水体无机碳条件对常见沉水植物生长和生理的影响

为了解水华引起的水体无机碳变化对沉水植物生长的影响,对8种沉水植物:金鱼藻、穗花狐尾藻、篦齿眼子菜、光叶眼子菜、微齿眼子菜、伊乐藻、菹草和黑藻在不同无机碳浓度下的生物量、株高、叶绿素以及光合和呼吸速率进行了比较研究.结果表明8种沉水植物均能利用HCO3-作为光合无机碳源,在1.5 mmoL/L外源HCO3-浓度下能促进金鱼藻、菹草和伊乐藻的生长,提高其光合速率;在2.5 mmol/L外源HCO3-浓度下能促进狐尾藻、光叶眼子菜、黑藻、微齿眼子菜和蓖齿眼子菜的生长,提高其光合速率.在CO32-为优势碳源时,8种沉水植物表现出不同的适应性,发现微齿眼子菜、篦齿眼子菜和黑藻在整个实验范围内生长未受抑制,且在不同浓度下表现生长和光合速率的促进,说明这三种沉水植物对[HCO3-]/[CO32-]比值和pH具有较广适应范围.而当CO32-成为优势碳源时,金鱼藻和伊乐藻的生长受到抑制,狐尾藻、菹草和光叶眼子菜均死亡,表明[HCO3-]/[CO32-]比值和pH是这5种沉水植物生长的重要限制因子.     

Particulate organic and dissolved inorganic carbon stable isotopic compositions in Taylor Valley lakes,Antarctica: the effect of legacy

In perennially ice-covered lakes of Taylor Valley, Antarctica, “legacy”, a carryover of past ecosystem events, has primarily been discussed in terms of nutrient and salinity concentrations and its effect on the current ecology of the lakes. In this study, we determine how residual pools of ancient carbon affect the modern carbon abundance and character in the water columns of Lakes Fryxell, Hoare, and Bonney. We measure the stable carbon isotopic compositions and concentrations of particulate organic carbon (POC) and dissolved inorganic carbon (DIC) in the water column of these lakes over four seasons (1999–2002). These data are presented and compared with all the previously published Taylor Valley lacustrine carbon stable isotopic data. Our results show that the carbon concentrations and isotopic compositions of the upper water columns of those lakes are controlled by modern processes, while the lower water columns are controlled to varying degrees by inherited carbon pools. The water column of the west lobe of Lake Bonney is dominated by exceptionally high concentrations of DIC (55,000–75,000 μmol l⁻¹) reflecting the long period of ice-cover on this lake. The east lobe of Lake Bonney has highly enriched δ¹³C_DIC values resulting from paleo-brine evaporation effects in its bottom waters, while its high DIC concentrations provide geochemical evidence that its middle depth waters are derived from West Lake Bonney during a hydrologically connected past. Although ancient carbon is present in both Lake Hoare and Lake Fryxell, the δ¹³C_DIC values in bottom waters suggest dominance by modern primary productivity-related processes. Anaerobic methanogenesis and methanotrophy are also taking place in the lower water column of Lake Fryxell with enough methane, oxidized anaerobically, to contribute to the DIC pool. We also show how stream proximity and high flood years are only a minor influence on the carbon isotopic values of both POC and DIC. The Taylor Valley lake system is remarkably stable in both inter-lake and intra-lake carbon dynamics. Handling editor: K. Martens     

Controls of streamwater dissolved inorganic carbon dynamics in a forested watershed

