Search for: All records

Abstract Evaluating stream water chemistry patterns provides insight into catchment ecosystem and hydrologic processes. Spatially distributed patterns and controls of stream solutes are well‐established for high‐relief catchments where solute flow paths align with surface topography. However, the controls on solute patterns are poorly constrained for low‐relief catchments where hydrogeologic heterogeneities and river corridor features, like wetlands, may influence water and solute transport. Here, we provide a data set of solute patterns from 58 synoptic surveys across 28 sites and over 32 months in a low‐relief wetland‐rich catchment to determine the major surface and subsurface controls along with wetland influence across the catchment. In this low‐relief catchment, the expected wetland storage, processing, and transport of solutes is only apparent in solute patterns of the smallest subcatchments. Meanwhile, downstream seasonal and wetland influence on observed chemistry can be masked by large groundwater contributions to the main stream channel. These findings highlight the importance of incorporating variable groundwater contributions into catchment‐scale studies for low‐relief catchments, and that understanding the overall influence of wetlands on stream chemistry requires sampling across various spatial and temporal scales. Therefore, in low‐relief wetland‐rich catchments, given the mosaic of above and below ground controls on stream solutes, modeling efforts may need to include both surface and subsurface hydrological data and processes. 

Abstract Hyporheic exchange is critical to river corridor biogeochemistry, but decameter‐scale flowpaths (∼10‐m long) are understudied due to logistical challenges (e.g., sampling at depth, multi‐day transit times). Some studies suggest that decameter‐scale flowpaths should have initial hot spots followed by transport‐limited conditions, whereas others suggest steady reaction rates and secondary reactions that could make decameter‐scale flowpaths important and unique. We investigated biogeochemistry along a 12‐m hyporheic mesocosm that allowed for controlled testing of seasonal and spatial water quality changes along a flowpath with fixed geometry and constant flow rate. Water quality profiles of oxygen, carbon, and nitrogen were measured at 1‐m intervals along the mesocosm over multiple seasons. The first 6 m of the mesocosm were always oxic and a net nitrogen source to mobile porewater. In winter, oxic conditions persisted to 12 m, whereas the second half of the flowpath became anoxic and a net nitrogen sink in summer. No reactive hot spots were observed in the first meter of the mesocosm. Instead, most reactions were zeroth‐order over 12 m and 54 hr of transit time. Influent chemistry had less impact on hyporheic biogeochemistry than expected due to large amounts of in situ reactant sources compared to stream‐derived reactant sources. Sorbed or buried carbon likely fueled reactions with rates controlled by temperature and redox conditions. Each reactant showed different hyporheic Damköhler numbers, challenging the characterization of flowpaths being intrinsically reaction‐ or transport‐limited. Future research should explore the prevalence and biogeochemical contributions of decameter‐scale flowpaths in diverse field settings. 

Abstract Hydrologic exchange processes are critical for ecosystem services along river corridors. Meandering contributes to this exchange by driving channel water, solutes, and energy through the surrounding alluvium, a process called sinuosity‐driven hyporheic exchange. This exchange is embedded within and modulated by the regional groundwater flow (RGF), which compresses the hyporheic zone and potentially diminishes its overall impact. Quantifying the role of sinuosity‐driven hyporheic exchange at the reach‐to‐watershed scale requires a mechanistic understanding of the interplay between drivers (meander planform) and modulators (RGF) and its implications for biogeochemical transformations. Here, we use a 2D, vertically integrated numerical model for flow, transport, and reaction to analyze sinuosity‐driven hyporheic exchange systematically. Using this model, we propose a dimensionless framework to explore the role of meander planform and RGF in hydrodynamics and how they constrain nitrogen cycling. Our results highlight the importance of meander topology for water flow and age. We demonstrate how the meander neck induces a shielding effect that protects the hyporheic zone against RGF, imposing a physical constraint on biogeochemical transformations. Furthermore, we explore the conditions when a meander acts as a net nitrogen source or sink. This transition in the net biogeochemical potential is described by a handful of dimensionless physical and biogeochemical parameters that can be measured or constrained from literature and remote sensing. This work provides a new physically based model that quantifies sinuosity‐driven hyporheic exchange and biogeochemical reactions, a critical step toward their representation in water quality models and the design and assessment of river restoration strategies. 

