Assessing biological water quality of Yalakdere stream (Yalova, Turkey) with benthic macroinvertebrate-based metrics

This study was carried out in Yalakdere, which is the most important stream in Yalova, Turkey, in order to determine biological water quality, by using macroinvertebrate-based metrics and a multimetric index that was developed. In addition, it was also aimed to investigate the effects of drought and highway construction on stream benthic macroinvertebrates during the study period. Samples of benthic macroinvertebrates and eighteen physicochemical variables were collected for one year period from four study sites monthly. A total of forty metrics in five main metric groups calculated based on benthic macroinvertebrates were evaluated. It was determined that fourteen benthic metrics were significantly correlated with physicochemical variables. Since the same type of metrics give similar results, only one candidate metric from each of the five metric groups was added to evaluate the multimetric index. During the drought observed throughout 2013–2014 in Turkey, the stream bed was dry in the summer months. According to the multimetric index results, the water quality of the first three sampling points before the drought ranged between Class I and Class III while the water quality after the drought (after October 2013) did not go above Class III. No significant difference was observed in the number of taxa detected in the stream after the drought. However, it was found that the number of organisms per square meter decreased seven times after the drought. It is concluded that the developed multimetric index is an effective tool to determine the stream conditions, antropogenic pressures such us highway constructions and the negative effects of summer droughts.