Publications - Angelo Coast Range Reserve

Golla, J. K.; Kuessner, M. L.; Henehan, M. J.; Bouchez, J.; Rempe, D. M.; Druhan, J. L.

The evolution of lithium isotope signatures in fluids draining actively weathering hillslopes Journal Article

In: Earth and Planetary Science Letters, vol. 567, no. 1, 2021.

Abstract | Links | BibTeX | Tags: Critical Zone, ERCZO, lithium isotopes, reactive transport, silicate weathering

@article{Golla2021,

title = {The evolution of lithium isotope signatures in fluids draining actively weathering hillslopes},

author = {J. K. Golla and M. L. Kuessner and M. J. Henehan and J. Bouchez and D. M. Rempe and J. L. Druhan},

doi = {10.1016/j.epsl.2021.116988},

year  = {2021},

date = {2021-08-01},

journal = {Earth and Planetary Science Letters},

volume = {567},

number = {1},

abstract = {The stable isotopes of lithium (Li) serve as a robust proxy of silicate weathering. The fate and transport of these isotopes in the dissolved load of major rivers have been characterized to infer changes in both contemporary weathering regimes and paleo-conditions. In this contribution, we deconvolve this integrated signal into the individual processes that fractionate Li at the inception of silicate weathering by directly measuring Li isotope ratios of waters (Li) transiting through a rapidly eroding first-order hillslope. We use these data to develop a multicomponent reactive transport framework, which shows that net dissolution of weathered material generates light Li signatures (as low as −9.2‰) in the shallow portion of the vadose zone. An increase in Li deeper into the vadose zone (as much as +18‰) reflects an increasing contribution of secondary mineral formation. Below the water table, congruent weathering occurs and imparts elevated cation concentrations and bedrock Li. Silicate weathering continues within the saturated zone as groundwater travels downslope (Li = +13 to + 24‰) to the stream. The stream signatures (Li = +28 to +29‰) reflect the terminus of this network of silicate weathering reactions and the relative magnitude of each contributing process (e.g., transitions in secondary mineral formation, dissolution of weathered material). We show that fluid progressing through the weathering profile of this first-order hillslope is distinguished by a sequence of characteristic Li isotope signatures, which can be reproduced in a forward, process-based model framework. This model development offers an improved quantitative basis for the use of metal(loid) stable isotopes in disentangling catchment-scale chemical weathering fluxes.},

keywords = {Critical Zone, ERCZO, lithium isotopes, reactive transport, silicate weathering},

pubstate = {published},

tppubtype = {article}

}

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Pedrazas, Michelle A.; Hahm, W. Jesse; Huang, Mong-Han; Dralle, David; Nelson, Mariel D.; Breunig, Rachel E.; Fauria, Kristen E.; Bryk, Alexander B.; Dietrich, William E.; Rempe, Daniella M.

The Relationship Between Topography, Bedrock Weathering, and Water Storage Across a Sequence of Ridges and Valleys Journal Article

In: JGR Earth Surface, vol. 126, no. 4, 2021.

Abstract | Links | BibTeX | Tags: bedrock weathering, Critical Zone, ERCZO, hillslope, unsaturated zone, water storage, Weathering

@article{Pedrazas2021,

title = {The Relationship Between Topography, Bedrock Weathering, and Water Storage Across a Sequence of Ridges and Valleys},

author = {Michelle A. Pedrazas and W. Jesse Hahm and Mong-Han Huang and David Dralle and Mariel D. Nelson and Rachel E. Breunig and Kristen E. Fauria and Alexander B. Bryk and William E. Dietrich and Daniella M. Rempe},

url = {https://angelo.berkeley.edu/jgr-earth-surface-2021-pedrazas-the-relationship-between-topography-bedrock-weathering-and-water-storage-across-a-1/},