Abstract Climate change is rapidly altering hydrological processes and consequently the structure and functioning of Arctic ecosystems. Predicting how these alterations will shape biogeochemical responses in rivers remains a major challenge. We measured [C]arbon and [N]itrogen concentrations continuously from two Arctic watersheds capturing a wide range of flow conditions to assess understudied event‐scale C and N concentration‐discharge (C‐Q) behavior and post‐event recovery of stoichiometric conditions. The watersheds represent low‐gradient, tundra landscapes typical of the eastern Brooks Range on the North Slope of Alaska and are part of the Arctic Long‐Term Ecological Research sites: the Kuparuk River and Oksrukuyik Creek. In both watersheds, we deployed high‐frequency optical sensors to measure dissolved organic carbon (DOC), nitrate (), and total dissolved nitrogen (TDN) for five consecutive thaw seasons (2017–2021). Our analyses revealed a lag in DOC: stoichiometric recovery after a hydrologic perturbation: while DOC was consistently elevated after high flows, diluted during rainfall events and consequently, recovery in post‐event concentration was delayed. Conversely, the co‐enrichment of TDN at high flows, even in watersheds with relatively high N‐demand, represents a potential “leak” of hydrologically available organic N to downstream ecosystems. Our use of high‐frequency, long‐term optical sensors provides an improved method to estimate carbon and nutrient budgets and stoichiometric recovery behavior across event and seasonal timescales, enabling new insights and conceptualizations of a changing Arctic, such as assessing ecosystem disturbance and recovery across multiple timescales. 

Hydrology and chemistry data for a spatially distributed synoptic and discharge campaign in the Augusta Creek Catchment (located in southwestern Michigan). The spatially distributed chemistry data was collected every 2-3 weeks from October 2021 to June 2024, and includes dissolved organic carbon (DOC), nitrate, sulfate, and chloride. Within 24 hours of collection samples were filtered through 0.45µm cellulose acetate membrane filters. We measured DOC (as non-purgeable organic carbon - NPOC), using two total organic carbon analyzers with total nitrogen units (Shimadzu TOC-V CPH with a TNM-1 and autosampler ASI-V before March 9 2023 and Shimadzu TOC-L CPH/CPN with a TNM-L ROHS and autosampler ASI-L after March 9 2023). For our analysis, we only include DOC/NPOC data after March 9 2023, due to discrepancies between the two instruments used. We measured anions (Cl-, NO3-, SO42-) using an ion chromatography system (Thermo Fisher Dionex, ICS1100 and ICS1000 and AS-DV autosampler). Our method detection limits were: 0.02 mg L-1 for anions and 0.43 mg L-1 for NPOC. Values that are "BDL" were below instrument detection limit. For values below method or instrument detection limit, we assigned concentrations of half the limit of quantification for the purpose of calculations and analyses. If this data is used in the future, values below the method detection limit will need to be filtered appropriately. Values that are NA were not analyzed. We collected discharge data during a period of baseflow from August 13-14, 2024 using two Sontek Flowtracker2 Acoustic Doppler Velocimeters. Discharge values were calculated using the Flowtracker’s mid-section method, measuring depth and velocity at ~20 stations across the stream width. Uncertainty in discharge (%) was also calculated by the Flowtracker instrument. To calculate specific discharge , we normalized our measured discharge by contributing area for each flow location. This data supports the paper: Weidner, C. R., Zarnetske, J. P., Kendall, A. D., Martin, S. L., Nesheim, S., & Shogren, A. J. (2025). Wetlands, groundwater and seasonality influence the spatial distribution of stream chemistry in a low‐relief catchment. Journal of Geophysical Research: Biogeosciences, 130, e2025JG008989. https://doi.org/10.1029/2025JG008989 Abstract: Evaluating stream water chemistry patterns provides insight into catchment ecosystem and hydrologic processes. Spatially distributed patterns and controls of stream solutes are well‐established for high‐relief catchments where solute flow paths align with surface topography. However, the controls on solute patterns are poorly constrained for low‐relief catchments where hydrogeologic heterogeneities and river corridor features, like wetlands, may influence water and solute transport. Here, we provide a data set of solute patterns from 58 synoptic surveys across 28 sites and over 32 months in a low‐relief wetland‐rich catchment to determine the major surface and subsurface controls along with wetland influence across the catchment. In this low‐relief catchment, the expected wetland storage, processing, and transport of solutes is only apparent in solute patterns of the smallest subcatchments. Meanwhile, downstream seasonal and wetland influence on observed chemistry can be masked by large groundwater contributions to the main stream channel. These findings highlight the importance of incorporating variable groundwater contributions into catchment‐scale studies for low‐relief catchments, and that understanding the overall influence of wetlands on stream chemistry requires sampling across various spatial and temporal scales. Therefore, in low‐relief wetland‐rich catchments, given the mosaic of above and below ground controls on stream solutes, modeling efforts may need to include both surface and subsurface hydrological data and processes. 

