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1. Similarities in Storage and Transport of Sulfate in Forested and Suburban Watersheds, Despite Anthropogenically Elevated Suburban Sulfate

   https://doi.org/10.1029/2023JG007588  

   Cosans, C L; Gomes, M L; Marsh, M J; Moore, J; Harman, C J (January 2024, Journal of Geophysical Research: Biogeosciences)

   Abstract Sulfate is a potential pollutant and important nutrient linked with the nitrogen, carbon, and phosphorus cycles. The importance of different anthropogenic sulfate sources in suburban streams (septic systems, fertilizer, road salt, and infrastructure) is uncertain, and the temporal dynamics of stream export sparsely documented. We study sources and export dynamics of sulfate in suburban and forested headwater catchments. Stream baseflow discharge and sulfate concentrations were strongly positively correlated in both watersheds with the highest values in spring. Suburban concentrations and fluxes (2.48–7.5 mg/L or 25.8–78.1 μM, 16.6 kg/ha/yr) were consistently higher than forested (0.56–2.78 mg/L or 5.8–28.9 μM, 5 kg/ha/yr). Following precipitation, sulfate concentrations in both forested and suburban streams increased to concentrations above pre‐storm values and remained high after peak discharge. These dynamics suggest that both catchments have a large pool of sulfate that can be mobilized under wet conditions. Ridge‐top forest soil samples contained 210 kg/ha stored, extractable sulfate. Current atmospheric sulfate deposition rates (5–7 kg/ha/yr) are approximately in balance with sulfate export in the forested stream. In the suburban watershed, we estimated septic fields contribute up to 11 kg/ha/yr (about half from surfactants) and lawn care up to 4.3 kg/ha/yr and are the most likely sources of elevated stream sulfate. Sulfate sulfur (4.9–5.8‰ forested; 6.1–7.0‰ suburban) and oxygen isotope values (0.7–2.0‰ forested; −0.1–4.1‰ suburban) are consistent with this interpretation, but do not provide strong corroboration due to large variation and overlap in estimated source values. 

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2. Improving model capability in simulating spatiotemporal variations and flow contributions of nitrate export in tile-drained catchments

   https://doi.org/10.1016/j.watres.2023.120489  

   Cao, Peiyu; Lu, Chaoqun; Crumpton, William; Helmers, Matthew; Green, David; Stenback, Greg (October 2023, Water Research)

   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. 

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3. New Predictors for Hydrologic Signatures: Wetlands and Geologic Age Across Continental Scales

   https://doi.org/10.1002/hyp.70080  

   Holt, Anne; McMillan, Hilary (February 2025, Hydrological Processes)

   In dry summer months, stream baseflow sourced from groundwater is essential to support aquatic ecosystems and anthropogenic water use. Hydrologic signatures, or metrics describing unique features of streamflow timeseries, are useful for quantifying and predicting these valuable baseflow and groundwater storage resources across continental scales. Hydrologic signatures can be predicted based on catchment attributes summarising climate and landscape and can be used to characterise baseflow and groundwater processes that cannot be directly measured. While past watershed‐scale studies suggest that landscape attributes are important controls on baseflow and storage processes, recent regional‐to‐global scale modelling studies have instead found that landscape attributes have weaker relationships with hydrologic signatures of these processes than expected compared to climate attributes. In this study, we quantify two landscape attributes, average geologic age and the proportion of catchment area covered by wetlands. We investigate if incorporating these additional predictors into existing large‐sample attribute datasets strengthens continental‐scale, empirical relationships between landscape attributes and hydrologic signatures. We quantify 14 hydrologic signatures related to baseflow and groundwater processes in catchments across the contiguous United States, evaluate the relationships between the new catchment attributes and hydrologic signatures with correlation analysis and use the new attributes to predict hydrologic signatures with random forest models. We found that the average geologic age of catchments was a highly influential predictor of hydrologic signatures, especially for signatures describing baseflow magnitude in catchments, and had greater importance than existing attributes of the subsurface. In contrast, we found that the proportion of wetlands in catchments had limited influence on our hydrologic signature predictions. We recommend incorporating catchment geologic age into large‐sample catchment datasets to improve predictions of baseflow and storage hydrologic signatures and processes across continental scales. 

