Chemical Weathering Of Minerals Research Articles

Lake Kivu River Tributaries Physicochemical Characteristics and Status of Waters, Democratic Republic of Congo Side

Rivers often play a vital role in the transport of major natural chemicals entering through a variety of pathways, including atmospheric inputs, chemical weathering of minerals, mechanical erosion of rocks and soil particles, and soil leaching. Increased anthropogenic activities on the shoreline of Lake Kivu combined with existing land use practices may increase changes in river water quality and composition. Knowing the physico-chemical and biological contribution of each tributary of the lake is vital for the management of its biodiversity. This study aimed at determining the physico-chemical characteristics, water quality indices and identifying the polluted tributary rivers that feed Lake Kivu on the Congo side. The physicochemical characteristics were determined for each water sample following water quantity protocol for each analysis at the Malacology Laboratory of the Biology Department of Lwiro Research Center. Two pollution level indices were used to determine the level of organic pollution in watercourses. The physico-chemical characteristics of rivers vary from one river to another depending on the anthropogenic activities around the different sub-basins of these rivers. The state of the rivers presented here reveals that the majority of them are moderately polluted and others slightly polluted. No rivers were very heavily polluted or good in the Lake Kivu basin on the DR Congo side. There is a strong or moderate correlation between certain parameters and the water quality indices used in this study (LISEC and OPI). Due to increase in anthropogenic activities near watercourses, further research is needed and the combination of several complex analytical methods should be used in the future to better characterize these waters.

Net Geochemical Release of Base Cations From 25 Forested Watersheds in the Catskill Region of New York

Chemical weathering of minerals is the principal mechanism by which base cations (Ca2+, Mg2+, K+, and Na+) are released and acidity is neutralized in soils, bedrock, and drainage waters. Quantifying the release of base cations from watershed soils is therefore crucial for the calculation of “critical loads” of atmospheric acidity to forest ecosystems. We used a mass-balance approach to estimate the rate of release of base cations in 25 headwater catchments in the Catskill region of New York, an area historically subject to high inputs of acid deposition. In 2010–2013, total net base cation release via geochemical processes averaged 1,704 eq ha–1 yr–1 (range: 928–2,622). Calcium accounted for 58% of this total, averaging 498 mol ha–1 yr–1 (range: 209–815). Mass balance estimates of net geochemical release of base cations were most strongly driven by stream export and biomass uptake fluxes, with only minor contributions from precipitation. Documented rates of base cation depletion from soil exchange sites in the region were also small relative to the net geochemical release rates. We observed a significant influence of bedrock type on net base cation release rates (P = 0.002), and a weak but significant negative correlation with watershed elevation (r = −0.51). Relationships with other geographic factors such as aspect and watershed size were not significant. Net base cation release was 4.5 times higher than precipitation inputs of SO42– and NO3–, suggesting that sources of acidity internal to the watershed are now more important drivers of weathering than acid deposition. Our data suggest that release of base cations from most Catskill forest soils is sufficient to neutralize existing inputs of acidity.

The Enrichment Process of Groundwater Fluorine in Sea Water Intrusion Area of Gaomi City, China.

A typical area, Gaomi City in China, was chosen to discuss the enrichment process of groundwater fluorine in sea water intrusion area. The groundwater had fluorine levels of 0.09-10.99 mg/L, with an average concentration of 1.38 mg/L. The high-fluorine groundwater was mainly distributed in the unconsolidated Quaternary sediments, where concentrations in 83.6% of the samples exceeded the national limit of 1.0 mg/L. The groundwater in the Quaternary sediments also had higher levels of Cl- , TDS, Mg2+ , and pH and lower levels of Ca2+ , Co, Ni, and Cu than that in the bedrock. The groundwater fluorine levels in the Quaternary sediments are positively correlated with Cl- , TDS, Mg2+ , pH, and negatively correlated with Ca2+ , γCa2+ /γMg2+ , Co, Ni, Cu. Geochemical indices of Cl- and TDS indicate sea water intrusion in the Quaternary high-fluorine groundwater area (F- > 1.0 mg/L), while they do not indicate any intrusion in the bedrock area. The chemical weathering of minerals was intensified with the intrusion of sea water. Cation exchange was confirmed to occur in the Quaternary sediments and was promoted by sea water intrusion. Cation exchange consumes part of groundwater Ca2+ and permits more F- dissolving. Consequently, in the Quaternary sediments, the groundwater was supersaturated with CaF2 minerals and undersaturated with MgF2 minerals when F- > 1.0 mg/L, while CaF2 and MgF2 minerals both are undersaturated when F- < 1.0 mg/L. Thus, the chemical weathering of minerals and cation exchange caused by sea water intrusion are the crucial processes controlling the groundwater fluorine levels, which should be considered when the groundwater fluorine enrichment mechanism is discussed along coastal zones.

The Enrichment Process of Groundwater Fluorine in Seawater Intrusion Area of Gaomi City, China.