doi = {10.1029/2020JF005848},

year  = {2021},

date = {2021-03-23},

urldate = {2021-03-23},

journal = {JGR Earth Surface},

volume = {126},

number = {4},

abstract = {Bedrock weathering regulates nutrient mobilization, water storage, and soil production. Relative to the mobile soil layer, little is known about the relationship between topography and bedrock weathering. Here, we identify a common pattern of weathering and water storage across a sequence of three ridges and valleys in the sedimentary Great Valley Sequence in Northern California that share a tectonic and climate history. Deep drilling, downhole logging, and characterization of chemistry and porosity reveal two weathering fronts. The shallower front is ∼7 m deep at the ridge of all three hillslopes, and marks the extent of pervasive fracturing and oxidation of pyrite and organic carbon. A deeper weathering front marks the extent of open fractures and discoloration. This front is 11 m deep under two ridges of similar ridge-valley spacing, but 17.5 m deep under a ridge with nearly twice the ridge-valley spacing. Hence, at ridge tops, the fraction of the hillslope relief that is weathered scales with hillslope length. In all three hillslopes, below this second weathering front, closed fractures and unweathered bedrock extend about one-half the hilltop elevation above the adjacent channels. Neutron probe surveys reveal that seasonally dynamic moisture is stored to approximately the same depth as the shallow weathering front. Under the channels that bound our study hillslopes, the two weathering fronts coincide and occur within centimeters of the ground surface. Our findings provide evidence for feedbacks between erosion and weathering in mountainous landscapes that result in systematic subsurface structuring and water routing.},

keywords = {bedrock weathering, Critical Zone, ERCZO, hillslope, unsaturated zone, water storage, Weathering},

pubstate = {published},

tppubtype = {article}

}

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Schmidt, Logan; Rempe, Daniella M.

Quantifying Dynamic Water Storage in Unsaturated Bedrock with Borehole Nuclear Magnetic Resonance Journal Article

In: Geophysical Research Letters, vol. 47, no. 22, pp. e2020GL089600, 2020.

Abstract | Links | BibTeX | Tags: Critical Zone, ERCZO, hydrogeophysics, neutron moderation nuclear magnetic resonance, vadose zone, water storage

Dawson, T. E.; Hahm, W. J.; Crutchfield-Peters, K.

Digging deeper: what the critical zone perspective adds to the study of plant ecophysiology Journal Article

In: New Phytologist, vol. 226, no. 3, pp. 666-671, 2020.

Abstract | Links | BibTeX | Tags: Critical Zone, ERCZO, nutrients, plant ecophysiology, soil, water, weathered bedrock

Rempe, Daniella; Dietrich, William

Direct observations of rock moisture, a hidden component of the hydrologic cycle Journal Article

In: Proceedings of the National Academy of Science of the United States of America, vol. 115, no. 11, pp. 2664-2669, 2018.

Abstract | Links | BibTeX | Tags: Critical Zone, deep vadose zone, ERCZO, evapotranspiration, rock moisture, water budget

@article{daniellaRempe2018,

title = {Direct observations of rock moisture, a hidden component of the hydrologic cycle},

author = {Daniella Rempe and William Dietrich},

url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/Proceedings-of-the-National-Academy-of-Sciences-2018-Rempe.pdf},

doi = {https://doi.org/10.1073/pnas.1800141115},

year  = {2018},

date = {2018-03-13},

journal = {Proceedings of the National Academy of Science of the United States of America},

volume = {115},

number = {11},

pages = {2664-2669},

abstract = {Recent theory and field observations suggest that a systematically varying weathering zone, that can be tens of meters thick, commonly develops in the bedrock underlying hillslopes. Weathering turns otherwise poorly conductive bedrock into a dynamic water storage reservoir. Infiltrating precipitation typically will pass through unsaturated weathered bedrock before reaching groundwater and running off to streams. This invisible and difficult to access unsaturated zone is virtually unexplored compared with the surface soil mantle. We have proposed the term “rock moisture” to describe the exchangeable water stored in the unsaturated zone in weathered bedrock, purposely choosing a term parallel to, but distinct from, soil moisture, because weathered bedrock is a distinctly different material that is distributed across landscapes independently of soil thickness. Here, we report a multiyear intensive campaign of quantifying rock moisture across a hillslope underlain by a thick weathered bedrock zone using repeat neutron probe measurements in a suite of boreholes. Rock moisture storage accumulates in the wet season, reaches a characteristic upper value, and rapidly passes any additional rainfall downward to groundwater. Hence, rock moisture storage mediates the initiation and magnitude of recharge and runoff. In the dry season, rock moisture storage is gradually depleted by trees for transpiration, leading to a common lower value at the end of the dry season. Up to 27% of the annual rainfall is seasonally stored as rock moisture. Significant rock moisture storage is likely common, and yet it is missing from hydrologic and land-surface models used to predict regional and global climate.},