Iinvestigated controls of stream dissolved inorganic carbon (DIC) sources andcycling along a stream size and productivity gradient in a temperate forestedwatershed in northern California. Dissolved CO₂ (CO_2(aq))dynamics in heavily shaded streams contrasted strongly with those of larger,open canopied sites. In streams with canopy cover > 97%, CO_{2 (aq)}was highest during baseflow periods (up to 540 M) and wasnegatively related to discharge. Effects of algal photosynthesis on CO_2(aq) were minimal and stream CO_{2 (aq)} was primarily controlledby groundwater CO_{2 (aq)} inputs and degassing losses to theatmosphere. In contrast to the small streams, CO_{2 (aq)} in larger,open-canopied streams was often below atmospheric levels at midday duringbaseflow and was positively related to discharge. Here, stream CO_2(aq) was strongly influenced by the balance between autotrophic andheterotrophic processes. Dynamics of HCO₃ ^– werelesscomplex. HCO₃ ^– and Ca²⁺ were positivelycorrelated, negatively related to discharge, and showed no pattern with streamsize. Stable carbon isotope ratios of DIC (i.e. ¹³C DIC)increased with stream size and discharge, indicating contrasting sources of DICto streams and rivers. During summer baseflows, ¹³C DIC were¹³C-depleted in the smallest streams (minimum of–17.7) due to the influence of CO_{2 (aq)} derived frommicrobialrespiration and HCO₃ ^– derived from carbonateweathering. ¹³C DIC were higher (up to –6.6)inthe larger streams and rivers due to invasion of atmospheric CO₂enhanced by algal CO_{2 (aq)} uptake. While small streams wereinfluenced by groundwater inputs, patterns in CO_{2 (aq)} and evidencefrom stable isotopes demonstrate the strong influence of stream metabolism andCO₂ exchange with the atmosphere on stream and river carbon cycles.     

Sources and fates of dissolved organic carbon in lakes as determined by whole-lake carbon isotope additions

Four whole-lake inorganic ¹³C addition experiments were conducted in lakes of differing trophic status. Inorganic ¹³C addition enriched algal carbon in ¹³C and changed the C-DOC by +1.5‰ to +9.5‰, depending on the specific lake. This change in C-DOC represented a significant input of algal DOC that was not completely consumed by bacteria. We modeled the dynamics in C-DOC to estimate the fluxes of algal and terrestrial carbon to and from the DOC pool, and determine the composition of the standing stock. Two experiments in lightly stained, oligotrophic lakes indicated that algal production was the source of about 20% of the DOC pool. In the following year, the experiment was repeated in one of these lakes under conditions of nutrient enrichment, and in a third, more humic lake. Algal contributions to the DOC pool were 40% in the nutrient enriched lake and 5% in the more humic lake. Spectroscopic and elemental analyses corroborated the presence of increased algal DOC in the nutrient enriched lake. Natural abundance measurements of the C of DOC in 32 lakes also revealed the dual contributions of both terrestrial and algal carbon to DOC. From these results, we suggest an approach for inferring the contribution of algal and terrestrial DOC using easily measurable parameters.     

The uptake of inorganic carbon by freshwater plants

Abstract. The uptake of bicarbonate for photosynthetic assimilation by charophyte plants uses a chemiosmotic mechanism involving primary outward active transport of H⁺ in 'acid zones' of the membrane, and passive H⁺ re-entry in spatially separate 'alkaline' zones. In the process large electric currents circulate in the medium, and large local pH changes occur; bicarbonate ions, diffusing inwards across the unstirred layer of medium, encounter a number of competing mechanisms for the transfer of the carbon across the membrane. These are:

• i.

  transport of H₂CO₃ by diffusion
• ii.

  transport of CO₂ by diffusion; or
• iii.

  co-transport of HCO₃ and H⁺.

The decision amongst these mechanisms is not yet possible. There are parallels between the charophytes and aquatic angiosperms that are indicated, and contrasts with the chlorophytes.     

