scholarly journals Global silicate weathering flux overestimated because of sediment–water cation exchange

2020 ◽  
Vol 118 (1) ◽  
pp. e2016430118
Author(s):  
Edward T. Tipper ◽  
Emily I. Stevenson ◽  
Victoria Alcock ◽  
Alasdair C. G. Knight ◽  
J. Jotautas Baronas ◽  
...  
Keyword(s):  
Cation Exchange ◽  
River Water ◽  
Chemical Weathering ◽  
Global Scale ◽  
Mineral Weathering ◽  
Climate Feedback ◽  
Silicate Weathering ◽  
Exchange Equilibrium ◽  
Silicate Mineral ◽  
River Water Chemistry

Rivers carry the dissolved and solid products of silicate mineral weathering, a process that removesCO2from the atmosphere and provides a key negative climate feedback over geological timescales. Here we show that, in some river systems, a reactive exchange pool on river suspended particulate matter, bonded weakly to mineral surfaces, increases the mobile cation flux by 50%. The chemistry of both river waters and the exchange pool demonstrates exchange equilibrium, confirmed by Sr isotopes. Global silicate weathering fluxes are calculated based on riverine dissolved sodium (Na+) from silicate minerals. The large exchange pool supplies Na+of nonsilicate origin to the dissolved load, especially in catchments with widespread marine sediments, or where rocks have equilibrated with saline basement fluids. We quantify this by comparing the riverine sediment exchange pool and river water chemistry. In some basins, cation exchange could account for the majority of sodium in the river water, significantly reducing estimates of silicate weathering. At a global scale, we demonstrate that silicate weathering fluxes are overestimated by 12 to 28%. This overestimation is greatest in regions of high erosion and high sediment loads where the negative climate feedback has a maximum sensitivity to chemical weathering reactions. In the context of other recent findings that reduce the netCO2consumption through chemical weathering, the magnitude of the continental silicate weathering fluxes and its implications for solid EarthCO2degassing fluxes need to be further investigated.

scholarly journals A dynamic local scale vegetation model for lycophytes (LYCOm)

2021 ◽  
Author(s):  
Suman Halder ◽  
Susanne K. M. Arens ◽  
Kai Jensen ◽  
Tais Wittchen Dahl ◽  
Philipp Porada
Keyword(s):  
Soil Carbon ◽  
Vascular Plants ◽  
Chemical Weathering ◽  
Vascular Tissue ◽  
Net Primary Production ◽  
Soil Microbial Activity ◽  
Global Scale ◽  
Local Scale ◽  
Climatic Conditions ◽  
Silicate Weathering

Abstract. Lycophytes (club mosses) represent a distinct lineage of vascular plants with a long evolutionary history including numerous extant and extinct species which started out as herbaceous plants and later evolved into woody plants. They enriched the soil carbon pool through newly developed root-like structures and promoted soil microbial activity by providing organic matter. These plants enhanced soil carbon dioxide (CO2) via root respiration and also modified soil hydrology. These effects had the potential to promote the dissolution of silicate minerals, thus intensifying silicate weathering. The weathering of silicate rocks is considered one of the most significant geochemical regulators of atmospheric CO2 on a long (hundreds of thousands to millions of years) timescale. The motivation for this study is to achieve an increased understanding of the realized impacts of vascular plants, represented by modern relatives to the most basal plants with vascular tissue and shallow root system, on silicate weathering and past climate. To this end, it is necessary to quantify physiological characteristics, spatial distribution, carbon balance, and the hydrological impacts of early lycophytes. These properties, however, cannot be easily derived from proxies such as fossil records, for instance. Hence, as a first step, a process-based model is developed here to estimate net carbon uptake by these organisms at the local scale, considering key features such as biomass distribution above and below ground, root distribution in soil regulating water uptake by plants besides, stomatal regulation of water loss and photosynthesis, and not withholding respiration in roots. The model features ranges of key physiological traits of lycophytes to predict the emerging characteristics of the lycophyte community under any given climate by implicitly simulating the process of selection. In this way, also extinct plant communities can be represented. In addition to physiological properties, the model also simulates weathering rates using a simple limit-based approach and estimates the biotic enhancement of weathering by lycophytes. We run the Lycophyte model, called LYCOm, at seven sites encompassing various climate zones under today’s climatic conditions. LYCOm is able to simulate realistic properties of lycophyte communities at the respective locations and estimates values of Net Primary Production (NPP) ranging from 126 g carbon m−2 year−1 to 245 g carbon m−2 year−1. Our limit-based weathering model predicts a mean chemical weathering rate ranging from 5.3 to 45.1 cm ka−1 rock with lycophytes varying between different sites, as opposed to 0.6–8.3 cm rock ka−1 without lycophytes, thereby highlighting the potential importance of such vegetation at the local scale for enhancing chemical weathering. Our modeling study establishes a basis for assessing biotic enhancement of weathering by lycophytes at the global scale and also for the geological past. Although our method is associated with limitations and uncertainties, it represents a novel, complementary approach towards estimating the impacts of lycophytes on biogeochemistry and climate.

