scholarly journals Deepening roots can enhance carbonate weathering

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.

scholarly journals Deepening roots can enhance carbonate weathering by amplifying CO<sub>2</sub>-rich recharge

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.

scholarly journals Temporary and net sinks of atmospheric CO<sub>2</sub> due to chemical weathering in subtropical catchment with mixing carbonate and silicate lithology

2020 ◽  
Vol 17 (14) ◽  
pp. 3875-3890
Author(s):  
Yingjie Cao ◽  
Yingxue Xuan ◽  
Changyuan Tang ◽  
Shuai Guan ◽  
Yisheng Peng
Keyword(s):  
Acid Deposition ◽  
Chemical Weathering ◽  
Dissolved Inorganic Carbon ◽  
Silicate Weathering ◽  
Carbonate Weathering ◽  
Weathering Rate ◽  
Weathering Rates ◽  
Hypsometric Integral ◽  
Co2 Sink ◽  
Chemical Weathering Rate

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.

scholarly journals Chemical weathering rates and atmospheric/soil CO2 consumption of igneous and metamorphic rocks under tropical climate in southeastern Brazil

2016 ◽  
Vol 443 ◽  
pp. 54-66 ◽  
Author(s):  
Alexandre Martins Fernandes ◽  
Fabiano Tomazini da Conceição ◽  
Eder Paulo Spatti Junior ◽  
Diego de Souza Sardinha ◽  
Jeferson Mortatti
Keyword(s):  
Chemical Weathering ◽  
Tropical Climate ◽  
Southeastern Brazil ◽  
Metamorphic Rocks ◽  
Soil Co2 ◽  
Weathering Rates ◽  
Co2 Consumption

scholarly journals Climatic Variabilities Control the Solute Dynamics of Monsoon Karstic River: Approaches from C-Q Relationship, Isotopes, and Model Analysis in the Liujiang River

Water ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 862 ◽  
Author(s):  
Jing Liu ◽  
Hu Ding ◽  
Min Xiao ◽  
Zhu-Yan Xu ◽  
Yuan Wei ◽  
...  
Keyword(s):  
Chemical Weathering ◽  
Carbonic Acid ◽  
Dissolved Inorganic Carbon ◽  
Climatic Variability ◽  
Sulfide Oxidation ◽  
Future Climate Change ◽  
Climate Change Scenarios ◽  
Soil Co2 ◽  
Solute Dynamics ◽  
The Impact

The dynamics of riverine solutes’ contents and sources reflect geological, ecological, and climatic information of the draining basin. This study investigated the influence of climatic variability on solute dynamics by the high-frequency hydrogeochemical monitory in the Liujiang River draining karst terrain of Guangxi Province, SW (Southwestern) China. In the study river, the content-discharge (C-Q) patterns of riverine solutes indicate that the majority of riverine solutes show similar dilution and near chemostatic behaviors responding to increasing discharge, especially geogenic solutes (such as weathering products from carbonate, silicate, and sulfide oxidation), whereas exogenous solutes (such as atmospheric input to riverine sulfate) and biological solutes (such as soil CO2) show higher contents with increasing discharge. Besides, the biological carbon is the main driver of the chemostatic behaviors of total dissolved inorganic carbon (DIC). The forward model results show that carbonate weathering dominates the water chemistry, and the weathering rates are intensified during high flow period due to additional inputs of weathering agents, i.e., the biologic carbonic acid from dissolution of soil CO2, indicated by δ13CDIC. In addition, there exists the strong capacity of CO2 consumption that is heavily dependent on climatic variables such as precipitation and air temperature in this study river. Our study highlights the impact of climatic variability on solutes dynamics and chemical weathering and thus must be better addressed in C models under future climate change scenarios.

scholarly journals Temporary and net sinks of atmospheric CO<sub>2</sub> due to chemical weathering in subtropical catchment with mixing carbonate and silicate lithology

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.

scholarly journals Rainfall and Human Impacts on Weathering Rates and Carbon-Nutrient Yields in the Watershed of a Small Mountainous River (Kaoping) in Southwestern Taiwan

