Frog Deformities Linked to Farm Pollution

Fertilizer runoff from farm fields could be causing an increase in frog deformities in North American lakes, according to a new study. 

In 1999, Pieter Johnson of Stanford University (now at University of Colorado) found that a flatworm parasite (Ribeiroia ondatrae) was a major cause of frogs with extra or malformed legs. "At low abundance, Ribeiroia ondatrae does not cause much damage," says Johnson, but he now believes fertilizer pollution may be to blame for boosting the number of parasites in lakes and ponds. Nutrient runoff from non-organic farms leads to accelerated eutrophication of lakes and ponds, which in turn has a cascade effect on the local food chain.

Johnson and his colleagues created 36 mini ponds that were filled with clear, non-polluted lake water. In half the tubs, they added 200 micrograms of phosphorus per liter of lake water. The tubs were populated with algae, as well as frogs and small aquatic snails. The snails, which feed on algae, are key to the flatworm parasite's life-cycle. The researchers found that by boosting nutrients and accelerating the growth of algae, the number and size of the water snails increased which in turn, pushed up parasite numbers. In tubs containing the additional nutrients, snail biomass increased by 50% and infected snails produced twice as many parasitic worms. The infection rate in frogs increased between two and five fold. http://www.precaution.org/lib/07/prn_farm_runoff_deforms_frogs.070925.htm