2002 Natural Resources Management

Home

The emergent population is dominated by cattails, though some small pockets of arrowhead and bulrush were noted near the fishing pier. Large water level fluctuations appear to have played a major role in limiting the development of a diverse native emergent community. This is not unexpected, since Bennett Lake has served an important stormwater management function for over 750 acres of the City. It is unclear how the aquatic vegetation community has changed over time. Clearly, historically high nutrient loadings and water level fluctuations have created a very resistant aquatic vegetation community dominated by a few aggressive species. Sediment Assessment Samples of lake sediment were also taken to attempt to gain a preliminary indication of the degree of enrichment of the sediments within Bennett Lake. As mentioned earlier in this report, the degree of lake sediment enrichment can be important, especially in shallow lakes, because the condition of the lake can be affected both by the phosphorus carried via runoff into the lake from the watershed as well as by the phosphorus released by the sediments within the lake. Lakes that have received large loadings of phosphorus over a long period of time tend to have much more enriched sediments than those that have not. Sediment samples were taken at the locations shown in Figure 5.2. The maximum depth of sediment sampling was approximately 5 feet because of limitations of the sampling equipment. Approximately the top 2 inches of sediment were sampled, since this is roughly the profile identified as contributing the bulk of recyclable phosphorus in many lakes. Somewhat surprisingly, the sediments sampled generated results that suggested the potential in -lake pool of mobile phosphorus is relatively small, equal to about 25% of the estimated loads contributed by the watershed. There are two likely reasons for this. First, the estimated watershed load is high because of the large amount of developed land discharging stormwater to the lake. Second, the deeper sediments in the lake are usually the most enriched but were not sampled effectively because of equipment limitations. City of Roseville 52 Parks Natural Resource Management