Reservoir Plankton Communities 
91 
Table 1. Surface water characteristics of Sutton Reservoir during 1985. 
Parameter 
H 2 0 temperature (°C) 
Secchi depth (m) 
pH 
Conductivity (juS/cm) 
P0 4 - P (mg / 1) 
N0 2 + N0 3 - N (mg / 1) 
Total alkalinity (mg/ 1 CaCo 3 ) 
Sodium (mg / 1) 
Chloride (mg/ 1) 
Chlorophyll a(pgl 1) 
Mean 
Range 
20.6 
5.6-32.2 
2.1 
1. 5-2.9 
6.6 
6.2-7. 5 
792 
510-935 
0.003 
0.001-0.008 
0.054 
0.01-0.17 
15.1 
4.7-32.6 
125.8 
89-250 
206.5 
160-260 
5.7 
1.6-13.2 
RESULTS AND DISCUSSION 
Phytoplankton densities in Sutton Reservoir ranged from 480 
units/ml in March to 7260 units/ml in June during 1985 (Fig. 2). 
Densities and chlorophyll a values were moderate compared with other 
lakes in the North Carolina coastal plain (NCDEM 1984). The 
Chlorophyceae and Cryptophyceae were the two most important 
phytoplankton classes, followed by the Bacillariophyceae and Cyano- 
phyceae, respectively. Nuisance blue-green algal blooms observed during 
1982 and 1983 were not manifested in 1985. Biomass as chlorophyll a 
was greatest in June when densities of Cryptomonas ovata, Peridinium 
spp., or larger diatom taxa such as Melosira were high (Fig. 2). Mean 
chlorophyll a levels (5.7 pg/ 1) suggest a mesotrophic state for Sutton 
Reservoir (Wetzel 1983). 
Thirty-five zooplankton taxa from the Copepoda, Cladocera, and 
Rotifera were identified from Sutton Reservoir samples collected during 
1985 (Table 2). A great majority of the taxa were rotifers, with the 
Brachionidae particularly well represented. Few of the crustaceans 
were numerically dominant in the reservoir. Those which were dominant 
included the copepods Diaptomus dorsalis and Eurytemora affinis and 
the cladocerans Daphnia ambigua and Bosmina coregoni (Table 3). 
Crustacean zooplankton densities displayed a bimodal peak in early 
spring and again in fall and winter, with a minimum from May through 
August. The rotifers generally maintained high densities from May 
through the end of the year, with various species of Brachionus and 
Keratella usually dominating. Other rotifers with high densities at 
various times included Ascomorpha sp. and Conochiloides natans. 
