resources (Leahy and others, 1990; Ayers 

and others, 2000). Trend analyses are important 

because they aid in understanding how 

anthropogenic activities have affected water 

quality in the past and how continued activity may 

affect future water quality. Trends also are an 

important tool to evaluate the effectiveness of 

environmental regulations designed to reduce the 

input of contaminants into aquatic systems. 

Trend analyses typically are applied to 

historical water-quality data sets that contain 

multiple years of water-quality records. When such 

historic data are lacking or incomplete, however, 

other techniques can be used to assess waterquality trends. One such technique is the chemical 

analysis of sediment cores from reservoirs and 

lakes (Eisenreich and others, 1989; Callender and 

Robbins, 1993; Van Metre and Callender, 1996). 

As soil erodes from land surfaces within a 

watershed, it is transported by streams to 

downstream lakes and reservoirs where it settles 

and accumulates. Trace elements and hydrophobic 

organic compounds, including organochlorine 

compounds and polycyclic aromatic hydrocarbons 

(PAHs), sorb to fine-grained sediment particles 

and, thus, are transported through the watershed 

and deposited at the bottom of lakes and reservoirs. 

By determining the age of the sediment in cores 

and measuring the concentrations of trace elements 

and hydrophobic organic compounds associated 

with the dated sediment, a record can be obtained 

of the trace elements and hydrophobic organic 

compounds input to the watershed over a period of 

time. This technique was used to document trends 

in the quality of runoff to lakes in the 6,000-mi2

Long Island-New Jersey (LINJ) NAWQA study 

area in order to examine the relation between 

runoff-water quality and past anthropogenic 

activities.

Purpose and Scope

This report describes trends in concentrations of seven selected trace elements and five 

hydrophobic organic compounds in multiple agedated sediment cores extracted from four lakes in 

small watersheds (less than 5 mi2) in the LINJ 

NAWQA study area. Three of the lakes are in 

northeastern New Jersey and one is on western 

Long Island, New York. Urban land use in the four 

watersheds ranges from 13.7 to 99.7 percent. The 

relation of trends in the concentrations of selected 

contaminants to changes in population and land use 

in the four watersheds also is described.
3

Acknowledgments

We thank the owners and managers of the 

lakes for providing access to and information about 

each lake. We thank Michael Dorsey, Kathryn 

Conko, Steven Terracciano, Craig Weiss, and 

Timothy Wilson of the USGS for their 

contributions during the field-work segment of this 

lake-sediment coring study. We also thank Kathryn 

Conko for performing the trace element laboratory 

analyses.

DESCRIPTION OF STUDY AREA

The LINJ study area encompasses the 

coastal watersheds of New Jersey, all of Long 

Island, New York, and a small part of southeastern 

New York that drain into New Jersey. With a 1990 

population of more than 12 million people 

concentrated in northeastern New Jersey and 

western Long Island, the study area is one of the 

more densely populated areas in the Nation (Ayers 

and others, 2000). Urban residential, commercial, 

and industrial land use dominate northeastern New 

Jersey and western Long Island. Three of the four 

study lakes are located in northeastern New Jersey 

and one is on western Long Island (fig. 1).

Clyde Potts Reservoir

Clyde Potts Reservoir, 5 mi west of 

Morristown, in Morris County, New Jersey, was 

constructed in 1931 as a water-supply reservoir for 

the Southeast Morris County Municipal Utilities 

Authority. The 2.08-mi2

 watershed that drains to 

the reservoir is in the upper Whippany River basin. 

The Clyde Potts Reservoir watershed is largely 

forested, with limited urban-residential 

development and population density (table 1). 

Therefore, atmospheric pathways are likely the 

predominant source of contaminants to the 

watershed. Clyde Potts Reservoir is considered to 

be minimally disturbed relative to the other lakes 

and is considered a reference site for this study.

Table 1. Characteristics of watersheds for Clyde Potts Reservoir, Orange Reservoir, and 

Packanack Lake in New Jersey and Newbridge Pond on Long Island, New York 

[Listed in order of increasing urban-residential land use and population density; Other, this landuse category is the sum of agricultural, water, wetland, and barren land; mi2, square mile]

Lake watershed

Mid-1990s land use, in percent of basin area 1990 population 

density

(people/mi2)

Basin 

area 

(mi2)

Urbanresidential

Urbanindustrial 

commercial

Forest Other

Clyde Potts Reservoir 12.2 1.5 77.7 8.6 386 2.1

Orange Reservoir 60.6 8.6 25.5 5.3 2,160 4.5

Packanack Lake 72.9 3.5 14.3 9.4 2,160 1.9

Newbridge Pond 87.2 12.5 0 .3 7,250 5.1
4

0

0

10 20 MILES

15 30 KILOMETERS

0 1 MILE

0 1 KILOMETER

0 1 MILE

0 1 KILOMETER

0 1 MILE

0 1 KILOMETER

0 1 MILE

0 1 KILOMETER

41¡

40¡30’

74¡30’ 74¡ 73¡30’

EXPLANATION

Urban residential

Urban commerical-industrial

Agriculture

Forest

Water

Wetlands

Barren

1990’s LAND USE

Figure 1. Location of the study lakes in New Jersey and Long Island, New York.

Lake watershed area

1930’s urban area

1950’s urban area

EXPLANATION

LAND USE

1970’s urban area

1990’s urban area

Study area boundary

Clyde Potts

Reservoir

Packanack Lake

Orange Reservoir

Newbridge Pond
5

Newbridge Pond

Newbridge Pond, just east of Merrick, in 

Nassau County, Long Island, New York, was 

constructed in 1895 to supply water to the City of 

New York. Its use as a water-supply source was 

abandoned a few decades later. Development of the 

3.1-mi2 watershed started in the early 1900’s with 

most development occurring in the 1920’s and 

1940’s. By the late 1940’s, the watershed was 

mostly developed as urban land. Compared to 

other study lakes, land use for the Newbridge Pond 

watershed had the highest percentage of urbanresidential and urban-industrial/commercial land 

use in the mid-1990’s (table 1). The 1990 

population density here is more than 7,250 people 

per square mile, which is at least 3 times that of 

any of the other lake watersheds in this study (table 

1). The watershed is intersected by two major 

highways--one near the southern outlet of the pond 

and the other in the central part of the basin (fig. 1).

Orange Reservoir

Orange Reservoir, in West Orange, Essex 

County, New Jersey, was constructed in the early 

1880’s as a water-supply reservoir and is currently 

(2002) maintained by the City of Orange for that 

purpose. The 4.5-mi2

 watershed is in the upper 

Rahway River basin. Development surrounding 

Orange Reservoir occurred rapidly in the early 

1900’s when public transportation opened 

commuter passage to Newark and Manhattan 

(Essex County, 2000). The population surrounding 

Orange Reservoir increased steadily from 1900 to 

1970, with the greatest increase between 1950 and 

1960 (New Jersey Department of Labor, 1991). 

The Orange Reservoir watershed has the second 

largest percentage of urban-industrial/commercial 

land use in the study area (8.6 percent); however, 

about 25 percent of the watershed remains forested 

(table 1).

Packanack Lake

Packanack Lake, in Wayne Township, 

Passaic County, New Jersey, was constructed in 

1930 on Packanack Brook in the Pompton River 

watershed. The population density of the 1.9-mi2

watershed is comparable to that of Orange 

Reservoir. Urban-residential is the predominant 

land use (table 1). The population of the area began 

to increase in the 1930’s, increased most from 1950 

to 1970, and stabilized or declined slightly since 

then (New Jersey Department of Labor, 1991).

