Attention:The NSF Public Access Repository (PAR) system and access will be unavailable from 5:00 PM ET until 8:00 PM ET on Friday, September 11 due to maintenance. We apologize for the inconvenience.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Improving model capability in simulating spatiotemporal variations and flow contributions of nitrate export in tile-drained catchments
Title: Improving model capability in simulating spatiotemporal variations and flow contributions of nitrate export in tile-drained catchments
It is essential to identify the dominant flow paths, hot spots and hot periods of hydrological nitrate-nitrogen (NO3-N) losses for developing nitrogen loads reduction strategies in agricultural watersheds. Coupled biogeochemical transformations and hydrological connectivity regulate the spatiotemporal dynamics of water and NO3-N export along surface and subsurface flows. However, modeling performance is usually limited by the oversimplification of natural and human-managed processes and insufficient representation of spatiotemporally varied hydrological and biogeochemical cycles in agricultural watersheds. In this study, we improved a spatially distributed process-based hydro-ecological model (DLEM-catchment) and applied the model to four tile-drained catchments with mixed agricultural management and diverse landscape in Iowa, Midwestern US. The quantitative statistics show that the improved model well reproduced the daily and monthly water discharge, NO3-N concentration and loading measured from 2015 to 2019 in all four catchments. The model estimation shows that subsurface flow (tile flow + lateral flow) dominates the discharge (70%-75%) and NO3-N loading (77%-82%) over the years. However, the contributions of tile drainage and lateral flow vary remarkably among catchments due to different tile-drained area percentages and the presence of farmed potholes (former depressional wetlands that have been drained for agricultural production). Furthermore, we found that agricultural management (e.g. tillage and fertilizer management) and catchment characteristics (e.g. soil properties, farmed potholes, and tile drainage) play important roles in predicting the spatial distributions of NO3-N leaching and loading. The simulated results reveal that the model improvements in representing water retention capacity (snow processes, soil roughness, and farmed potholes) and tile drainage improved model performance in estimating discharge and NO3-N export at a daily time step, while improvement of agricultural management mainly impacts NO3-N export prediction. This study underlines the necessity of characterizing catchment properties, agricultural management practices, flow-specific NO3-N movement, and spatial heterogeneity of NO3-N fluxes for accurately simulating water quality dynamics and predicting the impacts of agricultural conservation nutrient reduction strategies.  more » « less
Award ID(s):
1945036 1903722
PAR ID:
10505295
Author(s) / Creator(s):
; ; ; ; ;
Publisher / Repository:
Elsevier
Date Published:
Journal Name:
Water Research
Volume:
244
Issue:
C
ISSN:
0043-1354
Page Range / eLocation ID:
120489
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; (, Water Research)
    Tile drainage systems enhance agricultural productivity in poorly drained regions but also increase nitrate export, posing serious water quality challenges. This study employs the DLEM-catchment model to assess the effectiveness of in-field and edge-of-field practices in reducing nitrate loading across four tile-drained catchments in the U.S. Corn Belt. Simulated in-field practices include cover crops, crop rotation, fertilizer rate reductions, and optimized fertilizer timing, while edge-of-field measures focus on saturated riparian buffers (SRBs) and water quality wetlands (WQWs). Results show that cover crops and 10–20% fertilizer reductions are effective in-field strategies, reducing nitrate loading by 10.5% and 6.2–12.8%, respectively. Combining cropping system changes (e.g., cover crops or crop rotation) with fertilizer reductions produced the largest nitrate reductions, while fertilizer reductions combined with optimized application timing provided the most favorable balance between nitrate mitigation and minimal yield penalty. SRBs provided only minor catchment-scale improvements due to limited interception area, reducing nitrate loads by an additional 0.5%, although nitrate removal within the intercepted drainage area reached 19.9%. In contrast, WQWs are simulated to reduce nitrate loading by an additional 28.3% on average across the four catchments because of longer water residence times and enhanced biogeochemical processes. These results demonstrate that integrating in-field nutrient management with edge-of-field interception offers the greatest potential for sustained nitrate reduction. The variability in responses across catchments highlights the importance of site-specific, integrated management strategies that combine source reduction with downstream interception to improve water quality while sustaining crop productivity, consistent with emerging precision conservation frameworks. 
    more » « less
  2. ; ; ; ; (, Water Resources Research)
    The combination of high nitrogen (N) inputs on tile‐drained agricultural watersheds contributes to excessive nitrate loss to surface‐ and groundwater systems. This study combined water age modeling based on StorAge Selection functions and nitrate isotopic analysis to examine the underlying mechanisms driving nitrate export in an intensively tile‐drained mesoscale watershed typical of the U.S. Upper Midwest. The water age modeling revealed a pronounced inverse storage effect and strong young water preference under high‐flow conditions, emphasizing evolving water mixing behavior driven by groundwater fluctuation and tile drain activation. Integrating nitrate concentration‐isotope‐discharge relationships with water age dynamics disentangled the interactions between flow path variations and subsurface N cycling in shaping seasonally variable nitrate export regimes at the watershed scale. Based on these results, a simple transit time‐based and isotope‐aided nitrate transport model was developed to estimate the timescales of watershed‐scale nitrate reactive transport. Model results demonstrated variable nitrate source availability and a wetness dependence for denitrification, indicating that interannual nitrate chemostasis is driven by coupled and proportional responses of soil nitrate production, denitrification, and flow path activation to varying antecedent wetness conditions. These findings suggest that intensively tile‐drained Midwestern agricultural watersheds function as both N transporters and transformers and may respond to large‐scale mitigation efforts within a relatively short timeframe. Collectively, the results of this study demonstrate the potential of integrated water age modeling and nitrate isotopic analysis to advance the understanding of macroscale principles governing coupled watershed hydrologic and N biogeochemical functions. 
