P. Kankaala et al., CARBON BUDGET FOR THE PELAGIC FOOD-WEB OF THE EUPHOTIC ZONE IN A BOREAL LAKE (LAKE-PAAJARVI), Canadian journal of fisheries and aquatic sciences, 53(7), 1996, pp. 1663-1674
A carbon budget for the pelagic euphotic zone of a mesohumic, boreal l
ake was constructed, on the basis of enclosure experiments, in which e
ffects of pulses of humic matter and phosphorus were studied. Although
production of phytoplankton and bacteria was enchanced by additions o
f phosphorus, and of phosphorus and humic matter together, the effects
on zooplankton were less clear. The modest response of metazooplankto
n was partly due to the short time of the experiments, but it was also
due to loss of carbon through respiration in several steps of the mic
robial food chain Protozoans had key roles as grazers in the system; h
eterotrophic nanoflagellates were the most important grazers of bacter
ia, whereas ciliates were more important algal grazers than metazoopla
nkton. Indirect evidence suggested that ciliates formed a considerable
proportion of the food of metazooplankton. The amount of carbon relea
sed through respiration exceeded the sum of that fixed by primary prod
ucers and lost through sedimentation. If the climate change in the bor
eal zone increases loading of nutrients and humic matter into lakes, t
his imbalance between respiration and fixation of carbon can be expect
ed to increase.