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SFS Annual Meeting

2021 Detailed Schedule

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A global assessment of organic carbon metabolism and spiraling in running waters [Oral Presentation]

Cameron Braswell (Co-Presenter/Co-Author)
Virginia Tech, camman@vt.edu;

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

Austin Gray (Co-Presenter/Co-Author)
Duke University, adgray2@uncg.edu;

Carla López Lloreda (Co-Presenter/Co-Author)
Virginia Tech, carlalopez@vt.edu;

Lauren Morris (Co-Presenter/Co-Author)
Virginia Tech, laurenmorris@vt.edu;

Natalie Murphy (Co-Presenter/Co-Author)
Virginia Tech, nataliem14@vt.edu;

Bryce Onozuka (Co-Presenter/Co-Author)
Virginia Tech, bryce17@vt.edu;

Katherine Pérez Rivera (Co-Presenter/Co-Author)
Virginia Tech, kperezrivera@vt.edu;

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

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

Abstract: The amount of organic carbon (OC) transported to and respired in streams and rivers remains unresolved in landscape and global carbon budgets. We synthesized published rates of stream and river OC metabolism and transport, from small streams to large rivers (0.01-17814 m3/s) in >25 countries, to trace the fate of carbon in running waters. We used whole-ecosystem metabolism (gross primary production and ecosystem respiration; GPP, ER) modeled from diel whole-stream oxygen data to calculate heterotrophic respiration (HR). We estimated OC mineralization velocities (i.e., biological OC demand) and OC spiraling lengths (i.e., the average distance OC travels downstream before being respired) from HR and OC fluxes. Median GPP and ER was 0.6 and 1.7 gCm-2d-1 (n=891 sites). For sites with available OC transport estimates, OC travels <1 to >500 km before being respired (n=143 sites). Ongoing analyses of discharge- and temperature-metabolism relationships will quantify how metabolism responds to environmental changes across ecosystem sizes and biomes. Using results from streams draining different landscapes, we will highlight how OC spiraling estimates advance our understanding of (1) terrestrial-aquatic ecosystem connections and (2) the consequences of land use change for freshwater ecosystem function.

ANABAENA GROWTH AND ELEMENTAL STOICHIOMETRY RESPONSE TO SODIUM CHLORIDE SALINIFICATION IN A LABORATORY EXPERIMENT [Oral Presentation]

Samuel Dias (Primary Presenter/Author)
University of Arkansas, sadias@uark.edu;

Sally Entrekin (Co-Presenter/Co-Author)
Virginia Tech, sallye@vt.edu;

Natalie Clay (Co-Presenter/Co-Author)
Louisiana Tech University, nclay@latech.edu;

Michelle Evans-White (Co-Presenter/Co-Author)
University of Arkansas, mevanswh@uark.edu;

Abstract: Secondary salinization increases the levels of sodium (Na) and chloride (Cl) in freshwater systems and these elements can be a nutritional subsidy or stress depending the concentration. Terrestrial autotrophs often have ion concentrations that positively correlate with their environment and we examined if aquatic autotrophs also demonstrate this relationship. We tested the hypothesis that algal elemental composition positively reflects environmental conditions by culturing Anabaena inequalis, a common algal species, in laboratory microcosms in COMBO media with increasing NaCl additions (ambient, 0.35, 1, 5, 10 g/L). Alga sampling occurred on even days and elemental composition was examined from algal dry mass sampled on days 17-19 from a composite sample. Chlorophyll-a content for all treatments followed a logistic growth curve that peaked on day 16 with an inverse relationship being observed for maximum chlorophyll-a concentration and NaCl addition. An ANOVA revealed carbon:nitrogen differed by treatment (p-value = 0.0002) with carbon:nitrogen decreasing from ambient to 0.35 g/L NaCl then increasing with higher treatments. Algal magnesium, Na, potassium, Cl and phosphorus data are pending. Salinization could change algal elemental composition that impacts primary basal food resource quality and transfer through aquatic food webs.

ARE ECOLOGICAL CONCEPTS STRONGER THAN HUMAN IMPACT? MULTISCALE, MULTIDATASET EXAMINATION OF CONTROLS ON RIVER METABOLISM [Oral Presentation]

Anne Schechner (Primary Presenter/Author)
Kansas State University, anneschechner@ksu.edu;

Walter Dodds (Co-Presenter/Co-Author)
Kansas State University, wkdodds@ksu.edu;

Alain Maasri (Co-Presenter/Co-Author)
The Academy of Natural Sciences of Drexel University, alainmaasri@gmail.com;

John Costello (Co-Presenter/Co-Author)
South Dakota School of Mines and Technology, john.costello@mines.sdsmt.edu;

Scott Kenner (Co-Presenter/Co-Author)
South Dakota School of Mines and Technology, Scott.Kenner@sdsmt.edu;

Sudeep Chandra (Co-Presenter/Co-Author)
University of Nevada Reno, Global Water Center, limnosudeep@me.com;

Flavia Tromboni (Co-Presenter/Co-Author)
University of Nevada, Reno, ftromboni@unr.edu;

Battsengel Dashdorj (Co-Presenter/Co-Author)
South Dakota School of Mines and Technology, battsengel.dashdorj@mines.sdsmt.edu;

Abstract: Environmental protection and natural resource management are informed and limited by data availability. Aquatic priority areas do not necessarily match protected terrestrial areas, and river metabolism likely has linear and non-linear controls decoupled from global gradients affecting terrestrial energetics. We expand the geographic extent of metabolism estimates with 92 sites in three corresponding ecoregions across the Western and Central US and Mongolia, and evaluate classical broad-scale ecological concepts including expectations from global gradients, biomes, and the river continuum concept for applicability in the anthropocene. We link metabolism estimates with reach-to-watershed-scale hydrogeomorphology, vegetation, climate, and human impact to evaluate predictors and applicability of traditional ecological frameworks. We expected ecoregion similarities, but found land-use drivers override conceptual expectation. Metabolism estimates did not vary by country or ecoregion alone, or within Mongolia. We evaluated related and collinear metrics explanatory of metabolism: for example, velocity was not a driver, but percent of a reach with cobble-or-larger substrate was. We present most explanatory structures of variables by river type, scale, and location, and conclude that in macrosystem scale studies human interaction and multi-scale assessment are necessary to capture aquatic metabolism variation and make predictions.

CALCULATING FRESHWATER pCO2: COMPARING THE ACCURACY OF SPECTROPHOTOMETRIC AND ELECTROCHEMICAL pH MEASUREMENTS FOR EQUILIBRIUM CALCULATIONS IN FRESHWATER SYSTEMS [Oral Presentation]

Qipei Shangguan (Co-Presenter/Co-Author)
University of Montana, qipei.shangguan@umontana.edu;

Cory Beatty (Co-Presenter/Co-Author)
University of Montana, Department of Chemistry and Biochemistry, cory.beatty@mso.umt.edu;

Michael DeGrandpre (Co-Presenter/Co-Author)
University of Montana, michael.degrandpre@umontana.edu;

Fischer Young (Primary Presenter/Author)
University of Montana, Department of Chemistry and Biochemistry, fischer.young@umconnect.umt.edu;

Abstract: Inland waters are increasingly recognized for their role in the global carbon cycle, yet uncertainties involved in freshwater carbonate system calculations, i.e., the partial pressure of CO2 (pCO2), remain. This study compares spectrophotometric (indicator based) and electrochemical pH measurements and their application for calculation of pCO2. The accuracy and uncertainty of calculated pCO2 was determined from three different pH measurements (spectrophotometric pH, a laboratory grade pH electrode, and a field-ready pH electrode) along with total alkalinity (AT), temperature, and ionic strength. Our study found that, compared to an infrared reference method, pCO2 was overestimated with pH electrodes (+193 ± 200 µatm) but found good agreement with measured pCO2 values calculated from spectrophotometric pH (+10 ± 39 µatm). To further validate these results, a field study using autonomous sensors was undertaken. During this deployment, we found an average error in calculated pCO2 of 15 ± 75 µatm. This study highlights the need for more accurate pH measurements for pCO2 calculations. These findings will improve future freshwater pCO2 calculations and thus better quantify inland waters’ role in the global carbon budget.

