Ecological quality of the River Axios (N. Greece) during spring and summer, 1997

This study examines the applicability of five European biotic indices combined with the measurements of physicochemical parameters in order to determine the water quality at ten sites along the Greek part of the river Axios during the high flow (spring) and low flow season (summer) in 1997. The river Axios is situated in northern Greece, west of the city of Thessaloniki. Its source is located in the Former Yugoslavian Republic of Macedonia close to the city of Skopia. The Greek part of the river Axios receives mainly agricultural runoff but also urban sewage and industrial wastes. The following physicochemical parameters were measured in situ: substrate, flow, water temperature, pH, concentration and percentage saturation of dissolved oxygen, BOD5, conductivity and total dissolved solids. Total suspended solids, orthophosphates, nitrate, nitrite and ammonium were measured in vitro. The benthic macroinvertebrates, sampled with the 3 min kick/sweep method, were identified to the lowest possible taxonomic level. Three British and two Iberian biotic indices were applied. The data were analyzed with Twinspan, Fuzzy; Canonical Correspondence Analysis and Discriminant Analysis. The faunal composition was typical of a lowland river, i.e. the zoobenthos was not very diverse. The quality of the water was influenced by human activities during both seasons. The deterioration in water quality during spring was due to excess suspended solids of diffuse agricultural origin, and during summer was due to organic pollution. Lower discharge and impoundment accentuated this deterioration. Overall, changes in physicochemical parameters were in agreement with the results of the biological data, despite their instant nature. However, some problems arose with regard to the applicability of the European biotic indices, thus emphasizing the need to develop a Greek Biotic Index.