The atmospheric deposition of phosphorus and nitrogen on Lake Kivu

Abstract

Phosphorus and nitrogen are most often identified as the nutrients limiting algal biomass and productivity in aquatic ecosystems. Sources of new nutrients for lakes include riverine input, atmospheric deposition, N fixation, and occasionally groundwater. For many regions, the relative importance of atmospheric deposition is uncertain. Annual dynamics of wet and dry atmospheric nutrients (phosphorus and nitrogen) deposition on Lake Kivu were investigated at three land stations and one an island station to estimate lake wide atmospheric nutrient input to Lake Kivu. The highest dry P (TP) loading rates were recorded at the southern end of the Lake with lower rates in the north. Annual dry atmospheric deposition was higher than wet deposition in all the four sites. The estimation of dry TP and TN deposition to entire Lake Kivu (2370 km2) is 14.5 ± 16.26 kg m-2 yr-1 of TP and 506.3 ± 590.7 kg m-2 yr-1 of TN. And the wet TP and TN estimation rate for the all Lake Kivu was respectively 0.09 ± 0.07 kg m-2 yr-1 and 2.02 ± 0.16 kg m-2 yr-1. Phosphorus and nitrogen deposition rates in atmospheric deposition around Lake Kivu were similar to the existing estimates of atmospheric phosphorus and nitrogen inputs to other African Lakes. Both biomass burning and soil suspension particles were suggested as possible sources. These estimates should be viewed as a first order approximation of actual phosphorus and nitrogen deposition on the Lake.