The tank irrigation systems of Tamil Nadu support an agricultural area covering 61% of the state,(25) and allow for the growth of subsistence crops like rice, as well as market crops such as maize, sugar cane, and chili peppers. The functionality of the tanks, however, is considered to extend well beyond that of a water source for agriculture. They are essentially human-built ecosystems, providing economic, socio-cultural, and ecological services to their communities. Ecologically, these tank systems make up an extensive, interconnected web of manmade wetlands providing a broad range of ecosystem services, including flood control, nutrient and waste removal, provision of avian habitat, and increased biodiversity of flora and fauna. In Tamil Nadu alone, there are more than 39 000 tanks supporting wetland biodiversity and adding significantly to the country’s wetland wealth.(26) Tanks also enhance groundwater recharge and increase stream baseflow,(27) helping to revive rivers that have been depleted by large-scale diversions for canal irrigation and other uses.

Source :

http://pubs.acs.org/doi/full/10.1021/es4040182