Hydrogeochemical evolution and quality assessment of groundwater within the Atankwidi basin: the case of northeastern Ghana
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Silicate minerals
Geochemical Modeling
Dominance (genetics)
Understanding the controls on chemical weathering, especially of silicate minerals, remains a major challenge, despite its importance in controlling the evolution of the Earth's surface. In particular, it has proved hard to distinguish the temperature sensitivity of silicate weathering rates from other factors. Here we present a new compilation of chemical and physical erosion rates in small catchments and show that silicate weathering rates are not governed by any single parameter but require consideration in multiple dimensions. The overall variation in silicate weathering rates with physical erosion rates, rainfall, and temperature can be quantitatively described by a parameterization based on considering their limiting relationships. At lower erosion rates mineral supply limits weathering. At higher erosion rates there is abundant material but kinetic and therefore climatic factors limit weathering. A predictive model describing the field data based on transport and weathering (kinetically) limited scenarios yields theoretically sensible values for fitted parameters. In the transport-limited case, the supply of silicate cations from weathering is directly proportional to the supply of material by erosion, consistent with complete leaching of cations from fresh regolith. In the kinetically limited case, weathering scales directly with runoff, as the square root of erosion rate, and with an activation energy of 74 ± 29 kJ/mol, consistent with expected values in the Earth's surface settings.
Silicate minerals
Soil production function
Regolith
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Silicate minerals
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In small bodies of granite.The function of microbes to the weathering of silicate minerals has been gradually paid attention by environmental researchers and a series important research progress has been achieved recently.In the sterile nutrition environment,microbes have accelerated the weathering rate of silicate minerals in nature to get nutrient material from silicate minerals.Due to the interaction of microbes in the weathering process of silicate minerals,the generally stable minerals could be more easily weathered than the generally unstable minerals.Therefore,interaction of microbes could cause the weathering order of silicate minerals different to the normal sequence of chemical weathering.During the weathering process,microbes could make marks on the surface of the weathered silicate minerals and could change their chemical components and textures through the enrichment or migration of elements or minerals.All the activities of microorganisms described above are affected by following four factors:contents of nutritious matters,organic acid,biofilm,extracellular polymeric substance(EPS) and the redox reactions.
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Silicate minerals
Potassium silicate
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Silicate minerals
Saturation (graph theory)
Soil production function
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Silicate minerals
Regolith
Soil production function
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Weathering rates play a significant role in the evolution of geochemistry of the Earth's surface and region environments. The basic theories of calculation of weathering rates are the mass balance and the law of reactions between solutions and minerals. The behavior of the element in weathering is influenced by many factors including weathering of bedrock, atmospheric precipitation, runoff of water, export of biomass and anthropogenic inputs(such as fertilization). Chemical reactions between minerals and solutions contribute to the base cation release rate due to chemical weathering of silicate minerals, and the total specific rate of reaction will be the sum of the rates of the individual reactions. Three key parameters of reactions between solutions and minerals are Acidic Neutral Capacities(ANC). Base Cation/Aluminium ratio(BC/A)and Critical Loads(CL). Methods of calculation of weathering rates mainly include①PROFILE modeling; ②basic cation depletion; ③input output budget; and ④Stronium isotope ratio. The PROFILE modeling is a steady stated and integrated soil chemistry model. Weathering rate of a mineral is controlled by dissolvable rate of the mineral, exposed surface area of the mineral. soil moisture saturation and soil layer thickness, and the total weathering rate is obtained by adding the contributions from all minerals. The element depletion is mostly the depletion of base cation such as Ca, Na, K and Mg. In the calculation of weathering rate, it's assumed that Ti,Zr or Nb is resistant, and thus Ti,Zr or Nb is considered to be immobile during weathering. Weathering rate is calculated as the difference between outputs and inputs, provided that the study area is in steady state. In general, the input is considered as the contribution from precipitation, while the output is calculated as the sum of ①river transported dissolved fraction; ②river transported suspended non detrital fraction; and ③biotic nutrient net uptake. It is suggested that Sr isotope is not fractionated during biotic and chemical processes, and Sr isotopic compositions in different ecosystem exchangeable cation pools are mixtures derived from mineral weathering reactions and atmospheric aerosol.
Silicate minerals
Soil production function
Bedrock
Saturation (graph theory)
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Abstract Chemical weathering produces solutes that control groundwater chemistry and supply ecosystems with essential nutrients. Although microbial activity influences silicate weathering rates and associated nutrient fluxes, its relative contribution to silicate weathering in natural settings remains largely unknown. We provide the first quantitative estimates of in situ silicate weathering rates that account for microbially induced dissolution and identify microbial actors associated with weathering. Nanoscale topography measurements showed that fungi colonizing olivine [(Mg,Fe)2SiO4] samples in a Mg-deficient forest soil accounted for up to 16% of the weathering flux after 9 mo of incubation. A local increase in olivine weathering rate was measured and attributed to fungal hyphae of Verticillium sp. Altogether, this approach provides quantitative parameters of bioweathering (i.e., rates and actors) and opens new avenues to improve elemental budgets in natural settings.
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Soil production function
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