Carbon and oxygen dynamics of shallow aquatic systems: Process vectors and bacterial productivity

Torgersen, T.; Branco, B.

doi:10.1029/2007jg000401

Cited by 21 publications

(35 citation statements)

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“…Moreover, there is growing evidence that carbonate precipitation can be linked to NEP in both benthic 18 and planktonic 20 freshwater compartments. However, we lack direct evidence of carbonate precipitation in our lakes, and other factors potentially affecting the relationship between NEP and CO 2 supersaturation such as differential atmospheric exchange and anaerobic metabolism 21 , although unlikely in the surface waters of our deep systems, cannot be ruled out (Supplementary Methods). Therefore, additional direct evidence on the effect of carbonate precipitation on lake CO 2 supersaturation should be obtained to reach a solid conclusion.…”

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Carbonate weathering as a driver of CO2 supersaturation in lakes

et al. 2015

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Most lakes and reservoirs have surface CO 2 concentrations that are supersaturated relative to the atmosphere 1 . The resulting CO 2 emissions from lakes represent a substantial contribution to the continental carbon balance 2-4 . Thus, the drivers of CO 2 supersaturation in lakes need to be understood to constrain the sensitivity of the land carbon cycle to external perturbations 4-6 . Carbon dioxide supersaturation has generally been attributed to the accumulation of inorganic carbon in lakes where respiration exceeds photosynthesis 7,8 , but this interpretation has faced challenges 9-11 . Here we report analyses of water chemistry data from a survey of Spanish reservoirs that represent a range of lithologies, using simple metabolic models. We find that, above an alkalinity threshold of 1 mequiv. l −1 , CO 2 supersaturation in lakes is directly related to carbonate weathering in the watershed. We then evaluate the global distribution of alkalinity in lakes and find that 57% of the surface area occupied by lakes and reservoirs-particularly in tropical and temperate latitudes-has alkalinity exceeding 1 mequiv. l −1 . We conclude that lake inputs of dissolved inorganic carbon from carbonate weathering should be considered for the CO 2 supersaturation of lakes at both regional and global scales.There are two main mechanisms leading to CO 2 supersaturation in lakes and reservoirs: in situ net ecosystem production (NEP) imbalanced towards net heterotrophy 7 (that is, respiration exceeding photosynthesis); and inputs of groundwater or surface water with high dissolved inorganic carbon (DIC) content coming from both weathering of minerals and soil respiration in the watershed 10-14 . Among these, NEP is usually considered to be the main factor driving CO 2 supersaturation in lakes 7,8 . However, most studies relating CO 2 supersaturation to NEP have focused on relatively dilute, low-alkalinity lakes, despite the fact that CO 2 concentration in water is strongly modulated by the carbonate equilibrium (that is, the chemical reactions relating the different forms of DIC). Therefore, we lack conclusive evidence of the impact of NEP on CO 2 supersaturation in a range of systems showing contrasting DIC content.To test how DIC content can drive CO 2 supersaturation and modulate the relationship between NEP and CO 2 concentration, we use data from a nationwide study 15 including 202 measurements of dissolved oxygen (DO), DIC, alkalinity and CO 2 concentration in the surface layer of a set of Spanish reservoirs covering a wide range of DIC content and trophic states (Supplementary Table 1 and Data). We use the observed DO disequilibrium relative to the atmosphere as a surrogate for surface lake NEP, and investigate its impact on observed DIC and CO 2 concentrations considering three metabolic models. The models combine assumptions concerning the DIC loading from the watershed and the effect of lake NEP (Fig. 1a). All three models assume that the DIC generated during weathering of minerals in the watershed (DIC W ) dominates DIC...

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Carbonate weathering as a driver of CO2 supersaturation in lakes

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“…This mass balance on O 2 and TDIC thus includes respiration by fish, invertebrates, etc., as well as TDIC production and any chemical oxygen demand created by microbial processes (see also Torgersen and Branco, 2007). Total error on the calculation of gas exchange corrected O 2 and TDIC is estimated to be order 26% as dominated by assumptions regarding the rates of gas exchange.…”

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confidence: 99%

“…Prior to herbicide application (August 26-31) there is a general multiday progression in the negative O 2 direction. This occurs with indications of a significant bacterial carbon production term (Torgersen and Branco, 2007) as seen by the general multiday progression in a positive CO 2 direction in excess of CO 2 generated by a defined respiration stoichiometry. Clear indications of daytime photosynthesis are visible indicating a functioning primary productivity community producing oxygen in excess of loss via daytime respiration (which includes chemical oxygen demand driven by microbial processes).…”

