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Global change impacts important environmental drivers for pelagic gross primary production (GPP) in northern lakes, such as temperature, light, nutrient, and inorganic carbon availability. Separate and/or synergistic impacts of these environmental drivers on pelagic GPP remain largely unresolved. Here, we assess key drivers of pelagic GPP by combining detailed depth profiles of summer pelagic GPP with environmental and climatic data across 45 small and shallow lakes across northern Sweden (20 boreal, 6 subarctic, and 19 arctic lakes). We found that across lakes summer pelagic GPP was strongest associated with lake water temperatures, lake carbon dioxide (CO2) concentrations impacted by lake water pH, and further moderated by dissolved organic carbon (DOC) concentrations influencing light and nutrient conditions. We further used this dataset to assess the extent of additional DOC-induced warming of epilimnia (here named internal warming), which was especially pronounced in shallow lakes (decreasing 0.96°C for every decreasing m in average lake depth) and increased with higher concentrations of DOC. Additionally, the total pools and relative proportion of dissolved inorganic carbon and DOC, further influenced pelagic GPP with drivers differing slightly among the boreal, subarctic and Arctic biomes. Our study provides novel insights in that global change affects pelagic GPP in northern lakes not only by modifying the organic carbon cycle and light and nutrient conditions, but also through modifications of inorganic carbon supply and temperature. Considering the large-scale impacts and similarities of global warming, browning and recovery from acidification of lakes at higher latitudes throughout the northern hemisphere, these changes are likely to operate on a global scale.

In hardwater lakes, calcite precipitation is an important yet poorly understood process in the lacustrine carbon cycle, in which catchment-derived alkalinity (Alk) is both transformed and translocated. While the physico-chemical conditions supporting the supersaturation of water with respect to calcite are theoretically well described, the magnitude and conditions underlying calcite precipitation at fine temporal and spatial scales are poorly constrained. In this study, we used high frequency, depth-resolved (0-30 m) data collected over 18 months (June 2019 - November 2020) in the deeper basin of Lake Geneva to describe the dynamics of calcite precipitation fluxes at a fine temporal resolution (day to season) and to scale them to carbon fixation by primary production. Calcite precipitation occurred during the warm stratified periods when surface water CO 2 concentrations were below atmospheric equilibrium. Seasonally, the extent of Alk loss due to calcite precipitation (i.e., [30-42] g C m -2 ) depended upon the level of Alk in surface waters. Moreover, interannual variability in seasonal calcite precipitation depended on the duration of stratification, which determined the volume of the water layer susceptible to calcite precipitation. At finer timescales, calcite precipitation was characterized by marked daily variability with dynamics strongly related to that of planktonic autotrophic metabolism. Increasing daily calcite precipitation rates (i.e., maximum values 9 mmol C m -3 d -1 ) coincided with increasing net ecosystem production (NEP) during periods of enhanced water column stability. In these conditions, calcite precipitation could remove as much inorganic carbon from the productive layers as NEP. This study provides mechanistic insights into the conditions driving pelagic calcite precipitation, and quantifies its essential contribution to the coupling of organic and inorganic carbon cycling in lakes.

Mature Fine Tailings (MFT) generated from oil sands processing represent a growing environmental issue, as settling of these tailings’ emulsion can take decades, increasing the risk of the toxic material’s leaching if left untreated. This study uses advanced wet air oxidation (WAO) and wet air peroxide oxidation (WAPO) to break down the MFT emulsions for faster settling. Three oxidation time intervals (5, 15, and 30 min) were investigated using compressed air and hydrogen peroxide in a pressurized vessel of 3.1–3.4 MPa internal pressure and at 200 °C temperature. The results showed that the WAO process was able to break the MFT emulsion, release trapped water, and recover residual bitumen. The WAPO process was much faster in breaking the emulsion; however, the presence of extra oxidants also resulted in the degradation of the residual bitumen. The 5 min oxidation time interval was found to be sufficient in breaking emulsions, separating water from soil particles, and recovering residual bitumen under the tested conditions. The oxidation process proved to be efficient by degrading all inorganic carbon, whereas 70% of the dissolved organic carbon in the recovered water after oxidation comprised only low molecular weight biodegradable hydrocarbons. Therefore, the WAO process was capable of breaking the MFT emulsions and allowing a faster settling of these tailings, with the added benefit of recovering residual bitumen.

This work was supported by Marine Scotland through the Blue Carbon Forum. Additional support from the NERC Life Sciences Mass Spectrometry Facility (CEH_L_115_05_2018) allowed additional analytical work to be undertaken. BGS provided access to samples through their In-kind sample loan scheme (Loan: 273227). Continental shelf sediments are recognized as long-term stores of globally significant quantities of carbon (C) and potentially provide an important, yet largely overlooked climate regulation service via the Earth’s C cycle. Current understanding of the spatial distribution of sedimentary C across continental shelves remains poor, inhibiting the targeted management and potential inclusion of these globally significant C stores into national C budgets. Further understanding of the spatial heterogeneity of continental shelf sediments and associated C provides a foundation to quantify the organic carbon (OC) stock and better understand the role that marine sediments play in regulating the global climate and the potential for CO2 to be released through anthropogenic disturbance of these C stores. Utilizing a spectrum of available marine data, we have created bespoke sediment maps that quantify the surficial (top 10 cm) OC stock and highlight significant spatial heterogeneity in the distribution of sediments and their associated C content across the United Kingdom’s Exclusive Economic Zone (EEZ). The surficial sediments within the UK EEZ are estimated to store 524 ± 68 Mt of organic carbon (OC) and 2,582 ± 168 Mt of inorganic carbon (IC). The spatial mapping of this C highlights well-defined OC accumulation hotspots in fjords, estuaries and coastal muds, while large accumulations of IC are found in the tidally swept areas around Orkney, Shetland and the South West of England. Within the well-defined OC hotspots, muddy sediments store the greatest quantity of OC; the muds offer potentially valuable opportunities for targeted future management and protection of sedimentary C stores within the UK EEZ. In the future, if areas of the seafloor were to be managed to include the protection of these valuable sedimentary C resources, we recommend an initial focus on hotspots of high sedimentary OC density. Publisher PDF

To explore the mechanisms that mineralize poorly bioavailable natural organic carbon (OC), we measured the mineralization of OC in two lake waters over long-term experiments (up to 623 days) at different pH and iron (Fe) levels. Both the microbial and photochemical mineralization of OC was higher at pH acidified to 4 than at the ambient pH 5 or an elevated pH 6. During 244 days, microbes mineralized up to 60% of OC in the 10-mu m filtrates of lake water and more than 27% in the 1-mu m filtrates indicating that large-sized microbes/grazers enhance the mineralization of OC. A reactivity continuum model indicated that the acidification stimulated the microbial mineralization of OC especially in the later (> weeks) phases of experiment when the bioavailability of OC was poor. The reactive oxygen species produced by light or microbial metabolism could have contributed to the mineralization of poorly bioavailable OC through photochemical and biogenic Fenton processes catalyzed by the indigenous Fe in lake water. When Fe was introduced to artificial lake water to the concentration found in the study lakes, it increased the densities of bacteria growing on solid phase extracted dissolved organic matter and in a larger extent at low pH 4 than at pH 5. Our results suggest that in addition to the photochemical Fenton process (photo-Fenton), microbes can transfer poorly bioavailable OC into labile forms and CO2 through extracellular Fe-catalyzed reactions (i.e., biogenic Fenton process). (C) 2020 Elsevier Ltd. All rights reserved.

