Lake Pocotopaug Lake and Watershed Restoration Evaluation ...

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where many measurements would have been necessary to characterize the many small inflowsto Lake Pocotopaug. Instead, calculations were applied using land use and expected waterexport coefficients.The total annual water load (all inputs) to Lake Pocotopaug can be calculated based on the lakevolume (approximately 7,132,000 m 3 ) and the flushing rate (approximately 1.25 volumes/year).Using these values, Lake Pocotopaug receives approximately 8,915,000 m 3 of water per year.Subtracting precipitation and groundwater inputs yields an estimate of surface water inputs (5.5– 5.9 million cubic meters per year). Alternatively, a water flow rate per area can be applied tothe watershed to get similar results. Using a flow rate of 1.5 cfs/mi 2 (typical runoff for this areaof Connecticut) in a 3.7 mi 2 watershed yields a surface water input of approximately 5.6 millioncubic meters per year. Using both methods, a range of surface water input is generated (5.5 –5.9 million cubic meters/year).Stormwater input can be calculated by multiplying an expected runoff coefficient by annualrainfall and area subject to precipitation. The runoff coefficient used in the WMC report was 0.3for residential land and seems reasonable for this watershed. Using 0.3, 1.2 meters ofprecipitation and the watershed area (9,636,008 m 2 ), stormwater runoff is estimated to be 3.5million cubic meters per year.Dry weather, or base flow, was estimated by subtracting stormwater flow from the total surfacewater input (2.0 – 2.4 million cubic meters). It was also calculated using the average flow ratemeasured during this investigation (0.3 cfs). The base flow was calculated to be 2.7 millioncubic meters, comparable to the value obtained through subtraction above.Lake Pocotopaug Restoration Evaluation 28May 2002
6.0 WATER QUALITY6.1 In-Lake Water QualityTemperature and DO profiles at the two in-lake stations during April-November 2001 arepresented in Figure 7. Other water quality data are summarized in Table 10. Values recordedbelow the detection limit are reported as ½ the detection limit. 2001 in-lake values for eachsampling and a summary of all data (previous reports and 2001 data) are provided in AppendixB.Thermal stratification occurs when sunlight warms the upper waters but wind mixing isinsufficient to mix this warmer water all the way to the bottom of the waterbody. This is a naturalprocess, but has distinct implications for lake ecology, as the lower water layer can be a refugeor a detriment depending on how much oxygen is present. Lake Pocotopaug was beginning tothermally stratify in April 2001 and was almost destratified by September. The thermocline waspresent at five meters at LP-1 and at six meters at LP-2 in May. The thermocline dropped to 5.5and 6.5 meters at LP-1 and LP-2, respectively, come July and dropped another 0.5 meters inAugust. These results indicate that Lake Pocotopaug is a typical dimictic water body (twocomplete mixing events in spring and fall separated by summer thermal stratification).Oxygen stratification roughly followed thermal stratification (Figure 7). DO readings below thethermocline were often less than 1.0 mg/L. DO below 1.0 mg/L was recorded above thethermocline at both stations (6 and 7 meters, respectively) in August. Anoxic conditions werealso recorded above the thermocline in June 2000 (VLSG 2001). DO readings of less than 6mg/l, undesirable for many aquatic life forms, were never recorded at depths above 5 m.Turbidity is a measure of water clarity. Turbid waters are indicative of high levels of suspendedparticles that may include algal cells, silt, or resuspended sediments and are usually associatedwith poor water quality. Acceptable standards depend on water body use, but turbidity readingshigher than 10 nephalometric turbidity units (NTU) are indicative of potentially undesirable waterquality. Most “clean” New England lakes exhibit turbidity ranging from 1 to ~5 NTU. Maximumturbidity in Lake Pocotopaug surface water exceeded the 5 NTU threshold at LP-2 (5.2 NTUrecorded in August), but averages were below 5 NTU (2.8 and 2.7 NTU, Table 10).Turbidity was higher near the sediment-water interface. Settling particles accumulating in thedeeper areas of the reservoir were likely responsible, though accidental stirring of finesediments by the sampling procedure could have contributed to the higher readings.The pH varied little in time and space during the 2001 sampling (Table 10). pH ranged from 6.1to 8.5 SU, with the lower values measured near the bottom and the high values near thesurface. Mean pH ranged from 6.6 to 7.4 SU.Lake Pocotopaug Restoration Evaluation 29May 2002