CHEMICAL CONSTITUENTS 

SELECTED FOR ANALYSIS

Trace Elements

Trace elements occur in the environment 

as a product of geologic weathering and human 

activities that release point- and nonpoint-source 

contamination. No major point sources of trace 

elements are known to be present in these 

watersheds; however, potential nonpoint sources in 

study watersheds include runoff from urban 

surfaces, soil erosion, and atmospheric deposition 

of materials emitted from fossil-fuel combustion, 

including automobile exhaust and industrial metal 

processing (Brigham and others, 1997; Forstner 

and Wittman, 1983; Harte and others, 1991; Ondov 

and others, 1982). Once introduced to the 

environment, trace elements tend to sorb to finegrained sediments (Forstner and Wittman, 1983). 

These sediments are transported downstream until 

they reach areas of deposition such as lakes or 

reservoirs. The accumulation of trace-elementsorbed particles commonly makes sediments the 

most concentrated pool of trace elements in the 

aquatic environment (Miller and others, 1992). 

Arsenic (As), cadmium (Cd), chromium (Cr), lead 

(Pb), mercury (Hg), nickel (Ni), and zinc (Zn) were 

selected for detailed analysis in this study.
6

Organochlorine Compounds

Organochlorine compounds are a class of 

synthetic chemicals that include chlordane, 

dichlorodiphenyl-trichloroethane (DDT), dieldrin, 

and polychlorinated biphenyl compounds (PCBs), 

all of which have been widely used for agricultural 

and industrial purposes since World War II. 

Organochlorine compounds tend to be chemically 

stable, environmentally persistent, and toxic to 

living organisms (Nadakavukaren, 1995). 

Organochlorine compounds are similar to trace 

elements in that they tend to sorb to sediments 

carried in runoff and accumulate in the 

depositional areas of lakes and reservoirs. 

Introduced in 1947, chlordane was 

manufactured as a pesticide used to control soil 

pests, particularly termites (Harte and others, 

1991). Chlordane is stable in soils and is not 

degraded through hydrolysis, oxidation, or direct 

photolysis, making it environmentally persistent 

(U.S. Environmental Protection Agency, 1979). 

Possible modes of entry into the aquatic 

environment include drift from aerial spraying, 

surface runoff, subsurface seepage, misapplication, 

and domestic and industrial effluents (Canadian 

Council of Resource and Environment Ministers, 

1992). In 1978, the U.S. Environmental Protection 

Agency (USEPA) cancelled agricultural uses of 

chlordane; all uses were banned in 1988 (U.S. 

Environmental Protection Agency, 1997).

DDT was developed in 1939 as an 

agricultural insecticide. The early success of DDT 

in controlling insect pests led to its widespread use 

throughout the United States. It is not readily 

degraded through hydrolysis, oxidation, or direct 

photolysis, making it environmentally persistent 

(U.S. Environmental Protection Agency, 1979). In 

the aquatic environment, DDT binds strongly to 

sediment, making sorption a dominant fate process 

(U.S. Environmental Protection Agency, 1979). In 

1972, the USEPA banned the use of DDT after its 

toxic bioaccumulation effects on wildlife were 

discovered; however, because of its widespread use 

and long half-life, it is still commonly found in the 

environment (U.S. Environmental Protection 

Agency, 1997; Harte and others, 1991). In this 

study, total DDT was calculated as the sum of DDT 

and its degradation products DDD and DDE.

Dieldrin, a compound in the same class of 

insecticides as chlordane, was first synthesized in 

1948 and used primarily to control soil insects, 

including the corn rootworm (Ware, 1994). 

Dieldrin is environmentally persistent and strongly 

adsorbs to soil sediment (U.S. Environmental 

Protection Agency, 1979). The USEPA canceled 

most uses of dieldrin in 1971 (Sittig, 1980), 

although use as an alternative termiticide to 

chlordane was allowed until the mid-1980’s. 

PCBs were synthesized in the 1930’s and 

used as plasticizers, hydraulic lubricants, 

components in pesticides, and dielectric fluids in 

electric capacitors (Smith and others, 1988). PCBs 

are degraded only through slow biological 

pathways; therefore, they remain persistent in the 

environment (U.S. Environmental Protection 

Agency, 1979). They strongly sorb to sediment 

and organic matter, making areas of sediment 

deposition an important sink (U.S. Environmental 

Protection Agency, 1979). After four decades, 

production and use of PCBs were banned in 1979; 

however, PCBs are still present within the aquatic 

environment (U.S. Environmental Protection 

Agency, 1997; Harte and others, 1991). In the 

current analysis, total PCB concentration was 

calculated as the sum of three arochlors of PCBs 

(arochlor mixtures 1252, 1254, and 1260).

 

Polycyclic Aromatic Hydrocarbons

PAHs are a class of organic compounds 

with a fused-ring aromatic structure. PAHs result 

from the incomplete combustion of organic carbon, 

including the incomplete combustion of wood, 

solid waste, and fossil fuels. PAHs also can be 

derived directly from use and release of coal and 

oil products in the urban environment, including 

spillage or seepage of fossil-fuel products, 

industrial and domestic discharges, urban surface 

wash off, and atmospheric deposition (Rand and 

Petrocelli, 1985). PAHs are present in asphalt road 

surfaces, vehicle tires, and condensation from 

vehicle exhaust (Rand and Petrocelli, 1985). 
7

Therefore, runoff from paved surfaces is likely an 

important source of PAHs in the study watersheds. 

In this study, total PAH concentration was 

calculated as the sum of 60 individual PAH 

compounds.

COLLECTION, PROCESSING, 

ANALYSIS, AND AGE DATING OF 

SEDIMENT CORES

Collection, Processing, and Analysis

In September 1997, sediment cores were 

collected from the deepest area in each of the four 

study lakes. Cores were extracted using a 2.5-inchdiameter Benthos gravity corer and (or) a Wildco 

box corer1 measuring 6 by 6 inches square by 8 

inches tall. The plastic-lined corers were lowered 

with a winch from a 16-ft inflatable zodiac raft 

outfitted with a crane over the bow (Van Metre and 

Mahler, 1999). More information on coring can be 

found at the USGS web site http://tx.usgs.gov/

coring/.

Multiple cores were extracted from each 

site. The first core extracted at the site was used to 

visually describe the physical characteristics of the 

sediments, especially total thickness of lake 

sediment and depth of the pre-reservoir land 

surface. This information was an aid in selecting 

layers for chemical analysis. Additional cores then 

were collected for each type of chemical analysis. 

The contents of each core were carefully extruded 

to a prescribed vertical distance and 1- to 2-cmthick horizontal slices of sediment, which represent 

the desired discrete layers of sediment over time, 

were removed. Sediment analyzed for organic 

compounds was placed in baked glass jars and 

chilled pending submittal to the USGS National 

Water Quality Laboratory. Sediment for analysis 

of radionuclides and trace elements was placed in 

cleaned polyethylene jars and chilled pending 

analysis. 

Organic compounds (organochlorine 

compounds and PAHs) were measured by gas 

chromatography (Furlong and others, 1996; 

Foreman and others, 1995). Trace elements, with 

the exception of mercury, were measured by 

inductively coupled plasma/atomic adsorption 

spectrometry and graphite-furnace atomic 

adsorption (Arbogast, 1996). Mercury was 

analyzed by cold vapor atomic adsorption 

spectrometry. Cesium-137 (137Cs), a radionuclide 

used in age dating, was measured by radioactive 

counting (Callender and Robbins, 1993).

Age Dating

The assignment of dates to each respective 

horizontal slice or layer was based on date-depth 

markers and assumed rates of sedimentation 

between end points. The top of the core was 

assigned the sampling date (1997.75) and, if prereservoir material was discovered, the base was 

assigned the date of reservoir impoundment. For 

the Newbridge Pond cores, a date-depth marker 

was determined by use of 137Cs, a by-product of 

nuclear weapons testing that initially was detected 

in the atmosphere in 1953 and reached peak 

atmospheric concentrations in 1964. The 

concentration of 137Cs peaked at a 41-cm depth in 

the Newbridge Pond core; therefore, this layer was 

assigned a date of 1964.0. The rate of sediment 

accumulation between the date-depth marker 

(1964.0) and the top of the core (1997.75) was 

determined and, by assuming a constant 

sedimentation rate, was used to date the remaining 

layers of the core. 

