Lake ecosystems and their remediation: issues, potential and limits

Continental freshwater represents only around 3% of the earth's water volume, and of this, only 0.3% is surface water in liquid form. Lakes are the main reservoir (between 80 and 90%), divided into several hundred million units. Although lake water is in very short supply and its distribution across the globe is highly fragmented, lakes represent a key element in the earth's environment and in human development.

Lake ecosystems are places of biodiversity and varied uses, important to human societies. Over the centuries, lakes have served as frontiers or links, as sites of human development on their shores, as fishing resources*, as sources of drinking water, and then as tourist destinations. It's only recently that the development of limnology* has made it possible to identify the functioning of lake ecosystems, and then the ecological mechanisms that lead to their degradation (the founder of this discipline is François-Alphonse Forel, 1841-1912). It is now well documented that human activities are pushing most of these ecosystems beyond their ecological carrying capacity, i.e. their natural capacity to absorb disturbances and support uses.

The UN's environment program (unep.org) has identified five main factors underpinning the nature crisis: changes in land and sea use, climate change, pollution, intensive exploitation of natural resources and invasive species. Lakes are subject to all these pressures (apart from sea use) and, given their small volume compared to oceans or continental surfaces, are particularly sensitive to them, to such an extent that they are often regarded as "sentinels" of the state of the environment. To implement remediation measures, we need to understand the ecology of these apparently closed systems, which are in fact open to their environment via their watersheds and the atmosphere.

The aim of this article is to provide a basic understanding of how lake ecosystems function, particularly under the impact of anthropogenic pressures. Faced with the degradation of most of the world's lakes, this article presents a brief summary of the means and tools available for ecological restoration, based on case studies.