Chromophoric dissolved organic matter (CDOM), the light absorbing fraction of DOM, is abundant in many natural waters and plays important roles in aquatic photochemistry, light penetration, metal mobilization, and water treatment processes. CDOM provides useful estimates of dissolved organic carbon (DOC) concentrations, reactivity and source, and its spatial distribution can be determined from remotely sensed reflectance data. Here, we present an analysis of DOM in &gt; 250 lakes across three Upper Midwest states. The lakes include a wide range of color (a440 = 0.5-22 m-1) and DOC (2.7-47 mg/L). A strong hyperbolic trend was found between CDOM and SUVA levels, indicating that low- and high-CDOM waters differ in chemical composition and sources; spectral slope trends support this conclusion. We assessed the influence of watershed characteristics, including land use, on patterns of CDOM and DOC quantity and quality. In general, CDOM and DOC correlate well in highly colored lakes influenced by forests and wetlands. Low-CDOM lakes in agricultural and urban watersheds show less robust relationships, likely because autochthonous production contributes more strongly to the DOM pool. The CDOM data were used to calibrate remote sensing models to map CDOM across the region using Landsat imagery. Despite the importance of CDOM to understand regional carbon cycling and ecological properties, few water management agencies have routinely measured CDOM. The Landsat archive represents an opportunity to extend CDOM data spatially and through time. Using Landsat imagery from the 1980s through present, we mapped CDOM levels in lakes of northern Minnesota to identify regional patterns and trends. The results represent a rare multi-decadal time series on organic matter in lakes across a wide spatial scale and enhance our ability to assess the impacts of human-driven change on lake ecosystems.

Cross-scale advances in CDOM biogeochemistry: From molecular to ecoregional perspectives

253rd National Meeting (2017)

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