Total Dissolved Carbon Research Articles

Podejście do jakości wody w zlewni osadzonej w krajobrazie rolno-leśnym nieznacznie zdegradowanym przez działalność rolniczo-hodowlaną

The headwater streams constitute landscapes with their own entity and are strongly influenced by their environment. They have a large impact on health and integrity, both for water quality and wildlife downstream. Studies on water quality from atlantics agroforestry catchments are scarce. Knowledge about water quality in agroforestry headwater catchments is important for assessing downstream effects and as a baseline for net impacts of land-use change. We analyzed physicochemical water variables of a headwater stream framed in a rural-agroforestry catchment with very little agricultural area, low livestock density and very little human population in NW Spain. Stream water samples were collected at the catchment outlet at approximately biweekly intervals over three years. All water samples were analyzed for the following quality parameters: pH, water temperature (T), electrical conductivity (EC), dissolved oxygen (DO), chemical oxygen demand (COD), major cations (Ca, Mg, Na, K), anions (Cl, SO4), nutrients [total dissolved carbon (TDC), dissolved organic carbon (DOC), nitrites nitrogen (NO2-N), nitrate nitrogen (NO3-N), ammonium nitrogen, Kjeldahl nitrogen (KN), total nitrogen (TN), dissolved, particulate and total phosphorus (DP, PP, TP)], and suspended solids (SS). Discharge was also measured. The mean concentrations of major anions, cations and different forms of carbon, nitrogen and phosphorus were rather low compared to global “average” values. Overall, the mean values of the main physicochemical water quality indicators offers similar values to those found in other rural catchment in humid temperate climates with low agricultural activity and demography, although such concentrations could have been underestimated as they mostly correspond to regular sampling and therefore ignore the influence of rainfall-runoff events.

Carbon wet deposition flux and river carbon output in a forest watershed in permafrost region of the Da Xing'an Mountains.

Carbon wet deposition and river carbon output in river basins are important components of global carbon cycle. The assessment of both properties is of great significance for regional carbon budget. However, research on these topics in high-latitude permafrost regions in China is still lacking. We conducted dynamic monitoring of carbon wet deposition and carbon output in the river from May 28th to October 30th, 2022, in Laoyeling watershed, a typical forested watershed in the Da Xing'an Mountains permafrost region. We analyzed the variations of carbon component concentrations and fluxes in precipitation and river water, and estimated the contribution of carbon wet deposition to carbon output in the watershed. The results showed that wet deposition fluxes of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and total dissolved carbon (TDC) in the Laoyeling watershed were 1354.86, 684.59, and 2039.45 kg·km-2, respectively. The fluxes of DOC, DIC, TDC, particulate organic carbon (POC), particulate inorganic carbon (PIC), and total carbon (TC) in the river were 601.75, 1977.30, 2579.05, 125.13, 21.99, and 2726.17 kg·km-2, respectively. The contribution of TDC wet deposition to the river TDC output was 9941.89 kg, accounting for 17.6% of total output. The DIC concentration in the river showed significant seasonal differences, with increased runoff resulting from precipitation leading to a decrease in DIC concentration in the river and showing a clear dilution effect, while the concentrations of DOC, POC, and PIC increased, mainly due to erosion effect. In conclusion, carbon wet deposition flux in the Laoyeling watershed was mainly determined by precipitation, and its contribution to river carbon output was relatively small compared to other factor. Runoff was the dominant factor affecting river carbon output. The results would provide important insights into carbon cycling and carbon budget balance in permafrost regions under climate change.

Spatio-temporal characterization of dissolved organic matter in karst rivers disturbed by acid mine drainage and its correlation with metal ions

