For amphibians' sake, be careful with fertilizer

Last Updated: 
April 30, 2008

CORVALLIS, Ore. – It is good to be careful with fertilizer in the yard or garden for several reasons – water quality is a main concern; amphibian decline is another.

One species after another of amphibians is declining or becoming extinct, unable to keep pace with the rate of global change, according to a new study published this month in the scientific journal BioScience by Oregon State University zoologist Andrew Blaustein.

"We know that there are various causes for amphibian population declines, including UV-B light exposure, habitat loss, pesticide pollution, infections and other issues," said Blaustein, a professor of zoology at OSU and one of the world's leading experts on amphibian decline.

In the past, water was reasonably pure and clean. But increased "eutrophication" of freshwater ponds, due to use of modern fertilizers and waste from grazing animals, has led to higher rates of parasite infections. Chemical contamination of aquatic systems is also more common, explained Blaustein.

In the face of this and many other challenges, amphibians appear to be losing the battle. Of 5,743 known species of amphibians on Earth, 43 percent are in decline, 32 percent are threatened and 168 species are believed extinct. The impacts of changes are far more pervasive on amphibians than many other vertebrates, such as birds or mammals.

Blaustein's past research has shown that several frog, toad and other amphibian species, especially at their more vulnerable larval stages, can be highly susceptible to fairly low levels of nitrate and nitrite exposure. They discovered that a level of nitrogen-based compounds which the U.S. Environmental Protection Agency says is safe for human drinking water – a level often found in agricultural areas as a result of using crop fertilizers - is enough to kill some species of amphibians.

Nitrates and nitrites can come from rural or urban sources, not only from farming but also from use in home gardening, yard care and golf courses as well.

Fertilizing our lawns and gardens can accidentally lead to the contamination of surface waters - ponds, puddles, creeks, marshes, lakes and rivers - with additional nitrogen-based compounds.

As home gardeners we can help eliminate risk of exposure of amphibians to nitrogen-based compounds by being extra careful when using yard and garden fertilizers that include high concentrations of nitrogen-based compounds. To minimize the chance of excess nutrients from getting into surface waters,
Gail Glick Andrews, coordinator of the OSU Extension Well Water Program, suggests taking the following simple steps:

• Be careful when you are spreading fertilizers that they go only where they are needed. Sweep up dry fertilizer on a sidewalk or driveway before the rains carry it into the storm drain and into the local creek.

• Don't over-water after applying fertilizer. Too much water too quickly will promote runoff from your property, carrying your fresh fertilizer with it. Applying excessive amounts of water that does not run off will carry the nitrate to the groundwater before your plants can use it. This groundwater can eventually seep into surface water.

• Don't add fertilizers that your landscape does not need. Leave lawn clippings on the lawn, rather than removing them, thereby returning nutrients to the lawn without the need for as much fertilizer. Mow regularly to avoid too many clippings at once.

• If you have plants that look unhealthy, make sure lack of nitrogen is the problem before you add fertilizer. Nitrogen deficiency shows up in plants as leaves yellowing from the tips towards the stem, plants yellowing from the ground up, and stunted growth. Nitrogen fertilizer will not cure other problems.

• Often in western Oregon soils, the soil is too acidic for nitrogen to be taken up effectively. Check the soil's pH and use dolomite lime to increase the pH if needed, before adding fertilizer.

• Do not store any chemicals in areas that can get wet.

• Keep fresh animal manure covered if not in use. Store manure as far away from your wellhead as possible.

• Conserve water. The less excess flow, the less chance for leaching contaminants into any water. Use low flow devices such as drip irrigation and soaker hoses. Let your lawn go brown in the summer.

Scientists estimate that the rate of plant and animal extinction is greater now than any known in the last 100,000 years, the researchers note in their report. Amphibians are of particular interest because their physiology and complex life cycle often exposes them to a wider range of environmental changes than other species must face - they have permeable skin, live on both land and water and their eggs have no shells.

Author: Carol Savonen
Source: Andrew Blaustein, Gail Andrews