Temporary and net sinks of atmospheric CO&lt;sub&gt;2&lt;/sub&gt; due to chemical weathering in subtropical catchment with mixing carbonate and silicate lithology

Abstract. The study provided the major ion chemistry, chemical weathering rates and temporary and net CO2 sinks in the Bei Jiang, which was characterized as a hyperactive region with high chemical weathering rates, carbonate and silicate mixing lithology, and abundant sulfuric acid chemical weathering agent of acid deposition and acid mining drainage (AMD) origins. The total chemical weathering rate of 85.46 t km−2 a−1 was comparable to that of other rivers in the hyperactive zones between the latitudes 0 and 30∘. A carbonate weathering rate of 61.15 t km−2 a−1 contributed to about 70 % of the total. The lithology, runoff, and geomorphology had a significant influence on the chemical weathering rate. The proportion of carbonate outcrops had a significant positive correlation with the chemical weathering rate. Due to the interaction between dilution and compensation effect, a significant positive linear relationship was detected between runoff and total carbonate and silicate weathering rates. The geomorphology factors such as catchment area, average slope, and hypsometric integral value (HI) had nonlinear correlation with chemical weathering rate and showed significant scale effect, which revealed the complexity in chemical weathering processes. Dissolved inorganic carbon (DIC) apportionment showed that CCW (carbonate weathering by CO2) was the dominant origin of DIC (35 %–87 %). SCW (carbonate weathering by H2SO4) (3 %–15 %) and CSW (silicate weathering by CO2) (7 %–59 %) were non-negligible processes. The temporary CO2 sink was 823.41×103 mol km−2 a−1. Compared with the temporary sink, the net sink of CO2 for the Bei Jiang was approximately 23.18×103 mol km−2 a−1 of CO2 and was about 2.82 % of the “temporary” CO2 sink. Human activities (sulfur acid deposition and AMD) dramatically decreased the CO2 net sink, even making chemical weathering a CO2 source to the atmosphere.

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Temporary and net sinks of atmospheric CO2 due to chemical weathering in subtropical catchment with mixing carbonate and silicate lithology

10.5194/bg-2019-310 ◽

2019 ◽

Author(s):

Yingjie Cao ◽

Yingxue Xuan ◽

Changyuan Tang ◽

Shuai Guan ◽

Yisheng Peng

Keyword(s):

Acid Deposition ◽

Chemical Weathering ◽

Silicate Weathering ◽

Carbonate Weathering ◽

Weathering Rate ◽

Weathering Rates ◽

Beijiang River ◽

Hypsometric Integral ◽

Co2 Sink ◽

Chemical Weathering Rate

Abstract. The study provides the major ion chemistry, chemical weathering rates and temporary and net CO2 sinks in the Beijiang River, which was characterized as hyperactive region with high chemical weathering rates, carbonate and silicate mixing lithology and abundant sulfuric acid chemical weathering agent with acid deposition and AMD origins. The total chemical weathering rate of 85.46 t km−2 a−1 was comparable to other rivers in the hyperactive zones between the latitude 0–30°. Carbonate weathering rates of 61.15 t km−2 a−1 contributed to about 70 % of the total. The lithology, runoff and geomorphology had significant influence on the chemical weathering rate. The proportion of carbonate outcrops had significant positive correlation with the chemical weathering rate. Due to the interaction between dilution and compensation effect, significant positive linear relationship was detected between runoff and total, carbonate and silicate weathering rates. The geomorphology factors such as catchment area, average slope and hypsometric integral value (HI) had non-linear correlation on chemical weathering rate and showed significant scale effect, which revealed the complexity in chemical weathering processes. DIC-apportionment showed that CCW (Carbonate weathering by CO2) was the dominant origin of DIC (35 %–87 %) and that SCW (Carbonate weathering by H2SO4) (3 %–15 %) and CSW (Silicate weathering by CO2) (7 %–59 %) were non-negligible processes. The temporary CO2 sink was 823.41 103 mol km−2 a−1. Compared with the temporary sink, the net sink of CO2 for the Beijiang River was approximately 23.18 × 103 mol km−2 a−1 of CO2 and was about 2.82 % of the temporary CO2 sink. Human activities (sulfur acid deposition and AMD) dramatically decreased the CO2 net sink and even make chemical weathering a CO2 source to the atmosphere.

