Variability and drivers of CO2, CH4, and N2O concentrations in streams across the United States

UNC Libraries · 2026-04-08

Streams and rivers are major sources of greenhouse gases (GHGs) to the atmosphere, as carbon and nitrogen are converted and outgassed during transport. Although our understanding of drivers of individual GHG fluxes has improved with numerous site‐specific studies and global‐scale compilations, our ability to parse out interrelated physical and biogeochemical drivers of gas concentrations is limited by a lack of consistently collected, temporally continuous samples of GHGs and their associated drivers. We present a first analysis of such a dataset collected by the National Ecological Observatory Network across 27 streams and rivers across ecoclimatic domains of the United States. Average concentrations of CO 2 ranged from 36.9 ± 0.88 to 404 ± 33 μ mol L −1 , CH 4 from 0.003 ± 0.0003 to 4.99 ± 0.72 μ mol L −1 , and N 2 O from 0.015 to 0.04 μ mol L −1 and spanned ranges of previous global compilations. Both CO 2 and CH 4 were strongly affected by physical drivers including mean air temperature and stream slope, as well as by dissolved oxygen and total nitrogen concentrations. N 2 O was exclusively correlated with total nitrogen concentrations. Results suggested that potential for gas exchange dominated patterns in gas concentrations at the site level, but contributions of in‐stream aerobic and anaerobic metabolism, and groundwater also likely varied across sites. The highest gas concentrations as well as highest variability occurred in low‐gradient, warmer, and nonperennial systems. These results are a first step in providing unprecedented, continuous estimates of GHG flux constrained by temporally variable physical and biogeochemical drivers of GHG production.

Water temperature and catchment characteristics drive variation in carbon dioxide and methane emissions from small ponds in a peatland‐rich, high‐altitude tropical ecosystem

Limnology and Oceanography · 2025-11-04

Abstract Inland waters release significant amounts of carbon into the atmosphere, with small ponds acting as hot spots. High variability and limited research make emissions from small waterbodies a major source of uncertainty, especially in underrepresented tropical ecosystems where unique drivers remain poorly understood. We evaluated the magnitude and sources of variability in emissions from small waterbodies of the páramo—a tropical ecoregion in the Andes mountains, characterized by carbon‐rich soils. We measured partial pressure of carbon dioxide ( p CO 2 ), methane ( p CH 4 ) and CO 2 emissions from small (< 5000 m 2 ) waterbodies, 11 ponds and 1 wetland, 3 times in the wet season and returned to 8 sites in the dry season. Sites were always supersaturated in p CH 4 (1096 ± 1482 μ atm), but occasionally undersaturated in p CO 2 (1224 ± 1585 μ atm). Variability between ponds was high and primarily driven by elevation and water temperature. Catchment soil‐water connectivity was also predictive of p CO 2 . Mean wet‐season emission rates were 0.34 ± 0.54 g CO 2 ‐C m −2 d −1 and 0.012 ± 0.018 g CH 4 ‐C m −2 d −1 and surface area fluctuations were a large source of seasonal variability in some ponds. Though an open‐water transect of the wetland site was similar to ponds, we measured very high p CH 4 (1678 ± 2629 μ atm) and p CO 2 (5162 ± 3207 μ atm) along the wetland perimeter. Our findings provide essential insights for incorporating a significant yet understudied tropical ecosystem into the global carbon budget by confirming previous observations that small ponds can emit a disproportionately large amount of carbon to the atmosphere, but also highlighting the importance of variables other than pond size in controlling emission hot spots.

Carbon Emissions From Low‐Order Streams in a Tropical, High‐Elevation, Peatland Ecosystem Are Mediated by Catchment Morphology

Water Resources Research · 2025-04-01 · 3 citations

Abstract Inland waters emit large amounts of carbon and are key players in the global carbon budget. Particularly high rates of carbon emissions have been reported in streams draining mountains, tropical regions, and peatlands. However, few studies have examined the spatial variability of CO 2 concentrations and fluxes occurring within these systems, particularly as a function of catchment morphology. Here we evaluated spatial patterns of CO 2 in three tropical, headwater catchments in relation to the river network and stream geomorphology. We measured dissolved carbon dioxide ( p CO 2 ), aquatic CO 2 emissions, discharge, and stream depth and width at high spatial resolutions along multiple stream reaches. Confirming previous studies, we found that tropical headwater streams are an important source of CO 2 to the atmosphere. More notably, we found marked, predictable spatial organization in aquatic carbon fluxes as a function of landscape position. For example, p CO 2 was consistently high (>10,000 ppm) at locations close to groundwater sources and just downstream of hydrologically connected wetlands, but consistently low (<1,000 ppm) in high gradient locations or river segments with larger drainage areas. Taken together, our findings suggest that catchment area and stream slope are important drivers of p CO 2 and gas transfer velocity ( k ) in mountainous streams, and as such they should be considered in catchment‐scale assessments of CO 2 emissions. Furthermore, our work suggests that accurate estimation of CO 2 emissions requires understanding of dynamics across the entire stream network, from the smallest seeps to larger streams.

