Sunday, May 22, 2016
15:30 - 17:00

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15:30 - 15:45: / 311-312 QUANTIFYING VARIABILITY IN PEATLAND POREWATER CHEMISTRY IN THE CONTEXT OF A LARGE-SCALE CLIMATE CHANGE EXPERIMENT

5/22/2016  |   15:30 - 15:45   |  311-312

QUANTIFYING VARIABILITY IN PEATLAND POREWATER CHEMISTRY IN THE CONTEXT OF A LARGE-SCALE CLIMATE CHANGE EXPERIMENT Porewater chemistry is an important driver of vegetative, microbial, and geochemical processes in peatland ecosystems. We examined how porewater chemistry varied across temporal and spatial scales in the S1-bog in northern Minnesota, USA. Porewater chemistry varied considerably with depth into the peat, as ammonium concentrations increased 20-fold and total organic carbon (TOC) concentrations decreased by half from 0 to 3 m. These depth profiles were temporally dynamic, and some solutes varied more in near surface porewater (e.g., ammonium), while other solutes varied more at depth (e.g., TOC). Porewater chemistry also varied laterally across the bog. Surficial porewater chemistry near the bog margins reflected upland influences (e.g., higher calcium, pH), while chemistry in the middle of the bog reflected ombrotrophic (rainfed) characteristics (e.g., low nutrient, calcium, pH). Porewater chemistry was more temporally than spatially variable in near surface porewaters, and more variable spatially in deeper porewaters. The S1-bog is the location of a 10-year, ecosystem-scale climate change experiment, and thus quantifying variability in porewater chemistry is a necessary step in assessing and interpreting how climate change affects biogeochemical cycling in peatlands.

Natalie Griffiths (Primary Presenter/Author), Oak Ridge National Laboratory, griffithsna@ornl.gov;


Stephen D. Sebestyen ( Co-Presenter/Co-Author), USDA Forest Service-Northern Research Station, ssebestyen@fs.fed.us;


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15:45 - 16:00: / 311-312 SCALING FLUXES OF NITROGEN FIXATION BETWEEN CHAMBERS AND THE STREAM REACH

5/22/2016  |   15:45 - 16:00   |  311-312

SCALING FLUXES OF NITROGEN FIXATION BETWEEN CHAMBERS AND THE STREAM REACH In stream ecosystems with low nitrate availability, a fraction of gross primary productivity (GPP) drives nitrogen (N2) fixation. Historically, we estimated N2 fixation fluxes using chamber estimates and scaled them to the ecosystem level. However, chamber estimates do not account for heterogeneity of stream benthos. We estimated whole-stream GPP and N2 fixation using the diel change in dissolved N2 and argon gases compared to the expected dissolved gas saturation. We compared whole-stream and chamber estimates of GPP and N2 fixation. N2 fixation in 3 Wyoming streams ranged from 6.4 mmol N2m-2d-1 to 7.9 mmol N2m-2d-1. By comparison, chamber fluxes of GPP and N2 fixation were higher but similar to the diel measurements. The whole-stream method is preferable to chamber estimates because it accounts for streambed heterogeneity.

Hilary Madinger (Primary Presenter/Author), University of Wyoming, hilary.madinger@gmail.com;


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


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16:00 - 16:15: / 311-312 SCALING OF METABOLISM AND NUTRIENT UPTAKE IN A HEADWATER STREAM NETWORK: WHAT DRIVES ECOSYSTEM PROCESSES AT MULTIPLE MEASUREMENT SCALES?

