A historical analysis of the changes in connectivity and plant cover in Netley-Libau Marsh, Manitoba, Canada: Distinguishing the effects of Lake Winnipeg and Red River hydrology on coastal marsh emergent macrophyte areal extent
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Date
2019-03-30
Authors
Kowal, Paige
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Abstract
Netley-Libau Marsh in Manitoba, Canada is a 26 000 hectare coastal, freshwater marsh located at the mouth of the Red River on the south shore of Lake Winnipeg. Shoreline erosion and loss of emergent vegetation since 1929 has resulted in large expanses of open water and an overall degradation to the marsh ecosystem. Six coastal marshes of similar size and all connected to the south basin of Lake Winnipeg were selected for comparison to determine if marsh vegetation loss is widespread in Lake Winnipeg coastal marshes or limited to Netley-Libau Marsh. As a measure of degradation, open water area measurements of the study marshes were digitized from aerial and satellite images taken between the years of 1929 and 2015. Distinguishing the effects of Red River discharge into the west side of Netley-Libau Marsh from that of Lake Winnipeg regulation was confounded by the finding that direct river connection to the marsh was not firmly established until approximately 1970, just six years prior to the commencement of lake regulation. Red River discharges upstream of Netley-Libau Marsh did not significantly account for variation in open water areal extent within the two Netley-Libau Marsh study areas, nor did modelled Netley Cut discharges. Between 56-95% of the variation in open water areal extent within the six study marshes was explained by two growing seasons of average May-October Lake Winnipeg water levels. Variation in open water areal extent was not comparable in all six study marshes and the frequency and duration of low-water periods decreased after 1976. My findings show that the loss of habitat complexity and emergent vegetation in Lake Winnipeg coastal wetlands has been ongoing since the early 20th century and is attributed most heavily to the decrease in low-water periods in Lake Winnipeg levels. The greatest loss of open water area within Netley-Libau Marsh occurred in years when average Lake Winnipeg water surface elevation decreased to 217 metres above sea level during typical ice-free months (May-October). These findings highlight the importance of periodic lowering of Lake Winnipeg water levels in promoting coastal marsh vegetation growth and future habitat restoration efforts.
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Keywords
Emergent, Macrophyte, Hydrology, GIS, Netley-Libau
Citation
APA