Assessment of cumulative impacts on wetlands can benefit by recognizing three fundamental wetland categories: basin, riverine, and fringe. The geomorphological settings of these categories have relevance for water quality. Biogeochemical influences tend to be local rather than having a measurable affect on the larger body of water. Consequently, the function of these wetlands for critical habitat may warrant a category for protection from high nutrient levels and toxins, rather than expecting them to assume an assimilatory role. The relative proportion of these wetland types within a watershed and their status relative to past impacts can be used to develop strategies for wetland protection. Past impacts on wetlands, however, are not likely to be clearly revealed in water quality records from monitoring studies, either because records are too short or because too many variables other than wetland impacts affect water quality. It is suggested that hydrologic records be used to reconstruct historical hydroperiods in wetlands for comparison with current, altered conditions. Changes in hydroperiod imply changes in wetland function, especially for biogeochemical processes in sediments. Hydroperiod is potentially a more sensitive index of wetland function than surface areas obtained from aerial photographs. Finally, the depositional environment of wetlands is a landscape characteristic that has not been carefully evaluated nor fully appreciated. Impacts that reverse depositional tendencies also may accelerate rates of change, causing wetlands to be large net exporters rather than modest net importers. Increases in rates as well as direction can cause stocks of materials accumulated over centuries in wetland sediments to be lost within decades, resulting in nutrient loading to downstream aquatic ecosystems. (Copyright (c) 1988 Springer-Verlag New York Inc.)