keywords = {Critical Zone, deep vadose zone, ERCZO, evapotranspiration, rock moisture, water budget},

pubstate = {published},

tppubtype = {article}

}

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Grant, Gordon E.; Dietrich, William E.

The frontier beneath our feet Journal Article

In: Water Resources Research, vol. 53, no. 4, pp. 2605-2609, 2017.

Abstract | Links | BibTeX | Tags: Critical Zone, environmental problems, ERCZO, field studies, groundwater, landscape development, water

Kim, H

Water chemistry evolution through the critical zone PhD Thesis

2014.

Abstract | Links | BibTeX | Tags: Critical Zone

@phdthesis{Kim2014b,

title = {Water chemistry evolution through the critical zone},

author = {H Kim},

url = {https://escholarship.org/uc/item/636753xc},

year = {2014},

date = {2014-01-01},

abstract = {Water as it passes through the critical zone - from top of the trees to the bottom of the groundwater table - plays a critical role in chemical weathering of rocks and in the global carbon cycle. Although the chemistry of surface water (i.e. rivers and lakes) has been intensively monitored at high-frequency (<1 day), the temporal and spatial variability of groundwater chemistry in the critical zone, especially in the weathered bedrock zone, has been rarely observed. In many catchments located at temperate regions, nearly all rainwater infiltrates into subsurface, thus identifying the processes and environmental controls for the groundwater chemistry will be fundamental to understand the stream chemistry dynamics. Here, this dissertation directly monitored the groundwater chemistry flowing through a thick weathered argillite zone (5- 25m), underlain by a thin soil layer (<0.75m) in a hillslope in the Elder Creek catchment, located at Angelo Coast Range Reserve, Northern California. Groundwater samples from three locations along the hillslope (i.e. upslope, midslope and downslope) and the creek samples from adjacent Elder Creek were collected at 1-3 days frequency from late 2008 to early 2013 using a novel autonomous sampling methodology developed for this study. This study site has been intensively monitored (5- 30 minute frequency) for microclimate, groundwater table/ temperature, soil moisture/ temperature, and tree sap flows since 2008. Observations of the dynamics of major cations (Na, Mg, K, and Ca), Si, and reactive trace metals, led to the identification of three key governing processes, each occurring at specific locations within the critical zone, that are responsible for water chemistry evolution in the critical zone. During the rainy season, rain water and throughfall - rainwater that has penetrated through tree canopy - as it passes through the vadoze zone, rapidly gains major cations through via cation exchange reactions enhanced by elevated subsurface pCO2. At the same time, rainwater increases its Si concentration through dissolution of amorphous silica phases. This new water recharges the groundwater and in upslope and midslope wells, raising their groundwater table by 4-6 m. During this high flow regime, the connectivity between the groundwater and stream increases significantly. Therefore, this groundwater rapidly flows into the stream and the groundwater and stream display the similar chemistry (fast-flowing groundwater). During the dry season, the groundwater table and the stream discharge recede to their lowest levels and the cation concentrations of the groundwater become higher but its Si concentration decreases. During this season, the chemistry of groundwater is governed by thermodynamic equilibrium with the