Spatial and temporal variation in phytoplankton community structure in a southeastern U.S. reservoir determined by HPLC and light microscopy

Abstract

Spatial and temporal variation in phytoplankton community structure within a large flood-control reservoir (Sardis Reservoir, MS, USA) was investigated in relation to variation in physicochemical properties, location within the reservoir, hydraulic residence time (HRT), nutrient concentrations, temperature, and light conditions over a 14-month period. During periods of short HRT, phytoplankton communities throughout the reservoir were homogeneous in biomass, composition, and production. With a gradual increase in HRT from spring to summer, spatially heterogeneous phytoplankton communities developed along the longitudinal axis of the reservoir. During this period of longer HRT, diatoms and chlorophytes were a larger proportion of total phytoplankton biomass at shallow and more turbid locations near the head of the reservoir, whereas cyanobacteria were a larger proportion of the community at deeper and less turbid locations closer to the outflow. Seasonal succession of the phytoplankton community was represented by high abundance of diatoms in spring, increasing biomass of cyanobacteria through summer, and a secondary bloom of diatoms in fall. Species of Cyclotella, Asterionella, Nitzschia, and Ankistrodesmus were among the first colonizers in the early growing season, closely followed by Aulacoseira, whereas species of Staurastrum and Tetraedron appeared later in the spring. Species of Synedra, Crucigenia, Selenastrum, Scenedesmus, and Merismopedia occurred throughout the sampling period. As the diatoms started to decrease during mid-spring, cryptophytes increased, prior to dominance of species of Pseudanabaena in summer. Reservoir management of HRT, in combination with spatial variation in reservoir morphology and seasonal variation in temperature and riverine nutrient inputs, creates seasonally variable yet distinct spatial patterns in phytoplankton community biomass, composition, and production.