Can we see the nitrate from the trees? Examining the nitrogen paradox in neotropical streams [Oral Presentation]

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

Nick Marzolf (Co-Presenter/Co-Author)
North Carolina State University, nmarzol@ncsu.edu;

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

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

Abstract: High abundances of nitrogen (N) fixing trees in tropical forests with high soil N has been termed the N paradox, and has been used to explain higher tropical stream nitrate (NO3) concentrations compared to temperate counterparts. However, relationships between N fixing trees and stream NO3 concentrations have not been fully explored. We combined two unique datasets from La Selva Biological Station, Costa Rica: 20 years of monthly stream nitrate concentrations in six stream sites with 20 years of tree diameter measurements in nearby old growth tree plots. We hypothesized that years of higher growth of N fixing trees species would be correlated with higher stream water NO3 concentrations. We found that NO3 concentrations in the streams were high (150-350 µg L-1) and N fixing trees were very abundant in the plots. Contrary to our initial hypothesis, we found no correlation between stream mean annual NO3 concentrations and annual growth of either N fixing trees or all trees. Our results suggest that symbiotic N fixation from N fixing trees might not be as important as previously thought in explaining high NO3 concentrations in tropical streams.

DIFFICULTIES IN ESTIMATING ECOSYSTEM RESPIRATION IN A TRULY LARGE RIVER [Oral Presentation]

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

William Perkins (Co-Presenter/Co-Author)
Pacific Northwest National Laboratory, William.Perkins@pnnl.gov;

Sarah S. Roley (Primary Presenter/Author)
Washington State University, sarah.roley@wsu.edu;

Vanessa A. Garayburu-Caruso (Co-Presenter/Co-Author)
Pacific Northwest National Laboratory, vanessa.garayburu-caruso@pnnl.gov;

Abstract: In contrast to the wealth of metabolism data in small streams, metabolism estimates from truly large rivers are almost non-existent. Truly large rivers have low transverse mixing, substantial planktonic contributions, and often have discontinuities, such as large dams. As a result, we expect that such rivers will have metabolism patterns distinct from small streams. They also present new challenges to completing metabolism estimates. We continuously deployed dissolved oxygen (DO) and temperature sensors for 2.5y in the Hanford Reach of the Columbia River, in Washington, USA and estimated gross primary production (GPP) and ecosystem respiration (ER) with Bayesian inverse modeling using streamMetabolizer. GPP ranged from 4.69 to 19.80 g O2 m-2 d-1 with peak production coinciding with maximum temperature, in late summer. ER estimates were unreliable, however, because DO remained above saturation for weeks at a time. After correcting downstream DO for the effects of an upstream dam (85km), we found that GPP would need to be 12 times higher than ER, an improbable ratio, to explain the observed oversaturation. We conclude that accurate estimates of ER in truly large rivers will require novel approaches.

DIRECT AND INDIRECT EFFECTS OF RIPARIAN WOODY PLANT EXPANSION ON NITROGEN CYCLING IN GRASSLAND STREAMS AND RIPARIAN SOILS [Oral Presentation]

James Guinnip (Primary Presenter/Author)
Kansas State University, jguinnip@ksu.edu;

Walter Dodds (Co-Presenter/Co-Author)
Kansas State University, wkdodds@ksu.edu;

Abstract: Low-order grassland streams were historically open canopy systems, but this is changing worldwide due to woody plant expansion. Soil carbon and nitrogen stocks increase with woody expansion and it is unclear how these changes in riparian soils influence stream biogeochemistry. We measured rates of nitrification and denitrification in open and closed canopy streams and adjacent riparian soils to examine benthic and riparian nitrogen dynamics. We used path analysis to test hypotheses regarding direct and indirect effects of riparian woody plants on nitrification and denitrification. Stream surveys showed reaches dominated by woody plants exhibited structural changes seasonally; the proportion of epilithic biofilm cover was 48% lower in closed canopy reaches during the fall, while cover by coarse particulate organic matter was 61% higher. Path analyses suggest woody expansion directly influences riparian nitrification, and there are indirect effects on denitrification mediated by soil carbon and nitrate concentrations. Furthermore, woody plants indirectly affect benthic denitrification by influencing nitrate concentration in streams. We highlight that woody expansion may alter carbon and nitrogen dynamics in grassland streams. Future research should focus on specific mechanisms of the impact of riparian woody plant expansion on stream biogeochemistry.

DISSOLVED N2:AR RATIOS DESCRIBE THE BALANCE BETWEEN DENITRIFICATION AND N FIXATION ACROSS A NITROGEN:PHOSPHORUS GRADIENT IN EXPERIMENTAL POND SYSTEMS [Oral Presentation]

Jason M. Taylor (Primary Presenter/Author)
USDA, Agricultural Research Service, National Sedimentation Lab, jason.taylor@ars.usda.gov;

Thad Scott (Co-Presenter/Co-Author)
Baylor University, Thad_Scott@baylor.edu ;

Patrick Kelly (Co-Presenter/Co-Author)
Rhodes College, kellyp@rhodes.edu;

Isabelle Andersen (Co-Presenter/Co-Author)
Baylor University, isabelle_andesen1@baylor.edu;

Abstract: Quantifying net N2 flux, the balance between denitrification and nitrogen (N) fixation, may help solve the decades-long debate about the significance of N limitation in pond, lake, and reservoir ecosystems. We hypothesized that the stoichiometric imbalance between nitrogen and phosphorus (P) inputs into hypereutrophic experimental ponds would yield under- or over-saturated N2 gas concentrations and net zero N2 flux at the Redfield Ratio. We tested this concept by measuring diel N2:Ar patterns in twelve experimental pond mesocosms representing a N:P gradient ranging from ~2 to 110 (by atoms). Patterns in N2:Ar ratios across mesocosms varied over the diel cycle with minimum values occurring in late afternoon and maximum values occurring before or during sunrise hours. Overall, mesocosms with the lowest N:P ratios had N2:Ar values consistently below equilibrium, mesocosms with N:P ratios near Redfield ratios overlapped with equilibrium values, and mesocosms with high N:P ratios had N2:Ar values consistently above equilibrium. Our results confirm that water column N2:Ar values show promise for evaluating the direction of N fluxes within lakes and may help researchers determine the role of N fixation and denitrification in balancing stoichiometry of lakes across broad scales.

DISSOLVED ORGANIC CARBON: A LINK TO VITAL PROCESSES IN STREAMS AND LAKES [Oral Presentation]

Vanessa Czeszynski (Primary Presenter/Author)
River Studies Center and Department of Biology, University of Wisconsin – La Crosse, czeszyns.vanessa@uwlax.edu;

Eric Strauss (Co-Presenter/Co-Author)
River Studies Center and Department of Biology, University of Wisconsin – La Crosse, estrauss@uwlax.edu;

Abstract: Dissolved organic carbon (DOC) is a key component of the carbon cycle in aquatic systems and is essential for understanding aquatic ecosystem metabolism and functioning. However, higher levels of recent atmospheric deposition of DOC is causing increased staining, or browning, to occur in freshwater systems. Chromophoric dissolved organic material (CDOM) can be used to explain the optical properties of organic carbon. It is known for having a strong relationship with total DOC in many systems and has been used as a proxy for DOC in other studies. The objectives of this study were to determine the range in DOC and CDOM quantity in streams and lakes in the Northern Highlands region of the Midwest and to assess any differences in trends between the two system types. Sampling a variety of stained and unstained systems, we predicted a wide range in DOC and CDOM with a positive relationship between the two parameters. Additional spectrophotometric properties of water samples were analyzed. Overall, DOC ranged from 3.01-25.01 mg/L, and CDOM ranged from 4.25-32.29 mg/L. In both streams and lakes, the relationship between DOC, CDOM, and other spectrophotometric properties was highly linear.

DOES CHANGING LAND COVER ALTER N:P:SI RATIOS AND RISK FOR CYANOBACTERIAL BLOOMS IN STREAMS DRAINING INTENSIVE AGRICULTURE? [Oral Presentation]

Lienne Sethna (Primary Presenter/Author)
Indiana University, lsethna@iu.edu;

Todd Royer (Co-Presenter/Co-Author)
O’Neill School of Public and Environmental Affairs, Indiana University, Bloomington, tvroyer@indiana.edu;

Jennifer Tank (Co-Presenter/Co-Author)
University of Notre Dame, jtank@nd.edu;

Shannon Speir (Co-Presenter/Co-Author)
University of Notre Dame, sspeir@nd.edu;

Ursula Mahl (Co-Presenter/Co-Author)
University of Notre Dame, Ursula.H.Mahl.1@nd.edu;

Matt Trentman (Co-Presenter/Co-Author)
Flathead Lake Biological Station, University of Montana, matt.trentman@flbs.umt.edu;

Abstract: Agricultural streams often have a stoichiometric imbalance among nitrogen (N), phosphorus (P), and silicon (Si) which can contribute to the development of harmful algae blooms (HABs). Planting winter cover crops can retain N and P on the landscape, yet their effect on Si concentrations and stoichiometry is unknown. We analyzed three years of biweekly concentrations and loads of dissolved N, P, and Si in subsurface tile drains and stream water in two agricultural watersheds in northern Indiana. There was no significant difference in tile drain Si concentrations between fields with and without cover crops, although there were distinct seasonal patterns. Average tile drain Si concentrations (as SiO2) ranged between 7-12 mg/L with a mean value of 9 mg/L during the period of record. Comparatively, inorganic N and P concentrations varied over multiple orders of magnitude. To assess the risk of HAB formation, we calculated a stoichiometric index to quantify potential for non-siliceous algal growth facilitated by excess N and P relative to Si. Results show low potential for HABs during summer despite frequent summer HABs in surface waters, suggesting stoichiometric imbalances are not the sole driver of summer HABs.