Page 2 and 3: LAKE POCOTOPAUGLAKE AND WATERSHEDRE
Page 4 and 5: 11.3 Prevent algal blooms from occu
Page 6 and 7: LAYPERSON’S SYNOPSISLake Pocotopa
Page 8 and 9: The stocking of walleye in Lake Poc
Page 10 and 11: Lake Pocotopaug Restoration Evaluat
Page 12 and 13: Period Covered 1988• Pollution fr
Page 14 and 15: Recommendations included• Algacid
Page 16 and 17: Major EventDecember 1999 - Fish kil
Page 18 and 19: Table 5. Land Use from the CT DEP G
Page 22 and 23: Figure 4. Lake Pocotopaug Bathymetr
Page 24 and 25: Table 6. QA/QC on Water Quality Dat
Page 26 and 27: Soils - USDA at MAGIC UCONN Geograp
Page 28 and 29: Table 8. Water Quality Variables Me
Page 32 and 33: Phytoplankton samples were collecte
Page 36 and 37: Figure 7. 2001 Temperature and Diss
Page 38 and 39: Table 10 continued. 2001 Lake Pocot
Page 40 and 41: phytoplankton biomass (Wetzel 1983)
Page 42 and 43: Figure 9. Annual June, July and Aug
Page 44 and 45: elow 7:1 occurred on September 22,
Page 46 and 47: Table 12. 2001 Dry and Wet Weather
Page 48 and 49: Table 12 continued. 2001 Dry and We
Page 56 and 57: were identified to genus and enumer
Page 58 and 59: Table 13 continued. 2001 Phytoplank
Page 68 and 69: Figure 10. 2001 Phytoplankton Bioma
Page 70 and 71: The late summer bloom of blue-green
Page 72 and 73: Table 15. 2001 Zooplankton DensityZ
Page 74 and 75: Table 16. 2001 Zooplankton BiomassZ
Page 76 and 77: 7.0 RELATIONSHIPS AND TRENDS7.1 Pre
Page 78 and 79: Figure 13. 1991-2001 Surface Water
Page 80 and 81: Figure 15. 2001 Surface and Mid-dep
Page 82 and 83: Figure 16. 1991-2001 Chlorophyll a
Page 84 and 85:
Figure 18. 2001 Chlorophyll a vs. S
Page 86 and 87:
Figure 20. 1991-2001 July and Augus
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Table 17. Empirical Model Calculati
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Table 18. Total Phosphorus Loading
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Table 19. Wet Weather Loading Summa
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With the best possible treatment of
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water quality should focus on input
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10.0 MANAGEMENT NEEDS AND OBJECTIVE
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11.2 Reducing Total Phosphorus and
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undeveloped forest land, an opportu
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Figure 22. Buffer Strips for Pollut
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Figure 23. Catch Basin with Sump an
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early spring to capture what appear
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Figure 26. Infiltration Systems.Lak
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Figure 27. Constructed Treatment We
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Chemical TreatmentIn-stream chemica
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TABLE 21. MANAGEMENT OPTIONS FOR CO
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TABLE 21 continued. MANAGEMENT OPTI
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12.0 ADDITIONAL DATA NEEDSManagemen
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13.0 RECOMMENDED MANAGEMENT PROGRAM
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this point, but as a rough guide, a
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14.0 REFERENCESAd Hoc Lake Advisory
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Scheuler T.R., P.A. Kumble, & M.A.
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Appendix B:Supplemental Tables and
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Appendix D:Educational MaterialsLak
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