SFS Annual Meeting

Luke Jeffrey (Primary Presenter/Author)
Southern Cross Univeristy, luke.jeffrey@scu.edu.au;

Abstract: Freshwater wetland tree stems are an important and unconstrained source of methane, yet it is uncertain if there are internal microbial controls (i.e. methanotrophy) within tree bark that may reduce methane emissions. Using multiple lines of evidence, here we demonstrate that unique microbial communities dominated by methane-oxidising bacteria (MOB) dwell within bark of Melaleuca quinquenervia, a common, invasive and globally distributed lowland (sub)tropical species. In laboratory incubations, methane-inoculated M. quinquenervia bark mediated methane consumption (up to 96.3 µmol m-2 bark d-1) and there was a distinct isotopic ?13C-CH4 enrichment characteristic of MOB. Molecular analysis indicates unique microbial communities reside within the bark, with methane-oxidising bacteria primarily from the genus Methylomonas comprising up to 25 % of the total microbial community. Methanotroph abundance was linearly correlated to methane uptake rates (R2 = 0.76, p = 0.006). Finally, field-based methane oxidation inhibition experiments demonstrate that bark-dwelling MOB reduce methane emissions by ~36%. These multiple complementary lines of evidence indicate that bark-dwelling MOB represent a novel and potentially significant methane sink, and an important frontier for further research.

Andrew Murray (Co-Presenter/Co-Author)
Univeristy of North Carolina at Chapel Hill, armurray@live.unc.edu;

Diego Riveros-Iregui (Co-Presenter/Co-Author)
Univeristy of North Carolina at Chapel Hill, diegori@email.unc.edu;

Andrea C. Encalada (Co-Presenter/Co-Author)
Instituto BIOSFERA, Universidad San Francisco de Quito, Cumbayá, Ecuador Biológicas y Ambientales, Universidad San Francisco de Quito, Cumbaya, Ecuador, aencalada@usfq.edu.ec;

Esteban Suarez (Co-Presenter/Co-Author)
Universidad de San Francisco de Quito, esuarez@usfq.edu.ec;

Kriddie Whitmore (Primary Presenter/Author)
Univeristy of North Carolina at Chapel Hill, kriddie@email.unc.edu;

Abstract: High-altitude tropical grasslands, known as “páramos” have some of the largest ecosystem carbon stocks per unit area on Earth. They are characterized by wetland complexes that are drained by well-defined stream channels. Despite the potential for substantial rates of aquatic CO2 flux, greenhouse gas observations in these systems are rare. We evaluated the spatial and temporal variability of dissolved CO2 (pCO2), CO2 evasion, gas transfer velocity (k), and dissolved oxygen across a peatland-stream transition of a páramo watershed. Using discrete and continuous observations, we found CO2 evasion from stream surfaces to be controlled by turbulent flow and water velocity at the peatland outlet, and by CO2 availability further downstream. Temporal variability of k was driven by rapid increases in discharge following rain events, whereas the spatial variability of k was driven by channel morphology and hydrologic conditions. Absent of rainstorms, pCO2 and CO2 evasion maxima occurred prior to or immediately after sunrise. Taken together, our results highlight the role of tropical peatlands as sources of aquatic CO2 via lateral transport, at least while hydrologic connectivity between wetlands and streams allows for the mobilization of dissolved carbon downstream.

Clément Duvert (Co-Presenter/Co-Author)
Research Institute for the Environment andLivelihoods, Charles Darwin University, clem.duvert@cdu.edu.au;

Damien Maher (Co-Presenter/Co-Author)
Southern Cross Geoscience, Southern CrossUniversity, damien.maher@scu.edu.au;

Lindsay Hutley (Co-Presenter/Co-Author)
Research Institute for the Environment andLivelihoods, Charles Darwin University, lindsay.hutley@cdu.edu.au;

Christian Birkel (Co-Presenter/Co-Author)
Department of Geography and Water and Global Change Observatory, University of Costa Rica, christian.birkel@ucr.ac.cr;

Vanessa Solano (Primary Presenter/Author)
Research Institute for the Environment andLivelihoods, Charles Darwin University, vanessa.solano@cdu.edu.au;

