Remote sensing of Great Lakes water quality: Case studies of Saginaw Bay, Lake Huron and western Lake Erie.

摘要

Zebra mussels (Dreissena polymorpha) have initiated ecosystem-level water quality changes in the Great Lakes. Increased water clarity, as well as decreased chlorophyll abundances, have fundamentally altered the optical characteristics of shallow coastal basins and bays. The occurrence of major blooms of blue-green algae (predominantly Microcystis) in western Lake Erie and Saginaw Bay have also affected water clarity. Whereas in situ water quality studies rely on point data from shipboard sampling, laboratory experiments and enclosures, the scale and magnitude of Dreissena and Microcystis effects on surface water quality suggest an additional research application that involves satellite remote sensing. My thesis is that remote sensing technology will facilitate timely and cost-effective analyses of Dreissena and Microcystis effects on water quality.; Advanced Very High Resolution Radiometer (AVHRR) images estimate sea surface temperatures and reflectances in Saginaw Bay and western Lake Erie. The thermal bands document surface water mass movements over zebra mussel beds, whereas red and near-infrared channels estimate total suspended solids and Secchi disk depth. The thermal study traces thermal bar formation and movement offshore and the seasonal development of the warm coastal nearshore zone (Chapter 2). AVHRR reflectance imagery of Saginaw Bay from 1987 to 1993 documents the historical impact of Dreissena filtering on water quality variables (Chapter 3). A mixed general linear model describes seasonal and interannual changes in water quality before and after zebra mussels were established in Saginaw Bay. Imagery of extensive surface blooms of the toxic blue-green algae Microcystis in western Lake Erie illustrates AVHRR's ability to resolve spatial patterns (Chapter 4). Mean reflectances in the Maumee Bay region doubled from 2.0 percent in early August to 4.5 percent during mid-September, when the bloom was at its peak. Estimates of bloom spatial extent ranged from 250 to 1000 km{dollar}sp2{dollar}.; Satellite image analysis complements shipboard sampling efforts by providing frequent overflights and synoptic coverage of surface waters. Furthermore, satellite archives facilitate retrospective analyses during periods when in situ water quality data are not available. The vast opportunities for detailed spatial analyses of surface water variables enable cost-effective, long-term evaluation of zebra mussel and Microcystis effects in the Great Lakes.