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The rate of chemical weathering beneath a quiescent, surge-type, polythermal-based glacier, southern Spitsbergen, Svalbard

Annals of Glaciology ◽

10.1017/s0260305500011885 ◽

1997 ◽

Vol 24 ◽

pp. 27-31 ◽

Cited By ~ 18

Author(s):

J. L. Wadham ◽

A. J. Hodson ◽

M. Tranter ◽

J. A. Dowdeswell

Keyword(s):

Thermal Regime ◽

Chemical Weathering ◽

High Arctic ◽

Direct Link ◽

Water Fluxes ◽

Weathering Rate ◽

Weathering Rates ◽

Pertinent Data ◽

Chemical Weathering Rate ◽

Annual Discharge

Glacierized basins in the high Arctic are believed to be regions of low chemical weathering rates, despite the lack of pertinent data, because it is believed that water does not flow in significant quantities through subglacial drainage systems. We have calculated chemical weathering rates at Finsterwalderbreen, a polythermal, surge-type glacier in Svalbard. Rates of 320 and 150 meq Σ+ m−1 year−1 were measured in 1994 and 1995, respectively. The corresponding water fluxes were 4.1 × 107 and 1.7 × 107 m3. We estimate that we have measured ~72% of the total annual discharge, hence the true annual chemical weathering rates are ~440 and 210 meq Σ+ m−2 year−1, respectively This gives a mean annual chemical weathering rate of 330 meq Σ+ m−2 year−1, which approximates the continental average of 390 meq Σ+ m−2 year−1 and is intermediate between chemical weathering rates measured on cold-based glaciers (~110–160 meq Σ+ m−2 year−1) and temperate glaciers (450–1000 meq Σ+ m−2 year−1). This suggests that there may be a direct link between chemical weathering rates and thermal regime, and that glacierized basins in the high Arctic cannot necessarily be considered as regions of low chemical weathering and CO2 drawdown.

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Geochemistry of the dissolved loads during high-flow season of rivers in the southeastern coastal region of China: anthropogenic impact on chemical weathering and carbon sequestration

Biogeosciences ◽

10.5194/bg-15-4955-2018 ◽

2018 ◽

Vol 15 (16) ◽

pp. 4955-4971 ◽

Cited By ~ 4

Author(s):

Wenjing Liu ◽

Zhifang Xu ◽

Huiguo Sun ◽

Tong Zhao ◽

Chao Shi ◽

...

Keyword(s):

Nitric Acid ◽

Acid Deposition ◽

Anthropogenic Impact ◽

Chemical Weathering ◽

Dissolved Inorganic Carbon ◽

Coastal Region ◽

High Flow ◽

Silicate Weathering ◽

Chemical Compositions ◽

Co2 Consumption

Abstract. The southeastern coastal region is one of the most developed and populated areas in China. Meanwhile, it has been severely impacted by acid rain over many years. The chemical compositions and carbon isotope compositions of dissolved inorganic carbon (δ13CDIC) in river water in the high-flow season were investigated to estimate the chemical weathering and associated atmospheric CO2 consumption rates as well as the acid-deposition disturbance. Mass balance calculations indicated that the dissolved loads of major rivers in the Southeast Coastal River Basin (SECRB) were contributed to by atmospheric (14.3 %, 6.6 %–23.4 %), anthropogenic (15.7 %, 0 %–41.1 %), silicate weathering (39.5 %, 17.8 %–74.0 %) and carbonate weathering inputs (30.6 %, 3.9 %–62.0 %). The silicate and carbonate chemical weathering rates for these river watersheds were 14.2–35.8 and 1.8–52.1 t km−2 a−1, respectively. The associated mean CO2 consumption rate by silicate weathering for the whole SECRB was 191×103 mol km−2 a−1. The chemical and δ13CDIC evidence indicated that sulfuric and nitric acid (mainly from acid deposition) were significantly involved in the chemical weathering of rocks. There was an overestimation of CO2 consumption at 0.19×1012 g C a−1 if sulfuric and nitric acid were ignored, which accounted for about 33.6 % of the total CO2 consumption by silicate weathering in the SECRB. This study quantitatively highlights the role of acid deposition in chemical weathering, suggesting that the anthropogenic impact should be seriously considered in estimations of chemical weathering and associated CO2 consumption.