Abstract: While evasion represents the largest flux of carbon (C) from tropical streams, estimates are subject to large uncertainties and the source of evading C is often unknown. To estimate the potential contribution of internal metabolism to CO2 evasion, we monitored O2 and CO2 in a headwater stream of the Australian wet-dry tropics. Dissolved gas concentrations were measured at two sites along the stream, one riffle and one pool. Net stream metabolism was obtained via the one-station technique, while five methods were used to estimate the gas transfer velocity (k) and CO2 evasion: (1) floating chambers, (2) mass balance, (3) Bayesian multiday model, (4) night-time regression and (5) empirical equations based on hydraulics. Our results show that both reaches are highly heterotrophic, with respiration an order of magnitude higher than gross primary productivity. Respiration is higher at the pool while k and CO2 evasion are higher at the riffle. Direct methods (1, 2) are reliable and show similar results. Indirect methods (3, 4, 5), however, show large disparities and are unable to predict k under low water level conditions. Respiration can contribute up to 50% of evading C.

Marcia Macedo (Primary Presenter/Author)
Woodwell Climate Research Center, mmacedo@woodwellclimate.org;

Sarah Ludwig (Co-Presenter/Co-Author)
Columbia University, sml2278@columbia.edu;

Kathleen Savage (Co-Presenter/Co-Author)
Woodwell Climate Research Center, savage@woodwellclimate.org;

KathiJo Jankowski (Co-Presenter/Co-Author)
U.S. Geological Survey, Upper Midwest Environmental Sciences Center, kjankowski@usgs.gov ;

Kylen Solvik (Co-Presenter/Co-Author)
University of Colorado at Boulder, Kylen.Solvik@colorado.edu;

Paul Lefebvre (Co-Presenter/Co-Author)
Woodwell Climate Research Center, paul@woodwellclimate.org;

Leonardo Maracahipes-Santos (Co-Presenter/Co-Author)
Instituto de Pesquisa Ambiental da Amazônia, leonardo.maracahipes@ipam.org.br;

João Vitor Silva Costa (Co-Presenter/Co-Author)
Universidade Federal de Goiás, joaovsc17@gmail.com;

Ayanna Butler-Hooker (Co-Presenter/Co-Author)
Howard University, ayanna421.ab@gmail.com;

Abstract: Damming tropical streams has created hundreds of thousands of small reservoirs across Brazil’s agricultural frontier, a legacy of the country’s long history of cattle ranching. The low-oxygen conditions typical of these artificial wetlands favors methane production, yet we know little about their cumulative contribution to the global carbon budget. This study combines field measurements, remote sensing, and gas transfer modeling to quantify annual methane and carbon dioxide emissions from reservoirs in the Amazon-Cerrado region. Monthly field measurements from six representative reservoirs indicate strong seasonality, with the highest diffusive fluxes (~50 mg-C/m^2/d) observed at the onset of the rainy season and the lowest (~4 mg-C/m^2/d) at the peak of the dry season. Methane fluxes (per unit area) were inversely correlated with reservoir size, which ranged from 0.5-6 ha. Ebullitive fluxes dominated (63%) net emissions from large reservoirs, whereas outlet degassing (94%) dominated in small reservoirs. Preliminary maps based on Sentinel 1 and 2 data identified over 600,000 such reservoirs across the Amazon-Cerrado agricultural frontier – suggesting that they may be an important blind spot in our understanding of greenhouse gas contributions from inland waters in tropical regions.

Annika Linkhorst (Primary Presenter/Author)
Uppsala University, liannika@alumni.ethz.ch;

José Reinaldo Paranaíba (Co-Presenter/Co-Author)
Federal University of Juiz de Fora, jose.paranaiba@ecologia.ufjf.br;

Tonya DelSontro (Co-Presenter/Co-Author)
University of Waterloo, tonya.delsontro@uwaterloo.ca;

Nathan Barros (Co-Presenter/Co-Author)
Federal University of Juiz de Fora, nathanobarros@gmail.comnatha;

Raquel Mendonça (Co-Presenter/Co-Author)
Federal University of Juiz de Fora, fm.raquel@yahoo.com.br;

Carolin Hiller (Co-Presenter/Co-Author)
Uppsala University, carolin.hiller@uni-bayreuth.de;

Guilherme Millen Azevedo (Co-Presenter/Co-Author)
Federal University of Juiz de Fora, millen.guilherme@gmail.com;

David Rudberg (Co-Presenter/Co-Author)
Uppsala University, david.rudberg@lui.se;

