Current velocity significantly affected the biomass and shoot density of aquatic macrophytes in two slow-flowing rivers in western Canada. Studies of aquatic macrophyte communities at three sites on the Bow River, Alberta, Canada, between 1982 and 1985 showed that biomass decreased with increasing current velocity within the weed bed over the range 0.01-1 m/s; at current speeds in excess of 1 m/s, aquatic macrophytes were rare. Transplant experiments in which Potamogeton pectinatus was grown in pails containing three sediments differing in texture at three sites with different current velocities also demonstrated that biomass and shoot density were affected by both the direct effects of current velocity on plant shoots and its indirect effects on sediment nutrient concentrations. These results indicate that current velocity is an important factor regulating aquatic macrophyte biomass in flowing waters and suggest that even a relatively modest increase in current velocity within weed beds reduces the abundance of submerged aquatic plants.

Transplant experiments conducted in the South Saskatchewan River, Saskatchewan, Canada showed that the aquatic macrophyte, Potamogeton crispus, obtained most of its nutrients through the roots. When plants were grown in buckets containing high (602 μg∙g−1 total phosphorus; 712 μg∙g−1 total organic nitrogen) or low (258 μg∙g−1 total phosphorus; 109 μg∙g−1 total organic nitrogen) nutrient sediments and exposed to high (75 μg∙L−1 soluble reactive phosphorus (SRP); 530 μg∙L−1 total dissolved nitrogen (TDN), or low (10 μg∙L−1 SRP; 323 μg∙L−1 TDN) nutrient concentrations in the open water, biomass, shoot density and tissue nutrient concentrations were largely determined by sediment type, rather than open water chemistry. These results indicate that the roots are an important site of nutrient uptake for aquatic macrophytes in flowing waters.

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Studies of nutrient loadings, to shallow culturally eutrophied Alberta lakes, suggest internal inputs are significant. In this regard, estimation of bottom sediment P loads to Lake Wabamun (80 km 2 , 5.5 m x depth) were examined. Initially we determined the spatial variability in Total Organic Content (% loss on ignition) and Total Phosphorus, as indicators. Phosphorus fractions and biologically available phosphorus (BAP) were measured at specific stations. These data showed a very uniform distribution in sediment type with a Total Organic Content of 40.6 ± 3.3 (95% C.L.) at the west end, gradually declining to 26.3 ± 0.9 at the east end. Transects performed at routine monitoring stations indicate the representativeness of each station, e.g., station 2, 40.8 ± 1.3 (10 sites). One explanation of this uniformity is provided from 2 10Pb analysis of shallow cores which indicate mixing to a depth of 16 cm. This is also thought to explain the mechanics of P loading to the water phase. Finally, Total Organic Content relates well to BAP (r 2 = 0.80). It is hoped that this simple technique may well permit more precise extrapolation to whole lake BAP estimates at least on this lake.