Inorganic Carbon Dynamics Research Articles

Correction: Sources and Dynamics of Inorganic Carbon within the Upper Reaches of the Xi River Basin, Southwest China

[This corrects the article DOI: 10.1371/journal.pone.0160964.].

Dynamics of soil organic and inorganic carbon in the cropland of upper Yellow River Delta, China.

Soil inorganic carbon (SIC) and organic carbon (SOC) are important carbon reservoirs in terrestrial ecosystems. However, little attention was paid to SIC dynamics in cropland. We conducted a survey in the upper Yellow River Delta of North China Plain. We collected 155 soil samples from 31 profiles, and measured SOC, SIC and soluble Ca2+ and Mg2+ contents. Our results showed that mean SOC content decreased from 9.30 g kg−1 near the surface to 2.36 g kg−1 in 80–100 cm whereas mean SIC content increased from 10.48 to 12.72 g kg−1. On average, SOC and SIC stocks over 0–100 cm were 5.73 kg C m−2 and 16.89 kg C m−2, respectively. There was a significantly positive correlation (r = 0.88, P < 0.001) between SOC and SIC in the cropland. We also found that SIC had a significantly positive correlation with both soluble Ca2+ (r = 0.57, P < 0.01) and Mg2+ (r = 0.43, P < 0.05). Our study suggested that increasing SOC might lead to an increase in SIC stocks in the cropland of North China Plain. This study highlights the importance of SIC in the carbon cycle of China’s semi-arid region.

Estimates of ikaite export from sea ice to the underlying seawater in a sea ice–seawater mesocosm

Abstract. The precipitation of ikaite and its fate within sea ice is still poorly understood. We quantify temporal inorganic carbon dynamics in sea ice from initial formation to its melt in a sea ice–seawater mesocosm pool from 11 to 29 January 2013. Based on measurements of total alkalinity (TA) and total dissolved inorganic carbon (TCO2), the main processes affecting inorganic carbon dynamics within sea ice were ikaite precipitation and CO2 exchange with the atmosphere. In the underlying seawater, the dissolution of ikaite was the main process affecting inorganic carbon dynamics. Sea ice acted as an active layer, releasing CO2 to the atmosphere during the growth phase, taking up CO2 as it melted and exporting both ikaite and TCO2 into the underlying seawater during the whole experiment. Ikaite precipitation of up to 167 µmolkg−1 within sea ice was estimated, while its export and dissolution into the underlying seawater was responsible for a TA increase of 64–66 µmolkg−1 in the water column. The export of TCO2 from sea ice to the water column increased the underlying seawater TCO2 by 43.5 µmolkg−1, suggesting that almost all of the TCO2 that left the sea ice was exported to the underlying seawater. The export of ikaite from the ice to the underlying seawater was associated with brine rejection during sea ice growth, increased vertical connectivity in sea ice due to the upward percolation of seawater and meltwater flushing during sea ice melt. Based on the change in TA in the water column around the onset of sea ice melt, more than half of the total ikaite precipitated in the ice during sea ice growth was still contained in the ice when the sea ice began to melt. Ikaite crystal dissolution in the water column kept the seawater pCO2 undersaturated with respect to the atmosphere in spite of increased salinity, TA and TCO2 associated with sea ice growth. Results indicate that ikaite export from sea ice and its dissolution in the underlying seawater can potentially hamper the effect of oceanic acidification on the aragonite saturation state (Ωaragonite) in fall and in winter in ice-covered areas, at the time when Ωaragonite is smallest.

Sources and Dynamics of Inorganic Carbon within the Upper Reaches of the Xi River Basin, Southwest China.

