Using satellite imagery to assess macrophyte response to water-level manipulations in the Saskatchewan River Delta, Manitoba

Published source details Baschuk M.S., Ervin M.D., Clark W.R., Armstrong L.M., Wrubleski D.A. & Goldsborough G.L. (2012) Using satellite imagery to assess macrophyte response to water-level manipulations in the Saskatchewan River Delta, Manitoba. Wetlands, 32, 1091-1102.
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This study is summarised as evidence for the following.

	Action	Category
	Lower water level to restore degraded freshwater marshes Action Link

Lower water level to restore degraded freshwater marshes

A replicated, controlled, before-and-after study in 2007–2010 of six freshwater marshes in Manitoba, Canada (Baschuk et al. 2012) found that a partial but long-term drawdown of the water level affected the area covered by some marsh vegetation classes. In marshes where the water level was drawn down, there was significant variation over time in the coverage of five vegetation classes. There was an initial decline followed by recovery in the area of vegetation dominated by sedges Carex spp. (before: 141 ha; after one year: 103 ha; after three years: 127 ha), cattails Typha spp. (111 ha; 69 ha; 98 ha) and horsetails Equisetum spp. (9 ha; 2 ha; 20 ha). Coverage of dead vegetation showed the opposite pattern (15 ha; 80 ha; 13 ha). Coverage of vegetation dominated by bur-reeds Sparganium spp. increased steadily over time (<1 ha; 2 ha; 7 ha). There was no significant change over time in the coverage of other vegetation classes, including trees (see original paper for data). In marshes that were not drawn down, the area of all vegetation classes was stable over time (see original paper for data). Methods: This study focused on six 84–207 ha marshes within one wetland complex. From August 2007, the water level was lowered in three marshes (average depth: 30 cm; maximum depth: 60 cm) using water control structures. This level was maintained over the entire study period. In the other three marshes, the water level remained unnaturally high (average: 67 cm; maximum: 100 cm). The coverage of vegetation types was measured from satellite images, taken in the summer before (2007) and for three years after (2008–2010) drawdown.

(Summarised by: Nigel Taylor)