Dissolved organic matter (DOM) is widely present in surface water environments and plays a critical role in the biogeochemical cycling of metal ions. Metal ions in acid mine drainage (AMD) have seriously polluted karst surface water environments, but few studies have explored interactions between DOM and metal ions in AMD-disturbed karst rivers. Here, the composition and sources of DOM in AMD-disturbed karst rivers were investigated by fluorescence excitation-emission spectroscopy combined with parallel factor analysis. In addition, correlations between metal ions and other factors (DOM components, total dissolved carbon (TDC) and pH) were determined using structural equation modeling (SEM). Results showed that there were evident differences in the seasonal distribution of TDC and metal ion concentrations in AMD-disturbed karst rivers. The concentrations of DOC, dissolved inorganic carbon (DIC), and metal ions were generally higher in the dry season than in the wet season, with Fe and Mn pollution being the most pronounced. The DOM in AMD contained two types of protein-like substances that were mainly from autochthonous inputs, while DOM in AMD-disturbed karst rivers contained two additional types of humic-like substances from both autochthonous and allochthonous inputs. The SEM results showed that the influence of DOM components on the distribution of metal ions was greater than that of TDC and pH. Among the DOM components, the influence of humic-like substances was greater than that of protein-like substances. Additionally, DOM and TDC had direct positive effects on metal ions, while pH had a direct negative effect on these. These results further elucidated the geochemical interactions between DOM and metal ions in AMD-disturbed karst rivers, which will assist in the pollution prevention of metal ions in AMD.

Unravelling Nutrients and Carbon Interactions in an Urban Coastal Water during Algal Bloom Period in Zhanjiang Bay, China

Nutrients and carbon play important roles in algal bloom and development. However, nutrients and carbon interactions in the period of the spring algal bloom are not well understood. The aim of this study is to explore the nutrients and carbon interactions in the period of the spring algal bloom covering an urban Jinsha Bay (JSB) coastal water in Zhanjiang Bay (South China Sea) using in situ multidiscipline observation. The results showed that the average concentration of total nitrogen (TN), total phosphorus (TP), and dissolved silicon (DSi) was 97.79 ± 26.31 μmol/L, 12.84 ± 4.48 μmol/L, and 16.29 ± 4.00 μmol/L in coastal water, respectively. Moreover, the average concentration of total dissolved carbon (TDC), dissolved inorganic carbon (DIC) and organic carbon (DOC) in JSB was 2187.43 ± 195.92 μmol/L, 1516.25 ± 133.24 μmol/L, and 671.13 ± 150.81 μmol/L, respectively. Furthermore, the main dominant species were Phaeocystis globosa and Nitzschia closterium during the spring algal bloom. Additionally, the correlation analysis showed salinity (S) was significantly negatively correlated with nutrients, indicating that nutrients derived from land-based sources sustained spring algal bloom development. However, as the major fraction of TDC, DIC was significantly positively correlated with S, which was mainly derived from marine sources. Besides, the algal density showed a significant positive correlation with temperature (T) (p < 0.001) and dissolved oxygen (DO) (p < 0.001), but a significant negative correlation with DIC (p < 0.05), suggesting that spring algal blooms may be simulated by water T increase, and then large amounts of DIC and nutrients were adsorbed, accompanying DO release through photosynthesis in coastal water. This study revealed nutrients and carbon interactions in the spring algal bloom of urban eutrophic coastal water, which has implications for understanding the nutrients and carbon biogeochemical cycle and algal bloom mitigation under climate change and anthropogenic pressures in the future.

Environmental conditions and mechanisms restricting microbial methanogenesis in the Miquan region of the southern Junggar Basin, NW China

AbstractEarly microbial gas has been sealed in reservoirs in the Miquan region of NW China, with little or no supply of current microbial gas. To date, the environmental conditions and mechanisms restricting microbial methanogenesis are still unclear in the Miquan region. Thus, in this study, a series of gas and water samples from coalbed methane (CBM) exploitation wells and in situ coal samples were collected and analyzed to determine the potential for current microbial gas generation, the methanogenic pathways, the source of nutrients, the influence of the environmental conditions on in situ microbial communities and their methanogenesis, and the mechanisms restricting microbial methanogenesis. The gas-production simulation experiments revealed that the existing microbes in the coalbed water were less efficient at converting coal into methane under the approximate in situ conditions, which further verified that there was little or no supply of current microbial gas. The stable isotope compositions of the gas samples suggested that carbon dioxide (CO2) reduction was the dominant metabolic pathway for generating CBM, whereas the methanogenic communities contained a mixture of acetoclastic and methylotrophic methanogens in local areas. The nutrients available for the microbes mainly included the total dissolved nitrogen (TDN) and total dissolved carbon (TDOC), and the in situ dissolution of the coals was a significant source of the TDN, whereas the TDOC was mainly supplied by surface water. The microbes in the different tectonic settings were significantly controlled by different combinations of environmental factors, and there was no single environmental factor that completely dominated the spatial variability of the microbial communities. The gradual stagnation of the water environment led to an increase in salinity and a decrease in nutrients, which were likely the main factors restricting microbial methanogenesis under in situ conditions. Combined with the results of the rate-limiting stages of the anaerobic fermentation, the mechanisms restricting microbial methanogenesis can be finally determined in the Miquan region. These discoveries presented in this case study provide a significant supplement to the geological theory of CBM accumulation, and have a guiding significance for CBM development in the Miquan region.