Competitive dominance of the cyanobacterium Microcystis aeruginosa in nutrient-rich culture conditions with special reference to dissolved inorganic carbon uptake

The aim of the present study was to determine what factors contribute to the competitive advantage of cyanobacteria in eutrophic conditions. Mixed species batch culture experiments were conducted at three pHs (8.2, 8.8, 10.2) and irradiances (30, 90, 180 μmol photons m^?2 s^_1) between Microcystis aeruginosa Kützing and Staurastrum dorsidentiferum W. et West or Synedra ulna (Nitzsch) Ehrenberg, which always resulted in the dominance of M. aeruginosa. The final yields of competitors were often significantly lower than when cultured singly. The dominance of the surface‐loving M. aeruginosa appears to be related to its advantageous C0₂ uptake. To clarify the importance of dissolved inorganic carbon (DIC) as a selective factor, the effect of aeration was examined with M. aeruginosa. The growth of M. aeruginosa quickly stopped in nonaerated conditions, while it continued growing throughout the culture when aerated. This result indicates that DIC limitation easily occurs in static conditions and the viewpoint of C0₂ exchange efficiency would be helpful in discussing the competitive advantage of M. aeruginosa. When the three species were cultured at various ratios of surface area to volume (s/v), postulating it as an index of the gas exchange efficiency, the increases in population densities strongly correlated with s/v, and the relationships between the specific growth rate and s/v corresponded well to a Monod type saturation function. We found that M. aeruginosa had the lowest half‐saturation constant among the three, reflecting its high affinity for DIC.     

Escape of volcanic gas into shallow groundwater systems at Unzen Volcano (Japan): evidence from chemical and stable carbon isotope compositions of dissolved inorganic carbon

 Chemical and stable carbon isotopic analyses of dissolved inorganic carbon (DIC) were carried out for groundwater samples collected from cold springs and shallow wells in the Unzen volcanic region in 1999 and 2000. All of the data sets plotted on the carbon isotope ratio (δ¹³C) vs 1/DIC diagram can be explained by mixing of volcanic CO₂ with DIC equilibrated with soil CO₂. Groundwater DIC showing a high mixing ratio of volcanic CO₂ appears to have a tendency to distribute along two major faults near the activity center of the 1990–1995 eruption. This suggests that these faults are escape routes of volcanic CO₂ diffused into the volcanic edifice. The total flux of the volcanic DIC discharged from the cold springs is shown to be one to two orders of magnitude lower than the roughly estimated flux of volcanic CO₂ discharged from the summit during the eruptive period. Received: November 10, 2001 / Accepted: June 6, 2002 Acknowledgments The Unzen Scientific Drilling Project, Ministry of Education, Culture, Sports, Science and Technology (Japan), provided funding. We acknowledge G. Lyon and W. Gooley for stable carbon isotope measurement, K. Amita for DIC analysis, and students of Kyoto University and Okayama University of Science for assistance in field work. Correspondence to:S. Ohsawa     

Microbial control of dissolved organic carbon in lakes: research for the future

The dissolved organic carbon (DOC) of lakes dominates any budget of organic carbon in these systems. Limnologists are still limited by techniques and particularly by the lack of measurements of rates of microbial transformation and use of this DOC. There are now four different approaches to the study of the microbial control of DOC in lakes. The first is through measurements of the total DOC. Recent advances in measurement with high temperature combustion will likely lead to higher and more consistent measurements in freshwaters than previously. It is possible that a biologically active fraction may be identified. The second approach is through measurements of microbial incorporation and respiration of ¹⁴C-labeled organic matter. The kinetics of this process are well known but advances in measurement of the size of the substrate pool are still being made. The third approach is to use bacterial growth in batch or continuous flow experiments in order to understand how much of the total DOC can be decomposed by microbes. The assay in this approach may be microbial growth (thymidine incorporation, biomass changes) or change in the DOC (total concentrations, specific compounds, or fractions of the DOC by molecular weight). These methods are promising but are not developed enough for routine use. For example, growth measurements in the laboratory are all subject to experimental artifacts caused by changes in the DOC and in the bacterial populations. Finally, the fourth approach is through the use of isotopes of the natural DOC. In the sea this approach has given the age of the bulk DOC (¹⁴C data). In freshwaters it has great potential for differentiating between bacterial use of terrestrial DOC vs. use of algal-derived DOC (13C data). Stable isotopes are also useful for experimentally labeling DOC produced by algae and following the use of this material by bacteria.     

