Aquatic Geochemistry最新文献

Fe type clay minerals, Fe–montmorillonite, are expected to form in the nuclear waste repositories over a span of few years owing to the interaction of corrosion products from overpack and/or canister with bentonite consisting of montmorillonite (Mt) as the major clay mineral. Therefore, it is important to understand the properties of altered clay minerals, Fe–Mt. In the present study, the sorption behaviour of ¹³³Ba(II), one of the high-yield fission products of uranium-based fuels and analogue of ⁹⁰Sr (t_1/2?=?28.5 y), on Fe(II)–Mt and Fe(III)–Mt has been investigated. Retention behavior of Ba(II) on Fe–Mt has been studied at varying pH (3–9), ionic strength (0.001?M–1?M) and Ba(II) concentration (10^?9–10^?3 M) by batch sorption method. The distribution coefficient (K_d) of Ba(II) on Fe–Mt was found to be nearly independent of pH while it decreased with increasing ionic strength indicating ion exchange as the dominant Ba(II) sorption mode on Fe–Mt. Adsorption isotherm of Ba(II) exhibited linearity in the entire Ba(II) concentration range. A comparison of Ba(II) sorption behavior on Fe–Mt and Na–Mt has been made. The Fe released from both Fe(III)–Mt and Fe(II)–Mt was measured in all the sorption experiments and was found to be much less in the case of Fe(III)–Mt (≤?1.7?ppm) when compared to Fe(II)–Mt (~?25?ppm). The modeling of Ba(II) sorption profiles on Fe–Mt and Na–Mt has been carried out using FITEQL 4.0.

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.