EFFECT OF WINTER VEGETATIVE COVER ON DISSOLVED ORGANIC CARBON (DOC) INPUT TO STREAMS DRAINING INTENSIVELY FARMED WATERSHEDS [Oral Presentation]

Jennifer Tank (Co-Presenter/Co-Author)
University of Notre Dame, jtank@nd.edu;

Lienne Sethna (Co-Presenter/Co-Author)
Indiana University, lsethna@iu.edu;

Shannon Speir (Co-Presenter/Co-Author)
University of Notre Dame, sspeir@nd.edu;

Ursula Mahl (Co-Presenter/Co-Author)
University of Notre Dame, Ursula.H.Mahl.1@nd.edu;

Matt Trentman (Co-Presenter/Co-Author)
University of Notre Dame, matt.trentman@flbs.umt.edu;

Todd V. Royer (Primary Presenter/Author)
Indiana University Bloomington, troyer@indiana.edu;

Abstract: Agriculture in the central US has a fallow period of 5-7 months during which croplands are largely devoid of vegetation, leaving soils vulnerable to significant nutrient and carbon loss. We measured the effect of using winter cover crops on DOC losses from fields (through tile drains) and in-stream DOC loads for four years across two watersheds in northern Indiana. Water from tile drains had 1-5 mg/L DOC and cover crops reduced concentrations in one watershed and were neutral in the other. Movement of DOC to streams through tile drains was reduced by cover crops, but the strength of the effect varied seasonally and between watersheds. Molar DOC:nitrate ratios of the inputs were usually <1 due to nitrogen fertilization of cropland, and cover crops generally did not alter DOC:nitrate ratios because cover crops also reduced nitrate inputs. Winter vegetative cover has great potential for sequestering carbon in soils and our results support adoption of cover crops as a natural climate solution. The short-term impact on streams appears to be reduced DOC inputs from adjacent cropland, which has important implications for ecological and biogeochemical processes in these nitrate-rich streams.

EFFECTS OF BACILLUS THURINGIENSIS ISRAELENSIS ON METHANE DYNAMICS IN PONDS [Oral Presentation]

caroline Ganglo (Primary Presenter/Author)
University of Koblenz-Landau, Institute for Environmental Sciences, Department of Environmental Physics, Systemlink research training group, Fortstr. 7, 76829 Landau, Germany , ganglo@uni-landau.de;

Clara Mendoza-Lera (Co-Presenter/Co-Author)
iES, University of Koblenz-Landau (Germany), clara.mendozalera@gmail.com;

Alessandro Manfrin (Co-Presenter/Co-Author)
University of Koblenz-Landau, Institute for Environmental Sciences, Department of Environmental Physics, Systemlink research training group, Fortstr. 7, 76829 Landau, Germany, manfrin@uni-landau.de;

Andreas Lorke (Co-Presenter/Co-Author)
University Koblenz-Landau, Landau, Germany, andreas.lorke@uni-landau.de;

Abstract: Ponds are globally important emitters of methane (CH4), a highly potent greenhouse gas. Net emission rates of CH4 are the result of anaerobic production and aerobic oxidation of CH4. Bio-turbation and bio-irrigation, e.g. by chironomid larvae, may increase CH4 oxidation by enhancing oxygen transport into the sediment. Widely applied biological mosquito control agents Bacillus thuringiensis israelensis (Bti) can strongly reduce the abundance of non-target chironomids. We tested whether Bti application has implications for CH4 dynamics in ponds. We measured CH4 concentrations and fluxes in aquatic, aquatic-terrestrial, and terrestrial compartment of twelve small (147 m2) artificial ponds. Half of these ponds were treated three times with Bti (treatment ponds), while the remaining ponds were free of Bti (control ponds). Dissolved CH4 concentrations and fluxes varied widely over seasons, within, and between ponds. No significant differences of concentrations and fluxes were observed between Bti treated and control ponds. Our results suggest that Bti did not affect ecosystem-scale CH4 dynamics in the ponds. Further research is needed to determine whether potential effects were masked by large natural variability among replicated pond ecosystems.

EXCESSIVE NITRATE LOADING MAY APPROACH SATURATION IN A LARGE OLIGOTROPHIC RIVER [Oral Presentation]

Lisa Kunza (Primary Presenter/Author)
South Dakota School of Mines and Technology, lisa.kunza@sdsmt.edu;

Emily Stickney (Co-Presenter/Co-Author)
South Dakota School of Mines and Technology, emily.stickney@mines.sdsmt.edu;

Gregory Hoffman (Co-Presenter/Co-Author)
US Army Corps of Engineers, Gregory.C.Hoffman@usace.army.mil;

Kurt Chowanski (Co-Presenter/Co-Author)
South Dakota School of Mines and Technology, kurt.chowanski@sdsmt.edu;

Genevieve Hoyle (Co-Presenter/Co-Author)
Kootenai Tribe of Idaho, genhoyle@kootenai.org;

Shawn Young (Co-Presenter/Co-Author)
Kootenai Tribe of Idaho, young@kootenai.org;

Abstract: Water quality can decline with small land cover alterations in large watersheds. Previously, the Kootenai River was considered ultraoligotrophic and nitrate loading has increased 10-fold or more in some locations while P is relatively constant or declining. Excessive nitrate has skewed the N:P ratio to greater than 200:1 at times in some locations. We assessed the nutrient distribution in the Kootenai River associated with land cover. Downstream of surface mining operations, nitrate concentrations were elevated and decreased with distance but remained elevated above upstream concentrations. Nitrate removal is a function that is provided by the biota in an ecosystem. We estimated nitrate uptake through time in multiple reaches of the Kootenai River including locations below Libby Dam, the canyon section with the long-term nutrient addition zone, and the slow-moving meander section. Although we documented a decline in nitrate that indicates that nitrate is still being used by the biota, the magnitude of nitrate uptake varies. Saturation of these important processes would be detrimental and pass the nitrate load entirely to downstream ecosystems.

HETEROGENEITY IN A HOMOGENEOUS WATERSHED: FINE-SCALE SPATIAL DYNAMICS OF WATER CHEMISTRY IN A HEADWATER AGRICULTURAL STREAM [Oral Presentation]

Peter S. Levi (Primary Presenter/Author)
Drake University, peter.levi@drake.edu;

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

Alyssa Gerhardt (Co-Presenter/Co-Author)
Drake University, alyssa.gerhardt@drake.edu;

Jeffery Riggs (Co-Presenter/Co-Author)
Oak Ridge National Laboratory, riggsjs@ornl.gov;

Christopher R. DeRolph (Co-Presenter/Co-Author)
Oak Ridge National Laboratory, derolphcr@ornl.gov;

Allison M. Fortner (Co-Presenter/Co-Author)
Oak Ridge National Laboratory, fortneram@ornl.gov;

Abstract: Where industrial agriculture is prominent in the Midwest, USA, the landscape, and the human activity upon it, is generally homogeneous. For example, corn or soybeans are present for six months, bare soil is often present during the non-growing season, and high amounts of fertilizer are applied in discrete pulses. Is water quality in headwater streams draining these watersheds similarly homogeneous? We are deploying an unmanned surface vehicle (the ‘AquaBOT’) outfitted with a nitrate sensor and multiparameter sonde to map and analyze spatial patterns of water quality along a 2-km reach of Alleman Creek (Iowa) in 60-second intervals. Though some initial results are intuitive (e.g., daytime increase in water temperature), other parameters show a high degree of heterogeneity. For example, nitrate-N concentrations varied 10 to 12.5 mg/L along the stream reach in one early-summer run. The concentrations were often highest directly downstream of tile drain inputs, but we observed sporadic spikes in nitrate with no nearby tiles. The fine-scale data mapping from the AquaBOT can pinpoint chronic or acute nutrient inputs, which, in turn, can inform directed management efforts to reduce non-point source pollution and improve water quality.