Dynamics of Dissolved Carbon in Subalpine Forest Streams

Dissolved carbon (DC) in forest streams plays a crucial role in maintaining the structure and productivity of adjoining aquatic ecosystems as well as informing biogeochemical links between mountain forests and adjoining rivers. Nevertheless, the functions of forest stream DC dynamics are rarely incorporated into river management. To better understand the biogeochemical links between subalpine forests and adjoining streams, the seasonal dynamics of DC in 15 representative forest streams were investigated in a geographically fragile subalpine-gorge catchment in the upper reaches of the Yangtze River. Depending on stream characteristics and critical periods, the DC stocks in the streams ranged from 0.22 to 2.35 mg m−2 for total DC, from 0.10 to 1.66 mg m−2 for dissolved inorganic carbon (DIC), and from 0.12 to 1.27 mg m−2 for dissolved organic carbon (DOC). Moreover, the annual stocks of DC, DIC, and DOC were 1.01, 0.56, and 0.45 mg m−2, respectively. Correspondingly, the averaged export rates for DC, DIC, and DOC from the forest streams ranged from 0.27 to 1.98 mg s−1, from 0.24 to 1.48 mg s−1, and from 0.18 to 0.90 mg s−1, respectively, in the subalpine forest catchment. The annual export rates of total DC, DIC, and DOC were 1.06, 0.75, and 0.31 mg C s−1, respectively. In particular, the highest rates of export were 4.67, 3.53, and 1.34 mg s−1 for DC, DIC, and DOC, respectively, in the snowmelt period. The average ratios of DOC to DIC stock in the export water ranged from 0.23–2.41 for the 15 streams, and the average value was 0.85 during this one-year investigation. In addition, the maximum and minimum values of the DC stocks, their exports, and the DIC:DOC ratio were consistently observed during the snowmelt season and the late growing period. In summary, precipitation, temperature, water discharge rate, and sediment depth regulated the stocks and export rates of DC and its components. In general, forest streams are important links between the carbon biogeochemical cycle of subalpine forests and adjoining streams.

Advanced oxidation treatments of olive mill wastewater

New and innovative advanced oxidative processes for wastewater treatments are currently in the focus of scientific research and development for possible industrial implantation. The main aim of this study was to investigate the effect of cold plasma treatment, high intensity ultrasound and UV radiation with the addition of additives: H2O2, TiO2, FeCl3 x 6H2O on degradation and removal of complex organic compounds from olive mill wastewater (OMWW). Olive mill wastewater represents a potential ecological problem when it is raw disposed into the environment, because of its high organic load. OMWW samples (with and without additives) were treated by high-voltage plasma discharge at frequencies 60 Hz and 120 Hz in combination with pumped gases (nitrogen, air and oxygen) for 30 minutes, by UV radiation for 30 minutes and 10 minutes by high intensity ultrasound. Physico-chemical parameters of quality, chemical oxygen demand (COD), and total dissolved carbon (TOC) were determined. The results have shown the efficacy of plasma treatment in degradation of organic compounds as well as degradation and reduction of polyphenolic compounds. Reduction of colour and total dissolved carbon occurred in all treated samples, mostly with the addition of FeCl3 x 6H2O. Treatment with UV radiation and ultrasound proved to be the most efficient resulting in the 50% reduction of organic compounds after a 10-minute treatment.

