Numerous freshwater ecosystems, dense concentrations of humans along the eastern seaboard, extensive forests and a history of intensive land use distinguish the New England/Mid-Atlantic Region. Human population densities are forecast to increase in portions of the region at the same time that climate is expected to be changing. Consequently, the eects of humans and climatic change are likely to aect freshwater ecosystems within the region interactively. The general climate, at present, is humid continental, and the region receives abundant precipitation. Climatic projections for a 2 Â CO 2 atmosphere, however, suggest warmer and drier conditions for much of this region. Annual temperature increases ranging from 3±58C are projected, with the greatest increases occurring in autumn or winter. According to a water balance model, the projected increase in temperature will result in greater rates of evaporation and evapotranspiration. This could cause a 21 and 31% reduction in annual stream ¯ow in the southern and northern sections of the region, respectively, with greatest reductions occurring in autumn and winter. The amount and duration of snow cover is also projected to decrease across the region, and summer convective thunderstorms are likely to decrease in frequency but increase in intensity.
The dual eects of climate change and direct anthropogenic stress will most likely alter hydrological and biogeochemical processes, and, hence, the ¯oral and faunal communities of the region's freshwater ecosystems. For example, the projected increase in evapotranspiration and evaporation could eliminate most bog ecosystems, and increases in water temperature may increase bioaccumulation, and possibly biomagni®cation, of organic and inorganic contaminants. Not all change may be adverse. For example, a decrease in runo may reduce the intensity of ongoing estuarine eutrophication, and acidi®cation of aquatic habitats during the spring snowmelt period may be ameliorated.
Recommendations for future monitoring eorts include: (1) extending and improving data on the distribution, abundance and eect of anthropogenic stressors (non-point pollution) within the region; and (2) improving scienti®c knowledge regarding the contemporary distribution and abundance of aquatic species. Research recommendations include: (1) establishing a research centre(s) where ®eld studies designed to understand interactions between freshwater ecosystems and climate change can be conducted; (2) projecting the future distribution, activities and direct eects of humans within the region; (3) developing mathematical analyses, experimental designs and aquatic indicators that distinguish between climatic and anthropogenic eects on aquatic systems; (4) developing and re®ning projections of climate variability such that the magnitude, frequency and seasonal timing of extreme events can be forecast; and (5) describing quantitatively the ¯ux of materials (sediments, nutrients, metals) from watersheds characterized by a mosaic of land uses.