    more » « less
  3. ; ; ; ; ; ; ; (, Water Resources Research)
    Abstract Accurately quantifying and predicting the reactive transport of nitrate () in hydrologic systems continues to be a challenge, due to the complex hydrological and biogeochemical interactions that underlie this transport. Recent advances related to time‐variant water age have led to a new method that probes water mixing and selection behaviors using StorAge Selection (SAS) functions. In this study, SAS functions were applied to investigate storage, water selection behaviors, and export regimes in a tile‐drained corn‐soybean field. The natural abundance stable nitrogen and oxygen isotopes of tile drainage were also measured to provide constraints on biogeochemical transformations. The SAS functions, calibrated using chloride measurements at tile drain outlets, revealed a strong young water preference during tile discharge generation. The use of a time‐variant SAS function for tile discharge generated unique water age dynamics that reveal an inverse storage effect driven by the activation of preferential flow paths and mechanically explain the observed variations in isotopes. Combining the water age estimates with isotope fingerprinting shed new light on export dynamics at the tile‐drain scale, where a large mixing volume and the lack of a strong vertical contrast in concentration resulted in chemostatic export regimes. For the first time, isotopes were embedded into a water age‐based transport model to model reactive transport under transient conditions. The results of this modeling study provided a proof‐of‐concept for the potential of coupling water age modeling with isotope analysis to elucidate the mechanisms driving reactive transport. 
    more » « less
  4. ; ; ; ; (, Water Resources Research)
    Abstract Efforts to reduce nitrogen and carbon loading from developed watersheds typically target specific flows or sources, but across gradients in development intensity there is no consensus on the contribution of different flows to total loading or sources of nitrogen export. This information is vital to optimize management strategies leveraging source reductions, stormwater controls, and restorations. We investigate how solute loading and sources vary across flows and land‐use using high frequency monitoring and stable nitrate isotope analysis from five catchments with different sanitary infrastructure, along a gradient in development intensity. High frequency monitoring allowed estimation of annual loading and attribution to storm versus baseflows. Nitrate loads were 16 kg/km2/yr. from the forested catchment and ranged from 68 to 119 kg/km2/yr., across developed catchments, highest for the septic served site. Across developed catchments, baseflow contributions ranged from 40% of N loading to 75% from the septic served catchment, and the contribution from high stormflows increased with development intensity. Stormflows mobilized and mixed many surface and subsurface nitrate sources while baseflow nitrate was dominated by fewer sources which varied by catchment (soil, wastewater, or fertilizer). To help inform future sampling designs, we demonstrate that grab sampling and targeted storm sampling would likely fail to accurately predict annual loadings within the study period. The dominant baseflow loads and subsurface stormflows are not treated by surface water management practices primarily targeted to surface stormflows. Using a balance of green and gray infrastructure and stream/riparian restoration may target specific flow paths and improve management. 
    more » « less
  5. ; ; ; ; ; ; ; (, Water Resources Research)
    Abstract The production, transport, loss, and export of dissolved organic carbon (DOC) are closely connected with hydrometeorological drivers. While terrestrial production depends on biogeochemical variables like soil moisture, air temperature, and the contact area between water and organic matter sources, export is determined by water availability and flow paths within soil storage. This study aims to quantify how hydrometeorological drivers jointly control DOC production and export across spatial scales in a temperate snow‐dominated forested catchment. Using a parsimonious model to simultaneously optimize discharge and DOC concentrations, we leveraged over 14 years of high‐resolution (15‐min) hydrological data, along with weekly to monthly measurements of DOC concentrations, across nested catchments of varying sizes from small (7 km2), medium (170 km2), to large (480 km2). The simulations replicated daily hydrological (KGE ∼ 0.60) and DOC (KGE ∼ 0.60) concentration dynamics at all sites. Our findings indicate that shallow soil storage and antecedent precipitation (>45 days) significantly influence DOC dynamics across all three spatial scales, emphasizing the importance of connectivity in catchments' responses to hydrometeorological conditions. The influence of antecedent precipitation is of greater magnitude at larger scales, while pulses of DOC are more common at smaller scales due to rapid source activation. Our results highlight that model performance and the ability to realistically represent catchment processes are enhanced when hydrological and biogeochemical processes are considered simultaneously. Parsimonious models are crucial to evaluate how hydro‐biogeochemical processes vary across spatial scales and ultimately respond to human perturbations, such as climate change and extreme events. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Text Encoded Conversion
  • XML
  • Save / Share this Record
  • Send to Email