argillite at high pCO2 (slow-flowing groundwater). The groundwater may become fully equilibrated with reactive minerals such as calcite and clay minerals but may be far from equilibrium with primary minerals (e.g. albite). Silicon in the groundwater may form secondary minerals, decreasing its concentration. When this equilibrated groundwater enters the stream, its chemistry will be dramatically altered via degassing of CO2 leading to abiotic and biotic carbonate mineral precipitation at the hillslope-stream interface. The biotic calcite precipitation appears to increase the partitioning of Mg in calcite, decreasing the groundwater's Mg concentration by 30%. This fundamental hydrochemistry process framework explains the dynamics of reactive species, such as Fe and Mn. The Mn concentrations in the subsurface paralleled the behavior of major cations but varied by as much as 3 orders of magnitude vs. factors of 2 to 5 for major cations; the groundwater's Mn concentration rapidly decreased as the groundwater table rises and vice versa. Multiple lines of evidence suggest that Mn is mostly in dissolved form, and like major cations and that the controlling processes for major cations govern the Mn's behavior. However, even during the high flow regime, Mn in the fast-flowing groundwater is precipitated when it enters the stream, likely via Mn-oxide precipitation at the hillslope-stream interface. In contrast, Fe displayed no systematic correlation with the groundwater table dynamics or stream discharge. The highest Fe concentrations in both groundwater and stream were expressed at the beginning of the rainy season. In addition, the Fe concentration in the groundwater and stream display quite similar values. This suggests that Fe may be in colloidal form, likely organic-ligand bound. This organic ligand Fe- colloid may be more stable and less bio-available that dissolved elements; hence, Fe precipitation at the hillslope-stream interface may be negligible. This dissertation demonstrated that the slow-flowing groundwater transported through the deepest weathered bedrock zone plays a significant role in fluxes of solute and solid to the adjacent creek. The atmospheric inputs of major cations and Si were insignificant compared with the Elder Creek' solute fluxes while that of Mn was 1 -2 orders of magnitude higher than in Elder Creek's solute fluxes; rain and throughfall data for Fe are unreliable. The first process in the vadose zone is responsible for 55% (12 t/km2/year) of the annual cation fluxes. The slow-flowing component is responsible for the rest of 45% annual cation fluxes (9.4 t/km2/year). The third process - water chemistry transition at the hillslope-stream interface - will precipitate 29 t/km2/year of Ca + Mg (mostly as calcite) from the slow-flowing groundwater. This process is also responsible for precipitating approximately 0.2 t/km2/year of Mn and 0.02 t/km2/year of Fe, which are greater than their atmospheric inputs. These findings demonstrate that the loss by carbonate precipitation at the transition zone 1) is greater than the dissolved cation fluxes estimated based on the Elder Creek chemistry observations (21.4 t/km2/year); and 2) Fe and Mn are not accumulating in the system, unlike previously considered. The significant solute precipitation at the hillslope-stream interface suggests that the role of chemical weathering of rock may play a much greater role in sequestrating CO2 than the previously quantified. In addition, a large pool of chemical weathering solid fluxes has not been taken into account properly in the global element budgets.},