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Deepening roots can enhance carbonate weathering

10.5194/bg-2020-180 ◽

2020 ◽

Author(s):

Hang Wen ◽

Pamela L. Sullivan ◽

Gwendolyn L. Macpherson ◽

Sharon A. Billings ◽

Li Li

Keyword(s):

Carbon Cycle ◽

Reactive Transport ◽

Numerical Experiments ◽

Chemical Weathering ◽

Dissolved Inorganic Carbon ◽

Base Case ◽

Reaction Products ◽

Soil Co2 ◽

Carbonate Weathering ◽

Weathering Rates

Abstract. Carbonate weathering is essential in regulating atmospheric CO2 and carbon cycle at the century time scale. Plant roots have been known to accelerate weathering by elevating soil CO2 via respiration. It however remains poorly understood how and how much rooting characteristics (e.g., depth and density distribution) modify flow paths and weathering. We address this knowledge gap using field data from and reactive transport numerical experiments at the Konza Prairie Biological Station (Konza), Kansas (USA), a site where woody encroachment into grasslands is surmised to deepen roots. Results indicate that deepening roots potentially enhance weathering in two ways. First, deepening roots can control thermodynamic limits of carbonate dissolution by regulating how much CO2 transports downward to the deeper carbonate-rich zone. The base-case data and model from Konza reveal that concentrations of Ca and Dissolved Inorganic Carbon (DIC) are regulated by soil pCO2 driven by the seasonal fluctuation of soil respiration. This relationship can be encapsulated in equations derived in this work describing the dependence of Ca and DIC on temperature and soil CO2, which has been shown to apply in multiple carbonate-dominated catchments. Second, numerical experiments show that roots control weathering rates by regulating the amount of water fluxes that flush through the carbonate zone and export reaction products at dissolution equilibrium. Numerical experiments explored the potential effects of partitioning 40 % of infiltrated water to depth in woodlands compared to 5 % in grasslands. Soil CO2 data from wood- and grasslands suggest relatively similar soil CO2 distribution over depth, and only led to 1 % to 12 % difference in weathering rates if flow partitioning was kept the same between the two land covers. In contrast, deepening roots can enhance weathering by 17 % to 207 % as infiltration rates increased from 3.7 × 10−2 to 3.7 m/yr. Numerical experiments also indicated that weathering fronts in woodlands propagated > 2 times deeper compared to grasslands after 300 years at the infiltration rate of 0.37 m/yr. These differences in weathering fronts are ultimately caused by the contact time of CO2-charged water with carbonate rocks. We recognize that modeling results are subject to limitations in representing processes and parameters, but we propose that the data and numerical experiments allude to the hypothesis that (1) deepening roots can enhance carbonate weathering; (2) the hydrological impacts of rooting characteristics can be more influential than those of soil CO2 distribution in modulating weathering rates. We call for co-located characterizations of roots, subsurface structure, soil CO2 levels, and their linkage to water and water chemistry. These measurements will be essential to improve models and illuminate feedback mechanisms of land cover changes, chemical weathering, global carbon cycle, and climate.

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Geochemistry of the dissolved loads of rivers in Southeast Coastal Region, China: Anthropogenic impact on chemical weathering and carbon sequestration

10.5194/bg-2018-109 ◽

2018 ◽

Cited By ~ 1

Author(s):

Wenjing Liu ◽

Zhifang Xu ◽

Huiguo Sun ◽

Tong Zhao ◽

Chao Shi ◽

...

