Production and fluxes of inorganic carbon and alkalinity in a subarctic subterranean estuary

In this study, we focus on the biogeochemical processes that produce both dissolved inorganic carbon (DIC) and total alkalinity (TA) along a subarctic subterranean estuary (STE) located in the Gulf of St. Lawrence (Magdalen Island, Qc, Canada) in order to evaluate the DIC and TA fluxes as well as the buffering capacity of the exported groundwater to coastal waters. DIC and TA do not behave conservatively during mixing along the groundwater flow path and this implies the occurrence of internal redox reactions that control both their production and consumption. In addition, we show that the origin and composition of the organic carbon within the system alter the carbonate parameters by generating low pH conditions (5.9 - 7.2) and contributing to non-carbonate alkalinity (NCA) that accounts for more than 30% of TA. Whereas iron cycling plays a key role in the production of DIC in the fresh and low-salinity groundwaters, the precipitation of sulfide minerals neutralize the acidity produced by the metabolically produced CO2, in the saline groundwater where sulfate is available. The STE pCO2, computed from the DIC-pHNBS pair ranged from a few ppm to 16000 ppm that results in a CO2 evasion rate of up to 310 mol m−2d−1 to the atmosphere. Based on Darcy flow and the mean concentrations of DIC and carbonate alkalinity (Ac = TA - NCA) in the discharge zone, fluxes derived from submarine groundwater discharge were estimated at 1.43 and 0.70 mol m−2d−1 for DIC and Ac, respectively. Despite a major part of the metabolic CO2 being lost along the groundwater flow path, the SGD-derived DIC flux was still greater than the Ac flux, implying that groundwater discharge reduces the buffering capacity of the receiving coastal waters. This site-specific scale study demonstrates the importance of diagenetic reactions and organic matter remineralization processes on carbonate system parameters in STE. Our results highlight that subarctic STEs could be hot spots of CO2 evasion and a source of acidification to coastal waters that should be considered in carbon budgets

Investigating the effects of bench geometry and delay times on the blast induced vibrations in an open-pit quarry

The paper analyzes the results of research aimed to monitor, predict and minimize the ground vibrations induced by blasting in an open pit limestone quarry in Italy. Data on 135 vibrations taken from 18 production blasts and 2 signature blasts were examined, including the effects of the bench orientations. Blast vibrations at the quarry were monitored for approximately three months. The blast vibration magnitudes and frequencies and their effects were analysed by both the conventional PPV concept and a software that is able to predict the vibration amplitudes of a production blast at the target sites by modelling signature blast data. The results have been rated and classifi ed considering the peak particle velocities (PPV) measured in a number of critical areas near the quarry. A comparative analysis between the results predicted by the software and actual blast results was carried out. The benefi ts of the software were then highlighted, proving able to predict ground vibrations induced by blasting more reliably than the conventional site laws. Finally, based on the results, some arrangements were provided for two bench geometries employed at the quarry site

Comparative diagenesis at three sites on the Canadian continental margin

Diagenesis of carbon, oxygen, nitrogen, and manganese at three sites on the Canadian continental margin is quantitatively compared and contrasted using results from a computer code (CANDI) published by Boudreau (1996a). The data at Station 3 (Cabot Strait) are well explained by the steady state output from CANDI, assuming a porewater balance created by diffusion and reaction only, whereas the data from Stations 4 (Emerald Basin-Scotia Shelf) and 5 (Scotia Slope) are not consistent, in one way or another, with this simple model. The deviations between model and data at Station 4 are best explained by nonsteady-state diagenesis. Model fits to the Station 5 ΣCO2 observations are improved dramatically by adding some irrigation at this site, but the ΣNH3 distribution appears to be subject to an additional anomalous transport to the O2 zone and subsequent oxidation to NO-3. The mechanism for this latter phenomena is unknown and in need of future research. In addition, the O2 and ΣCO2 profiles at all sites require the existence of at least two reactive organic matter types; furthermore, the initial amounts of these OM types at each station is strongly dependent on the intensity of particle bioturbation. Ammonia is preferentially regenerated at Station 3 at a high ratio of about 25 N to 106 C. The net kinetics of the deeper removal of Mn2+ appear to be fractional-order with respect to the concentration of this species, suggesting multiple removal processes. Finally, an oxidant balance, assuming steady state, indicates a considerable difference in the use of oxidants at each station even though the O2 fluxes are similar