A typical area, Gaomi City in China, was chosen to discuss the enrichment process of groundwater fluorine in seawater intrusion area. The groundwater had fluorine levels of 0.09-10.99 mg/L, with an average concentration of 1.38 mg/L. The high-fluorine groundwater was mainly distributed in the unconsolidated Quaternary sediments, where concentrations in 83.6% of the samples exceeded the national limit of 1.0 mg/L. The groundwater in the Quaternary sediments also had higher levels of Cl- , TDS, Mg2+ , pH and lower levels of Ca2+ , Co, Ni, Cu than that in the bedrock. The groundwater fluorine levels in the Quaternary sediments are positively correlated with Cl- , TDS, Mg2+ , pH, and negatively correlated with Ca2+ , γCa2+ /γMg2+ , Co, Ni, Cu. Geochemical indexes of Cl- and TDS indicate seawater intrusion in the Quaternary high-fluorine groundwater area (F- > 1.0 mg/L), while they do not in the bedrock area. The chemical weathering of minerals was intensified with the intrusion of seawater. Cation exchange was confirmed to occur in the Quaternary sediments, and was promoted by seawater intrusion. Cation exchange consumes part of groundwater Ca2+ and permits more F- dissolving. Consequently, in the Quaternary sediments, the groundwater was super-saturated with CaF2 minerals and under-saturated with MgF2 minerals when F- > 1.0 mg/L, while CaF2 and MgF2 minerals both are under-saturated when F- < 1.0 mg/L. Thus, the chemical weathering of minerals and cation exchange caused by seawater intrusion are the crucial processes controlling the groundwater fluorine levels, which should be considered when the groundwater fluorine enrichment mechanism is discussed along coastal zones. This article is protected by copyright. All rights reserved.

Comment on carbon dioxide emissions by rock organic carbon oxidation

In a holistic study of the modern-day Mackenzie River Basin, [Horan and others (2019)][1] budget the uptake and release of atmospheric CO2 by chemical weathering of minerals and biospheric organic carbon burial and, in particular, quantify the important contribution that kerogen oxidation plays in

Mineral Weathering and Bedrock Weakening: Modeling Microscale Bedrock Damage Under Biotite Weathering

Bedrock weakening is of wide interest because it influences landscape evolution, chemical weathering, and subsurface hydrology. A longstanding hypothesis states that bedrock weakening is driven by chemical weathering of minerals like biotite, which expand as they weather and create stresses sufficient to fracture rock. We build on recent advances in rock damage mechanics to develop a model for the influence of multimineral chemical weathering on bedrock damage, which is defined as the reduction in bedrock stiffness. We use biotite chemical weathering as an example application of this model to explore how the abundance, aspect ratio, and orientation affect the time‐dependent evolution of bedrock damage during biotite chemical weathering. Our simulations suggest that biotite abundance and aspect ratio have a profound effect on the evolution of bedrock damage during biotite chemical weathering. These characteristics exert particularly strong influences on the timing of the onset of damage, which occurs earlier under higher biotite abundances and smaller biotite aspect ratios. Biotite orientation, by contrast, exerts a relatively weak influence on damage. Our simulations further show that damage development is strongly influenced by the boundary conditions, with damage initiating earlier under laterally confined boundaries than under unconfined boundaries. These simulations suggest that relatively minor differences in biotite populations can drive significant differences in the progression of rock weakening. This highlights the need for observations of biotite abundance, aspect ratio, and orientation at the mineral and field scales and motivates efforts to upscale this microscale model to investigate the evolution of the macroscale fracture network.

Iron stocks of buried Podzols: Endogenic iron deficits and potential exogenic enrichment in the Maashorst region, SE Netherlands

Podzolation is the dominant soil forming process in chemical poor sandy soils. It is well studied how iron concentrations of podzols are effected by translocation of active iron from eluvial to illuvial horizons and leaching to the aquifer. Iron stocks of Podzols, in contrasts, have not been widely studied for comparison purposes of individual soil horizons or between soils. In this study we provide an analysis of the iron stocks for two buried Podzols developed in Late-Glacial aeolian coversands. Chemical analyses of the active and immobile iron fractions in each of the horizons in both profiles show that more iron has been involved in the podzolation process, than the amount which can be derived by chemical weathering of minerals in the overlying soil horizons. This deficit in endogenic iron therefore requires exogenic enrichment to explain the observed iron concentrations during podzolation. The contribution of exogenic iron was studied using micrometeorites as a proxy for atmospheric deposition. These particles of cosmic origins are part of a continuous flux of iron-rich materials into the Earth's atmosphere and they are deposited over time on every square meter of land surface. Their extraction from ectorganic F horizon of initial Podzols helped illustrate that atmospheric deposition in the form of aerosol and aeolian (e.g. Sahara) dust, micrometeorites and other hydrolysable particles are a relevant iron contribution in soil development. The requisite active iron for podzolation can therefore be derived from chemical weathering of atmospheric iron sources in the acidic soil environment.

