SFS Annual Meeting

5/23/2019  |   14:00 - 14:15   |  251 AB

CARBON CYCLING IN STREAMS Soils are currently leaching out their organic matter at an increasing pace in aquatic ecosystems. The implications for stream biogeochemistry and food webs remain largely unknown, notably the metabolic balance (biotic CO2 emissions) and reciprocal subsidies between primary producers and bacteria. Here high frequency monitoring using sensors were deployed in two catchments to show how the daily flux of dissolved organic carbon is respired away by bacteria over an annual cycle. A whole ecosystem experiment tested the effects of labile organic carbon addition on carbon cycling, C:N:P stoichiometry, biotic CO2 emission, trophic transfer efficiencies. Isotopic probing allowed to trace the added carbon through the food web and quantify the reciprocal carbon subsidies between primary producers and bacteria. Part of the carbon derived from natural allochthonous organic matter can feed the autotrophs via the CO2 produced by stream bacterial respiration, intermingling the green and brown webs. The interaction between autotrophs and bacteria shifted from mutualism to competition with carbon addition under nutrient limitation (N, P) increasing biotic CO2 emissions. Without nutrient limitation, mutualism could be reinforced by a positive feedback loop, preventing further biotic CO2 emissions.

Benoit Demars (Primary Presenter/Author), Norwegian institute for water research (NIVA), benoit.demars@outlook.com;


Nikolai Friberg (Co-Presenter/Co-Author), Norwegian Institute for Water ResearchNorwegian Institute for Water Research (NIVA), Oslo, Norway , Nikolai.Friberg@niva.no;


Barry Thornton (Co-Presenter/Co-Author), The James Hutton Institute, barry.thornton@hutton.ac.uk;


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5/23/2019  |   14:15 - 14:30   |  251 AB

INFLUENCE OF CATCHMENT MORPHOLOGY ON BIO-PHYSICAL DRIVERS OF CARBON FLUXES IN HEADWATER STREAMS Stream ecosystems are control points for carbon transformations and fluxes. The dual role of streams as conduits for CO2 evasion and downstream carbon transport as well sites of carbon retention and metabolism has been established by numerous studies. In order to integrate these disparate roles, it is imperative to empirically identify the role of ecological communities in partitioning carbon between these different pools. Our study elucidates the influence of biological processes on catchment scale carbon fluxes. We monitored biological (e.g. metabolic) and physical carbon fluxes and in-situ carbon processing in two adjacent montane headwater catchments with varying ambient carbon concentrations. We observed that headwater streams exhibited substantial seasonal and spatial variation in (1) the balance of physical and biological carbon fluxes and (2) the degree of biological influence over carbon cycling, with local-scale variables (e.g. carbon source area configuration) acting as more important predictors of the magnitude of biological carbon fluxes than longitudinal network structure. Our findings help elucidate catchment scale drivers that control the balance of bio-physical fluxes and identify network positions (or times of the year) when ecological communities play a significant role in mediating catchment-scale carbon fluxes.

Erin Seybold (Primary Presenter/Author), Kansas Geological Survey, University of Kansas, erinseybold@ku.edu;


Brian McGlynn (Co-Presenter/Co-Author), Duke University, brian.mcglynn@duke.edu;


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5/23/2019  |   14:30 - 14:45   |  251 AB

INTEGRATING DIEL PATTERNS IN DISSOLVED OXYGEN, CARBON DIOXIDE, AND METHANE FOR AN IMPROVED UNDERSTANDING OF RESPIRATION REGIMES IN STREAMS Increasing spatial coverage and long-term records of high-frequency dissolved oxygen (O2) data have improved our understanding of metabolic regimes in freshwaters, but the contributions of anaerobic processes to carbon cycling are largely absent from stream metabolism frameworks. High-frequency O2, CO2, and CH4 data offer unique opportunities to integrate aerobic and anaerobic metabolism into our understanding of freshwater ecosystem function. Here we use simultaneous 10-30min O2, CO2, and CH4 sensor data over ~60 days to compare patterns in diel variation and estimate whole-ecosystem carbon metabolism in a Virginia stream draining mixed developed-agricultural land use. CO2 and CH4 peaked at night, mirroring diel O2. Diel variation exceeded day-to-day variation for all gases, with 24-hour min-max exceeding 5 ppmO2, 100 ppmCH4, and 1000 ppmCO2. The expansion and contraction of diel amplitude differed between CO2 and CH4 over the course of our monitoring period. Further, the time to return to pre-storm dynamics differs among the processes controlling O2, CO2, and CH4. Ongoing work is using sensors, stable isotopes, and organic matter analyses to simulate the processes controlling in-stream aerobic and anaerobic carbon metabolism.

