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Wetlands; Water quality; Glacial lakes


We investigated the influence of vegetated wetlands on water quality of two eastern South Dakota glacial prairie lakes. Surface water from a 5,880 ha pastured basin drains into a 90 ha upstream Typha wetland and enters Lake Enemy Swim passing 400 m through Typha-Scirpus littoral wetland. A second 1,290 ha basin characterized by row crops and pasture drains into a 260 ha open water slough entering L. Enemy Swim adjacent to Typha-Scirpus littoral wetland. Water enters Lake Cochrane from two smaller drainage basins. Water from a 180 ha basin consisting of a pasture and wet meadow enters the lake after passing about 100 m through Typha-Scirpus littoral wetland. A second basin consisting of 120 ha of mixed row crops, pasture and wetlands drains into an open water sediment retention pond and enters L. Cochrane after passing 50 m through Typha-Scirpus littoral wetland.

At each lake, we measured water quality parameters in upstream drainages, in littoral wetlands, and at midlake sites in 1992 and 1993. In both lakes all forms of N were lesser and Fe were greater in concentration than all other sites in the drainages from upstream vegetated areas. Both N and P concentrations were greatest in the drainages from upstream open water areas resulting in small Si:P and Si:N ratios, and large N:Fe ratios. Concentrations of N and P decreased and Si:P and Si:N ratios increased passing through vegetated littoral wetlands, thus decreasing the likelihood of triggering phytoplankton shifts from desirable diatoms to undesirable bluegreen algal blooms.

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