Lake Pocotopaug Lake and Watershed Restoration Evaluation ...

More documents

Recommendations

Info

Chemical TreatmentIn-stream chemical treatment involves the dosing of stream flows with alum or other coagulantsto bind phosphorus and coagulate sediments to promote settling. During this process,phosphorus permanently complexes with aluminum or another binding agent, rendering itunavailable for biological uptake by algae. Clarification of drinking water uses alum extensively,and removal of phosphorus from wastewater in tertiary treatment systems often involves alum.This in-stream treatment technology has been successfully applied in other regions, especiallyFlorida. The primary application of this technology has been for phosphorus removal whereother BMPs were not viable. Phosphorus removal rates ranging from 50-95% have beenreported. Removal rates ranging from 50-99% have also been documented for other pollutantssuch as suspended solids, nitrogen, color, and bacteria. The alum treatment performed in thelake itself was intended to inactivate past inputs from the watershed; application in thewatershed would constitute pre-entry inactivation.Although effective, this technique is not recommended for Lake Pocotopaug due to highoperational and maintenance costs. A dosing station would be needed for each dischargepoint, with at least four major locations possible. It may be possible to selectively treat the mostproblematic discharges, but this would not be considered until other means of controlling loadshave been explored, attempted, and dismissed.11.3 Prevent algal blooms from occurring and maximize water clarityAlgal blooms are an issue at Lake Pocotopaug. Low nutrient availability typically controls algalgrowth, but not to the desired extent in this system. Blooms have occurred when totalphosphorus concentrations were as low as 10 ug/L, a level considered safe in most systems.This problem may be due to the types of algae present (a high volume to mass ratio blue-greenis dominant in blooms), additional nutrient sources not being measured by water columnmonitoring (sediment uptake) or lack of substantial zooplankton grazing. When consideringgraphs of the relationship between water clarity and chlorophyll or phosphorus, LakePocotopaug falls along the outside edge of the range of observed values. That is, while theobserved relationships are within the range observed elsewhere, this lake is experiencing aboutas high a level of production per unit of available phosphorus as allowed anywhere and as low awater clarity per unit of chlorophyll as might be expected. This means that management mustaim to do better than average – there is nothing average about Lake Pocotopaug!The most preferable approach to eliminating algal blooms involves reducing the in-lakephosphorus concentrations even further, but there are practical limits to this approach. Allmethods described previously will reduce incoming phosphorus concentrations, but at best wemight reasonably expect a 60% reduction in the in-lake concentration of phosphorus could berealized. This should reduce the probability of blooms, but in-lake concentrations will still behigh enough at times to fuel algal blooms in this lake. Acting to reduce loading isrecommended, but it may not be sufficient by itself to achieve the desired results.Lake Pocotopaug Restoration Evaluation 108May 2002
Means by which algal blooms might be controlled through in-lake actions and the primaryadvantages and disadvantages are listed in Table 21. Most have some applicability to LakePocotopaug, but with what has been learned to date, many can be eliminated as front linemethods going forward from here. Further in-lake phosphorus inactivation should not be ruledout, but it does not seem appropriate to pursue this approach further until other sources ofphosphorus loading have been addressed. Use of algaecides is generally not a good ideaexcept in emergencies, as direct and indirect side effects can be substantial. Some techniques,such as large-scale dredging, drawdown or hypolimnetic withdrawal are minimally applicable tothis case. A review of options in Table 21 suggests that the most advantageous in-lake method(after the phosphorus inactivation approach implemented in 2001) is biological control throughenhanced grazing by zooplankton on algae.Biological, or top-down control, is a form of biomanipulation in which biological components ofan aquatic system are altered to create a cascading effect within the food web that results insome desirable change. In this and many other cases that change would be increase waterclarity. Reducing predation on zooplankton by panfish, currently very abundant in LakePocotopaug, should increase zooplankton size and density. Larger and more abundantzooplankton will be a more effective phytoplankton grazing influence, thereby reducing algaldensity. This relationship has been demonstrated in the lab, in small ponds, and in some fairlylarge lakes, with each increase in size of resource accompanied by a longer time period toachieve the desired biological structure and enhanced water clarity.Biological interactions are quite complicated, however, and not nearly as consistent as chemicalor physical control methods. The normal approach to enhancing grazing by zooplanktoninvolves either directly removing panfish or stocking predator fish to consume more panfish.The latter approach is generally considered preferable, but adds a step and further complicatesthe chain of events. If the stocked predator fish reproduce, their young may eat zooplankton forsome time before switching to the target panfish assemblage, so zooplankton predationintensity tends to vary considerably over time. Some algae resist grazing fairly well, allowingblooms to form in the presence of abundant zooplankton. However, empirical research hasshown that the degree of zooplankton grazing is a major factor in where a lake is positionedwithin the range of possible chlorophyll and water clarity values for a given phosphorusconcentration.The stocking of walleye in Lake Pocotopaug may have the desired affect. Walleye werestocked in several lakes throughout Connecticut in an effort to increase fishing diversity, but oneof the prerequisites for successful walleye introduction is an abundant population of small perch.Lake Pocotopaug certain provides that condition, and if enough walleye were stocked in LakePocotopaug, panfish densities should decrease, zooplankton body size and abundance shouldincrease, and phytoplankton densities should decrease. A fisheries study is warranted todetermine if enough fish were stocked to have this secondary effect on Lake Pocotopaug.Lake Pocotopaug Restoration Evaluation 109May 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 20 and 21:
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 30 and 31:
Page 32 and 33:
Phytoplankton samples were collecte
Page 34 and 35:
where many measurements would have
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 50 and 51:
Page 52 and 53:
Page 54 and 55:
Page 56 and 57:
were identified to genus and enumer
Page 58 and 59:
Table 13 continued. 2001 Phytoplank
Page 60 and 61:
Page 62 and 63:
Page 64 and 65: Table 13 continued. 2001 Phytoplank
Page 66 and 67: Table 14 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
Page 88 and 89: Table 17. Empirical Model Calculati
Page 90 and 91: Table 18. Total Phosphorus Loading
Page 92 and 93: Table 19. Wet Weather Loading Summa
Page 94 and 95: With the best possible treatment of
Page 96 and 97: water quality should focus on input
Page 98 and 99: 10.0 MANAGEMENT NEEDS AND OBJECTIVE
Page 100 and 101: 11.2 Reducing Total Phosphorus and
Page 102 and 103: undeveloped forest land, an opportu
Page 104 and 105: Figure 22. Buffer Strips for Pollut
Page 106 and 107: Figure 23. Catch Basin with Sump an
Page 108 and 109: early spring to capture what appear
Page 110 and 111: Figure 26. Infiltration Systems.Lak
Page 112 and 113: Figure 27. Constructed Treatment We
Page 116 and 117: TABLE 21. MANAGEMENT OPTIONS FOR CO
Page 118 and 119: TABLE 21 continued. MANAGEMENT OPTI
Page 130 and 131: 12.0 ADDITIONAL DATA NEEDSManagemen
Page 132 and 133: 13.0 RECOMMENDED MANAGEMENT PROGRAM
Page 134 and 135: this point, but as a rough guide, a
Page 136 and 137: 14.0 REFERENCESAd Hoc Lake Advisory
Page 138 and 139: Scheuler T.R., P.A. Kumble, & M.A.
Page 140 and 141: Appendix B:Supplemental Tables and
Page 142: Appendix D:Educational MaterialsLak
show all

Lake Pocotopaug Lake and Watershed Restoration Evaluation ...

Create successful ePaper yourself

Delete template?

Save as template?