Cooperative Fish and Wildlife Research Units Program: Maine
Education, Research and Technical Assistance for Managing Our Natural Resources

Maine’s abundant lakes are important to the state’s economy and the quality of living enjoyed by the state’s permanent and seasonal residents. Maintaining quality of this resource is a priority of the state natural resource management agencies as well as of interest to the public using the lakes. Monitoring lake water quality can be accomplished with an in situ sampling program, however, only a small percentage of the state’s lakes are monitored annually owing in part to their remoteness. In addition, temporal and spatial variations in lake condition can affect how representative a collected sample is of the true lake condition. Sensors mounted on a satellite platform enable frequent remote collection of data to assess environmental conditions over a large area. A variety of remote sensors have been used for many years to monitor a variety of lake attributes, including lake water clarity, trophic status, and change in these conditions with watershed land use change across a range of landscapes, lake sizes, and lake trophic conditions. There are caveats for using these remotely acquired data as indicators of lake water quality condition; for example, relationships established in one area between lake water clarity measured with Secchi disk depth and sensor reflectance recorded on a particular type and temporal series of satellite imagery cannot be assumed to apply in another area without calibration in the area of interest across the range of measured Secchi depth and reflectance data. Once relationships between Secchi disk and satellite imagery data are calibrated however, archived data enable a spatially comprehensive assessment of recent lake conditions as well as an opportunity for retrospective analysis of lake condition that can be compared to current as well as changing land conditions in the lake watershed. We will compile and compare a comprehensive data set of satellite imagery and available Secchi depth and chlorophyll a data collected in Maine’s lakes to establish relationships between the remotely and locally collected data and identify limitations of the remote sensing data for monitoring lake water clarity and trophic condition. We also will conduct a retrospective assessment of Maine’s lake water clarity with archived Secchi depth and chlorophyll a data and satellite imagery to identify trends in lake water clarity. Our objectives are: 1) Determine if Landsat data can reliably duplicate late water clarity assessment with Secchi Depth and chlorophyll a data collected at selected lakes. 2) Determine temporal frequency (when, how often) and spatial limitations (resolution, location) of image collection for lake water clarity monitoring to complement field data collection programs. 3) Retrospective analysis of Maine’s lake water clarity based on archived remote sensing data.