Erin R. Hotchkiss (Primary Presenter/Author), Virginia Tech, ehotchkiss@vt.edu;


Stephen Plont (Co-Presenter/Co-Author), Virginia Tech, plontste@vt.edu;


Brynn ODonnell (Co-Presenter/Co-Author), Virginia Tech, brynno@vt.edu;


Morgan Gallagher (Co-Presenter/Co-Author), Virginia Tech, mtg3@vt.edu;


Kristen Bretz (Co-Presenter/Co-Author), Virginia Tech, kabretz@vt.edu;


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5/23/2019  |   14:45 - 15:00   |  251 AB

DIEL VARIATION IN THE STABLE ISOTOPE SIGNATURE OF CO₂ IN PRODUCTIVE STREAMS Dissolved carbon dioxide (CO₂) dynamics in streams are the product of multiple biogenic, geogenic, and atmospheric sources and processes. Spatial variation in the isotopic signature of CO₂ (¹³C-CO₂) has been used to attribute CO₂ to different sources, but diel temporal variation in ¹³C-CO₂ has rarely been used to separate variation catchment sources of CO₂ from in-stream CO₂ production and consumption. Here we continuously monitored dissolved oxygen, CO₂, pH, and temperature with sensors and used discrete water samples for analysis of ¹³C-CO₂, alkalinity, and dissolved inorganic carbon (DIC) over four, 24 h periods in three streams in Montana and Arizona, USA. Diel variation in CO₂ ranged up to 19.8 mmol CO₂ L^-1 and 4.9 ‰ ¹³C-CO₂ with the highest concentrations of CO₂ and the most depleted ¹³C at night. We report how estimates of gross primary productivity and ecosystem respiration vary among models which incorporate CO₂ isotopes and use asynchrony in the timing of CO₂ and ¹³C-CO₂ to inform our understanding of in-stream carbon transformations. Modeling diel variation in stable C-CO₂ isotopes can help our understanding of how whole-stream metabolic rates that influence stream carbon storage, transformation, and transport.

Joanna Blaszczak (Primary Presenter/Author), University of Nevada, Reno, jblaszczak@unr.edu;


Robert O. Hall (Co-Presenter/Co-Author), Flathead Lake Biological Station, University of Montana, bob.hall@flbs.umt.edu;


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5/23/2019  |   15:00 - 15:15   |  251 AB

INTEGRATING CONTINUOUS SENSOR DATA WITH OBSERVATIONAL SAMPLING AT A CONTINENTAL SCALE TO ENABLE ESTIMATES OF CARBON FLUX, REAERATION AND METABOLISM IN STREAMS The National Ecological Observatory Network (NEON) deploys instrumentation and collects samples on a continental scale in atmospheric, terrestrial, and aquatic systems. Measurement collocation across these components allows for linking and comparing data related to ecological parameters across air, land, and freshwaters. The NEON aquatic program will enable quantifying the impacts of climate change, land use, and biological invasions on freshwater populations and processes. Data processing of NEON measurements is standardized, quality-controlled, and freely available through a publicly accessible online data portal (data.neonscience.org). Samples are collected bi-weekly from 24 streams and 3 rivers and monthly from 7 lakes for dissolved greenhouse gas concentrations (CO2, N2O, and CH4) and water chemistry, including dissolved organic carbon concentrations and alkalinity. At the same time, sensors collect data at aleast every 5 minutes for dissolved oxygen, pressure (water level), temperature, PAR, and fDOM, a DOC proxy. At stream sites, reaeration tracer experiments (simultaneous conservative and gas tracer injection) are performed 6 times per year. Dissolved gas concentrations, physical parameters, continuous discharge, and inorganic and organic carbon concentrations derived from the NEON dataset enable estimates of metabolism and carbon fluxes in streams.

Kaelin Cawley (Primary Presenter/Author), National Ecological Observatory Network (NEON) operated by Battelle, kcawley@battelleecology.org;


Keli Goodman (Co-Presenter/Co-Author), National Ecological Observatory Network (NEON) operated by Battelle, kgoodman@battelleecology.org;


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5/23/2019  |   15:15 - 15:30   |  251 AB

EMISSIONS OF CARBON DIOXIDE FROM HEADWATER STREAMS ACROSS AN URBANIZATION GRADIENT Freshwater ecosystems exert considerable influence over material cycles and fluxes from the watershed to global scale. Recent studies show river networks contribute significantly to global carbon (C) budgets and are important sources of carbon dioxide (CO2) by outgassing a large fraction of the C they receive from terrestrial ecosystems. Thus, a better understanding of the factors controlling C delivery to and processing within river networks across flow conditions is critical for improving our ability to predict how changing climatic patterns and land use will alter rates of aquatic C emissions. We have installed sensor packages measuring dissolved CO2, dissolved oxygen, water temperature, light, and stage at four headwater streams of differing land use to quantify CO2 emissions over a range of seasons, flow conditions, and storm responses. The terrestrial and aquatic contribution to this flux will be analyzed via stream metabolism estimates. Initial results suggest storm events act as hot moments of CO2 emissions as reaeration rates increase and terrestrially derived CO2 is delivered to the stream and quickly emitted. Further analyses will examine how land use alters the CO2 concentration-discharge relationship across sites.

Wilfred M. Wollheim (Co-Presenter/Co-Author), University of New Hampshire, wil.wollheim@unh.edu;


Andrew Robison (Primary Presenter/Author), University of New Hampshire, andrew.robison@unh.edu;


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