Forecasting agriculturally driven global environmental change.

During the next 50 years, which is likely to be the final period of rapid agricultural expansion, demand for food by a wealthier and 50% larger global population will be a major driver of global environmental change. Should past dependences of the global environmental impacts of agriculture on human population and consumption continue, 10(9) hectares of natural ecosystems would be converted to agriculture by 2050. This would be accompanied by 2.4- to 2.7-fold increases in nitrogen- and phosphorus-driven eutrophication of terrestrial, freshwater, and near-shore marine ecosystems, and comparable increases in pesticide use. This eutrophication and habitat destruction would cause unprecedented ecosystem simplification, loss of ecosystem services, and species extinctions. Significant scientific advances and regulatory, technological, and policy changes are needed to control the environmental impacts of agricultural expansion.

Volatilization of toxaphene from Lakes Michigan and Superior.

The pesticide toxaphene was used extensively on cotton in the southern United States until its use was restricted in 1982. It was previously reported that the upper Great Lakes have received toxaphene by gas absorption following long-range transport from the south and are currently saturated with respect to toxaphene. However, the rate of loss of toxaphene from Lakes Michigan and Superior had been estimated using sparse or estimated data, and thus, these estimates had high uncertainties. For this investigation, samples were collected to provide extensive data on air, water, and sediment concentrations of toxaphene for the upper Great Lakes for the period 1997-98. These data were used to calculate the annual and seasonal fluxes of toxaphene from water to air and sediment. Lake Superior is 200-1000% saturated with toxaphene, and Lake Michigan is 200-500% saturated. It seems clear that both lakes will outgas toxaphene into the atmosphere for some considerable time in the future, and Lake Superior, because of its generally lower water temperatures and higher toxaphene concentration, will outgas toxaphene even longer than will Lake Michigan.

Toxaphene in the Great Lakes.

This paper presents the most current data for toxaphene in the water, sediments, and biota of the Laurentian Great Lakes of North America. Concentrations in water range from 1.1 ng/L in Lake Superior to 0.17 ng/L in Lake Ontario. Lake Superior has the highest water concentration, which is contrary to the pattern seen for other pollutants. The observed log particle-water partition coefficient was 4.5. Recent sediments had similar concentrations among the lakes (approx. 15 ng/g dry weight), but different homolog compositions. The log bioaccumulation factors (BAFs) normalized to lipid or organic carbon were 5.8, 6.5, 6.3, 6.7, 6.7, and 7.0 for phytoplankton, net zooplankton, Mysis, Bythotrephes, sculpin, and lake trout. These data clearly show that toxaphene biomagnifies in the foodweb.