The results of eight years Plawnowice reservoir restoration by hypolimnetic withdrawal

摘要

The inter-reservoir enrichment phenomenon was exploited to curtail the reservoir eutrophication process. The Plawnowice reservoir (South Poland - Upper Silesia Region) has an area of 225 ha, volume of 29 mln m3 / and a depth of 15 meters. According tothe monitoring results in the years 1993 - 1998 the reservoir was qualified as hypotrophic. Beginning in December 2003 a bottom pipe for hypolimnetic withdrawal was installed. In the period 2004 - 2010 a negative phosphorous balance was achieved. The discharge load of total phosphorous was at the beginning twice as high as the inflowing. During the first eight years with an inflow of 75 Mg P, the removed load of total phosphorus was 103 Mg P. In effect the net balance was 28 Mg P. The load, in respectto the surface area, of 2.2 to 3.3 gP/m2 per year was reduced to a negative load of - 0.48 to -3.3 gP/m2. The hypolimnetic maximum concentration of orthophosphates equal to 1.254 mg P-P04/dm3 in 2004, was reduced to 0.236 mg P-P04/dm3 in 2011. The respective factors and rate of eutrophication curtailing, including changes of nitrogen compounds have been discussed. Also changes of pH and visibility of the Secchie disc where presented. It was concluded that presented method of hypolimnetic withdrawal is alasting and effective process.