A spatially explicit watershed-scale analysis of dissolved organic carbon in Adirondack lakes

Terrestrial ecosystems contribute significant amounts of dissolved organic carbon (DOC) to aquatic ecosystems. Temperate lakes vary in DOC concentration as a result of variation in the spatial configuration and composition of vegetation within the watershed, hydrology, and within-lake processes. We have developed and parameterized a spatially explicit model of lake DOC concentrations, using data from 428 watersheds in the Adirondack Park of New York. Our analysis estimates watershed loading to each lake as a function of the cover type of each 10 x 10 m grid cell within the watershed, and its flow-path distance to the lake. The estimated export rates for the three main forest cover types were 37.7-47.0 kg C.ha(-1).yr(-1). The four main wetland cover types had much higher rates of export per unit area (188.4-227.0 kg C.ha(-1).yr(-1)), but wetlands occupied only 11%, on average, of watershed area. As a result, upland forests were the source of similar to70% of DOC loading. There was evidence of significant interannual variation in DOC loading, correlated with interannual variation in precipitation. Estimated net in situ DOC production within the lakes was extremely low (<1 kg C.ha(-1).yr(-1)). Many of the lakes have large watersheds relative to lake volume and have correspondingly high flushing rates. As a result, losses due to lake discharge generally had a larger effect on lake DOC concentrations than in-lake decay. Our approach can be readily incorporated within a GIS framework and allows examination of scenarios such as loss of wetlands, alterations in forest management, or increases in conserved areas, as a function of the unique configuration of individual watersheds.