5/21/2015  |   10:30 - 10:45   |  102B

INFLUENCE OF SUBSTRATE SIZE AND BIOFILM GROWTH ON ANOMALOUS SOLUTE TRANSPORT IN EXPERIMENTAL STREAMS AT ND-LEEF In alluvial systems, biofilms grow on solid surfaces in benthic and hyporheic regions where they process dissolved solutes. Biofilms alter substrate characteristics and can change dynamics in porous space. We hypothesized that biofilms would increase solute residence time distributions (RTD) in benthic and (micro)hyporheic regions. Using experimental streams at Notre Dame's Linked Experimental Ecosystem Facility (ND-LEEF), we had four different substrate configurations: two homogeneous sediments (all pea gravel vs. all coarse gravel) and two heterogeneous sediments (alternating sections of each vs. well-mixed, 50/50 distribution). We measured the RTDs of the rhodamine-WT tracer multiple times over 5mo of biofilm colonization and growth. We found that as biofilm growth increased, the power-law exponent of the RTD decreased, with the tails of the distributions becoming heavier, suggesting prolonged retention in the presence of biofilms. Although the underlying substrate signature persisted over time, with coarse gravel streams clearing faster than streams with pea gravel, all streams had a similar pattern of the power-law exponent decreasing over time as biofilm developed. These results emphasize the dynamic relationship and feedback between the physical and biological environments.

Antoine Aubeneau (Primary Presenter/Author), Purdue University, aubeneau@gmail.com;


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


Brittany Hanrahan (Co-Presenter/Co-Author), USDA Agricultural Research Service, br.hanrahan@gmail.com;


Diogo Bolster (Co-Presenter/Co-Author), University of Notre Dame, diogo.bolster.5@nd.edu;

5/21/2015  |   10:45 - 11:00   |  102B

TURBULENT HYPORHEIC EXCHANGE IN PEMEABLE SEDIMENTS Solute delivery from the water column into a streambed strongly influences metabolism in rivers. Current hydrological models simplify surface-subsurface (hyporheic) exchange by treating each domain separately, constraining turbulent flows to the water column. Studies have shown, however, that turbulence penetrates into permeable sediments. Evidence is lacking for how this highly coupled flow regime influences hyporheic exchange.

We characterized the dynamics of turbulent exchange between surface and porewaters in a 2.5 m recirculating flume. The channel was packed with 3.8 cm PVC spheres to form a coarse gravel bed, with a total depth of 21 cm. We implanted microsensors onto an array of spheres to measure in situ salt concentrations within the streambed. Water was recirculated in the channel, and concentrated salt solution was continuously injected upstream of the sensor array.

We observed high-frequency (1-10 Hz) concentration fluctuations at bed depths of at least 4.75 cm, and sporadic low-frequency fluctuations at depths of 12.5 cm. Spectral analysis revealed increased filtering of high frequencies with depth. These results demonstrate that turbulent mixing impacts hyporheic exchange deep into permeable streambeds.

Kevin Roche (Primary Presenter/Author), Northwestern University, kevinroche2012@u.northwestern.edu ;


Aaron Packman (Co-Presenter/Co-Author), Northwestern University, a-packman@northwestern.edu;

5/21/2015  |   11:00 - 11:15   |  102B

LIMITS OF TRANSIENT STORAGE ASSUMPTIONS FOR HEAT: USING RESIDENCE TIME DISTRIBUTION TO ESTIMATE MEAN TEMPERATURE OF HYPORHEIC DISCHARGE MONTANE ALLUVIAL STREAMS Hyporheic influence on channel temperature is most prominent in streams with expansive (hyporheic cross section >> channel cross section) coarse grained aquifers. We combined estimates of residence time distribution with a novel application of the advection-dispersion equation to calculate the mean temperature patterns of hyporheic discharge from expansive aquifers. Our results show that mean hyporheic discharge temperature is substantially different from the mean temperature of the hyporheic zone. Yet some transient storage models calculate solute or heat exchange between the channel and transient storage zone based on a mean concentration or temperature in the transient storage zone. Such an assumption may be reasonable for a small hyporheic zone, but misrepresents the influence of an expansive hyporheic zone on surface water temperature. Results from a prototype, quasi-1-D model -- which subdivides the hyporheic zone by residence time and simulates heat transfer among the sub-zones and the channel –- provides a more complete representation of hyporheic-channel heat dynamics in alluvial, montane streams.

