The nitrogen phosphorus relationship in mountain lakes: Influence of atmospheric input, watershed, and pH

Abstract

The impact of high N input on the trophic status of small mountain lakes as modified by the type of watershed and stage of acidification in two central European mountain ranges (the High Tatra Mts. and the Sumava Mts.) is reported. Atmospheric N deposition enhanced nitrate concentrations of lake water, but the type of watershed determined both the share of nitrate in the pool of total N and its concentrations, which increased from forest to meadow to rocky watersheds. Ratios of total N to total P (TN : TP) generally reflected highest nitrate concentrations in alpine lakes, where soils and vegetation were sparse in the watersheds, and were lowest in forest lakes, where the N retention capacities of watersheds have not yet been exceeded. In alpine lakes, TN : TP reached a maximum level at pH values from 4.8 to 6.2, reflecting low TP concentrations in lakes at this stage of acidification. Because atmospheric N deposition may contribute to lake acidification, it may paradoxically also contribute to oligotrophication.