The influence of wetlands, decaying organic matter, and stirring by wildlife on the dissolved oxygen concentration in eutrophicated water holes in the Seronera River, Serengeti National Park, Tanzania

The dissolved oxygen concentration (DO) was sampled during a diurnal cycle in three water holes heavily used by wildlife and with distinctive biological features along the Seronera River. The DO fluctuated widely (by up to 11.5 mg l⁻¹) as a function of time, mechanical stirring and aeration by animals, and the presence of fringing wetlands. The DO cycle was successfully modeled (within 0.3 mg l⁻¹) by assuming that the four dominant processes were photosynthesis and respiration by algae near the surface, trapping by wetlands, decomposition of dead organic matter on the bottom, and stirring/aeration by hippos. The rate of DO decline from the decay of dead organic matter was equal to the rate of DO removal by algal respiration at night.     

Environmental chemistry of rivers and lakes, part v: a comparative study of the chemical and physicochemical characteristics of organic carbon dissolved in river and lake waters

To determine the chemical and physicochemical characteristics of dissolved organic carbon in the Ado River and the Yasu River, the main rivers flowing into Lake Biwa, the adsorption behavior onto hydrous iron oxide (HIO) and the reactivity to KMnO₄ oxidant were investigated in parallel with measurement of the distribution profiles of dissolved organic carbon (DOC) along the rivers. In one year of observation at the mouths of the two rivers, DOC concentrations were found to vary in the Ado over the range 0.28–1.21 mg C l⁻¹ and in the Yasu over the range 1.01–2.68 mg C l⁻¹. Act-DOC, one of the fractions separated from the total DOC by its adsorption-active character onto HIO at pH 4, was thought primarily to control the variation of total DOC, as in Lake Biwa. The int-DOC, another fraction separated by its adsorption-inert or -inactive character onto HIO, remained at almost a steady value around 0.18 ± 0.07 mg C l⁻¹ in the Ado, which was lower than that (0.35 ± 0.05 mg C l⁻¹) in Lake Biwa. The act-DOC in river waters was reactive to KMnO₄ oxidant, showing a linear relation with the amount of permanganate consumed for the reaction (chemical oxygen demand: COD). In river waters, the relation can be approximated by a straight line expressed as COD (mg O₂ l⁻¹) = 0.64 × act-DOC (mg C l⁻¹) − 0.02. In contrast, in the lake water the relation was COD (mg O₂ l⁻¹) = 0.97 × act-DOC (mg C l⁻¹) − 0.50. Received: March 3, 1999 / Accepted: December 2, 1999     

Origin and fate of organic carbon in the freshwater part of the Scheldt Estuary as traced by stable carbon isotope composition

We investigated the seasonal and geographical variation in the stable carbon isotope ratios of total dissolved inorganic carbon (¹³C_POC) and suspended matter (¹³C_POC) in the freshwater part of the River Scheldt. Two major sources of particulate organic matter (POM) occur in this riverine system: riverine phytoplankton and terrestrial detritus. In winter the lowest ¹³C_DIC values are observed due to enhanced input of CO₂ from decomposition of ¹³C-depleted terrestrial plant detritus (average ¹³C_DIC = –/14.3). During summer, when litter input from terrestrial flora is the lowest, water column respiration on POM of terrestrial origin is also the lowest as evidenced by less negative ¹³C_DIC values (average ¹³C_DIC = –9.9). In winter the phytoplankton biomass is low, as indicated by low chlorophyll a concentrations (Chl a < 4.5 gl^–1), compared to summer when chlorophyll a concentrations can rise to a maximum of 54 gl^–1. Furthermore, in winter the very narrow range of ¹³C_POC (from –26.5 to –27.6) is associated with relatively high C/N ratios (C/N > 9) suggesting that in winter a major fraction of POC is derived from allochthonous matter. In summer ¹³C_POC exhibits a very wide range of values, with the most negative values coinciding with high Chl a concentrations and low C/N ratios (C/N < 8). This suggests predominance of phytoplankton carbon in the total particulate carbon pool, utilising a dissolved inorganic carbon reservoir, which is already significantly depleted in ¹³C. Using a simple two source mixing approach a reconstruction of the relative importance of phytoplankton to the total POC pool and of ¹³C/¹²C fractionation by phytoplankton is attempted.     

