Aquatic Geochemistry最新文献

Stream carbon fluxes are one of the major components in the global C cycle, yet the discrimination of the various sources of stream carbon remains to a large extent unclear and less is known about the biogeochemical transformations that accompany the transfer of C from soils to streams. Here, we used patterns in stream water and groundwater δ¹³C values in a small forested tropical headwater catchment to investigate the source and contribution from the soil carbon pools to stream organic and inorganic carbon behavior over seasonal scales. Stream organic carbon (DOC and POC) comes mainly from the upper rich soil organic carbon horizons and derived from total organic carbon (TOC) of biogenic source. The isotopic compositions δ¹³C_TOC, δ¹³C_DOC and δ¹³C_POC of these carbon species were very close (??30‰ to ??26‰) and typical of the forested C3 vegetation. The relationship observed between DOC and log pCO₂ and δ¹³C_DIC indicated that besides the considerable CO₂ evasion that occurs as DIC is transported from soils to streams, there were also other processes affecting the stream DIC pool. In-stream mineralization of DOC and mixing of atmospheric carbon had a significant influence on the δ¹³C_DIC values. These processes which varied seasonally with hydrological changes represent the main control on DOC and DIC cycling in the wet tropical milieu. The rapid turnover of carbon on hillside soils, the transformation of TOC to DOC in wetland soils and further mineralization of stream DOC to DIC favor the evasion of C, making the zone a source of carbon to the atmosphere.

In aquatic systems a reaction between tetrathionate and cyanide results in the formation of thiocyanate. We have studied kinetics of the reactions of tetrathionate with free cyanide and two cyanide complexes, hexacyanoferrate(II) and hexacyanoferrate(III), at the environmentally relevant conditions. For the reaction between tetrathionate and free cyanide, the rate constant and the activation energy, but not the reaction order, strongly depend on pH. Our observations allow to propose the following pathways of thiocyanate formation by the reactions of free cyanide with tetrathionate: (1) tetrathionate reacts relatively slow with hydrogen cyanide at acidic and neutral conditions; and (2) tetrathionate reacts relatively fast with cyanide anion under highly alkaline conditions. Depending on environmental conditions, the half-lives of the reaction between free cyanide and tetrathionate will be in the ranges of hours to several years. Reactions of tetrathionate with hexacyanoferrate(II) and hexacyanoferrate(III) have no environmental significance as they are slower than the decomposition of tetrathionate. Strategy for improvement of analytical protocols for analysis of tetrathionate and cyanide is proposed based on the detected kinetics parameters.

Geomorphological (landform) aspects have long been known to control groundwater conditions in an area. Thus, combining the hydrogeological and geomorphological aspects (lithology, genesis, and morphology) becomes a prospective approach for understanding and delineating the hydrogeochemical processes in an area. The idea is then applied in Kulonprogo, Java, Indonesia, that consists of several landforms with minimum anthropogenic influence, in order to identify and quantify the hydrogeochemical processes that are responsible for hydrogeochemical facies changes in each landform. The groundwater facies based on Kurlov classification in each landform are strongly influenced by the water–rock interaction process as it presented in the Gibbs curve. The magnitude of saturation indices and mass transfer is also diverse that caused a distinction of hydrogeochemical facies and processes in each landform. For instance, the evolution of groundwater in the denudational hill to the fluviomarine plain occurs from Ca–HCO₃ to Na?+?K–Ca–HCO₃. The analysis of Durov diagram and inverse modeling—using PHREEQ—reveals that the hydrogeochemical processes that occur in most of the landform are ion exchange, weathering or dissolution, and precipitation. Further, oxidation–reduction and mixing only occur in few landforms. The further investigation from mass balance calculation that constructs from inverse modeling reveals some interesting findings and hypotheses, such as the construction of gypsum probably found in the deeper layer on swale as a result of pyrite dissolution of 1.074?×?10^?3 mmol, and it is responsible in escalating Ca²⁺ and SO₄^2?. Another finding is that although the calcite mineral mostly related to the past-marine environment, such as in the east denudational hill, the calcite in the west part is formed as a breakdown of 3.225?×?10^?3 mmol anorthite.