Soil development along primary succession sequences on moraines of Hailuogou Glacier, Gongga Mountain, Sichuan, China

Soil properties related to soil development were measured in six profiles over approximately 180 years of soil development on recessional moraines of the Hailuogou Glacier , Sichuan of southwestern China. It is hypothesized that soil development is strictly time-dependent. Field and laboratory work indicate that as soil develops from initially coarse gravel outwash , the properties undergo a progressive physical and chemical change such that there is a considerable profile differentiation between the youngest and the oldest soils. The pH is also highly stratified; it decreases with time from 8.5 to 4.2 in the upper mineral soil and increases with depth in all profiles. Accumulation of soil organic C and N increases with time but the rates of accumulation become slower with time. Within the investigated timespan, soil C and N accumulated to a considerable level of 3.5 and 0.6 kg/m 2 respectively, with mean annual rates of 28 g/m 2 for carbon and 3.5 g/m 2 for nitrogen. The rapid accumulation of organic C and N accelerates the processes of soil formation, but the content of organic C and N did not reach a steady-state during the observed timespan. The accumulation of soil organic matter results in increased acid production and in the chemical weathering of minerals that promote formation and translocation of the clay fraction and leaching of carbonate; it is also directly responsible for development of soil properties such as cation exchange capacity (CEC), and bulk density.

Biological potential of low-temperature aqueous environments on Mars

We have explored chemical weathering of probable martian materials at low temperatures based on the increasing evidence for non-hydrothermal water at or near the martian surface. Chemical weathering of minerals at low temperatures (as low as 0 °C) in aqueous environments on Mars can provide geochemical energy to support construction of potential martian organisms. Here, we examine the geochemical energy available from the interaction of the martian surface or near-surface materials with low-temperature water. We calculate the Gibbs free energy for 13 different weathering reactions that are likely to be important on Mars. The aqueous weathering of 1 kg of an ultramafic rock such as the Chassigny meteorite under present martian conditions can support the construction of ~30 g of microbes. The aqueous weathering of 1 kg of a basaltic rock on Mars can support the construction of ~26 g of biomass under present martian conditions and ~32 grams for conditions probable in the past. This means that ~1.3×1019 g of potential biomass could have been supported from weathering a global layer of rock 1 m thick. Thus, low-temperature water–rock reactions on Mars can produce abundant geochemical energy for potential martian microbes.

An anoxic event and other biogeochemical effects of the Pantanal wetland on the Paraguay River

The Paraguay River was sampled throughout the annual cycle at two sites located downriver from most of the Pantanal, and major tributaries were occasionally sampled close to their entry into the Pantanal. The floodplains strongly modulate the discharge regime and substantially reduce runoff by enhancing evapotranspirative losses. Contact of the river water with the floodplain results in depletion of dissolved O2, oversaturation of CO2 and CH4 loss of suspended sediments, and reduced export of N and P. Oxygen depletion and associated chemical changes are most marked when river water first contacts the floodplain; in 1995, the water remained anoxic throughout the river channel for 6 weeks, causing massive fish mortality. Bottle incubations showed that the rate of O2 consumption by the river water during the anoxic event was high at first (7.2 µM h−1) but declined exponentially over several hours and was not stimulated by organic carbon and nutrient additions. The O2 demand may be due largely to bacterial CH4 oxidation; the concentration of CH4 in the river was particularly high (∼31 µM) at the time of the incubations. The O2 depletion corresponded with higher concentrations of most major ions, Si, and dissolved organic carbon but was not accompanied by elevated concentrations of inorganic N and P, H2S, or most of the 46 dissolved trace elements that were measured. In contrast to O2 depletion and associated chemical changes, sediment retention by the floodplains was greatest at maximum river stages. Most chemical weathering of minerals seems to take place in the upland drainage basins rather than on the floodplains, and most major solutes display conservative mixing in the river‐floodplain system.

Uptake of Nutrients in a Plantation ofAcacia mangiumin Relation to Decrease in Soil Amounts

Abstract Amounts of total nitrogen, phosphorus, potassium, calcium, magnesium, manganese, and sodium in the humus layer and plant-available or exchangeable nutrients in the top 30 cm of the soil were determined before planting and in a 45-month-old plantation of Acacia mangium. Amounts were lower in the plantation than before planting owing to plant uptake and leaching. However, for potassium and calcium the difference was much smaller than the amounts in the plantation biomass, indicating that the plants had taken up nutrients from soil depths below 30 cm or had utilized other sources of nutrients. The other main sources of nutrients were mineralization of dead logs, big branches, and roots, none of which had been included in the humus sampling, and chemical weathering of minerals. The supply of plant nutrients through atmospheric input was low, and there was a negligible input of nutrients dissolved in laterally flowing water because the investigated plot was situated near the water divide. The investig...