Humans, Freshwater, Species

Endangered Coahuilan box turtle in Mexico

Previously, I talked about habitat loss of species. Little do we know, freshwater is facing greater pressure from humans and extinction is fast approaching freshwater species..

"Massive mismanagement and growing human needs for water are causing freshwater ecosystems to collapse, making freshwater species the most threatened on Earth. Extinction rates for freshwater species including fish, frogs, crocodiles and turtles were four to six times higher than their terrestrial and marine cousins." - Diversitas, an international group of biodiversity experts 

It is not beyond imagination that human source of threats are not restricted within habitat loss. Dudgeon and his team suggested that impact posed by humans consist of five main categories:

Five major categories on freshwater biodiversity

The impact of human on freshwater is interrelated with their other influences, as demonstrated above. Pollution is one of the most serious problems. Water pollution from domestic and industrial sources leads to excessive nutrient enrichment and the growth of other chemicals like endocrine disrupters. This chemical will cause disturbance to the hormone systems of species. Hence, it leads to possible depletion of species. Habitat alterations such as forest clearance, as mentioned previously, can change the surrounding of the homeland of species. For instance, it will increase river sediment loads and lead to shoreline erosion. The disproportionate water distribution for plants and animals (Surface freshwater habitats contain only 0.01% of world's water but are housing 40% of global fish diversity and 25% of global vertebrate diversity), together with the other harmful effects brought by humans, make freshwater species highly vulnerable to extinction. 

Not convinced?

The edge of extinction is actually highly visible in many places, where a lot of freshwater species are now endangered due to disturbance from humans. In Spain, record of threatened freshwater fish can be dated back from 1986.  

Percentages of endangered freshwater fish in Spain
Ex?: Probably extinct, E: endangers, V: vulnerable, R: rare, I: indeterminate, K: insufficiently known, NT: not threatened 

Unthreatened species significantly decreased. In 1992, there was 1% of freshwater fish at the edge of extinction. Amount of rare species raised 7%, including Hucho hucho, Salelinus fontinalis and Ictalurus melas. 

Hucho hucho

Salvelinus fontinalis

Ictalurus melas

Human, not surprisingly have played a crucial role in effecting the endangered fish. Construction of 11, 000 large dams in Spanish rivers has jeopardised survival of migratory species. These dams also led to significant loss of habitat with establishments of large reservoirs, water-flow regulation and water withdrawal. 

Here's a quick summary: Freshwater habitat, contains the most endangered species. They are highly affected by human activity and modification to the surroundings. There were already 20% of freshwater species that had gone extinct. Given the limitation on research in vast freshwater species, it is likely that more than that are close to extinction. Have people thought about the consequences before building dams and clearing forests?