Cleaning up sediment in some Maryland waterways could also benefit the state's soils. Under a new trust agreement with the Maryland Port Authority, ARS will find new ways to recycle the 5 million cubic yards of dredge spoils removed each year from the port of Baltimore and its estuarine tributaries. ARS scientists are considering poultry litter as a potential additional ingredient to turn the spoils into a soil substitute. Dredge spoils have a head start on becoming a soil substitute, because they originated as soil eroded from land and deposited on lake, ocean, bay and river bottoms. But the spoils have a low organic matter content. Adding poultry litter would remedy this, and the supply is plentiful: Each year, Maryland produces an estimated 339,000 tons of poultry litter. The spoils have two other problems: salt and acidity (low pH). The dredge spoils pick up salt in estuarine environments around the Chesapeake Bay. To counteract this salinity, scientists will search for ways to leach out the salts so the spoils can be applied to land. The spoils also become highly acid when they're removed from the water and exposed to air. To reduce the acidity, the researchers will test adding calcium-containing ash and gypsum byproducts from electric power plants. The University of Maryland's Wye Institute will field-test recommendations expected to emerge from the spoil-to-soil experiments in the next two or three years. If successful, the methods could be applied to sediment dredged from ports anywhere, including fresh and saltwater ports.
Soil Microbial Systems Laboratory, Beltsville, MD
Lawrence J. Sikora, (301) 504-9384, lsikora@asrr.arsusda.gov

Constructing artificial wetlands in streams can improve water quality by removing nitrogen that otherwise would continue downstream. As a test, scientists with ARS and North Carolina State University, Raleigh, built an in-stream wetland 600 yards long and 60 yards wide. The scientists stabilized the wall of a beaver dam along the stream to create the wetland. The water was 6 feet deep at the wetland's lower end, but much of it was less than 2 feet deep. About 40 percent of the 8-acre wetland was covered by aquatic weeds; another 40 percent was mainly trees. The wetland's area was less than 1 percent that of the watershed that drained through it. Yet it lowered the amount of nitrate-N in the stream by about 40 percent. The reduction was highest in warm months, when wetland inflow water was high in nitrate-N level (about 7 parts per million) but outflow was less than 1 part per million. The nitrate was likely being taken up by the plants (trees and weeds) or denitrified—changed to gaseous nitrogen by beneficial bacteria that thrive under low oxygen conditions. Dissolved oxygen in wetland water was generally less than 50 percent saturation with little or no oxygen in sediment. The project in the Herrings Marsh Run watershed in Duplin County, NC, was part of a USDA Water Quality Demonstration Project in the Coastal Plain of North Carolina.
Coastal Plains Soil, Water and Plant Research Center, Florence, SC
Patrick G. Hunt, (803) 669-5203, hunt@florence.ars.usda.gov

During the summers of 1996 and 1997, ARS scientists assisted in a study that matched frog breeding calls in farm ponds and wetlands on Maryland's Eastern Shore with the timing of pesticide applications on adjacent crop fields. The multi-agency study, funded by USDA's Natural Resources Conservation Service, is part of an investigation into the potential role of pesticides in amphibian decline in Maryland and elsewhere. An NRCS biologist identified the species by recording the males' nighttime mating songs and seining the ponds for tadpoles, while the ARS scientists sampled the pond water for 20 major pesticides. Out of the 7 to 10 species found in ponds, the breeding period of tiny green tree frogs, southern leopard frogs and green frogs best coincided with routine pesticide applications. This puts their tadpoles at the greatest risk of toxic effects from spray drift or surface water runoff. To verify the field findings, the scientists have applied the commercial pesticides Bicep and Lorsban at common application rates to 21 lab aquaria with green tadpoles living in them, at the Patuxent Wildlife Research Center, U.S. Department of the Interior, Laurel, MD. They also applied the pesticides to 12 outdoor experimental ponds at the Patuxent center. Green tree frogs, green frogs and southern leopard frogs live in these ponds. The scientists chose Bicep, a herbicide, because its active ingredients are atrazine and metolachlor, two herbicides commonly applied on farms and detected in the farm ponds and wetlands. Lorsban was chosen because it contains chloropyrifos, a commonly applied insecticide. Preliminary results reveal that combined application of the herbicide followed by the insecticide, at typical farm application levels, can cause impaired development, delayed metamorphosis and up to 100-percent mortality of wild tadpoles.
Environmental Chemistry Laboratory, Beltsville, MD
Clifford P. Rice, (301) 504-6398,crice@asrr.arsusda.gov

A new tool for decontaminating soil could come from a genetically engineered "cousin" of natural Rhizobium bacteria discovered on alfalfa plant roots by ARS scientists. The altered Rhizobium species, R. meliloti, secretes enzymes that break down environmental contaminants called hydrocarbons. Some of these, like toluene and benzene, are commonly found in fuel, solvents and other products. But such hydrocarbons become hazardous waste once they enter the environment. Engineering R. meliloti for toxic clean-up duty is the work of scientists at ARS; Howard University, Washington, D.C.; the University of Maryland-Eastern Shore; the National Institutes of Health; and the U.S. Army Corps of Engineers. The Corps is funding the work in search of new, environmentally friendly methods of restoring contaminated soil at military bases and elsewhere. Conventional techniques, like excavating soil, are costly and often impractical. In greenhouse studies using alfalfa, the altered bacteria partially degraded a salt-form of toluene called meta-toluate at concentrations of 136 parts per million, a fairly toxic level. Unlike a human clean-up crew, the microbes need not fear the potential for respiratory and neurological harm from toluene exposure. Scientists also are testing the bacteria's ability to degrade dinitrotuluene, or DNT. Used to make plastic, DNT poses an environmental hazard since it doesn't readily decompose.
Molecular Plant Pathology Laboratory, Beltsville, MD
David Kuykendall, (301) 504-5736, dkuykend@asrr.arsusda.gov

Last Updated: November 13, 1998
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