The summer metabolic balance in the epilimnion of southeastern Quebec lakes

Abstract

On the basis of data collected in Quebec lakes, del Giorgio and Peters (1994) and Carignan et al. (2000) have come to opposite conclusions regarding the metabolic balance between heterotrophy and autotrophy in lakes in general. In the present study, epilimnetic oxygen and carbon dioxide saturation was measured in 33 lakes from the St. Lawrence Lowlands region of Quebec to examine the extent of epilimnetic net heterotrophy (i.e., O2:CO2 balance) in lakes of different characteristics. We found that ~75% of the lakes were undersaturated with oxygen and supersaturated with CO2. There was a strong negative relationship between the departures of O2 and CO2 from saturation. What has not been noted elsewhere is that oxygen concentrations were negatively related to dissolved organic carbon (DOC) concentration, and, therefore, metabolic gas balances could be predicted from DOC; a value between 4 and 6 mg L−1 DOC corresponds to metabolic equilibrium. Because most of the lakes in del Giorgio and Peters (1994) had DOC concentrations above this threshold and most lakes in Carignan et al. (2000) were below, their apparently contradictory conclusions can be reconciled within a larger general theory. Contrary to studies elsewhere, however, we found that the degree of oxygen undersaturation increased with lake trophic status, expressed either as total phosphorus or nitrogen concentrations.

Magnitude and regulation of bacterioplankton respiratory quotient across freshwater environmental gradients

“…Inland waters are often supersaturated in carbon dioxide (CO 2 ) (del Giorgio et al, 1997;Prairie et al, 2002) and, although covering only 1% of the earth's surface, they seemingly emit CO 2 to the atmosphere at a rate that is of a similar order of magnitude as that of fossil fuel combustion or C uptake by oceans (Battin et al, 2009;Tranvik et al, 2009). Some of these CO 2 emissions originate from BR fueled by terrestrially derived organic C (Karlsson et al, 2007;McCallister and del Giorgio, 2008).…”

Assessing carbon dynamics in natural and perturbed boreal aquatic systems

“…Terrigenous OM is mainly funneled into lakes by rivers and surface runoffs [Schindler et al, 1997] and helps to sustain the aquatic food web through incorporation of DOC into bacterial biomass and/or through its respiration by heterotrophic bacteria [Pace et al, 2004;Berggren et al, 2007;McCallister and del Giorgio, 2008]. Indeed, lakes with DOC concentrations higher than 0.42-0.50 mmol L À1 generally behave as net heterotrophic systems, leading to high pCO 2 and low oxygen supersaturation levels [Prairie et al, 2002]. Increases in the inputs of terrigenous OM into aquatic systems through flooding (e.g., reservoirs impoundment, erection of beaver dams) or wood harvesting on the watershed thus profoundly affect C cycling in aquatic systems [Duchemin et al, 1995[Duchemin et al, , 1999Tremblay et al, 2005].…”

Linking diel patterns in community respiration to bacterioplankton in an oligotrophic high‐elevation lake

“…In unproductive aquatic habitats bacterioplankton biomass can exceed phytoplankton biomass (Simon et al 1992), and bacteria account for a majority of total pelagic community respiration (CR; Biddanda et al 2001). Heterotrophic bacterioplankton respiration is fueled by autochthonous (aquatic-derived) and allochthonous (terrestrially derived) dissolved organic carbon (DOC), the total concentration of which generally predicts the net metabolic balance of a system (Prairie et al 2002). In oligotrophic systems with low concentrations of DOC, rates of respiration tend to be nearly the same as gross primary production (Hanson et al 2003), suggesting a tight coupling between the metabolism of heterotrophic bacterioplankton and phytoplankton.…”