Scientific Investigations Report 2007–5290

Prepared in cooperation with the National Park Service

Water quality of streams in and near the Delaware Water Gap National Recreation Area, Pennsylvania and New Jersey, 2002–04

By R. Edward Hickman and Jeffrey M. Fischer

Scientific Investigations Report 2007–5290

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Abstract

Water samples were collected during 2002–04 at monitoring stations on 14 streams either within or entering the Delaware Water Gap National Recreation Area. The samples were collected from April through December of each year, mostly under low (base-flow) conditions, and were analyzed for major ions and nutrients (nitrogen and phosphorus). Results of the analyses, in concert with land-use information in the drainage basins associated with the samples, were used to define water-quality characteristics; to identify relations among water quality, streamflow, and season; and to establish a baseline and develop a method that could be used to detect future changes in water quality.

For a given water-quality characteristic, median values commonly varied among the 14 water-quality monitoring stations. For example, the median concentration of total phosphorus at the station on Sand Hill Creek (0.033 milligrams per liter as P) was four times the corresponding median concentration at the station on Vancampens Brook (0.008 milligrams per liter as P).

Results of correlations between median values of water-quality characteristics and land-use characteristics of the drainage basins indicate that agricultural practices and the presence of wetlands could be important factors affecting the concentrations of total nitrogen and total phosphorus in these streams. Results of analyses of samples from the nine stations without permitted wastewater facilities in their basins indicate that medians of both total phosphorus and total nitrogen increased with an increase in the area of agricultural land in the drainage basins; the levels of significance are 0.01 for total phosphorus and 0.01 for total nitrogen. When only the seven stations without permitted wastewater facilities and with less than 5 percent of the basin in agricultural land are considered, median concentrations of total phosphorus and total nitrogen increased with an increase in the area of wetlands in the basins; the levels of significance are 0.003 for total phosphorus and 0.03 for total nitrogen.

Linear equations between values of each water-quality characteristic at a station, streamflow, and season were developed by use of Tobit regression. The variations of water quality with streamflow and with season were identified from these equations.

Concentrations of total phosphorus, total nitrogen, and attenuation turbidity increased with increasing streamflow at more stations than concentrations decreased with increasing streamflow. Concentrations of dissolved orthophosphate phosphorus, dissolved nitrate plus nitrite, dissolved ammonia, and major ions decreased with increasing streamflow at more water-quality stations than concentrations increased with increasing streamflow.

Most water-quality characteristics varied with season at most stations due to reasons other than the seasonal variation in streamflow. Concentrations of total phosphorus and total nitrogen during the summer (July–September) often exceeded concentrations during the spring (April–June) and fall (October–December). As one example, concentrations of total nitrogen at the monitoring station on Big Flat Brook are between 0.1 and 0.2 milligrams per liter as N in the spring and fall, but increase to between 0.2 and 0.3 milligrams per liter as N during the summer.

A method based on the linear equations relating water quality to streamflow and season was developed to detect differences in water quality between current (2002–04) and future conditions. Changes in water quality would be identified by detecting differences between the intercept of the equation with current water quality and the intercept of the corresponding equation with future water quality. The intercept represents an estimate of the water quality at a station with a streamflow of 1 cubic foot per second during a season in which the seasonal variation of water quality is minimal.

The method to detect future changes in water quality allows for an estimate of the minimum amount of change from current water quality (2002–04) that can be detected. For example, if 10 measurements are made in the future, the minimum detectable changes in total phosphorus or total nitrogen at any of the stations are 4–12 percent of the intercepts in equations with current water quality.


Contents

Abstract

Introduction

Purpose and Scope

Description of the Study Area

Previous Investigations

Design and Methods of Study

Collection of Water-Quality and Land-Use Data

Field and Laboratory Methods

Analyses of Data

Modification of Values Reported by Laboratory

Calculation of Medians with Nondetect Values

Creation of Boxplots with Nondetect Values

Summary of Water-Quality Values in Blanks and Replicates

Relations Between Water-Quality and Basin Characteristics

Equations Relating Water-Quality Characteristics, Streamflow, and Season

Variation of Water Quality with Streamflow

Variation of Water Quality with Season

Detection of Future Changes in Water Quality

Water Quality of Streams in and near the Delaware Water Gap National Recreation Area, 2002-04