Increased temperature and carbon availability enhanced nitrous oxide production due to incomplete denitrification in river sediments [Oral Presentation]

Shannon Speir (Primary Presenter/Author)
University of Notre Dame, sspeir@nd.edu;

Jennifer L. Tank (Co-Presenter/Co-Author)
University of Notre Dame, tank.1@nd.edu;

Jason M. Taylor (Co-Presenter/Co-Author)
USDA, Agricultural Research Service, National Sedimentation Lab, jason.taylor@ars.usda.gov;

Amelia Grose (Co-Presenter/Co-Author)
Michigan State University, groseame@msu.edu ;

Abstract: Streams and rivers are key sources of nitrous oxide, a powerful greenhouse gas, and incomplete denitrification results in nitrous oxide production, which is influenced by nitrate and organic carbon (C) availability, as well as water temperature. Moreover, few studies have experimentally isolated these drivers, especially in flowing waters. We used sediment core incubations conducted at 15C and 25C paired with membrane inlet mass spectrometry (MIMS) to understand how nitrate and C availability, as well as temperature influence nitrous oxide production rates and yields (as %) from sediment denitrification. In general, conditions that enhanced sediment denitrification rates also increased nitrous oxide production. At both temperatures, we observed higher nitrous oxide production with added C, and, at 25C, rates remained high across the nitrate gradient. Nitrous oxide yields were highest at 15C due to low total denitrification rates. Contrary to previous findings, C additions increased nitrous oxide yields at both low and high temperatures. Our results suggest that as global temperatures warm and rivers “brown,” enhancing C supply, nitrous oxide production from riverine sediments will likely increase.

Integrating perspectives on dissolved organic carbon removal and whole-stream metabolism [Oral Presentation]

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

Jacob Riney (Co-Presenter/Co-Author)
Virginia Tech, jaker98@vt.edu;

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

Abstract: Quantifying whole-stream dissolved organic carbon (DOC) metabolism is needed to better integrate inland waters into whole ecosystem carbon budgets. To understand how in-stream DOC metabolism affects DOC removal, export, and terrestrial loading fluxes, we compared DOC removal in two streams estimated using two common methods: (1) bioassays to measure water column DOC uptake velocity; and (2) daily rates of stream metabolism and OC spiraling (i.e., complete OC removal) calculated from fluorescent dissolved organic matter, oxygen, and water level sensor data. We compared how in-stream OC removal estimated from these two methods affected terrestrial OC loading and DOC export using a mass balance model. Mean OC mineralization velocity (0.07 ± 0.04 m/d (±SD)) was greater than mean bioassay DOC uptake velocity (0.01 ± 0.01 m/d). In model simulations, more DOC was removed when using OC mineralization velocity (0.5 to 17.0%) estimates compared to bioassay DOC uptake velocity (0.02 to 4.2%). We highlight how measurement uncertainty of in-stream DOC processing can have confounding effects when estimating terrestrial-aquatic DOC fluxes and removal. By integrating whole-stream metabolism with DOC transport, we can better quantify the role of running waters in the global carbon cycle.

LOCAL AND REACH-SCALE ASSESSMENTS OF STRUCTURE AND FUNCTION: GRADIENTS OF NUTRITIONAL AND METABOLIC CHARACTER [Oral Presentation]

Jacob Prater (Primary Presenter/Author)
University of Montana, jacob.prater@umontana.edu;

Abstract: Classic assessments of river systems characterized longitudinal variation in community structure and ecosystem function as a result of systematic downstream changes in river attributes. However, differing perspectives of streams have since been introduced, many of which recognize the importance of both reach-, and local-scale assessments of ecosystem structure and function. Using two study sites along a 20-km reach of the Clark Fork River, MT, we demonstrate both local and reach-scale influences on stream character. Total nitrogen (N) and phosphorous (P) were greater at the upstream site at 0.11 ± 0.04 mg L-1 N and 0.28 ± 0.7 mg L-1 P, relative to 0.05 ± 0.03 mg L-1 N and 0.02 ± 0.01 mg L-1 P at the downstream site. N demand doubled from 0.0836 ± 0.02 to 0.174 ± 0.04 g N m-2 d-1 from the upstream to downstream sites. At the reach scale, the system acted as a sink for N over the duration of sampling with an effective uptake rate of -64.09 ± 0.98 mg NO3-N m-2 d-1. Together, point measures and reach-scale assessment suggest that local influences integrate over space to create longitudinal river function.

MODELING DELAYED RESPIRATION OF LABILE DOC IN A STREAM [Oral Presentation]

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

Michelle Baker (Co-Presenter/Co-Author)
Utah State University, michelle.baker@usu.edu;

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

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

Abstract: Dissolved organic carbon (DOC) represents a large fluvial flux of carbon and supports respiration in streams. DOC comprises many compounds with varying reactivity, such that the DOC we measure in transport is the DOC that is not cycling quickly. Hence, it is difficult to study reactivity and fate of the DOC pool. To address this problem, we added 13C labeled glucose and plant litter leachate in separate slug additions to a tiny spring stream in Montana. Uptake was high for both carbon sources and matched that from other tracer studies. Mineralization of the DOC into the dissolved inorganic carbon pool (measured as CO2 using cavity ringdown spectroscopy) was a small fraction of what was removed. Mineralization was initially high, but then tailed off for >20 h following the slug addition. A compartment model with a range of residence times of DOC in biomass pools reflected this pattern: some tracer DOC was immediately respired while more was fully incorporated into biomass within the study reach and respired during the next 24 hours. Ongoing work seeks to quantify differences in respiration lags among DOC sources.

NITROGEN FIXATION AND DENITRIFICATION CO-OCCUR IN STREAMS ACROSS THE UNITED STATES [Oral Presentation]

Erin Eberhard (Co-Presenter/Co-Author)
Michigan Technological University , ekeberha@mtu.edu;

Michelle Catherine Kelly (Co-Presenter/Co-Author)
Michigan Technological University, mckelly1@mtu.edu;

Kevin Nevorski (Co-Presenter/Co-Author)
Michigan Technological University, kcnevors@mtu.edu;

Amy Marcarelli (Primary Presenter/Author)
Michigan Technological University, ammarcar@mtu.edu;

Abstract: We conducted a cross-ecoregion study to test the hypothesis that N-fixation and denitrification will co-occur in streams across a range of reactive N concentrations. Between 2017 and 2019, we sampled 30 streams in 13 ecoregions, using chambers to quantify N2 flux using membrane inlet mass spectrometry, N-fixation using acetylene reduction, denitrification using acetylene block, and microbial assemblages using functional genes and taxonomic diversity. 25 of the study streams were part of the National Ecological Observatory Network or StreamPULSE, which provided data on water temperature, light, nutrients, discharge and metabolism. We found that N-fixation rates were detectable most frequently on rock, wood, and/or macrophyte substrates in around half of the streams surveyed. Denitrification potential was detected in all streams, with rates 1-2 orders of magnitude higher than N-fixation rates, and net N2 flux rates were positive, indicating net denitrification. Rates were not related to N concentrations, despite the common simplifying assumption that denitrification dominates under high N and N-fixation occurs under low N conditions. Additional analyses are exploring reach to watershed characteristics, and metabolic regimes as drivers of cross-ecoregion patterns in processes.

NUTRIENT PROCESSING DOMAINS: NET MATERIAL BALANCE, EXCHANGE POTENTIAL, AND AVAILABILITY EFFECT [Oral Presentation]

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

Geoffrey C Poole (Co-Presenter/Co-Author)
Montana State University, gpoole@montana.edu;

H. Maurice Valett (Primary Presenter/Author)
University of Montana, Division of Biological Sciences, maury.valett@umontana.edu;

Abstract: A Nutrient Processing Domain (NPD) is a realm in functional space occupied by stream reaches that share similar biogeochemical character and distinguishes how hydrologic exchange and in-stream processes combine to impart biogeochemical character. Location within functional space (“reach character”) is determined empirically using changes in discharge, material transport, and concentration that occur within the reach. We applied this approach to 11 years of bi-weekly water concentration of nitrogen (N) and phosphorus (P) from the Upper Clark Fork River, MT, to address how net material balance, exchange potential, and availability differed seasonally among three reaches. Effective solute fluxes for nitrate-N calculated via mass-balance revealed that reaches ranged from net sources (194.7 mg N/m2/d) to sinks (-60.0 mg NO3-N/m2/d) while simultaneously acting as soluble reactive P sinks (-3.6 mg P/m2/d) and sources (16.0 mg P/m2/d). Solute fluxes for Total N and Total P were closely linked to changes in hydraulic load while those for nitrate and SRP were less so. The NPD approach simultaneously assesses key features entailed in material balance and provides a conceptual framework for considering the distribution, interactions, and implications of river reaches in distinct realms of biogeochemical behavior.