Ecosystem metabolism estimates from the National Ecological Observatory Network (NEON) stream and river sites

Scientific Data · 2025-03-21

Expanded availability of estimates of ecosystem metabolism and gas exchange from the worlds streams and rivers is rapidly revising estimates of river contributions to global carbon budgets. Here, we present estimates of gross primary production, ecosystem respiration, and gas exchange from 27 streams and rivers across North America, including Puerto Rico, using data from the National Ecological Observatory Network (NEON). Further, we explore how aggregating and processing input data influences model outputs, expanding the methodological knowledge in approaching sensor collection and manipulation for ecosystem-scale modelling. We apply filters to input data to determine how different approaches to quality control of raw data influence the quantity and precision of estimates of ecosystem metabolism. Model estimates are high priority measures of ecosystem function that integrate additional NEON data products that will allow further understanding of stream and river biogeochemistry and ecosystem function across time and space.

Cryptic chemoautotrophic and methanotrophic processes complicate the use of carbon stable isotopes in rivers

2025-03-31 · 1 citations

The use of carbon stable isotopes has contributed to many important discoveries regarding the base of consumer production in freshwater ecosystems. There is increasing recognition for the prevalence of anoxic conditions and the contributions of methane-derived carbon to freshwater food webs, highlighting the potential for methanotrophy and chemoautotrophy to complicate interpretations of δ13C values in consumer biomass. These reduced substrates are sometimes cryptic, or present at such low concentrations that they might not provide an obvious carbon source, especially in rivers which are typically conceptualized as well-oxygenated. At most, chemoautotrophy and methanotrophy might be important, yet overlooked, carbon sources and at least, even a small amount of these isotopically lighter contributions could complicated assessments of basal carbon sources to river food webs. An improved application of carbon-based stable isotope mixing models to freshwater ecosystems, and subsequent inferences of dietary resources, is limited by three major assumptions reviewed herein. These assumptions include: representation of dietary end members using bulk sampling of organic matter sources, estimation of fractionation rates associated with microbial oxidation reactions, and the decision of whether or not to include proxies for the heavily fractionated biomass of chemoautotrophs and methanotrophs. With improved recognition and continued study of these assumptions, the conceptualization of basal carbon sources can be expanded to include the redox complexity of both lentic and lotic systems, and could expand how we conceptualize the boundaries of river food webs. This has implications for recognition and management of habitat heterogeneity in freshwaters.

Author Correction: User-focused evaluation of National Ecological Observatory Network streamflow estimates

UNC Libraries · 2025-03-01

User-focused evaluation of National Ecological Observatory Network streamflow estimates

UNC Libraries · 2025-03-01

Carbon fluxes and In-Stream Metabolism in a High-Altitude Tropical Peatland Ecosystem of The Andes Mountains

2025-03-14

The importance of rivers and streams to the global carbon cycle is well established, and increasingly. research has emphasized the role of in-stream metabolism on carbon transformation within aquatic environments. However, while stream metabolism studies are abundant in northern latitudes, research on tropical streams remains notably scarce. In this study, we characterized carbon fluxes into and out of a small stream in a tropical, peatland-rich ecosystem of the Andes mountains. We measured dissolved oxygen, carbon dioxide, and discharge every 15 minutes at 4 locations downstream of a large peatland. Measurements were collected semi-continuously for a period of 12 months. CO2evasion was both measured directly and estimated indirectly for comparison. We used continuous dissolved oxygen to estimate daily ecosystem respiration (ER) and gross primary production (GPP) throughout the study period using a Bayesian-based metabolism model. Our results unveiled both seasonal and event-driven patterns in carbon dynamics throughout the year. At the peatland outlet, the stream channel was strongly heterotrophic throughout the study period (GPP

Author Correction: User-focused evaluation of National Ecological Observatory Network streamflow estimates

UNC Libraries · 2025-03-01

Macroinvertebrates incorporate ancient carbon through use of chemoautotrophic and photoautotrophic resources in a model floodplain setting

Freshwater Science · 2025-07-03