Most of the earthworms commonly found in the U.S. are non-native, originating in Europe and transported to and around the U.S. by human activities. Although viewed as beneficial in farm fields and gardens, these invasive earthworms are damaging deciduous forests. Earthworms feed on fallen leaves, and can remove an entire autumn's leaf fall in less than one year. Without a protective leaf layer, exposed forest soils are subject to erosion, seedling death, and nutrient loss. In soils invaded by earthworms, rainwater can rapidly transport mineral nutrients away from plant roots and into nearby streams or lakes. A spatial, mathematical model of the Kalamazoo River, MI, watershed will be used to study how earthworms in forests and farm fields increase the amount of nitrogen in river ecosystems.
Nitrogen pollution of terrestrial and aquatic ecosystems is of great current concern. Nitrogen transported from land to streams and lakes pollutes those water bodies and has been implicated in causing the "dead zone" in the Gulf of Mexico. Many strategies, such as vegetation buffer strips, are being used to remove nitrogen before it can pollute waterways, yet earthworms may be hindering the ability of plants to remove nitrogen. Invasive earthworms are continually being transported to new areas as fishing bait, in potted plants, and on truck tires. Once earthworms invade, they are nearly impossible to remove. A mathematical model of earthworm invasion will be used to highlight areas of the landscape that should be managed to slow the loss of nitrogen. This study will provide strategies needed by land managers to control earthworms and thereby protect forests and aquatic habitats.