Graphical abstract, While traditional laboratory methods of determining soil organic carbon (SOC) content are generally simple, this becomes more challenging when carbonates are present in the soil; such is commonly found in semi-arid areas. Additionally, soil inorganic carbon (SIC) content itself is difficult to determine. This study uses visible near infrared (VisNIR) spectra to predict SOC and SIC contents of samples, and the impact of including soil pH and soil total carbon (STC) data as predictor variables was evaluated. The results indicated that combining available soil pH and STC content data with VisNIR spectra dramatically improved prediction accuracy of the Cubist models. Using the full suite of predictor variables, Cubist models trained on the calibration dataset (75%) could predict the validation dataset (25%) for SOC content with a Lin’s concordance correlation coefficient (LCCC) of 0.94, and an LCCC of 0.83 for SIC content. This is compared to an LCCC of 0.81 and 0.35 for SOC and SIC content, respectively, when no ancillary soil data was included with VisNIR spectra as predictor variables. These results suggest that there may be promise for using other readily available soil data in combination with VisNIR spectra to improve the predictions of different soil properties. • It can be laborious and expensive to measure soil organic and inorganic carbon content with traditional laboratory methods, and there has been recent focus on using spectroscopic techniques to overcome this. • This study demonstrates that combining ancillary soil data (pH and total carbon content) with these spectroscopic techniques can considerably improve predictions of SOC and SIC content.

International audience; The effect of an invasive infaunal suspension-feeding bivalve, the Manila clam Ruditapes philippinarum, on benthic inorganic carbon and nutrient fluxes was examined through in situ incubations. Measurements were performed in spring and summer on a tidal sandflat of the Rance estuary (south part of the Western English Channel) colonized by the Manila clam after its deliberate introduction in the 1990's. Benthic inorganic carbon fluxes were measured using light and dark benthic chambers both at emersion and immersion. Benthic nutrient fluxes were measured using dark benthic chambers at immersion. Inorganic carbon (IC) and ammonium sediment release under darkness at immersion reached 5.60 mmol m-2 h-1 and 441 μmol m-2 h-1 respectively for a clam density of 291 ind m-2. The sediment IC-release under darkness was lower during emersion than during immersion, probably due to the reduced activity of infauna at low tide. Under ambient light, a sediment IC-uptake was systematically measured at emersion, indicating a net autotrophy under the condition of measurements (125 < surface PAR < 1670 μmol m-2 s-1), while either sediment IC-uptake or release was measured at immersion according to light variation (20 < underwater PAR < 990 μmol m-2 s-1). The highest gross community primary production, calculated from highest IC-fluxes at light (i.e. net community production) and highest IC-fluxes at dark (i.e. community respiration), was similar at emersion and immersion and reached 6.2 mmolC m-2 h-1. These results suggest that the metabolic activity of the invasive Manila clam Ruditapes philippinarum contributes to increase inorganic C and ammonium sediment release. These regenerated nutrients may support microphytobenthic production which appeared particularly high on this intertidal sand flat.

We investigated the implications of low rainfall and reduced water level for changes in nutrients and chlorophyll-a in a subtropical lake, and how these changes affected levels and atmospheric fluxes of CO2. Based on nine consecutive years of monthly monitoring of pH, alkalinity, oxygen, and temperature, we calculated the pCO(2) and CO2 flux and related these to environmental drivers. Variations in annual rainfall, with extreme low levels along 2012-2014 caused the water level to decrease up to 1 m. Low water levels were associated with higher concentrations of chlorophyll-a and organic carbon as well as reduced water transparency. Under these conditions, pCO(2) increased and the lake was predominantly a source of CO2 to the atmosphere. Applying a generalized linear model, we found that water temperature, water column stability, and water level were linked to pCO(2). The influences of predicted regional changes in rainfall associated with low water levels will according to our model further deteriorate the water quality and enhance CO2 emissions from the lake to the atmosphere.

Anammox-based processes have been commonly applied for the treatment of reject water (high nitrogen content and low C:N ratio), in the sidestream line of urban wastewater tretament plants (WWTP). However, in recent years, it has increased the interest in applying anammox-based processes in the mainstream line (lower nitrogen content), which accounts for the majority of the influent nitrogen to the WWTP. But the application of autotrophic nitrogen removal by PNA has some challenges to deal, such as low anammox growth rate, mainly at low-temperature conditions, and the suppression of nitratation process. This thesis aimed at studying suitable operational strategies to deal with the challenges aforementioned, in order to achieve stable PNA at mainstream urban WWTP. The main strategies investigated were (i) extremely low dissolved oxygen (DO); (ii) effects of temperature; (iv) influence of different IC:N ratios; and (iv) different reactors configurations: sequencing batch (SBR) and plug-flow reactor Els processos basats en la tecnologia anammox s'han aplicat habitualment per al tractament de l’aigua de retorn de centrígues (major contingut de nitrogen i baixa relació C: N) a la línia de fangs de les estacions depuradores de aigües residuals (EDARs). No obstant això, en els darrers anys, ha augmentat l'interès en aplicar processos basats en anammox en la línia principal de l'aigua (menor contingut de nitrogen), que representa la majoria del nitrogen que es aportat a una EDAR. Però l’aplicació de l’eliminació autotrófic de nitrogen té alguns reptes a tractar, com la baixa taxa de creixement de les bacteris anammox, principalment en condicions de baixa temperatura i la supressió del procés de nitratació. Aquesta tesi té com a objectiu estudiar estratègies operatives adequades per fer front als reptes esmentats, per tal d’aconseguir un PNA estable a les principals EDARs urbanes. Les principals estratègies investigades van ser (i) oxigen dissolt (DO) extremadament baix; (ii) efectes de la temperatura; (iv) influència de diferents ràtios IC: N; i (iv) diferents configuracions de reactors: discontinu seqüencial (SBR) i de flux de pistó

Future acidification of coastal seas will depend not only on the development of atmospheric CO2 partial pressure (pCO(2)), but also on changes in the catchment areas, exchange with the adjacent ocean, and internal cycling of carbon and nutrients. Here we use a coupled physical-biogeochemical Baltic Sea model to quantify the sensitivity of pH to changes both in external forcing and internal processes. The experiments include changes in runoff, supply of dissolved inorganic carbon (DIC) and total alkalinity (A(T)), nutrient loads, exchange between the Baltic and North Seas, and atmospheric pCO(2). We furthermore address the potential different future developments of runoff and river loads in boreal and continental catchments, respectively. Changes in atmospheric pCO(2) exert the strongest control on future pH according to our calculations. This CO2-induced acidification could be further enhanced in the case of desalination of the Baltic Sea, although increased concentrations of A(T) in the river runoff due to increased weathering to some extent could counteract acidification. Reduced nutrient loads and productivity would reduce the average annual surface water pH but at the same time slightly increase wintertime surface water pH (the annual pH minimum). The response time of surface water pH to sudden changes in atmospheric pCO(2) is approximately one month, whereas response times to changes in e.g. runoff and A(T)/DIC loads are more related to residence times of water and salt (> 30 years). It seems unlikely that the projected future increase in atmospheric pCO(2) and associated pH reduction could be fully counteracted by any of the other processes addressed in our experiments.

