Regulation of phytoplankton and bacterioplankton production by nutrient availability and advective losses in a large river impoundment (Kentucky Lake)

This study quantifies production by phytoplankton and bacterioplankton in Kentucky Lake reservoir and Ledbetter embayment. Five study sites were chosen representing a gradient of water residence time from the embayment to the main channel of the reservoir. Sampling for productivity, biomass, and phytoplankton community composition occurred monthly between May and November 1997. Manipulations of nitrogen and phosphorus in experimental enclosures were used to assess short term nutrient limitation of bacteria and phytoplankton. The embayment did not appear to be an important source of phytoplankton or bacterial biomass or production for the reservoir. Phytoplankton community structure primarily shifted in response to seasonal variation. Results suggest water residence time may influence phytoplankton and bacterial growth through advective loss and control of nutrient availability. Phytoplankton progress from weak phosphorus limitation in early summer to strong nitrogen limitation in late summer. Limitation in the embayment was more severe. Bacteria did not respond to nutrient additions, and seemed to be regulated by water residence time in the main channel.