NEW: Annual Report - George Mason University

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increasing. Corbicula is having a comeback after a major dieback during the early to mid 1990’s. In the cove trawl catches continued a decline begun in 2002 led by decreases in adult and juvenile white perch which began to decrease in 2001. For the last two years, white perch were substantially below half of the trawl collection, a condition unseen since 1990. This condition may be an actual decrease in the white perch stocks or merely a shift in their location since the population is not confined to the cove. The mean catch per trawl of blueback herring was high in 2003 while alewife was lower. In the river trawl catches were actually somewhat higher than in 2002 and above the median value over the course of the study. White perch made up about half of the total catch, similar to recent years. Larger numbers of brown bullhead, channel catfish, tessellated darter, and hogchoker have been caught since 2000. All are known to feed on benthic animals which may have increased with dredge spoil placement. In seine samples, the catch of banded killifish remained strong and dominated all other species. Blueback herring, alewife, and spottail shiner were caught in numbers comparable to most previous years. The abundance of white perch was very low, primarily due to fewer young-of-year in the catch. The catch of inland silverside was also low. The occurrence of both adults and larvae in the creek was clear evidence of spawning by alewife in Pohick Creek in 2003. Alewife larvae were collected in early to mid April in the creek just below the outfall from the Noman M. Cole Pollution Control Plant. The adults were observed there and about a kilometer upstream at the base of a series of low waterfalls. Since 1996, we have collected either adult alewife or alosine larvae in Pohick Creek every year except 2002. Alewife adults were also observed in the creek in 2004, though identification of larvae caught there is still in progress. No blueback herring adults were caught in Pohick Creek in either 2003 or 2004 continuing the record since 1988. Gizzard shad adults were caught in Pohick Creek in both 2003 and 2004. Larval gizzard shad were also caught in 2003, and spawning certainly occurred in the creek in 2003 and probably in 2004, too. Water quality in Pohick Creek remains good enough to support spawning by alewife and gizzard shad. Perhaps consideration should be given to modifying the creek environment to encourage more spawning or better survival of the young larvae and to protect the adult fishes from fishermen.. The 20-year record of data from Gunston Cove and the nearby Potomac River is starting to reveal many interesting long-term trends that will aid in the continued management of the watershed and point source inputs. v
vi We recommend that: 1. Long term monitoring should continue. The revised schedule initiated in 2004 which focuses sampling in April through September should capture the major trends affecting water quality and the biota. 2. Results of special mini-studies conducted during 2004 should be evaluated to determine if further changes in sampling or analysis are justified. 3. Efforts should be made to publish these results in the peer-reviewed literature. 4. The feasibility of continuous monitoring buoys in the river and cove should be explored.
Page 1 and 2: An Ecological Study of Gunston Cove
Page 3 and 4: ii An Ecological Study of Gunston C
Page 5: iv were collected on three sample d
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 and 44: 36 Bosmina Density by Station (#/L)
Page 45 and 46: 38 Moina Density by Station (#/m 3
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 59 and 60:
52 Table 7 Adult and Juvenile Fish
Page 61 and 62:
54 Table 9 Adult and Juvenile Fish
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
Page 95 and 96:
88 Chlorophyll a, Surface (ug/L) 10
Page 97 and 98:
90 PBmax (ug C/ug Chl a/hr) 30 25 2
Page 99 and 100:
92 D. Zooplankton Trends: 1990-2003
Page 101 and 102:
94 Brachionus (#/L) 1000.0 100.0 10
Page 103 and 104:
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
Page 135 and 136:
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,
Page 155 and 156:
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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