scholarly journals ¡Cuba! River Water Chemistry Reveals Rapid Chemical Weathering, the Echo of Uplift, and the Promise of More Sustainable Agriculture

GSA Today ◽  
2020 ◽  
Vol 30 (3) ◽  
pp. 4-10 ◽  
Author(s):  
Paul Bierman ◽  
Rita Yvelice Sibello Hernández ◽  
Amanda H. Schmidt ◽  
Héctor Alejandro Cartas Aguila ◽  
Yoelvis Bolaños Alvarez ◽  
...  
Keyword(s):  
Sustainable Agriculture ◽  
Water Chemistry ◽  
River Water ◽  
Chemical Weathering ◽  
River Water Chemistry

scholarly journals Sr isotopic characteristics in two small watersheds draining silicate and carbonate rocks: implication for studies on seawater Sr isotopic evolution

2014 ◽  
Vol 18 (2) ◽  
pp. 559-573
Author(s):  
W. H. Wu ◽  
H. B. Zheng ◽  
J. H. Cao ◽  
J. D. Yang
Keyword(s):  
River Water ◽  
Carbonate Rocks ◽  
Chemical Weathering ◽  
Silicate Weathering ◽  
86Sr Ratio ◽  
Weathering Rates ◽  
Isotopic Compositions ◽  
Small Watersheds ◽  
Isotopic Evolution ◽  
The Pearl River

Abstract. We systematically investigated the Sr isotopic characteristics of a small silicate watershed, the Xishui River a tributary of the Yangtze River, and a small carbonate watershed, the Guijiang River a tributary of the Pearl River. The results show that the two rivers have uncommon Sr isotopic characteristics compared with most small watersheds. Specifically, the silicate watershed (Xishui River) has relatively high Sr concentrations (0.468 to 1.70 μmol L−1 in summer and 1.30 to 3.17 μmol L−1 in winter, respectively) and low 87Sr/86Sr ratios (0.708686 to 0.709148 in summer and 0.708515 to 0.709305 in winter). The carbonate watershed (Guijiang River) has low Sr concentrations (0.124 to 1.098 μmol L−1) and high 87Sr/86Sr ratios (0.710558 to 0.724605). As the 87Sr/86Sr ratios in the Xishui River are lower than those in seawater, the 87Sr/86Sr ratio of seawater will decrease after the river water is transported to the oceans. Previous studies have also shown that some basaltic watersheds with extremely high chemical weathering rates reduced the seawater Sr isotope ratios. In other words, river catchments with high silicate weathering rates do not certainly transport highly radiogenic Sr into oceans. Therefore, the use of the variations in the seawater 87Sr/86Sr ratio to indicate the continental silicate weathering intensity may be questionable. In the Guijiang River catchment, the 87Sr/86Sr ratios of carbonate rocks and other sources (rainwater, domestic and industrial waste water, and agricultural fertilizer) are lower than 0.71. In comparison, some non-carbonate components, such as sand rocks, mud rocks, and shales, have relatively high Sr isotopic compositions. Moreover, granites accounted for only 5% of the drainage area have extremely high 87Sr/86Sr ratios with an average of greater than 0.8. Therefore, a few silicate components in carbonate rocks obviously increase the Sr isotopic compositions of the river water.

scholarly journals Hydro-Geochemistry of the River Water in the Jiulongjiang River Basin, Southeast China: Implications of Anthropogenic Inputs and Chemical Weathering

2019 ◽  
Vol 16 (3) ◽  
pp. 440 ◽  
Author(s):  
Xiaoqiang Li ◽  
Guilin Han ◽  
Man Liu ◽  
Kunhua Yang ◽  
Jinke Liu
Keyword(s):  
River Water ◽  
River Basin ◽  
Human Activities ◽  
Chemical Weathering ◽  
Silicate Weathering ◽  
Carbonate Weathering ◽  
Southeast China ◽  
Anthropogenic Inputs ◽  
Weathering Process ◽  
Jiulongjiang River

