Plankton ecology of Lake James, North Carolina

Effects of water column stability and wind-induced physical disturbances on plankton diversity and biomass were studied from March 1997 to August 1999 in Lake James, North Carolina. Wind disturbances were computed as a Wedderburn Number, the ratio of depth-based density generated buoyancy to mixing energy generated by the wind. Daily wind energy available for disturbing the water column was computed from average wind velocity and directional data from a meteorological station. Lake length values used for Wedderburn Numbers were modified by a cosine-corrected "effective" fetch calculation. Effective fetch calculations compensate for basin orientation, land sheltering, and wind direction on the win forces that disturb the water column. Mixing depth and water buoyancies used in Wedderburn Calculations were based on temperature-density profiles obtained from monthly HydrolabRTM DataSonde4 measurements assuming mixed layer depths of 3, 10, and 15 meters. Monthly wind-generated instability frequencies were calculated as the number of days W < 1, or the number of days the calculated wind shear exceeded buoyant stabilities of the water column at the depths selected for this study.; Plankton and water quality data were sampled monthly. Continuous temperature profiles were taken at two stations using Onset Tidbit temperature loggers. Weather data was recorded at 5 minute intervals from a meteorological station near the Linville dam.; A total of 65 phytoplankton and 42 zooplankton taxa were collected from Lake James during 1997--1999 study period. Taxa were identified to the lowest level possible based on the keys available. Species diversity of plankton assemblages was determined by analyses of numbers of species, numbers of individuals, and Shannon's diversity index. Cell volume and biomass of each species were calculated by measuring average dimensions and approximating the geometric shapes that most closely resembled the species. For colonial forms, volume per colony was determined by multiplying individual cell volume by the average number of cells per colony.; Spearman rank correlation coefficients between phytoplankton and zooplankton diversity and biomass were --0.003 and --0.36 respectively in the Linville basin and were --0.094 and --0.13 respectively in the Catawba basin.; Phytoplankton community structure was significantly different between the two basins (p < 0.1), but zooplankton community structure was not significantly different (p > 0.1). Phytoplankton and zooplankton species diversity was significantly different between the years in the Linville basin (p < 0.1), but not in the Catawba basin. Plankton biomass and diversity were highest during 1998.