2020 ◽  
Vol 12 (18) ◽  
pp. 7689
Author(s):  
Jia-Jang Hung ◽  
Chun-Yi Yang ◽  
I-Jen Lai ◽  
Yuan-Hui Li
Keyword(s):  
Chemical Weathering ◽  
Dissolved Inorganic Carbon ◽  
Human Impacts ◽  
Total Carbon ◽  
Spatial And Temporal Variability ◽  
Drought Period ◽  
Weathering Rates ◽  
Southwestern Taiwan ◽  
Physical And Chemical ◽  
Mountainous River

This study presents the influence of rainfall and human perturbation on physical and chemical weathering rates, and carbon and nutrient yields in the basin of the Kaoping, a small mountainous river (SMR) in southwestern Taiwan. The study was derived principally from the spatial and temporal variability of aquatic geochemistry in the river during wet (1999–2000) and drought (2002) periods. The total, physical, and chemical weathering rates in the river basin ranged respectively from 4739, 3601, and 1138 g m−2 year−1 in the wet period to 1072, 656, and 416 g m−2 year−1 in the drought period, resulting mainly from a large difference in rainfall and river discharge between the two periods. The wet and drought periods were likely associated with La Niña and El Niño events, respectively. The weathering rates of the wet period were much higher than those reported from the world’s river basins, showing the unique characteristics of the SMR. The total carbon yield was derived mainly from dissolved inorganic carbon and was much higher in the wet period (140 g C m−2 year−1) than in the drought period (53.7 g C m−2 year−1). Taking silicate weathering (54.7 ± 10.2%) slightly over carbonate weathering (48.6 ± 9.5%) in determining dissolved ion loads, the Kaoping catchment may currently consume 0.155–0.298 MtC/year atmospheric CO2 without considering the CO2 released from chemical weathering. The nutrient yields were controlled mainly by human inputs but also enhanced by increased rainfall. Both regional and local climatic conditions and human impacts likely determined the weathering rates and total yields of carbon and nutrients. The SMRs may collectively contribute significantly to global fluxes of terrestrial sediments, geochemical matters, carbon, and nutrients to oceans.

scholarly journals Reconciling atmospheric CO2, weathering, and calcite compensation depth across the Cenozoic

2021 ◽  
Vol 7 (4) ◽  
pp. eabd4876
Author(s):  
Nemanja Komar ◽  
Richard E. Zeebe
Keyword(s):  
Carbon Cycle ◽  
Critical Role ◽  
Carbonate Weathering ◽  
Weathering Rates ◽  
Marine Organic Matter ◽  
Novel Approach ◽  
Compensation Depth ◽  
Long Term Trends ◽  
Cenozoic Era

The Cenozoic era (66 to 0 million years) is marked by long-term aberrations in carbon cycling and large climatic shifts, some of which challenge the current understanding of carbon cycle dynamics. Here, we investigate possible mechanisms responsible for the observed long-term trends by using a novel approach that features a full-fledged ocean carbonate chemistry model. Using a compilation of pCO2, pH, and calcite compensation depth (CCD) observational evidence and a suite of simulations, we reconcile long-term Cenozoic climate and CCD trends. We show that the CCD response was decoupled from changes in silicate and carbonate weathering rates, challenging the continental uplift hypothesis. The two dominant mechanisms for decoupling are shelf-basin carbonate burial fractionation combined with proliferation of pelagic calcifiers. The temperature effect on remineralization rates of marine organic matter also plays a critical role in controlling the carbon cycle dynamics, especially during the warmer periods of the Cenozoic.

scholarly journals Chemical weathering pathways in the central Himalaya – new constraints from DI14C and δ34S

2020 ◽  
Author(s):  
Maarten Lupker ◽  
Lena Märki ◽  
Guillaume Paris ◽  
Thomas Blattman ◽  
Negar Haghipour ◽  
...  
Keyword(s):  
Sulfuric Acid ◽  
Carbon Cycle ◽  
Chemical Weathering ◽  
Carbonic Acid ◽  
Dissolved Inorganic Carbon ◽  
Pyrite Oxidation ◽  
Central Himalaya ◽  
Princeton University ◽  
Radiocarbon Data ◽  
The Impact