Pollutant removal and biodegradation assessment of tannery effluent treated by conventional Fenton oxidation process

In this research, the performance of a Fenton batch reactor (FBR) for the treatment of tannery effluent (TE) has been studied by applying response surface methodology (RSM). In the context of RSM, three important Fenton parameters (Fe and H2O2 concentrations and solution pH) were suitably changed within a full experimental design, allowing the definition of a set of 27 FBR experiments performed in batch mode. From the RSM analysis, the Fenton oxidation process showed the best removal response for chemical oxygen demand (COD) (80%), color (90%), turbidity (95%), and sludge (70%), as well as an increase in the percentage of biodegradation from 0.19 to 0.3 (BOD5/COD ratio) when conducted under conditions of 5 mg Fe2+ L−1, 75 mg H2O2 L−1, and pH 4 with a 60 min reaction time. Additionally, quick consumption of the initial concentration of H2O2, as observed in an acidic solution pH (∼3.5) containing dissolved iron, led to rapid yield of hydroxyl radicals (HO•), making it possible to oxidize the organic pollutants in the raw TE more efficiently. By performing kinetic experiments on the best pollutant removal, it was observed that there were high reductions in the amounts of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and total dissolved carbon (TDC). Conversely, an increase in the initial concentration of total dissolved nitrogen (TDN) was also observed, suggesting a partial mineralization of nitrogen compounds such as ammonia, nitrate, and nitrite. The Fenton reaction coupled to the Zahn-Wellens test indicated and increase in the biodegradability (Dt 79%) of the treated TE. Gas Chromatography – Mass Spectrometry (GC–MS) analysis identified contaminants present in the raw TE and persistent in the samples treated by the Fenton reaction coupled to the Zahn-Wellens test. Based on the overall results, the Fenton process has been shown to be a simple and suitable way to treat TE efficiently. The process could also be used as a pre-treatment of a conventional biological system, being applied in the degradation of toxic and recalcitrant contaminants contained in TE.

Brazilian inland water bio-optical dataset to support carbon budget studies in reservoirs as well as anthropogenic impacts in Amazon floodplain lakes: Preliminary results

Abstract. This work presents ongoing efforts and preliminary results for building a dataset that represents the first and most comprehensive bio-optical information available on Brazilian inland waters to support the development of remote sensing algorithms for monitoring aquatic systems. From 2012 to 2014 optical and limnological data was gathered along thirteen field campaigns in five Brazilian reservoirs, in an irrigation and domestic water supply reservoir located in semi-arid northeast of the country and in Amazonian floodplain lakes, thus covering the diversity of Brazilian inland waters. At each site 20 stations, on average, were sampled to acquire profiles of the following optical variables: absorption, attenuation, scattering, and backscattering coefficients and radiances/irradiances spectra above and in-water. Alongside these measurements, water samples were collected for determining concentrations of chlorophyll-a (Chl-a), Total Suspended Solid (TSS), Total Dissolved Carbon (TDC) and its organic/inorganic fractions, CDOM absorption, phytoplankton specific absorption [aph*] and Non-Algal Particles absorption [aNAP*]. Preliminary results show that Chl-a concentrations ranged from 0.6 to 243μg/L in reservoirs and 0.90 to 92μg/L in Amazonian lakes, while TSS concentrations ranged from 0.3 to 31mg/L in reservoirs and 0.5 to 162mg/L in Amazonian lakes. In situ beam attenuation coefficients ranged from 1.4 to 16m-1 in reservoirs and 12.5 to 38m-1 in Amazonian lakes, while diffuse attenuation coefficients of downwelling irradiance over the Photosynthetically Active Radiation (Kd(PAR)) extended from 0.35 to 4.5m-1 in reservoirs and 1.69 to 13.30m-1 in Amazonian lakes. Our research group is building this dataset anticipating future demands for algorithm validation regarding OLI/Landsat8 data and ESA Sentinel missions to be launched as of 2015.

Effect of CO2 Bubbling into Aqueous Solutions Used for Electrochemical Reduction of CO2 for Energy Conversion and Storage

CO2 bubbling into electrolytes is widely used for the electrochemical and photoelectrochemical reduction of CO2 as a carbon source. However, the effects of the CO2 bubbling into the electrolytes have rarely been studied and are not clear. The CO2 bubbling into different electrolytes such as KHCO3, K2CO3, KCl, and KOH was investigated in this research. The concentrations of total dissolved carbon (TC), H2CO3* (sum of dissolved CO2 and H2CO3), HCO3–, and CO32– in different solutions before and after bubbling with CO2 until saturation were evaluated. The CO2 bubbling caused the pH of the electrolytes to decrease and affected the existence forms of the dissolved carbonaceous species. After bubbling with CO2, the major form of dissolved CO2 in KHCO3, K2CO3, and KOH was HCO3–, while H2CO3* was the dominant species in KCl, HCl, and H2O. The ratio of H2CO3*/TC reduces as the concentration of KHCO3 increases, which is possibly the reason for the decrease of CO2 reduction by the solution of high KHCO3 concentration...