The most massive and fast-eroding thaw slump of the Northern Hemisphere located in the Yana Uplands of Northern Yakutia was investigated to assess in detail the cryogenic inventory and carbon pools of two distinctive Ice Complex stratigraphic units and the uppermost cover deposits. Differentiating into modern and Holocene near-surface layers (active layer and shielding layer), highest total carbon contents were found in the active layer (18.72 kg m&minus, 2), while the shielding layer yielded a much lower carbon content of 1.81 kg m&minus, 2. The late Pleistocene upper Ice Complex contained 10.34 kg m&minus, 2 total carbon, and the mid-Pleistocene lower Ice Complex 17.66 kg m&minus, 2. The proportion of organic carbon from total carbon content is well above 70% in all studied units with 94% in the active layer, 73% in the shielding layer, 83% in the upper Ice Complex and 79% in the lower Ice Complex. Inorganic carbon is low in the overall structure of the deposits.

It is well-documented in the visible and near-infrared reflectance spectroscopy (VNIRS) studies that soil moisture content (SMC) negatively affects the prediction accuracy of soil attributes. This work was undertaken to remove the negative effect of SMC on the on-line prediction of soil organic carbon (SOC). A mobile VNIR spectrophotometer with a spectral range of 305–1700 nm and spectral resolution of 1 nm (CompactSpec, Tec5 Technology, Germany) was used for the spectral measurements at four farms in Flanders, Belgium. A total of 381 fresh soil samples were collected and divided into a calibration set (264) and a validation set (117). The validation samples were processed (air-dried and grind) and scanned with the same spectrophotometer in the laboratory. Three SMC correction methods, namely, external parameter orthogonalization (EPO), piecewise direct standardization (PDS), and orthogonal signal correction (OSC) were used to correct the on-line fresh spectra based-on its corresponding laboratory spectra. Then, the Cubist machine learning method was used to develop calibration models of SOC using the on-line spectra (after correction) of the calibration set. Results indicated that the EPO-Cubist outperformed the PDS-Cubist and the OSC-Cubist, with considerable improvements in the prediction results of SOC (coefficient of determination (R2) = 0.76, ratio of performance to deviation (RPD) = 2.08, and root mean square error of prediction (RMSEP) = 0.12%), compared with the corresponding uncorrected on-line spectra (R2 = 0.55, RPD = 1.24, and RMSEP = 0.20%). It can be concluded that SOC can be accurately predicted on-line using the Cubist machine learning method, after removing the negative effect of SMC with the EPO method.

The aim of this study was to investigate the PHB and glycogen accumulation dynamics in two photobioreactors inoculated with different monocultures of wastewater-borne cyanobacteria, using a three-stage feeding strategy (growth phase, feast-famine phase and feast phase). Two cyanobacterial monocultures containing members of Synechocystis sp. or Synechococcus sp. were collected from treated wastewater and inoculated in lab-scale photobioreactors to evaluate the PHB and glycogen accumulation. A third photobioreactor with a complex microbial community grown in real wastewater was also set up. During each experimental phase different concentrations of inorganic carbon were applied to the cultures, these shifts allowed to discern the accumulation mechanism of carbon storage polymers (PHB and glycogen) in cyanobacteria. Conversion of one into the other was directly related to the carbon content. The highest PHB and glycogen contents (5.04%dcw and 69%dcw, respectively) were achieved for Synechocystis sp.

Soil carbon (C) in three Ginkgo (Ginkgo biloba L.) agroforestry systems, afforestation (Ginkgo alone, G), and an agricultural cropping system were compared over a five-year period. The agroforestry systems were Ginkgo + Wheat (Triticum aestivum L.) + Peanut (Arachis hypogaea L., GWP), Ginkgo + Mulberry (Morus alba L., GM), and Ginkgo + Rapa (Brassica napus L.) + Peanut (GRP). The agricultural system consisted of wheat and peanut (WP). Total soil carbon (TSC), soil organic (SOC) and inorganic carbon (SIC), and the pools of five SOC chemical fractions were measured. TSC and SOC were always lower under WP than the G-based planting systems, and TSC in the latter increased significantly across years in the top 20 cm. Stocks of SIC under WP were significantly greater than the G-based systems, whereas SOC fractions tended to be lower. Most fractions increased across years but not in WP.

International audience; Soils act as a sink or a source of atmospheric carbon, and great efforts are made to monitor soil organic carbon stocks, but soil inorganic carbon (SIC) stocks are not measured by many national- and continental-scale soil monitoring networks. Topsoil (0-30cm) SIC concentrations were determined for >2000 sites on a regular 16-km grid as part of the French, Reseau de Mesures de la Qualite des Sols (RMQS). We used design-based statistical methods to calculate unbiased estimates of the mean SIC concentration and total stocks across France. Model-based methods were used to determine the uncertainty of these estimates and to map the spatial distribution of these quantities. Observations of inorganic carbon were highly skewed and did not conform to standard statistical models. Data were normalized using a nonparametric transformation. The estimates and predictions of inorganic carbon are baselines against which the results of future phases of the network can be compared. We found that the total topsoil inorganic carbon stocks in France amount to 1070 +/- 61 Tg, ca. one-third of the corresponding organic carbon stocks. Spatial distribution of SIC was strongly linked to the underlying geology. We tested the reliability of estimating SIC concentrations and stocks from the French Soil Test Database, which contains the results of 280000 soil analyses requested by farmers between 1990 and 2004. A biased estimate of soil inorganic carbon concentrations resulted, presumably because soil samples were selected according to concerns of farmers rather than by a statistical design.

