The chemical and biological response of two remote mountain lakes in the Southern Central Alps (Italy) to twenty years of changing physical and chemical climate

Abstract

Two small high mountain lakes in the Alps were monitored in 1984-2003 to follow their response to changes in human impact, such as deposition of atmospheric pollutants, fish stocking and climate change. The results were compared to occasional samplings performed in the 1940s, and to the remains found in sediment cores. When monitoring started, the most acid-sensitive of them, Lake Paione Superiore, was acidified, with evident effects in its flora and fauna: benthic diatoms assemblage was shifted towards acidophilous species, and zooplankton lost the dominant species, Arctodiaptomus alpinus. Palaeolimnological studies outlined that lake acidification paralleled the increasing input of long-range transported industrial pollutants, traced by spherical carbonaceous particles. On the contrary, the biota of Lake Paione Inferiore appeared to be mainly affected by fish stocking. In the last twenty years, decrease in acid load from the atmosphere led to an improvement in lake water quality, with an increase in both pH and alkalinity. First signs of biological recovery were identified, such as change in diatom flora and appearance of sensitive species among benthic insects. However, climate change and episodic deposition of Saharan dust were important driving factors controlling lake water chemistry. Further monitoring to assess the effects of climate change and of the increasing load of nitrogen and other pollutants is recommended

Phytoplankton of a mountain lake (L’adové pleso, the Tatra Mountains, Slovakia): Seasonal development and first indications of a response to decreased acid deposition

“…Recently, the first signs of biological response following chemical recovery of strongly acidified mountain lakes have been reported from many regions (Vrba et al, 2003;Marchetto et al, 2004). Our results suggest that even lakes that were not so seriously affected by antropogenic acidification can undergo noticeable changes.…”

“…Although it did not reach abundances higher than 3 cells mL −1 in 2000-2001, finding of this pennate diatom characterised by affinities to higher pH (Hörnström, 2002) can also be considered as a sign of changing chemical characteristic of Ľadové pleso. An increased importance of diatoms within the planktonic community in response to increasing pH was recently observed in Lago Paione Superiore in the Italian Alps (Marchetto et al, 2004).…”

“…Planktonic communities of high mountain or high latitude lakes are known to be controlled mostly by allogenic perturbations that are characterised by high interannual variation (Hinder et al, 1999). Consequently, patterns of lake water recovery can also be influenced by climate change (Marchetto et al, 2004). Further study of Ľadové pleso is therefore needed to confirm, whether observed change of its phytoplankton community can be unambiguously related to the decrease of acid deposition followed by the chemical recovery of lake water.…”

Lacustrine particle dynamics in high-altitude Estany Redó (Spain) - a high resolution sediment trap study

“…4). This phenomenon has recently been observed also in other ice-covered lakes in the Alps, Scandinavia and Siberia (Marchetto et al 2004;Sturm et al 2005). In 1984, small first productivity peaks occurred during the open-water phase in July/August, followed by maximum productivity peaks in November/December.…”

Measured and modelled trends in European mountain lakes: results of fifteen years of cooperative studies

“…Monitoring data show that in Lochnagar (Scotland), the increase in NO 3 -deposition completely balanced the decrease in SO 4 2-, and the lake pH did not show any trend (Rose et al 2004). In contrast, in Lake Paione Superiore (Italy), steady NO 3 -and decreasing SO 4 2-deposition led to an improvement in lake pH and alkalinity (Marchetto et al 2004). As a consequence, no change in the lake biota was detected in the former, while the improved condition of the latter allowed a partial recovery of the diatom community and the reappearance of some sensitive species in zooplankton and zoobenthos.…”