Key Points We compared tools for describing streamflow timeseries, including streamflow metrics, wavelet, and Fourier analysis Each method indicated streamflow data are structured: variability at short timescales is negatively correlated with long timescales Globally, dams were less correlated with streamflow regime than catchment size and climate were 

Hypoxia, or dissolved oxygen (DO) at low enough levels to impair organisms, is a particularly useful indicator of the health of freshwater ecosystems. However, due to limited sampling in headwater networks, the degree, distribution, and timing of hypoxia events are not known across the vast majority of most river networks. We thus sought to clarify the extent of hypoxia in headwater networks through three years of instrumentation of 78 sites across eight temperate, agricultural watersheds. We observed broadly distributed hypoxia, occurring 4 % of the time across 51 of the 78 sites over 20 months. The hypoxia was driven by three mechanisms: storm events, drying, and rewetting, with drying as the most common driver of hypoxia (55 % of all hypoxic event types). Drying induced hypoxia was most severe in smaller streams (Strahler orders ≤ 3), whereas storm events pref- erentially induced hypoxia in the larger streams (Strahler orders 3–5). A large diversity in DO trajectories to- wards hypoxia depended on hydrologic event type, with subsequent expected differences in mortality profiles of a sensitive species. Predictive models showed the most vulnerable sites to hypoxia were small streams with low slope, particularly during hot, low discharge periods. Despite variation among hypoxic events, there was remarkable similarity in the rate of DO drawdown during hypoxia events (ca. 1 mg O2 L− 1 d− 1). This drawdown similarity may be a useful rule-of-thumb for managers, and we hypothesize that it is either a signal of increasing lateral inflow of low DO water or a signal of increasing downstream oxygen demand. Overall, we posit that hypoxia is likely a common feature of most headwater networks that often goes undetected. Headwater hypoxia may become more common under increasingly dry conditions associated with climate and water resource management changes, with important implications for biological communities and biogeochemical processes. 

Climate change is an existential threat to the vast global permafrost domain. The diverse human cultures, ecological communities, and biogeochemical cycles of this tenth of the planet depend on the persistence of frozen conditions. The complexity, immensity, and remoteness of permafrost ecosystems make it difficult to grasp how quickly things are changing and what can be done about it. Here, we summarize terrestrial and marine changes in the permafrost domain with an eye toward global policy. While many questions remain, we know that continued fossil fuel burning is incompatible with the continued existence of the permafrost domain as we know it. If we fail to protect permafrost ecosystems, the consequences for human rights, biosphere integrity, and global climate will be severe. The policy implications are clear: the faster we reduce human emissions and draw down atmospheric CO 2 , the more of the permafrost domain we can save. Emissions reduction targets must be strengthened and accompanied by support for local peoples to protect intact ecological communities and natural carbon sinks within the permafrost domain. Some proposed geoengineering interventions such as solar shading, surface albedo modification, and vegetation manipulations are unproven and may exacerbate environmental injustice without providing lasting protection. Conversely, astounding advances in renewable energy have reopened viable pathways to halve human greenhouse gas emissions by 2030 and effectively stop them well before 2050. We call on leaders, corporations, researchers, and citizens everywhere to acknowledge the global importance of the permafrost domain and work towards climate restoration and empowerment of Indigenous and immigrant communities in these regions.