The marine angiosperm Posidonia oceanica is a mediterranean endemism of great ecological significance. As other marine plants, P. oceanica has adapted secondarily to the marine environment and develop anew different mechanisms to colonize it. Among others, this plant has developed a plasma membrane system for the direct uptake of bicarbonate. In this work we have developed both NO3- and Cl- selective microelectrodes for the continuous monitoring of the intracellular (cytosolic) NO3- and Cl-. In the light, leaf mesophyll cells show a cytosolic NO3- concentration of 5.7±0.2 mM (n=10), while in the dark cytosolic NO3- raises up to 8.7±1.1 mM; these values are in the range of concentrations quoted for Arabidopsis thaliana (Cookson et al., 2005). The enrichment of natural seawater (NSW) with 3 mM NaHCO3 caused a decrease of the cytosolic NO3- concentration of 1 mM and a decrease of the cytosolic concentration of Cl- of 3.5 mM. The saturation of NSW with 1000 µL CO2 L-1 produced a lower diminution of the cytosolic NO3- (0.3 mM). In the presence of 0.1 mM of the plasma membrane permeable inhibitor of the carbonic anhydrase (EZ) the diminution of cytosolic NO3- caused by the same concentration of CO2 was much lower, 0.1 mM. The addition of inorganic carbon, either HCO3- or CO2, has an effect on the cytosolic mechanisms for anionic homeostasis, one of which is the opening of the slow anion channels. These channels are permeable to NO3- and Cl- and could elicit the efflux of these ions. In P. oceanica, the response in the presence of EZ points out that the inorganic carbon species that cause the NO3-/Cl- efflux is HCO3-. This effect could contribute to plant biomass N dilution observed in elevated CO2. References: Cookson et al. 2005. Plant Physiology 138, 1097–1105. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

This paper describes the sampling and analysis of biogeochemical parameters collected in the Rockall Trough in January/February of 2009, 2010, 2011 and 2012. Sampling was carried out along two transects, one southern and one northern transect each year. Samples for dissolved inorganic carbon (DIC) and total alkalinity (TA) were taken alongside salinity, dissolved oxygen and dissolved inorganic nutrients (total-oxidized nitrogen, nitrite, phosphate and silicate) to describe the chemical signatures of the various water masses in the region. These were taken at regular intervals through the water column. The data are available on the CDIAC database, http://cdiac.ornl.gov/ftp/oceans/Rockall_Trough/.

Our knowledge on cyanobacterial molecular biology increased tremendously by the application of the “omics” techniques. Only recently, metabolomics was applied systematically to model cyanobacteria. Metabolomics, the quantitative estimation of ideally the complete set of cellular metabolites, is particularly well suited to mirror cellular metabolism and its flexibility under diverse conditions. Traditionally, small sets of metabolites are quantified in targeted metabolome approaches. The development of separation technologies coupled to mass-spectroscopy- or nuclear-magnetic-resonance-based identification of low molecular mass molecules presently allows the profiling of hundreds of metabolites of diverse chemical nature. Metabolome analysis was applied to characterize changes in the cyanobacterial primary metabolism under diverse environmental conditions or in defined mutants. The resulting lists of metabolites and their steady state concentrations in combination with transcriptomics can be used in system biology approaches. The application of stable isotopes in fluxomics, i.e. the quantitative estimation of carbon and nitrogen fluxes through the biochemical network, has only rarely been applied to cyanobacteria, but particularly this technique will allow the making of kinetic models of cyanobacterial systems. The further application of metabolomics in the concert of other “omics” technologies will not only broaden our knowledge, but will also certainly strengthen the base for the biotechnological application of cyanobacteria.

Article, Short-term experiments indicate that seawater acidification can cause a decrease in the rate of calcification by coccolithopores, but the relationship between carbonate chemistry and coccolithophore calcification rate in natural assemblages is still unclear. During the Malaspina 2010 circumnavigation, we measured primary production, calcificatiion, coccolithophore abundance, particulate inorganic carbon (PIC) concentration, and the parameters of the carbonate system, along basin-scale transects in the tropical Atlantic, Indian and Pacific oceans. Euphotic layer-integrated calcification and mean cell-specific calcification to primary production (CP/PP) ratio was relatively invariant among ocean basins, with an overall mean value of 0.05+-0.04. Extrapoling this value to the entire ocean would result in a global pelagic calcification rate of 2.4 PtC /year. The mean PIC concentration in surface waters was 1.8 +-1.6 mgC/m3 and its turnover time averaged 20 d. We combined our data of calcification, primary production, and carbonate chemistry from Malaspina 2010 with those obtained during two previous cruises in the northern Arabian Sea. Both the CP/PP ratio and cell-specific calcification were largely constant across a wide range of calcite saturation rate (1.5-6.5), [HCO3-]/[H+] (0.08-0.24; mol:umol), and pH (7.6-8.1), which indicates that calcification by natural coccolithophore assemblages was independent of carbonate chemistry. Our results suggest that coccolithophore calcification, at least in tropical regions, may not be decreasing in the currently acidifying ocean.

Even though the suitability of macrophytes to act as a carbon source to food webs has been questioned by some studies, some others indicate that macrophyte-derived carbon may play an important role in the trophic transfer of organic matter in the food web of shallow lakes. To evaluate the importance of macrophytes to food webs, we collected primary producers-macrophytes and periphyton-and consumers from 19 South American shallow lakes and analyzed their carbon stable isotopes composition (d13C). Despite the diversity of inorganic carbon sources available in our study lakes, the macrophytes' d13C signatures showed a clear bimodal distribution: 13C-depleted and 13C-enriched, averaging at -27. 2 and -13. 5‰, respectively. We argue that the use of either CO2 or HCO3 - by the macrophytes largely caused the bimodal pattern in d13C signals. The contribution of carbon from macrophytes to the lake's food webs was not straightforward in most of the lakes because the macrophytes' isotopic composition was quite similar to the isotopic composition of periphyton, phytoplankton, and terrestrial carbon. However, in some lakes where the macrophytes had a distinct isotopic signature, our data suggest that macrophytes can represent an important carbon source to shallow lake food webs. © 2012 Springer Science+Business Media Dordrecht

NOTICE: this is the author’s version of a work that was accepted for publication in Deep Sea Research Part I: Oceanographic Research Papers. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Deep Sea Research Part I: Oceanographic Research Papers, [Volume 68, (June 2012)] doi: 10.1016/j.dsr.2012.05.011, http://www.sciencedirect.com/science/article/pii/S0967063712001185, peer-reviewed, The accumulation of anthropogenic CO2 in the oceans is altering seawater carbonate chemistry. Investigation and monitoring of the carbonate parameters is therefore necessary to understand potential impacts on ocean ecosystems. Total alkalinity (AT) and dissolved inorganic carbon (CT) were sampled across the Rockall Trough in Feb 2009 (CE0903) and Feb 2010 (CE10002) as part of a baseline study of inorganic carbon chemistry in Irish shelf waters. The results have been compared with data from WOCE surveys A01E (Sept 1991), A01 (Dec 1994), AR24 (Nov 1996) and A24 (June 1997). The 2009 and 2010 datasets provide a snapshot of the biogeochemical parameters which can act as a baseline of inorganic carbon and acidity levels in surface waters of the Rockall Trough in late winter for future comparison since previous surveys in the area have been affected by biological activity. The dataset also offers the possibility to compare decadal changes in subsurface waters. The temporal evolution of anthropogenic carbon (D Cant) between the 1990s and 2010 was evaluated using two separate methods; (i) a comparison of the concentrations of CT between surveys, after correcting it for remineralisation of organic material and formation and dissolution of calcium carbonate (D CT-abio) and (ii) an extended Multiple Linear Regression was used to calculate the D Cant (D Cant eMLR). There was an increase in D CT-abio and D Cant eMLR of 1874 umol kg1 and1974 umol kg1, respectively, in the subsurface waters between 1991 and 2010, equivalent to a decrease of 0.0407± 0.003 pH units over the 19 year period. There was an increasein both D CT-abio and D Cant eMLR of 874 umol kg1 in Labrador Sea Water (LSW) in the Trough between 1991 and 2010, and LSW has acidified by 0.0297±0.002 pH units over the same time period. A reduction in calcite and aragonite saturation states was observed, which may have implications for calcifying organisms in the region.

