Action Plan for the Town of Chatham Ponds

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defined as DO < 1 mg/l) phosphorus adsorbed to the lake bottom sediments become soluble and diffuses into the overlying water. As ponds become more productive, anoxia is measured higher in the water column. This relationship for the Chatham ponds is displayed in Figure 4. The axes are maximum depth of ponds, and maximum percent of the water column affected by anoxia (from the 2000 – 2002 data sets). Note that two ponds, Black Pond-mid and Stillwater Pond, plot outside of the general pattern. The extent of anoxia in these ponds is higher than the other ponds. Schoolhouse Pond, in contrast, has less anoxia, indicating higher water quality. The shallowest ponds (Perch, Pickerel, Black-west, Ryder, Blue, Mary’s, Mill and Trout Ponds) do not develop oxygen depletion in the lower waters. Soluble phosphorus entering these ponds with the groundwater will become incorporated into the biota. Ponds deep enough to stratify and productive enough to experience seasonal anoxia have elevated concentrations of phosphorus in the lower waters. In some lakes, wind-induced mixing and internal waves (seiches) may entrain the phosphorus-rich water into the upper sunlit layer where the nutrient can support algal growth (the photic zone) during the summer stratified period. White Pond Goose Pond Stillwater Pond Schoolhouse Pond Lovers Lake Figure 4 Maximum Depth and Extent of Anoxia Barclay Pond Emery Pond Black Pond-east Max Extent of Anoxia (m) Max Depth (m) Trout Pond Mill Pond Black Pond-mid Mary's Pond Blue Pond Ryder Pond Black Pond-west Pickerel Pond Perch Pond 0 2 4 6 8 10 12 14 16 18 Depth (m) One measure of the probability of mixing between the upper and lower waters is the Osgood Index, named for the limnologist who developed an empirical relationship between lakes’ surface area and depth, and the stability of the water column. Small, deep lakes are less likely to have wind-induced mixing of deep waters into the photic zone. Conversely, shallower lakes with larger surface area are more susceptible to wind mixing and phosphorus released from sediments may become entrained into the upper waters and available to support algal growth during the stratified EcoLogic LLC and 11 November 20, 2003 Rev. 3 Stearns & Wheler LLC
period (Osgood 1988). Ponds with very low indices (less than approximately 4) are polymictic , exhibiting only ephemeral stratification. As the index increase, so does stability of the water column. Ponds with indices greater than about 20 are very stable; and would tend to mix later in the fall. Intermediate lakes would be susceptible to mixing of hypolimnetic waters during strong wind events; these ponds may destratify earlier in the fall when light and temperature conditions would support an algal bloom. Several of the Chatham Ponds are somewhat susceptible to this internal phosphorus loading during summer as summarized in Table 6. However, all the Chatham kettle ponds mix throughout the water column in the fall, as the waters cool and the thermal gradient (and thus density differences) between the upper and lower layers breaks down. Phosphorus in the lower waters is distributed throughout the water column and is available for algal uptake given favorable conditions of light and temperature. Table 6 Potential for Sediment Phosphorus to Enter Photic Zone during Summer Pond Mean Depth (m) Surface Area (ha) Anoxia Maximum TP, lower waters * µg/l Black -east N/A 2 Yes 88 N/A Osgood Index Probability of Entrainment during stratified period Emery 3 5.7 Yes 246 12.6 Moderate Barclay N/A 1.2 Yes 89 N/A Lovers Lake 5 15.2 Yes 173 12.8 Moderate Schoolhouse 7.7 7.5 Yes 56 28.2 Low Stillwater 6 7.6 Yes 326 21.8 Low Goose Pond 7.6 16.7 Yes 13 18.6 Low White Pond 7 16.3 Yes 223 17.3 Low *Based on 2000 – 2002 monitoring data, Town of Chatham Water Quality Laboratory The water quality and aquatic habitat data collected during the 2001 – 2002 field investigations indicates that the Chatham Ponds are in various stages of eutrophication. While the data are somewhat limited, representing few sampling points, they do provide a basis for making an assessment of trophic state using the standard indicators described in Table 2. The final column in Table 7 represents a professional judgment of trophic state. EcoLogic LLC and 12 November 20, 2003 Rev. 3 Stearns & Wheler LLC
Page 1 and 2: Action Plan for the Town of Chatham
Page 3 and 4: List of Tables Page Table 1. Data S
Page 5 and 6: FOX POND HARWICH STILLWATER POND MI
Page 7 and 8: techniques on controlling the conce
Page 9 and 10: Pond Historical Data (pre 1990) Ple
Page 11 and 12: Table 4 Status of Chatham Ponds, ba
Page 13: the Barnstable County Department of
Page 17 and 18: 7. Summary of Findings Finding: Wat
Page 19 and 20: • Permanent drawdown to accelerat
Page 21 and 22: 9. Priority Actions for the Town of
Page 23 and 24: Appendix A. Summary of Regulatory S
Page 25 and 26: Category 1 (continued): Control Inp
Page 27 and 28: Category 2 (continued): Alter Inter
Page 29 and 30: Category 3 (continued): Mitigate th

Action Plan for the Town of Chatham Ponds

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