Freshwater ecosystems - threats and management

 Freshwater ecosystems account for less than 0.01% of the planet’s total surface area but they support more than 100,000 species, including fish, worms, mollusks, crayfish and insect larvae. But these freshwater systems are now among the most endangered habitats in the world, due to human development, pollution, and climate change.

Fewer than 70 of the world’s 177 longest rivers remain free of man-made obstructions. Also, more than half of the world’s wetlands have disappeared since 1900, a particular concern because these places serve as nature’s water treatment facilities—cleaning water of chemicals and other pollutants. Development, logging, pollution, agriculture and poor management put freshwater systems—and the water they produce for people—at risk.

Freshwater biodiversity loss

Freshwaters cover only about 0.5% of the earth’s surface, but are home to nearly 10% of all known species, including a third of all vertebrates.

 Despite this abundance of biodiversity, freshwater ecosystems are among the most threatened on Earth. According to the World Wildlife Fund’s Living Planet Index, freshwater fish, birds, mammals and reptiles and amphibians have declined by three-quarters over the last 40 years, which is significantly more than the declines in ocean and land wildlife.

The International Union for Conservation of Nature Red List reveals that 35% of freshwater amphibians are threatened or extinct, 46% of mammals and 38% of turtles.

Freshwater threats

Of all the Earth’s ecosystems, freshwater ecosystems have been hit hardest by human activities. Key threats include dams, farming and industry, water extraction, pollution, flow change, invasive species, over-harvesting of species, and climate change.To make the management of freshwater ecosystems even more challenging, these threats often interact in ways that are difficult to predict. These complex and interacting threats are often ignored, leading to the loss of species. 

Habitat loss and degradation are primarily due to deforestation, farming activities and dams. When these activities occur in an upper-catchment area, sediment is carried into rivers and lakes, causing significant negative impacts on freshwater species.

Unsustainable water extraction – for irrigation, industry and urban consumption – is a major threat to freshwater species. Over-harvesting of freshwater species (particularly fish) is, in turn, a threat to these ecosystems.

Infrastructure development – including dams  – also modifies water flow. There are perhaps one million dams globally, fragmenting rivers into isolated sections. Freshwater species – including fish, molluscs and reptiles – often can’t adapt to these changes and are at increased risk of extinction.

 Pollution is another significant threat to these habitats. Fertiliser runoff from farming and the dumping of industrial pollutants directly into rivers and lakes have resulted in areas so poisoned that they can no longer support their normal range of species.

Invasive species have played a major role in disrupting freshwater ecosystems. For example, The European carp (Cyprinus carpio), is a pest that out-competes native fish. It was first introduced to Australian waterways more than 100 years ago and has spread to every state and territory and now the government has plans to introduce a herpes virus to control carp.

Climate change presents another threat to freshwater habitats, particularly to those species that can’t migrate or compensate for higher temperatures. In Australia, extreme weather fluctuations and natural disasters such as floods and droughts are projected to become more common, placing freshwater biodiversity under further stress.

As threats intensify, the risk to freshwater wildlife will increase. Vulnerable freshwater ecosystems will be particularly susceptible to further loss of species.

The best way to help freshwater species is to restore rivers. This might include fencing out livestock, stabilising river banks, removing weeds, replanting native vegetation and expanding floodplain areas. Farm and land management such as rotating pasture, reducing erosion through smart burning practices, and better management of pesticides and nutr