Groundwater extraction for fish farms can cause land to sink at rates of a quarter-metre a year, according to a study of China’s Yellow River delta1. The subsidence is causing local sea levels to rise nearly 100 times faster than the global average.

Global sea levels are rising at about 3 millimetres a year owing to warming waters and melting ice. But some places are seeing a much faster rise — mainly because of sinking land. Bangkok dropped by as much as 12 centimetres a year in the 1980s thanks to groundwater pumping. Oil fields near Houston, Texas, experienced a similar drop during the 1920s because of oil extraction. Deltas can also sink as old river sediments compact under their own weight and water carrying replacement sediments is held back by dams or diverted for irrigation. “You can get crazy rates of sea-level rise,” says James Syvitski, a geologist at the University of Colorado Boulder and a co-author of the study, published online in Geophysical Research Letters1.

The researchers found that parts of the Yellow River delta are dropping by up to 25 centimetres a year, probably because of groundwater extraction for onshore fish tanks. The link between aquaculture and subsidence has attracted little international notice. “This is a new one on me,” says Stephen Brown, a fisheries scientist at the US National Marine Fisheries Service in Silver Spring, Maryland. “We are concerned about the effect of sea-level rise on fish; not the other way around,” he says.

http://www.nature.com/news/fish-farms-cause-relative-sea-level-rise-1.13569