Comparison of organic materials for the passive treatment of synthetic neutral mine drainage contaminated by nickel: Adsorption and desorption kinetics and isotherms

ABSTRACT: Sorption is an effective process for the remediation of mine water with low metal concentrations. To identify promising low-cost organic sorbents for nickel (Ni), adsorption and retention properties of peat, compost, brown algae, sawdust, and wood ash were compared. Batch adsorption and desorption experiments were conducted at pH 7 in 0.05 M NaNO3 solutions to simulate the ionic strength and pH of a contaminated neutral drainage. Results of adsorption kinetic experiments were best represented by the Elovich model and the fastest rates were obtained with peat (796,075 mg g−1 min−1) and compost (791 mg g−1 min−1). Results of equilibration adsorption experiments were fitted to Langmuir and Freundlich isotherms and the highest adsorption capacities were observed for peat (around 22 mg g−1) and compost (around 9 mg g−1). Desorption experiments revealed that peat and compost adsorbed more Ni and also released a lower percentage of the adsorbed metal upon exposure to Ni-free solutions

Mixing and its effects on biogeochemistry in the persistently stratified, deep, tropical Lake Matano, Indonesia

This is the publisher's version, also available electronically from http://www.aslo.orgIn the > 590-m deep, tropical Lake Matano (Indonesia), stratification is characterized by weak thermal gradients (< 2°C per 500 m) and weak salinity gradients (< 0.14% per 500 m). These gradients persist over seasons, decades, and possibly centuries. Under these nearly steady-state conditions, vertical eddy diffusion coefficients (Kz) cannot be estimated by conventional methods that rely on time derivatives of temperature distributions. We use and compare several alternative methods: one-dimensional k-ε modeling, three-dimensional hydrodynamic modeling, correlation with the size of Thorpe instabilities, and correlation with the stability frequency. In the thermocline region, at 100-m depth, the Kz is ~ 5 × 10-6 m2 s-1, but, below 300 m, the small density gradient results in large (20 m) vertical eddies and high mixing rates (Kz ~ 10-2 m2 s-1). The estimated timescale of water renewal in the monimolimnion is several hundred years. Intense evaporation depletes the surface mixed layer of 16O and 1H isotopes, making it isotopically heavier. The lake waters become progressively isotopically lighter with depth, and the isotopic composition in the deep waters is close to those of the ground and tributary waters. The vertical distribution of Kz is used in a biogeochemical reaction-transport model. We show that, outside of a narrow thermocline region, the vertical distributions of dissolved oxygen, iron, methane, and phosphorus are shaped by vertical variations in transport rates, rather than by sources or sinks

Comparison of organic materials for the passive treatment of synthetic neutral mine drainage contaminated by nickel: Short- and medium-term batch experiments

ABSTRACT: This paper addresses the comparison of various low-cost organic materials for the passive treatment of circum-neutral pH contaminated mine water. First, the effectiveness of five organic materials to remove Ni from a contaminated neutral drainage (CND) was compared in short-term batch experiments (24 h) at various pH values. Second, based on results of the short-term experiments, two substrates (brown algae and sawdust) were eliminated and three (horticultural peat, compost, wood ash) were compared along with a new substrate (field-collected surface peat) in medium-term (56 days) batch experiments to treat CND. In these experiments, calcite was added to peat samples and all substrates performed equally well, sequestering over 97% of the Ni. Chemical extractions revealed that Ni was more strongly bound to the horticultural peat-calcite (HD-peat-calcite) residue than to the field-collected peat-calcite (LT-peat-calcite) residue. Compost, because of its higher density, was identified as the most promising candidate for sorption-based fixed-bed column experiments. Nevertheless, wood ash should not be discarded as its alkaline properties favor nickel removal

