Laserfiche WebLink
cattail and reed canary grass, both of which are aggressive invasive species not native to this <br />area. <br />Sediment Assessment <br />Samples of lake sediment were also taken to get a preliminary indication of the degree of <br />enrichment of the sediments within Langton Lake. The degree of lake sediment enrichment can <br />be important, especially in shallow lakes, because the condition of the lake can be affected both <br />by the phosphorus carried via runoff into the lake from the watershed as well as by the <br />phosphorus released by the sediments within the lake. Lakes that have received large loadings of <br />phosphorus over a long period of time tend to have much more enriched sediments than those <br />that have not. <br />Sediment samples were taken at the locations shown in Figure 5.1. Samples were taken only in <br />the open water portions of the middle and south cell. Approximately the top 2 inches of <br />sediment were sampled, since this is roughly the profile identified as contributing the bulk of <br />recyclable phosphorus in many lakes. Sampling results are summarized below: <br />• The sediments of the middle cell appear to be only moderately enriched, with a mobile <br />phosphorus mass in the upper 2 inches of the sediment profile equal to about 2/3 the <br />average annual loading estimated for the watershed. <br />*The sediments in the south cell appear to be highly enriched, especially in the southern <br />section of the south cell. The estimated mass of phosphorus in the top 2 inches of <br />lake sediment is over 3 times the calculated average annual loading contributed by <br />runoff from the watershed to this cell. <br />Based on this information, any significant improvement in lake water quality will likely require <br />that sediment phosphorus in the southern portion of the southern cell be dealt with, either <br />through removal of the sediment or application of a chemical precipitant such as alum to <br />inactivate the phosphorus. It should be noted however, that significant improvements in water <br />clarity in the shallow lake system may increase the density of submergent as well as emergent <br />plant communities in the open water areas of the lake. <br />City of Roseville 45 <br />Parks Natural Resource Management <br />