Geochemical evaluation of CO2 injection and containment in a depleted gas field

The short- and long-term geochemical impact of CO2 injection into a depleted gas reservoir (DGR) is investigated using reservoir/geochemical modeling with TOUGH2/TOUGHREACT and 1D kinetic diffusion modeling with PHREEQC (caprock/well-cement). Simulations of CO2 injection into the reservoir predict displacement and buoyancy of post-production CH4, as well as dry-out of the near-well zone. We computed that the areal extent of the CH4/brine dominated zone and the dry-out zone are relatively small compared to the CO2/brine dominated zone after well-closure. For the current DGR model we therefore conclude that it is reasonable to model geochemical reactions in the reservoir without taking into account post-production CH4. Although the CO2 dissolution capacity of the studied DGR is smaller compared to a deep saline aquifer of similar size, the modeling predicts that dissolution and subsequent CO2 mineral trapping proceed faster. Precipitation of dawsonite and magnesite were yet predicted at initial CO2 partial pressure (PCO2) of 9.3bar, while these minerals were not identified in reservoir samples. This could indicate that their tendency of precipitation is overestimated by the model and hence the database used. This has significant impact on long-term modeled bulk porosity and PCO2. Simulations of CO2 diffusion through the caprock show that mineral reactions significantly retard the total dissolved carbon (TDC) plume. After 10,000 years, 99% of the TDC is present within the first 6.4m above the reservoir contact. The progression of the TDC plume in the caprock is sensitive to the composition, kinetic rates, and surface area of primary and secondary minerals. Cement alteration modeling shows progressive carbonation of cement phases, resulting in three zones of distinct mineralogy and porosity. The three zones are predominantly characterized by: (i) unaltered cement, (ii) portlandite dissolution, and (iii) calcite precipitation. The simulated thickness of the affected zone is 3.8cm after 100 years. This distance is sensitive to kinetic rate constants of C–S–H phases, but less sensitive to kinetic rate constant of portlandite. In summary, our applied methodology provides quantitative predictions of the geochemical impact of CO2 on the DGR storage complex. The methodology can be used for screening of potential DGR storage locations and to define criteria for minimal caprock and cement sheet thickness, for assuring short- and long-term integrity of the storage location.

Effects of long-term land use change on dissolved carbon characteristics in the permafrost streams of northeast China

Permafrost soils act as large sinks of organic carbon but are highly sensitive to interference such as changes in land use, which can greatly influence dissolved carbon loads in streams. This study examines the effects of long-term land reclamation on seasonal concentrations of dissolved carbons in the upper reaches of the Nenjiang River, northeast China. A comparison of streams in natural and agricultural systems shows that the dissolved organic carbon (DOC) concentration is much lower in the agricultural stream (AG) than in the two natural streams (WAF, wetland dominated; FR, forest dominated), suggesting that land use change is associated with reduced DOC exporting capacity. Moreover, the fluorescence indexes and the ratio of dissolved carbon to nitrogen also differ greatly between the natural and agricultural streams, indicating that the chemical characteristics and the origin of the DOC released from the whole reaches are also altered to some extent. Importantly, the exporting concentration of dissolved inorganic carbon (DIC) and its proportion of total dissolved carbon (TDC) substantially increase following land reclamation, which would largely alter the carbon cycling processes in the downstream fluvial system. Although the strong association between the stream discharge and the DOC concentration was unchanged, the reduction in total soil organic carbon following land reclamation led to remarkable decline of the total flux and exporting coefficient of the dissolved carbons. The results suggest that dissolved carbons in permafrost streams have been greatly affected by changes in land use since the 1970s, and the changes in the concentration and chemical characteristics of dissolved carbons will last until the alteration in both the traditional agriculture pattern and the persistent reclamation activities.

