Bilans wodny śródleśnego oczka wodnego

Duży wpływ na kształtowanie się zasobów wodnych w zlewniach leśnych mają śródleśne oczka wodne, których wody często w okresach posusznych zasilają wody gruntowe terenów przyległych [4, 5]. Badania wykazały, że niedobory wody mogą występować z coraz większym nasileniem zarówno na terenach użytkowanych rolniczo jak i leśnie. Zmniejszenie tych niedoborów może być realizowane poprzez właściwe gospodarowanie zasobami wodnymi oraz działaniami mającymi na celu ich zwiększenie. W ostatnich latach podejmuje się coraz więcej prac w zakresie wykonywania małych budowli piętrzących na istniejących ciekach, rowach i śródleśnych oczkach wodnych, w celu ograniczenia bezproduktywnego odpływu wody ze zlewni leśnych, a tym samym zwiększenia zasobów wodnych w tych zlewniach, bez negatywnych skutków ekologicznych [6, 7]. Wymaga to jednak poprawnego określenia bilansów wodnych tych terenów, w tym bilansów wodnych śródleśnych oczek wodnych. Takie działania mogą się przyczynić do optymalnego kształtowania gospodarki wodnej na obszarach leśnych, z zachowaniem wymogów ochrony środowiska przyrodniczego. Celem pracy było określenie bilansu wodnego śródleśnego oczka wodnego intensywnie zasilanego wodami źródliskowymi z terenów przyległych.

The paper presents the results of research carried in 1999/2000 and 2006/2007 hydrological years in catchment of forest pond No. 5. The pond is located at Siemianice Experimental Forest Farm (National Road no. 11 Poznań- Bytom, about 15 km south-east from Kępno - Laski Forestry) of Poznań University of Life Sciences. The forests of this forestry are within range of Nizina Południowo-Wielkopolska, on Wysoczyzna Wieruszowska, which is differential morainic plain, cut with the river Prosna headwaters. Hydrological year 1999/2000, in which precipitation was 84 mm higher than average multiyear precipitation, was a wet year. Second period, hydrological year 2006/2007 was medium-wet, as precipitation was 20 mm higher than average multiyear precipitation. Area of the pond's catchment is about 20 ha and it's an afforested catchment, with predominance of fresh habitats, where 104 years old pine is predominant species of tree stand. The soil covering the largest area is dear brown soil, and the most common type of soil is loamy sand, covering silty clay deposits. The pond No. 5 - area about 0.097 ha, average depth 1.0 m - is intensively supplied by spring waters from adjacent areas. Excess water leaves the pond through Thomson's overflow to the nearest drainage ditch. According to the information from the local residents, the pond No. 5 used to be a fish pond before the Second World War. Water balance of mentioned pond was calculated according to formula: P+Hdg=Eo+?Ro+Hps+Hr, where: P - precipitation (mm), Hdg - inflow to pond from adjacent areas (mm), Eo - evaporation from pond surface (mm), ?Ro - change of retention in pond (mm), Hps - uncontrolled filtration trough banks (mm), Hr - outflow from pond trough the ditch (mm). The balance equation assumes, that the uncontrolled amount of water filtrating from pond No. 5 through banks (Hps) to the ditch is 20% of the outflow value, measured in Thomson's overflow. Amount of water flowing out from the pond (Hr) is given considering the pond's surface. Small variability of the water level and outflows registered on the dispatch was characteristic for pond No. 5. Especially during summer half-years differences between minimal and maximal level of water were the smallest. Analyses, carried in researching period, show, that water balance of pond No. 5 was mostly impacted in a large extend by inflows to the pond from adjacent areas (side of incomes) and by outflow from the pond through the ditch and uncontrolled filtration through banks (side of outcomes). Neither precipitation nor evaporation from the pond's surface or changes of the retention in the pond had influence on water balance of pond No. 5. It was found, that the small variability of water level in pond No. 5, caused by the supply from ground waters, and constant outflow of water to thenearest ditch had stabilizing influence on the water resources of the pond. This can be noticed while analyzing water flows in years 1999/2000 and 2006/2007, which were different considering hydrological characteristics, however the values of water flows were stable.