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1. Mountain Stream Ecosystem Metabolism and Nitrogen Cycling Responses to Hydroclimatic Volatility

   https://doi.org/10.1029/2025JG009229  

   Loria, Kelly; Lowman, Heili; Genzoli, Laurel; Krause, Jasmine; Harpold, Adrian; Chandra, Sudeep; Blaszczak, Joanna R (October 2026, Journal of Geophysical Research: Biogeosciences)

   Abstract Changing hydroclimatic conditions increase streamflow variability and add uncertainty to predictions of watershed nutrient export and ecosystem function. Mountain headwater streams are especially sensitive to climate shifts due to their dependence on seasonal snowpack. We explored how changes in mountain precipitation affect the synchrony between hydrologic processes (peak flow and baseflow onset) and biological processes (metabolism and nutrient uptake) that control nitrogen dynamics. We monitored two mountain streams in the Lake Tahoe basin (California and Nevada, USA)—a larger open‐canopy stream and a smaller, shaded stream—over two dry water years and one substantially wetter water year. On average, the large stream received more annual light, was warmer, and had higher inorganic nitrogen demand compared to the small stream. From dry to wet years, the onset of baseflow was delayed by ∼40 days in both streams, shortening the optimal window for benthic algae growth by over a month and substantially reducing the potential for in stream nitrogen uptake. Concurrently, cumulative annual gross primary production declined by 86% (Δ −248 g O₂m⁻² yr⁻¹) in the large stream and 93% (Δ −26 g O₂m⁻² yr⁻¹) in the small stream. Mean daily ammonium supply increased by 47% (Δ + 0.01 g m⁻² d⁻¹) in the large stream and by 112% (Δ + 0.16 g m⁻² d⁻¹) in the small stream. These findings highlight the critical role of streams in regulating nutrient dynamics and show that even neighboring or hydrologically similar streams can exhibit distinct biogeochemical responses to hydroclimatic variability. 

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2. Use of geostatistical models to evaluate landscape and stream network controls on post‐fire stream nitrate concentrations

   https://doi.org/10.1002/hyp.14689  

   Rhea, Allison E; Covino, Timothy P; Rhoades, Charles C; Brooks, Alexander C (September 2022, Hydrological Processes)

   Abstract Forested watersheds provide many ecosystem services, such as the filtration of sediment, pollutants, and nutrients, which are increasingly threatened by wildfire. For example, stream nutrient concentrations often increase following wildfire and can remain elevated for decades, making downstream waters susceptible to eutrophication. We investigated the drivers of persistent elevated stream nutrients, specifically nitrate (NO₃⁻), in nine watersheds that were burned 16 years prior by the Hayman fire, Colorado, USA. We evaluated the ability of multiple linear regression and spatial stream network modeling approaches to predict observed concentrations of the biologically active solute NO₃⁻and the conservative solute sodium (Na⁺) which serves as a partial control. Specifically, we quantified the degree to which landscape and stream network characteristics predict stream solute concentrations. Stream Na⁺exhibited strong spatial autocorrelation that was primarily controlled by topography and hydrology. In contrast, stream NO₃⁻had higher spatial variability and was inversely correlated to vegetation cover, measured as mean normalized differenced moisture index (NDMI). Spatially heterogeneous wildfire behaviour left intact forest patches interspersed with high burn severity patches dominated by shrubs and grasses which contributes to the spatial variability in stream NO₃⁻concentrations. Post‐fire vegetation also interacts with watershed structure to influence stream NO₃⁻patterns. For example, severely burned convergent hillslopes in headwaters positions were associated with the highest stream NO₃⁻concentrations due to the high proportional influence of hillslope water in these locations. Our findings suggest that targeted reforestation in severely burned convergent hillslopes in headwater positions may enhance the recovery of stream NO₃⁻concentrations to pre‐fire levels. 

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3. Hydrologic connectivity with peatland soils drives very high carbon fluxes in a tropical, mountain stream

   https://doi.org/10.1007/s10533-026-01327-x  

   Whitmore, Keridwen M; DelVecchia, Amanda G; Jaramillo, Ricardo; Chimbolema, Segundo; Suárez, Esteban; Riveros-Iregui, Diego A (June 2026, Biogeochemistry)

