Impacts of land-use on concentrations of nutrients in runoffs: Preliminary results in small catchment areas.
Hakala, Ilpo; Huitu, Eeva; Mäkelä, Suvi; Arvola, Lauri
Diffuse loadings of nutrients from agricultural areas is an acute problem for a great number of lakes in Finland. The concentrations of nutrients in the runoff waters tend to rise as the proportion of agricultural area increases. The loads and concentrations depend on several interacting parameters. Some of them are quite evident like weather, soil and landscape properties of the drainage basins, but the effects of human activities are still a complicated challenge for scientists. In this study the annual variations of nutrient concentrations of 21 small drainage areas of Lake Pääjärvi (Southern Finland) were studied. The proportion of agricultural land varied from 0 to 54 %. High concentrations of nitrogen and phosphorus were generally associated with the proportion of cultivated land, but also with the spring storm flows. The concentration of inorganic nitrogen was clearly correlated with the proportion of fields. The maximum annual load of total nitrogen was 2065 and total phosphorus 51.3 kg km-2 a-1 from field dominated areas. The maximum load of total nitrogen was about 10 times higher than the minimum value observed in the forested drainage areas. The same relation was observed also in the total phosphorus loads.