Importance of light limitation, nutrient availability, and hydrology in controlling the abundance and composition of the phytoplankton community of Herrington Lake (KY) was investigated over a two-year period. Selected environmental parameters were measured every two weeks (April-October) at five sampling stations located along the longitudinal gradient of the reservoir. In addition, short-term (48hr) nutrient enrichment experiments were conducted to assess the spatial and temporal variations in nutrient limitation. Phytoplankton growth responses to the combined addition of nitrogen (NO3) and phosphorus (PO4) were greater than those resulting from the addition of either nutrient alone. These results indicate that phytoplankton production was closely co-limited by the availability of both N and P. The magnitude of the phytoplankton responses to nutrient additions was greatest at downstream stations and in late summer suggesting that those populations experience more severe nutrient limitation. Significant interannual variations in nutrient limitation and primary production were observed during this study period (1995-1996). In 1995, nutrient limitation was more severe than in 1996. Above average rainfall and discharge in 1996 coincided with increased productivity (mg C/m3/hr) and minimal nutrient limitation. Phytoplankton community composition showed similar patterns of seasonal succession in both years
