TY - JOUR
T1 - The Shallow and Deep Hypothesis
T2 - Subsurface Vertical Chemical Contrasts Shape Nitrate Export Patterns from Different Land Uses
AU - Zhi, Wei
AU - Li, Li
N1 - Funding Information:
This study was supported by a seed grant from the Penn State Institute of Computation and Data Science and the U.S. Department of Energy (DOE) Subsurface Biogeochemical Research (SBR) program (DE-SC0016221). We appreciate the manuscript handling by the associate editor Dr. Daniel Giammar and constructive and incisive comments from three anonymous reviewers that have significantly improved the paper.
Publisher Copyright:
Copyright © 2020 American Chemical Society.
PY - 2020/10/6
Y1 - 2020/10/6
N2 - Eutrophication has threatened water resources worldwide, yet mechanistic understanding on controls of nutrient export remains elusive. This work tests the shallow and deep hypothesis: subsurface vertical chemical contrasts regulate nitrate export patterns under different land use conditions. We synthesized data from 228 watersheds and used reactive transport modeling (500 simulations) under broad land use, climate, and geology conditions. Data synthesis indicated that human perturbation has amplified chemical contrasts in shallow water (e.g., soil water) versus deep waters (e.g., groundwater), inducing primarily flushing patterns (concentrations increase with streamflow) in agriculture lands and dilution patterns (concentrations decrease with streamflow) in urban watersheds. Results revealed a quantitative relationship between export patterns and shallow-versus-deep concentration contrasts, underscoring the often-overlooked role of nutrient distribution over depth. Results challenge the commonly held perception that legacy stores in agricultural lands induce chemostasis where concentrations vary negligibly with streamflow. They suggest that nitrate concentrations from agricultural lands will escalate during large hydrological events, which can exacerbate nutrient export problems as flooding events intensify in the future climate.
AB - Eutrophication has threatened water resources worldwide, yet mechanistic understanding on controls of nutrient export remains elusive. This work tests the shallow and deep hypothesis: subsurface vertical chemical contrasts regulate nitrate export patterns under different land use conditions. We synthesized data from 228 watersheds and used reactive transport modeling (500 simulations) under broad land use, climate, and geology conditions. Data synthesis indicated that human perturbation has amplified chemical contrasts in shallow water (e.g., soil water) versus deep waters (e.g., groundwater), inducing primarily flushing patterns (concentrations increase with streamflow) in agriculture lands and dilution patterns (concentrations decrease with streamflow) in urban watersheds. Results revealed a quantitative relationship between export patterns and shallow-versus-deep concentration contrasts, underscoring the often-overlooked role of nutrient distribution over depth. Results challenge the commonly held perception that legacy stores in agricultural lands induce chemostasis where concentrations vary negligibly with streamflow. They suggest that nitrate concentrations from agricultural lands will escalate during large hydrological events, which can exacerbate nutrient export problems as flooding events intensify in the future climate.
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U2 - 10.1021/acs.est.0c01340
DO - 10.1021/acs.est.0c01340
M3 - Article
C2 - 32812426
AN - SCOPUS:85092681366
VL - 54
SP - 11915
EP - 11928
JO - Environmental Science & Technology
JF - Environmental Science & Technology
SN - 0013-936X
IS - 19
ER -