The carbon isotopic composition (δ13C) of dissolved and particulate inorganic carbon (DIC; PIC) was used to compare and analyze the origin, dynamics and evolution of inorganic carbon in two headwater tributaries of the Xi River, Southwest China. Carbonate dissolution and soil CO2 were regarded as the primary sources of DIC on the basis of δ13CDIC values which varied along the Nanpan and Beipan Rivers, from −13.9‰ to 8.1‰. Spatial trends in DIC differed between the two rivers (i.e., the tributaries), in part because factors controlling pCO2, which strongly affected carbonate dissolution, differed between the two river basins. Transport of soil CO2 and organic carbon through hydrologic conduits predominately controlled the levels of pCO2 in the Nanpan River. However, pCO2 along the upper reaches of the Nanpan River also was controlled by the extent of urbanization and industrialization relative to agriculture. DIC concentrations in the highly urbanized upper reaches of the Nanpan River were typical higher than in other carbonate-dominated areas of the upper Xi River. Within the Beipan River, the oxidation of organic carbon is the primary process that maintains pCO2 levels. The pCO2 within the Beipan River was more affected by sulfuric acid from coal industries, inputs from a scenic spot, and groundwater than along the Nanpan River. With regards to PIC, the contents and δ13C values in the Nanpan River were generally lower than those in the Beipan River, indicating that chemical and physical weathering contributes more marine carbonate detritus to the PIC along the Beipan River. The CO2 evasion flux from the Nanpan River was higher than that in the Beipan River, and generally higher than along the middle and lower reaches of the Xi River, demonstrating that the Nanpan River is an important net source of atmospheric CO2 in Southwest China.

The role of in hospite zooxanthellae photophysiology and reef chemistry on elevated pCO2 effects in two branching Caribbean corals: Acropora cervicornis and Porites divaricata

Previous studies suggest uniform reductions in coral calcification under ocean acidification (OA); however, greater tolerance has been observed under natural diel metabolic signals present on reefs. In addition, few studies have examined the role of in hospite zooxanthellae energetics on coral OA tolerance. In this study, we examined zooxanthellae photosynthesis and coral calcification responses using seawater with natural metabolic dissolved inorganic carbon (DIC) dynamics from a fringing back reef on Little Cayman Island, Caribbean. The experimental design included Acropora cervicornis and Porites divaricata microcolonies grown in continuously flowing seawater with (∼1000 μatm) and without (∼500 μatm) CO2 enrichment to year 2100 predicted levels. Calcification rates were measured weekly, while linear extension and zooxanthellae photosynthesis were determined at the termination of the 28 d experiment. Results showed A. cervicornis microcolonies maintained both photosynthesis and calcification under elevated CO2 partial pressure (pCO2) relative to controls. However, photosynthesis and calcification rates of P. divaricata microcolonies were reduced by ∼80 and 20%, respectively, under relatively high [DIC]:[H+] ratios and aragonite saturation states (Ωarag). Porites divaricata calcification response to elevated pCO2 was linked to photophysiological dysfunction of the algal symbiont, an indicator that this species was metabolically depressed under elevated pCO2. In contrast to calcification, linear extension rates were unaffected by pCO2 in both species. Future studies should investigate how elevated pCO2 may compromise zooxanthellae–coral interactions with an emphasis on DIC uptake pathways.

Inorganic carbon dynamics and CO2 flux associated with coal-mine drainage sites in Blythedale PA and Lambert WV, USA

Drainage from coal mines, where carbonate dissolution is driven by sulfuric acid, can result in a net transfer of geologically-bound carbon to the atmosphere. The flux and downstream evolution of dissolved inorganic carbon (DIC) is presented for two coal mine sites that discharge high concentrations of DIC (3.7–4.5 mM C) producing a total flux of DIC from the mine from 13 to 249 kg-C/year (18–364 metric tons of CO2/year). More than 65 % of the total DIC is lost via CO2 evasion with the remaining DIC is exported downstream as dissolved species. The fate of the DIC depends upon the pH of the water which is controlled by evasion of CO2, the concentration of pre-existing alkalinity, carbonate precipitation and dissolution, and metal hydrolysis reactions. The CO2 concentrations and fluxes from the study sites are comparable to those estimated from literature data for other coal mine sites in the Appalachian region. The total flux estimated from a dataset of 140 coal mines was comparable in magnitude to the CO2 emissions from a small coal-fired power plant. The extent of CO2 degassing from mine waters is poorly constrained because (1) flux estimates can be biased low when acid waters are excluded in alkalinity-based estimates; (2) flux estimates can be biased high if non-carbonate alkalinity is present in the mine waters; and (3) mine waters react rapidly following discharge hampering the measurement process. The study sites presented illustrate the impact of coal mining as an anthropogenic influence on carbon cycling; however, more data are necessary to fully estimate the importance of this impact on regional scales.