As the second largest carbon pool, soil has a high CO₂ content, and it has an important impact on water–rock interactions and the bacterial community structure and diversity in soils. In this paper, three sets of laboratory simulation experiments under six levels of partial pressure CO₂ (pCO₂) conditions were used to analyze and study the CO₂–water–rock interactions and the bacterial community structure and diversity changes in soil under normal temperature and pressure. Results (1) The change of pCO₂ had an obvious influence on the chemical components. The dissolution of CO₂ led to the dissolution of dolomite and calcite, which increased the concentrations of HCO₃^?, Ca²⁺, and Mg²⁺ significantly. (2) The influence of pCO₂ on the bacterial community structure and diversity was different, and the bacterial community structure became more complex and diverse with the extension of the experiment time. In the experiments, Proteobacteria and Firmicutes were the main dominant phyla, and Gammaproteobacteria and Bacilli were the main dominant classes. The abundance of Bacteroidetes and Bacteroidia was significantly increased with the increasing pCO₂. (3) pH had a significant influence on the bacterial community structure during the experiments, and the influences of different chemical components, such as HCO₃^?, Ca²⁺, Mg²⁺, total dissolved solids (TDS), and K⁺, on the abundance of different bacterial species were significantly different. This work can provide a theoretical basis for the technology of bacterial–geological storage of CO₂, and it has important significance for the protection of the groundwater environment and the soil ecosystem.

Seagrass systems are integral components of both local and global carbon cycles and can substantially modify seawater biogeochemistry, which has ecological ramifications. However, the influence of seagrass on porewater biogeochemistry has not been fully described, and the exact role of this marine macrophyte and associated microbial communities in the modification of porewater chemistry remains equivocal. In the present study, carbonate chemistry in the water column and porewater was investigated over diel timescales in contrasting, tidally influenced seagrass systems in Southern California and Bermuda, including vegetated (Zostera marina) and unvegetated biomes (0–16?cm) in Mission Bay, San Diego, USA and a vegetated system (Thallasia testudinium) in Mangrove Bay, Ferry Reach, Bermuda. In Mission Bay, dissolved inorganic carbon (DIC) and total alkalinity (TA) exhibited strong increasing gradients with sediment depth. Vertical porewater profiles differed between the sites, with almost twice as high concentrations of DIC and TA observed in the vegetated compared to the unvegetated sediments. In Mangrove Bay, both the range and vertical profiles of porewater carbonate parameters such as DIC and TA were much lower and, in contrast to Mission Bay where no distinct temporal signal was observed, biogeochemical parameters followed the semi-diurnal tidal signal in the water column. The observed differences between the study sites most likely reflect a differential influence of biological (biomass, detritus and infauna) and physical processes (e.g., sediment permeability, residence time and mixing) on porewater carbonate chemistry in the different settings.

Since the seminal work of Milliman and Syvitski (J Geol 100:525–544, 1992), there has been interest in evaluating the significance of small mountainous river (SMRs) systems and their role in the transport of both solutes, and especially sediments, to the world ocean. Although some data exist from portions of the Earth’s mountainous regions, the majority of this work has been focused in the western Pacific Ocean and Caribbean regions. During those previous studies, workers have sought to evaluate the interconnection between physical erosion and chemical erosion rates. We report herein on the riverine geochemistry of five rivers draining northern Spain and six rivers draining southern Italy. The geochemistry of these rivers is dominated by calcium carbonate weathering and input from either evaporite dissolution or marine aerosols, or both. Silicate mineral weathering is also occurring but it is not the dominant process. Using previously tabulated annual total suspended load data, we have calculated both physical and chemical erosion yields from seven of the eleven rivers under investigation where complete data sets are available. The physical yields are much higher in the Italian rivers, while chemical yields of all rivers are in a similar range. Our work adds new information on SMRs from geographical regions that have not previously been evaluated within this global context.

