16. Freshwaters: Global Distribution, Biodiversity, Ecosystem Services, and Human Pressures

Freshwaters are among the most dynamic, diverse, and complex ecosystems globally. Lakes, rivers, and ponds cover about 1% of the Earth’s surface; however, these systems contain 10% of all animals and one-third of all vertebrates. In addition, freshwaters provide a wide range of ecosystem services that are fundamental for human well-being, including clean water, recreation value, and food. At the same time, freshwaters are under immense human pressure due to overexploitation, habitat degradation, invasion, climate change, dam construction, as well as emerging stressors such as light, noise, and synthetic chemicals. Consequently, freshwater biodiversity is declining three to six times faster than biodiversity in marine and terrestrial realms, and ecosystem services are being eroded in unprecedented ways. Globally, wetlands have declined by 75% over the past decades, and out of 242 rivers longer than 1,000 km, only 86 remain free flowing. Hence, one-third of all freshwater species are currently threatened, and global freshwater megafauna populations even declined by 88% from 1970 to 2012. We need to carefully, and fundamentally, rethink future management strategies for freshwater ecosystems due to conflicting interests for conservation and exploitation. Freshwaters must be managed as hybrid systems, i.e., as a resource for human use as well as extremely valuable and diverse ecosystems. Furthermore, we must establish a blueprint of freshwater life to increase awareness about the enormous value of freshwaters and their rich biodiversity. Most importantly, however, we need to preserve the remaining free-flowing rivers, intact wetlands, and unspoiled lakes—for the sustainable benefit of humans and nature alike.