Two decades of inorganic carbon dynamics along the West Antarctic Peninsula

Abstract. We present 20 years of seawater inorganic carbon measurements collected along the western shelf and slope of the Antarctic Peninsula. Water column observations from summertime cruises and seasonal surface underway pCO2 measurements provide unique insights into the spatial, seasonal, and interannual variability in this dynamic system. Discrete measurements from depths &gt; 2000 m align well with World Ocean Circulation Experiment observations across the time series and underline the consistency of the data set. Surface total alkalinity and dissolved inorganic carbon data showed large spatial gradients, with a concomitant wide range of Ωarag (&lt; 1 up to 3.9). This spatial variability was mainly driven by increasing influence of biological productivity towards the southern end of the sampling grid and meltwater input along the coast towards the northern end. Large inorganic carbon drawdown through biological production in summer caused high near-shore Ωarag despite glacial and sea-ice meltwater input. In support of previous studies, we observed Redfield behavior of regional C / N nutrient utilization, while the C / P (80.5 ± 2.5) and N / P (11.7 ± 0.3) molar ratios were significantly lower than the Redfield elemental stoichiometric values. Seasonal salinity-based predictions of Ωarag suggest that surface waters remained mostly supersaturated with regard to aragonite throughout the study. However, more than 20 % of the predictions for winters and springs between 1999 and 2013 resulted in Ωarag &lt; 1.2. Such low levels of Ωarag may have implications for important organisms such as pteropods. Even though we did not detect any statistically significant long-term trends, the combination of on\\-going ocean acidification and freshwater input may soon induce more unfavorable conditions than the ecosystem experiences today.

Inorganic and organic carbon dynamics in forested soils developed on contrasting geology in Slovenia—a stable isotope approach

Soil carbon dynamics were studied at four different forest stands developed on bedrocks with contrasting geology in Slovenia: one plot on magmatic granodiorite bedrock (IG), two plots on carbonate bedrock in the karstic-dinaric area (CC and CD), and one situated on Pleistocene coalluvial terraces (FGS). Throughfall (TF) and soil water were collected monthly at each location from June to November during 2005–2007. In soil water, the following parameters were determined: T, pH, total alkalinity, concentrations of Ca2+ and Mg2+, dissolved organic carbon (DOC), and Cl− as well as δ13CDIC. On the other hand, in TF, only the Cl− content was measured. Soil and plant samples were also collected at forest stands, and stable isotope measurements were performed in soil and plant organic carbon and total nitrogen and in carbonate rocks. The obtained data were used to calculate the dissolved inorganic carbon (DIC) and DOC fluxes. Statistic analyses were carried out to compare sites of different lithologies, at different spatial and temporal scales. Decomposition of soil organic matter (SOM) controlled by the climate can explain the 13C and 15 N enrichment in SOM at CC, CD, and FGS, while the soil microbial biomass makes an important contribution to the SOM at IG. The loss of DOC at a soil depth of 5 cm was estimated at 1 mol m−2 year−1 and shows no significant differences among the study sites. The DOC fluxes were mainly controlled by physical factors, most notably sorption dynamics, and microbial–DOC relationships. The pH and pCO2 of the soil solution controlled the DIC fluxes according to carbonate equilibrium reactions. An increased exchange between DIC and atmospheric air was observed for samples from non-carbonate subsoils (IG and FGS). In addition, higher δ13CDIC values up to −19.4 ‰ in the shallow soil water were recorded during the summer as a consequence of isotopic fractionation induced by molecular diffusion of soil CO2. The δ13CDIC values also suggest that half of the DIC derives from soil CO2 indicating that 2 to 5 mol m−2 year−1 of carbon is lost in the form of dissolved inorganic carbon at CC and CD after carbonate dissolution. Major difference in soil carbon dynamics between the four forest ecosystems is a result of the combined influence of bedrock geology, soil texture, and the sources of SOM. Water flux was a critical parameter in quantifying carbon depletion rates in dissolved organic and inorganic carbon forms.