For other cores, alternative date-depth 

markers were used because the 137Cs peak was not 

sufficiently defined. In the cores analyzed for trace 

elements at Clyde Potts and Orange Reservoirs, 

peak concentrations of lead were assigned a date of 

1975, an approximate date in which peak 

concentrations have been reported in reservoir 

sediment (Callender and Van Metre, 1997). 

1

Use of brand, trade, or firm names is for descriptive purposes only and does not constitute endorsement by the 

U.S. government.
8

Sampling dates and lead peaks that are evident 

3.75 and 15 cm from the top of the Clyde Potts and 

Orange Reservoir cores, respectively, were used as 

date-depth markers to determine sedimentation 

rates. In the Orange Reservoir core analyzed for 

hydrophobic organic compounds, the peak 

concentration of total DDT, observed 23 cm from 

the top of the core, was assigned a date of 1962. 

This date is an approximation based on data from 

other NAWQA reservoir cores that indicate a 

consistent peak in total DDT concentrations 

occurred in the early 1960’s (Van Metre and 

Callender, 1996). Sedimentation rates were 

determined for the Orange Reservoir core on the 

basis of the 1962 total DDT peak and the sampling 

date. In the Clyde Potts core that was analyzed for 

hydrophobic organic compounds, the total PCB 

peak occurred 12.5 cm from the top of the core. 

This layer was assigned a date of 1970.0, an 

approximation based on data from other reservoir 

cores that indicate a consistent total PCB peak in 

the late 1960’s (Van Metre and others, 1998). This 

date-depth marker was used with the sampling date 

to determine the sedimentation rate in the Clyde 

Potts Reservoir core. 

 For the Packanack Lake cores, the 

assumption of constant sedimentation was 

problematic. For the core that was analyzed for 

hydrophobic organic compounds, when the 

impoundment date and a constant sedimentation 

rate were used, age estimates resulted in peak 

concentrations of total DDT dated in the early 

1980’s, much later than typically observed in many 

other lake and reservoir cores collected in 

NAWQA studies (Van Metre and others, 1998). 

For the core that was analyzed for trace elements, a 

sharp increase in copper concentrations at 18 cm 

from the top was correlated with the onset of 

copper sulfate (CuSO4) treatments of the lake, 

which began in approximately 1953 (Phillip 

Gianinio, Packanack Lake Country Club and 

Community Association, oral commun., 1999). 

Age estimates made using the copper date-depth 

marker and assuming a constant sedimentation rate 

resulted in peak lead concentrations dated in the 

late 1980’s, which is also much later than typically 

observed in other lake and reservoir cores collected 

in NAWQA studies (Callender and Van Metre, 

1997). Results indicate that mass sedimentation 

rates likely decreased between the occurrence of 

the date-depth markers and the top of the core. 

Callender and Robbins (1993) found that 

decreasing sedimentation rates were common in 

reservoirs and typically fit an exponential model. 

Following their approach, an exponential 

sedimentation model was fit to the Packanack Lake 

cores. For the core analyzed for hydrophobic 

organic compounds, the date of the pre-reservoir 

surface, the DDT maxima, and the sampling date 

were used as control points in the model. The 

same model variables, scaled to a smaller overall 

sedimentation rate, were fit to the core analyzed for 

trace elements with the copper date-depth marker 

and the sampling date as control points. Although 

there is uncertainty associated with the designation 

of dates to individual sample intervals in the cores, 

corroborative evidence provided by multiple datedepth markers, including total DDT peaks, total 

PCB peaks, and lead peaks, indicates that most 

dates are probably within a few years of actual 

deposition dates. 

Data Analysis

Spearman’s rank correlation was used to 

evaluate trends in constituent concentrations in the 

lake cores. The significance of Spearman’s Rho 

coefficient (p) was determined on the basis of the 

number of observations in each analysis. 

Spearman’s Rho coefficients were considered to be 

statistically significant at a 95-percent confidence 

interval (p<0.05). Constituent concentrations with 

“less than” remarks were estimated to be 50 

percent of the reporting limit for use in the 

correlation analyses. Concentrations of 

organochlorine compounds with “less than” 

remarks for core layers with dates prior to the 

known synthesis date of the respective compound 

were assummed to be zero and removed from trend 

analyses. Linear regression analyses were 

performed to evaluate relations between decadal 

average concentrations of lead and zinc, and 

decadal population. Historical population data 

specific to each basin could not be obtained; 

therefore, population was estimated by summing 
9

decadal population data of municipalities 

surrounding each basin (New Jersey Department of 

Labor, 1991). Lead, zinc, and population data were 

log-transformed to obtain a normal distribution 

(Shapiro-Wilk p-values > 0.05).

OCCURRENCE OF, AND TRENDS IN, 

TRACE ELEMENTS

Trace elements derived from geologic and 

anthropogenic sources tend to sorb to fine-grained 

sediment in streams and accumulate at the bottoms 

of lakes and reservoirs. All selected trace elements 

were detected throughout all four cores. The cores 

analyzed for trace elements contained sediment 

dated as follows: Newbridge Pond, about 1959; 

Packanack Lake, about 1947; Orange Reservoir, 

about 1921; and Clyde Potts Reservoir, about 1935.

Depositional rates in the trace-element 

cores differed among the lakes. The highest linear 

sedimentation rate of 0.47 in/yr (1.2 cm/yr) was 

observed in the Newbridge Pond core. The rate 

was 0.16 in/yr (0.4 cm/yr) for the Orange Reservoir 

and Packanack lake cores and 0.04 in/yr (0.1 cm/

yr) for the Clyde Potts Reservoir core. 

Arsenic

Sedimentary concentrations of arsenic in 

lake cores ranged from about 5 to 27 μg/g (fig. 2). 

This variation probably reflects differences in 

watershed geology and indigenous sediment inputs 

as much as differences in anthropogenic inputs 

from the application of arsenical pesticides. 

Concentrations were lowest and most consistent in 

the Packanack Lake core, whereas the largest 

concentrations and variations were observed in the 

Clyde Potts Reservoir core. These results can be 

attributed to the geology of the areas. No 

significant trend (p=0.38) was evident in the Clyde 

Potts Reservoir core, although concentrations in 

recently deposited sediment were more than 2.5 

times the concentrations at the base of the core. 

Concentrations of arsenic in sediment in the 

Newbridge Pond core had a statistically significant 

upward trend (p=0.59) from the oldest to most 

recently deposited sediment (table 2; fig. 2). The 

upward trend reflects concentrations in recently 

deposited sediment that were more than 2.0 times 

the concentrations at the base of the Newbridge 

Pond core. A significant upward trend (p=0.89) in 

arsenic concentrations was observed from the base 

of the Packanack Lake core to the peak 

concentration in 1961; however, no significant 

trend (p =-0.49) was observed from the 1961 peak 

to the most recently deposited sediments. 

Concentrations in recent sediment remain nearly 

1.5 times those in sediment at the base of the 

Packanack Lake core. No significant trend 

(p=0.10) was evident for arsenic concentrations 

from the base of the Orange Reservoir core to the 

peak concentration in 1984; however, a significant 

downward trend (p=-0.94) was observed from the 

1984 peak concentration to the most recently 

deposited sediment. Arsenic concentrations in 

recently deposited sediment remain approximately 

1.2 times the concentrations at the base of the 

Orange Reservoir core. 

Cadmium

Concentrations of cadmium in lake cores 

were low (from 0.4 to 2.0 μg/g, fig. 2) relative to 

those of other trace elements, except mercury. 

Concentrations were lowest and exceptionally 

stable in the Clyde Potts Reservoir core, for which 

no significant trends (p=-0.37) were observed 

(table 2; fig. 2). The largest variations and 

concentrations of cadmium were evident in the 

Newbridge Pond core. Concentrations generally 

increased from older to more recent sediments in 

all three urban lakes. A significant upward trend 

(p=0.76) in cadmium concentrations was evident 

from the base of the Newbridge Pond core to the 

peak concentration in 1982, followed by a 

significant downward trend (p=-0.53) from the 

1982 peak to the most recently deposited sediment. 