Progression of N fixation during a riverine algal bloom [Oral Presentation]

Rafael Feijó de Lima (Primary Presenter/Author)
University of Montana, rafael.feijo@mso.umt.edu;

Thomas Horner (Co-Presenter/Co-Author)
University of Montana, thomas.horner@umconnect.umt.edu;

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

H. Maurice Valett (Co-Presenter/Co-Author)
University of Montana, Division of Biological Sciences, maury.valett@umontana.edu;

Abstract: The Upper Clark Fork River (UCFR) suffers from anthropogenic (N) enrichment that, coupled with naturally high Phosphorous (P) availability and sunlight, lead to annual nuisance filamentous algae (Cladophora) blooms often leading to a secondary N-fixing cyanobacterial bloom reflecting N-limitation. Under such conditions, N-fixation can play a significant role in stimulating primary productivity. We used the acetylene reduction technique to quantify N-fixation along the progression of blooms in a 5th-order section of the UCFR. A suite of associated environmental variables was measured in order to determine the environmental controls to N fixation and the consequences of enhanced N-fixation to the system. Over the course of the algal bloom, standing crops of phycocyanin increased linearly to a maximum of 65 mg/m2). Following dominance by Cladophora, N-fixation rates increased from 0.15 to 3.3 mg/m2*h-1, then slowly decreased towards the end of the growing season. The N/P ratios of the water column shifted from 0.3 to 9.3, mostly due to the increase in availability of ammonium. Light and temperature explained 70% of the variation in phycocyanin corrected N fixation. Enhanced algal growth due to N-Fixation was associated with declines in ambient P concentrations.

QUANTIFYING THE ROLE OF SUBSTRATE AND BIOFILM COLONIZATION IN CONTROLLING NITRIFICATION RATES USING EXPERIMENTAL STREAMS [Oral Presentation]

Anna Vincent (Primary Presenter/Author)
University of Notre Dame, avincen5@nd.edu;

Jennifer Tank (Co-Presenter/Co-Author)
University of Notre Dame, jtank@nd.edu;

Shannon Speir (Co-Presenter/Co-Author)
University of Notre Dame, sspeir@nd.edu;

Ursula Mahl (Co-Presenter/Co-Author)
University of Notre Dame, Ursula.H.Mahl.1@nd.edu;

Elise Snyder (Co-Presenter/Co-Author)
The University of Notre Dame, esnyder4@nd.edu;

Abagael Pruitt (Co-Presenter/Co-Author)
University of Notre Dame, apruitt2@nd.edu;

Abstract: While nitrogen fertilizer is essential for agriculture, it often moves into waterways when applied in excess. Microbially-mediated nitrification rapidly converts fertilizer-derived ammonium to nitrate, which contributes to eutrophication. Substrate homogenization and riparian canopy clearing are also common in agricultural streams, but we lack understanding on how they alter nitrification. We assessed the influence of substrate (course vs. fine) and biofilm colonization (light vs. dark) on nitrification rates. We conducted replicated short-term ammonium additions in experimental streams containing different benthic substrates (i.e., sand, pea gravel, cobble, mixed) to estimate reach-scale ammonium uptake and nitrate production, combined with laboratory assays to estimate nitrification potential. Ammonium demand (as uptake velocity, Vf) differed among substrates and with biofilm colonization, and was highest on coarse substrates (cobble, pea gravel) under open canopy (ANOVA, p<0.001). We also documented reach-scale nitrate production for about half of ammonium releases, with highest production on mixed substrate under dark conditions. Assay nitrification rates were highest on pea gravel (p<0.001), but there were no differences between light vs. dark biofilms. Thus far, results suggest complex interactions between substrate type and biofilm colonization, but both contribute to nitrification dynamics in small streams.

Spatial and Temporal Nutrient Trends in a Shallow, Eutrophic Freshwater Bay [Oral Presentation]

Morgan Hughes (Primary Presenter/Author)
Kent State University, mhughe32@kent.edu;

Abstract: Many coastal bays contain farmland within their watersheds. Agricultural runoff contains high concentrations of nitrogen (N) and phosphorus (P), which drains into these systems throughout the year. This can cause harmful algal blooms (HABs) that impact animal and human health. Understanding the trends and behaviors of N and P in these ecosystems will help us to control HABs. Sandusky bay is a shallow coastal bay in Lake Erie, which typically experiences harmful algal blooms (HABs) every year. Our goal was to determine how N and P concentrations vary temporally and spatially in Sandusky Bay. Levels of N and P in the water were measured at multiple timepoints and locations over three summers (2017-2019). For both N and P, the nutrient concentrations declined along the flow path from the West, where the Sandusky River empties into the bay, to the East where the Bay connects with Lake Erie. N concentrations decreased throughout the season, while P was more variable. Across sampling sites, surface water nutrient concentrations reflect gradients in sediment geochemistry and nutrient content. Continued research will explore mechanisms of N and P sediment removal in Sandusky Bay and adjacent wetlands.

STRENGTHS AND WEAKNESSES OF USING INCUBATION METHODS TO MEASURE EGESTION IN AQUATIC VERTEBRATES [Oral Presentation]

Rana El-Sabaawi (Co-Presenter/Co-Author)
University of Victoria, rana@uvic.ca;

Emily May (Primary Presenter/Author)
University of Victoria, emilymay@uvic.ca;

Abstract: Ecological stoichiometry uses mass-balance to evaluate how organisms convert dietary nutrients into waste. However, most aquatic research evaluates excreted wastes without considering egested wastes, as it is difficult both to collect egesta and to accurately analyze its nutrient content. We have systematically analyzed incubation methods to determine their efficacy in measuring egestion. We fed wild-caught stickleback, incubated them in 2L of water for 24 hours at one of two temperatures (16°C or 22°C), and checked for egestion at fixed intervals. We then estimated the mean quantity of phosphorus (P) leached from feces using the hindgut contents of euthanized fish as a fecal proxy. Egestion occurrence varied. While 82% and 75% of fish egested within 24 hours of feeding at 17°C and 22°C respectively, only 38% and 6% cleared their guts, making mass-balance analysis impossible. Furthermore, feces leached a mean of 41% (sd: 26.3) of its P during 2, 4, and 16 hour fecal incubations. These results imply that short incubations underestimate both quantity and nutrient content of egesta in aquatic animals. Therefore, researchers should incorporate other methods, such as foregut-hindgut analyses, with their incubation experiments to accurately evaluate egestion.

Surface and groundwater denitrification create contrasting patterns of carbon, nitrogen, and sulfur at watershed scales [Oral Presentation]

Mary Proteau (Primary Presenter/Author)
Brigham Young University, mary.proteau@gmail.com;

Emilee Severe (Co-Presenter/Co-Author)
Brigham Young University, emileesevere25@gmail.com;

Isabella Errigo (Co-Presenter/Co-Author)
Brigham Young University, ierrigo95@gmail.com;

Benjamin Abbott (Co-Presenter/Co-Author)
Brigham Young University, Department of Plant and Wildlife Sciences, benabbott@byu.edu;

Sayedeh Sayedi (Co-Presenter/Co-Author)
Brigham Young University, Department of Plant and Wildlife Sciences, sarasayedi91@gmail.com ;

Gilles Pinay (Co-Presenter/Co-Author)
CNRS-OSUR, Rennes, France, gilles.pinay@univ-rennes1.fr;

Tamara Kolbe (Co-Presenter/Co-Author)
Swedish University for Agricultural Science, Uppsala, Sweden, tamara.kolbe@slu.se;

Abstract: Nitrogen and phosphorus pollution have triggered eutrophication in most freshwater and coastal ecosystems, contributing to a loss in biodiversity and costing the global economy trillions every year. Much of the research on nutrient transport and retention has focused on surface environments, which are both easy to access and biologically active. However, recent research suggests that subsurface processes and characteristics may be more important in determining watershed-level nutrient fluxes and removal than previously understood. We tested the importance of residence time, biogeochemical reaction rate, and flowpath in determining nitrate concentration by collecting a biogeochemical dataset from 14 wells and 12 streams in a small watershed in western France. Water chemistry in both the surface and subsurface showed high temporal variability, but groundwater was substantially more spatially variable, attributable to long transport times (10-60 years) and patchy distribution of electron donors. Isotopes of nitrate and sulfate revealed fundamentally different processes dominating the surface (heterotrophic denitrification and sulfur reduction) and subsurface (autotrophic denitrification and sulfate production from weathering). Characterizing how these worlds are both linked and decoupled is critical to meeting water quality targets and ensuring water security in the Anthropocene.