The response of inorganic carbon distributions and dynamics to upwelling-favorable winds on the northern Gulf of Mexico during summer

Upwelling-favorable winds and an offshore-distributed Mississippi and Atchafalaya River plume trajectory were observed in summer 2009 in contrast to the mean conditions from 2002 to 2010 (upwelling-unfavorable winds and an alongshore river plume trajectory), a set of conditions which was also observed in summer 2007. The responses of dissolved inorganic carbon (DIC) distributions and dynamics to upwelling-favorable winds are studied by comparing the contrasting conditions between summer 2009 and summer 2007 on the northern Gulf of Mexico. Patterns of surface water partial pressure of CO2 (pCO2), DIC, δ13C in DIC, and total alkalinity (TA) determined in July 2009 and August 2007 were strongly related to river plume trajectories, and differed between the two summers.The slope of the relationship between dissolved oxygen (DO) and DIC in summer 2007 was comparable to the Redfield O/C ratio of 1.3, which was attributed to respiration of organic matter in the bottom water. The slope of the DO and DIC relationship and δ13CDIC values in bottom waters during July 2009 were clearly affected by mixing since their salinities were <35. A three end-member mixing model was used to remove mixing effects in (1) δ13CDIC, to estimate the organic source of respiration, and (2) in DIC concentrations, to calculate DIC removal and release. δ13CDIC results in both summers were consistent with an apparent release of DIC in hypoxic waters (DO less than 2mgL−1) associated with respiration of surface organic matter. The area-weighted surface DIC removal (i.e., biological production) was lower in 2009 than in 2007 on the shelf, as the plume was distributed offshore. The release of DIC in bottom waters was higher over the shelf in 2009 and was surmised to be related to stronger mixing, which was favorable for the DO supply for respiration. Overall, surface waters on the continental shelf in the region of study in July 2009 acted as a weak CO2 source to the atmosphere, but a weak CO2 sink in August 2007. We contend that the inorganic carbon distribution and concentrations on the shelf were related to regional wind forcing, through its influence on the distribution of coastal currents and plume trajectories and their subsequent impact on biogeochemical processes.

Temporal dynamics of groundwater-dissolved inorganic carbon beneath a drought-affected braided stream: Platte River case study

Impacts of environmental changes on groundwater carbon cycling are poorly understood despite their potentially high relevance to terrestrial carbon budgets. This study focuses on streambed groundwater chemistry during a period of drought-induced river drying and consequent disconnection between surface water and groundwater. Shallow groundwater underlying vegetated and bare portions of a braided streambed in the Platte River (Nebraska, USA) was monitored during drought conditions in summer 2012. Water temperature and dissolved inorganic carbon (dominated by HCO3−) in streambed groundwater were correlated over a 3 month period coinciding with a decline in river discharge from 35 to 0 m3 s−1. Physical, chemical, and isotopic parameters were monitored to investigate mechanisms affecting the HCO3− trend. Equilibrium thermodynamic modeling suggests that an increase of pCO2 near the water table, coupled with carbonate mineral weathering, can explain the trend. Stronger temporal trends in Ca2+ and Mg2+ compared to Cl− are consistent with carbonate mineral reequilibria rather than evaporative concentration as the primary mechanism of the increased HCO3−. Stable isotope trends are not apparent, providing further evidence of thermodynamic controls rather than evaporation from the water table. A combination of increased temperature and O2 in the dewatered portion of the streambed is the most likely driver of increased pCO2 near the water table. Results of this study highlight potential linkages between surface environmental changes and groundwater chemistry and underscore the need for high-resolution chemical monitoring of alluvial groundwater in order to identify environmental change impacts.

