Hydrochemical consequences of feeding flow-through reservoirs with contaminated water

The research concerned flow-through reservoirs fed with contaminated river water. The aim of the research was to recognize the impact of reservoirs on fluvial transportation of contaminants. Three reservoirs, situated in the Upper-Silesian region (southern Poland) and operating in different environmental conditions, were selected for the research: Pogoria I reservoir - operating in the quasi-natural direct catchment (with fluvial load of industrial-municipal wastewater), Przeczyce reservoir - under agricultural anthropopressure, and Dzierzno Due reservoir - under urban-industrial anthropopressure. The research included analyses of the quality of river water flowing into and leaving the reservoirs and calculation of contaminant loads at the inflows and outflows. The research showed that Pogoria I reservoir neutralised inflowing contaminants, thus purifying the river water. Nitrogen and phosphorus compounds were particularly efficiently retained. Electrolytic conductance of water in Pogoria was reduced by up to 50%. Przeczyce reservoir was alimented with eutrophic water (especially rich in biogenic elements) from agricultural land. The reservoir accumulated contaminants at the initial stage of the research. After several years, however, it started releasing some of the accumulated substances, causing an increase in contamination of river water with e.g. organic substances. The data concerning Przeczyce reservoir revealed that reservoirs can purify water from some substances and simultaneously cause an increase in contamination with other substances. Selectivity of hydrochemical impact of reservoirs was particularly visible in case of Dzierzno Due reservoir, which received wastewater from the urban-industrial catchment. It largely reduced the loads of suspended matter, phosphates or zinc, among other substances, at the same time causing secondary contamination with substances like ammonia, lead or cadmium. The results of the research show individuality of reservoirs in terms of their impact on fluvial transportation of substances. It might be believed, however, that each reservoir which is fed with contaminated water will have at least partly (selectively) contaminating impact in the course of time. That should be related to increasing eutrophication in conditions of limited capacity of accumulation of contaminants in the limnic environment. Detailed assessment of transfer of substances by a particular reservoir would require individual research for that reservoir