Rights statement: This is the author’s version of a work that was accepted for publication in Chemical Geology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Chemical Geology, 571, 2021 DOI: 10.1016/j.chemgeo.2021.120172
Accepted author manuscript, 3.69 MB, PDF document
Available under license: CC BY-NC-ND: Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License
Final published version
Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
}
TY - JOUR
T1 - Contemporary systematics of vadose zone nitrate capture by speleothem carbonate
AU - Wynn, P.M.
AU - Ambler, S.
AU - Grefe, I.
AU - Soto, D.X.
AU - Surridge, B.W.J.
AU - Gabitov, R.I.
AU - Barker, P.A.
AU - Anwar, J.
AU - Quin, A.
AU - Pereira, M.G.
AU - Grant, H.K.
N1 - This is the author’s version of a work that was accepted for publication in Chemical Geology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Chemical Geology, 571, 2021 DOI: 10.1016/j.chemgeo.2021.120172
PY - 2021/6/20
Y1 - 2021/6/20
N2 - The movement of nitrate through the vadose zone has major implications for environmental and human health. This issue is particularly prevalent in karst terrain where agricultural activity, thin soils and dual permeability compound the problem of high nitrate loading to the overlying ecosystem. However, a paucity of records which document vadose zone nitrate concentrations prior to the 21st century render legacy nitrate dynamics, source attribution and baseline conditions to be poorly parameterised. Speleothems growing within karst cave settings may provide an opportunity to obtain records of vadose zone nitrate contamination which extend throughout the anthropogenic era. Here, we use dual isotope analysis of δ15NNO3 and δ18ONO3 in a contemporary study at Cueva-cubío del Llanío, N. Spain, designed to examine the transformation of nitrate between surface to cave environment, taking account of biogeochemical transformation, karst hydrology and partitioning as controls on the delivery of nitrate to the speleothem record. Concentrations of nitrate within speleothem calcite are low (measured range of 0.05 mM to 0.37 mM) due to partitioning (DNO3) across the dripwater-calcite interface. Values of δ15NNO3 extracted from cave waters in Cueva-cubío del Llanío (range +2.0 to +7.0‰) are shown to be excellent indicators of nitrate source and demonstrate no fractionation during incorporation into speleothem carbonate (range of δ15NNO3 in speleothem carbonate +1.6‰ to +6.4‰). Values of δ18ONO3 contained within cave waters (range −2.5‰ to +6.0‰) and speleothem carbonate (range +12.3‰ to +32.3‰) reflect a mixed signal of source, biogeochemical processing and hydrological pathway, providing critical insight into the behaviour of the karst aquifer. Contemporary systematics at Cueva-cubío del Llanío therefore confirm speleothem carbonate contains an excellent record of vadose zone nitrate. Analysis of nitrate contained within speleothem carbonate from other regions confirms the ubiquitous nature of partitioning across the water‑carbonate interface and the use of speleothem nitrate isotopes for recording surface ecosystem processes and vadose zone behaviour. Application of these principles to dated speleothem records should provide critical timeseries of nitrate loading, enabling understanding and remediation against the presence of vadose zone legacy nitrate.
AB - The movement of nitrate through the vadose zone has major implications for environmental and human health. This issue is particularly prevalent in karst terrain where agricultural activity, thin soils and dual permeability compound the problem of high nitrate loading to the overlying ecosystem. However, a paucity of records which document vadose zone nitrate concentrations prior to the 21st century render legacy nitrate dynamics, source attribution and baseline conditions to be poorly parameterised. Speleothems growing within karst cave settings may provide an opportunity to obtain records of vadose zone nitrate contamination which extend throughout the anthropogenic era. Here, we use dual isotope analysis of δ15NNO3 and δ18ONO3 in a contemporary study at Cueva-cubío del Llanío, N. Spain, designed to examine the transformation of nitrate between surface to cave environment, taking account of biogeochemical transformation, karst hydrology and partitioning as controls on the delivery of nitrate to the speleothem record. Concentrations of nitrate within speleothem calcite are low (measured range of 0.05 mM to 0.37 mM) due to partitioning (DNO3) across the dripwater-calcite interface. Values of δ15NNO3 extracted from cave waters in Cueva-cubío del Llanío (range +2.0 to +7.0‰) are shown to be excellent indicators of nitrate source and demonstrate no fractionation during incorporation into speleothem carbonate (range of δ15NNO3 in speleothem carbonate +1.6‰ to +6.4‰). Values of δ18ONO3 contained within cave waters (range −2.5‰ to +6.0‰) and speleothem carbonate (range +12.3‰ to +32.3‰) reflect a mixed signal of source, biogeochemical processing and hydrological pathway, providing critical insight into the behaviour of the karst aquifer. Contemporary systematics at Cueva-cubío del Llanío therefore confirm speleothem carbonate contains an excellent record of vadose zone nitrate. Analysis of nitrate contained within speleothem carbonate from other regions confirms the ubiquitous nature of partitioning across the water‑carbonate interface and the use of speleothem nitrate isotopes for recording surface ecosystem processes and vadose zone behaviour. Application of these principles to dated speleothem records should provide critical timeseries of nitrate loading, enabling understanding and remediation against the presence of vadose zone legacy nitrate.
KW - Aquifers
KW - Biogeochemistry
KW - Calcite
KW - Carbonation
KW - Caves
KW - Ecosystems
KW - Groundwater resources
KW - Isotopes
KW - $+15$/N
KW - Agricultural activities
KW - Biogeochemicals
KW - Cave waters
KW - Environmental health
KW - Human health
KW - Karst terrains
KW - Nitrate loadings
KW - Soil permeability
KW - Vadose Zone
KW - Nitrates
U2 - 10.1016/j.chemgeo.2021.120172
DO - 10.1016/j.chemgeo.2021.120172
M3 - Journal article
VL - 571
JO - Chemical Geology
JF - Chemical Geology
SN - 0009-2541
M1 - 120172
ER -