Lake Pocotopaug Lake and Watershed Restoration Evaluation ...

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The late summer bloom of blue-greens is consistent with conditions in past years. Water claritywas higher for longer in the summer than in most recent years, but the eventual decline to levelsundesirable for contact recreation suggests that the successful inactivation of phosphorus indeeper sediments of the lake is not the whole answer to controlling algae in Lake Pocotopaug.Hypolimnetic phosphorus levels were indeed very low in 2001, and epilimnetic phosphorusconcentrations rarely >10 ug/L, but the bloom still occurred. This is an unusual phenomenon insouthern New England lakes and warrants further investigation.It has been hypothesized that a bloom of toxic golden algae in the fall of 1999 was responsiblefor the fish kill of late 1999 and early 2000. It is assumed that an increase in claritycorresponded to a die off of those algae, with release of the toxin into the water. Althoughplausible, this scenario does not appear to be consistent with observed 2001 conditions. Nohaptophytes were found in the Pocotopaug samples collected in the fall and early winter of2001. Even if those specific types of golden algae known to be potentially toxic are present inLake Pocotopaug, the densities observed in 2001 appear too low to elicit a toxic response byfish. Fish did again school up at the mouths of tributaries to the lake, and there was anoticeable increase in clarity in December, but the increase in clarity corresponds to a shift togreater dominance by non-haptophyte golden algae. It is possible that algae bloomed and diedoff between the November and December sampling dates, but this is highly speculative.6.3.2 Chlorophyll aChlorophyll a samples were collected utilizing the same methods as phytoplakton. However,chlorophyll a samples were taken from April to September only.Chlorophyll is the green pigment in plants, with chlorophyll a common to all plants and oftenused as a surrogate for biomass or primary production potential in aquatic environments.Values 10 µg/l usually impart somecolor to the water. Values >20 µg/l are often associated with undesirable conditions, with levels>100 µg/l often described as appearing like a “paint spill” or “pea soup”. Chlorophyll breaksdown into other pigments that can be measured, with phaeophytin usually taken as an indicatorof dying algae. Even a healthy algae community will have some phaeophytin, but it should be aminor component of the total chlorophyll concentration.Total chlorophyll a concentration in Lake Pocotopaug ranged from 1.5 to 14.8 µg/l with anaverage of 6.0 and 5.5 µg/l for LP-1 and LP-2, respectively (Table 10). Most of this pigmentwas active, healthy chlorophyll. As seen in the past, nuisance levels of phytoplankton exist atchlorophyll levels below the 20 ug/L threshold in Lake Pocotopaug. Values at peakphytoplankton biomass were between 6 and 11 ug/L. Therefore Wetzel’s (1983) cutoff value of4 µg/l for overfertilized (eutrophic) systems is a more appropriate target for mean chlorophylllevels in Lake Pocotopaug than the 10 ug/L threshold. This represents enough of a food baseLake Pocotopaug Restoration Evaluation 64May 2002
to support a thriving fishery but not enough to present any aesthetic or safety issues forswimmers and boaters.6.3.3 ZooplanktonThe zooplankton of Lake Pocotopaug were sampled at two stations monthly from April toSeptember. A net with 53 um mesh size was towed through 30 m of water, yielding aconcentrate from 942 liters of water. Concentrates were examined in a Sedgewick Raftercounting chamber at 40x to 100x with brightfield optics. Zooplankters were identified, measuredand enumerated (Table 15). Results were converted to biomass based on genus-specificlength-weight regressions (Table 16).Types of zooplankton in Lake Pocotopaug were typical of southern New England lakes, withprotozoans, rotifers, copepods and cladocerans all present, as well as the phantom midgeChaoborus (found in two samples). Copepods and cladocerans were the most abundantzooplankters, but overall abundance was quite low in most samples. A biomass of >100 ug/L isgenerally considered necessary to provide adequate fish food and filter enough lake water on adaily basis to exercise some control over algal abundance. Only the May sample from station 1exhibited a biomass >100 ug/L, and over half the biomass values were
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LAKE POCOTOPAUGLAKE AND WATERSHEDRE
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11.3 Prevent algal blooms from occu
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LAYPERSON’S SYNOPSISLake Pocotopa
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The stocking of walleye in Lake Poc
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Lake Pocotopaug Restoration Evaluat
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Period Covered 1988• Pollution fr
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Recommendations included• Algacid
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Major EventDecember 1999 - Fish kil
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Table 5. Land Use from the CT DEP G
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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
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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 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 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 114 and 115: Chemical TreatmentIn-stream chemica
Page 116 and 117: TABLE 21. MANAGEMENT OPTIONS FOR CO
Page 118 and 119: TABLE 21 continued. MANAGEMENT OPTI
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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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