In the Newbridge Pond core, cadmium 

concentrations in recently deposited sediment were 

nearly 4.0 times the concentrations at the base. 

Cadmium concentrations had significant upward 

trends from the oldest to the most recently 

deposited sediment in the Orange Reservoir and 
10

Table 2. Statistically significant trends in concentrations of trace elements and hydrophobic 

organic compounds in sediment cores from Clyde Potts Reservoir, Orange Reservoir, and 

Packanack Lake in New Jersey and Newbridge Pond on Long Island, New York 

[ND = insufficient data for test; dashes (--) = no trend detected; significant upward trend in red; significant downward trend 

in blue; (0.59), Spearman’s Rho coefficient; * = significance at 95 percent confidence level; ** = significance at 99 percent 

confidence level]

Constituent

Direction of trend(s)

Clyde Potts Reservoir Newbridge Pond Orange Reservoir Packanack Lake

Trace elements

Arsenic --

Significant upward trend 

from older to younger 

sediments (0.59**)

No significant trend to 

1984, downward trend 

since then (-0.94**)

Significant upward trend to 

1961 (0.89**), no 

significant trend since then

Cadmium --

Significant upward trend 

to 1982 (0.76**),

downward trend since 

then (-0.53*)

Significant upward trend 

from older to younger 

sediments (0.79**)

Significant upward trend 

from older to younger 

sediments (0.69**)

Chromium -- -- -- --

Lead

Significant upward trend 

to 1975 (0.98**), no trend 

since then

Significant upward trend 

to 1976 (0.96**),

downward trend since 

then (-0.99**)

Significant upward trend 

to 1975 (0.97**),

downward trend since 

then (-0.93**)

Significant upward trend to 

1978 (0.99**), downward 

trend since then (-0.90**)

Mercury --

Significant upward trend 

to 1968 (0.94**),

downward trend since 

then (-0.93**)

Significant upward trend 

from older to younger 

sediments (0.90**)

Significant upward trend to 

1960 (0.89*), downward 

trend since then (-0.96**)

Nickel --

Significant upward trend 

from older to younger 

sediments (0.49**)

--

Significant upward trend 

from older to younger 

sediments (0.67**)

Zinc

Significant downward 

trend from older to 

younger sediments

(-0.50*)

Significant upward trend 

from older to younger 

sediments (0.93**)

Significant upward trend 

from older to younger 

sediments (0.95**)

Significant upward trend 

from older to younger 

sediments (0.95**)

Hydrophobic Organic Compounds

Chlordane

Significant upward trend 

from older to younger 

sediments (0.68**)

Significant upward trend 

to 1969 (1.00**),

downward trend since 

then (-0.76**)

Significant upward trend 

from older to younger 

sediments (0.75**)

--

Dieldrin ND

Significant upward trend 

to 1970 (1.00**),

downward trend since 

then (-0.65*)

ND --

Total DDT --

No significant trend to 

1962, downward since 

then (-0.81**)

Significant downward 

trend from older to 

younger sediments

(-0.85**)

--

Total PCB --

Significant upward trend 

to1962 (1.00**), 

downward trend since 

then (-0.62*)

--

Significant upward trend to 

1973 (0.73*), significant 

downward trend since then 

(-0.74*)

Total PAH --

Significant upward trend 

from older to younger 

sediments (0.89**)

--

Significant upward trend 

from older to younger 

sediments (0.71**)
11

1910

1920

1930

1940

1950

1960

1970

1980

1990

2000

10 100 1,000 10,000 100,000

ZINC CONCENTRATIONS, IN MICROGRAMS PER GRAM

APPROXIMATE YEAR OF DEPOSITION

1910

1920

1930

1940

1950

1960

1970

1980

1990

2000

20 30 40 50 60 70 80 90

NICKEL CONCENTRATIONS, IN MICROGRAMS PER GRAM

APPROXIMATE YEAR OF DEPOSITION

1910

1920

1930

1940

1950

1960

1970

1980

1990

2000

0 0.5 1 1.5 2 2.5 3

MERCURY CONCENTRATIONS, IN MICROGRAMS PER GRAM

APPROXIMATE YEAR OF DEPOSITION

1910

1920

1930

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1950

1960

1970

1980

1990

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10 100 1,000 10,000

LEAD CONCENTRATIONS, IN MICROGRAMS PER GRAM

APPROXIMATE YEAR OF DEPOSITION

1910

1920

1930

1940

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1960

1970

1980

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2000

50 70 90 110 130 150 170

CHROMIUM CONCENTRATIONS, IN MICROGRAMS PER GRAM

APPROXIMATE YEAR OF DEPOSITION

1910

1920

1930

1940

1950

1960

1970

1980

1990

2000

0.0 0.5 1.0 1.5 2.0 2.5

CADMIUM CONCENTRATIONS, IN MICROGRAMS PER GRAM

 APPROXIMATE YEAR OF DEPOSITION

1910

1920

1930

1940

1950

1960

1970

1980

1990

2000

0 5 10 15 20 25 30

ARSENIC CONCENTRATION, IN MICROGRAMS PER GRAM

APPROXIMATE YEAR OF DEPOSITION

Figure 2. Vertical distribution of trace elements in sediment cores from Clyde Potts Reservoir, Orange

Reservoir and Packanack Lake in New Jersey and Newbride Pond on Long Island, New York.

EXPLANATION

Clyde Potts Reservoir

Newbridge Pond

Orange Reservoir

Packanack Lake
12

Packanack Lake cores (p=0.79 and 0.69, 

respectively). Concentrations in the most recently 

deposited sediment in the Orange Reservoir and 

Packanack Lake cores were 1.4 and 1.6 times, 

respectively, the concentrations at the base of the 

cores.

Chromium

Concentrations of chromium in lake cores 

ranged from about 60 to 160 μg/g (fig. 2) and were 

highly variable in all four cores. Concentrations 

generally were highest in the Orange Reservoir 

core, whereas concentrations were lowest in the 

Clyde Potts Reservoir core. In the Clyde Potts 

Reservoir core, concentrations in recently 

deposited sediment were about one-third the 

concentrations at the base of the core; however, no 

statistically significant downward trend (p=-0.44) 

was observed in the overall core (table 2; fig. 2). 

Concentrations appear to have generally increased 

from older to more recent sediments in all three 

urban lakes; however, no significant trends 

(p=0.00, 0.44 and 0.41, respectively) were 

observed for chromium in the Newbridge Pond, 

Orange Reservoir, and Packanack Lake cores. 

Lead

Concentrations of lead in lake cores ranged 

from about 25 to 2,340 μg/g (fig. 2). 

Concentrations in the Newbridge Pond core 

generally were an order of magnitude higher 

relative to those in cores from the other lakes. The 

Clyde Potts Reservoir core reflected the smallest 

anthropogenic effect because, in general, 

concentrations of lead in this core were lower than 

those in other cores. In all cores, peak lead 

concentrations were 2 to 10 times the concentration 

at the base of each respective core. Peak 

concentrations occurred between 1975 and 1978, 

when the use of lead as a gasoline additive was 

phased out. 

Lead concentrations in cores from all four 

lakes had significant upward trends (p=0.98, 0.96, 

0.97, and 0.99 for Clyde Potts Reservoir, 

Newbridge Pond, Orange Reservoir, and 

Packanack Lake, respectively) from the base of the 

cores to peak concentrations from 1975 to 1978 

(table 2; fig. 2). No significant trend (p=-0.67) was 

evident in lead concentrations in the Clyde Potts 

Reservoir core since the peak in 1975; however, 

significant downward trends (p=-0.99, -0.93, and -

0.90, respectively) in lead concentrations were 

evident in the Newbridge Pond core since a 1976 

peak, in the Orange Reservoir core since a 1976 

peak, and in the Packanack Lake core since a 1978 

peak. Lead concentrations in recently deposited 

sediment were comparable to concentrations at the 

base of the Clyde Potts Reservoir and Orange 

Reservoir cores, whereas concentrations in recent 

sediment remained considerably elevated relative 

to concentrations at the base of the Newbridge 

Pond and Packanack Lake cores.

