TY - JOUR
T1 - Combining stable isotopes and spatial stream network modelling to disentangle the roles of hydrological and biogeochemical processes on riverine nitrogen dynamics
AU - Hu, Minpeng
AU - Yu, Zhongjie
AU - Griffis, Timothy J.
AU - Baker, John M.
N1 - We gratefully acknowledge the assistance of Carlos Guacho and Corey Mitchell (University of Illinois at Urbana-Champaign) during field sampling and laboratory analysis. This research was supported by NSF projects AGS 2110430, NSF projects AGS 2110241, USDA-NIFA Hatch project ILLU-875-983, USDA-NIFA Grant 2018-67019-27808, NSFC project 42107393.
PY - 2025/2/1
Y1 - 2025/2/1
N2 - Intensive agricultural activities have significantly altered watershed hydrological and biogeochemical processes, resulting in water quality issues and loss of ecosystem functions and biodiversity. A major challenge in effectively mitigating nitrogen (N) loss from agricultural watersheds stems from the heterogeneity of N transformation and transport processes that complicates accurate quantification and modeling of N sources and sinks at the watershed scale. This study utilized stable isotopes of water and nitrate (NO3−) in conjunction with spatial stream network modeling (SSNMs) to explore watershed hydrology, N transformation, and sources within a mesoscale river network in the U.S. Corn Belt (Cannon River Watershed, Minnesota) under contrasting hydrological conditions. The results show that the wet season had elevated riverine NO3− concentration (medium: 8.4 mg N L−1), driven by high watershed wetness conditions that mobilizes NO3− from the near-surface source zone. Furthermore, the strong hydrologic connectivity also reduced the denitrification potential by shortening water travel times. In comparison, the dry season showed lower NO3− concentrations (0.9 mg N L−1) and stronger denitrification NO3− isotope signals. During this period, the decrease in hydrologic connectivity shifted the predominant water source to deep groundwater, with longer water travel time promoting denitrification. After accounting for isotopic fractionations during nitrification and denitrification, we identified fertilizer N as the main NO3− source during the wet season (98.2±1.3%), whereas the dry season showed contributions from diverse sources (64.4±11.9% fertilizer, 26.0±15.8% soil N, and 9.5±6.0% manure and sewage). During the dry season, karst regions with high hydrologic connectivity display increased shallow groundwater inputs, carrying elevated NO3− levels from leaching of applied chemical fertilizers. These findings highlight the importance of integrating drainage water management and N accumulation in groundwater into nutrient management strategies to develop adaptive measures for controlling N pollution in agricultural watersheds.
AB - Intensive agricultural activities have significantly altered watershed hydrological and biogeochemical processes, resulting in water quality issues and loss of ecosystem functions and biodiversity. A major challenge in effectively mitigating nitrogen (N) loss from agricultural watersheds stems from the heterogeneity of N transformation and transport processes that complicates accurate quantification and modeling of N sources and sinks at the watershed scale. This study utilized stable isotopes of water and nitrate (NO3−) in conjunction with spatial stream network modeling (SSNMs) to explore watershed hydrology, N transformation, and sources within a mesoscale river network in the U.S. Corn Belt (Cannon River Watershed, Minnesota) under contrasting hydrological conditions. The results show that the wet season had elevated riverine NO3− concentration (medium: 8.4 mg N L−1), driven by high watershed wetness conditions that mobilizes NO3− from the near-surface source zone. Furthermore, the strong hydrologic connectivity also reduced the denitrification potential by shortening water travel times. In comparison, the dry season showed lower NO3− concentrations (0.9 mg N L−1) and stronger denitrification NO3− isotope signals. During this period, the decrease in hydrologic connectivity shifted the predominant water source to deep groundwater, with longer water travel time promoting denitrification. After accounting for isotopic fractionations during nitrification and denitrification, we identified fertilizer N as the main NO3− source during the wet season (98.2±1.3%), whereas the dry season showed contributions from diverse sources (64.4±11.9% fertilizer, 26.0±15.8% soil N, and 9.5±6.0% manure and sewage). During the dry season, karst regions with high hydrologic connectivity display increased shallow groundwater inputs, carrying elevated NO3− levels from leaching of applied chemical fertilizers. These findings highlight the importance of integrating drainage water management and N accumulation in groundwater into nutrient management strategies to develop adaptive measures for controlling N pollution in agricultural watersheds.
KW - Hydrologic connectivity
KW - Isotopic fractionation
KW - Karst critical zone
KW - River network
KW - Source identification
KW - Tile drainage
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U2 - 10.1016/j.watres.2024.122800
DO - 10.1016/j.watres.2024.122800
M3 - Article
C2 - 39571524
AN - SCOPUS:85209591927
SN - 0043-1354
VL - 269
JO - Water Research
JF - Water Research
M1 - 122800
ER -