&lt;p&gt;Chemical weathering at Earth&amp;#8217;s surface releases soluble elements from rocks to streams and the oceans, interacting with the global carbon cycle along multiple pathways. The carbon budget of continental erosion is strongly dependent on the nature and relative importance of these pathways [1]. Weathering of silicate minerals with carbonic acid represents a long-term net sink of atmospheric CO&lt;sub&gt;2&lt;/sub&gt;. However, chemical weathering by other acids, such as pyrite oxidation-derived sulfuric acid, represents a net CO&lt;sub&gt;2&lt;/sub&gt; source to the atmosphere [2]. Constraining the net balance of acids and lithology involved in weathering reactions is therefore paramount to budget the impact of chemical weathering on the carbon cycle. In this contribution, we present preliminary radiocarbon data measured on dissolved inorganic carbon (DI&lt;sup&gt;14&lt;/sup&gt;C) from stream and spring waters in the central Himalaya of Nepal. DI&lt;sup&gt;14&lt;/sup&gt;C is a promising tracer of the different chemical weathering reaction pathways [3], and DI&lt;sup&gt;14&lt;/sup&gt;C values in the central Himalaya span across the natural spectrum. To constrain sulfate sources, measurements of &amp;#948;&lt;sup&gt;34&lt;/sup&gt;S on dissolved sulfate complement this dataset [4], which also shows considerable variability ranging between -15 to +18 &amp;#8240;. Inverting the dissolved ion composition and their isotopic constraints provide constraints on the proportions of carbonic and sulfuric acid weathering of silicates and carbonates. These results will then be compared with catchment lithological, geomorphological and climatic parameters.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;[1] Berner and Berner, 2012 - Princeton University Press&amp;#160;&amp;#160;&lt;/p&gt;&lt;p&gt;[2] Calmels et al., 2007 &amp;#8211; Geology 35-11&lt;/p&gt;&lt;p&gt;[3] Blattmann et al., 2019 &amp;#8211; Scientific Reports 9&lt;/p&gt;&lt;p&gt;[4] Turchyn et al., 2013 &amp;#8211; EPSL 374&lt;/p&gt;

scholarly journals Glacial weathering, sulfide oxidation, and global carbon cycle feedbacks

2017 ◽  
Vol 114 (33) ◽  
pp. 8716-8721 ◽  
Author(s):  
Mark A. Torres ◽  
Nils Moosdorf ◽  
Jens Hartmann ◽  
Jess F. Adkins ◽  
A. Joshua West
Keyword(s):  
Carbon Cycle ◽  
Chemical Weathering ◽  
Dissolved Inorganic Carbon ◽  
Global Climate ◽  
Sulfide Oxidation ◽  
Global Carbon Cycle ◽  
Hydrochemical Data ◽  
Future Work ◽  
Global Carbon

Connections between glaciation, chemical weathering, and the global carbon cycle could steer the evolution of global climate over geologic time, but even the directionality of feedbacks in this system remain to be resolved. Here, we assemble a compilation of hydrochemical data from glacierized catchments, use this data to evaluate the dominant chemical reactions associated with glacial weathering, and explore the implications for long-term geochemical cycles. Weathering yields from catchments in our compilation are higher than the global average, which results, in part, from higher runoff in glaciated catchments. Our analysis supports the theory that glacial weathering is characterized predominantly by weathering of trace sulfide and carbonate minerals. To evaluate the effects of glacial weathering on atmospheric pCO2, we use a solute mixing model to predict the ratio of alkalinity to dissolved inorganic carbon (DIC) generated by weathering reactions. Compared with nonglacial weathering, glacial weathering is more likely to yield alkalinity/DIC ratios less than 1, suggesting that enhanced sulfide oxidation as a result of glaciation may act as a source of CO2 to the atmosphere. Back-of-the-envelope calculations indicate that oxidative fluxes could change ocean–atmosphere CO2 equilibrium by 25 ppm or more over 10 ky. Over longer timescales, CO2 release could act as a negative feedback, limiting progress of glaciation, dependent on lithology and the concentration of atmospheric O2. Future work on glaciation–weathering–carbon cycle feedbacks should consider weathering of trace sulfide minerals in addition to silicate minerals.

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