In cooperation with the Houston-Galveston Area Council (H-GAC) and the
Texas Natural Resource Conservation Commission
under the authorization of the Texas Clean Rivers Act

Nutrient Loading and Selected Water-Quality and Biological Characteristics of Dickinson Bayou Near Houston, Texas, 1995–97

By Jeffery W. East, Edna M. Paul, and Stephen D. Porter

U.S. Geological Survey
Water-Resources Investigations Report 98–4012

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Contents

Abstract

Introduction

Purpose and Scope

Description of Study Area

Acknowledgments

Data Collection

Rainfall

Streamflow

Water Quality

Biological

Quality Assurance/Quality Control

Data Compiled From Other Sources

Nutrient Loading

Sources

Streamflows and Concentrations

Monthly Samples

Storm-Event Samples

Low-Flow Synoptic-Survey Samples

High-Flow Synoptic-Survey Samples

Quality-Assurance/Quality-Control Samples

Loads

Rainfall Deposition

Point Source

Nonpoint Source

Water-Quality Characteristics

Properties, Biochemical Oxygen Demand, Fecal Coliform Bacteria, and Toxicity

Nutrient Concentrations Based on Selected Factors

Flow Conditions

Seasonality

Land Use

Nutrients in Bottom Sediment and Suspended Sediment

Biological Characteristics

Periphyton Algal Identification and Enumeration

Chlorophyll

Summary

Selected References

Appendix 1—Algal Identification and Enumeration Data

Figures

Tables

VERTICAL DATUM AND ABBREVIATIONS

Sea Level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929—a geodetic datum derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called Sea Level Datum of 1929.

Abbreviations:

cm, centimeter
cols./100 mL, colonies per 100 milliliters
ft, foot
ft/s, foot per second
ft³/s, cubic foot per second
in., inch
L, liter
lb/d, pound per day
(lb/d)/mi², pound per day per square mile
µm, micrometer
mg/L, milligram per liter
mg/m², milligram per square meter
mi, mile
mi², square mile
TU, U.S. Environmental Protection Agency toxicity unit

Abstract

Data were collected at 10 stations in the Dickinson Bayou watershed near Houston, Texas, from March 1995 through February 1997 to estimate the concentrations, loads, and yields of selected nutrients that enter the bayou; to characterize the effects on nutrient concentrations of flow conditions, seasonality, and land use; and to identify nutrient sources (point or nonpoint) inferred from the occurrence and abundance of algal species in the benthic algal community. These data included rainfall samples, streamflow measurements, stream-water-quality samples, and biological samples, in addition to quality-assurance/quality-control samples.

Estimates of loads of selected nutrients for the 106-square-mile watershed during the study were made for point sources and nonpoint sources. Point-source loading data are available only for ammonia nitrogen. Approximately 21.3 pounds per day of ammonia nitrogen is estimated from point sources during the study period. Nonpoint-source loads are estimated for eight nutrient forms: 7.84 pounds per day of dissolved ammonia nitrogen, 5.79 pounds per day of dissolved nitrite nitrogen, 215 pounds per day of dissolved Kjeldahl nitrogen, 350 pounds per day of total Kjeldahl nitrogen, 40.1 pounds per day of dissolved nitrite plus nitrate nitrogen, 67.6 pounds per day of total phosphorus, 46.6 pounds per day of dissolved phosphorus, and 42.8 pounds per day of dissolved orthophosphate. Rainfall-deposition rates also are estimated for comparison with point- and nonpoint-source loads. Deposition rates are 110 pounds per day of dissolved ammonia nitrogen, 120 pounds per day of dissolved nitrate nitrogen, and 15.8 pounds per day of dissolved phosphorus.

Statistical tests were used to determine whether there are significant differences between nutrient concentrations during low-flow and during high-flow conditions. For basins with rural/mixed and urban land uses, nutrient concentrations generally are significantly different (greater) during storm events than during low flow, indicating accumulation in the watershed and subsequent washoff of nutrients. However, nutrient concentrations in storm-event samples consisting predominantly of runoff from a pasture are not significantly greater than those in low-flow samples. Statistical tests for seasonality indicate that dissolved ammonia nitrogen is significantly different in at least one season for all land uses (rural/residential, rural/mixed, and pasture) except urban. Concentrations tend to increase in the spring and early summer months, possibly from fertilizer application and subsequent washoff.

Constituent-yield data were used to make direct comparisons of the nonpoint-source load contributions from four stations with watersheds of different land use. These comparisons lead to three conclusions: (1) For all nutrient species except orthophosphate, urban land use is the largest nonpoint-source contributor, (2) Kjeldahl nitrogen is the most abundant nutrient species, and (3) organic nitrogen accounts for the major part of the Kjeldahl nitrogen.

Algal samples were collected at seven stations and were analyzed for periphyton identification and enumeration, and chlorophyll a and chlorophyll b concentrations. The large relative abundance of soil algae at stations in the middle of the watershed likely indicates the cumulative effects on water quality of agricultural nonpoint sources. Farther downstream near the State Highway 3 bridge, and downstream of three major tributary inflows, the increase in abundance of soil algae to a larger-than-expected level might reflect water-quality influences from predominantly urban nonpoint sources in the drainage basins of the three major tributary inflows. Nutrient concentrations do not appear to limit algal production in the upper (non-tidal) reach of Dickinson Bayou; but nutrient concentrations could have been limiting benthic-algal production in the lower (tidal) reach of the bayou during the time of the synoptic survey. If nitrogen is the limiting resource for algal productivity in the tidal reach of Dickinson Bayou, eutrophication of the system could be (at least partially) mitigated if nonpoint-source nutrient loads into the Bayou were reduced.

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