Keyword(s):

Sulfuric Acid ◽

Acid Deposition ◽

Chemical Weathering ◽

Dissolved Inorganic Carbon ◽

Coastal Region ◽

Carbon Isotope Ratio ◽

Silicate Weathering ◽

Chemical Compositions ◽

Mass Balance Calculation ◽

Co2 Consumption

Abstract. Southeast coastal region is the most developed and populated area in China. Meanwhile, it has been the most severe acid rain impacted region for many years. The chemical compositions and carbon isotope ratio of dissolved inorganic carbon (δ13CDIC) of rivers were investigated to evaluate the chemical weathering and associated atmospheric CO2 consumption rates. Mass balance calculation indicated that the dissolved loads of major rivers in the Southeast Coastal Rivers Basin (SECRB) were contributed by atmospheric (14.4 %, 6.6–23.4 %), anthropogenic (17.8 %, 0–55.2 %), silicate weathering (38.3 %, 10.7–74.0 %) and carbonate weathering inputs (29.4 %, 3.9–62.0 %). The silicate and carbonate chemical weathering rates for these river watersheds were 10.0–29.6 t km−2 a−1 and 1.0–54.1 t km−2 a−1, respectively. The associated mean CO2 consumption rate by silicate weathering for the whole SECRB were 167 × 103 mol km−2 a−1. The chemical and δ13CDIC evidences indicated that sulfuric acid (mainly from acid deposition) was significantly involved in chemical weathering of rocks. The calculation showed an overestimation of CO2 consumption at 0.19 × 1012 g C a−1 if sulfuric acid was ignored, which accounted for about 25 % of the total CO2 consumption by silicate weathering in the SECRB. This study quantitatively highlights that the role of sulfuric acid in chemical weathering, suggesting that acid deposition should be considered in studies of chemical weathering and associated CO2 consumption.

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Supply-limited weathering regime in a tropical shields basin (Ogooué River basin, Gabon)

10.5194/egusphere-egu2020-18181 ◽

2020 ◽

Author(s):

Jean-Sébastien Moquet ◽

Julien Bouchez ◽

Jean-Jacques Braun ◽

Sakaros Bogning ◽

Auguste Mbonda ◽

...

Keyword(s):

Chemical Weathering ◽

Biogeochemical Cycles ◽

Tectonic Activity ◽

Silicate Weathering ◽

Weathering Rate ◽

Weathering Rates ◽

Erosion Rates ◽

The World ◽

Weathering Intensity

At the global scale and on geological time scales, mechanical erosion and chemical weathering budgets are linked. Together, these processes contribute to the formation and the degradation of the Earth&#8217;s critical zone and to the biogeochemical cycles of elements. While the weathering of hot and humid shields areas exhibit low weathering rates because of the depth of the mature depleted soil mantle there, shields areas dominate the continents areas over intertropical regions and, therefore, represent a significant proportion of the global delivery of dissolved matter to the oceans. In addition, these environments are under supply-limited conditions (the weathering rate is limited by the low rates of the erosion) and thus particularly sensitive to long-term variability erosion rates. Despite this importance, weathering-erosion budgets and rates estimation in these environments is sparse, and generally performed at a local scale (soil profiles) or, when performed at a larger catchment scale, the intra cratonic characteristics variabilities (e. g. the diversity of mechanical erosional regimes) are usually not singled out.In the present study, we explored the variability of the weathering intensity of the Ogoou&#233; sub-basins (Western central Africa, Gabon) as a function of their geomorphologic, tectonic and lithological setting variability. We analyzed major and trace elements concentration and the strontium and neodymium isotopes of water, suspended matter sediments and bedload sampled in 24 Ogoou&#233; tributaries (September 2017 campaign). Our results show that shield areas exhibit a high variability of chemical weathering intensity, which follows the erosional regime characteristics of the studied sub-basins, likely related to their tectonic activity. Three regions can be distinguished: The Bateke plateau (East sub-basins - PB), is composed of pure sandstones (quartz) and is inert in term of tectonic activity and therefore in term of erosion and weathering budget; the northern sub-basins (NB) are subjected to low tectonic activity and exhibit slightly higher erosion and weathering intensity than PB region and, by comparison, southern sub-basins (SB) exhibits uplift activity which is traduced by more intensive erosion and weathering processes.The annual dissolved solid budget of the Ogoou&#233; basin is ~2.52 t.yr-1 for a rate of 11.7 t.km-2.yr-1. According to the source discrimination method performed based on the geochemical analysis, the atmospheric inputs contributes to around 20% to the TDS, the silicate weathering contribution dominates the dissolved exports throughout 70% of its production while the carbonates weathering lowly contributes to the TDS production.By comparison to the other large shields rivers, this basin exhibit a lower range of chemical silicate weathering rate than most of the world&#8217;s large rivers, with values similar to those of the Congo River. This new dataset provides a key information to complete the World River chemistry database, which is limited for inter-tropical regions, especially in tectonically quiescent environments. Moreover, this study provides new data for tropical shields contexts allowing for the exploration of the interactions between erosion rates and climate in the control of continental weathering rates, and their relationships with long-term carbon cycle and short-term biogeochemical cycles.

