ABSTRACT:

Inland waters are increasingly being recognized for their key role in the global carbon budget, processing and emitting significant amounts of carbon. Tropical peatlands store some of the highest carbon densities on Earth, but hydrological connectivity’s role in regulating carbon processing and greenhouse gas flux within their headwater stream networks remains poorly understood. We evaluated spatial variability of carbon fluxes across 20 km of stream network in a glacier-fed stratovolcano catchment in the Ecuadorian Andes, measuring dissolved CO2 (pCO2), dissolved oxygen, dissolved methane (pCH4), dissolved organic carbon, specific conductance, pH, temperature, channel geometry, and water velocity. Each stream showed a unique longitudinal pattern of CO2 concentration and flux, indicating that evasion is regulated by localized landscape elements and connectivity. Distinct pCO2-DOC relationships across sub-catchments reflected heterogeneity in carbon sources and processing. Wetland-dominated reaches showed substantially elevated CH4:CO2 ratios relative to glacier and spring-fed reaches, suggesting connectivity to peatland soils drives in-stream methane dynamics. Spring-fed headwaters acted as extreme CO2 point sources, with most evasion occurring within a few hundred meters of groundwater emergence. Recently deglaciated terrain appears to offset carbon emissions and promote net carbon sink behavior. Reactive transport modeling (BioRT-HBV) indicated hydrologic source controlled CO2 delivery, while CH4 differences between similarly shallow-flow-dominated reaches reflected how carbon processing partitioned between the two gases. Collectively, these findings demonstrate that in-stream carbon dynamics vary substantially over small spatial scales, driven by localized landscape elements and hydrologic connectivity, offering new insight into carbon cycling in these understudied ecosystems.

ABSTRACT:

The global carbon (C) cycle increasingly recognizes the importance of inland waters, and in particular, headwater streams. These streams transport and transform C that has been produced on land and will ultimately be delivered to the ocean, stored in the ground, or released to the atmosphere. Studies that quantify C fluxes in inland waters traditionally focus on one type of aquatic system (i.e., wetland, stream, lake), leaving a gap in our understanding of how hydrologic processes affect whole ecosystem C fluxes across the continuum from terrestrial to aquatic systems. In this study, we characterized C flux dynamics across ~4 km of a first-order, spring-fed stream within a stratovolcano catchment of the Andes Mountains. We collected a suite of environmental variables, including dissolved carbon dioxide (pCO2), dissolved methane (pCH4), specific conductance, and temperature, across 38 points throughout the catchment. Additionally, we collected soil CO2 efflux in areas adjacent to the stream as well as morphological data on stream channel including width, depth, slope, and water velocity to calculate gas transfer velocity (k600) and aquatic CO2 evasion. Our analysis revealed pronounced longitudinal gradients and spatial heterogeneity in aquatic C concentrations and fluxes, which contrasted drastically with the lack of such spatial heterogeneity in terrestrial C fluxes. The stream was highly enriched in dissolved CO2 where the spring emerged, but rapidly off gassed 99.5% of the pCO2 in the first kilometer of the stream channel. The calculated aquatic evasion exhibited a similar decreasing pattern, although it was also influenced by k600 and other variables. Our findings reveal that spatial patterns of aquatic and terrestrial CO2 fluxes to the atmosphere are decoupled longitudinally and provide insight into ecosystem-scale dynamics of C across tropical catchments in complex terrain.

ABSTRACT:

Working database for NSF-funded southeastern urban beaver project (Atlanta, GA; Charlotte, NC; and Durham, NC). Data will be added as papers are published, with clear indication of which dataset is used for each paper.
Latitude and longitude coordinates for sampling sites are in the Urban Ecosystems paper.
Currently this resource contains a .csv file of chemistry of grab samples collected from March 11, 2021-December 10, 2021 and used in the 2023 submission to Urban Ecosystems.