Is the tetrasporophyte of Asparagopsis armata (Bonnemaisoniales) limited by inorganic carbon in integrated aquaculture?1

Seaweeds cultivated in traditional land‐based tank systems usually grow under carbon‐limited conditions and consequently have low production rates, if no costly artificial source of inorganic carbon is supplied. In integrated aquaculture, the fish effluents provide an extra source of dissolved inorganic carbon (DIC) to seaweeds due to fish respiration. To evaluate if the tetrasporophyte of Asparagopsis armata (Harv.) F. Schmitz (the Falkenbergia stage) is carbon limited when cultivated with effluents of a fish (Sparus aurata) farm in southern Portugal, we characterized the DIC forms in the water, assessed the species photosynthetic response to the different DIC concentrations and pH values, and inferred for the presence of a carbonic anhydrase (CA)–mediated mechanism. Results showed that A. armata relies mainly on CO₂ to meet photosynthetic needs. Nevertheless, from pH 7.5 upward, the CO₂ supply to RUBISCO seems to derive also from the external dehydration of HCO₃^– mediated by CA. The contribution of this mechanism was essential for A. armata to attain fully saturated O₂‐evolution rates at the natural seawater DIC concentration (2–2.2 mM) and pH values (～8.0). We revealed in this study that seaweeds cultivated in fish‐farm effluents benefit not only from a rich source of ammonia but also from an important and free source of DIC for their photosynthesis. If supplied at relatively high turnover rates (～100 vol · d^?1), fish‐farm effluents provide enough carbon to maximize the photosynthesis and growth even for species with low affinity for HCO₃^–, avoiding the artificial and costly supply of inorganic carbon to seaweed cultures.     

The requirement for external carbonic anhydrase in diatoms is influenced by the supply and demand for dissolved inorganic carbon

Photosynthesis by marine diatoms contributes significantly to the global carbon cycle. Due to the low concentration of CO₂ in seawater, many diatoms use extracellular carbonic anhydrase (eCA) to enhance the supply of CO₂ to the cell surface. While much research has investigated how the requirement for eCA is influenced by changes in CO₂ availability, little is known about how eCA contributes to CO₂ supply following changes in the demand for carbon. We therefore examined how changes in photosynthetic rate influence the requirement for eCA in three centric diatoms. Modeling of cell surface carbonate chemistry indicated that diffusive CO₂ supply to the cell surface was greatly reduced in large diatoms at higher photosynthetic rates. Laboratory experiments demonstrated a trend of an increasing requirement for eCA with increasing photosynthetic rate that was most pronounced in the larger species, supporting the findings of the cellular modeling. Microelectrode measurements of cell surface pH and O₂ demonstrated that individual cells exhibited an increased contribution of eCA to photosynthesis at higher irradiances. Our data demonstrate that changes in carbon demand strongly influence the requirement for eCA in diatoms. Cell size and photosynthetic rate will therefore be key determinants of the mode of dissolved inorganic carbon uptake.     