THE GAS THEY PASS: TRACE GAS CONCENTRATION PATTERNS ACROSS NEON STREAMS [Oral Presentation]

Amanda DelVecchia (Primary Presenter/Author)
Duke University, amanda.delvecchia@duke.edu ;

Emily Bernhardt (Co-Presenter/Co-Author)
Duke University, emily.bernhardt@duke.edu;

Spencer Rhea (Co-Presenter/Co-Author)
Duke University, spencer.rhea@duke.edu;

Abstract: Regional and global carbon budgets recognize that rivers emit substantial amounts of carbon, often driven by groundwater contributions and the respiration of terrestrial organic matter. Although rivers display high variation in greenhouse gas (GHG) flux, upscaling exercises tend to treat river segments as equivalent. The NEON dataset, spanning 26 sites from 2016-2020, facilitates a comprehensive understanding of how GHG concentrations and flux vary across streams. We synthesized chemical and spatial data from NEON sites data to understand variation in GHG concentrations and flux, interrelationships between GHG concentrations, and correlation with watershed-scale properties including channel and catchment slopes, land cover, and soil type. We found that mean CO2 concentrations ranged from <10 to 600 umol/L across sites, CH4 from <0.1 to 9 ?mol/L and N2O from <0.01 to 0.05 ?mol/L. Pearson correlation values between CO2 and CH4 ranged from 0.06 to 0.79, suggesting high variation in relationships between aerobic and anaerobic metabolism that could be related to geomorphology, groundwater – surface water exchange, and methane sources. Our findings will elaborate on the potential to improve our upscaled predictions of stream GHG flux by considering channel and catchment scale characteristics.

THE RIVER INFORMATION CONTINUUM: INTEGRATING INFORMATION INTO FRESHWATER META-ECOSYSTEM SCIENCE [Oral Presentation]

Chelsea J. Little (Primary Presenter/Author)
Simon Fraser University, chelsea_little@sfu.ca;

James Stegen (Co-Presenter/Co-Author)
Pacific Northwest National Laboratory, james.stegen@pnnl.gov;

Abstract: Fluxes of matter, energy, and information over space and time contribute to ecosystems’ functioning and stability. Organisms’ behavioral, developmental, and life history responses to information: that which reduces their uncertainty about the state of the world. These responses can ripple through trophic interactions to influence ecosystem processes. In watershed meta-ecosystems, communities use not only local resources, but also those exported from upstream. These resources, including organic matter (OM), consist not just of matter and energy, but also of information. Yet the effect of the longitudinal structure of OM identity on biological communities has primarily been considered through a lens of OM as a resource. Here, we posit that the assemblage of organic molecules that make up OM pools, and the information they contain, can also be expected to follow general patterns along the river continuum. Associations between thermodynamically favorable compounds and higher aerobic respiration rates suggest that microbes use information carried by organic molecules to preferentially target them as resources. From this starting point, we explore the potential consequences of spatially structured information landscapes in watersheds and propose new research directions to address this exciting frontier.

THE STOICHIOMETRY OF LAKE RESTORATION [Oral Presentation]

Eric Moody (Primary Presenter/Author)
Middlebury College, ekmoody@middlebury.edu;

Gardner Olson (Co-Presenter/Co-Author)
Middlebury College, golson@middlebury.edu;

Grace Wilkinson (Co-Presenter/Co-Author)
University of Wisconsin-Madison, wilkinso@iastate.edu;

Abstract: Lakes in human-dominated landscapes are increasingly eutrophic and impaired. Managers have thus employed a variety of strategies to reduce nutrient loading and restore ecosystem function. In the agriculturally-dominated state of Iowa, a statewide nutrient reduction strategy and lake restoration program has targeted reduction in nitrogen pollution while legacy phosphorus in soils and sediments continues to release P to lakes. We examined the stoichiometric consequences of these restoration activities using an 18 -year dataset from 130 publicly significant lakes in Iowa. Nutrient reduction strategies have successfully reduced N concentrations in both restored and unrestored lakes. However, P concentrations have increased in unrestored lakes while restored lakes exhibited no significant change in P. As a result, water column TN:TP has generally decreased in Iowa lakes over the past two decades. Surprisingly, this has not coincided with corresponding changes in phytoplankton or Cyanobacteria biomass. Our results suggest that stoichiometric trait shifts in zooplankton communities led to consistent top-down control on phytoplankton biomass. The general lack of responses in key metrics like phytoplankton and Cyanobacteria biomass to restoration could be explained by these stoichiometric shifts.

UNDERSTANDING HOW REACH TRANSPORT TIMES INFLUENCE CONFIDENCE IN STREAM ECOSYSTEM METABOLIC RATES INFERRED FROM DO AND DIC SIGNALS [Oral Presentation]

Robert Payn (Primary Presenter/Author)
Montana State University, Montana Institute on Ecosystems, rpayn@montana.edu;

Michael DeGrandpre (Co-Presenter/Co-Author)
University of Montana, Department of Chemistry and Biochemistry, michael.degrandpre@mso.umt.edu;

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

Qipei Shangguan (Co-Presenter/Co-Author)
University of Montana, qipei.shangguan@umontana.edu;

Madison Foster (Co-Presenter/Co-Author)
Montana State University, madisonjfoster@gmail.com;

Abstract: The travel time of a stream reach interacts with the air-water gas exchange rate to influence confidence in estimates of metabolism from dissolved oxygen (DO) dynamics over that reach. However, shielding of dissolved inorganic carbon (DIC) from the influence of air-water exchange due to chemical partitioning to non-gaseous solutes suggests that the influence of reach travel time on uncertainty may differ for estimates of metabolism from DIC. We performed numerical experiments on simulated reaches that varied only with reach travel time, and we used the distributions of Monte Carlo ensembles of metabolism parameter estimates from DO and DIC to assess the relative changes in inferential confidence with variation in travel time. The relative patterns in uncertainty in metabolism estimates from DO and DIC varied similarly with reach transport times. However, inferential confidence was higher at all travel times for estimates from DIC relative to DO, due to the higher sensitivity of the DIC-pCO2 model output to metabolism parameters. This work contributes to a better understanding of the ideal reach lengths that should be used for inference of stream ecosystem metabolic rates from multiple dissolved metabolites.

VEGETATION ASSEMBLAGES DRIVE PATTERNS IN DAILY METABOLISM IN A DAMMED, EUTROPHIC RIVER [Oral Presentation]

Laurel Genzoli (Primary Presenter/Author)
University of Montana, laurel.genzoli@umontana.edu;

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

Abstract: Unlike in terrestrial biomes, which are defined by their vegetation structure and related productivity regimes, the extent to which vegetation assemblages drives fluxes of river metabolism is unknown. To investigate the effects of vegetation assemblages on river metabolism, we calculated daily gross primary production (GPP) and ecosystem respiration (ER) at 11 reaches from June through September in the eutrophic Klamath River, where a gradient of flow and substrate stability below hydroelectric dams facilitate variation in vegetation assemblages. We scaled percent cover of macrophytes and filamentous algae from snorkeling surveys at the 11 reaches to biomass (AFDM, g/m2). Macrophytes were dominant at reaches below the dams and declined with downriver distance from the dams. Cladophora replaced macrophytes from ~150 km downstream from the dams to the estuary. Reach mean and maximum GPP were not related to total vegetation biomass or vegetation type, but mean and maximum ER were higher at sites with more macrophyte biomass, driving lower rates of summer mean net ecosystem production (NEP) at macrophyte-dominated sites. Declines in the ration of GPP to ER following the GPP peak drove the lower seasonal means of NEP at macrophyte-dominated sites.

