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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 sedirt�ent enrichment can <br />be important, especially in shallow lakes, because the condition of the lake can be affected both <br />by the phospharus carricd 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 tirne 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. Sarnples were taken only in <br />the open water portions of the zniddle and south cell. Approximately the top 2 inches of <br />sediment were sampled, since this is roughly the profile identified as contzibuting 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 znoderately enriched, with a <br />mobile phosphorus mass in the upper 2 inches of the sediment profile equal to about <br />2/3 the avera�e annual loading �stimated for the watershed. <br />� The sediments in the south ceil appear to be highly enriehed, especially in the <br />southern section of the south cell. The estimated mass of phosphorus in the top 2 <br />inches of Iake sediznent is over 3 times the calculated average annual loadin� <br />contributed by runoff from the watershed to this cell. <br />Bascd 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 si�nificant iznproveznents in water <br />clarity in the shallow lake system may increase the density of submergent as well as emer�ent <br />plant cor�nmunitics in the open water areas of the lake. <br />City of Roseville `�� <br />Parks Natt�ral Resotarce Managenae�zt <br />