keywords = {Critical Zone},

pubstate = {published},

tppubtype = {phdthesis}

}

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Water as it passes through the critical zone – from top of the trees to the bottom of the groundwater table – plays a critical role in chemical weathering of rocks and in the global carbon cycle. Although the chemistry of surface water (i.e. rivers and lakes) has been intensively monitored at high-frequency (<1 day), the temporal and spatial variability of groundwater chemistry in the critical zone, especially in the weathered bedrock zone, has been rarely observed. In many catchments located at temperate regions, nearly all rainwater infiltrates into subsurface, thus identifying the processes and environmental controls for the groundwater chemistry will be fundamental to understand the stream chemistry dynamics. Here, this dissertation directly monitored the groundwater chemistry flowing through a thick weathered argillite zone (5- 25m), underlain by a thin soil layer (<0.75m) in a hillslope in the Elder Creek catchment, located at Angelo Coast Range Reserve, Northern California. Groundwater samples from three locations along the hillslope (i.e. upslope, midslope and downslope) and the creek samples from adjacent Elder Creek were collected at 1-3 days frequency from late 2008 to early 2013 using a novel autonomous sampling methodology developed for this study. This study site has been intensively monitored (5- 30 minute frequency) for microclimate, groundwater table/ temperature, soil moisture/ temperature, and tree sap flows since 2008. Observations of the dynamics of major cations (Na, Mg, K, and Ca), Si, and reactive trace metals, led to the identification of three key governing processes, each occurring at specific locations within the critical zone, that are responsible for water chemistry evolution in the critical zone. During the rainy season, rain water and throughfall – rainwater that has penetrated through tree canopy – as it passes through the vadoze zone, rapidly gains major cations through via cation exchange reactions enhanced by elevated subsurface pCO2. At the same time, rainwater increases its Si concentration through dissolution of amorphous silica phases. This new water recharges the groundwater and in upslope and midslope wells, raising their groundwater table by 4-6 m. During this high flow regime, the connectivity between the groundwater and stream increases significantly. Therefore, this groundwater rapidly flows into the stream and the groundwater and stream display the similar chemistry (fast-flowing groundwater). During the dry season, the groundwater table and the stream discharge recede to their lowest levels and the cation concentrations of the groundwater become higher but its Si concentration decreases. During this season, the chemistry of groundwater is governed by thermodynamic equilibrium with the argillite at high pCO2 (slow-flowing groundwater). The groundwater may become fully equilibrated with reactive minerals such as calcite and clay minerals but may be far from equilibrium with primary minerals (e.g. albite). Silicon in the groundwater may form secondary minerals, decreasing its concentration. When this equilibrated groundwater enters the stream, its chemistry will be dramatically altered via degassing of CO2 leading to abiotic and biotic carbonate mineral precipitation at the hillslope-stream interface. The biotic calcite precipitation appears to increase the partitioning of Mg in calcite, decreasing the groundwater’s Mg concentration by 30%. This fundamental hydrochemistry process framework explains the dynamics of reactive species, such as Fe and Mn. The Mn concentrations in the subsurface paralleled the behavior of major cations but varied by as much as 3 orders of magnitude vs. factors of 2 to 5 for major cations; the groundwater’s Mn concentration rapidly decreased as the groundwater table rises and vice versa. Multiple lines of evidence suggest that Mn is mostly in dissolved form, and like major cations and that the controlling processes for major cations govern the Mn’s behavior. However, even during the high flow regime, Mn in the fast-flowing groundwater is precipitated when it enters the stream, likely via Mn-oxide precipitation at the hillslope-stream interface. In contrast, Fe displayed no systematic correlation with the groundwater table dynamics or stream discharge. The highest Fe concentrations in both groundwater and stream were expressed at the beginning of the rainy season. In addition, the Fe concentration in the groundwater and stream display quite similar values. This suggests that Fe may be in colloidal form, likely organic-ligand bound. This organic ligand Fe- colloid may be more stable and less bio-available that dissolved elements; hence, Fe precipitation at the hillslope-stream interface may be negligible. This dissertation demonstrated that the slow-flowing groundwater transported through the deepest weathered bedrock zone plays a significant role in fluxes of solute and solid to the adjacent creek. The atmospheric inputs of major cations and Si were insignificant compared with the Elder Creek’ solute fluxes while that of Mn was 1 -2 orders of magnitude higher than in Elder Creek’s solute fluxes; rain and throughfall data for Fe are unreliable. The first process in the vadose zone is responsible for 55% (12 t/km2/year) of the annual cation fluxes. The slow-flowing component is responsible for the rest of 45% annual cation fluxes (9.4 t/km2/year). The third process – water chemistry transition at the hillslope-stream interface – will precipitate 29 t/km2/year of Ca + Mg (mostly as calcite) from the slow-flowing groundwater. This process is also responsible for precipitating approximately 0.2 t/km2/year of Mn and 0.02 t/km2/year of Fe, which are greater than their atmospheric inputs. These findings demonstrate that the loss by carbonate precipitation at the transition zone 1) is greater than the dissolved cation fluxes estimated based on the Elder Creek chemistry observations (21.4 t/km2/year); and 2) Fe and Mn are not accumulating in the system, unlike previously considered. The significant solute precipitation at the hillslope-stream interface suggests that the role of chemical weathering of rock may play a much greater role in sequestrating CO2 than the previously quantified. In addition, a large pool of chemical weathering solid fluxes has not been taken into account properly in the global element budgets.

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