Rafael Almeida (Co-Presenter/Co-Author)
Cornell University, rafaelmarquesjf@yahoo.com.br;

Roseilson do Vale (Co-Presenter/Co-Author)
Federal University of Western Pará, roseilsondovale@gmail.com;

Anastasija Isidorova (Co-Presenter/Co-Author)
Uppsala University, anastasija.isidorova@ebc.uu.se;

Fábio Roland (Co-Presenter/Co-Author)
Federal University of Juiz de Fora, fabio.roland@ufjf.edu.br;

Sebastian Sobek (Co-Presenter/Co-Author)
Uppsala University, sebastian.sobek@ebc.uu.se;

Abstract: Methane (CH4) and carbon dioxide (CO2) emissions from reservoirs make up for 1.3% of the global anthropogenic greenhouse gas emission, and reservoir emissions are expected to increase with climate change. We present here the results from three years of extensive field studies in four Brazilian reservoirs, aiming to identify spatio-temporal patterns and drivers of CH4 and CO2 emissions from reservoir water surfaces, for robust future emission estimates. We found that CH4 and CO2 emissions varied greatly at different timescales. Seasonal variability was identified as the most important temporal scale to be covered for ebullition inventories. Patterns of spatial variability in diffusive emission differed between seasons, and overall, spatial variability was large for all pathways. For both ebullition and diffusion, river inflow areas were prone to elevated greenhouse gas emission, and the most productive reservoir was highest in total CO2-equivalent emission. We suggest that for retrieving solid emission estimates from tropical reservoirs, there is no alternative to time-consuming measurements in the field. Measurements should be repeated at least once during each hydrological season and cover different morphological regions at high resolution, including areas with and without river inflows, and different water column depths.

Alberto Borges (Primary Presenter/Author)
University of Liège, alberto.borges@uliege.be;

George Allen (Co-Presenter/Co-Author)
Texas A&M University, geoallen@tamu.edu;

Cédric Morana (Co-Presenter/Co-Author)
University of Liège, Cedric.Morana@uliege.be;

Thibault Lambert (Co-Presenter/Co-Author)
University of Lausanne, thibault.lambert@unil.ch;

Christian Teodoru (Co-Presenter/Co-Author)
KU Leuven, cristian_teodoru@yahoo.com;

Steven Bouillon (Co-Presenter/Co-Author)
KU Leuven, steven.bouillon@kuleuven.be;

Abstract: We carried out ten field expeditions between 2010 and 2015, in the lowland part of the Congo River network, to describe the spatial variations of fluvial dissolved carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) concentrations. We investigated the drivers of the spatial variations of dissolved CO2, CH4 and N2O concentrations by analysing co-variations with several other biogeochemical variables, aquatic metabolic processes (primary production and respiration), catchment characteristics (land cover) and wetland spatial distribution. We test the hypothesis that spatial patterns of CO2, CH4 and N2O are partly due to the connectivity with wetlands, in particular with a giant wetland of flooded forest in the core of the Congo basin, the “Cuvette Centrale Congolaise” (CCC). The integrated CO2 emission from the Congo River network (251±46 TgC yr-1) was more than three times higher than terrestrial net ecosystem exchange (NEE) on the whole catchment. It is unlikely that the fluvial CO2 emissions were sustained by the hydrological carbon export from terra firme soils (typically very small compared to terrestrial NEE), but most likely, they were sustained by wetlands (with a much higher hydrological connectivity with rivers and streams).

Loris Deirmendjian (Primary Presenter/Author)
IRD, UR 234, GET, 14 Avenue E. Belin, 31400, Toulouse, France, lorisdeir@gmail.com;

Moustapha Moussa (Co-Presenter/Co-Author)
Université de Ngaoundéré, Faculté des Sciences, BP 454 Ngaoundéré, Cameroun, moustapha.moussa.ird@gmail.com;

David Sebag (Co-Presenter/Co-Author)
Normandie Univ, UNIROUEN, UNICAEN, CNRS, M2C, 76000 Rouen, France , david.sebag@univ-rouen.fr;

Jean-Jacques Braun (Co-Presenter/Co-Author)
IRD, UR 234, GET, 14 Avenue E. Belin, 31400, Toulouse, France, jjbraun1@gmail.com;

