engleski

Water quality and pollution by hazardous substances of a small lowland stream under different hydrological conditions

This study investigates water quality and hazardous substances toxic to aquatic life in a small lowland stream under different hydrological conditions. The objective was to explore links among hydrology, water chemistry and microbial contamination in a stream predominantly impacted by structural degradation of stream morphology (channelization and straightening), agricultural land use in the catchment, and by a high load of treated wastewater. Sampling was carried out during spring high (HWL, > 200 cm), summer low (LWL, <100 cm), and autumn and winter medium (MWL, 100-200 cm) water levels at seven sites exposed to distinct pollution level. The results showed that water quality decreases in correspondence of stream segments receiving the critical amount of wastewaters and runoff from the surrounding agricultural area. Organochlorine pesticides (OCP), hexachlorocyclohexanes (HCHs) and DDT and its derivatives were measured in 96%, 88% and 38% of water samples. Three to six time higher concentrations of OCP than water quality standards were determined in autumn (MWL) due to leaching from the surrounding agricultural area. Extremely high values of faecal streptococci, intestinal enterococci, and Escherichia coli were found at sites downstream of the municipal wastewater discharge during spring (HWL) and autumn (MWL), most probably because of an inefficient urban sewage treatment and a significant amount of precipitation in a relatively short time before sampling. Traditionally, legislation has been focusing on controlling emissions from point sources. However, our results show that this focus needs to expand on controlling emissions from diffuse sources, such as the agricultural use of fertilizers and pesticides.

hydrology, water chemistry, microbial contamination

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