ThepCO₂in boreal lakes: Organic carbon as a universal predictor?

Abstract

[1] During the past two decades, it has become evident that a majority of lakes are net conduits of CO 2 to the atmosphere. This insight has implications both for lake metabolism per se and for assessing the role of lakes in the global C cycle. The concentration of dissolved organic carbon (DOC), which constitutes >90% of the total organic carbon (TOC), has been identified as a key driver of partial pressure of CO 2 (pCO 2 ). A crucial question is whether one may identify global relationships in the DOC-pCO 2 relationship in lakes or whether this has to be determined regionally or locally. A second major aspect is how to best predict CO 2 as a function of DOC. Based on a survey of pCO 2 and a range of lake and catchment variables in 112 lakes, we support the view that DOC is by far the most important determinant of pCO 2 while groundwater influx has a minor contribution. Contrary to expectations, total phosphorus (P) also apparently contributed positively to pCO 2 , owing to the fact that most P in these lakes is on the form of allochthonously organic P, and thus correlates strongly with DOC. Physical principles dictate that even a lake completely devoid of DOC should have a nonzero pCO 2 . This is not reflected in power models, which imply that the pCO 2 approaches zero with zero DOC. Based on this study as well as published data on DOC-pCO 2 relationships, we argue that identity link gamma-generalized linear models are appropriate for predicting pCO 2 in lakes and that their application makes it possible to reach reasonably accurate global models for how pCO 2 relates to DOC and other environmental factors.

Lake‐size dependent physical forcing drives carbon dioxide and methane effluxes from lakes in a boreal landscape

“…1300 m) than lakes in our study (cf. Table 1), Larsen et al (2011) found TOC concentration (range 0.25-24.5, mean 3.9 mg L 21 ) to be the best predictor (R 2 5 0.73) of partial pressure of carbon dioxide (P CO 2 ), but lake area as a single predictor did not explain the variability of P CO 2 . We found a strong relationship between CH 4 and CO 2 concentrations and lake-area-related stability, especially during the summer stratification in the lakes located in the boreal forest area in a flat landscape (maximum altitude difference , 71 m).…”

“…The significant correlation between CO 2 and TOC concentrations has been reported for several lakes and regions, but the variance of CO 2 explained (R 2 ) by TOC or dissolved organic carbon has varied from , 10% (Kortelainen et al 2006) up to 70% (Larsen et al 2011). In 112 Norwegian lakes sampled in October and located within a greater range of altitude (.…”

“…Thus, in many recent analyses of lake-rich landscapes, the role of small lakes has received much attention, because the small headwater lakes are more typically characterized by higher concentrations of allochthonous organic carbon than the larger lowland lakes (Xenopoulos et al 2003;Hanson et al 2007;Einola et al 2011). In the boreal region, high fluxes of total organic carbon (TOC), originating mainly from peatland and forested catchments (Kortelainen 1993;Humborg et al 2010), are among the most important factors contributing to CO 2 supersaturation and oxygen consumption in the lake water columns and sediments (Salonen et al 1983;Larsen et al 2011). As a result of anaerobic decomposition of organic matter, high concentrations of CH 4 are typical in eutrophic lakes with an anoxic hypolimnion but also in sheltered forest lakes, which likewise develop marked and prolonged hypolimnetic anoxia.…”

Magnitude and regulation of bacterioplankton respiratory quotient across freshwater environmental gradients

“…These patterns suggest that the net metabolic balance of freshwater ecosystems is not only related to their nutrient and organic matter inputs, but also to the nature of dominant pools of organic carbon that are consumed and respired by pelagic bacteria. Knowledge of the character of these pools may, in turn, contribute to understanding of why lakes in different regions differ in their relationships between DOC and pCO 2 (Larsen et al, 2011). The fundamental role of substrate control of bacterial RQ and community metabolism was further highlighted by the Biolog results, showing that bacterial communities in high RQ systems were characterized by their capacity to degrade oxidized organic acids, whereas communities in low RQ systems were optimized for degrading reduced compounds, such as lipids (Figure 4c).…”

Environmental Impacts—Lake Ecosystems

“…DOC thus has negative impacts on primary producers both by competing for photons and by stimulating their major nutrient competitors. Increased levels of terrestrially-derived DOC in concert with reduced availability of inorganic phosphorus in lakes may shift systems further towards net heterotrophy and thus a net CO 2 release (Sobek et al 2003;Larsen et al 2011c).…”