Historical aerial photographs and a geographic information system (GIS) to determine effects of long-term water level fluctuations on wetlands along the St. Marys River, Michigan, USA

Abstract

The water levels of the Great Lakes fluctuate as much as ± 1 m from their respective long-range mean elevations in response to changes in climatic conditions. Coastal wetland areas on each Great Lake expand or contract in response to the long-term water level fluctuations. The water level of the St. Marys River, a connecting channel between Lakes Superior and Huron, is largely controlled by the level of Lake Huron. The St. Marys River wetlands expand and contract in a fashion similar to wetlands on the lakes. Data on St. Marys River wetland areas were derived from historical aerial photographs and placed in a Geographic Information System (GIS) to analyze the effects of water level fluctuations. The GIS was used to measure wetland area changes between the years for which photographic data were available. Use of GIS allowed quantification of wetland area changes, estimation of response rates and description of inter-class transfer dynamics, for five coastal wetland classes influenced by long-term water level fluctuations.