Spatial and temporal patterns in the hydrology, water chemistry and algal nutrient status of Delta Marsh, as influenced by the hydrology of adjoining Lake Manitoba.
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Between 2002 and 2005, I examined spatial and temporal patterns in the hydrology, water chemistry, and algal nutrient-limitation status (N and/or P) in Delta Marsh, a 18,500-ha coastal lacustrine freshwater marsh on the south shore of Lake Manitoba, to determine the influence of surface water exchange with Lake Manitoba on these properties. Daily and annual marsh water level changes were found to be highly correlated with those of the lake, during some of the highest and lowest long-term water levels in recorded history. The average magnitude of water level changes in the marsh ranged from to a few centimeters to half a meter, which is significant in shallow coastal wetlands systems like Delta Marsh where the average depths are ≤ 1 m. In general, marsh sites located closest to the lake were influenced to the greatest degree by the flushing and dilution effect of the lake. Spatially, in connected sections of the marsh concentrations of dissolved inorganic and total N (DIN-N and TN), total reactive and total phosphorus (TRP-P and TP), dissolved organic carbon (DOC), chloride (Cl-), sulfate (SO4-), alkalinity and conductivity decreased with decreasing distance to Lake Manitoba. Regardless of east and west location and the distance of connected marsh sites from Lake Manitoba, annual variation in water level was the most significant predictor of differences in several water chemistry characteristics between sample sites including DIN-N, TN, TRP-P, TP, alkalinity, DOC, Cl-, SO4-, and conductivity. Annually, concentrations of DIN-N, TN, alkalinity, DOC, Cl-, SO4- and conductivity were negatively correlated with increasing water depth, and the spatial variation in the concentration of these water chemistry parameters also decreased with increasing water level. Results of nutrient diffusing substrata bioassay experiments indicated that periphyton biomass in the marsh was predominately limited by N. The predominance of N limitation in Delta Marsh was found to be significantly negatively correlated with water column N concentrations, but not correlated with P concentrations. Collectively, this study illustrates the important role of lake connection and hydrological influence on the structure and function of adjoining coastal freshwater wetlands.