Mercury

Concentrations of mercury in lake cores, 

like those of cadmium, were relatively low 

compared to other trace elements. Concentrations 

ranged from about 0.26 to 2.6 μg/g (fig. 2), with 

highest concentrations found in the Orange 

Reservoir core and lowest concentrations found in 

the Clyde Potts Reservoir and Packanack Lake 

cores. Concentrations generally increased from 

oldest to more recent sediments in all three urban 

lakes. Mercury concentrations peaked in the 

1960’s in the Newbridge Pond and Packanack Lake 

cores but increased steadily in the Orange 

Reservoir core.

No significant trend (p=-0.04) was evident 

for mercury concentrations in the Clyde Potts 

Reservoir core (table 2; fig. 2). A significant 

upward trend (p=0.90) was observed for mercury 

concentrations in the Orange Reservoir core; 

concentrations in recently deposited sediment were 

more than 1.8 times the concentrations at the base 

of the core. A significant upward trend (p=0.94) 

was observed from the base of the Newbridge Pond 

core to a peak mercury concentration in 1968; 

however, a significant downward trend (p=-0.93) 

was observed since 1968. Mercury concentrations 
13

in recently deposited sediment are only slightly 

higher than concentrations at the base of the 

Newbridge Pond core (fig. 2). Similarly, for the 

Packanack Lake core, a significant upward trend 

(p=0.89) was observed to a 1960 peak 

concentration followed by a significant downward 

trend (p=-0.96) in sediment deposited since 1960. 

Concentrations in recently deposited sediment, 

however, were nearly twice those observed at the 

base of the Packanack Lake core (fig. 2). 

Nickel

Concentrations of nickel in lake cores 

ranged from about 23 to 81 μg/g (fig. 2). The 

highest concentrations were present in the Orange 

Reservoir and Newbridge Pond cores, whereas the 

lowest concentrations were present in the Clyde 

Potts Reservoir and Packanack Lake cores. No 

significant trends were evident for nickel 

concentrations in the Clyde Potts and Orange 

Reservoir cores (p=-0.27 and 0.31, respectively) 

(table 2; fig. 2). Concentrations in cores from the 

other two urban lakes, in general, increased from 

oldest to more recent sediments. Significant 

upward trends (p=0.49 and 0.67, respectiviely) in 

nickel concentrations were evident in the 

Newbridge Pond and Packanack Lake cores; 

however, concentrations in recently deposited 

sediment were only 1.3 and 1.5 times the 

concentrations at the base of the Newbridge Pond 

and Packanack Lake cores, respectively. 

Zinc

Concentrations of zinc in lake cores ranged 

from about 67 to 11,800 μg/g (fig. 2), the highest 

range of the trace elements sampled. Zinc 

concentrations were highest in the Newbridge 

Pond core and generally were two orders of 

magnitude higher than those in the other lake cores 

(fig. 2). The Clyde Potts Reservoir core reflected 

the smallest anthropogenic effect; a significant 

downward trend (p=-0.50) in zinc concentrations 

from oldest to youngest sediment was observed 

(table 2; fig. 2). Zinc concentrations generally 

increased from oldest to more recent sediment in 

the cores of the three urban lakes. Significant 

upward trends (p=0.93, 0.95, and 0.95 for 

Newbridge Pond, Orange Reservoir, and 

Packanack Lake, respectively) were evident in 

cores from the urban lakes; zinc concentrations in 

recent sediment were 2 to 3 times the 

concentrations at the base of each respective core.

OCCURRENCE OF, AND TRENDS IN, 

HYDROPHOBIC ORGANIC 

COMPOUNDS

Hydrophobic organic compounds 

(organochlorine pesticides, PCBs, and PAHs) tend 

to sorb to fine-grained sediment and consequently 

accumulate in sediments of lakes and reservoirs. 

The sediment used in organochlorine compound 

analysis dated to approximately 1970 in the Clyde 

Potts Reservoir core, 1952 in the Newbridge Pond 

core, 1932 in the Packanack Lake core, and 1950 in 

the Orange Reservoir core.

The highest linear sedimentation rate 

(1.2 cm/yr) was observed in the Newbridge Pond 

core, followed by 0.7 cm/yr and 0.6 cm/yr in the 

Orange Reservoir and Packanack Lake cores, 

respectively. The lowest linear sedimentation rate 

(0.5 cm/yr) was observed in the minimally affected 

Clyde Potts Reservoir core. 

Chlordane

Concentrations of chlordane in lake cores 

ranged from about 5.9 to 14,000 μg/kg (fig. 3), the 

highest range of the four organochlorine 

compounds sampled. Concentrations were highest 

in the Newbridge Pond core and generally were 

one to three orders of magnitude greater than those 

in other lake cores (fig. 3). The Clyde Potts 

Reservoir core reflected the smallest anthropogenic 

effect, with the lowest chlordane concentrations of 

all lakes (fig. 3). A significant upward trend in 

chlordane concentrations (p=0.56) was observed 

from the oldest to most recently deposited 

sediment in the Clyde Potts Reservoir core 
14

(table 2); however, concentrations in recently 

deposited sediment were only slightly elevated 

relative to those at the base of the core (fig. 3). 

Chlordane concentrations in the three urban lakes 

generally increased from the oldest to the most 

recently deposited sediment. Concentrations in the 

Packanack Lake core were highly variable and, as 

a result, no significant trend (p=0.26) was observed 

(table 2; fig. 3). A significant upward trend 

(p=1.00) was evident in sediment from the base of 

the Newbridge Pond core to the peak chlordane 

concentration in 1970. In sediment deposited since 

1970, a significant downward trend (p=0.76) in 

concentrations was observed (table 2; fig. 3). In 

the Orange Reservoir core, a significant upward 

trend (p=0.75) in chlordane concentrations was 

evident from the oldest sediment to the most 

recently deposited sediment. Chlordane 

concentrations in recently deposited sediment were 

more than 2 and 3 times the concentrations at the 

base of the Newbridge Pond and Orange Reservoir 

cores, respectively (fig. 3). 

Dieldrin

Dieldrin concentrations were less than the 

detection limit at all depths in the Clyde Potts and 

Orange Reservoir cores (fig. 3). Dieldrin initially 

was detected in the Packanack Lake core in 1953 

sediment at a concentration of 12 μg/kg. It was 

detected intermittently in sediment deposited after 

1953 at similarly low concentrations, although no 

significant trend (p=0.13) was evident (table 2; fig. 

3). Dieldrin was detected in the Newbridge Pond 

core at an initial concentration of 42 μg/kg in 1952 

sediment, at a peak concentration of 470 μg/kg in 

1970 sediment, and at approximately 150 μg/kg in 

the most recent sediment (fig. 3). A significant 

upward trend (p=1.00) was observed from the base 

of the Newbridge Pond core to the 1970 peak 

concentration, followed by a significant downward 

trend (p=-0.65) from 1970 to the most recently 

deposited sediment.

