(NewsTarget) Runoff from industrial farming and ranching appears to be the ultimate cause behind the surge in deformities among North American frogs in the past several decades, according to a new study published in theThe problem of frog deformity in North America is only one part of a global decline in amphibian populations that is increasingly alarmist biologists and conservationists. One of the apparent causes for the decline is that an increasing number of frogs are improperly developing out of the tadpole stage."We continue to see malformed amphibians all over the place, and yet very little is being done to address those questions or even understand them," said lead researcher Pieter Johnson of the University of Colorado at Boulder."You can get five or six extra limbs. You can get no hind limbs. You can get all kinds of really bizarre, sick and twisted stuff."Johnson's team created 36 artificial ponds in Wisconsin, to which they added snails and frog tadpoles. To some ponds, they also added nitrogen and phosphorus -- nutrients commonly found in fertilizer and animal waste. In these ponds, the researchers observed a great increase in the population of both snails and the eggs of microscopic parasites called trematodes, along with a higher rate of trematode infection in the frogs.In nature, trematodes infect snails and reproduce in their bodies. The parasites are then expelled into the water, where they infect frog tadpoles and burrow into the spots where their limbs are developing. Often, this leads to deformities in those spots. When the deformed frogs are eaten by birds, the parasites are defecated back into the environment.Nitrogen and phosphorus runoff from agriculture have long been known to lead to explosive algae growth. This growth provides more food and habitat for aquatic snails, thus beginning the chain that leads to frog deformities