Concentration and characteristics of dissolved carbon in the Sanjiang Plain influenced by long-term land reclamation from marsh

Since the 1960s, the marshes in the Sanjiang Plain, Northeast China, which are an important reservoir for dissolved carbon, have undergone long-term reclamation to farmland, resulting in elevated marsh loss and degradation on a large scale. This study compared the concentrations of dissolved carbon, as well as the chemical characteristics of dissolved organic carbon (DOC), in natural marshes, a degraded marsh, and drainage ditches sampled during the growing seasons between 2008 and 2010 to clarify the temporal–spatial variability of the dissolved carbon in the fluvial system influenced by the long-term reclamation. The results show that the average concentrations of total dissolved carbon (TDC) and DOC are considerably greater in the natural marshes than in the degraded marsh and drainage ditches. The average DOC concentration for the natural marshes, approximately 35.53±5.15mgL−1, is approximately 2.39 times that in the degraded marsh (14.84±4.21mgL−1) and 2.77 times the average value in the ditches (12.84±4.49mgL−1). The dissolved inorganic carbon (DIC) exhibits increased trends in the drainage ditches compared with the natural marshes, whereas the hydrophobic fraction of DOC is present at lower concentrations in the degraded marsh and ditches. Fluorescence indices also indicate that the DOC in the degraded marsh and ditches has a simpler humification structure. In total, the long-term reclamation has led to great variability in the DOC concentration and chemical characteristics in the fluvial system. Changes in the DOC production potential and hydrological regimes due to sustained reclamation are deemed the predominant causes of this effect. The continuously decreased DOC concentration and high variability of DOC in the surface fluvial systems are inevitable if reclamation continues in the Sanjiang Plain. More importantly, the presence of tyrosine and tryptophan-like substances in the ditches indicates that there has been extensive agricultural organic pollution in the fluvial systems. This pollution could lead to more unexpected impacts on the downriver aquatic system. To avoid a destructive ecological crisis in the future, adjustment of the reclamation policy and agricultural management measures in the Sanjiang Plain is urgently needed.

Dissolved organic carbon and nitrogen dynamics in the Douro River estuary, Portugal

Dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) are metabolically important in estuaries. Their availability is influenced by organic matter inputs (internal and external) as well as by internal microbial transformations within the system. In this study, spatial and seasonal dynamics of DOC and DON were evaluated in the Douro River estuary (Portugal). Monthly surveys were performed from October 2005 to December 2006 along a salinity gradient at three different depths. DOC and DON were calculated by subtracting the respective inorganic components (dissolved inorganic carbon, DIC, and dissolved inorganic nitrogen, DIN) from total dissolved carbon (TDC) and total dissolved nitrogen (TDN). In the Douro River estuary, DIC exhibits a linear and positive distribution as a function of salinity, indicating an input of DIC into the estuary from coastal waters. This pattern of distribution along the salinity gradient was also observed for total particulate matter, since a decreasing trend upstream was observed. In contrast, the results showed a general nonconservative behaviour of DOC along the estuarine transect during most months. This typical deviation from conservative mixing was mainly associated with sewage DOC sources into the lower and middle estuary. On average, DON concentrations represented 52–88% of the TDN. Along the transect, relationships between DIN and DON with salinity were generally conservative, decreasing towards the mouth, highlighting the fluvial source of such nitrogen forms; however, occasional DON sewage loads were registered. Estimated global Douro River watershed exports of DOC and DON to coastal waters yielded values of 420 kg C m–2 yr–1 and 125 kg N m–2 yr–1, respectively, which are high when compared with previously predicted levels from global models of DOC and DON export.

Suspended sediments in river ecosystems: Photochemical sources of dissolved organic carbon, dissolved organic nitrogen, and adsorptive removal of dissolved iron

We generated suspended sediment solutions using river sediments and river water at concentrations similar to those observed during 1.5 year floods (Q1.5) and a dam removal (∼325 mg L−1) on the Deep River, North Carolina. Suspended sediment solutions were exposed to simulated solar radiation, equivalent to one clear, summer day at the study site (35°N). Concentrations of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), total dissolved nitrogen (TDN), dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON), soluble reactive phosphorus (SRP) and total dissolved iron (Fed) were measured before and after exposure. Total dissolved carbon (TDC) budgets for each experiment were produced using DOC and DIC data. Sediment suspensions in the presence of simulated solar radiation were significant sources of dissolved C (119 ± 11 μmol C L−1 d−1; ± values indicate 1 standard error) and DON (1.7 ± 0.5 μmol N L−1 d−1) but not DIN or SRP. Extrapolations through the Deep River water column suggest that suspended sediments in the presence of light represent dissolved organic matter fluxes of 3.92 mmol C m−2 d−1 and 40 μmol N m−2 d−1. Additionally, sediment suspensions lowered river water Fed concentrations immediately (∼24%) and progressively (∼40–90%) in both light and dark treatments. Our research suggests suspended sediments in river ecosystems are potential sources of dissolved organic C and dissolved organic N while effectively removing Fed from the water column.