Seagrass ecosystems are expected to benefit from the global increase in CO2 in the ocean because the photosynthetic rate of these plants may be C-i-limited at the current CO2 level. As well, it is expected that lower external pH will facilitate the nitrate uptake of seagrasses if nitrate is cotransported with H+ across the membrane as in terrestrial plants. Here, we investigate the effects of CO2 enrichment on both carbon and nitrogen metabolism of the seagrass Zostera noltii in a mesocosm experiment where plants were exposed for 5 months to two experimental CO2 concentrations (360 and 700 ppm). Both the maximum photosynthetic rate (Pm) and photosynthetic efficiency (alpha) were higher (1.3- and 4.1-fold, respectively) in plants exposed to CO2-enriched conditions. On the other hand, no significant effects of CO2 enrichment on leaf growth rates were observed, probably due to nitrogen limitation as revealed by the low nitrogen content of leaves. The leaf ammonium uptake rate and glutamine synthetase activity were not significantly affected by increased CO2 concentrations. On the other hand, the leaf nitrate uptake rate of plants exposed to CO2-enriched conditions was fourfold lower than the uptake of plants exposed to current CO2 level, suggesting that in the seagrass Z. noltii nitrate is not cotransported with H+ as in terrestrial plants. In contrast, the activity of nitrate reductase was threefold higher in plant leaves grown at high-CO2 concentrations. Our results suggest that the global effects of CO2 on seagrass production may be spatially heterogeneous and depend on the specific nitrogen availability of each system. Under a CO2 increase scenario, the natural levels of nutrients will probably become limiting for Z. noltii. This potential limitation becomes more relevant because the expected positive effect of CO2 increase on nitrate uptake rate was not confirmed. Fundacao para a Ciencia e a Tecnologia [SFRH/BD/21487/2005]; POCI; FSE; COST; EC; EU info:eu-repo/semantics/publishedVersion

In large-scale microalgal production in tubular photobioreactors, the build-up of O(2) along the tubes is one of the major bottlenecks to obtain high productivities. Oxygen inhibits the growth, since it competes with carbon dioxide for the Rubisco enzyme involved in the CO(2) fixation to generate biomass. The effect of oxygen on growth of Nannochloropsis sp. was experimentally determined in a fully controlled flat-panel photobioreactor operated in turbidostat mode using an incident photon flux density of 100 μmol photons m(-2) s(-1) and with only the oxygen concentration as variable parameter. The dissolved oxygen concentration was varied from 20 to 250% air saturation. Results showed that there was no clear effect of oxygen concentration on specific growth rate (mean of 0.48 ± 0.40 day(-1)) upon increasing the oxygen concentration from 20% to 75% air saturation. Upon further increasing the oxygen concentration, however, a linear decrease in specific growth rate was observed, ranging from 0.48 ± 0.40 day(-1) at a dissolved oxygen concentration of 75% air saturation to 0.18 ± 0.01 day(-1) at 250% air saturation. In vitro data on isolated Rubisco were used to predict the quantum yield at different oxygen concentrations in the medium. The predicted decrease in quantum yield matches well with the observed decrease that was measured in vivo. These results indicate that the effect of oxygen on growth of Nannochloropsis sp. at low light intensity is only due to competitive inhibition of the Rubisco enzyme. At these sub-saturating light conditions, the presence of high concentrations of oxygen in the medium induced slightly higher carotenoid content, but the increased levels of this protective antioxidant did not diminish the growth-inhibiting effects of oxygen on the Rubisco.

Depletions of total CO2, nitrate, phosphate and silicate in the surface layer were calculated for cruise ANT XXII/3 with FS Polarstern in March 2005 for estimating the annual net community production. East-west across the Weddell Sea the variation of all depletions is similar, but this holds to a lesser extent for silicate. Depletions in March 2005 are 2-3 times larger than those in January 1993 for the same transect. Very low N:P and C:P depletion ratios seem to point to dominance of diatoms, in the central Weddell Sea more than in the margin. Estimates of annual net community productions are about 1.8 and 3.5 mol C m(-2) year(-1) for the interior Weddell Sea and a near-margin region, respectively. The region does not comply with the classical view of a marginal ice zone with high productivity. Net community production is similar to annual export production, implying that remineralization in the ensuing winter be minor.

The effect of inorganic carbon on ozone self-decomposition was examined in this study. Experiments were carried out under a wide concentration range of inorganic carbon of 0–30 mgC/L. First, the rate constant in the overall description model with nth order reaction on dissolved ozone was evaluated. A clear difference in the rate constants with and without inorganic carbon was observed even when the concentration of inorganic carbon was as low as 3 mgC/L; the difference with and without inorganic carbon was almost one order of magnitude. Reaction rate constant was lower with an increase of inorganic carbon concentration. The reaction rate constants were in the range from 1.4 × 10−5–1.9 × 10−4 (mg/L)−1sec.−1 under pH of 6.8–8.1 and inorganic carbon concentration of 6–30 mgC/L and converged on the order of 1.0 × 10−4 (mg/L)−1sec.−1. The difference of the second-order reaction rate constant under the practical range of pH and inorganic carbon concentration was one order of magnitude at most. Depression of ozo...