Who rules, hot or cold spots? Implications of small-scale heterogeneity for reach-scale N uptake in streams [Oral Presentation]

Clara Mendoza-Lera (Primary Presenter/Author)
iES, University of Koblenz-Landau (Germany), clara.mendozalera@gmail.com;

Stephani Bernasconi (Co-Presenter/Co-Author)
Stroud Water Research Centre, sbernasconi@stroudcenter.org ;

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

Jinjun Kan (Co-Presenter/Co-Author)
Stroud Water Research Center, jkan@stroudcenter.org;

Christine Anlanger (Co-Presenter/Co-Author)
University Koblenz-Landau, Landau, Germany, christine.anlanger@uni-landau.de;

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

Abstract: Hot spots of Nitrogen (N) processing in streams are proposed to be linked to areas of high flow as it increases the mass transfer of nutrients into the biofilms. By definition, hot spots are small areas that influence biogeochemical processes at larger scales (i.e. reach scale). We proposed that N uptake at the reach scale will increase with increasing the area of high flow. In six indoor 4-m flumes with comparable mean flow we varied the frequency distribution of high flow areas (from 0 to 100%) using ripple-like bedforms. After four weeks of biofilm colonization, we made an addition of 15N-NO3 for 9 hours in re-circulating mode. Our results show that as the frequency distribution of high flow areas increased, flume N uptake decreased. In fact, the extent of the cold spots created by the bed elements at their lee side was larger than that of the hot spots, reducing N uptake. Since in this context hot and cold spots are strongly linked, our results suggest that instead of spotting hot spots, cold spots could provide stronger predictions of N uptake at the reach scale.

WHOLE WETLAND DENITRIFICATION POTENTIAL IN AGRICULTURALLY IMPACTED WETLANDS [Oral Presentation]

Amy Hansen (Primary Presenter/Author)
University of Kansas, amy.hansen@ku.edu;

Abstract: In agriculturally impacted watersheds, wetlands are valued for their capacity to intercept and remove nutrients that otherwise might degrade water quality in river networks. Vegetation in these wetlands tends toward monocultures of tolerant species such as Typha spp., which suppresses other vegetation via dense canopies and detrital mats. In this study, we investigated the contribution of vegetation to nitrate removal via assimilation and enhanced denitrification in two agriculturally impacted wetlands. Denitrification rates were assessed on all available solid substrates, which included sediments, detritus, and surfaces of live vegetation. Areal denitrification rates were greatest on sediments but occurred on all substrates including detritus and living biomass surfaces. Per area, denitrification potential for non-sediment substrates accounted for 20 % of total nitrate removal via denitrification. Dissolved oxygen measurements showed that anoxic conditions, which favor denitrification, extended over half the water column depth for over 12 hours every day. These results suggest that, from a watershed management perspective, the aggressive biomass accumulation of Typha canopies may be well matched with the aggressive nitrate loading in intensively managed agricultural landscapes.

BUILDING A BROAD-SCALE ECOLOGICAL STOICHIOMETRY DATABASE [Poster Presentation]

Casey Brucker (Primary Presenter/Author)
University of Wyoming, brucker.casey@gmail.com;

Sarah M Collins (Co-Presenter/Co-Author)
University of Wyoming, sarah.collins@uwyo.edu;

Jessica Corman (Co-Presenter/Co-Author)
University of Nebraska - Lincoln, jesscorman@gmail.com;

Halvor Halvorson (Co-Presenter/Co-Author)
University of Central Arkansas, hhalvorson@uca.edu;

Amy Krist (Co-Presenter/Co-Author)
University of Wyoming, krist@uwyo.edu;

Abstract: The supply of elements and energy governs biological activity from cellular to ecosystem scales. Previous studies have used the ecological stoichiometry framework to examine how the relative supply of elements influences biogeochemistry and food webs in freshwater ecosystems. However, our ability to test stoichiometric theory at broad spatial scales across numerous lakes and streams has been hampered by the lack of a comprehensive stoichiometry database. Our group is using published data, individual investigator datasets, and data from the National Ecological Observatory Network to establish a public database for use toward the understanding of regional to continental-scale stoichiometric controls in inland aquatic ecosystems. We aim to engage community members in contributing to the database and using the database to understand the consequences of stoichiometry for ecosystems, communities, organisms, and evolution. In this poster, we detail our plans and our progress on data synthesis, and we seek feedback and data contributions from the freshwater science community. Ultimately, we hope that active engagement with the community will make the database a more useful and accessible resource for stoichiometry research.

Development of an In-Situ Dissolved Organic Carbon Sampler for Aquatic Systems [Poster Presentation]

Alec Johnson (Primary Presenter/Author)
University of Montana, alec.johnson@umconnect.umt.edu;

Abstract: This presentation will outline an in-situ aquatic sampler, named the Deployable Underwater Chemical Sampler (DUCS). DUCS uses a smart sampling method where an acid preservative is mixed with collected sample, and acidified samples are then stored within a long length of tubing. The preservative acts as a tracer to determine where samples start and stop, while simultaneously correcting for dilution factor using conductivity. Following deployment, samples within long tubing are dispensed to a series of vials. Individual sample locations, with associated dilution factors, are found using a small volume conductivity probe. DUCS can collect preserved samples at higher frequencies than other commercially available samplers making this sampler ideal for high-frequency DOC sampling – something which is needed to more fully understand DOC variability in aquatic systems. DUCS can also potentially be used for in situ sampling and preservation of other chemical species such as trace metals. In addition to evaluating this sampler in-lab, data from DUCS deployments in the Clark Fork River (CFR) near Missoula, MT will also be presented.

EFFICACY OF RESTORED RIPARIAN WETLANDS OF WESTERN KENTUCKY TO SEQUESTER NITROGEN [Poster Presentation]

Tyler Befus (Primary Presenter/Author)
Murray State University, tbefus@murraystate.edu;

Karen Baumann (Co-Presenter/Co-Author)
Murray State University, kbaumann1@murraystate.edu;

Kinga Stryszowska-Hill (Co-Presenter/Co-Author)
Murray State University, kstryszowskahill@murraystate.edu;

Michael Flinn (Co-Presenter/Co-Author)
Murray State University, mflinn@murraystate.edu;

Abstract: Wetlands can help prevent nitrogen-rich runoff from reaching the Gulf of Mexico. The USDA Natural Resources Conservation Service has been restoring wetlands as part of the Wetlands Restoration Program and has been active in western Kentucky. To determine the effectiveness of these restorations, we are collecting monthly grab samples at our four primary riparian sites to track seasonal variations in nitrate concentrations in the wetlands and adjacent streams. We also use ISCO automatic water samplers to capture discrete water samples during flooding events to determine inflow and outflow nitrate concentrations. In addition, we are quantifying hydrology and collecting physiochemical data to help understand factors that influence nutrient concentration variation. Preliminary results show nitrate concentrations increase 100-200% between upstream and further downstream sites as well as elevated concentrations during the colder, winter months. Within the wetlands, nitrate levels generally decrease as flood water passes through them by 35-40% on average. Understanding nitrogen dynamics in these sites will help direct future restoration efforts focused on nutrient reduction.

HOW DO METABOLIC STOICHIOMETRIC RATIOS INFLUENCE WHOLE-STREAM METABOLISM ESTIMATES FROM DISSOLVED OXYGEN AND CARBON DIOXIDE SIGNALS? [Poster Presentation]

Lyra Reynolds (Primary Presenter/Author)
Montana State University, lareynolds00@comcast.net;

Robert Payn (Co-Presenter/Co-Author)
Montana State University, Montana Institute on Ecosystems, rpayn@montana.edu;

Madison Foster (Co-Presenter/Co-Author)
Montana State University, madisonjfoster@gmail.com;

Abigail Northup (Co-Presenter/Co-Author)
Montana State University, abigailnorthrup.mt@gmail.com;

Qipei Shangguan (Co-Presenter/Co-Author)
University of Montana, qipei.shangguan@umontana.edu;

Michael DeGrandpre (Co-Presenter/Co-Author)
University of Montana, Department of Chemistry and Biochemistry, michael.degrandpre@mso.umt.edu;

Abstract: Models of dissolved oxygen (DO) dynamics in streams typically quantify metabolic rates in terms of oxygen transformation alone, without consideration of ties to carbon dynamics. To understand the influence of primary production (GPP) and respiration (ER) on oxygen and carbon together, some understanding of the associated stoichiometric ratios is required. Our past inverse modeling efforts have suggested that signals of dissolved inorganic carbon (DIC) and DO lead to substantially different estimates of GPP when the ratio of DO production to DIC consumption is assumed to be unity. To better understand this phenomenon, we performed a sensitivity analysis to assess the stoichiometric ratios necessary to rectify the information about metabolism available from DIC and DO. Based on data collected in the Upper Clark Fork River (Montana, USA), these sensitivity analyses suggest that reconciliation of metabolism estimates occurs when the ratio of dissolved inorganic carbon consumed to oxygen produced by GPP is 0.31 and when the ratio of inorganic carbon produced to oxygen consumed by ER is 1.1. Further research on metabolic stoichiometry is a critical step toward using DIC to increase the amount of information available about metabolism from DO alone.

