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Daphnia Density by Station (#/m 3 ) 800 600 400 200 Gunston Cove Study - 2003 Station 7 Station 9 0 Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Figure 48. Daphnia Density by Station (#/m 3 ). 37 Daphnia, the common waterflea, is one of the most efficient grazers of phytoplankton in freshwater ecosystems. In the tidal Potomac River it is present, but not as common as Diaphanosoma. It is typically most common in spring. Daphnia reached highest densities in the cove during May and early June, but the densities were rather low (Figure 48). In the river an even more subdued peak was observed in the spring. Ceriodaphnia in the cove exhibited a similar May-June peak as Daphnia in the cove, but also had a maximum in early July (Figure 49). In the river, a very subdued peak was found in late July-early August. Ceriodaphnia Density by Station (#/m 3 ) 600 500 400 300 200 100 Gunston Cove Study - 2003 Station 7 Station 9 0 Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Figure 49. Ceriodaphnia Density by Station (#/m 3 ). Ceriodaphnia, another common large-bodied cladoceran, is usually present in numbers similar to Daphnia. Like all waterfleas, the juveniles look like miniature adults and grow through a series of molts to a larger size and finally reach reproductive maturity. Most reproduction is asexual except during stressful environmental conditions.
38 Moina Density by Station (#/m 3 ) 1000 800 600 400 200 Gunston Cove Study - 2003 Station 7 Station 9 0 Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Figure 50. Moina Density by Station (#/m 3 ). Moina is another waterflea that is often observed in the tidal Potomac River. Like the other cladocera mentioned so far, Moina grazes on phytoplankton to obtain its food supply. Moina had a single distinct peak in abundance in early July in both Gunston Cove and the Potomac mainstem. The peak was about 900/m 3 in the cover while the river attained a lesser density of 200/m 3 . Leptodora, the large cladoceran predator, was found at relatively high levels in the cove in early July. In the river the maximum was much lower and occurred in late June. Leptodora Density by Station (#/m 3 ) 160 140 120 100 80 60 40 20 Gunston Cove Study - 2003 Station 7 Station 9 0 Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Figure 51. Leptodora Density by Station (#/m 3 ). Leptodora is substantially larger than the other cladocera mentioned. Also different is its mode of feeding – it is a predator on other zooplankton. It normally occurs for brief periods in the late spring or early summer.
Page 1 and 2: An Ecological Study of Gunston Cove
Page 3 and 4: ii An Ecological Study of Gunston C
Page 5 and 6: iv were collected on three sample d
Page 7 and 8: vi We recommend that: 1. Long term
Page 9 and 10: 2 INTRODUCTION This section reports
Page 11 and 12: 4 Table 1 Sampling Dates and Weathe
Page 13 and 14: 6 immediately with formalin to a co
Page 15 and 16: 8 subsample of known volume and res
Page 17 and 18: 10 A. Climate and Hydrological Fact
Page 19 and 20: 12 B. Physico-chemical Parameters:
Page 21 and 22: 14 Dissolved Oxygen (mg/L) 16 14 12
Page 23 and 24: 16 pH, NC Lab 9.5 9.0 8.5 8.0 7.5 7
Page 25 and 26: 18 Secchi Depth (m) 1.2 1.0 0.8 0.6
Page 27 and 28: 20 Ammonia Nitrogen (mg/L) 0.30 0.2
Page 29 and 30: 22 Organic Nitrogen (mg/L) 1.2 1.0
Page 31 and 32: 24 N/P Ratio (by mass) 60 50 40 30
Page 33 and 34: 26 C. Phytoplankton Chlorophyll a,
Page 35 and 36: 28 Figure 32. Phytoplankton Density
Page 37 and 38: 30 The dominant cyanobacteria on a
