Note: original title using the term fertilizer was corrected to read atrazine
Leopard frog
Courtesy Heather Dietz
A recent study showed that atrazine in pond water could lead to a higher population of snails, which harbor parasites that also infect frogs. For the study, Lucinda Johnson and her colleagues at UMD collected leopard frogs from 18 wetlands near St. Cloud, Minnesota. The researchers found a positive correlation between the amount of atrazine in a wetland and the number of parasites in that wetland's frogs. The parasite in question is a tiny worm called a trematode. They can have a negative effect on frog populations.
More fertilizer = more pond scum (periphyton)
More periphyton (snail food) = more snails
More snails = more snail parasites (trematodes)
More trematodes = more trematode larva attacking tadpoles
Larva infested tadpoles and frogs have lower survival rates when atrazine is present
The trematode worm that infects the frogs gets passed to frog-eating birds like herons and egrets. Inside the birds, the worms develop to adulthood. The adults produce eggs that are released into water with the birds' feces. The eggs hatch, develop into larvae, and burrow into snails. After further development, they burrow their way out again and swim in search of tadpoles. They infect them, the tadpoles turn into frogs, and the cycle continues.
Source articleUMNews: The tadpoles tale .
Article in Nature: Agrochemicals increase trematode infections in a declining amphibian species
It's interesting that the trematode and atrazine theories have come together, instead of competing. (We did a short posting on similar research in September 2007.)
Science Buzz did a mini exhibit about these freaky frogs back in 2005. Here's the web posting. If you scroll down into the comments, you'll find descriptions of many of the theories/experiments scientists were running with as they attempt to solve the mystery of the freaky frogs.
in my opion, if people know that they are hurting the frogs with this fertilizer... why keep using it just so you have flowers!!!
Atrazine isn't a fertilizer; it's an herbicide--a weed killer. (Art, what IS the link between atrazine and algae growth? Why does it kill some plants, but spare algae?)
And people aren't using atrazine on flowers. According to "The tadpoles' tale" (above link),
"According to a 2003 EPA report, atrazine is estimated to be the most heavily used herbicide in the United States, being applied primarily on corn and sugarcane and on residential lawns in Florida and the Southwest. On a per unit area basis, the heaviest uses occur in parts of Delaware, Iowa, Illinois, Indiana, Ohio, and Nebraska. Atrazine, according to a report in Scientific American, is found in 57 percent of U.S. streams, the product of runoff from agricultural fields. Once in a stream, it may be carried to lakes, ponds, and other wetlands.
Incidentally, Minnesotans use a lot of atrazine because we grow a lot of corn.
Liza, Thanks for clarifying that atrazine is an herbicide. I normally take more time writing these articles, but "whipped this one out in 30 minutes".
The "link" is statistical. I do not think there is any claim that it is causative (correction: see bottom quote). The presence of phosphorus (from fertilizer) appeared to play a complementary role when atrazine was present.
A statistical analysis showed that of all the factors that could be at work, the presence of atrazine in water was the best predictor of higher parasite loads and reduced immune cell counts. Also, higher levels of phosphorus, a component of fertilizer, appeared to play a complementary role when atrazine was present.
Also from the research abstract:
A mesocosm experiment demonstrated that, relative to control tanks, atrazine tanks had immunosuppressed tadpoles, had significantly more attached algae and snails, and had tadpoles with elevated trematode loads, further supporting a causal relationship between atrazine and elevated trematode infections in amphibians.
Science Buzz is supported by the National Science Foundation.
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