Freshwater ecosystems

Biologically, freshwater ecosystems are amongst the Earth’s most diverse. Lakes, rivers, and wetlands cover less than 1% of the Earth’s surface, but support over 10% of all known species– drawn widely for microbes, higher plants, invertebrates, and vertebrates. Among the latter in particular, this proportion rises to over 33% because of the large richness in fresh waters of fish, amphibians and birds, which use inland waters or their margins during their lifecycle. These numbers reflect the role of fresh waters in the origin of life and the physical habitat structure into which species have since radiated.

Yet for most people, including professional scientists, much of this biological wealth is hidden beneath the water’s surface. The biological richness of freshwater ecosystems is not only intrinsically important. In combination, processes driven by freshwater organisms contribute to a range of goods and services on which people depend. The purification of water, the disposal of pollutants, the attenuation of floods. The production of fish, the harnessing or transfer of energy that supports a wide range of other organisms in a satiated environment. In addition to being hotspots for biological diversity, fresh waters are also hot spots for human use. Water is arguably the most fundamental resource on which we all depend, and which is fundamental to life on Earth.

Across the world, over 50% of accessible freshwater is appropriated by people, dominantly for agriculture, which accounts for over 90% of our global water footprint. Dams impound around 10,000 cubic kilometres of water, over five times the volume contained in the Earth’s rivers. Water quality is impaired globally, too, from rivers polluted by intentional waste disposal, or incidentally by runoff from agriculture and other land uses. Around 1500 cubic kilometres of wastewater are released annually into the Earth’s rivers, almost equivalent to total river volume. Nitrogen fluxes in many rivers now exceed pre-industrial background levels, by at least 2 and up to 20 times. Across the European Union, around 60% of surface water bodies fail to reach good ecological status.

It is this juxtaposition of biological diversity and human exploitation that has given rise to rates of species extinction in rivers, lakes, and wetlands, that are more rapid than in any other ecosystem. The worldwide fund for nature, living planet index, an index [INAUDIBLE] from the numbers of many populations of many freshwater species, shows freshwater animals declining by over 80% over the last 40 years. Over twice the rates for land, 38%, and sea, 36%. And these trends are accelerating. This ecological degradation of fresh waters reflects the effects of climate change. The exploitation of fresh waters. The degradation of habitats. The effects of invasive, non-native species, and pollution.

And they are corroborated by other data, such as the red list of endangered species compiled by the International Union for Conservation of Nature.