Total Dichlorodiphenyl-trichloroethane

Concentrations of total DDT in lake cores 

ranged from about 3.5 to 4,460 μg/kg, with the 

highest concentrations observed in the Newbridge 

Pond core (fig. 3). Lowest concentrations were 

found in the Clyde Potts Reservoir core, reflecting 

the smallest anthropogenic effect (fig. 3). Total 

DDT concentrations in recent sediments in the 

Clyde Potts core were approximately one-half the 

concentrations at the base of the core; however, the 

downward trend (p=-0.37) was not significant 

(table 2; fig. 3). No significant trend (p=-0.05) in 

total DDT concentrations was observed in the 

Packanack Lake core; however, concentrations in 

the most recently deposited sediment were elevated 

relative to concentrations at the base of the core 

(table 2; fig. 3). In the two other urban cores, 

distinct peaks in total DDT concentrations were 

evident in 1962. In the Orange Reservoir core, a 

significant upward trend (p=1.00) was observed 

from the base of the core to the 1962 peak. From 

1962 to the most recently deposited sediment, a 

significant downward trend (p=-0.78) in total DDT 

concentrations was evident (table 2; fig.3). This 

downward trend resulted in total DDT 

concentrations in recently deposited sediment that 

were approximately one-fifth the concentrations at 

the base of the core. The upward trend in total 

DDT concentrations from the base of the 

Newbridge Pond core to the 1962 peak was not 

statistically significant (p=0.80); however, the 

downward trend observed from the peak to the 

most recently deposited sediment was significant 

(p=-0.81). As a result, total DDT concentrations in 

the most recently deposited sediment were less 

than one-half the concentrations found at the base 

of the Newbride Pond core (fig. 3). 
15

1930

1940

1950

1960

1970

1980

1990

2000

1,000 10,000 100,000 1,000,000

APPROXIMATE YEAR OF DEPOSITION

TOTAL PAH CONCENTRATION, IN MICROGRAMS PER KILOGRAM

Figure 4. Vertical distribution of total polycyclic aromatic hydrocarbons (PAHs) in sediment cores from

Clyde Potts Reservoir, Orange Reservoir, and Packanack Lake in New Jersey and Newbridge Pond 

on Long Island, New York.

EXPLANATION

Clyde Potts Reservoir

Newbridge Pond

Orange Reservoir

Packanack Lake

1930

1940

1950

1960

1970

1980

1990

2000

100 1,000 10,000

TOTAL PCB CONCENTRATION, IN MICROGRAMS PER KILOGRAM

APPROXIMATE YEAR OF DEPOSITION

Year of cancellation of all uses

1 10

EXPLANATION

1930

1940

1950

1960

1970

1980

1990

2000

100 1,000 10,000

TOTAL DDT CONCENTRATION, IN MICROGRAMS PER KILOGRAM

APPROXIMATE YEAR OF DEPOSITION

1 10

Year of synthesis of compound

Year of cancellation of all uses

Open symbols indicate no detections

EXPLANATION

1930

1940

1950

1960

1970

1980

1990

2000

100 1,000

APPROXIMATE YEAR OF DEPOSITION

DIELDRIN CONCENTRATION, IN MICROGRAMS PER KILOGRAM 

1 10

EXPLANATION

Year of synthesis of compound 

Year of cancellation of most uses

Year of cancellation of all uses

Open symbols indicate no detections

1930

1940

1950

1960

1970

1980

1990

2000

100 1,000 10,000 100,000

EXPLANATION

APPROXIMATE YEAR OF DEPOSITION

CHLORDANE CONCENTRATION, IN MICROGRAMS PER KILOGRAM

Year of synthesis of compound 

Year of cancellation of agricultural uses

Year of cancellation of all uses

Open symbols indicate no detections

1 10

Figure 3. Vertical distribution of organochlorine compounds in sediment cores from Clyde Potts 

Reservoir, Orange Reservoir, and Packanack Lake in New Jersey and Newbridge Pond on 

Long Island, New York.
16

Total Polychlorinated Biphenyls

Concentrations of total PCBs (fig. 3) 

ranged from about 10 to 116 μg/kg in the cores 

from the three New Jersey lakes but were one to 

two orders of magnitude higher in the Newbridge 

Pond core (maximum of 1,910 μg/kg). Total PCBs 

in the Newbridge Pond core increased from an 

initial concentration of 69 μg/kg in 1952 sediment 

to a peak of 1,910 μg/kg in 1962 sediment. Total 

PCB concentrations in sediment deposited since 

1962 decreased to approximately 600 μg/kg in the 

most recently deposited sediments (fig. 3). The 

upward trend in total PCBs to the 1962 peak 

sediment concentration was significant (p=1.00), 

as was the downward trend (p=-0.62) from the 

1962 peak to the most recently deposited sediment 

(table 2). 

Concentrations of total PCBs in the Clyde 

Potts Reservoir core, like those of other 

hydrophobic organic compounds, generally were 

lower than concentrations in other cores (fig. 3). 

Although concentrations of total PCBs in the Clyde 

Potts core were highly variable, a significant 

downward trend (p=-0.60) from the oldest to most 

recently deposited sediment was observed (table 2; 

fig. 3). In the Packanack Lake core, a significant 

upward trend (p=0.73) was observed in total PCB 

concentrations from the base to the 1973 peak 

concentration (table 2; fig. 3). A significant 

downward trend (p=-0.74) was evident in sediment 

deposited since the 1973 peak; however, total PCB 

concentrations in recently deposited sediment 

remained elevated relative to concentrations in the 

base of the core (table 2; fig. 3). Total PCB 

concentrations were variable throughout the 

Orange Reservoir core and showed no significant 

trend (p=-0.18). 

Polycyclic Aromatic Hydrocarbons

PAHs were detected throughout the four 

cores in concentrations that ranged from about 

1,700 μg/kg (Packanack Lake) in 1932 sediment to 

a peak concentration of about 230,000 μg/kg 

(Newbridge Pond) in 1997 sediment (fig. 4). 

Concentrations of PAHs generally were lower in 

the Clyde Potts Reservoir core than in cores from 

the urban lakes; however, the PAH concentations 

were lowest at the base of the Packanack Lake core 

(fig. 4), which contained sediment deposited prior 

to the urbanization of the watershed. No 

significant trends (p=-0.06 and 0.34, respectively) 

in total PAH concentrations were evident in the 

Clyde Potts Reservoir and Orange Reservoir cores 

(table 2; fig. 4); however, significant upward trends 

(p=0.89 and 0.71, respectively) were observed in 

the Newbridge Pond and Packanack Lake cores. 

Total PAH concentrations in recently deposited 

sediment in Newbridge Pond and Packanack Lake 

were more than 8 times the concentrations at the 

base of each respective core.

EFFECT OF WATERSHED 

CHARACTERISTICS AND 

REGULATORY ACTION ON 

CONSTITUENT CONCENTRATIONS 

IN SEDIMENT

Trace Elements

Lead and zinc are associated with the use 

of automobiles; lead was a major component of 

gasoline until its removal in the mid-1970’s, and 

zinc is a component of rubber tires and a byproduct of fossil fuel combustion (Callender and 

Rice, 2000). In all lakes, significant upward trends 

were observed for lead concentrations in sediment 

deposited from the base of the core to the peak in 

the mid-1970’s. The effect of automobile use on 

the distribution of lead in sediment was supported 

further by the significant downward trends 

observed for all lakes, except Clyde Potts 

Reservoir, in the sediments deposited after phaseout of leaded gasoline. Upward trends in zinc 

concentrations were significant throughout the 

cores from the three urban lakes. In Orange 

Reservoir and Packanack Lake, the concentrations 

of both elements began to increase in the mid1940’s to early 1950’s, concurrent with an increase 

in the number of automobiles fueled by leaded 

gasoline (Callender and Rice, 2000). 
17

Callender and Rice (2000) demonstrated 

that traffic density is highly correlated with 

population density. To demonstrate further the 

relation between automobile use and the 

distribution of lead and zinc in sediment, 

regression analyses were performed that relate 

decadal sedimentary concentrations to total 

decadal population of municipalities surrounding 

the study lakes. The results indicate a significant 

correlation (R2

=0.67; p<0.01) between total 

surrounding population and lead concentration in 

sediment deposited prior to the removal of lead 

from gasoline (fig. 5). Similarly, a significant 

relation (R2

=0.53; p<0.01) was observed between 

total surrounding population and zinc 

concentrations throughout the cores (fig. 6). These 

findings are consistent with those of Callender and 

Rice (2000), who determined that traffic density 

was a predictor of lead and zinc concentrations in 

the environment.

