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1. Long‐Term Stream Chemistry Patterns in a Boreal Watershed Underlain With Discontinuous Permafrost

   https://doi.org/10.1029/2025JG009126  

   Kraus, K L; Jones, J B (December 2025, Journal of Geophysical Research: Biogeosciences)

   Abstract The consequences of climate change on boreal ecosystems are evident in declining permafrost extent, amplifying positive climate feedback loops, and altering the timing and intensity of hydrologic events. Thawing permafrost in the discontinuous permafrost zone could affect carbon and nutrient cycling in stream ecosystems. We examined stream chemistry and climate trends over a 20+‐year period across catchments in the Caribou Poker Creeks Research Watershed underlain with varying extents of permafrost (4%–53%). The study aimed to evaluate patterns in dissolved inorganic carbon (DIC,pCO₂), dissolved organic carbon (DOC), nitrogen (Dissolved organic nitrogen, and NO₃⁻), geochemical solutes (Ca²⁺, Mg²⁺, SO₄²⁻), and discharge to determine how altered terrestrial flowpaths and climate change‐related trends in temperature and precipitation have transformed solute transport in high‐latitude watersheds during the ice‐free season. We analyzed long‐term trends in stream chemistry using Thiel‐Sen analysis and a mixed effects model to quantify the influence of abiotic factors on solute concentrations. Results indicate significant declines in DOC (−109.0 to −169.9 μg L⁻¹ yr⁻¹) andpCO₂(−24.1 ppmv yr⁻¹) in higher permafrost extent sub‐catchments. The highest permafrost catchment is experiencing the greatest amount of change, contrasting sharply with opposite to fewer trends in the catchments with lower permafrost extent. Model results indicate the importance of moisture conditions and discharge (p < 0.05), especially for changes in organic solutes. As climate change progresses, the role of these abiotic factors and permafrost thaw will remain important for solute transport dynamics in boreal headwater streams, with consequences for in‐stream communities and downstream solute yields. 

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2. Lateral Dissolved Organic Carbon Losses Represent ∼10% of Upland Tundra Carbon Losses and Include Seasonal Permafrost Contributions

   https://doi.org/10.1029/2025JG009067  

   Kelley, A K; Axler, Z; Ledman, J; De_La_Torre, M; Ebert, C H; Springer, A E; Kaufman, D S; Schuur, E_A G (November 2025, Journal of Geophysical Research: Biogeosciences)

   Abstract We investigated lateral dissolved organic carbon (DOC) fluxes from lower‐order streams in upland tundra underlain by permafrost to assess their contribution to carbon (C) sink or source strength. The study site, located in Healy, Alaska, is within the Panguingue Creek watershed (66 km²), where permafrost acts as a confining layer for soil pore water. We examined how seasonal hydrology affects DOC export to understand lateral C flux contributions to the site's net ecosystem C balance. Previous estimates of vertical gas exchange (net CO₂uptake and release) indicated a loss of 52.5 g C m⁻² yr⁻¹and methane was estimated to lead to an additional loss of 6.4 ± 0.20 CO₂‐equivalent (g CO₂–C m⁻² yr⁻¹) suggesting the site is a net C source. We found that a second‐order stream exported an additional 5.0 g DOC m⁻² yr⁻¹laterally, which is approximately 10% of the vertical CO₂loss, reinforcing the site's source status. Accounting for CO₂, CH₄, and DOC, total C losses were estimated to be 64 g C m⁻² yr⁻¹. Further, we found that shoulder seasons played a key role in C export, with the spring freshet alone accounting for 59% of total DOC flux. Seasonality also influenced DOC age, with older, permafrost‐derived DOC exported primarily during spring and fall. These findings underscore the significance of lateral pathways in permafrost C budgets and highlight DOC as a critical, seasonally variable component of C loss. 

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3. Influence of infrastructure on water quality and greenhouse gas dynamics in urban streams

   https://doi.org/10.5194/bg-14-2831-2017  

   Smith, Rose M.; Kaushal, Sujay S.; Beaulieu, Jake J.; Pennino, Michael J.; Welty, Claire (January 2017, Biogeosciences)