Inorganic carbon dynamics of melt-pond-covered first-year sea ice in the Canadian Arctic

Abstract. Melt pond formation is a common feature of spring and summer Arctic sea ice, but the role and impact of sea ice melt and pond formation on both the direction and size of CO2 fluxes between air and sea is still unknown. Here we report on the CO2–carbonate chemistry of melting sea ice, melt ponds and the underlying seawater as well as CO2 fluxes at the surface of first-year landfast sea ice in the Resolute Passage, Nunavut, in June 2012. Early in the melt season, the increase in ice temperature and the subsequent decrease in bulk ice salinity promote a strong decrease of the total alkalinity (TA), total dissolved inorganic carbon (TCO2) and partial pressure of CO2 (pCO2) within the bulk sea ice and the brine. As sea ice melt progresses, melt ponds form, mainly from melted snow, leading to a low in situ melt pond pCO2 (36 μatm). The percolation of this low salinity and low pCO2 meltwater into the sea ice matrix decreased the brine salinity, TA and TCO2, and lowered the in situ brine pCO2 (to 20 μatm). This initial low in situ pCO2 observed in brine and melt ponds results in air–ice CO2 fluxes ranging between −0.04 and −5.4 mmol m−2 day−1 (negative sign for fluxes from the atmosphere into the ocean). As melt ponds strive to reach pCO2 equilibrium with the atmosphere, their in situ pCO2 increases (up to 380 μatm) with time and the percolation of this relatively high concentration pCO2 meltwater increases the in situ brine pCO2 within the sea ice matrix as the melt season progresses. As the melt pond pCO2 increases, the uptake of atmospheric CO2 becomes less significant. However, since melt ponds are continuously supplied by meltwater, their in situ pCO2 remains undersaturated with respect to the atmosphere, promoting a continuous but moderate uptake of CO2 (~ −1 mmol m−2 day−1) into the ocean. Considering the Arctic seasonal sea ice extent during the melt period (90 days), we estimate an uptake of atmospheric CO2 of −10.4 Tg of C yr−1. This represents an additional uptake of CO2 associated with Arctic sea ice that needs to be further explored and considered in the estimation of the Arctic Ocean's overall CO2 budget.

Drivers of inorganic carbon dynamics in first‐year sea ice: A model study

AbstractSea ice is an active source or a sink for carbon dioxide (CO2), although to what extent is not clear. Here, we analyze CO2 dynamics within sea ice using a one‐dimensional halothermodynamic sea ice model including gas physics and carbon biogeochemistry. The ice‐ocean fluxes, and vertical transport, of total dissolved inorganic carbon (DIC) and total alkalinity (TA) are represented using fluid transport equations. Carbonate chemistry, the consumption, and release of CO2 by primary production and respiration, the precipitation and dissolution of ikaite (CaCO3·6H2O) and ice‐air CO2 fluxes, are also included. The model is evaluated using observations from a 6 month field study at Point Barrow, Alaska, and an ice‐tank experiment. At Barrow, results show that the DIC budget is mainly driven by physical processes, wheras brine‐air CO2 fluxes, ikaite formation, and net primary production, are secondary factors. In terms of ice‐atmosphere CO2 exchanges, sea ice is a net CO2 source and sink in winter and summer, respectively. The formulation of the ice‐atmosphere CO2 flux impacts the simulated near‐surface CO2 partial pressure (pCO2), but not the DIC budget. Because the simulated ice‐atmosphere CO2 fluxes are limited by DIC stocks, and therefore &lt;2 mmol m−2 d−1, we argue that the observed much larger CO2 fluxes from eddy covariance retrievals cannot be explained by a sea ice direct source and must involve other processes or other sources of CO2. Finally, the simulations suggest that near‐surface TA/DIC ratios of ∼2, sometimes used as an indicator of calcification, would rather suggest outgassing.