The distribution of trace elements in 

sediment at Clyde Potts Reservoir is consistent 

with the distribution expected in a minimally 

altered watershed. Concentrations of five of the 

seven trace elements (arsenic, cadmium, 

chromium, mercury, and nickel) remained 

relatively static throughout the depth of the core 

(fig. 2) and were not found to have significant 

trends.

The Packanack Lake and Orange 

Reservoir cores contained sediment deposited prior 

to major population increases, which allows an 

assessment of the effects of urbanization on the 

concentration of trace elements in sediment. 

Increases in trace-element concentrations in the 

sediment at Packanack Lake coincided with a 

period of rapid population growth. Concentrations 

of arsenic and mercury generally increased after 

1952 (fig. 2), whereas lead, nickel, and zinc 

concentrations generally increased after 1955 (fig. 

2). Although the greatest change in total 

population in the land surrounding Packanack Lake 

occurred from 1960 to 1970, the population change 

from 1950 to 1960 was nearly four times the 

change in any decade dating back to impoundment 

of the lake (fig. 7). These findings are consistent 

with those of other investigators who have related 

increases in sedimentary trace-element 

concentrations to urbanization (Callender and 

Rice, 2000; Callender and Van Metre 1997; Van 

Metre and others, 1996). Concentrations of four 

selected trace elements (lead, mercury, nickel, and 

zinc) in Orange Reservoir increased from 1938 to 

1946. These increases occurred prior to the first 

major period of growth in the area surrounding 

Orange Reservoir, which occurred between 1950 

and 1960 (fig. 7). Although the increases cannot 

be attributed directly to urbanization on the basis of 

population data, the concentration data indicate 

that some type of anthropogenic disturbance 

occurred in the watershed during this period of 

sediment deposition. 

The Newbridge Pond core did not include 

sediment deposited prior to urbanization, which 

makes it impossible to assess the effects of urban 

development on trace-element concentrations in 

sediment; however, elevated concentrations of 

trace elements relative to those found in the 

reference lake (Clyde Potts Reservoir) and other 

less urbanized lakes, combined with significant 

upward trends in trace-element concentrations, are 

evidence of anthropogenic effects. For example, 

lead and zinc concentrations were significantly 

elevated compared to those in cores from the other 

lakes; the elevated concentrations may result from 

the larger total population and greater automobile 

use in areas surrounding the pond. 

Since the enactment of the Clean Air Act 

of 1970, lead emissions have been reduced by 98 

percent as a result of the phase-out of leaded 

gasoline and controls on industrial emissions 

(Callender and Van Metre, 1997). The result of 

this phase-out was evident in the sediment cores of 

the four study lakes. Peak lead concentrations in 

all lakes coincided with the phase-out of leaded 

gasoline in the mid-1970’s (fig.1). Callender and 

Van Metre (1997) reported temporally similar 

peaks and reductions in lead concentrations in 

reservoir sediment nationwide. Although lead 

concentrations are declining, they remain elevated 

relative to historical concentrations at the four 

study lakes, as well as other reservoirs sampled 

across the Nation (Callender and Van Metre, 1997).

 
18

EXPLANATION

Clyde Potts Reservoir

Newbridge Pond

Orange Reservoir

Packanack Lake

1930

1940

1950

1960

1970

1980

1990

2000

0 25,000 50,000 75,000 100,000 125,000 150,000

YEAR

Figure 7. Population of municipalities adjacent to 

Clyde Potts Reservoir, Orange Reservoir, and

Packanack Lake in New Jersey and Newbridge

Pond on Long Island, New York, 1930-1990.

POPULATION

R2 = 0.53

1.50

1.70

1.90

2.10

2.30

2.50

2.70

2.90

3.10

3.00 3.50 4.00 4.50 5.00 5.50

Figure 6. Relation of log-transformed decadal 

zinc concentrations in sediment cores to logtransformed decadal population of the 

municipalities adjacent to Clyde Potts Reservoir,

Orange Reservoir, and Packanack Lake in 

New Jersey and Newbridge Pond on Long Island,

New York.

LOG-TRANSFORMED DECADAL POPULATION

LOG-TRANSFORMED DECADAL ZINC CONCENTRATIONS

R2 = 0.67

1.00

1.50

2.00

2.50

3.00

3.50

3.00 3.50 4.00 4.50 5.00 5.50

Figure 5. Relation of log-transformed decadal 

lead concentrations in sediment cores to logtransformed decadal population of the 

municipalities adjacent to Clyde Potts Reservoir, 

Orange Reservoir, and Packanack Lake in 

New Jersey and Newbridge Pond on Long Island, 

New York.

LOG-TRANSFORMED DECADAL POPULATION

LOG-TRANSFORMED DECADAL LEAD CONCENTRATION
19

Organochlorine Compounds

The detection of organochlorine 

compounds in the lake sediment cores is an 

indication of past use and environmental 

persistence of these compounds within the study 

watersheds. All of the organochlorine compounds 

evaluated in this study had been banned from use 

in the United States for at least 1 decade prior to 

sampling; however, concentrations of three of the 

four compounds were detected at all four lakes. 

Organochlorine concentrations generally 

were elevated in cores from Orange Reservoir and 

Newbridge Pond, whose watersheds have a high 

percentage of urban-industrial/commercial-land 

use and total population in surrounding areas. In 

contrast, concentrations in sediment at Clyde Potts 

Reservoir, the study reference site, generally were 

low relative to those in sediment in the more 

developed basins. 

Concentrations of organochlorine 

compounds in Newbridge Pond sediment were of 

particular concern. The peak chlordane 

concentration in sediment cores was from one to 

three orders of magnitude greater than that at other 

lakes in this study and more than two orders of 

magnitude greater than those in sediment cores 

sampled in other urban environments in the United 

States (P.C. Van Metre, U.S. Geological Survey, 

written commun., 1998). Peak total DDT 

concentration was about 3.5 to 100 times the peaks 

in other lakes in this study and about 5 times the 

highest peak concentration reported nationally. 

The peak concentration of total PCBs was more 

than 25 times the peak concentrations in other 

study lakes and more than 5 times the next greatest 

peak concentration in the Nation. Peak dieldrin 

concentrations, like those of other organochlorine 

compounds, were approximately 30 times the peak 

concentration at Packanack Lake, the only other 

study lake where it was detected. Newbridge Pond 

had the highest dieldrin peak of lakes sampled 

across the Nation; the concentration was more than 

80 times the next highest peak. 

A general decline in concentrations of 

organochlorine compounds was evident in cores 

from the four study lakes. At Newbridge Pond, 

concentrations of all four compounds were found 

to have significant downward trends from peak 

concentrations. With the exception of chlordane in 

the Clyde Potts Reservoir and Orange Reservoir 

cores, concentrations of the four organochlorine 

compounds were determined to have significant 

downward trends from peak concentrations to 

those in recently deposited sediment or nonsignificant trends throughout the core (table 2). 

These results indicate that concentrations of 

organochlorine compounds in lake sediment either 

are declining or remaining static. These results are 

consistent with those of other investigations of 

organochlorine concentrations in sediment, which 

showed general downward trends (Van Metre and 

others, 1997; Van Metre and others, 1998). On the 

basis of these findings and because of the 

regulatory actions prohibiting the production and 

use of these compounds, the downward trends in 

concentrations of organochlorine compounds in 

sediment are expected to continue. Concentrations 

in the lakes, particularly Newbridge Pond, remain 

elevated relative to concentrations at the base of 

each respective core (fig. 3). Furthermore, the 

persistent nature of these compounds indicates that 

a substantial amount of time may be required to 

purge them completely from the watershed.