This study focuses on the chemical weathering process under the influence of human activities in the Jiulongjiang River basin, which is the most developed and heavily polluted area in southeast China. The average total dissolved solid (TDS) of the river water is 116.6 mg/L and total cation concentration ( TZ + ) is 1.5 meq/L. Calcium and HCO 3 − followed by Na + and SO 4 2 − constitute the main species in river waters. A mass balance based on cations calculation indicated that the silicate weathering (43.3%), carbonate weathering (30.7%), atmospheric (15.6%) and anthropogenic inputs (10.4%) are four reservoirs contributing to the dissolved load. Silicates (SCW) and carbonates (CCW) chemical weathering rates are calculated to be approximately 53.2 ton/km2/a and 15.0 ton/km2/a, respectively. When sulfuric and nitric acid from rainfall affected by human activities are involved in the weathering process, the actual atmospheric CO 2 consumption rates are estimated at 3.7 × 105 mol/km2/a for silicate weathering and 2.2 × 105 mol/km2/a for carbonate weathering. An overestimated carbon sink (17.4 Gg C / a ) is about 27.0% of the CO 2 consumption flux via silicate weathering in the Jiulongjiang River basin, this result shows the strong effects of anthropogenic factors on atmospheric CO 2 level and current and future climate change of earth.

scholarly journals Continental weathering using combined Hf-Nd isotope system and clay mineralogy: new insights for the Late Cretaceous climate

2021 ◽  
Author(s):  
Pauline Corentin ◽  
Emmanuelle Puceat ◽  
Pierre Pellenard ◽  
Nicolas Freslon ◽  
Michel Guiraud ◽  
...  
Keyword(s):  
Clay Mineral ◽  
Late Cretaceous ◽  
Chemical Weathering ◽  
Clay Mineralogy ◽  
Global Scale ◽  
Climatic Conditions ◽  
Silicate Weathering ◽  
Nd Isotope ◽  
Continental Weathering ◽  
The Impact

<p>The Late Cretaceous period records a pronounced decrease in marine temperatures at a global scale initiating the last greenhouse-icehouse transition, whose origin still remains enigmatic. Continental weathering represents a major sink of atmospheric CO<sub>2</sub> through silicate weathering reactions yet the importance of this process in the Late Cretaceous cooling has only been scarcely explored.</p><p>In this study we explore the impact of the eastern South American margin uplift, concomitant to the long-term Late Cretaceous cooling, on the evolution of chemical weathering of the Brazilian margin, using a new proxy of silicate weathering based on the coupled Lu-Hf and Sm-Nd isotope systems in clays. This proxy, expressed as Δε<sub>Hf</sub>, has been recently calibrated in modern environments (Bayon et al., 2016) but has only been scarcely applied to deep-time environments. This proxy, applied on sediments from DSDP site 356 on the São Paulo Plateau, highlights a marked increase in silicate chemical weathering of the southeastern Brazilian margin from the Santonian to the Maastrichtian, also supported by the evolution of the chemical index of alteration (CIA) and clay mineralogy.</p><p>This increase follows an episode of enhanced mechanical erosion of the margin revealed in the Turonian to Santonian by an increase of primary clay mineral (illite, chlorite) and Ti/Al ratio, linked to the tectonic uplift of the margin. Clay mineral assemblages additionally point to an evolution of local climatic conditions from arid to a more hydrolysing climate following this episode, that we link to a “rain shadow effect” affecting the eastern side of the newly formed relief that would have enhanced chemical weathering of the margin.</p><p>Importantly the temporal coincidence of the increase in chemical weathering depicted here with the marked acceleration of the global cooling recorded worldwide during the Campanian points to a potentially important role of this process on the overall climate decline initiating the descent into our icehouse climate mode. Although records from additional sites are needed to establish the spatial extent of the margin affected by this process, our new dataset brings new insights about the impact of tectonic forcing on climate.</p><p>Bayon et al. (2016) EPSL 438, p. 25-36.</p>

Impacts of early vegetation on biogeochemical cycles

2021 ◽  
Author(s):  
Suman Halder ◽  
Philipp Porada
Keyword(s):  
Soil Carbon ◽  
Root Respiration ◽  
Chemical Weathering ◽  
Soil Microbial Activity ◽  
Global Scale ◽  
Local Scale ◽  
Climatic Conditions ◽  
Silicate Weathering ◽  
Soil Microbial ◽  
Simple Limit

