The effects of storm water on Lake Vaxjosjon

• The aim of the present study was to determine the pollution load originating from storm water on Lake Vaxjosjon. Each year about 1,050,000 m3 of storm water are discharged into the lake. Storm water represents a substantial pollution source for the lake and therefore also a main reason for the hypertrophic conditions in the lake. In order to evaluate the effects of the discharged storm water on the ecological conditions in the lake, an investigation was carried out using available information on storm water quality together with complementary sampling and flow measurements. Two different time scales were considered to be important: a short time scale for evaluating effects on the receiving waters due to shock loads of toxic substances (hours and days) and a long time scale for evaluating the effects of nutrients (years). In order to investigate effects concerning the short time scale, a computer-based runoff model was used. For the long time scale a daily precipitation series from 1970 to 1983 was used. The results showed that approximately 37% of the annual load of total phosphorus and 70% of the annual load of total nitrogen originate from storm water. Also a considerable portion of the annual heavy metal load originates from storm water (zink 51%, copper 55%). The annual total phosphorus load on Lake Vaxjosjon is 0.63 g/m2 lake area and year. The storm water part represents a phosphorus load equal to 0.23 g/m2 lake area and year. The acceptable load of phosphorus, for mesotrophic conditions in the lake, is about 0.2 g/m2 lake area and year. In order to improve the water quality in Lake Vaxjosjon sediment dredging of the bottom sediments needs to be undertaken. The sediments consists of an organic rich, phosphorus and nitrogen accumulated, black, anaerobic deposit, causing internal nutrient loading during summer periods.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Oceanografi, hydrologi och vattenresurser (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Oceanography, Hydrology and Water Resources (hsv//eng)

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