Production-Consumption of CO₂ in Reservoirs and Lakes in Relation to Plankton Metabolism

Abstract

We present data on metabolism, primary production and respiration, and their relationship to CO₂ effluxes of a three-year study conducted in northeastern Canada, in two distinct boreal regions where large hydroelectric reservoirs have been established. In each region, the youngest and oldest reservoirs were sampled, as well as three to four natural lakes surrounding each reservoir.

The trophic status of all the sampled ecosystems ranged from oligotrophic, in lakes and the oldest (23 and 35 years-old) reservoirs, to mesotrophic in the youngest (1 and 7 years-old) reservoirs. The areal gross primary production (AGP) to areal planktonic respiration (APR) ratio varied from lower than 1 to higher than 1 in any given system. Differences in the AGP/APR ratio were related to season; lower in spring, higher in summer, both in reservoirs and in lakes. Within reservoirs differences in the ratio were also a function of the maximum depth of the sampled station. The AGP/APR ratio tended to be higher in the deeper than in the shallower stations. A very strong relationship (r²=0.93) was found between CO₂ evasive fluxes and the total respiration of the system. The contribution of gross primary production (GPP) to total planktonic respiration (TPR) was higher in lakes (from > 50 to 200%) than in reservoirs. In reservoirs, the % of GPP to TPR varied by < 10% in the spring in the older oligotrophic reservoir, to more than 100% in the 7 year-old mesotrophic reservoir in summer.