The biogeochemistry of tropical lakes: A case study from Lake Matano, Indonesia

This is the publisher's version, also available electronically from http://onlinelibrary.wiley.comWe examined the chemical composition of the water column of Lake Matano, Sulawesi Island, Indonesia, to document how the high abundances of Fe (hydr)oxides in tropical soils and minimal seasonal temperature variability affect biogeochemical cycling in lakes. Lake Matano exhibits weak thermal stratification, yet a persistent pycnocline separates an oxic epilimnion from anoxic meta- and hypolimnions. The concentration of soluble P in the epilimnetic waters is very low and can be attributed to scavenging by Fe (hydr)oxides. Chromium concentrations in the epilimnion are high (up to 180 nmol L−1), but below U.S. Environmental Protection Agency guidelines for aquatic ecosystems. The concentration of chromium decreases sharply across the oxic-anoxic boundary, revealing that the hypolimnion is a sink for Cr. Flux calculations using a one-dimensional transportreaction model for the water column fail to satisfy mass balance requirements and indicate that sediment transport and diagenesis play an important role in the exchange of Fe, Mn, P, and Cr between the epilimnion and hypolimnion. Exchange of water between the epilimnion and hypolimnion is slow and on a time scale similar to temperate meromictic lakes. This limits recycling of P and N to the epilimnion and removal of Cr to the hypolimnion, both of which likely restrict primary production in the epilimnion. Owing to the slow exchange, steep concentration gradients in Fe and Mn species develop in the metalimnion. These concentration gradients are conducive to the proliferation of chemoautotrophic and anoxygenic phototrophic microbial communities, which may contribute a significant fraction to the total primary production in the lake

Global fjords as transitory reservoirs of labile organic carbon modulated by organo-mineral interactions

Funding: This work is financially supported by the Shanghai Frontiers Science Center of Polar Science (SCOPS), National Natural Science Foundation of China (NSFC) for Excellent Young Scientists Fund Program (Overseas). J.C.F. has been supported by the European Community’s 7th Framework Programme FP7 2007/2013, Marie-Curie Actions (grant no. 238111).The global carbon cycle is strongly modulated by organic carbon (OC) sequestration and decomposition. Whereas the extent of OC sequestration is relatively well-constrained in marine sedimentary basins, there are few quantitative estimates of its susceptibility to decomposition. Fjords are widely distributed hotspots of sedimentation, and currently account for 11% of annual OC burial in marine sediments. Here, we adopt fjords as model systems to investigate the reactivity of sedimentary OC by assessing the distribution of the activation energy (termed E) required to break OC covalent bonds. Our results reveal that OC in fjord sediments is more labile than that in global sediments, which is governed by unique OC provenance and organo-mineral interactions. We estimated that 61±16% of the sedimentary OC in fjords is degradable. Once this OC is remobilized and remineralized during glacial periods (sea level lowstands), the CO2 produced could counterbalance up to 50 ppm of atmospheric CO2 decrease in glacial times, making fjords critical actors in dampening glacial-interglacial climate fluctuations through negative carbon cycling loops.Publisher PDFPeer reviewe

Contrasting effects of acidification and warming on dimethylsulfide 2 concentrations during a temperate estuarine fall bloom mesocosm 3 experiment

