Monitoring long time trends in lake CDOM using Landsat image archive

Lakes play a substantial role both as regulators and integrators of present, past and future climate change. A critical parameter to study the role of lakes in global carbon cycle is dissolved organic carbon, DOC, and its colored component CDOM (Colored Dissolved Organic Matter). CDOM data series exist for a very limited number of lakes. For example Swedish lakes monitoring database includes CDOM data for selected lakes since sixties. However, for most lakes in the world the only potential source of information about theirs CDOM content is satellite data. Landsat series satellite's data has been collected from seventies. In the present study we assess suitability of Landsat data for lake CDOM mapping. Our results indicate that radiometric resolution of Landsat sensor limits it's use in mapping lake CDOM concentration. We observed increase in CDOM in water samples collected over last 45 years in some basins of Lake Mälaren and in a few smaller lakes although the trends were less noticeable since 1984 when we have Landsat data available. Landsat data from these measuring stations did not show significant trend.