Organic and inorganic carbon dynamics in a karst aquifer: Santa Fe River Sink‐Rise system, north Florida, USA

AbstractSpatiotemporal variations in dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), major ions concentrations and other geochemical parameters including stable carbon isotopes of DIC (δ13CDIC), were measured in surface water and deep and shallow well water samples of the Santa Fe River Sink‐Rise eogenetic karst system, north Florida, USA. Three end‐member water sources were identified: one DOC‐rich/DIC‐poor/δ13CDIC‐depleted, one DOC‐poor/DIC‐rich/δ13CDIC‐enriched, and one enriched in major ions. Given their spatiotemporal distributions, they were presumed to represent soil water, upper aquifer groundwater, and deep aquifer water sources, respectively. Using assumed ratios of Na+, Cl, and SO42− for each end‐member, a mixing model calculated the contribution of each water source to each sample. Then, chemical effects of biogeochemical reactions were calculated as the difference between those predicted by the mixing model and measured species concentrations. In general, carbonate mineral dissolution occurred throughout the Sink‐Rise system, surface waters were net autotrophic and the subsurface was in metabolic balance, i.e., no net DOC or DIC production or consumption. However, there was evidence for chemolithoautotrophy, perhaps by hydrogen oxidizing microbes, at some deep aquifer sites. Mineralization of this autochthonous natural dissolved organic matter (NDOM) led to localized carbonate dissolution as did surface water‐derived NDOM supplied to shallow well sites during the highest flow periods. This study demonstrates linkages between hydrology, abiotic and microbial processes and carbon dynamics and has important implications for groundwater quality, karst morphologic evolution, and hydrogeologic projects such as aquifer storage and recovery in karst systems.

Coupled oxygen and dissolved inorganic carbon dynamics in coastal ocean and its use as a potential indicator for detecting water column oil degradation

Following the disastrous 2010 Deepwater Horizon oil spill, numerous studies have been carried out to investigate the impact of the oil spill on a variety of environments. However, it is currently unknown whether the spilled oil transported to the coastal ocean has caused any discernible perturbation to the inorganic chemistry of the water column. In this work we compared and contrasted a multiyear dataset (2006–2012) collected in the northern Gulf of Mexico continental shelf, an area subject to frequent summer hypoxia. Before and after the oil spill, apparent oxygen utilization (AOU) and dissolved inorganic carbon (DIC) in bottom water samples all showed consistent relationship that was close to Redfield reaction stoichiometry. However, we observed a possible oil degradation signal in the bottom waters during a July 2010 cruise as manifested by a significant deviation from all other years in the relationship between AOU and DIC. Based on stable carbon isotope analysis of bottom water DIC from a July 2011 cruise in the same region, oil carbon degradation in the water column was likely negligible and the shelf water had returned to the pre-spill conditions.

Tidal downwelling and implications for the carbon biogeochemistry of cold‐water corals in relation to future ocean acidification and warming

