Estimation of long-term bacterial respiration and growth efficiency in Lake Kinneret

Semi-annual averaged values of photosynthetic carbon fixation (PCF), community respiration (CR), bacterial productivity (BP) and zooplankton carbon biomass, measured biweekly or monthly, were used to obtain long-term estimates of bacterial respiration (BR) and bacterial growth efficiency (BGE) in Lake Kinneret from 2001 through 2007. We posited that CR=BR+phytoplankton respiration (PR)+zooplankton respiration (ZR). Based on the results of independent experimental series, PR was estimated as 0.3 x gross primary production (GPP) and GPP as 1.5 x PCF. ZR was determined by multiplying zooplankton carbon biomass, measured biweekly, with published respiration rates for major zooplankton groups. From these data, we calculated BR and consequently BGE, determined as BP/(BR+BP). Over the entire study period, BR averaged 49 (+/-10)% of CR and was consistently higher during the first half of the year. Semi-annual averaged BGE ranged from 26% to 53%, mean 39 (+/-9)%. Similar values of BGE were obtained if we did not use the measured values for ZR, but estimated BR+ZR from CR-PR and then assumed that BR ranged from two to three times ZR. The approach outlined in this paper can be useful for determining BGE in aquatic systems where long-term data sets of PCF, CR and BP are available.