Seasonal and spatial distribution of bacterial biomass and the percentage of viable cells in a reservoir of Alabama

Spatial community dynamics of bacterioplankton were evaluatedalong the length of the former stream channel of Elledge Lake,a small reservoir in western Alabama. The reservoir was stronglystratified from April to October with up to a 10°C temperaturedifference across the 1 m deep metalimnion. Bacterial biomasswas highest during late summer, with a general pattern of increasingabundance from the inflowing river (10 µg C l^-1) to thedam (20–30 µg C l^-1). Bacterial numbers also increasedfollowing a >10-fold increase in turbidity associated witha major precipitation event, although only 10% of these cellswere viable. The percentage of viable cells generally increasedthrough the stratified period with 50–70% viable cellsin late summer. Overall, an average of 38% of bacterial cellswere viable, with a range from <20 to 70%. Although thesevalues were similar to those found by others, additional patternswere identified that have not been previously observed: a markeddecline in viable cells was found following turbid storm inflowsand increases in the percentage of viable cells occurred duringspring warming and following autumnal mixing events. Althougha modest increase in abundance occurred along the gradient frominflow down-reservoir to the dam, bacterial abundance did notincrease near the dam in a pattern coincident with the commonlyobserved increased algal biomass in the lacustrine portion ofreservoir ecosystems. The increases observed in bacterial viabilitymoving from the inflowing rivers towards the dam and later instratified periods stress the importance of differences in environmentalconditions in time and space in regulating bacterial biomassand development, as well as of shifts that would be anticipatedaccompanying altered hydrological regimes under climatic change.