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January 26,2024 Don Peterson Page 5 of 21 Reference: Water Quality Assessment of Silver View Pond,Mounds View,MN Table 2 Ran e of concentrations for water qualit parameters Parameter Concentration Range Eutrophication Standards for Shallow Lakes (n=2) 1 m North Central Hardwood Forest Ecoregion Chl-a(pg/L) 20-24 20 TP(pg/L) 69—112 60 Ortho-P(pg/L) 10 N/A TN(mg/L) 1.18—1.26 N/A TKN (mg/L) 1.18— 1.26 N/A Nitrite/nitrate(mg/L) <0.03 N/A Vertical profiles of physicochemical parameters are shown in Table 3. In a small shallow pond like Silver View Pond, we expect well-mixed conditions such that temperature and pH are consistent throughout the water column. Dissolved oxygen (DO)tends to decrease from the surface towards the sediments due to the demand for oxygen during microbially-driven organic matter decomposition and other oxygen-consuming geochemical processes. In early September when the profile data was collected, the pond had extensive coverage of floating aquatic plants such as duckweed and watermeal (discussed in more detail below), which can cut off the oxygen supply from the atmosphere across the air-water interface. Combined with the oxygen demand, DO in Silver View Pond was extremely low. Dissolved oxygen concentrations below 2 mg/L are considered hypoxic and would be detrimental to aquatic organisms that are not tolerant of low DO conditions. Table 3. Ph sicochemical parameters collected at 0 5 m increments in the water column. Depth Temperature DO (m) ( (°C) (mg/L) pH 0 23.88 2.86 7.56 0.5 23.92 2.35 7.55 1 23.81 1.52 7.5 1.5 23.73 0.2 7.31. Aquatic Vegetation Community Silver View Pond is shallow with a mean depth of approximately 6.5 ft. Consequently, the pond is shallow enough to support aquatic vegetation growth across its entire surface area, and indeed the pond experiences significant coverage by aquatic vegetation in the summer growing season. Figure 2 shows the points surveyed in Silver View Pond and conveys the number of individual taxa found at each location. Submerged aquatic vegetation (SAV) metrics from the two surveys are shown in Table 4 and Table 5. The diversity of aquatic plant species in Silver View Pond is relatively high for a small, shallow urban stormwater pond. Shallow ponds and lakes tend to be either macrophyte-dominated or algae-dominated2. Systems may alternate from one state to another and experience unstable periods that reflect high densities of algae 2 Scheffer, Marten. Ecology of Shallow Lakes. The Netherlands: Kluwer Academic Publishers, 2004. Design with community in mind