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Scientific Investigations Report 2010–5088

Prepared in cooperation with the New Jersey Department of Environmental Protection

Trends in the Quality of Water in New Jersey Streams, Water Years 1998–2007

By R. Edward Hickman and Bonnie J. Gray

ABSTRACT

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Trends were determined in flow-adjusted values of selected water-quality characteristics measured year-round during water years 1998–2007 (October 1, 1997, through September 30, 2007) at 70 stations on New Jersey streams. Water-quality characteristics included in the analysis are dissolved oxygen, pH, total dissolved solids, total phosphorus, total organic nitrogen plus ammonia, and dissolved nitrate plus nitrite. In addition, trend tests also were conducted on measurements of dissolved oxygen made only during the growing season, April to September. Nearly all the water-quality data analyzed were collected by the New Jersey Department of Environmental Protection and the U.S. Geological Survey as part of the New Jersey Department of Environmental Protection Ambient Surface-Water Quality Monitoring Network.

Monotonic trends in flow-adjusted values of water quality were determined by use of procedures in the ESTREND computer program. A 0.05 level of significance was selected to indicate a trend. Results of tests were not reported if there were an insufficient number of measurements or insufficient number of detected concentrations, or if the results of the tests were affected by a change in data-collection methods.

Trends in values of dissolved oxygen, pH, and total dissolved solids were identified using the Seasonal Kendall test. Trends or no trends in year-round concentrations of dissolved oxygen were determined for 66 stations; decreases at 4 stations and increases at 0 stations were identified. Trends or no trends in growing-season concentrations of dissolved oxygen were determined for 65 stations; decreases at 4 stations and increases at 4 stations were identified. Tests of pH values determined trends or no trends at 26 stations; decreases at 2 stations and increases at 3 stations were identified. Trends or no trends in total dissolved solids were reported for all 70 stations; decreases at 0 stations and increases at 24 stations were identified.

Trends in total phosphorus, total organic nitrogen plus ammonia, and dissolved nitrate plus nitrite were identified by use of Tobit regression. Two sets of trend tests were conducted—one set with all measurements and a second set with all measurements except the most extreme outlier if one could be identified. The result of the test with all measurements is reported if the results of the two tests are equivalent. The result of the test without the outlier is reported if the results of the two tests are not equivalent.

Trends or no trends in total phosphorus were determined for 69 stations. Decreases at 12 stations and increases at 5 stations were identified. Of the five stations on the Delaware River included in this study, decreases in concentration were identified at four.

Trends or no trends in total organic nitrogen plus ammonia were determined for 69 stations. Decreases and increases in concentrations were identified at six and nine stations, respectively.

Trends or no trends in dissolved nitrate plus nitrite were determined for 66 stations. Decreases and increases in concentration were identified at 4 and 19 stations, respectively.

First posted August, 2010

For additional information contact:
Director, New Jersey Water Science Center
U.S. Geological Survey
810 Bear Tavern Rd., Suite 206
West Trenton, NJ 08628
http://nj.usgs.gov/

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Suggested citation:

Hickman, R. E., and Gray, B.J., 2010, Trends in the quality of water in New Jersey streams, water years 1998–2007: U.S. Geological Survey Scientific Investigations Report 2010–5088, 70 p.



Contents

Abstract

Introduction

Purpose and Scope

Description of Study Area

Previous Studies

Study Methods and Design

Field and Laboratory Measurements

Stations Included in this Study

Field and Laboratory Methods

Development of Data Sets to be Analyzed

Recensoring of some Nondetect Values

Calculation of Total Organic Nitrogen plus Ammonia

Selection of One Measurement in each Season of each Water Year

Calculation of Summary Statistics

Identification of Trends in Water Quality

Seasonal Kendall Test

Tobit Regression

Comparison of Trends from this Study with Trends from Previous Studies

Comparison of pH Values before and after a Change in Field Methods

Trends in the Quality of Water in New Jersey Streams

Trends determined from the Seasonal Kendall Test

Dissolved Oxygen

pH

Total Dissolved Solids

Trends Determined from Tobit Regression

Total Phosphorus

Total Organic Nitrogen plus Ammonia

Dissolved Nitrate plus Nitrite

Summary of Trends by Station

Summary and Conclusions

References Cited



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