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eastern arm of the pond where the outlet is located. In essence, the pond is performing as it was designed; the majority of the incoming phosphorus is removed before being carried downstream to Rice Creek. The average total phosphorus concentration was lowest on June 24 (83-ug/L), but was relatively constant the -rest of the summer, varying between 95 and 101 ug/L) (Figure 5). Chlorophyll Chlorophyll is a convenient measure of the algal density (and hence primary productivity) in a lake. It is clear from the chlorophyll data that algal growth is controlled by the variation in phosphorus concentration described above. A scatter plot relating chlorophyll and total phosphorus shows a statistically significant relationship with a correlation coefficient (r) of 0.85 (P< 0.01; Figure 6). This relationship strongly suggests that phosphorus availability in Silver View Pond is limiting the growth of algae. As sediment -borne phosphorus settles out and is lost to the sediments, less algae can grow. As with phosphorus, chlorophyll concentrations declined as water moved through the pond toward the outlet at the east end. Chlorophyll concentration averaged 39 ug/L over the summer, and was fairly constant over time until the last sampling date when the three sites averaged 51 ug/L (Figure 7). Since phosphorus was did not appear to be higher on September 2 than on the earlier sampling dates, (although the anomalous phosphorus concentration of 935 ug/L occurred on that date), there may have been slightly more chlorophyll produced per unit phosphorus. Nitrogen In eutrophic systems such as Silver View Pond, nitrogen limitation of algal growth is common, because an excess of phosphorus allows algae to increase until the next most abundant nutrient becomes limiting; this nutrient is almost always nitrogen. In general, it is thought that systems with a total nitrogen -to -total phosphorus (TN/TP) ratio less than about 15=to-1 are limited by nitrogen. Silver View Pond has an average TN/TP ratio of 13.4 -to -1, indicating that the pond's algae are slightly nitr6gen- limited. This is important because blue-green algae are likely to dominate nitrogen -limited systems because many blue-green species can obtain nitrogen from the atmosphere whereas other types of algae cannot. Blue-green algae are nuisance algae because they tend to form relatively large, unsightly colonies that float at the water surface. Occasionally blue -greens cause other problems, such as odors as they decay or toxic blooms that can harm animals (both wild and domestic) that consume the water. 82