New methods for the direct determination of dissolved inorganic, organic and total carbon in natural waters by Reagent-Free™ Ion Chromatography and inductively coupled plasma atomic emission spectrometry

New methods have been developed and applied successfully for the determination of dissolved inorganic, organic and total carbon in water samples. The new methods utilize two instrumental setups, Reagent-Free™ Ion Chromatography (RF™-IC) and inductively coupled plasma atomic emission spectrometry (ICP-AES). Dissolved inorganic carbon (DIC) was measured in untreated samples along with Cl −, F − and SO 4 2− using RF™-IC and by in-line mixing with 0.1 M HNO 3 to enhance CO 2 removal in the nebulizer, followed by ICP-AES analysis. Total dissolved carbon (TDC) was measured by in-line mixing with 0.1 M NaOH following ICP-AES analysis. Dissolved organic carbon (DOC) was obtained as the difference between DIC and TDC. Only non-volatile organic carbon could be detected by the present method. The workable limits of detection obtained in the present study were 0.5 mM (RF™-IC) and 0.1 mM (ICP-AES) for dissolved inorganic and organic carbon, respectively. The power of the new methods lies in routine analysis of DIC and DOC in samples of natural waters of variable composition and salinity using analytical techniques and facilities available in most laboratories doing water sample analysis. The techniques are sensitive and precise, can be automated using gas-tight sample vials and auto-samplers, and are independent of most elemental interferences with the exception of chloride overload by saline samples when using RF™-IC. The new methods were successfully applied for analysis of DIC and DOC in selected samples of natural and synthetic waters.

Variation in the total dissolved carbon isotope composition of thermal waters of the Island of Ischia (Italy) and its implications for volcanic surveillance

During surveys conducted in 1997, 30 thermal waters (for a total of 39 analysis) were collected from shallow wells utilised for resort spas on the Island of Ischia. Well temperatures ranged from 25° to 82°C and their depths from 30 to 150 m. Pools with temperatures of 26° to 67°C were also sampled on the northern flank of the Mt. Epomeo. The samples were analysed for bulk chemical composition, as well as H, O and C isotope composition. Isotopic analyses of water samples showed wide variations in both deuterium and oxygen-18, which ranged from −37.4 to +8.1‰ and −6.8 to +1.1‰, respectively. Overall δ 13 C in total dissolved carbon (TDC) ranged from −11.5 to +2.3‰, and computed δ 13 C of CO 2(g) results ranged from −18.5 to −1.72‰. Water samples with CO 2 content of up to about 1 bar partial pressure exhibited δ 13 C ( CO 2) ranging from −4 to −1‰. Water samples varied chemically from low-salinity HCO 3 well waters (1–4 g/l) of essentially meteoric origin, to high-salinity Cl waters (up to 40 g/l). Mixing processes from local groundwater, seawater and evaporated waters have also been identified. Models for the chemical and isotopic data on the thermal manifestations have been developed for low- and high-pressure conditions in order to assess the isotopic composition of deep CO 2, assuming that this component is continuously added to the solutions until degassing occurs at shallow depths or at the surface. Constraints due to the reaction of water with volcanic glass have been taken into account for in the computations in addition to those relative to the carbon components participating in the carbonate equilibria. Results from such simulations indicate that deep CO 2 added to the shallow waters probably has a carbon isotope composition ≥−2‰, which most likely stems from a mixed magmatic–sedimentary origin.

Hydraulic Seals and Their Origin: Evidence from the Stable Isotope Geochemistry of Dolomites in the Middle Ordovician St. Peter Sandstone, Michigan Basin

