Hydrochemical character and spatiotemporal variations in a heavily modified river of western Greece

Abstract.

A 22-year series of monthly hydrochemical data from the Acheloos River in western Greece, which flows through four reservoirs, was analysed in order to assess and interpret its hydrochemical regime, spatial differentiations, seasonal variations and interannual trends. The data set was controlled for its quality and gaps in measurements were filled by a formula, developed for that purpose. The river's composition is attributed to rock weathering, precipitation quantity and quality, catchment altitude and in-lake biological activity. Regarding nutrients, organic carbon and dissolved oxygen, the water quality is good. Downstream of the last large impoundment, the river behaves as a heavily modified water body, with minimum solute concentrations in summer. Further downstream, the seasonal hydrochemical regime tends towards a natural one. Interannual climate variations influence water composition significantly. In dry-warm year periods evapotranspiration processes 'concentrate' reservoir water, enhance salt accumulation in soil pores and contribute to a mineralization of Acheloos River water.