Michael L. Pace
Institute of Ecosystem Studies

One of the strong impacts of terrestrial environments on aquatic ecosystems is the transfer of dissolved organic matter from land to water. This material arises from the degradation of plants in soils and litter. Some of the material eventually dissolves in solution and flows to streams and lakes. Water rich in terrestrial-derived dissolved organic carbon (DOC) has a brown color and is readily visible in "stained" lakes. About 50% of the lakes in the Adirondacks have DOC > 5 mg/L and correspondingly are colored brown. DOC has significant effects on light penetration in lakes, particularly harmful ultraviolet light. DOC also is implicated in the transformation of mercury into a toxic form that concentrates as it moves through lake food chains.

Variation in DOC among lakes is the result of vegetation cover within the watershed, hydrology, the presence or absence of wetlands, and within-lake processes. We developed models to predict the variation in lake DOC concentrations, using data from over 600 lakes and associated watersheds in the Adirondack Park of New York. Our analyses make use of detailed geographic information system (GIS) data for land cover as illustrated by the map below of several Adirondack watersheds. Best models currently explain over half of the observed variation in lake DOC. Wetlands contribute the most DOC to lakes per unit area, but upland forests are also important sources because forests dominate overall land coverage. Current efforts are extending initial models to investigate riparian areas as sources or modifiers of DOC loading to lakes. Our approach can be readily incorporated within a GIS framework allowing evaluation of scenarios related to losses of wetlands, alterations in forest management, or increases in conserved areas.