Summary of Water-Quality Characteristics at Each Station

Results of Analyses of Blanks and Replicates

Variation of Water Quality with Basin Characteristics

Linear Equations Relating Water Quality, Streamflow, and Season

Variation of Water Quality with Streamflow and Season

Detection of Future Changes in Water Quality

Summary and Conclusions

References Cited

Appendixes—

1. Methods used to determine flow at stations on streams in and near the Delaware Water Gap National Recreation Area, Pa. and N.J., at times of water-quality-sample collection, 2002–04

2. A brief description of Tobit regression

3. Summary statistics for water-quality characteristics in samples from water-quality monitoring stations on streams in and near the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

4. Equations relating water quality, streamflow, and season at stations on streams in and near the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

Figures

1–2. Maps showing—

1. The Delaware Water Gap National Recreation Area and vicinity, Pa. and N.J.

2. Stream water-quality monitoring stations and associated drainage basins in and near the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

3–14. Graphs showing—

3. Land use in drainage basins associated with water-quality monitoring stations on streams in and near the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

4. Distribution of values of (A) pH, acid-neutralizing capacity, specific conductance, dissolved calcium, (B) attenuation turbidity, total phosphorus, dissolved oxygen, total nitrogen, dissolved nitrate plus nitrite, and dissolved chloride at each water-quality monitoring station on streams in and near the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

5. Median concentrations of (A) total phosphorus and (B) total nitrogen at water-quality monitoring stations as a function of agricultural land use and the presence of permitted wastewater facilities in associated drainage basins, for streams in and near the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

6. Median concentrations of total phosphorus and total nitrogen at water-quality stations as a function of wetland area and the presence of permitted wastewater facilities in associated drainage basins, for streams in and near the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

7. Median values of attenuation turbidity at water-quality monitoring stations as a function of wetland area in the associated drainage basins, for streams in and near the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

8. Concentration of dissolved nitrate plus nitrite as a function of (A) streamflow and (B) day of the year at the water-quality monitoring station (01438754) on Adams Creek below Long Meadow Brook near Edgemere, Pa., near the border of the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

9. Total phosphorus as a function of (A) streamflow and (B) day of the year at the water-quality monitoring station (01438892) on Dingmans Creek above Dingmans Falls near Dingmans Ferry, Pa., near the border of the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

10. Total nitrogen concentration as a function of (A) streamflow and (B) day of the year at the water-quality monitoring station (01439830) on Big Flat Brook at Tuttles Corner, Pa., near the border of the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

11. Attenuation turbidity as a function of streamflow at the water-quality monitoring station (01438700) on the Raymondskill Creek near Milford, Pa., near the border of the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

12. Dissolved chloride as a function of (A) streamflow and (B) day of the year at the water-quality monitoring station (01439570) on the Sand Hill Creek at Bushkill, Pa., near the border of the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

13. Values of pH as a function of streamflow at the water-quality monitoring station (01439680) on the Little Bush Kill at Bushkill, Pa., near the border of the Delaware Water Gap National Recreation Area, Pa. and N.J.,2002–04

14. Dissolved oxygen concentration as a function of streamflow at the water-quality monitoring station (01438700) on the Raymondskill Creek near Milford, Pa., near the border of the Delaware Water Gap National Recreation Area, Pa. and N.J., July-September, 2002–04

Tables

1. Water-quality monitoring stations on streams in and near the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

2. Land-use characteristics of basins associated with water-quality monitoring stations on streams in and near the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

3. Number of measurements of physical characteristics, plant nutrients, major ions, and organic compounds at stations on streams in and near the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

4. Selected water-quality characteristics measured at stations on streams in and near the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

5. Summary of results of analyses of blanks and replicates from water-quality monitoring stations on streams in and near the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

6. Results of correlation tests between median values of water-quality characteristics at each water-quality monitoring station and the land use in the drainage basin, for streams in and near the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

7. Identification of increases and decreases in values of selected water-quality characteristics with increasing streamflow, at stations on streams in and near the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

8. Identification of water-quality characteristics with values that varied with season, at stations on streams in and near the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04

9. Minimum detectable differences between current (2002–04) and future water-quality values for stations on streams in and near the Delaware Water Gap National Recreation Area, Pa. and N.J., 2002–04, assuming 10 future measurements


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