Stéphane Audry (Co-Presenter/Co-Author)
Géosciences Environnement Toulouse (GET?Université de Toulouse, CNRS, IRD), Université de Toulouse Paul Sabatier, 14 Avenue Edouard?Belin, 31400 Toulouse, France, stephane.audry@get.omp.eu;

Henriette Ateba Bessa (Co-Presenter/Co-Author)
7Institut de Recherches Géologiques et Minières/Centre de Recherches Hydrologiques, BP 4110, Yaoundé, Cameroun, henrietteateba@gmail.com;

Ibrahima Adamou (Co-Presenter/Co-Author)
Université de Ngaoundéré, Faculté des Sciences, BP 454 Ngaoundéré, Cameroun, aibrahima@hotmail.com;

Benjamin Ngounou Ngatcha (Co-Presenter/Co-Author)
Université de Ngaoundéré, Faculté des Sciences, BP 454 Ngaoundéré, Cameroun, ngatchaben@gmail.com;

Frédéric Guérin (Co-Presenter/Co-Author)
IRD, UR 234, GET, 14 Avenue E. Belin, 31400, Toulouse, France, guefre@gmail.com;

Abstract: We established the riverine carbon (C) budget of the tropical Nyong Watershed (Cameroon) considering the lateral hydrological inputs of C from land (i.e., from forest groundwater) and from wetlands to the river network, the C degassing from the river network and the export to the ocean. The different C fluxes were estimated independentely, allowing to close the C budget of the Nyong basin from an approach not based on a mass balance of the inputs and outputs of C at the catchment scale. On average throughout the year, we showed that wetlands exported 60% of the total C transferred laterally to surface waters, the remaining 40% being transferred by forest groundwater (surface runoff was negligible). In addition, heterotrophic respiration in rivers averaged at less than 7% of the average degassing rate, which indicates that it is unlikely that the CO2 emissions from the river network were sustained by river heterotrophy. All together, we show the importance of lateral inputs from different land use (i.e., forest groundwater and wetlands) on the riverine C budget. Further, neglecting wetland-river connectivity may lead to the misrepresentation of C dynamics in tropical river networks.

Nick Marzolf (Primary Presenter/Author)
Jones Center at Ichauway, nick.marzolf@jonesctr.org;

Gaston Small (Co-Presenter/Co-Author)
University of St Thomas, gaston.small@stthomas.edu ;

Carissa Ganong (Co-Presenter/Co-Author)
Missouri Western State University, carissa.ganong@gmail.com;

Alonso Ramírez (Co-Presenter/Co-Author)
North Carolina State University, alonso.ramirez@ncsu.edu;

Catherine Pringle (Co-Presenter/Co-Author)
Odum School of Ecology, University of Georgia, cpringle@uga.edu;

Marcelo Ardon (Co-Presenter/Co-Author)
North Carolina State University, mlardons@ncsu.edu;

Abstract: The role of streams in the carbon cycle remains unconstrained, especially where FCO2 evasion is high. Tropical stream C cycling is understudied compared to temperate systems, and these systems could be the highest FCO2 due to high temperatures, organic matter inputs, and high respiration both in-stream and in surrounding soils. We present in-stream O2 and CO2 measurements from a headwater stream, Costa Rica to explore variability in ecosystem processes and combine with riparian well CO2 to estimate CO2 fluxes in the reach. O2 - CO2 data reveal CO2 supersaturation with groundwater CO2 inputs and larger production of in-stream CO2 than O2. FCO2 was less than hydrologic export of CO2 and HCO3- revealing an component of C cycling in streams that needs further estimates. Discharge was predictive of CO2 fluxes, showing positive correlation with ECO2, EHCO3, and GWCO2, and negatively correlated with NEP and FCO2. We note seasonality in fluxes, with wet season fluxes of ECO2, EHCO3, and GWCO2 greater than during the dry season, and greater gas variability in CO2 than O2. Our results highlight the importance discharge on lateral inputs and FCO2 in tropical headwater streams.?