The estuarine mixing zone of the Tana River (northern Kenya) and an extensive deltaic area just south of the estuary were sampled in April 2004 with the aim of identifying the distribution, sources, and processing of particulate and dissolved organic carbon (POC, DOC) and inorganic carbon (DIC). C4 inputs from the catchment contributed similar to 50% to the POC pool in the Tana River and estuary, and in the mangrove creek water column and intertidal sediments. The delta C-13 values of DOC, however, were typically much more negative than that of POC, indicating a substantially higher contribution by C3 and/or mangrove-derived carbon in the DOC pool. The undersaturation of O-2, high pCO(2), and the nonconservative nature of DIC and delta C-13(DIC) suggest a strongly heterotrophic water column, particularly in the freshwater part of the Tana and in the tidal creeks in the delta, where high additional inputs of organic matter were observed. However, some of these sites showed delta O-18(DO) signatures lower than the atmospheric equilibrium (i.e., +24.2%(0)) indicative of significant O-2 production by photosynthesis. Therefore, the heterotrophic signature in the water column is likely the result of a strong interaction with the large intertidal areas, whereby respiratory activity in sediments and in the overlying water column during tidal inundation leave a marked signature on the water column. This is confirmed by the covariation between salinity-normalized total alkalinity and DIC, whose slope indicates an important role for anaerobic diagenetic processes. If our data are representative for other large river systems in the region, current estimates are likely to underestimate suspended matter and both inorganic and organic C fluxes to the Indian Ocean from tropical east Africa. ispartof: Limnology and oceanography vol:52 issue:1 pages:46-59 status: published

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The hydrothermal-vent tubeworm Riftia pachyptila relies entirely on its intracellular chemoauto- trophic symbionts to sustain its metabolism. The host must therefore provide them with inorganic metabolites, including carbon. This study describes a tool for studying cell processes occurring in a bacteria-contain- ing cell by the dissociation of trophosome cell types. The physiological assays performed on cell preparations fo- cused on carbon dioxide conversion and transport pro- cesses. Trophosome tissue was mechanically dissociated, resulting in cell suspensions enriched in small (7-20 lm) bacteriocytes, which were viable for several hours. In addition, medium-term cell cultures were also attempted. As a start to the understanding of the CO2 metabo- lism of these cells, we were interested in evidence of carbonic anhydrase (CA) isoforms, ATPases and chlo- ride exchangers. Variations in intracellular and extra- cellular pH, and in intracellular concentrations of sodium, potassium and chloride, were followed after addition of selective inhibitors. The data presented here suggest the occurrence of potential cytosolic and mem- brane-associated carbonic anhydrase isoforms in the bacteriocytes, proton-driven sodium-ATPases and a well represented anion transporter exchanging intracellular chloride against extracellular anions.

Short-term effects of increasing pCO(2); 380 ppm (LC) vs. 700 ppm (HC); at different nitrogen levels; 5 mu M nitrate (LN) vs. 50 mu M (HN); on the contents of protein, mycosporine-like amino acids (MAAs), phenolic compounds and total fatty acids, antioxidant activity, calcification and C: N ratios were analyzed in 3 eulittoral Mediterranean macroalgae with different bio-optical characteristics and carbon assimilation efficiencies: Cystoseira tamariscifolia (Heterokontophyta), Ulva rigida (Chlorophyta) and Ellisolandia elongata (Rhodophyta). After acclimation to different pCO(2) and nitrogen conditions for 6 d, the algae were subjected to a 4 degrees C temperature increase for 3 d. Increasing temperature and pCO(2) produced alterations in the biochemical composition of the 3 macroalgae. Short-term variations of protein levels were observed in U. rigida, with clearly decreased values in the HCLN treatment. In C. tamariscifolia, protein decreased after the temperature increase but only under LC. The interaction of temperature and N affected phenolic compounds only in U. rigida and the content of MAAs in E. elongata. The functional patterns of the 3 macroalgae in response to the pCO(2), nitrogen and temperature regimes may be explained in terms of their bio-optical characteristics and antioxidant activity. The vulnerability and acclimation of the 3 species to the expected variations of climate change factors are discussed.

A Monitoring-PAM fluorometer with high temporal resolution (every 5 min) was used to assess the effects on photosynthesis in Ulva rigida (Chlorophyta) during exposure to 2 different CO2 conditions: current ('LC', 390 ppm), and the predicted level for the year 2100 ('HC', 700 ppm) in a crossed combination with 2 different daily pulsed nitrate concentrations ('LN', 5 mu M and 'HN', 50 mu M) and 2 temperature regimes (ambient and ambient +4 degrees C). Effective quantum yield (Delta F/F-m') in the afternoon was lower under HCLN conditions than under the other treatments. The decrease in Delta F/F-m' from noon to the afternoon was significantly lower under +4 degrees C compared to ambient temperature. Maximal quantum yield (F-v/F-m) decreased during the night with a transient increase 1 to 3 h after sunset, whereas a transient increase in Delta F/F-m' was observed after sunrise. These transient increases have been related to activation/ deactivation of the electron transport rate and the relaxation of non-photochemical quenching. Relative electron transport rate was higher under the LC and +4 degrees C treatment, but the differences were not significant due to high variability in daily irradiances. Redundancy analysis on the data matrix for the light periods indicates that photosynthetically active radiation through the day is the main variable determining the physiological responses. The effects of nutrient levels (mainly carbon) and experimental increase of temperature were low but significant. During the night, the effect of nutrient availability is of special importance with an opposite effect of nitrogen compared to carbon increase. The application of the Monitoring-PAM to evaluate the effects of environmental conditions by simulating climate change variations under outdoor-controlled, semi-controlled conditions is discussed.

An understanding of the temperature-dependence of solubility of carbon dioxide (CO2) in water is important for many industrial processes. Voluminous work has been done by both quantum chemical methods and molecular dynamics (MD) simulations on the interaction between CO2 and water, but a quantitative evaluation of solubility remains elusive. In this work, we have approached the problem by considering quantum chemically calculated total energies and thermal energies, and incorporating the effects of mixing, hydrogen bonding, and phonon modes. An overall equation relating the calculated free energy and entropy of mixing with the gas-solution equilibrium constant has been derived. This equation has been iteratively solved to obtain the solubility as functions of temperature and dielectric constant. The calculated solubility versus temperature plot excellently matches the observed plot. Solubility has been shown to increase with dielectric constant, for example, by addition of electrolytes. We have also found that at the experimentally reported concentration of enzyme RuBP in bundle sheath cells of chloroplast in C-4 green plants, the concentration of CO2 can effectively increase by as much as a factor of 7.1-38.5. This stands in agreement with the observed effective rise in concentration by as much as 10 times.

