An official website of the United States government
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
This content will become publicly available on December 8, 2026
Importance of seasonality and watershed size on carbon dioxide evasion in Arctic streams
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.
more »
« less
- PAR ID:
- 10689326
- Publisher / Repository:
- ADC
- Date Published:
- Journal Name:
- Environmental Research: Ecology
- Volume:
- 4
- Issue:
- 4
- ISSN:
- 2752-664X
- Page Range / eLocation ID:
- 045004
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
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.more » « less
-
Abstract The transformation of permafrost-derived dissolved organic carbon (DOC) to CO2is mediated by interacting photodegradation and biodegradation processes that influence DOC lability and persistence in Arctic aquatic systems. Here, we experimentally evaluated the relative roles of photodegradation and biodegradation pathways on DOC concentration and age along a hydrologic continuum from soil pore water to a first-order stream to a second-order stream draining permafrost soils during spring freshet. Spring freshet is characterized by pulses of DOC, resulting from interactions of snowmelt with modern surface soils and vegetation as well as pulses of older DOC, stored overwinter. In our study, we incubated spring freshet waters and exposed these waters to photodegradation, biodegradation, and combined photo-biodegradation pathways. We observed a 7%–72% DOC loss at all sites within the 2 month incubation. Photodegradation produced the greatest losses and strongest radiocarbon (Δ1⁴C) shifts, particularly when combined with biodegradation. Radiocarbon signatures revealed three DOC pools: young, labile carbon; old, labile carbon; and old, stable carbon. Soil pore waters released from a warming permafrost landscape exhibited rapid DOC losses and large radiocarbon shifts within 24 h, indicating the presence of a highly labile, old DOC pool that may be released with increased permafrost thaw. Contrary to expectations, photodegradation remained important in second-order streams, with greater DOC losses observed over time than from biodegradation alone. These results suggest that photodegradation enhances microbial access to otherwise resistant DOC, especially older, permafrost-derived fractions. Our findings provide mechanistic insight into how light and microbial processes interact to transform permafrost DOC, with implications for understanding DOC fate following permafrost thaw.more » « less
-
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.more » « less
-
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
