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VI. WATER QUALITY A.Methods Water quality samples were taken from three locations in Silver View Pond on June 24, July 22, August 13, and September 2, 1989. Sampling locations are shown -in Figure 4. Zooplankton were sampled with a standard Wisconsin net equipped with a 80 micron bucket, phytoplankton (algae) samples were preserved with Lugol's solution, and water samples were filtered through a 0.5 micron glass -fiber filter and frozen for chlorophyll analysis. Chlorophyll was extracted with a 80-15-5 mixture of acetone -methanol -water for 24 hours and quantified at 665 nanometers (the wavelength for green pigment) on a Model 24 Beckman spectrophotometer. Surface -water samples were submitted to Northern Lake Service, Inc. (Crandon, WI) for analysis of total phosphorus, total nitrogen, and, for the last two sampling dates, the sum of nitrate plus nitrite. It was not possible for the laboratory to analyze total nitrogen on the July 22 samples because the storage period for these samples was exceeded. Secchi disk data were not collected because transparency was generally to the sediment surface even in the deepest parts of the pond. B. Results Phosphorus Phosphorus is typically the limiting nutrient for aquatic plant growth in metro area lakes. The level of eutrophy in a lake or pond is typically a function of the water body's phosphorus concentration. A concentration of 20 to 30 ug/L (micrograms per liter or parts per billion) is considered the point where a mesotrophic water body becomes eutrophic. It is clear from the phosphorus data collected (Table 2) that Silver View Pond is eutrophic but that its three arms are not similar in water quality. For instance, the east sampling location always has the lowest phosphorus concentration, often by a factor of two. This location had an average phosphorus concentration of 65 ug/L (range 58- 73), in contrast to an average of 123 ug/L (range 120-125) for the west sampling location. The south sampling location was intermediate, with an average phosphorus concentration of 96 ug/L (range 70-120; the September 2 south sample was not included, as it appears this sample was contaminated, having a concentration of 935 ug/L). These phosphorus data suggest that most of the phosphorus load is introduced in the west and south arms of the pond, �. and that at least 25 to 50 percent of the phosphorus is being lost to the sediment by the time the water reaches the 79