Extensive data have been collected on the carbon dioxide system during the post monsoon season in the eastern Bay of Bengal and the Andaman Sea of the northeastern Indian Ocean. The vertical distribution of temperature and salinity in the eastern Bay of Bengal were similar to that in the Andaman Sea down to 700-800 m. Below 1200 m depth the salinity remained constant at 34.90 in the Andaman Sea whereas it decreased to 34.80 in the eastern Bay of Bengal. On the other hand, deep waters (> 1200 m) of the Andaman Sea were warmer than those of the Bay of Bengal by approximately 2 degreesC. Dissolved oxygen concentrations in the subsurface waters were higher in the Andaman Sea than in the central Bay of Bengal and Arabian Sea due to lower rates of regeneration. Total alkalinity, and pCO(2) showed similar distribution patterns both in the eastern Bay of Bengal and the Andaman Sea up to a depth of 1000-1200 m. Below this depth, their concentrations were higher in the latter than compared to former due to warmer waters. Carbonate saturation depth with respect to aragonite was shallow (approximately 300 m) in the Andaman Sea whereas deeper waters were found to be under saturated with respect to calcite., Des données extensives sur le système dioxyde de carbone ont été recueillies en saison post-mousson dans la partie est du golfe du Bengale et la mer d’Andaman (océan Indien NE). La distribution verticale de la température et de la salinité est similaire dans ces deux parties jusqu’à l’horizon 700 à 800 m. En dessous de 1200 m, la salinité demeure constante, autour de 34.90, en mer d’Andaman, alors qu’elle décroît à 34.80 dans le golfe du Bengale. D’un autre côté, l’eau profonde, au-dessous de 1200 m est plus chaude en mer d’Andaman d’environ 2°C comparé au golfe du Bengale. Les teneurs en oxygène dissous des eaux de subsurface sont plus élevées en mer d’Andaman qu’au cœur du golfe du Bengale ou qu’en mer d’Arabie, en raison d’une moindre régénération. L’alcalinité totale et la pCO2 présentent des distributions similaires dans les deux zones jusqu’à une profondeur de 1000 à 1200 m. En dessous, les concentrations sont plus élevées en mer d’Andaman en raison de la présence d’eaux plus chaudes. La profondeur de saturation en carbonates en regard de l’aragonite est moindre (environ 300 m) en mer d’Andaman, alors que les eaux plus profondes sont sous-saturées en calcite.

Modern high-rate anaerobic wastewater treatment processes are rapidly becoming popular for industrial wastewater treatment. However, until recently stable process conditions could not be guaranteed for alcoholic wastewaters containing higher concentrations of methanol. Although methanol can be directly converted into methane by methanogens, under specific conditions it can also be converted into acetate and butyrate by acetogens. The accumulation of volatile fatty acids can lead to reactor instability in a weakly buffered reactor. Since this process was insufficiently understood, the application of high-rate anaerobic reactors was highly questionable. This research investigated the environmental factors that are of importance in the predominance of methylotrophic methanogens over acetogens in a natural mixed culture during anaerobic wastewater treatment in upflow anaerobic sludge bed reactors. Technological and microbiological aspects were investigated. Additionally, the route by which methanol is converted into methane is also presented

13 pages, 6 figures, 3 tables, additional supporting information may be found in the online version of this article http://onlinelibrary.wiley.com/doi/10.1002/2012PA002419/suppinfo, Relaxation-type models have good skill at reproducing glacial-interglacial transitions in climatic variables. Here we propose a simple two-box and two-state relaxation-type model for the upper ocean (surface and permanent thermocline layers) where dissolved inorganic carbon/nutrients are supplied by the deep ocean and through remineralization within the upper ocean. The model is tuned using genetic algorithms to simulate the atmospheric CO2 time series for the last four glacial-interglacial cycles. The fit to the data is very good, with correlations above 0.8, as the upper ocean responds to shifts in (1) the intensity of the meridional overturning circulation, from off to on during the glacial-interglacial transition, and (2) the size and sign of net primary production, with respiration greatly exceeding primary production during interglacial periods and production larger than respiration during the glacial phase. The glacial-interglacial transitions are interpreted as shifts between two distinct metabolic states of the Earth system, with high/low supply of dissolved inorganic carbon and nutrients to the productive upper ocean during interglacial/glacial periods. Key Points The interglacial is dominated by enhanced remineralization and deep-ocean supply The glacial decrease arises from upper ocean net primary production The state transients follow patterns analogous to living beings ©2013. American Geophysical Union. All Rights Reserved, This work has been funded through projects MOC2 (CTM2008-06438-C02) and TIC-MOC (CTM2011-28867) of the R+D Spanish research program and through project Fisiocean (PIF08-006-1) of CSIC’s frontier program. PDLF has been partly supported through a FI-AGAUR fellowship from the Catalan government

The 13C signature of forty-five macroalgal species from intertidal zones at Ca´diz Bay was analysed in order to research the extension of diffusive vs. non-diffusive utilisation of dissolved inorganic carbon (DIC) and to perform a comparison with data published for other bio-geographic regions. The v13C values ranged from !6.8& to !33&, although the span of variation was different depending on the taxa. Thus, v13C for Chlorophyta varied from !7& (Codium adhaerens) to !29.6& (Flabellia petiolata), while all the Phaeophyceae (excepting Padina pavonica with v13C higher than !10&) had values between !10&, and !20&. The widest variation range was recorded in Rhodophyta, from values above !10& (Liagora viscida) to values lower than !30& obtained in three species belonging to the subclass Rhodymeniophycidae. Accordingly, the mean v13C value calculated for red algae (!20.2&) was significantly lower than that for brown (!15.9&) and green algae (!15.6&). Most of the analysed red algae were species inhabiting crevices and the low intertidal fringe which explains that, on average, the shaded-habitat species had a v13C value lower than those growing fully exposed to sun (i.e. in rockpools or at the upper intertidal zone). The comparison between the capacity for non-diffusive use of DIC (i.e. active or facilitated transport of HCO3 ! and/or CO2) and the v13C values reveals that values more negative than !30& indicate that photosynthesis is dependent on CO2 diffusive entry, whereas values above this threshold would not indicate necessary the operation of a non-diffusive DIC transport mechanism. Furthermore, external carbonic anhydrase activity (extCA) and v13C values were negatively correlated indicating that the higher the dependence of the photosynthesis on the CO2 supplied from HCO3 ! via extCA, the lower the v13C in the algal material. The comparison between the v13C values obtained for the analysed species and those published for species inhabiting other bio-geographic areas (warm-temperate, cold and polar) suggests that globally (at least for the red and brown algae) the non-diffusive entry of DIC is more widely spread among the species from Ca´diz Bay than among those of polar regions. If it is assumed that nondiffusive use of DIC implies saturation of photosynthesis at the present-day CO2 concentration in seawater, our data indicate that the potential impact of the acidification on photosynthesis in the seaweed communities will be different depending on the latitude. info:eu-repo/semantics/publishedVersion