   Streams and rivers are significant sources of nitrous oxide (N₂O), carbon dioxide (CO₂), and methane (CH₄) globally, and watershed management can alter greenhouse gas (GHG) emissions from streams. We hypothesized that urban infrastructure significantly alters downstream water quality and contributes to variability in GHG saturation and emissions. We measured gas saturation and estimated emission rates in headwaters of two urban stream networks (Red Run and Dead Run) of the Baltimore Ecosystem Study Long-Term Ecological Research project. We identified four combinations of stormwater and sanitary infrastructure present in these watersheds, including: (1) stream burial, (2) inline stormwater wetlands, (3) riparian/floodplain preservation, and (4) septic systems. We selected two first-order catchments in each of these categories and measured GHG concentrations, emissions, and dissolved inorganic and organic carbon (DIC and DOC) and nutrient concentrations biweekly for 1 year. From a water quality perspective, the DOC : NO₃⁻ ratio of streamwater was significantly different across infrastructure categories. Multiple linear regressions including DOC : NO₃⁻ and other variables (dissolved oxygen, DO; total dissolved nitrogen, TDN; and temperature) explained much of the statistical variation in nitrous oxide (N₂O, r² =  0.78), carbon dioxide (CO₂, r² =  0.78), and methane (CH₄, r² =  0.50) saturation in stream water. We measured N₂O saturation ratios, which were among the highest reported in the literature for streams, ranging from 1.1 to 47 across all sites and dates. N₂O saturation ratios were highest in streams draining watersheds with septic systems and strongly correlated with TDN. The CO₂ saturation ratio was highly correlated with the N₂O saturation ratio across all sites and dates, and the CO₂ saturation ratio ranged from 1.1 to 73. CH₄ was always supersaturated, with saturation ratios ranging from 3.0 to 2157. Longitudinal surveys extending form headwaters to third-order outlets of Red Run and Dead Run took place in spring and fall. Linear regressions of these data yielded significant negative relationships between each gas with increasing watershed size as well as consistent relationships between solutes (TDN or DOC, and DOC : TDN ratio) and gas saturation. Despite a decline in gas saturation between the headwaters and stream outlet, streams remained saturated with GHGs throughout the drainage network, suggesting that urban streams are continuous sources of CO₂, CH₄, and N₂O. Our results suggest that infrastructure decisions can have significant effects on downstream water quality and greenhouse gases, and watershed management strategies may need to consider coupled impacts on urban water and air quality. 

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4. A New Coupled Biogeochemical Modeling Approach Provides Accurate Predictions of Methane and Carbon Dioxide Fluxes Across Diverse Tidal Wetlands

   https://doi.org/10.1029/2023JG007943  

   Oikawa, P Y; Sihi, D; Forbrich, I; Fluet‐Chouinard, E; Najarro, M; Thomas, O; Shahan, J; Arias‐Ortiz, A; Russell, S; Knox, S H; et al (October 2024, Journal of Geophysical Research: Biogeosciences)

   Abstract Tidal wetlands provide valuable ecosystem services, including storing large amounts of carbon. However, the net exchanges of carbon dioxide (CO₂) and methane (CH₄) in tidal wetlands are highly uncertain. While several biogeochemical models can operate in tidal wetlands, they have yet to be parameterized and validated against high‐frequency, ecosystem‐scale CO₂and CH₄flux measurements across diverse sites. We paired the Cohort Marsh Equilibrium Model (CMEM) with a version of the PEPRMT model called PEPRMT‐Tidal, which considers the effects of water table height, sulfate, and nitrate availability on CO₂and CH₄emissions. Using a model‐data fusion approach, we parameterized the model with three sites and validated it with two independent sites, with representation from the three marine coasts of North America. Gross primary productivity (GPP) and ecosystem respiration (R_eco) modules explained, on average, 73% of the variation in CO₂exchange with low model error (normalized root mean square error (nRMSE) <1). The CH₄module also explained the majority of variance in CH₄emissions in validation sites (R² = 0.54; nRMSE = 1.15). The PEPRMT‐Tidal‐CMEM model coupling is a key advance toward constraining estimates of greenhouse gas emissions across diverse North American tidal wetlands. Further analyses of model error and case studies during changing salinity conditions guide future modeling efforts regarding four main processes: (a) the influence of salinity and nitrate on GPP, (b) the influence of laterally transported dissolved inorganic C on R_eco, (c) heterogeneous sulfate availability and methylotrophic methanogenesis impacts on surface CH₄emissions, and (d) CH₄responses to non‐periodic changes in salinity. 

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5. Season and Antecedent Conditions Impact Concentration‐Discharge Relationships for Dissolved Organic Carbon and Alkalinity in a Southeast Alaskan Watershed

   https://doi.org/10.1029/2025JG009090  

   Delbecq, Claire; Fellman, Jason B; Bellmore, J Ryan; Whitney, Emily J; Fitzgerald, Kevin; Falke, Jeffrey A (January 2026, Journal of Geophysical Research: Biogeosciences)

   Abstract Fluvial export of dissolved carbon plays an important role in watershed‐scale biogeochemistry. Predicted changes in climate are expected to impact watershed hydrologic regimes, and in turn, the sources and export of dissolved carbon from watersheds. Here, we utilize high resolution measurements of discharge and dissolved carbon concentration to examine how concentration‐discharge (CQ) relationships vary seasonally and during high flow events over the main runoff season (May–October) in a temperate forested watershed in Southeast Alaska. Concentration‐discharge relationships for dissolved organic carbon (DOC) and alkalinity demonstrated strong seasonal patterns, with more linear relationships in May and June versus other months. Changing power law model slopes (bvalues; the exponent in a power law regression between runoff and carbon yields) indicated potentially shifting watershed sources (biogenic vs. geologic) and contrasting dominant flowpaths (shallow vs. deeper groundwater) for DOC and alkalinity over the sampling period. During the largest storm event of the study, DOC and alkalinitybvalues shifted from an overall pattern of transport (meanb = 1.58 values >1.0 indicate transport limitation) and source limitation (meanb = 0.48, values <1.0 indicate source limitation) to chemostatic (DOC,b = 0.99; alkalinity,b = 1.019). In June through August, patterns in hysteresis index suggest that CQ relationships were altered when storms followed in close succession to each other. Together, these findings indicate that seasonal and antecedent flow conditions play a role in dissolved carbon export from forested watersheds. Understanding these dynamics, particularly during winter months, will become increasingly important as changes to hydroclimate impact riverine carbon export. 

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