The octanol–water partition coefficients (K_ow) of the aristolochic acids, AA I and AA II, were determined using the traditional shake-flask method as a function of pH and ionic strength. These compounds have been implicated in the etiology of Balkan endemic nephropathy, but evidence of a plausible exposure pathway remains elusive, and research is constrained by the absence of critical physical–chemical parameters on these compounds. Apparent K_ow values were determined across a range of pH and ionic strength conditions. The results show that the apparent K_ow decreased by approximately four orders of magnitude as pH increased from 2 to 9. The pH dependence was well described by a simple model that calculated the apparent K_ow based on the ionization fractions and intrinsic K_ow values for the neutral and ionized species. Higher ionic strength solutions resulted in higher K_ow values at high pH, but had no effect at low pH. These results suggest that transport of aristolochic acids will be highly dependent on pH and ionic strength, with significant aqueous-phase transport at neutral to slightly alkaline conditions, with the highest mobility occurring under low ionic strength conditions, and the possibility of significant partitioning to nonpolar phases, such as soil organic matter or plant material, at low pH. Much of the region where BEN is prevalent is a karst environment, and pH values are generally above 8, thus leaching and groundwater transport are favored, which can suggest possible exposure routes.

Ultra-trace (<?1?ng?g^?1) rare earth elements and yttrium (REE?+?Y) and high field strength element (HFSE) geochemistry of freshwater can constrain element sources, aqueous processes in hydrologic catchments, and the signature of dissolved terrestrial fluxes to the oceans. This study details an adapted method capable of quantifying?≥?38 elements (including all REE?+?Y, Nb, Ta, Zr, Hf, Mo, W, Th, U) with minimal sample preparation in natural water aliquots as low as?≤?2?mL. The method precision and accuracy are demonstrated using measurement of the National Research Council – Conseil national de recherches Canada (NRC-CNRC) river water certified reference material (CRM) SLRS-6 sampled from the Ottawa River (OR). Data from SLRS CRM are compared to those of new, filtered (<?0.45?μm) stream water samples from the central Ottawa River basin (ORB), and discussed in terms of processes and geochemical signatures inherited from the highly evolved igneous/metamorphic Archean and Proterozoic bedrock in the catchment. The ORB waters have significantly LREE?>?HREE-enriched REE?+?Y patterns, small natural positive Y and Gd anomalies, and negative Eu and Ce anomalies. These REE?+?Y features are coherent downstream in the OR apart from amplification of Eu and Ce anomalies during REE removal/dilution. The OR samples capture a downstream decrease in sparingly soluble HFSE (Th, Nb, Ta, Zr, Hf), presumably related to their colloid-particulate removal from the dissolved load, accompanied by crustal Zr/Hf (32.5?±?5.1) and supercrustal Nb/Ta (25.1?±?7.7) ratios. Subcrustal Th/U (0.17–0.96) and supercrustal Mo/W (12.0–74.5) ratios in all ORB waters indicate preferential release and aqueous solubility of U?>?Th and Mo?>?W, with the latter attributed primarily to preferential W adsorption on soil or upstream aquatic (oxy)(hydr)oxide surfaces.

Chemical weathering in the Himalayan river basins is among the highest in the world and has received vast research attention related to past climate change. Many early estimates of chemical weathering are based on a small number of water property data that ignore those spatial and seasonal variations. Therefore, this study analyzed spatial and seasonal variations in chemical weathering in the Mekong Basin, where the geology, climate, and hydrologic cycle of the basin vary significantly from the lower to upper reaches and from dry to rainy seasons. We separately estimated the origins of dissolved elements and potential CO₂ consumption rates using the numerous chemical compositions of river water throughout the entire basin and in both seasons. The CO₂ consumption rate in the rainy season is three to five times that in the dry season that may be due to the high temperature and precipitation. Despite the low temperatures and dryness of the upper and middle basins, the CO₂ consumption rate is approximately twice that in the lower reaches; this can be attributed to active physical denudation in steep mountainous areas which increases the surface area for water–rock interactions. The total CO₂ consumption obtained by combining each season and basin was 48?70?×?10⁹?mol/a and 148?159?×?10⁹?mol/a for silicate and carbonate weathering, respectively, which are almost half the values of previous estimates. Our results suggest that seasonally and spatially separated evaluations are important for generating estimates of chemical weathering in large Himalayan rivers.