HYPORHEIC ZONE HYDROLOGY IN EXPERIMENTAL ANNULAR FLUMES [Poster Presentation]

Hayley Oakland (Primary Presenter/Author)
Montana State University, hayleyoakland@montana.edu;

Elizabeth Mohr (Co-Presenter/Co-Author)
Montana State University, elizabethjmohr@gmail.com;

Samuel Fritz (Co-Presenter/Co-Author)
Montana State University, samuel.fritz2@student.montana.edu;

Geoffrey Poole (Co-Presenter/Co-Author)
Montana State University, Montana Institute on Ecosystems, gpoole@montana.edu ;

Lindsey Albertson (Co-Presenter/Co-Author)
Montana State University , lindsey.albertson@montana.edu;

Abstract: Experimental flumes are useful analogs for the study of ground and surface water exchange in streams. Annular flumes containing stream substrate may serve as useful systems to study hyporheic hydrology because water is continuously in contact with the substrate. However, the conformity between annular flume hydrology and known hyporheic dynamics has never been explored. We monitored salt tracers under alternative annular flume configurations and compared results to a power law residence time distribution (RTD) commonly seen in natural systems. We explored variability in the RTD associated with sediment dune shape, water pump placement, and flume water draw-down. Annular flumes exhibited a power law RTD under a variety of configurations. Our results suggest that the use of annular flumes can reproduce realistic hyporheic hydrology, particularly the power law RTD.

NUTRIENT EXCRETION BY STREAM FISH IN BRAZIL’S ATLANTIC RAINFOREST: TESTING ECOLOGICAL THEORIES [Poster Presentation]

Priscila Cunha (Primary Presenter/Author)
Universidade do Estado do Rio de Janeiro, priscilacunhaoli@gmail.com;

Eugenia Zandona (Co-Presenter/Co-Author)
Universidade do Estado do Rio de Janeiro, eugenia.zandona@gmail.com;

Vinicius Neres-Lima (Co-Presenter/Co-Author)
Universidade do Estado do Rio de Janeiro, vinicius.lima.eco@gmail.com;

Peter B. McIntyre (Co-Presenter/Co-Author)
Cornell University, pmcintyre777@gmail.com;

Abstract: Recent discussions of the factors regulating nutrient excretion by fish have focused on predictions from Ecological Stoichiometry (ES) and the Metabolic Theory of Ecology (MTE). ES posits that imbalances between the composition of the diet and body tissues should determine nutrient excretion rates. Whereas, MTE states that metabolism, mostly influenced by body size and temperature, are the primary controls on nutrient excretion. Each framework has been supported by data, but they are rarely tested together. In this study, we measured excretion rates of nitrogen (NH4) and phosphorus (SRP), body N:P stoichiometry, body size, and temperature for 12 species of fish from an Atlantic rainforest stream in Brazil. We fitted 8 separate models reflecting different combinations of ES (body N:P, armor classification, and feeding guild) and MTE (body size, temperature) variables. For both N and P excretion, only body size was included in the best model (scalling coefficient of 0.55 for N and 0.64 for P). Therefore, we conclude that the ES framework has relatively little predictable effect on nutrient excretion compared to the scaling of metabolism with body size.

RIPARIAN VEGETATION IS THOUGH, WITH MANY CHEMICAL DEFENSES AND LOW NUTRIENTS ALONG A NEOTROPICAL ALTITUDE GRADIENT [Poster Presentation]

Pavel Garcia (Primary Presenter/Author)
Organismal Biology, Ecology and Evolution Program, University of Montana, pavel.garciasoto@umontana.edu;

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

Abstract: Tropical riparian vegetation seems to be poor on nutrients and has a great amount of chemical and physical defenses. Several studies propose that tropical riparian vegetation at higher altitudes would have traits more similar to temperate riparian vegetation, becoming a better food source for aquatic shredders. Here, we assessed traits of chemical and physical defenses and nutrient content of 70 neotropical plant species along an altitudinal gradient. We expected a negative relationship between chemical and physical defenses and altitude, while a positive relationship between nutrient content and altitude. We sampled fresh shed leaf in 5 streams along an altitudinal gradient from 160- 2000 masl, and measured % P, %N, %Phenols, % Tannin, % Lignin, and % Cellulose. Results show a high variation among the 70 tested species. The dominance of high chemical and physical defenses among all sites, independently of altitude. The prevalence of low-quality leaf litter suggests that other factors such as water temperature would explain the higher diversity of shredders observed at high altitudes in tropical streams.

Temperature effects on nutrient uptake in heterotrophic streams [Poster Presentation]

Nathan Tomczyk (Primary Presenter/Author)
University of Georgia, nathan.tomczyk@gmail.com;

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

Anna Kaz (Co-Presenter/Co-Author)
University of Tennessee, akaz@vols.utk.edu;

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

Vlad Gulis (Co-Presenter/Co-Author)
Coastal Carolina University, vgulis@coastal.edu;

Jonathan P. Benstead (Co-Presenter/Co-Author)
The University of Alabama, jbenstead@ua.edu;

Abstract: Warming is expected to increase the rates of biological reactions in stream ecosystems, with unknown consequences for the linked cycling of carbon, nitrogen, and phosphorus. Nutrient uptake may increase proportionally to respiration with increases in temperature; however, if the carbon or nutrient use efficiency of microbial communities changes systematically with temperature, the relationship between nutrient uptake and temperature may deviate from that of respiration with temperature. We conducted a laboratory experiment to test whether the temperature sensitivities of respiration and nutrient uptake deviate in natural heterotrophic communities. We conditioned leaf litter in natural streams, brought the leaves into the laboratory, and measured the uptake of phosphorus across a range of temperatures (4-20 C) using dark-bottle incubations. We found that the temperature sensitivity of phosphorus uptake is considerably lower (0.40 eV) than that predicted for respiration (0.65 eV), suggesting that nutrient uptake rates may increase less than respiration rates with warming. Thus, as rates of carbon loss outpace increases in phosphorus uptake, we may expect relatively less phosphorus to be retained in forested headwater streams as they warm.

USING STREAM NITRATE SIGNALS TO UNDERSTAND LANDSCAPE CONTROLS ON STREAM CHEMISTRY [Poster Presentation]

Madison Foster (Primary Presenter/Author)
Montana State University, madisonjfoster@gmail.com;

Robert Payn (Co-Presenter/Co-Author)
Montana State University, Montana Institute on Ecosystems, rpayn@montana.edu;

Stephanie Ewing (Co-Presenter/Co-Author)
Department of Land Resources and Environmental Sciences, Montana State University, Bozeman, MT, USA, stephanie.ewing@montana.edu;

Caitlin Mitchell (Co-Presenter/Co-Author)
Montana State University, mitchellcm17@gmail.com;

Ann Marie Reinhold (Co-Presenter/Co-Author)
Montana State University, Montana Institute on Ecosystems, reinhold@montana.edu;

Matthew Driesler (Co-Presenter/Co-Author)
Montana State University, matthew.driesler@student.montana.edu;

Abstract: Stream nitrate signals reflect spatially aggregated biogeochemical and physical processes across a watershed and within the stream ecosystem. Stream processing and mixing of inflows with variable nitrate concentrations influence diel variation in nitrate signals in distinct ways, but the controls on the relative influence of the landscape units driving these processes remain unclear. We hypothesize that autotrophic uptake within the stream ecosystem combines with variable hydrologic connectivity with discrete landscape units to create distinct daily patterns of nitrate concentrations in parcels of water traveling a stream reach. We measured high-frequency changes in nitrate concentrations for parcels of water traveling reaches of two agricultural headwater streams in Central Montana. While both streams are highly productive, they have different hydrogeologic settings and varying contributions from riparian-processed low-nitrate water and upland high-nitrate waters. Preliminary data show differences between streams in the phase and amplitude of diel nitrate processing signals, as well as variation in daily average nitrate processing. These results suggest landscape controls on the influence of inflowing waters on diel variation in nitrate processing and stream nitrate concentrations.