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


Byron Amerson (Co-Presenter/Co-Author), Montana State University, byron.amerson@gmail.com;


Katie Fogg (Co-Presenter/Co-Author), Montana State University, s.katie.fogg@gmail.com;


Scott O'Daniel (Co-Presenter/Co-Author), Confederated Umatilla Tribes, scottodaniel@ctuir.org;


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


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


Clemente Izurieta (Co-Presenter/Co-Author), Montana State University, Montana Institute on Ecosystems, clemente.izurieta@cs.montana.edu;

5/21/2015  |   11:15 - 11:30   |  102B

EULERIAN VERSUS LAGRANGIAN PERSPECTIVES ON LIGHT AVAILABILITY IN A LARGE RIVER Large rivers have played a minor role in lotic ecosystem ecology historically dominated by streams. One limitation to studying rivers is methodological: Eulerian techniques developed in streams are effective for measuring benthic processes that influence well-mixed systems, but are inappropriate for measuring variability within the water column. As river size increases, the spatial scale of movement and environmental heterogeneity experienced by planktonic organisms increases, requiring a Lagrangian approach to measure exposure and response to environmental conditions. To explore the difference between Eulerian and Lagrangian approaches, we examined light within the water column of a large river (Neuse River; Q = 68 m³ s^-1 during study) using an autonomous, neutrally-buoyant Lagrangian drifter (HydroSphere, Planktos Instruments) combined with stationary Eulerian sensor nests. The drifter cycled constantly throughout the water column while traversing 42 km of river in 24 hr; Lagrangian light intensity was twice as variable compared to sensor nests (Eulerian) bracketing the reach. By measuring this Lagrangian variability in light and travel time we can better integrate large river processes with existing conceptual frameworks in lotic ecosystem ecology.

John Gardner (Primary Presenter/Author), Duke University, john.r.gardner@duke.edu;


Scott Ensign (Co-Presenter/Co-Author), Stroud Water Research Center, ensign@stroudcenter.org;


Martin Doyle (Co-Presenter/Co-Author), Duke University, martin.doyle@duke.edu;


Ryan Neve (Co-Presenter/Co-Author), Planktos Instruments, ryan@planktosinstruments.com ;

5/21/2015  |   11:30 - 11:45   |  102B

IS THE LANDCOVER CASCADE SYSTEM-SPECIFIC? A CASE STUDY IN SAND-BED STREAMS OF THE SOUTHEASTERN US SANDHILLS ECOREGION The Landcover Cascade Concept (LCC), developed from high-gradient mountain streams, has not been tested in low-gradient systems, such as in coastal plains streams. We quantified LC, hydrology (Hyd), geomorphology (Geo), habitat (Hab), and macroinvertebrate functional composition (FC) in 42 SE-USA Sandhills streams, and compared 4 structural equation models with LCC using Akaike’s criteria. The primary latent (derived) variable gradients were 1) LC from managed pine plantation to native longleaf pine, 2) Hyd related to increasing low and high stage duration, 3) Geo related to increasing channel enlargement, 4) Hab related to substrate size/ variation and FPOM, and 5) FC related to shredder to filterer/scraper/multivoltine taxa. The hydrology master variable model best explained influence of LC on FC (AIC weight=0.81; FC R2=52%) and thus showed the largest direct effect on biota. Further, the largest indirect effect of LC on FC was mediated by Hyd, suggesting that hydrologic variation related to LC, rather than LC directly, was most important factor linking LC to FC. Results suggest that LCC-predicted direct effects of LC on instream variables do not apply to low-gradient, sand-bed systems.

Stephen A. Sefick (Primary Presenter/Author), Auburn University, sas0025@auburn.edu;


Ely Kosnicki (Co-Presenter/Co-Author), The College at Brockport – State University of New York, ekosnick@brockport.edu;


Michael Paller (Co-Presenter/Co-Author), Savannah River National Laboratory, michael.paller@srnl.doe.gov;


Jack W. Feminella (Co-Presenter/Co-Author), Auburn University, feminjw@auburn.edu;

5/21/2015  |   11:45 - 12:00   |  102B

TROPICAL STREAMS AT RISK: GULLY FORMATION FROM INTENSIVE AGRICULTURE AS DRIVER OF STREAM DEGRADATION Degradation of streams draining intensive agriculture in the humid tropics may be driven by gully formation from the combination of heavy seasonal rainfall associated with agricultural practices. However, the formation of gullies in association with intensive agriculture is rarely assessed. I investigated the impacts of intensive agriculture on gully formation in an area cultivated with sugarcane for over 60 years in Brazil. I used the slope-area criteria to evaluate the relation between existing channel heads and surveyed erosive features using form-based thresholds. Among 137 features surveyed, 98% were permanent and ephemeral gullies; 94% occurred below the threshold line of existing channel heads, suggesting that gullies are being formed in regions unfavorable for gully formation. The presence of gullies in recent stage of formation (i.e., ephemeral gullies, 36% of 137) suggests that sugarcane management enhances gully formation. By exacerbating gullying, intensive agriculture may impair streams as they become more hydrologically connected to their uplands, and excess water and sediments is delivered to stream ecosystems.

Maíra Bezerra (Primary Presenter/Author), University of Maryland, mbezerra@umd.edu;


Margaret Palmer (Co-Presenter/Co-Author), National Socio-Environmental Synthesis Center, mpalmer@sesync.org;


Solange Filoso (Co-Presenter/Co-Author), University of Maryland Center for Environmental Science, filoso@umces.edu;


Silvio Frosini de Barros Ferraz (Co-Presenter/Co-Author), University of São Paulo, USP/ESALQ, Dept of Forest Sciences, Brazil, silvio.ferraz@usp.br;