5/22/2016  |   16:00 - 16:15   |  311-312

SCALING OF METABOLISM AND NUTRIENT UPTAKE IN A HEADWATER STREAM NETWORK: WHAT DRIVES ECOSYSTEM PROCESSES AT MULTIPLE MEASUREMENT SCALES? Identifying how ecosystem process rates vary spatially is crucial for understanding the role of streams in river networks. A first step is determining whether small-scale measurements effectively estimate whole-reach rates. We quantified ecosystem processes (respiration [ER], gross primary production [GPP], ammonium uptake [NH4]) in nine 1st-4th order streams throughout the Coweeta Creek basin (Macon County, NC) using whole-reach measurements and recirculating chambers. The degree of mismatch between measurement scales varied by stream and process, but tended to increase with stream size. Chamber ER was 6-58x higher than whole-stream ER in the 5 largest streams, driven in part by very low values of whole-reach ER in those sites (0.01-0.15 gO2m-2d-1). Conversely, whole-reach GPP was 2-14x higher than corresponding chamber measurements in 8 of 9 streams, and the mismatch was positively correlated with stream discharge. Whole-stream estimates of NH4 uptake also exceeded chamber rates in larger streams. Examining potential drivers of processes at each scale, including organic matter, temperature, and light, may help elucidate causes of discrepancies to allow reasonable comparison of rates from different scales to facilitate estimation of network-scale functions.

Kaitlin J. Farrell (Primary Presenter/Author), University of Georgia, farrellkj2@gmail.com;


Amy D. Rosemond ( Co-Presenter/Co-Author), University of Georgia, rosemond@uga.edu;


Ford Ballantyne ( Co-Presenter/Co-Author), University of Georgia, fb4@uga.edu;


Chao Song ( Co-Presenter/Co-Author), University of Georgia, chaosong@uga.edu;


John S. Kominoski ( Co-Presenter/Co-Author), Florida International University, jkominoski@gmail.com;


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16:15 - 16:30: / 311-312 THE EFFECT OF SEDIMENT PARTICLE SIZE ON BENTHIC COMMUNITY RESPIRATION AND PRODUCTIVITY IN HIGH LATITUDE STREAMS

5/22/2016  |   16:15 - 16:30   |  311-312

THE EFFECT OF SEDIMENT PARTICLE SIZE ON BENTHIC COMMUNITY RESPIRATION AND PRODUCTIVITY IN HIGH LATITUDE STREAMS Metabolic rates are commonly scaled by projected area, which normalizes observations relative to a square meter of stream bottom. However, the total substrate surface area available for biogeochemical interactions is greater than the projected area depending on the size and distribution of benthic sediments. We evaluated the effect of sediment particle size on benthic metabolism by measuring four sizes of native river sediments (D50 particle size = 13, 31, 51, 84mm) in recirculating chambers. Rates of community respiration and gross primary production for each size class were normalized by projected area and substrate surface area was quantified to evaluate traditional scaling approaches. Projected area-normalized rates of respiration decreased significantly with increasing particle size, but had no significant effect on primary production. Subsequently, substrate surface area explained 31 percent of the variation in projected area-normalized community respiration (p<0.001) and had minimal influence on rates of gross primary production (p=0.298). The significant interaction between substrate surface area and respiration suggests that information about the size and distribution of benthic sediment could improve our ability to scale certain measurements of ecosystem function.

Samuel P. Parker (POC,Primary Presenter), University of Vermont, samuel.parker@uvm.edu;


William Breck Bowden ( Co-Presenter/Co-Author), University of Vermont, breck.bowden@uvm.edu;


Michael Flinn ( Co-Presenter/Co-Author), Murray State University, michael.flinn@murrystate.edu;


Joshua Benes ( Co-Presenter/Co-Author), University of Vermont, Joshua.Benes@uvm.edu;


Kyle Arndt ( Co-Presenter/Co-Author), AEC Corporation, kyleaarndt@gmail.com;


Courtney Giles ( Co-Presenter/Co-Author), James Hutton Institute, courtney.giles@hutton.ac.uk;


Derrick Jent ( Co-Presenter/Co-Author), University of Florida, dgjent@ufl.edu ;


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16:30 - 16:45: / 311-312 STREAM NETWORK STRUCTURE AND SPATIAL MEASUREMENT SCALES INFLUENCE DISSOLVED ORGANIC CARBON CHARACTERIZATIONS ACROSS A WATERSHED

