Catchment biogeochemistry modifies long-term effects of acidic deposition on chemistry of mountain lakes

Using relationships between the composition of precipitation and emission rates of sulphur and nitrogen compounds and dust from 1978 to 2012, we modelled concentrations of sulphate, nitrate, ammonium, chloride, and base cations and pH of precipitation in the Tatra Mountains (central Europe) back to 1900. The modelled precipitation chemistry exhibited a high degree of temporal coherence with the lake water chemistry in 1937 and during the period 1984-2014. The ionic composition of lake water reflected progress in their acidification until the late 1980s, and then a rapid recovery. The response of lake water chemistry to changes in precipitation chemistry differed for individual ions, nutrients, and among lakes, predominantly reflecting the proportions of soil in their catchments. Important differences occurred in nutrient concentrations. In-lake concentrations of dissolved organic carbon (DOC) and total organic nitrogen (TON) exhibited inverse patterns to nitrate. DOC and TON were higher in lakes with a higher proportion of soil in the catchments, and increased in many lakes during recovery from acidification, while nitrate concentrations were higher and decreased most steeply in the catchments with sparse soils. Lake water concentrations of total phosphorus (TP) were spatially similar to that of DOC and TON, but increased most steeply during recovery in lakes with a high proportion of till soils. Our results indicate that chemical recovery of mountain ecosystems is seriously modified by catchment biogeochemistry and may result not only in elevated DOC leaching, but also in an increase of terrestrial export of TON and TP to the receiving surface waters.