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 × 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 ∼70% 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.