Deepening roots can enhance carbonate weathering by amplifying CO<sub>2</sub>-rich recharge
<p>Carbonate weathering is essential in regulating atmospheric CO<span class="inline-formula"><sub>2</sub></span> and carbon cycle at the century timescale. Plant roots accelerate weathering by elevating soil CO<span class="inline-formula"><...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-01-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/18/55/2021/bg-18-55-2021.pdf |
| _version_ | 1828242117934186496 |
|---|---|
| author | H. Wen P. L. Sullivan G. L. Macpherson S. A. Billings L. Li |
| author_facet | H. Wen P. L. Sullivan G. L. Macpherson S. A. Billings L. Li |
| author_sort | H. Wen |
| collection | DOAJ |
| description | <p>Carbonate weathering is essential in regulating atmospheric
CO<span class="inline-formula"><sub>2</sub></span> and carbon cycle at the century timescale. Plant roots accelerate
weathering by elevating soil CO<span class="inline-formula"><sub>2</sub></span> 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.</p>
<p>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 CO<span class="inline-formula"><sub>2</sub></span> 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 <span class="inline-formula"><i>p</i></span>CO<span class="inline-formula"><sub>2</sub></span> 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 CO<span class="inline-formula"><sub>2</sub></span>. 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 CO<span class="inline-formula"><sub>2</sub></span> data
suggest relatively similar soil CO<span class="inline-formula"><sub>2</sub></span>
distribution over depth, which in woodlands and grasslands leads only to 1 % to
<span class="inline-formula">∼</span> 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 <span class="inline-formula">∼</span> 17 % to
200 % as infiltration rates increased from 3.7 <span class="inline-formula">×</span> 10<span class="inline-formula"><sup>−2</sup></span> 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
<span class="inline-formula">></span> 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 CO<span class="inline-formula"><sub>2</sub></span>-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 CO<span class="inline-formula"><sub>2</sub></span>–carbonate contact in the deep
subsurface and (2) the hydrological impacts of rooting characteristics can
be more influential than those of soil CO<span class="inline-formula"><sub>2</sub></span> distribution in modulating
weathering rates. We call for colocated characterizations of roots,
subsurface structure, and soil CO<span class="inline-formula"><sub>2</sub></span> 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.</p> |
| first_indexed | 2024-04-12T22:09:59Z |
| format | Article |
| id | doaj.art-873a07bd76034355a543cc04b792ac0e |
| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-04-12T22:09:59Z |
| publishDate | 2021-01-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Biogeosciences |
| spelling | doaj.art-873a07bd76034355a543cc04b792ac0e2022-12-22T03:14:48ZengCopernicus PublicationsBiogeosciences1726-41701726-41892021-01-0118557510.5194/bg-18-55-2021Deepening roots can enhance carbonate weathering by amplifying CO<sub>2</sub>-rich rechargeH. Wen0P. L. Sullivan1G. L. Macpherson2S. A. Billings3L. Li4Department of Civil and Environmental Engineering, Pennsylvania State University, University Park, PA 16802, United StatesCollege of Earth, Ocean, and Atmospheric Science, Oregon State University, Corvallis, OR 97331, United StatesDepartment of Geology, University of Kansas, Lawrence, KS 66045, United StatesDepartment of Ecology and Evolutionary Biology and Kansas Biological Survey, University of Kansas, Lawrence, KS 66045, United StatesDepartment of Civil and Environmental Engineering, Pennsylvania State University, University Park, PA 16802, United States<p>Carbonate weathering is essential in regulating atmospheric CO<span class="inline-formula"><sub>2</sub></span> and carbon cycle at the century timescale. Plant roots accelerate weathering by elevating soil CO<span class="inline-formula"><sub>2</sub></span> 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.</p> <p>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 CO<span class="inline-formula"><sub>2</sub></span> 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 <span class="inline-formula"><i>p</i></span>CO<span class="inline-formula"><sub>2</sub></span> 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 CO<span class="inline-formula"><sub>2</sub></span>. 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 CO<span class="inline-formula"><sub>2</sub></span> data suggest relatively similar soil CO<span class="inline-formula"><sub>2</sub></span> distribution over depth, which in woodlands and grasslands leads only to 1 % to <span class="inline-formula">∼</span> 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 <span class="inline-formula">∼</span> 17 % to 200 % as infiltration rates increased from 3.7 <span class="inline-formula">×</span> 10<span class="inline-formula"><sup>−2</sup></span> 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 <span class="inline-formula">></span> 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 CO<span class="inline-formula"><sub>2</sub></span>-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 CO<span class="inline-formula"><sub>2</sub></span>–carbonate contact in the deep subsurface and (2) the hydrological impacts of rooting characteristics can be more influential than those of soil CO<span class="inline-formula"><sub>2</sub></span> distribution in modulating weathering rates. We call for colocated characterizations of roots, subsurface structure, and soil CO<span class="inline-formula"><sub>2</sub></span> 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.</p>https://bg.copernicus.org/articles/18/55/2021/bg-18-55-2021.pdf |
| spellingShingle | H. Wen P. L. Sullivan G. L. Macpherson S. A. Billings L. Li Deepening roots can enhance carbonate weathering by amplifying CO<sub>2</sub>-rich recharge Biogeosciences |
| title | Deepening roots can enhance carbonate weathering by amplifying CO<sub>2</sub>-rich recharge |
| title_full | Deepening roots can enhance carbonate weathering by amplifying CO<sub>2</sub>-rich recharge |
| title_fullStr | Deepening roots can enhance carbonate weathering by amplifying CO<sub>2</sub>-rich recharge |
| title_full_unstemmed | Deepening roots can enhance carbonate weathering by amplifying CO<sub>2</sub>-rich recharge |
| title_short | Deepening roots can enhance carbonate weathering by amplifying CO<sub>2</sub>-rich recharge |
| title_sort | deepening roots can enhance carbonate weathering by amplifying co sub 2 sub rich recharge |
| url | https://bg.copernicus.org/articles/18/55/2021/bg-18-55-2021.pdf |
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