   Abstract Inland waters receive large quantities of carbon from the surrounding landscape and are active sites of carbon transport, transformation, and emission. Global carbon emission estimates are limited by sparse and unevenly distributed carbon flux observations, particularly in the tropics. We evaluated hydrological and metabolic controls on carbon export variability from a large peatland in a tropical ecosystem typical of the Northern Andes mountains. We recorded dissolved CO₂(pCO₂), dissolved oxygen (DO), and discharge at 15-min intervals 5 m downstream of a peatland outlet (Station 1) and at 3 additional locations downstream (Stations 2, 3 and 4) from July 2019 until Jan 2020 and from June 2021 until March 2023. Continuous measurements of DO and discharge were also measured 2 km away in a stream draining an adjoining catchment (Station 5). Discrete measurements of dissolved organic carbon (DOC) and dissolved methane (pCH₄) were collected in June-July of 2021 and 2022. Stream discharge was a primary control onpCO₂and DOC in the stream network at both seasonal and event scales. DOC concentration increased with discharge and whilepCO₂decreased during higher flows, CO₂loading increased. Pronounced seasonal changes were observed with lowestpCO₂recorded at the peatland outlet in wet months (June–August: 5845 ± 2325 ppm, mean ± standard deviation), and the highest in dry months (Nov-Feb, 16,677 ± 3685 ppm). Anoxic or hypoxic conditions persisted for over half of our study and measurements ofpCH₄at the peatland outlet were very high (982 ± 797 ppm), underscoring the importance of anaerobic activity in this system. Aerobic processes also influencedpCO₂dynamics. Aquatic metabolism at Station 5 (29 July–19 Oct 2021) was net heterotrophic, with ER exceeding GPP and netpCO₂production (mean ER: − 6.5 g O₂m⁻²d⁻¹, GPP: 0.44 g O m⁻²d⁻¹). Our study highlights the role of hydrologic connectivity and diverse biogeochemical processes in shaping carbon export and cycling in páramo streams, which results inpCO₂andpCH₄levels among the highest reported in streams and rivers worldwide. 

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4. Synchrony of Nitrogen Wet Deposition Inputs and Watershed Nitrogen Outputs Using Information Theory

   https://doi.org/10.1029/2023WR034794  

   Murray, Desneiges S; Moges, Edom; Larsen, Laurel; Shattuck, Michelle D; McDowell, William H; Wymore, Adam S (October 2023, Water Resources Research)

   Abstract Nitrogen (N) wet deposition chemistry impacts watershed biogeochemical cycling. The timescale and magnitude of (a)synchrony between wet deposition N inputs and watershed N outputs remains unresolved. We quantify deposition‐river N (a)synchrony with transfer entropy (TE), an information theory metric enabling quantification of lag‐dependent feedbacks in a hydrologic system by calculating directional information flow between variables. Synchrony is defined as a significant amount of TE‐calculated reduction in uncertainty of river N from wet deposition N after conditioning for antecedent river N conditions. Using long‐term timeseries of wet deposition and river DON, NO₃⁻, and NH₄⁺concentrations from the Lamprey River watershed, New Hampshire (USA), we constrain the role of wet deposition N to watershed biogeochemistry. Wet deposition N contributed information to river N at timescales greater than quick‐flow runoff generation, indicating that river N losses are a lagged non‐linear function of hydro‐biogeochemical forcings. River DON received the most information from all three wet deposition N solutes while wet deposition DON and NH₄⁺contributed the most information to all three river N solutes. Information theoretic algorithms facilitated data‐driven inferences on the hydro‐biogeochemical processes influencing the fate of N wet deposition. For example, signals of mineralization and assimilation at a timescale of 12 to 21‐weeks lag display greater synchrony than nitrification, and we find that N assimilation is a positive lagged function of increasing N wet deposition. Although wet deposition N is not the main driver of river N, it contributes a significant amount of information resolvable at time scales of transport and transformations. 

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5. Importance of seasonality and watershed size on carbon dioxide evasion in Arctic streams

   https://doi.org/10.1088/2752-664X/ae212d  

   Hock, Macall; Liljedahl, Anna K; Zona, Donatella (December 2025, Environmental Research: Ecology)

   Abstract Arctic headwater streams play a crucial role in the carbon cycle, contributing disproportionately to carbon dioxide (CO₂) evasion despite their small size and surface area. In this study, we examined how seasonal hydrologic patterns, such as spring snowmelt (freshet), mid-summer low-flows (baseflow) and the late summer period in August and early September (late-season), influence CO₂evasion in Arctic headwater streams (1–9 km²basin size; 1–4 stream orders) near Utqiagvik, Alaska. During three summers, we measured key environmental parameters (CO₂partial pressure, water temperature, discharge, dissolved organic carbon (DOC), gas transfer velocity) and CO₂evasion using a floating chamber. CO₂evasion followed distinct seasonal patterns with the highest evasion rates during freshet, followed by the late-season, and the lowest during baseflow. Despite its short duration (10 d), freshet accounted for 22% more total CO₂evasion than the 36 d late-season period. The descending peakflow within freshet had the highest median evasion rate (2486 mg C–CO₂m⁻²d⁻¹) of the entire season, while the ascending portion of the peakflow had the lowest (448 mg C–CO₂m⁻²d⁻¹). These two freshet periods showed a statistically significant difference (p< 0.05). Water temperature, DOC, andpCO₂explained 35%, 30% and 67% of freshet evasion variability, respectively. No measured parameters reliably predicted CO₂evasion for the baseflow or late-season periods, suggesting increased hydrologic and biological complexity. The stream showed supply-limitation during freshet but transitioned to chemostatic behavior thereafter. By synthesizing our measurements with previously published data, we show that small streams (<1 km²watersheds) exhibit ∼10-times the CO₂evasion rates than large waterways (>1000 km²). We also find that across the Arctic, only ∼15% of riverine CO₂measurements capture the freshet period. Together, the omission of small streams and the underrepresentation of freshet likely lead to a systematic underestimation of CO₂losses from Arctic surface waters to the atmosphere. 

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