Page 39 and 40: 32 Total phytoplankton biovolume ca
Page 41 and 42: 34 Melosira Figure 44. Phytoplankto
Page 43: 36 Bosmina Density by Station (#/L)
Page 47 and 48: 40 Diaptomus Density by Station (#/
Page 49 and 50: 42 E. Ichthoplankton Larval fishes
Page 51 and 52: 44 Clupeid Larvae (#/10m 3 ) 50 40
Page 53 and 54: 46 Table 4 Adult and Juvenile Fish
Page 55 and 56: 48 The abundance of each species in
Page 57 and 58: 50 Average Number of Fish per Trawl
Page 63 and 64: 56 Average Fish per Seine 600 500 4
Page 65 and 66: 58 Macrobenthos (#/m 2 ) 500 400 30
Page 67 and 68: 60 Total phosphorus levels were fai
Page 69 and 70: 62 Table 10 Correlation and Linear
Page 71 and 72: 64 Water Temperature (oC) 35 30 25
Page 73 and 74: 66 Chloride (mg/L) 350 300 250 200
Page 75 and 76: 68 Dissolved Oxygen (% saturation)
Page 77 and 78: 70 Light Attenuation Coefficient (m
Page 79 and 80: 72 Lab pH, GMU 11 10 9 8 7 Station
Page 81 and 82: 74 Total Alkalinity (mg/L CaCO3), G
Page 83 and 84: 76 Biochemical Oxygen Demand (mg/L)
Page 85 and 86: 78 Volatile Suspended Solids (mg/L)
Page 87 and 88: 80 Soluble Reactive Phosphorus (mg/
Page 89 and 90: 82 Un-ionized Ammonia Nitrogen (mg/
Page 91 and 92: 84 Nitrite Nitrogen (mg/L) 0.100 0.
Page 93 and 94: 86 Nitrogen:Phosphorus Ratio 70 60
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88 Chlorophyll a, Surface (ug/L) 10
Page 97 and 98:
90 PBmax (ug C/ug Chl a/hr) 30 25 2
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92 D. Zooplankton Trends: 1990-2003
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94 Brachionus (#/L) 1000.0 100.0 10
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96 Filinia (#/L) 1000.0 100.0 10.0
Page 105 and 106:
98 Polyarthra (#/L) 1000.0 100.0 10
Page 107 and 108:
100 Diaphanosoma (#/m3) 100000.00 1
Page 109 and 110:
102 Chydorid Cladocera (#/m3) 1000.
Page 111 and 112:
104 Copepod Nauplii (#/L) 1000.0 10
Page 113 and 114:
106 Clupeid Larvae (#/10m3) 1000.0
Page 115 and 116:
108 Atherinid Larvae (#/10m3) 10.00
Page 117 and 118:
110 F. Adult and Juvenile Fish Tren
Page 119 and 120:
112 Table 14 Mean catch of adult an
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
118 Mean Catch Per Trawl 50 40 30 2
Page 127 and 128:
120 Mean Catch Per Trawl 8 6 4 2 Tr
Page 129 and 130:
122 Mean Catch Per Trawl 120 100 80
Page 131 and 132:
124 Mean Catch Per Trawl 16 14 12 1
Page 133 and 134:
126 Seines The mean annual catch pe
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128 Table 19 The number of seines i
Page 137 and 138:
130 Mean Catch Per Seine 300 250 20
Page 139 and 140:
132 Mean Catch Per Seine 250 200 15
Page 141 and 142:
134 G. Benthos Trends Oligochaetes
Page 143 and 144:
136 Amphipods (#/m2) 16 12 8 4 Stat
Page 145 and 146:
138 Corbicula (#/m2) 40 30 20 10 St
Page 147 and 148:
140 Table 21 Summary of Important T
Page 149 and 150:
142 observed through 1995. This has
Page 151 and 152:
144 being filled. A dredged channel
Page 153 and 154:
146 Anadromous Fish Survey Pohick,
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148 sized fishes were seen, an atte
Page 157 and 158:
150 Table 3. Fish eggs and larvae c
Page 159 and 160:
152 Total 7 11 237 13 2 64 119 (2.3
Page 161 and 162:
154 Table 7. Adult anadromous and s
Page 163 and 164:
156 Table 8. Summary of alewife spa
Page 165 and 166:
158 Spawning information on gizzard
Page 167 and 168:
160 The information that pertains t
Page 169 and 170:
162 lower reaches of Pohick Creek i
Page 171 and 172:
164 Table 13. Catches of adult clup
Page 173 and 174:
Appendix A Phytoplankton Species Di
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