<p>Lycophytes (club mosses) represent a distinct lineage of vascular plants with a long history including numerous extant and extinct species. They enriched the soil carbon pool through newly developed root-like structures and promoted soil microbial activity by providing organic matter. They enhanced soil carbon dioxide (CO<sub>2</sub>) via root respiration and also modified soil hydrology. These effects had the potential to promote the dissolution of silicate minerals, thus intensifying silicate weathering. The weathering of silicate rocks is considered one of the most significant geo-chemical regulators of atmospheric CO<sub>2</sub> on a long (hundreds of thousands to millions of years) timescale. The motivation for this study is to achieve an increased understanding of the realized impacts of lycophytes on silicate weathering and past climate. To this end, it is necessary to quantify physiological characteristics, spatial distribution, the carbon balance, and hydrological impacts of early lycophytes. These properties, however, cannot be easily derived from proxies. Hence, as a first step, a process-based model is developed here to estimate net carbon uptake by these organisms at the local scale, considering key features such as root distribution, stomatal regulation of water loss, and root respiration.<br>The model features ranges of key physiological traits of lycophytes to predict the emerging characteristics of the lycophyte community under any given climate by implicitly simulating the process of selection. In this way, also extinct plant communities can be represented.<br>In addition to physiological properties, the model also simulates weathering rates using a simple limit-based approach and estimates the biotic enhancement of weathering by lycophytes. We run the Lycophyte model, called LYCOm, at seven sites encompassing various climate zones under today's climatic conditions. LYCOm is able to simulate realistic properties of lycophyte communities at the respective locations and estimates an average NPP ranging from 245 g carbon m<sup>-2</sup> year<sup>-1</sup> in Costa Rica to 126 g carbon m<sup>-2</sup> year<sup>-1</sup> in Estonia. Our limit-based weathering model predicts a chemical weathering rate ranging from 0.026 to 0.31 mm rock a<sup>-1 </sup>, thereby highlighting the potential importance of lycophytes at the local scale for enhancing chemical weathering. Our modeling study establishes a basis for assessing biotic enhancement of weathering by lycophytes at the global scale and also for the geological past. </p>

scholarly journals The Contribution of Groundwater to the Salinization of Reservoir-Based Irrigation Systems

Agronomy ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 512
Author(s):  
Michiele Gebrehiwet ◽  
Nata T. Tafesse ◽  
Solomon Habtu ◽  
Berhanu F. Alemaw ◽  
Kebabonye Laletsang ◽  
...  
Keyword(s):  
Water Quality ◽  
Cation Exchange ◽  
Irrigation Water ◽  
Groundwater Potential ◽  
Hydrochemical Facies ◽  
Command Area ◽  
Silicate Weathering ◽  
Irrigation Water Quality ◽  
Carbonate Minerals ◽  
Watershed Area

This study evaluates the cause of salinization in an irrigation scheme of 100 ha supplied from a reservoir. The scheme is located in Gumselasa catchment (28 km2), Tigray region, northern Ethiopia. The catchment is underlain by limestone–shale–marl intercalations with dolerite intrusion and some recent sediments. Water balance computation, hydrochemical analyses and irrigation water quality analyses methods were used in this investigation. Surface waters (river and reservoir) and groundwater samples were collected and analyzed. The water table in the irrigated land is ranging 0.2–2 m below the ground level. The majority of groundwater in the effective watershed area and the river and dam waters are fresh and alkaline whereas in the command area the groundwater is dominantly brackish and alkaline. The main hydrochemical facies in the groundwater in the effective watershed area are Ca-Na-SO4-HCO3, Ca-Na- HCO3-SO4, and Ca-Na-Mg-SO4-HCO3. The river and dam waters are Mg-Na-HCO3-SO4 and HCO3-SO4-Cl types, respectively. In the command area the main hydrochemical facies in the groundwater are Ca-Na-HCO3-SO4 and Ca-Na-Mg-SO4-HCO3. Irrigation water quality analyses revealed that salinity and toxicity hazards increase from the effective watershed to the irrigated land following the direction of the water flow. The results also showed that the analyzed waters for irrigation purpose had no sodicity hazard. The major composition controlling mechanisms in the groundwater chemistry was identified as the dissolution of carbonate minerals, silicate weathering, and cation exchange. One of the impacts of the construction of the dam in the hydrologic environment of the catchment is on its groundwater potential. The dam is indirectly recharging the aquifers and enhances the groundwater potential of the area. This increment of availability of groundwater enhanced dissolution of carbonate minerals (calcite, dolomite, and gypsum), silicate weathering and cation exchange processes, which are the main causes of salinity in the irrigated land. The rising of the brackish groundwater combined with insufficient leaching contributed to secondary salinization development in the irrigated land. Installation of surface and subsurface drainage systems and planting salt tolerant (salt loving) plants are recommended to minimize the risk of salinization and salt accumulation in the soils of the irrigated land.

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