摘要：Studies were conducted to characterize the hydrogeology of a dune watershed and examine the impact of a dam on plant community dynamics. Hydrostratigraphic units of the watershed, the Old Ausable River Channel (OARC) watershed, consisted of a basal unit of grey clayey-silt till, overlain in succession by three layers of sediments—lacustrine sand, shoreface sediments of sand and gravel, and aeolian dune sand. The thickness of aquifer sediments ranged from 1 m to about 25 m. The total area of the watershed is only a few hundred hectares that contribute water to the OARC through baseflow. The dam has essentially separated the channel into two distinct ecological units (north and south). To its north Chara vulgaris was the dominant species because of very low turbidity and elevated calcium and magnesium carbonates and bicarbonates in channel water. Other major associates in the community were Myriophyllum verticillatum. Wolffia spp. and Lemna minor. To the south of the dam two other aquatic plant communities, M. spicatum—Elodea canadensis and Vallisneria americana—Potamogeton pulcher, dominanted primarily because of higher turbidity and backflow of nutrient rich water from an adjoining river channel in the spring. The OARC is displaying many symptoms of eutrophication, and some of the plant species that indicate high nutrient content have already started to invade the northern parts of the channel.
