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
The research described here was performed during 1993 and 1994 in the context of studies on the recovery of Lake Orta from acidification after the liming conducted from May 1989 to June 1990. The causes of the pollution were due to the oxidation of ammonium sulphate discharged from a factory producing rayon by a cupro-ammoniacal method and to the loads of heavy metals (Cu, Cr, Ni, Zn) derived from plating factories. One year after liming, an increase in pH and a marked decrease in metal concentrations were observed, and as a consequence some qualitative and quantitative changes were observed in 1992-93 in the planctonic communities and in the littoral macrobenthic fauna. This paper presents qualitative and quantitative data on macrobenthos collected along a transect between the littoral and the maximal depth in the Buccione Basin, which was directly affected by the effluents of the rayon factory. The data revealed some quantitative repopulation of this community, especially along the littoral. Qualitatively, however, the macrobenthos was still quite poor, consisting essentially of Oligochaeta and Diptera Chironomidae. The former were rare and mainly represented by Naididae between 15 and 22 m, while the Tubificidae were well represented in the littoral and the profundal zones. As regards the Chironomidae, the genera Procladius and Chironomus gr. thummi extended as far as the maximum depth, while others, such as Ablabesmyia, Parakiefferiella bathophila and Dicrotendipes gr. nervosus were mostly distributed in the littoral layers. Among the other taxonomic groups only the Trichoptera and the Diptera Ceratopogonidae were quantitatively significant. However, many systematic entities typical of the less polluted Italian subalpine lakes are still absent. In fact, the colonisation of Lake Orta by macrobenthic organisms is still influenced by the increased concentrations of heavy metals in the sediment precipitated from the water column. The research included analysis of lake water and sediments chemistry to obtain information on the trophic level of the environment
Lake Orta has been interested since 1926 by severe industrial pollution, due to the effluents of a rayon (artificial silk) factory that discharged huge amounts of copper and ammonia. As a consequence, the benthic fauna faced noticeable changes, becoming extremely poor in species. However, after extensive liming (in 1989-90), the biotic communities of the lake showed many signs of recovery, and in 1996 it was decided to study the benthos composition and abundance in detail, to assess whether the lake restoration resulted in a complete recovery of this biotic compartment. Actually, both the small number of taxa, and the low abundance of the benthos, indicate that the sedimentary environment is still very stressed. In fact, albeit this study shows that benthos fauna is actively recolonising Lake Orta bottom, spreading from river mouths, in 1996 the benthic community cannot be considered fully organised
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