The impact of storm water runoff on a small urban stream

Abstract

Annual limit values were taken from the Lithuanian EPA requirements for the management of storm water runoff with a focus on prevention and control of contamination. Eleven composite samples of stream bottom sediments, each consisting of ten sub-samples, were collected in 2006. Toxicity screening from sediments was performed using the plant Lepidium sativum according to modified I. Magone’s methodology (Magone I, Bioindication of phytotoxicity of transport emission. In: Kachalova O-L, Zinatne (eds) Bioindication of toxicity of transport emissions in the impact of highway emissions on natural environment. Riga, pp 108-116, 1989). The level of toxic impact of Lepidium sativum (compared to control) was assessed according to the modified method of Wang (Rev Environ Contam Toxicol 126:88-127, 1992). Results The mean pH of urban storm water runoff does not vary much from neutral, but range values are quite different, from 4.0 up to 8.7. The highest concentration of SS reached 800 mg L-1, TPH-2.4 mg L-1, BOD7-300 mg O2 L-1 and CODCr-1,400 mg L-1. The SS was above the limit in 64% of total amount of grab samples, TPH-37%, BOD7-41% and CODCr-55%. The toxicity analysis of the bottom sediments showed varying toxicity of bottom sediments along the stream. From nine analysed samples of bottom sediments, 30% had weak toxicity, 30% medium and 30% strong toxicity on the test organism plant L. sativum. There was one single sample with no toxic effects, so that the results showed that urban storm water has an unacceptable environmental impact on recipients. It was also indicated that storm water runoff discharge alone is not the potential source of toxicity of bottom sediments. The litter demonstrated a weak toxicity of bottom sediments as well.