Ecophysiology matters: linking inorganic carbon acquisition to ecological preference in four species of microalgae (Chlorophyceae)

The effect of CO₂ supply is likely to play an important role in algal ecology. Since inorganic carbon (C_i) acquisition strategies are very diverse among microalgae and C_i availability varies greatly within and among habitats, we hypothesized that C_i acquisition depends on the pH of their preferred natural environment (adaptation) and that the efficiency of C_i uptake is affected by CO₂ availability (acclimation). To test this, four species of green algae originating from different habitats were studied. The pH‐drift and C_i uptake kinetic experiments were used to characterize C_i acquisition strategies and their ability to acclimate to high and low CO₂ conditions and high and low pH was evaluated. Results from pH drift experiments revealed that the acidophile and acidotolerant Chlamydomonas species were mainly restricted to CO₂, whereas the two neutrophiles were efficient bicarbonate users. CO₂ compensation points in low CO₂‐acclimated cultures ranged between 0.6 and 1.4 μM CO₂ and acclimation to different culture pH and CO₂ conditions suggested that CO₂ concentrating mechanisms were present in most species. High CO₂ acclimated cultures adapted rapidly to low CO₂ condition during pH‐drifts. C_i uptake kinetics at different pH values showed that the affinity for C_i was largely influenced by external pH, being highest under conditions where CO₂ dominated the C_i pool. In conclusion, C_i acquisition was highly variable among four species of green algae and linked to growth pH preference, suggesting that there is a connection between C_i acquisition and ecological distribution.     

Effects of lime-induced inorganic carbon reduction on the growth of three aquatic macrophyte species

Lime application to aquatic systems may be an effective means of stressing macrophyte growth and promoting changes in species assemblage by inducing temporary dissolved inorganic carbon (DIC) limitation of productivity. Shoot and root growth response to lime (as Ca(OH)₂) application was investigated for three macrophyte species (Elodea canadensis, Stuckenia pectinata, and Vallisneria americana) grown in experimental outdoor mesocosms. Lime was applied to mesocosms at three treatment levels to maintain pH for 1 week at 9.8–10.0 (1.64 mM), 10.3–10.5 (at the bicarbonate–carbonate equivalence point; 3.00 mM), and 10.8–11.0 (4.34 mM). pH recovered to control levels in all treated mesocosms 20 days after lime application. After treatment, HCO₃⁻ and DIC declined by 66, 93, and 93% and 60, 89, and 87%, respectively, versus increasing lime application. Concentrations remained lower in treated mesocosms versus the control throughout post-treatment. Differential growth response was observed in the 1.64 and 3.00 mM treatments, suggesting species-specific tolerances to both DIC concentration and form. V. americana was most sensitive to lime as the 1.64 mM treatment resulted in 54% shoot growth suppression versus the control and shoot plus root biomass loss in the 3.00 and 4.34 mM treatments. S. pectinata and E. canadensis exhibited net shoot and root growth (although significantly lower than controls) in both the 1.64 and 3.00 mM treatments and complete growth suppression in the 4.34 mM treatment. Selective control and shifts in species assemblage may be possible by adjusting lime concentration in relation to compensation point and needs to be investigated under field conditions.     

Photosynthetic use of light and inorganic carbon in air and water by the intertidal alga Petalonia fascia (Scytosiphonales, Phaeophyta)

The photosynthetic performance of the intertidal alga Petalonia fascia (0. F. Muller) Kuntze (Scytosiphona-ceae, Phaeophyta) has been investigated, both in air and water, by analyzing the relationship between apparent photosynthesis rate and photon irradiance and inorganic carbon. In relation to the use of photon irradiance, it was found that the net photosynthetic capacity in water was 5.7 times that in air (fully hydrated thallus). The light compensation point was achieved at 5.9 and 3.0 μmol photons m^?2 s^?1 in air and water, respectively. The light onset-saturation parameter and the photosynthetic efficiency were 77% and 25% greater in water than in air, respectively. The dark respiration rate was one-third greater when emersed in comparison to submersion conditions. These data suggest that the photosynthetic response to irradiance in P. fascia is similar to that in infralittoral species rather than the intertidal species. This assessment can be explained by the winter seasonality of the bladed stage of growth, when storms and waves permit a permanent hydrated status of P. fascia that in the intertidal zone. Moreover, the minimum tissue water content that permitted active photosynthesis in the alga was around 20%. The net photosynthetic capacity as a function of inorganic carbon (C) concentration in water was 1.5 times that in air. Photosynthesis was saturated in both media with respect to the availability of inorganic C in natural conditions. The affinity to inorganic C, and the carbon conductance, were two orders of magnitude higher in air than in water. However, the higher photosynthetic capacity when submerged in comparison to emersion conditions suggests that P. fascia can assimilate the external HCO₃,– or the occurrence of a CO₂ concentrating mechanism in this species.     