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Deepening roots can enhance carbonate weathering by amplifying CO2-rich recharge

Biogeosciences ◽

10.5194/bg-18-55-2021 ◽

2021 ◽

Vol 18 (1) ◽

pp. 55-75

Author(s):

Hang Wen ◽

Pamela L. Sullivan ◽

Gwendolyn L. Macpherson ◽

Sharon A. Billings ◽

Li Li

Keyword(s):

Carbon Cycle ◽

Reactive Transport ◽

Numerical Experiments ◽

Chemical Weathering ◽

Dissolved Inorganic Carbon ◽

Base Case ◽

Soil Co2 ◽

Carbonate Weathering ◽

Deep Subsurface ◽

Weathering Rates

Abstract. Carbonate weathering is essential in regulating atmospheric CO2 and carbon cycle at the century timescale. Plant roots accelerate weathering by elevating soil CO2 via respiration. It however remains poorly understood how and how much rooting characteristics (e.g., depth and density distribution) modify flow paths and weathering. We address this knowledge gap using field data from and reactive transport numerical experiments at the Konza Prairie Biological Station (Konza), Kansas (USA), a site where woody encroachment into grasslands is surmised to deepen roots. Results indicate that deepening roots can enhance weathering in two ways. First, deepening roots can control thermodynamic limits of carbonate dissolution by regulating how much CO2 transports vertical downward to the deeper carbonate-rich zone. The base-case data and model from Konza reveal that concentrations of Ca and dissolved inorganic carbon (DIC) are regulated by soil pCO2 driven by the seasonal soil respiration. This relationship can be encapsulated in equations derived in this work describing the dependence of Ca and DIC on temperature and soil CO2. The relationship can explain spring water Ca and DIC concentrations from multiple carbonate-dominated catchments. Second, numerical experiments show that roots control weathering rates by regulating recharge (or vertical water fluxes) into the deeper carbonate zone and export reaction products at dissolution equilibrium. The numerical experiments explored the potential effects of partitioning 40 % of infiltrated water to depth in woodlands compared to 5 % in grasslands. Soil CO2 data suggest relatively similar soil CO2 distribution over depth, which in woodlands and grasslands leads only to 1 % to ∼ 12 % difference in weathering rates if flow partitioning was kept the same between the two land covers. In contrast, deepening roots can enhance weathering by ∼ 17 % to 200 % as infiltration rates increased from 3.7 × 10−2 to 3.7 m/a. Weathering rates in these cases however are more than an order of magnitude higher than a case without roots at all, underscoring the essential role of roots in general. Numerical experiments also indicate that weathering fronts in woodlands propagated > 2 times deeper compared to grasslands after 300 years at an infiltration rate of 0.37 m/a. These differences in weathering fronts are ultimately caused by the differences in the contact times of CO2-charged water with carbonate in the deep subsurface. Within the limitation of modeling exercises, these data and numerical experiments prompt the hypothesis that (1) deepening roots in woodlands can enhance carbonate weathering by promoting recharge and CO2–carbonate contact in the deep subsurface and (2) the hydrological impacts of rooting characteristics can be more influential than those of soil CO2 distribution in modulating weathering rates. We call for colocated characterizations of roots, subsurface structure, and soil CO2 levels, as well as their linkage to water and water chemistry. These measurements will be essential to illuminate feedback mechanisms of land cover changes, chemical weathering, global carbon cycle, and climate.

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