Pelagic Metabolism in Three Young Boreal Reservoirs (La Romaine Complex) and its Influence on CO2 Dynamics
Abstract
Most reservoirs to date have been shown to be net sources of CO2 to the atmosphere, and although these emissions have been generally associated to the decomposition of organic C pools in the flooded soils and vegetation, the origin of the excess CO2 has seldom been explored. The balance between catabolic and anabolic metabolism in a reservoir, as well as burial of terrestrially-derived organic C and inputs of soil-derived CO2, will determine if they act as net sources or sinks of carbon, and also the magnitude of the source or sink function. Here we focus on the metabolic component, and in particular, we explore the potential contribution of pelagic metabolism to the observed patterns in surface water CO2 in three young boreal hydroelectric reservoirs along La Romaine River in Northeastern Québec. Concentrations and fluxes of CO2 and CH4 have been monitored since flooding of the first reservoir, together with ancillary environmental data that allow for the construction of detailed C balances. Here we present preliminary results for two years, where we estimated pelagic gross primary production (GPP), respiration (R) and the resulting net ecosystem production (NEP) for the ice-free period, using an approach that combines the concentration and isotopic signatures of oxygen in surface waters. This is a valuable method to investigate metabolism as it avoids long incubations and allow to carry metabolic measurements in time and space at remote and inaccessible systems. Metabolic rates were variable within and among reservoirs, with no difference in either GPP nor R among reservoirs, or among sampled campaigns or years. In most sample occasions, R was higher than GPP, indicating net system heterotrophy and that pelagic metabolism was a contributor to the CO2 supersaturation. Both GPP and R were positively related to phosphorous concentrations, but not to nitrogen, suggesting that P remobilization could have a major impact in system metabolism. R and NEP were strongly related to CO2 partial pressure, and on average, pelagic NEP explained between 20 and 35% of the observed CO2 emissions in these reservoirs. These results suggest that the processing and mineralization within surface waters of organic matter derived from either the flooded soils or from the catchment plays an important role in sustaining reservoir CO2 emissions.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMH114.0001B
- Keywords:
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- 3322 Land/atmosphere interactions;
- ATMOSPHERIC PROCESSES;
- 0458 Limnology;
- BIOGEOSCIENCES;
- 0466 Modeling;
- BIOGEOSCIENCES;
- 1807 Climate impacts;
- HYDROLOGY