Threatened and stressed mountain lakes of Europe: Assessment and progress

Mountain regions are cold environments that are hostile to human occupation and widely regarded as places where the air is clean, water is pure and ecosystems are pristine. Yet many mountain regions, especially in Europe, are far from pristine. In the 1980s, research showed that mountain lakes were especially vulnerable to acid deposition and sediment core studies at many sites demonstrated that some mountain lakes had become acidified over the course of the last century. Since then, studies of the water chemistry, biology and history of lakes across the different European mountain regions have increased our understanding of the processes within these systems, their ecological condition and the threats facing them. These studies have demonstrated that: i) gradients of sulphur, nitrogen, metals and persistent organic pollutant deposition occur from relatively uncontaminated regions in Spain and Central Norway to regions of heavy pollution loading in central and eastern Europe;ii) nitrate and sulphate concentrations in lake water reflect the gradients in atmospheric deposition;iii) concentrations of mercury, lead and cadmium in fish tissue show marked regional differences;iv) the spatial pattern of organochlorine concentrations in fish and in sediments follow the pattern for other pollutants, although there is also good evidence for the selective cold trapping of some compounds both at high latitudes and at high altitudes;v) fish suffer physiological stress in mountain lake-water of low ionic strength;vi) climate change over the last century is likely to have induced significant changes in lake ice-cover and water column stratification and mixing in some regions and these have in turn influenced the structure and productivity of biological communities; This paper provides a review of the research undertaken on European mountain lakes over the past 30 years. In particular, it highlights the stresses faced by these vulnerable systems and the effects these have had, continue to have, and are likely to have on mountain lake ecosystems in future.