三株铜绿微囊藻对外源无机碳利用的研究

本文研究了三株铜绿微囊藻在不同条件下光合放氧对外源溶解无机碳的响应。当温度从20℃上升到30℃时,三株铜绿微囊藻的光合放氧速率都显著增加。随着反应介质pH值从7．0上升到9．0,铜绿微囊藻的光合放氧逐渐增强,其最大光合放氧速率显著增大。胞外碳酸酐酶抑制剂乙酰唑胺（acetazolamide,AZ）对铜绿微囊藻的光合放氧无显著影响,而碳酸酐酶抑制剂乙氧苯丙噻唑磺胺（ethoxyzolamide,EZ）则抑制其光合放氧。通过酶动力学方程拟合,得出这三株铜绿微囊藻的表观无机碳亲和力常数K0.5（DIC）均低于50Lmol／L,显示出铜绿微囊藻对外源无机碳的亲和力较高。在20-30℃范围内,温度的变化对微囊藻无机碳亲和力无显著影响,表明环境温度不影响其对外源无机碳利用的能力。当反应介质pH值升高,铜绿微囊藻FACHB905和PCC7806的K0.5（DIC）增大,而铜绿微囊藻FACHB469的K0.5（DIC）值却减小。在加入AZ和EZ后铜绿微囊藻的K0.5（DIC）值均无显著变化。本文还比较了铜绿微囊藻与莱氏衣藻在介质pH值变化和加入碳酸酐酶抑制剂条件下光合放氧的不同响应。结果表明,莱氏衣藻的光合放氧随反应介质pH值的升高而减弱,而AZ和EZ均抑制莱氏衣藻的光合放氧。当反应介质pH值升高以及加入AZ或EZ后,莱氏衣藻的K0.5（DIC）值均减小。     

Origin and fate of dissolved inorganic carbon ininterstitial waters of two freshwater intertidalareas: A case study of the Scheldt Estuary, Belgium

Processes affecting the concentration and isotopiccomposition of dissolved inorganic carbon (DIC) wereinvestigated in pore waters of two freshwaterintertidal areas of the Scheldt Estuary, Belgium. Porewater ¹³C_DIC values from marshes andmudflats varied from –27 to +13.4, these very largevariations reflect the contribution of differentcarbon sources to the DIC pool.In pore waters of the upper mudflat, river water DICand dissolution of calcite contribute to a lesserextent (10% and 16% respectively) to the total DICpool. Results indicate that inorganic carbon added tothe pore water of the mudflats has a ¹³Cvalue of +20.3 in May 1998. These strongly enriched¹³C_DIC values suggest that the majorcontribution (up to three-quarters) to total DIC isCO₂ derived from methanogenesis.In pore waters of the marshes, CO₂ derived fromorganic matter degradation (–27.5) and river DIC(–11.5 to –16.1) are the major sources of inorganiccarbon contribution to the total DIC pool. In porewaters from a marsh site colonised by willow trees,the contribution from CO₂ derived from organicmatter degradation is larger than in pore waters froman area with only reed vegetation. In the latter caseriver water DIC is the major source of pore waterDIC.