Midwestern Urban Stream Water Quality Data Analysis and Evaluation

The City of Davenport Water Pollution Control Plant (POTW), a large Iowa Grade IV facility, treats wastewater from the cities of Davenport, Bettendorf, Panorama Park and Riverdale, Iowa. The POTW discharges under a National Pollution Discharge Elimination (NPDES) permit into the Mississippi River. The POTW laboratory is certified for routine and atypical analyses.The POTW has been sampling various surface water sites in the Mississippi River and the Duck Creek watershed for 25 years. The sampling program was initiated to evaluate the affect of the POTW discharge on the Mississippi River and expanded to evaluate sewer system impacts on urban streams. Analytical work conducted early in the program consisted of NPDES permit parameters with more analyses such as herbicides and hydrocarbons added in recent years.The primary focus of this study is Duck Creek in Davenport. Duck Creek is 14 miles long and drains an area of 53 square miles. Three major and numerous small streams discharge into Duck Creek. The watershed encompasses rural, suburban, and urban areas and has undergone significant urbanization during the past 25 years.Review of analytical findings indicate:Fecal coliform bacteria concentrations commonly exceed recreation standards.Ammonia and nitrate nitrogen nutrient concentrations are generally as high in these urban streams as in agricultural streams.Limited sampling indicates common lawn herbicides are ubiquitous in the watershed.Concentrations of selected trace elements, such as cadmium, lead, and zinc mercury, are elevated above reference agricultural stream levels in these urban streams, possibly caused by emissions from industrial and municipal activities and motor vehicles.Dissolved oxygen levels at times drop below acceptable levels to protect aquatic life.Deteriorated water quality and sediment, as well as habitat disturbances, contribute to degraded biological communities as indicated by benthic macroinvertebrate sampling. Pollution-tolerant algae and aquatic invertebrates (such as worms and midges) tend to prevail at the development affected sites.Increasing impervious surface area and engineered drainage decreases stormwater detention, increases runoff and the resulting stream flow, contributes to soil and stream bank erosion and deteriorated water quality. It appears that larger peak flows, increased drainage, and streambed cutting are destabilizing the stream equilibrium and subsequently lowering the quality of micro aquatic habitats.