Experiments were conducted on the calcareous red alga, Corallina elongata, a species representative of shallow water vegetal cover in Mediterranean areas with biomass ranging from 820 to 2544 gDW.m-2, in order to estimate its productivity and calcification rates. Carbonate and oxygen budgets were estimated on samples incubated in situ under natural light cycles, by measuring initial and final dissolved oxygen, pH and alkalinity levels. In light conditions, oxygen concentrations and pH values increased as a consequence of oxygen production and carbon dioxide consumption due to the productivity process, and were a direct function of sample biomass. Strictly-reverse dynamics were recorded in dark conditions. A comparison of photosynthetic performances was conducted on a non-calcareous green alga, Ulva rigida, which showed higher rates of oxygen production and pH modification than C. elongata, but no significant change in total alkalinity. For C. elongata, a significant decrease in total alkalinity with incubation time was observed under light conditions, which was directly related to the algal sample biomass (R2 = 0.95; n=16). Light to dark calcification ratio (L/D) was about 3.6. In these experiments, the photosynthetic quotient of C. elongata was 0.89, its net carbon productivity was 2.5 g C.m-2.d-1, gross production to daily respiration (Pg/R) was about 4.9 and its calcification rate was estimated at 13.8 g CaCO3.m-2.d-1. Los experimentos se efectuaron sobre el alga calcárea roja, Corallina elongata, un representante de aguas someras en áreas mediterráneas con biomasa comprendida entre los límites de 820 GDW m-2, y 2544 GDW m-2para estimar su productividad y las tasas de calcificación. Las concentraciones de carbonato y oxígeno fueron estimados sobre muestras incubadas in situ bajo ciclos naturales de luz, midiendo el oxígeno disuelto al inicio y al final, así como los niveles de alcalinidad y pH. En condiciones de luz, las concentraciones de oxígeno y el pH aumentaron como consecuencia de la producción de oxígeno y el consumo de dióxido de carbono debido al proceso de productividad, y eran una función directa de la biomasa de la muestra. La dinámica estrictamente inversa fue registrada en condiciones de oscuridad. Una comparación del funcionamiento fotosintético se llevó a cabo sobre un alga nocalcárea verde, Ulva rigida, que presentó tasas más altas de producción de oxígeno y variación de pH que C. elongata, pero ningún cambio significativo en alcalinidad total. Para C. elongata, una disminución significativa en alcalinidad total con el tiempo de incubación fue observada en condiciones de luz, que directamente fueron relacionadas con la biomasa de muestra algal (R2 = 0.95; n=16). La relación entre la calcificación a la luz y a la oscuridad (L/D) fue aproximadamente 3.6. En estos experimentos, el cociente fotosintético de C. elongata fue 0.89, su productividad neta de carbono, 2.5 g C.m-2.d-1, la relación producción total respecto a la respiración diaria (Pg/R), 4.9 y su tasa de calcificación, 13.8 g CaCO3. C.m-2.d-1.

In analogy to the Fe hypothesis, the Zn hypothesis states that Zn may limit primary production in some regions of the world oceans and therefore influence the global carbon cycle. The proposed mechanism is via carbon limitation due to a lack of the cofactor Zn in carbonic anhydrase. In the current conceptual model for the use of inorganic carbon by E huxleyi, carbonic anhydrase in the chloroplast generates CO2 from HCO3- at the site where CO2 is fixed by ribulose bisphosphate carboxylase oxygenase (Rubisco). The H+ that is required in this reaction comes from calcification. From this it can be expected that carbonic anhydrase affects the use of HCO3- in photosynthesis. First, we grew E. huxleyi under ZN2+ limitation. The K-1/2 for growth of E. huxleyi is 19 +/- 8 pmol L-1 ZN2+ with a minimum requirement of 9 +/- 3 pmol L-1. Additions of both ethylenediaminetetraacetic acid (EDTA) and ZnCl2 show that EDTA is not detrimental to E. huxleyi up to a concentration of 200 mumol L-1. Then we grew E. huxleyi under ZN2+-HCO3- colimitation to test the conceptual model outlined above. The results were partly inconsistent with the model. Contrary to what was expected from the conceptual model, the efficiency of CO2 use decreased when both ZN2+ and HCO3- concentrations were low, even though the experiment was conducted at a constant high concentration of CO2. This shows that ZN2+, and possibly carbonic anhydrase activity, are needed for CO2 fixation also. In accordance with the model, we found that ZN2+ affects the efficiency of HCO3- use by E huxleyi. Since the lowest ZN2+ concentration in the Northeast Pacific is similar to0.4 pmol L-1, Zn limitation of E. huxleyi growth may indeed occur.

Real wastewater was treated with a consortium of indigenous microalgae and bacteria (MaB) in sequencing batch reactors (SBR) while the hydraulic retention time (HRT) reduced from of 3 days (5 batches) to 2 days (6 batches). Biomass uptake and nitrification were the main ammonium removal pathways (about 96% for both HRTs) and phosphate levels stayed within the European limit of 1 mg P L−1. The alkalization due to lack of inorganic carbon triggered free ammonia inhibition and partial nitrification. Consequently, the total nitrogen removal could not satisfy the EU standard. Extreme pH levels (pH > 9.5) occurred more frequently in the SBR with HRT of 3 days, leading to culture collapse and biomass washout. Maintaining the pH below 8.0 seems crucial for an efficient treatment. The pH of the SBR with HRT of 2 days was more moderate, making this HRT advantageous for the single-step MaB treatment of weak wastewaters.

In alkaline freshwater systems, the apparent absence of carbon limitation to gross primary production (GPP) at low CO2 concentrations suggests that bicarbonates can support GPP. However, the contribution of bicarbonates to GPP has never been quantified in lakes along the seasons. To detect the origin of the inorganic carbon maintaining GPP, we analyze the daily stoichiometric ratios of CO2-O-2 and alkalinity-O-2 in a deep hardwater lake. Results show that aquatic primary production withdraws bicarbonate from the alkalinity pool for two-thirds of the year. Alkalinity rather than CO2 is the dominant inorganic carbon source for GPP throughout the stratified period in both the littoral and pelagic environments. This study sheds light on the neglected role of alkalinity in the freshwater carbon cycle throughout an annual cycle.

We investigated the environmental factors providing signals for gamete release in fucoid algae, with a particular focus on the inhibitory effect of water motion. The release of gametes by Fucus distichus occurred in still water under high light and was associated with the depletion of dissolved inorganic carbon (DIC) in tide pools isolated from the ocean during daytime low tides. Diurnal patterns of gamete release that lasted for 2-3 d, as in natural populations, were found in receptacles cultured in a 12 h light: 12 h dark photoperiod under calm conditions or in a simulated tidal regime. Constant light disrupted the diurnal component of release, however, suggesting that an endogenous circadian periodicity was absent. The effects of increased [DIC] on cultured receptacles under calm conditions were similar to the inhibitory effects of high water motion; both conditions reduced release in several species from both tide pool and intertidal habitats. Bicarbonate concentration, rather than carbon dioxide, or carbonate, was shown to be the component of the DIC system most closely correlated (inversely) with gamete release in the intertidal fucoid Pelvetia compressa. The hypothesis that gamete release is triggered by DIC depletion in the unstirred boundary layer during periods of low water motion in the light was further supported by experiments with P. compressa. These showed that gamete release was not inhibited by high water motion when DIC was absent. In the same experiments, high water motion inhibited release at 2 and 20 mmol/L DIC, confirming that the sensitivity of gamete release to water motion is DIC dependent. The ability of fucoid algae to couple physiological processes (e.g., photosynthesis) with life history events (gamete release) allows external fertilization to occur under favorable hydrodynamic conditions, and may contribute greatly to reproductive success in organisms inhabiting periodically turbulent environments.