May a fast-flushing dystrophlc headwater lake mitigate acid rain?

Abstract

Mass budget data for the dystrophic headwater lake “Huzenbacher See” (Black Forest, Germany) revealed annual in-lake retention rates for sulfate, protons, nitrate and “negative alkalinity” with values up to 15%, 43%, 60%, and 48%, respectively. These rates are related to the sum of all relevant annual loadings entering the lake from the watershed by eleven gauged lake tributaries, by groundwater inflow into the lake and by open precipitation on the lake and its floating Sphagnum peat mat surfaces. Microbial processes as denitrification, nitrate reduction and sulfate reduction are likely involved in the in-lake retention of imported acidity and the in-lake alkalinity generation. The hypolimnion of the lake and its sediments, the littoral soils and the floating Sphagnum peat mat, which surrounds the central part of the lake, are among the sites where these anaerobic processes can occur. Nitrate uptake by the floating Sphagnum peat mat, by the littoral stands of the macrophyte Nuphar lutea, and by phytoplankton can support this in-lake alkalinity generation, too.