Changes in Nutrient Concentrations of Two Streams in Western Lithuania with Focus on Shrinkage of Agriculture and Effect of Climate, Drainage Runoff and Soil Factors

Abstract

The causal relationship of changes in nitrogen and phosphorus concentrations in the Akmena-Danė River and its largest tributary, the Eketė River, was analysed for the period 1999–2014. Results showed that the annual concentrations of NH4-N and PO4-P significantly decreased in the Eketė River over the research period. NH4-N also significantly decreased in the Akmena-Danė River. This was mostly due to the shrinkage of agriculture, i.e., the reduction in agricultural land area, total farm and animal numbers and other agricultural activities. The effect of other factors such as air temperature, precipitation rate, shift of precipitation maximum from warm to cold season, drainage runoff from the large tile-drained areas, soil types and the slight increase in forested land was also examined.