Polycyclic Aromatic Hydrocarbons

The accumulation of PAHs in sediment has 

been related to factors associated with urbanization 

and industrialization, particularly the incomplete 

combustion of fossil fuels (Pereira and others, 

1999). The results of this study are somewhat 

consistent with this finding in that sediments from 

the lake in the minimally urbanized watershed 

(Clyde Potts Reservoir) were determined to contain 

relatively static and low concentrations of PAHs 

compared to those from other lakes. Furthermore, 

Newbridge Pond and Packanack Lake, the two 

watersheds with the highest urban-residential land 

use, were found to have significant upward trends 

in PAH concentrations throughout the cores. These 

upward trends in PAH concentrations were 

consistent with increasing total population of the 

areas surrounding Newbridge Pond and Packanack 

Lake. PAH concentrations at the base of the 
20

Packanack Lake core, the only core to include 

sediment deposited prior to urbanization and 

widespread automobile use, were lower than those 

determined at the reference site. These results are 

consistent with those of Van Metre and others 

(2000), who reported increased PAH 

concentrations in reservoirs and lakes within 

urbanized watersheds with high vehicular traffic. 

The distribution of PAHs in the Orange Reservoir 

core deviated somewhat from this relation. 

Although concentrations were elevated relative to 

those in the lakes with less developed watersheds, 

PAH concentrations in the Orange Reservoir core 

actually decreased between 1950 and 1970, when 

the total population of the surrounding area was 

increasing. 

In the three urban-lake cores, significant 

upward trends were observed either to peak 

concentrations or throughout the core for most 

trace elements and hydrophobic organic 

compounds. This indicates that changes in 

population, land use, and chemical use in the 

urbanized watersheds over the period of 

sedimentary record have contributed to upward 

trends in concentrations. Although downward 

trends were observed for some constituents in the 

years after their concentrations peaked, 

concentrations of most constituents remain 

elevated in the most recently deposited sediments 

in urban lake cores relative to those in the base of 

each respective core and relative to those in the 

reference lake cores. Similar trends in 

concentrations of trace elements and hydrophobic 

organic compounds have been observed in other 

urban-lake-sediment cores across the United States 

(Callender and Rice, 2000; Van Metre and others, 

2000; Van Metre and others, 1998; Van Metre and 

others, 1997).

SUMMARY AND CONCLUSIONS

Sediment cores from three urban lakes, 

two in New Jersey and one on Long Island, New 

York, and from one non-urban lake in New Jersey 

were analyzed for trace elements and hydrophobic 

organic compounds. Spearman’s rank correlation 

was used to evaluate trends in constituent 

concentrations. Core layers were dated by use of 

cesium-137, copper, lead, or DDT profiles.

Trace elements (arsenic, cadmium, 

chromium, lead, mercury, nickel, and zinc) were 

detected throughout the cores of all four lakes. 

Concentrations of most elements, with the 

exception of arsenic, were higher in the cores from 

the three lakes within urbanized watersheds than in 

the core from the largely forested, reference 

watershed (Clyde Potts Reservoir). The highest 

concentrations of cadmium, lead, and zinc were 

found in the Newbridge Pond core on Long Island, 

New York. Concentrations of lead and zinc in the 

Newbridge Pond core generally were one and two 

orders of magnitude greater than concentrations in 

cores from the other lakes, respectively. The 

highest concentrations of chromium, mercury, and 

nickel were present in the core from Orange 

Reservoir in New Jersey. 

Results of trend analyses indicate that 

concentrations of trace elements in lake sediments, 

with the exception of chromium, were affected by 

urbanization. Concentrations in cores from the 

urban lakes showed significant upward trends from 

older to more recent sediment either to peak 

concentrations or throughout the entire core for all 

trace elements, except chromium at all three lakes 

and arsenic and nickel from Orange Reservoir. 

This indicates that changes in population and land 

use within the urbanized watersheds over the 

period of sedimentary record could have 

contributed to the upward trends in trace-element 

concentrations. Although downward trends were 

observed for some trace elements after their peaks 

in cores from urban lakes, concentrations of all 

trace elements remained elevated in the most 

recently deposited sediments relative to 

concentrations in the base of each respective core. 

No significant trends were detected, 

however, in concentrations of five of seven trace 

elements in the sediment core from minimally 

urbanized Clyde Potts Reservoir. Concentrations 

of zinc in the Clyde Potts Reservoir core had a 

significant downward trend from oldest to 

youngest sediments, and concentrations of lead had 

a significant upward trend to a peak in 1975. 
21

Changes in concentrations of lead and 

zinc, trace elements associated with automobile 

use, were highly correlated with changes in total 

decadal population of the area surrounding the 

reservoirs. Population is an indicator of vehicular 

traffic, which is an indicator of gasoline use (a 

probable lead source) and tire wear (a probable 

zinc source). Lead concentrations over time were 

highly correlated with population in the vicinity of 

all lakes until the peak concentration in sediment 

deposited in the mid-1970’s. Concentrations of 

lead in lake sediment generally decreased since the 

use of leaded gasoline was phased out in the mid1970’s. Although this downward trend was 

significant, concentrations of lead in recent 

sediment from urban lakes remain elevated relative 

to sediment deposited at the base of the cores. Zinc 

concentrations were highly correlated with 

population over the entire depth of the core. In 

general, zinc concentrations increased in the three 

urbanized watersheds, presumably in response to 

increasing population and vehicular use; however, 

this trend was not evident in the Clyde Potts 

Reservoir watershed, where vehicular use is 

minimal. 

Detectable concentrations of chlordane, 

total DDT, and total PCBs were found in sediment 

from all lakes. Dieldrin was detected only in the 

Newbridge Pond and Packanack Lake cores. 

Sedimentary concentrations of organochlorine 

compounds, in general, have decreased since 

regulatory action was taken to discontinue their 

production and use in the 1970’s and 1980’s. 

Concentrations of the four organochlorine 

compounds, except chlordane in the Clyde Potts 

and Orange Reservoir cores, had significant 

downward trends from peak concentrations to 

recently deposited sediment or non-significant 

trends throughout the core; however, because of 

the environmental persistence of these compounds, 

they are still found in detectable concentrations a 

decade after their use was discontinued. 

Concentrations generally were higher at 

Newbridge Pond and Orange Reservoir, 

watersheds with increased population and urbanindustrial/commercial-land use, than at Clyde Potts 

Reservoir, the forested, reference site. 

Concentrations of organochlorine compounds were 

particularly high at Newbridge Pond where 

concentrations were much higher than at other 

urban reservoirs sampled nationally. Without 

additional input of these compounds, the general 

downward trend in concentrations at most sites 

probably will continue; however, the persistence of 

these compounds indicates that a substantial 

amount of time may be required to purge them 

completely from the watersheds.

PAH concentrations in sediment generally 

increased with population and urbanization, 

presumably as a result of the increased fossil-fuel 

combustion (gasoline and home-heating fuels) and 

other uses (roads and parking lots paved with 

asphalt) associated with increased urban 

development and vehicular traffic. This finding is 

supported by low concentrations of PAHs in 

Packanack Lake sediments in the 1930’s, before 

the watershed was urbanized and when 

automobiles were comparatively rare. As vehicular 

use and urbanization increase in these watersheds, 

the general increase in PAH concentrations in lake 

sediments can be expected to continue. Many PAH 

compounds are known to be toxic to some aquatic 

organisms, therefore, an upward trend might be a 

cause for concern for the health of aquatic life in 

streams that drain the more populated (greater than 

2,000 people per square mile) watersheds of the 

study area. 

Data from this study indicate that changes 

in population, land use, and chemical use in the 

urbanized watersheds over the period of 

sedimentary record have contributed to upward 

trends in concentrations of trace elements and 

hydrophobic organic compounds. Although 

downward trends were observed for some 

constituents in the years after their concentrations 

peaked, concentrations of most constituents in 

urban lake cores remain elevated in the most 

recently deposited sediments relative to the base of 

each respective core and relative to those in the 

reference lake cores. Similar trends in 

concentrations of these constituents have been 

observed in other urban-lake-sediment cores across 

the United States.
22

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