Regionally extensive, overpressured natural gas pools within the St. Peter Sandstone (Middle Ordovician) of the Michigan basin are bounded by rock types that include 3-7-m-thick zones of low-permeability, low-porosity carbonates or diagenetically banded quartz sandstones. Replacive dolomite from an approximately 5-m-thick carbonate interval in the east-central portion of the Michigan basin has very low ^dgr13C values that systematically decrease from approximately -5^pmil at the top to -10^pmil (PDB) at the base. ^dgr18O values for the replacive dolomite also decrease systematically with depth from approximately 27 to 23^pmil (SMOW). These data suggest an upward decrease in isotope exchange between the replacive dolomitization fluid and the precursor rock (i.e., the system was rock dominated at the top of the carbonate interval), which implies upward, cross-formational movement of the dolomitizing fluid. Fluid-rock interaction modeling suggests that the dolomitizing fluid had a total dissolved carbon (TDC) content of approximately 4000 ppm and a ^dgr13C value of -27^pmil, which indicates that the carbon was primarily derived from organic diagenesis. Sr isotope and major element data suggest that this dolomitizing fluid had a modified seawater origin. Carbonate intervals in the St. Peter Sandstone contain dolomite cement in quartz sandstone laminations and fractures that have ^dgr13C values that closely mimic the large ^dgr13C variations of the adjacent replacive dolomite with depth. This correlation indicates that the replacive dolomite controlled the ^dgr13C value of the carbon dissolved in the parent fluids of the later dolomite cement. Moreover, these data suggest that the parent fluids of the dolomite cement were not confined to a common fracture network, but flowed pervasively through the carbonate intervals. The ^dgr13C values of dolomite cement in diagenetically banded quartz sandstone intervals from three locations in the central portion of the Michigan basin range from -9 to -4^ mil and are relatively invariant at a particular locality; therefore, the TDC of the dolomitizing fluid in the central Michigan basin is interpreted to have contained only about 20-30% organic carbon. The fact that all dolomites analyzed in the St. Peter Sandstone have much lower ^dgr13C values than carbonates in adjacent formations indicates that dolomitization and the formation of hydraulic seals were related to organic matter diagenesis.

Productivity across the Cretaceous/Tertiary boundary in high latitudes

In low and middle latitudes, the Cretaceous/Tertiary boundary is marked by a sudden and pronounced decrease in δ13C values of near-surface-water carbonates and a reduction in the surface-to-bottom δ13C gradient. These isotopic data have been interpreted as evidence of a decline in surface-water productivity that was responsible for the extinction of many planktic foraminiferal species and other marine organisms at or near the K/T boundary. We present planktic and benthic foraminiferal isotopic data from two almost biostratigraphically complete sections at Ocean Drilling Program Site 738 in the antarctic Indian Ocean and at Nye Klov in Denmark. These data suggest that planktic carbonate δ13C values in high latitudes may not have decreased dramatically at the K/T boundary; thus, surface-water productivity may not have been reduced as much as in low and middle latitudes. Comparison of the records of Site 738 with those of ODP Sites 690 and 750 indicates a pronounced decline in δ13C values of planktic and benthic foraminifera and fine-fraction/bulk carbonate ∼200 000 yr after the K/T boundary. This reflects a regional shift in the carbon isotopic composition of oceanic total dissolved carbon (TDC) and correlates with a similar change in benthic foraminiferal δ13C values at mid- and low-latitude Deep Sea Drilling Project Sites 527 and 577. This oceanographic event was followed by the ecosystem's global recovery ∼500 000 yr after the K/T boundary. These data suggest that the environmental effects of the K/T boundary may have been less severe in the high-latitude oceans than in tropical and subtropical regions.

Geochemical and climatic effects of increased marine organic carbon burial at the Cenomanian/Turonian boundary

Perhaps the most significant event in the Cretaceous record of the carbon isotope composition of carbonate1,2, other than the 1–2.5 ‰ negative shift in the carbon isotope composition of calcareous plankton at the Cretaceous/Tertiary boundary3, is the rapid global positive excursion of ∼2 ‰ (13C enrichment) which took place between ∼91.5 Myr and 90.3 Myr (late Cenomanian to earliest Turonian (C/T boundary event))1,4,5. This excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon (TDC) reservoir resulting from an increase in rate of burial of 13C-depleted organic carbon, which coincided with a major global rise in sea level5 during the so-called C/T oceanic anoxic event (OAE)6. Here we present new data, from nine localities, which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the C/T boundary7,8 is nearly synchronous with that for carbonate and is widespread throughout the Tethys and Atlantic basins (Fig. 1), as well as in more high-latitude epicontinental seas. The postulated increase in the rate of burial of organic carbon may have had a significant effect on CO2 and O2 concentrations in the oceans and atmosphere, and consequent effects on global climate and sedimentary facies.