Laserfiche WebLink
* The ernergent populaiion is dorninated by ca�aijs, though some small pockets of <br />arrowhead and huln.�sh were noted ncar the fishing pier. <br />• Largc tivater level fluctuations appear to have played a major role in limitin� the <br />development of a diverse native emergent community. This is not unexpected, since <br />Bennett Lake has served an important stormwater management function for over 75� <br />acres of the City. <br />It is unclear how the aquatic vegetation community has changed over time. Clcarly, historically <br />high nutrient loadin�s and water level �7uctuations have created a very resistant aquatic <br />vegetation community dominated by a few aggressive species. <br />Sediment Assessment <br />Samples of lake sediment were also taken to attempt to gain a preliminary indication of the <br />degree of enrict�ment of the sediments within Bennett Lake. As mentioned earlier in this report, <br />the degzee of lake sediment enrichxnent can be important, especially in shailow Iakes, because <br />the condition of the lake can be affected both by the phosphorus cazxied via runaff into the lake <br />from the watershed as well as by thc phosphorus released by the sediments within the lake. <br />Lakes that have received large loadings of phosphorus over a long period of time tend to have <br />much more enriched sediments ti�an those that have not_. <br />Sediment samples wcre taken at the locations shown in Figure 5.2. The maximum depth of <br />sediment samplin� was approximately 5 feet because of limitations of Che sam.pling equipment. <br />Approximately the top 2 znches of sedirnent were sampled, since this is roughly the profile <br />identified as contributing Ehe bulk of recyclable phosphorus in many lakes. Somewhat <br />surprisinQly, the sediments sampled generated results that suggested the potentia� in-lake pool of <br />mobile phosphorus is relatively small, equal to about 25°Io of the estimated loads contributed hy <br />the watershed. There arc two likely reasons for this. First, the estimated watershed load is high <br />because of the larje amount of cfeveloped land discharging stormwater to the lake. Second, the <br />dceper sediments in the lake are usually the most enriched but were not sampled effectively <br />because of eyuipment limitations. <br />Crty nf Roseville 50 <br />Parks Natrrral Kesource Managenrent <br />