Cold-water coral (CWC) reefs are recognized as ecologically and biologically significant areas that generate habitats and diversity. The interaction between hydrodynamics and CWCs has been well studied at the Mingulay Reef Complex, a relatively shallow area of reefs found on the continental shelf off Scotland, UK. Within 'Mingulay Area 01' a rapid tidal downwelling of surface waters, brought about as an internal wave, is known to supply warmer, phytoplankton-rich waters to corals growing on the northern flank of an east-west trending seabed ridge. This study shows that this tidal downwelling also causes short-term perturbations in the inorganic carbon (CT ) and nutrient dynamics through the water column and immediately above the reef. Over a 14h period, corresponding to one semi-diurnal tidal cycle, seawater pH overlying the reef varied by ca. 0.1 pH unit, while pCO2 shifted by >60μatm, a shift equivalent to a ca. 25year jump into the future, with respect to atmospheric pCO2 . During the summer stratified period, these downwelling events result in the reef being washed over with surface water that has higher pH, is warmer, nutrient depleted, but rich in phytoplankton-derived particles compared to the deeper waters in which the corals sit. Empirical observations, together with outputs from the European Regional Shelf Sea Ecosystem Model, demonstrate that the variability that the CWC reefs experience changes through the seasons and into the future. Hence, as ocean acidification and warming increase into the future, the downwelling event specific to this site could provide short-term amelioration of corrosive conditions at certain times of the year; however, it could additionally result in enhanced detrimental impacts of warming on CWCs. Natural variability in the CT and nutrient conditions, as well as local hydrodynamic regimes, must be accounted for in any future predictions concerning the responses of marine ecosystems to climate change.

Distribution of dissolved inorganic carbon and net ecosystem production in a tropical brackish water lagoon, India

Chilika, the second largest lagoon of the world was studied for 2 years on monthly basis to understand the dissolved inorganic carbon (DIC) dynamics through mass balance approach. The study revealed that during the low flow period the lagoon is net autotrophic (Net ecosystem production (NEP)=33Mgd−1) resulting in a sink of DIC whereas remains net heterotrophic during the high flow period (NEP=−3099Mgd−1). DIC concentration significantly varied with respect to seasons as well as sectors owing to fresh water discharge and biological activity of both pelagic and benthic communities. Sectoral mixing model showed negative residuals (sink of DIC) in all sectors during low flow, attributable to primary production (PP) as evidenced by strong correlation with residuals (r=−0.51, p<0.05). During high flow, DIC residuals of the entire lagoon (except southern sector) were positive (source of DIC) possibly due to bacterial mineralization as evidenced by δ13CDIC isotopic signature. The estimated net community production (NCP) in pelagic compartment was 14mgCm−2d−1 during the low flow period. and −148mgCm−2d−1 during high flow indicated dominating community respiration. The lagoon sediment acted as a net source of DIC throughout the study period.

Fluctuating water levels control water chemistry and metabolism of a charophyte‐dominated pond

Summary To investigate seasonal variability and importance of environmental drivers of ecosystem metabolism in a shallow pond characterised by low and fluctuating water depth, clear water and shortage of nutrients, we measured primary production and respiration during May–September and examined their relationships to environmental parameters (light, temperature and pH). Using a combination of free water measurements of O2, pH, temperature and conductivity, in situ mesocosm and laboratory bottle experiments, we documented extreme daily variations in environmental variables (e.g. 0–700 mmol O2 m−3, pH 7.5–9.5, 18–32 °C) and high and variable areal rates of gross primary production (GPP, 30–316 mmol O2 m−2 day−1) and community respiration (R, 26–318 mmol O2 m−2 day−1). These rates of benthic charophytes under oligotrophic conditions are comparable to those obtained by pelagic phytoplankton communities under highly eutrophic conditions. By using sediment resources, benthic charophytes can achieve high biomasses and high metabolic rates. Pond metabolism reflected the physiology of the dominant charophyte, with light‐saturated photosynthesis occurring during 55% of the light hours. Experiments and photosynthetic models showed inorganic carbon limitation of GPP at pHs above 9.5 during mid‐summer periods of low water levels, while R was strongly influenced by temperature. According to open water measurements of O2, the pond was net autotrophic (mean NEP = 12 ± 13 (SD) mmol O2 m−2 day−1) but net heterotrophic when based on dissolved inorganic carbon (DIC) dynamics (10 ± 29 mmol CO2 m−2 day−1), suggesting that the significant input of DIC in inflowing water from the surrounding limestone soils mimics elevated respiration.