5/22/2016  |   16:30 - 16:45   |  311-312

STREAM NETWORK STRUCTURE AND SPATIAL MEASUREMENT SCALES INFLUENCE DISSOLVED ORGANIC CARBON CHARACTERIZATIONS ACROSS A WATERSHED Dissolved organic carbon (DOC) is a master variable in aquatic ecosystems. We must understand variability across scales to interpret the stream-groundwater interface (hyporheic zone, HZ) role in controlling DOC fate and transport. Here, we conducted a unique network-wide synoptic sampling campaign of a lowland third-order watershed. There were 16 sites spanning 3 reach orders. We sampled 6 sub-surface depths up to 20 cm in 3 bed locations at each site. We investigated variance of DOC properties across four spatial scales—finest to coarsest: point, site, reach, and watershed. We hypothesized first, that the range of variability of HZ DOC concentration decreases with stream order due to integration and homogenization of DOC sources and hydrologic flowpaths, and second, that fine scale DOC measurements do not relate to realized DOC variance at larger scales. Indeed, the range of DOC variability was greatest at first-order and smallest at third-order streams, and fine scale measurements did not accurately reflect variability at the coarse scale. However, reach-scale was most coupled to watershed-scale variance, indicating that reach-scale measurements are reasonably representative of watershed-scale variability.

Joseph Lee-Cullin (Primary Presenter/Author), Department of Earth and Environmental Sciences, Michigan State University, USA, cullinjo@msu.edu;


Jay Zarnetske ( Co-Presenter/Co-Author), Department of Earth and Environmental Sciences, Michigan State University, USA, jpz@msu.edu;


Sydney Ruhala ( Co-Presenter/Co-Author), Department of Earth and Environmental Sciences, Michigan State University, USA, ruhalasy@msu.edu;


Stephen Plont ( Co-Presenter/Co-Author), Department of Earth and Environmental Sciences, Michigan State University, USA, plontste@msu.edu;


Evan Wiewiora ( Co-Presenter/Co-Author), Department of Earth and Environmental Sciences, Michigan State University, USA, wiewiora@msu.edu;


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16:45 - 17:00: / 311-312 CARBON TRANSPORT, LOSSES, AND REPLENISHMENT IN A BOREAL RIVER DISCONTINUUM: PROCESSES CONTROLLING LARGE-SCALE PATTERNS

5/22/2016  |   16:45 - 17:00   |  311-312

CARBON TRANSPORT, LOSSES, AND REPLENISHMENT IN A BOREAL RIVER DISCONTINUUM: PROCESSES CONTROLLING LARGE-SCALE PATTERNS Despite increasing interest in the role of freshwaters in the carbon cycle, distinct sources sustaining freshwater metabolism and carbon fluxes are not well budgeted. We measured carbon transport and emissions within a dammed boreal river, and estimated the processes supporting observed patterns of carbon dynamics. We used river elevation profiles and reservoir outflow emissions to target potential hotspots of carbon inputs and mineralization relative to evasion. Reach- and river-scale gas exchange and CO2/CH4 emissions were estimated with flux chambers and modeling. Flux chamber measurements alone cannot describe river-scale patterns of emissions. In contrast to measurable shifts in pre/post incubation dissolved organic matter (DOM) and microbial assemblages, we observed little change in DOM composition or DOC/CO2/CH4 with longitudinal synoptic sampling. While much of the Romaine River appears to be at steady state with respect to carbon concentrations, inverse modeling identified substantial carbon replenishment needed to support rates of DOC decay and CO2/CH4 emissions. We will discuss the advantages of coupling small-scale measurements with large-scale sampling and simulations to elucidate the complex dynamics of carbon losses, replenishment, transformation, and transport in freshwaters.

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


Paul A. del Giorgio ( Co-Presenter/Co-Author), Université du Québec à Montréal, del_giorgio.paul@uqam.ca;


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