Phosphorus loading of mountain lakes: Terrestrial export and atmospheric deposition

Abstract

We studied the atmospheric deposition of phosphorus (P) forms along an elevation gradient, and its contribution to the total external P loading of lakes in the Tatra Mountains and the Bohemian Forest, from 1998 to 2009. The aim was to evaluate how topographical (soil and vegetation pools in the catchment) and morphological (catchment‐to‐lake area ratio) characteristics of catchment–lake systems affect in‐lake nutrient structures in remote mountain areas. Concentrations of dissolved organic carbon (DOC), total phosphorus (TP), and total organic nitrogen (TON) were closely related (p < 0.001) to each other in lakes and their inlets. Terrestrial TP export (57–1183 μmol m−2 yr−1 on a catchment area basis) and lake‐water TP concentrations (0.05–1.0 μmol L−1) were closely associated with DOC leaching, exhibiting significant (p < 0.001) exponential relationships with increasing soil cover in the catchments. Precipitation fluxes of TP (460–918 μmol m−2 yr−1, average 692 μmol m−2 yr−1, with 50% being soluble reactive P) increased with precipitation along the elevation gradient and were highest in windy mountain areas. The C : N and C : P ratios of external nutrient inputs to the lakes were higher for terrestrial than atmospheric sources by a factor of ∼ 4 and 32, respectively, and the relative atmospheric contribution to the total external P loading of lakes was inversely related to the soil cover of catchments and the ratio between catchment and lake areas. The different composition and proportion of terrestrial and atmospheric nutrient inputs to mountain lakes along the vegetation zones determine the stoichiometric balance between the DOC and P available as nutrients for the food webs of natural mountain lakes.