Forty Years of Change in the Bulrush Marshes of the St. Lawrence Estuary and The Impact of the Greater Snow Goose
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During its spring and fall migrations, the Greater Snow Goose (Chen caerulescens atlanticus) stages in the marshes along the St. Lawrence Estuary in southern Quebec, where it feeds on three-square bulrush (Schoenoplectus americanus) rhizomes. The goose population has grown from 70 000 birds to around one million over the last 40 years, thus increasing pressure on these tidal marshes. To determine the impact of geese on the ecological integrity of the marshes over this period, we used IKONOS satellite imagery and aerial photographs to classify vegetation types. We estimated changes in bulrush cover using the eCognition image analysis software (Trimble). We examined the spectral, textural, and contextual characteristics of the identified classes. The proportion of bulrush cover has declined significantly in the lower marsh since around 1980, and bulrush has been gradually replaced by wild rice (Zizania aquatica var. brevis). We also documented the erosion between the lower and upper marshes along most of the shoreline.
KeywordsRemote sensing Bulrush Marsh Greater Snow Goose Object-based classification Erosion
This study is part of a larger project funded by the Arctic Goose Joint Venture. The IKONOS images used in this study were kindly provided by Guy Létourneau of the St. Lawrence Centre of Environment Canada in Montréal. Thanks also to Léo Provencher of the Department of Applied Geomatics at the Université de Sherbrooke for his most useful advice over the course of this project.
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