Abstract

To identify the sources of selected constituents in urban streams and better understand processes affecting water quality and their effects on the ecological condition of urban streams and the Little Blue River in Independence, Missouri the U.S. Geological Survey in cooperation with the City of Independence Water Pollution Control Department initiated a study in June 2005 to characterize water quality and evaluate the ecological condition of streams within Independence. Base-flow and stormflow samples collected from five sites within Independence, from June 2005 to December 2008, were used to characterize the physical, chemical, and biologic effects of storm runoff on the water quality in Independence streams and the Little Blue River. The streams draining Independence—Rock Creek, Sugar Creek, Mill Creek, Fire Prairie Creek, and the Little Blue River—drain to the north and the Missouri River. Two small predominantly urban streams, Crackerneck Creek [12.9-square kilometer (km²) basin] and Spring Branch Creek (25.4-km² basin), were monitored that enter into the Little Blue River between upstream and downstream monitoring sites. The Little Blue River above the upstream site is regulated by several reservoirs, but streamflow is largely uncontrolled. The Little Blue River Basin encompasses 585 km² with about 168 km² or 29 percent of the basin lying within the city limits of Independence. Water-quality samples also were collected for Rock Creek (24.1-km² basin) that drains the western part of Independence.

Data collection included streamflow, physical properties, dissolved oxygen, chloride, metals, nutrients, common organic micro-constituents, and fecal indicator bacteria. Benthic macroinvertebrate community surveys and habitat assessments were conducted to establish a baseline for evaluating the ecological condition and health of streams within Independence. Additional dry-weather screenings during base flow of all streams draining Independence were conducted to identify point-source discharges and other sources of potential contamination. Regression models were used to estimate continuous and annual flow-weighted concentrations, loadings, and yields for chloride, total nitrogen, total phosphorus, suspended sediment, and Escherichia coli bacteria densities.

Base-flow and stormflow water-quality samples were collected at five sites within Independence. Base-flow samples for Rock Creek and two tributary streams to the Little Blue River exceeded recommended U.S. Environmental Protection Agency standards for the protection of aquatic life for total nitrogen and total phosphorus in about 90 percent of samples, whereas samples collected at two Little Blue River sites exceeded both the total nitrogen and total phosphorus standards less often, about 30 percent of the time. Dry-weather screening identified a relatively small number (14.0 percent of all analyses) of potential point-source discharges for total chlorine, phenols, and anionic surfactants.

Stormflow had larger median measured concentrations of total common organic micro-constituents than base flow. The four categories of common organic micro-constituents with the most total detections in stormflow were pesticides (100 percent), polyaromatic hydrocarbons and combustion by-products (99 percent), plastics (93 percent), and stimulants (91 percent). Most detections of common organic micro-constituents were less than 2 micrograms per liter. Median instantaneous Escherichia coli densities for stormflow samples showed a 21 percent increase measured at the downstream site on the Little Blue River from the sampled upstream site. Using microbial source-tracking methods, less than 30 percent of Escherichia coli bacteria in samples were identified as having human sources.

Base-flow and stormflow data were used to develop regression equations with streamflow and continuous water-quality data to estimate daily concentrations, loads, and yields of various water-quality contaminants. Estimated chloride concentrations rarely exceeded the Missouri acute standard for the protection of aquatic life (about 1 percent) and at only one site, Spring Branch Creek. The chronic standard for chloride concentration at all sites was estimated to be exceeded between 2 and 30 percent of the time. Large specific conductance values measured in the Adair Creek Basin near Interstate 70 during dry-weather screening indicated potential chloride concentrations of about 1,100 milligrams per liter, well above acute standards for the protection of aquatic life, but were not modeled. Estimated average daily total nitrogen and total phosphorus concentrations for the streams draining Independence were greater than U.S. Environmental Protection Agency recommended guidelines more than 85 percent of the time. Estimated concentrations for the Little Blue River sites exceeded the standard for total nitrogen more than 50 percent of the time and more than 80 percent of the time for total phosphorus. The estimated average daily sediment yield for the Little Blue River during the study period increased downstream, so that estimated annual suspended sediment loads were two to three times larger downstream with only about a 20 percent increase in total drainage area. Observed road, commercial, and residential construction activities in the lower portions of the stream basins draining Independence likely contributed to the larger suspended sediment loads. Estimated average daily Escherichia coli densities at both Little Blue River sites exceeded the Missouri standard 70 percent of the time.

Benthic macroinvertebrate samples collected in 2007 and 2008 found no sites, including reference sites, to be fully biologically supporting. Streams with a Stream Condition Index (SCI) of 16 to 20 are considered to be fully biologically supporting. The Little Blue River sites had an average SCI score of 12 and the streams draining Independence had an average SCI score of 10 and rated as partially biologically supporting. Habitat assessments were conducted in 2008. Scores for the Independence sites varied in a narrow range. The assessment factors having the most effect on lowering habitat scores were increased fine sediment deposition, channel alteration, poor bank stability, and loss or absence of bank and riparian vegetation.

Two streams draining Independence, Crackerneck Creek and Spring Branch Creek, contributed about 76 percent of the increase between sites on the Little Blue River in estimated chloride load, about 22 percent of the increase in total nitrogen load, and about 13 percent of the increase in total phosphorus load. Larger relative percentage contributions from the tributary streams occurred during lower flows. Estimated flow-weighted Escherichia coli densities also increased downstream. Contaminants mobilized through surface runoff to the municipal separate storm sewer system, and possibly sanitary sewer overflows, are more important in the smaller, more urbanized streams draining Independence than in the Little Blue River. Data collected for this study indicated that potential exists for decreasing concentrations, and consequently loads, of some contaminants to streams associated with suspended sediment in stormflow by the continuing implementation of best management practices to decrease sediment loads in streams.

First posted August 27, 2010