During the last decades, European countries have gone through considerable effort to reduce emissions of acidifying sulfur and nitrogen compounds. In Switzerland since the 1990s, S emissions have been reduced by ≥ 85% and emissions of oxidized-N have been reduced by ≥ 50%.
Despite these great efforts, N-deposition is still very high reaching 20-30 kg ha-1 y-1 and alpine ecosystems, besides N-enrichment and acidification, are facing climate changes with strong impacts on their biota. Global warming has been very rapid and intense and the Alps are experiencing one of the highest increase in average annual temperature (~2°C) with relevant impacts on the cryosphere.
What are the effects of the global warming on acid-sensitive ecosystems, are climate changes affecting the acidification recovery of swiss alpine lakes?
We investigated since 2014 the catchment of Lago Nero, a high alpine basin located in the southern swiss Alps, with the aim to (i) assess the input-output budgets of deposition, runoff and water soil chemistry, (ii) investigate the cryosphere (permafrost and rock glacier) and his potential to alter the chemical composition of the lake and (iii) to survey the ecological impacts of the acidifying depositions on the biological communities.
Results/Conclusions
The input-output budgets indicate that Lago Nero is affected by exceptionally high deposition of N, ranging from 10.6-19.3 kg ha-1 y-1, confirming that the N-nutrient enrichment critical load of ~3 kg. ha-1 y-1 for high alpine sites is largely exceeded.
Current deposition of sulfur is low (< 6 kg ha-1 y-1). Nonetheless the monitoring of the cryosphere revealed high concentration of S and partially N in the rock glacier and permafrost meltwater, which may contribute to maintain high release of acidifying elements and is likely to have ecological effects on the sensitive biota of the watershed. Probable storage of ground ice during the 1970s and its significant melting in the last decades may explain the high amounts of S measured in the outflow of the cryosphere (percent net export up to +200%).
To assess the deposition impacts in the watershed, a vegetation survey was performed at the beginning of the vegetative period, consisting of a quantitative and a qualitative analysis of the plant species composition. The quantitative survey has shown that species richness is relatively poor (average species richness per subplot: 7.8) and that the community is dominated by species adapted to nutrient-poor and rather acid soils, including species like Carex curvula and Homogyne alpina.