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confidence: 99%

“…A finer timescale resolution of ecosystem function (order 1 h) can be obtained using the process vector approach defined in Torgersen and Branco (2007). Figure 4A and 4B show the propagation of the process vector (Torgersen and Branco, 2007) before (Fig.…”

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confidence: 99%

“…4B) herbicide application with the time period September 4-8 (herbicide applied September 5) repeated to emphasize the change. Process vectors (Torgersen and Branco, 2007) track net change in both TDIC and O 2 (both gas exchange corrected and whole ecosystem integrated) in (x-axis) O 2 versus (y-axis) TDIC space as a function of time. Using standard stoichiometries for photosynthesis, respiration and multiple microbial metabolisms (see the "windrose" given in Fig.…”

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In Situ Observation of Whole Lake Gross Primary Productivity: Response to and Recovery from Copper Algaecide Application

Torgersen¹

2009

Environmental Engineering Science

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The fortuitous presence of in situ equipment capable of high-resolution (time/space) measures of O 2 and total dissolved inorganic carbon (TDIC) enabled the response and recovery of a small pond to copper algaecide application to be monitored. Algaecide application to the pond significantly impacted the gross primary productivity (GPP) of the pond over a timescale of less than 4 days. By day 3-4 (postapplication), GPP had recovered to preherbicide levels and net ecosystem productivity (NEP) returned to a positive value. This indicated a timescale for copper algaecide impact on GPP of the order 1ϩ day and duration of impact of the order 3 days. Observed timescales for GPP recovery (3-4 days) indicate that algaecide effectiveness is not significantly controlled by mixing processes in this pond but is most likely influenced by the rate of removal of Cu to the sediment and the rate of Cu release from the chelating agent in K-tea. Observed recovery timescales for GPP (3-4 days) occurring during minimal inflow also indicate that significant nutrient recycling (internal loading) occurs to fuel the recovery of GPP. Thus, as an agent for the overall reduction in primary productivity of a polymictic pond ecosystem, a single copper application may not have a significant long-term impact on primary productivity.

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The role of metabolism in modulating CO₂ fluxes in boreal lakes

Bogard

Giorgio

2016

Global Biogeochemical Cycles

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Lake CO2 emissions are increasingly recognized as an important component of the global CO2 cycle, yet the origin of these emissions is not clear, as specific contributions from metabolism and in‐lake cycling, versus external inputs, are not well defined. To assess the coupling of lake metabolism with CO2 concentrations and fluxes, we estimated steady state ratios of gross primary production to respiration (GPP:R) and rates of net ecosystem production (NEP = GPP‐R) from surface water O2 dynamics (concentration and stable isotopes) in 187 boreal lakes spanning long environmental gradients. Our findings suggest that internal metabolism plays a dominant role in regulating CO2 fluxes in most lakes, but this pattern only emerges when examined at a resolution that accounts for the vastly differing relationships between lake metabolism and CO2 fluxes. Fluxes of CO2 exceeded those from NEP in over half the lakes, but unexpectedly, these effects were most common and typically largest in a subset (~30% of total) of net autotrophic lakes that nevertheless emitted CO2. Equally surprising, we found no environmental characteristics that distinguished this category from the more common net heterotrophic, CO2 outgassing lakes. Excess CO2 fluxes relative to NEP were best predicted by catchment structure and hydrologic properties, and we infer from a combination of methods that both catchment inputs and internal anaerobic processes may have contributed this excess CO2. Together, our findings show that the link between lake metabolism and CO2 fluxes is often strong but can vary widely across the boreal biome, having important implications for catchment‐wide C budgets.

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Carbon and oxygen dynamics of shallow aquatic systems: Process vectors and bacterial productivity

Cited by 21 publications

References 41 publications

Carbonate weathering as a driver of CO2 supersaturation in lakes

Carbonate weathering as a driver of CO2 supersaturation in lakes

In Situ Observation of Whole Lake Gross Primary Productivity: Response to and Recovery from Copper Algaecide Application

The role of metabolism in modulating CO₂ fluxes in boreal lakes

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Carbon and oxygen dynamics of shallow aquatic systems: Process vectors and bacterial productivity

Cited by 21 publications

References 41 publications

Carbonate weathering as a driver of CO2 supersaturation in lakes

Carbonate weathering as a driver of CO2 supersaturation in lakes

In Situ Observation of Whole Lake Gross Primary Productivity: Response to and Recovery from Copper Algaecide Application

The role of metabolism in modulating CO2 fluxes in boreal lakes

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The role of metabolism in modulating CO₂ fluxes in boreal lakes