Mingyang Tian (Co-Presenter/Co-Author)
Universität Hamburg, mingyang.tian@studium.uni-hamburg.de;

Kaimin Shih (Co-Presenter/Co-Author)
THE UNIVERSITY OF HONG KONG, kshih@hku.hk ;

Chun Ngai Chan (Co-Presenter/Co-Author)
THE UNIVERSITY OF HONG KONG, eric0326@connect.hku.hk;

Xiankun Yang (Co-Presenter/Co-Author)
Guangzhou University, yangxk@gzhu.edu.cn;

Lishan Ran (Co-Presenter/Co-Author)
THE UNIVERSITY OF HONG KONG, lsran@hku.hk;

Boyi Liu (Primary Presenter/Author)
THE UNIVERSITY OF HONG KONG, boyiliu@connect.hku.hk;

Abstract: CO2 efflux at the water–air interface is an essential component of the riverine carbon cycle. However, the lack of spatially resolved CO2 emission measurement still hinges the accuracy of estimates on global riverine CO2 emissions. By deploying floating chambers, seasonal changes in river water CO2 partial pressure (pCO2) and CO2 evasion from the Dongjiang River in South China were investigated. Lateral soil CO2 input and dilution effect caused by precipitation played critical roles in controlling riverine pCO2 in small rivers, while the decomposition of allochthonous organic carbon is responsible for pCO2 variability in large rivers. Majority of the surveyed rivers were net CO2 source, exhibiting substantial seasonal variations. The mean CO2 flux was 300.1 and 264.2 mmol m?2 d?1 during the wet season for large and small rivers, respectively, 2-fold larger than that during the dry season. The absence of commonly observed higher CO2 fluxes in small rivers could be associated with the depletion effect caused by abundant and consistent precipitation in this subtropical monsoon catchment.

Carla López-Lloreda (Primary Presenter/Author)
Virginia Tech, carla.lpez09@gmail.com;

Allison Herreid (Co-Presenter/Co-Author)
USDA-ARS, allison.herreid@usda.gov;

William H McDowell (Co-Presenter/Co-Author)
University of New Hampshire, bill.mcdowell@unh.edu;

Abstract: Disturbances, such as droughts and hurricanes, can dramatically alter the structure and function of stream ecosystems. Large inputs of organic matter, riparian canopy opening and sustained impacts on hydrology following a disturbance can result in important changes in biogeochemical processes like greenhouse gas (GHG) production. To explore the impacts of disturbance on GHG dynamics, we measured dissolved carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) concentrations weekly in 8 montane streams in the Luquillo Experimental Forest, Puerto Rico during a drought (2015) and before and after Hurricane María (2017). Following the hurricane, we saw increased concentrations of and variability in CO2 and N2O across all sites but no apparent overall changes during drought. CH4 increased during drought conditions at a subset of the sites, possibly due to changing redox conditions. CH4 also increased after the hurricane at two sites from the same watershed that have a strong groundwater influence and relatively low oxygen availability. These results highlight how GHG dynamics and their response to disturbance might be influenced by antecedent and local site conditions and underscores the need for increased research regarding these processes in these frequently disturbed landscapes.

Diana Oviedo-Vargas (Primary Presenter/Author)
Stroud Water Research Center, doviedo@stroudcenter.org;

Marc Peipoch (Co-Presenter/Co-Author)
Stroud Water Research Center, mpeipoch@stroudcenter.org;

Melinda Daniels (Co-Presenter/Co-Author)
Stroud Water Research Center, mdaniels@stroudcenter.org;

Abstract: Contributions of greenhouse gases from tropical headwaters to the global carbon cycle are underrepresented. We measured carbon dioxide (CO2) and methane (CH4) emissions from Marilín and Yegüitas, two headwater streams in the transitional dry forest of Costa Rica. For this, we collected water samples for analysis of CO2 and CH4 concentrations and conducted continuous solute and gas tracer injections in 100-m study reaches to determine discharge (Q) and gas exchange rates (K). Only a few kilometers apart, but on different sides of the continental divide, Marilín is perennial and wetter than Yegüitas, which is intermittent. Average CH4 concentration was similar at both sites (~550ppm), whereas average CO2 was much higher at Yegüitas (~16,800ppm) than at Marilín (~5,600ppm). At Marilín (Q =10L/s, travel time, tt = 40min), emissions averaged 915 µmolCO2/m2/day and 2 µmolCH4/m2/day; comparable to values reported for other tropical headwaters. We were not able to determine K at Yegüitas because of an unexpected long tt (~5hr), which was likely due to a high subsurface transient storage and significant subsurface flow. Traditional gas tracer methods to measure K in small streams are not appropriate for these hydrologic conditions.