The effects of ocean acidification and warming on the concentrations of dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) were investigated during a mesocosm experiment in the Lower St. Lawrence Estuary (LSLE) in the fall of 2014. Twelve mesocosms covering a range of pHT (pH on the total hydrogen ion concentration scale) from 8.0 to 7.2, corresponding to a range of CO2 partial pressures (pCO2) from 440 to 2900 μatm, at two temperatures (in situ and C5 °C; 10 and 15 °C) were monitored during 13 days. All mesocosms were characterized by the rapid development of a diatom bloom dominated by Skeletonema costatum, followed by its decline upon the exhaustion of nitrate and silicic acid. Neither the acidification nor the warming resulted in a significant impact on the abundance of bacteria over the experiment. However, warming the water by 5 °C resulted in a significant increase in the average bacterial production (BP) in all 15 °C mesocosms as compared to 10 °C, with no detectable effect of pCO2 on BP. Variations in total DMSP (DMSPt DparticulateCdissolved DMSP) concentrations tracked the development of the bloom, although the rise in DMSPt persisted for a few days after the peaks in chlorophyll a. Average concentrations of DMSPt were not affected by acidification or warming. Initially low concentrations of DMS (< 1 nmol L-1) increased to reach peak values ranging from 30 to 130 nmol L-1 towards the end of the experiment. Increasing the pCO2 reduced the averaged DMS concentrations by 66%and 69%at 10 and 15 °C, respectively, over the duration of the experiment. On the other hand, a 5 °C warming increased DMS concentrations by an average of 240% as compared to in situ temperature, resulting in a positive offset of the adverse pCO2 impact. Significant positive correlations found between bacterial production and concentrations of DMS throughout our experiment point towards temperatureassociated enhancement of bacterial DMSP metabolism as a likely driver of the mitigating effect of warming on the negative impact of acidification on the net production of DMS in the LSLE and potentially the global ocean.Fil: Benard, Robin. Laval University; CanadáFil: Ferreyra, Gustavo Adolfo. Laval University; CanadáFil: Michael, Scarratt. Maurice Lamontagne Institute, Fisheries And Oceans; CanadáFil: Sonia, Michaud. Maurice Lamontagne Institute, Fisheries And Oceans ; CanadáFil: Michel, Starr. Maurice Lamontagne Institute, Fisheries And Oceans; CanadáFil: Alfonso, Mucci. Université Mcgill; CanadáFil: Ferreyra, Gustavo Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Gosselin, Michel. Institut Des Sciences de la Mer de Rimouski; CanadáFil: Tremblay, Jean-Éric. Laval University; CanadáFil: Lizotte, Martine. Laval University; CanadáFil: Yang, Gui Peng. Ocean University; Chin

Ocean deoxygenation caused non-linear responses in the structure and functioning of benthic ecosystems

Les teneurs en O2 de l'océan mondial ont diminué progressivement au cours des dernières décennies, principalement en raison des activités humaines et du réchauffement climatique. Néanmoins, les effets à long terme de la désoxygénation sur les communautés macrobenthiques, la biogéochimie des sédiments et leurs interactions mutuelles demeurent mal compris. Dans cette étude, nous évaluons la réponse des assemblages de macrofaune benthiques et de la dynamique biogéochimique sédimentaire aux concentrations décroissantes d'O2 le long du gradient persistant d'O2 dissous dans l'eau de fond de l'estuaire et du golfe du Saint-Laurent (QC, Canada). Nous avons observé plusieurs réponses non linéaires de la biodiversité et de la dynamique biogéochimique sédimentaire face à la diminution de la concentration en O2 avec un seuil situé à environ 63 μM. En dessous de ce seuil, les assemblages de communautés macrobenthiques changent, et les taux de bioturbation diminuent drastiquement pour atteindre des niveaux presque nuls. En conséquence, la séquence des accepteurs d'électrons utilisés pour minéraliser la matière organique sédimentaire se contracte vers la surface du sédiment, tandis que les composés réduits s'accumulent plus près (jusqu'à 0.5 à 2.5 cm selon le composé) de l'interface sédiment-eau. Nos résultats illustrent la capacité des espèces bioturbatrices à compenser les conséquences biogéochimiques de la désoxygénation et peuvent contribuer à prédire les futurs changements dans les écosystèmes benthiques. The O2 content of the global ocean has been declining progressively over the past decades, mainly because of human activities and global warming. Nevertheless, how long-term deoxygenation affects macrobenthic communities, sediment biogeochemistry and their mutual feedback remains poorly understood. Here, we evaluate the response of the benthic assemblages and biogeochemical functioning to decreasing O2 concentrations along the persistent bottom-water dissolved O2 gradient of the Estuary and Gulf of St. Lawrence (QC, Canada). We report several of non-linear biodiversity and functional responses to decreasing O2 concentrations, and identify an O2 threshold that occurs at approximately at 63 μM. Below this threshold, macrobenthic community assemblages change, and bioturbation rates drastically decrease to near zero. Consequently, the sequence of electron acceptors used to metabolize the sedimentary organic matter is squeezed towards the sediment surface while reduced compounds accumulate closer (as much as 0.5–2.5 cm depending on the compound) to the sediment–water interface. Our results illustrate the capacity of bioturbating species to compensate for the biogeochemical consequences of hypoxia and can help to predict future changes in benthic ecosystems. -- Keywords : benthic biodiversity ; benthic fluxes ; biogeochemistry ; bioturbation ; hypoxia ; nutrients ; oxygen ; sediment