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4. Global warming potential of farming systems across England: possible mitigation and co-benefits for water quality and biodiversity

   https://doi.org/10.1007/s13593-025-01015-4  

   Zhang, Yusheng; Collins, Adrian L (April 2025, Agronomy for Sustainable Development)

   Abstract Agriculture is a key contributor to gaseous emissions causing climate change, the degradation of water quality, and biodiversity loss. The extant climate change crisis is driving a focus on mitigating agricultural gaseous emissions, but wider policy objectives, beyond net zero, mean that evidence on the potential co-benefits or trade-offs associated with on-farm intervention is warranted. For novelty, aggregated data on farm structure and spatial distribution for different farm types were integrated with high-resolution data on the natural environment to generate representative model farms. Accounting for existing mitigation effects, the Catchment Systems Model was then used to quantify global warming potential, emissions to water, and other outcomes for water management catchments across England under both business-as-usual and a maximum technically feasible mitigation potential scenario. Mapped spatial patterns were overlain with the distributions of areas experiencing poor water quality and biodiversity loss to examine potential co-benefits. The median business-as-usual GWP20 and GWP100, excluding embedded emissions, were estimated to be 4606 kg CO₂eq. ha⁻¹(inter-quartile range 4240 kg CO₂eq. ha−¹) and 2334 kg CO₂eq. ha⁻¹(inter-quartile range 1462 kg CO₂eq. ha⁻¹), respectively. The ratios of business-as-usual GHG emissions to monetized farm production ranged between 0.58 and 8.89 kg CO₂eq. £⁻¹for GWP20, compared with 0.53–3.99 kg CO₂eq. £⁻¹for GWP100. The maximum mitigation potentials ranged between 17 and 30% for GWP20 and 19-27% for GWP100 with both corresponding medians estimated to be ~24%. Here, we show for the first time that the co-benefits for water quality associated with reductions in phosphorus and sediment loss were both equivalent to around a 34% reduction, relative to business-as-usual, in specific management catchment reporting units where excess water pollutant loads were identified. Several mitigation measures included in the mitigation scenario were also identified as having the potential to deliver co-benefits for terrestrial biodiversity. 

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5. The Influence of Geomorphology on Storage and Surface Water–Groundwater Interactions in Mountainous Headwater Streams

   https://doi.org/10.1002/hyp.70361  

   Perry, Zachary; Segura, Catalina; Brooks, J Renée; Takaoka, Sadao; Swanson, Frederick J (January 2026, Hydrological Processes)

   ABSTRACT We investigated the influence of landslide deposits on hydrologic connectivity and subsurface water movement in small headwater catchments in the Western Cascades, Oregon, USA. We examined isotopic variations in surface water across multiple catchments, comparing wet and dry periods to assess how antecedent moisture influences hydrologic connectivity and groundwater interactions. Seasonal shifts in δ¹⁸O values reveal that hydrologic connectivity increases during wet conditions, resulting in more uniform isotopic signatures across catchments due to enhanced vertical and lateral water movement in the subsurface. In contrast, during dry periods there was greater spatial variability in δ¹⁸O, reflecting localised groundwater contributions and reduced connectivity. Notably, some catchments with high proportions of earthflow terrain maintain consistent water isotopic ratios across seasons, suggesting persistent groundwater inputs from landslide deposits. Spatial patterns in δ¹⁸O also point to subsurface inter‐catchment flow paths facilitated by landslide deposits. Streamflow measurements during the dry season further support these findings. Catchments underlain by older, stabilised landslide deposits had highly variable unit discharge and frequent periods of flow cessation, consistent with weaker subsurface connectivity and limited water retention. In contrast, catchments draining active earthflows maintained relatively high unit discharges and perennial flow, indicating stronger subsurface linkages and greater potential for water accumulation that sustains both flow and ongoing slope movement. We estimated storage potential within landslide deposits and then used this to estimate catchment storage potential. Catchment storage was negatively correlated to variability in isotopic ratios, indicating an inverse relationship between catchment storage and variability in water sources in both space and time. Overall, our results demonstrate that geomorphic setting—particularly the presence and structure of landslide deposits—can exert strong control on the spatial distribution of hydrologic connectivity in mountain catchments. These insights improve our understanding of how subsurface properties mediate water movement and streamflow resilience under varying climate conditions. 

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