Influence of Seaweed Aquaculture on Marine Inorganic Carbon Dynamics and Sea‐air CO2 Flux

AbstractOn the basis of field data measured during four cruises from April 2011 to January 2012, spatial and seasonal variations of CO2 dynamics and aqueous pCO2 were investigated in the seaweed aquaculture area, Lidao town, China. Results showed that the mean annual concentrations of dissolved inorganic carbon (DIC), HCO3−, CO32−, and CO2 were 2024.79 ± 146.96, 1842.41 ± 132.13, 170.02 ± 42.82, and 12.35 ± 2.52 µmol/L, respectively. There were no significant differences between areas in concentrations of DIC and HCO3− (P &gt; 0.05), while the differences for the concentration of CO2 was very significant (P &lt; 0.01). The mean annual values of aqueous pCO2 and sea‐air CO2 flux were 287.80 ± 37.90 µatm and −32.71 ± 17.23 mmol/m2/d, respectively. There were very significant differences (P &lt; 0.01) for aqueous pCO2 and sea‐air CO2 flux not only between different areas, but also between different seasons. The buffer factor β indicates that, inside the seaweed area, inorganic carbon dynamics are mainly influenced by photosynthesis and respiration process.

Inorganic and organic carbon dynamics in a limed acid soil are mediated by plants

Lime is commonly used to overcome soil acidification in agricultural production systems; however, its impact on inorganic and organic soil carbon dynamics remains largely unknown. In a column experiment, we monitored rhizosphere effects on lime dissolution, CO2 effluxes, and the concentrations of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) in leachate from an acidic Kandosol. The experiment consisted of four treatments viz: soil only (control), soil + lime, soil + wheat, and soil + lime + wheat. We measured CO2-C effluxes at 7, 43 and 98 days after planting (DAP) and leachate was collected at 56 and 101 DAP. The soil CO2-C efflux rate increased significantly with lime addition at 7 and 43 DAP compared to control. At 43 DAP, the largest increase in CO2-C effluxes was observed in the lime + wheat treatment. However, at 98 DAP similar CO2-C effluxes were observed from wheat and lime + wheat treatments, suggesting that most of the lime was dissolved in the lime + wheat treatment. Both DOC and DIC concentrations in the leachate increased significantly with lime and wheat only treatments (cf. control). In contrast to DOC, there was an increase in the DIC concentration in the soil leachate from lime + wheat treatment columns at 101 DAP (significant wheat × lime interaction), thus, accentuating the pronounced role of wheat roots. We conclude that plant mediated dissolution of lime increased the concentration of DIC in the soil leachate, while both liming and presence of plants enhanced DOC leaching.

Budgets of organic and inorganic carbon in a Mediterranean coastal lagoon dominated by submerged vegetation

In this article, we studied the fluxes of organic and inorganic (DIC) carbon in a coastal lagoon dominated by highly productive macrophyte meadows (Albufera des Grau, Balearic Islands). Seasonal and annual carbon budgets were performed from estimates of whole-system fluxes, and the fate of organic matter production was evaluated through a stable isotope exploration of the food web. The results showed an extremely intense cycling of DIC, with a turnover between 65 and 13 times faster than water turnover. The metabolic fluxes were the main contributors to the seasonal and annual DIC budgets, which were secondarily affected by calcite precipitation, atmospheric exchange and hydrological fluxes. The inorganic carbon dynamics was strongly determined by the seasonal cycle of the meadows. Accordingly the air–water CO2 flux shifted seasonally, and the lagoon was a sink of atmospheric CO2 during the vegetated period and a source during the period without macrophytes. The high macrophytic production played a minor role in the lagoon food web, which apparently relied on phytoplanktonic or allochthonous organic matter. A fast decomposition of macrophytic biomass appeared to be the main destiny of the annual macrophytic production, which was only secondarily buried in the sediments.