More Like this

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. 

   more » « less
2. The Role of Lithology on Concentration‐Discharge Relationships and Carbon Export in Two Adjacent Headwater Catchments

   https://doi.org/10.1029/2024WR037086  

   Giggy, L; Zimmer, M (April 2025, Water Resources Research)

   Abstract Headwater catchments have strong impacts on downstream waterways, near‐shore ecosystems, and the quality of water available for growing human populations. Thus, understanding how water and solutes are exported through these upland landscapes is critically important. A growing body of literature highlights the interaction of topography, climate, and the critical zone structure as a key control on streamflow and chemical export. However, more focused work is needed to pinpoint how variability in subsurface structure across lithologically complex regions impacts streamflow and chemical signals at catchment outlets. Here, we aim to better understand how lithology and subsurface critical zones modulate streamflow response and solute export patterns in two central coastal California headwater catchments that are similar in topography, vegetation, and climate but have different lithologies. We monitored streamflow and collected surface water samples at the catchment outlets for dissolved major ions and organic carbon (DOC) for two consecutive water years. The catchment with mélange bedrock displayed much flashier hydrologic behavior with 7.8 times higher peak flow values and 1.9 times higher mean event concentrations of DOC, suggesting shorter and shallower hydrologic flow paths that likely arise from regions of shallower bedrock. Despite distinct hydrologic behavior and DOC export, dissolved major ion concentrations were broadly similar and chemostatic, which may be driven by rapid chemical reactions in the critical zone of both catchments. Our work contributes to building an integrated understanding of how subtle differences in catchment structure can have profound impacts on how water and solutes are routed through headwater catchments. 

   more » « less
3. Temperature and Flow Control Organic Carbon Metabolism in Boreal Headwater Streams

   https://doi.org/10.1029/2024JG008281  

   Iannucci, F M; Jones, J B; Olson, K L; Muscarella, M E; Hotchkiss, E R (October 2024, Journal of Geophysical Research: Biogeosciences)

   Abstract Metabolism in stream ecosystems alters the fate of organic carbon (OC) received from surrounding landscapes, but our understanding of in‐stream metabolic processes in boreal ecosystems remains limited. Determining the factors that regulate OC metabolism will help predict how the C balance of boreal streams may respond to future environmental change. In this study, we addressed the question: what controls OC metabolism in boreal headwater streams draining catchments with discontinuous permafrost? We hypothesized that metabolism is collectively regulated by OC reactivity, phosphorus availability, and temperature, with discharge modulating each of these conditions. We tested these hypotheses using a combination of laboratory experiments and whole‐stream ecosystem metabolism measurements throughout the Caribou‐Poker Creeks Research Watershed (CPCRW) in Interior Alaska, USA. In the laboratory experiments, respiration and dissolved OC (DOC) removal were both co‐limited by the supply of reactive C and phosphorus, but temperature and residence time acted as stronger controls of DOC removal. Ecosystem respiration (ER) was largely predicted by discharge and site, with some variance explained by gross primary production (GPP) and temperature. Both ER and GPP varied inversely with watershed permafrost extent, with an inverse relationship between temperature and permafrost extent providing one plausible explanation. Our results provide some of the first evidence of a functional response to permafrost thaw in stream ecosystems and suggest the role of metabolism in landscape C cycling may increase as climate change progresses. 

   more » « less
4. Controls on the Respiration of Ancient Carbon Draining From Permafrost Soils Into Sunlit Arctic Surface Waters

   https://doi.org/10.1029/2023JG007853  

   Rieb, E C; Polik, C A; Ward, C P; Kling, G W; Cory, R M (May 2024, Journal of Geophysical Research: Biogeosciences)

   Abstract The thawing of ancient organic carbon stored in arctic permafrost soils, and its oxidation to carbon dioxide (CO₂, a greenhouse gas), is predicted to amplify global warming. However, the extent to which organic carbon in thawing permafrost soils will be released as CO₂is uncertain. A critical unknown is the extent to which dissolved organic carbon (DOC) from thawing permafrost soils is respired to CO₂by microbes upon export of freshly thawed DOC to both dark bottom waters and sunlit surface waters. In this study, we quantified the radiocarbon age and¹³C composition of CO₂produced by microbial respiration of DOC that was leached from permafrost soils and either kept in the dark or exposed to ultraviolet and visible wavelengths of light. We show that permafrost DOC most labile to microbial respiration was as old or older (ages 4,000–11,000 a BP) and more¹³C‐depleted than the bulk DOC in both dark and light‐exposed treatments, likely indicating respiration of old,¹³C‐depleted lignin and lipid fractions of the permafrost DOC pool. Light exposure either increased, decreased, or had no effect on the magnitude of microbial respiration of old permafrost DOC relative to respiration in the dark, depending on both the extent of DOC oxidation during exposure to light and the wavelength of light. Together, these findings suggest that photochemical changes affecting the lability of permafrost DOC during sunlight exposure are an important control on the magnitude of microbial respiration of permafrost DOC in arctic surface waters. 

   more » « less
5. Geomorphic complexity influences coarse particulate organic matter transport and storage in headwater streams

   https://doi.org/10.3389/frwa.2023.1227167  

   Fogel, Caleb B; Lininger, Katherine B (September 2023, Frontiers in Water)

   Coarse particulate organic matter (CPOM; organic matter 1–100 mm in diameter, excluding small wood) stored in streams provides an important energy source for aquatic ecosystems, and CPOM transport provides downstream energy subsidies and is a pathway for watershed carbon export. However, we lack understanding of the magnitude of and processes influencing CPOM storage and transport in headwater streams. We assessed how geomorphic complexity and hydrologic regime influence CPOM transport and storage in the Colorado Front Range, USA. We compared CPOM transport during snowmelt in a stream reach with high retentive feature (e.g., wood, cobbles, and other features) frequency to a reach with low retentive feature frequency, assessing how within-a-reach geomorphic context influences CPOM transport. We also compared CPOM transport in reaches with differing valley geometry (two confined reaches versus a wide, multi-thread river bead) to assess the influence of geomorphic variations occurring over larger spatial extents. Additionally, we compared CPOM storage in accumulations in reaches (n= 14) with flowing water or dry conditions in late summer and investigated how small pieces of organic matter [e.g., woody CPOM and small wood (>1 min length and 0.05–1 min diameter or 0.5–1 min length and >0.1 min diameter)] influence CPOM storage. We found that within-a-reach retentive feature frequency did not influence CPOM transport. However, valley geometry influenced CPOM transport, with a higher CPOM transport rate (median: 1.53 g min⁻¹) downstream of a confined stream reach and a lower CPOM transport rate (median: 0.13 g min⁻¹) downstream of a low gradient, multi-thread river bead. Additionally, we found that particulate organic carbon (POC) export (0.063 Mg C) in the form of CPOM was substantially lower than dissolved organic carbon (DOC) export (12.3 Mg C) in one of these headwater streams during the 2022 water year. Dry reaches stored a higher volume of CPOM (mean = 29.18 m³ha⁻¹) compared to reaches with flowing water (15.75 m³ha⁻¹), and woody CPOM pieces trapped 37% of CPOM accumulations. Our results demonstrate that the influence of geomorphic context on CPOM transport depends on the scale and type of geomorphic complexity, POC may be lower than DOC export in some headwater streams, and small woody organic material is important for trapping CPOM small streams. 

   more » « less