SFS Annual Meeting

6/05/2024  |   10:30 - 10:45   |  Independence Ballroom D

Duckweed enhances carbon emissions but slows the aerobic decomposition of organic matter in small ponds Dense blooms of floating vegetation in the family Lemnaceae (duckweed) are globally ubiquitous in small nutrient-rich bodies of water. Their rapid growth and turnover cover a pond’s surface and limit oxygen diffusion into the water while delivering labile organic matter to sediments, potentially enhancing methane (CH4) emissions. In this study, we hypothesized that while duckweed blooms may enhance emissions of CH4 and carbon dioxide (CO2), induction of hypoxia below the water surface may slow the aerobic decomposition of organic matter. In winter and summer, we sampled twenty small ponds across Jefferson County, KY, and compared diffusive and ebullitive fluxes of CH4 and CO2, dissolved oxygen availability, and sediment organic matter (SOM) concentrations and aerobic decomposition rates in ponds with and without duckweed. CH4 and CO2 fluxes, SOM concentrations, and SOM decomposition rates (with aeration) were significantly higher in duckweed-covered ponds. However, substantially lower oxygen concentrations in duckweed ponds significantly slowed rates of aerobic decomposition. These findings highlight the dual role of duckweed in the carbon balance of small wetlands, as duckweed-covered ponds may simultaneously emit and store more carbon (C). Future efforts must, therefore, weigh these effects of floating plants to obtain a holistic understanding of C cycling in these small ponds.

Mark C. Tierney (Primary Presenter/Author), University of Louisville, mark.tierney@louisville.edu;

John H. Loughrin (Co-Presenter/Co-Author), United States Department of Agriculture, john.loughrin@usda.gov;

Stacy W. Antle (Co-Presenter/Co-Author), United States Department of Agriculture, stacy.antle@usda.gov;

Carlijn Jalink (Co-Presenter/Co-Author), Wageningen University, carlijn.jalink@wur.nl;

Jeroen de Klein (Co-Presenter/Co-Author), Wageningen University, jeroen.deklein@wur.nl;

Andrew S. Mehring (Co-Presenter/Co-Author), University of Louisville, andrew.mehring@louisville.edu;

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6/05/2024  |   10:45 - 11:00   |  Independence Ballroom D

Consequences of Freshwater Salinization for aquatic bacterial community, ecosystem function, and risk of impairment Salinization of freshwater aquatic ecosystems is a widespread and chronic challenge degrading water quality and stressing aquatic ecosystems. Salinization intensity can range from relatively small concentrations to pulses of marine concentrations. Very high salinity is a known stressor for aquatic communities adapted to freshwaters; however, most chronic salinization levels fall within the freshwater range. But surprisingly, we know the least about the response of microbial communities to salinization and resulting biogeochemistry in this range. Our overarching objective has been to determine the microbial and biogeochemical consequences of salinization within the freshwater range. Our approach combines laboratory mesocosm experiments and watershed observations. In controlled mesocosms, we find that small increases in salinity within the freshwater range have a strong effect on microbial community diversity, microbially mediated ecosystem functions, carbon partitioning, and the survival of fecal indicator bacteria (FIB). The effect size is mediated by salt type, where specific ions can alter the impacts of salinization. In watersheds of Virginia, we find similar changes in the levels of FIB concurrent with the laboratory experiments. Cumulatively, these results indicate that even mild freshwater salinization could have significant consequences for aquatic ecosystem functions and the risk of bacterial impairments.

Meredith Steele (Primary Presenter/Author), Virginia Polytechnic Institute and State University, steelem@vt.edu;

Brian Badgley (Co-Presenter/Co-Author), Virginia Polytechnic Institute and State University, badgley@vt.edu;

Stephen DeVilbiss (Co-Presenter/Co-Author), U.S. Geological Survey (USGS), sdevilbiss@usgs.gov;

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6/05/2024  |   11:00 - 11:15   |  Independence Ballroom D

Growth, loss, and benthic recruitment of phytoplankton in a mid-order river Accumulation of suspended algae in mid-size rivers is generally limited by transport time, yet occasional accrual of phytoplankton biomass along river reaches can suggest unrealistically high growth rates of river algae. Hydraulic storage in backwaters and benthic retention are two hypotheses that can explain this phenomenon. However, both hypotheses were developed to explain phytoplankton dynamics during baseflow conditions. At high flows (i.e., storm events), backwaters become highly connected to the main river flow and resuspension of benthic algae depletes quickly due to substantial shear stress. Under these conditions, phytoplankton populations are effectively flushed out of the system and reseted to a recovery period. We are interested in how net planktonic growth, deposition, and benthic recruitment influence phytoplankton biomass across changing conditions of river flow. Here, we use continuous data upstream and downstream of a 20-km long river section with nine consecutive low-head dams within it to model phytoplankton dynamics over nearly 3 years with Bayesian parameter estimation. We estimate model priors for water residence time (3.5 - 15.2 hours), chlorophyll concentration in backwaters (0.3 - 12.7 ug/L), and benthic chlorophyll (6.6 - 101.3 mg/m2) from multiple lagrangian and synoptic samplings along the reach. Preliminary results show a small contribution of slow-moving waters to river phytoplankton accrual despite the numerous low-head dams representing between 10 - 28% of the reach volume. Instead, our results seem to support the benthic retention hypothesis and its effects on river phytoplankton dynamics before and after storm events.

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

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

Rachel Leonard (Co-Presenter/Co-Author), Stroud Water Research Center / University of Delaware, rleonard@stroudcenter.org;

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

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

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6/05/2024  |   11:15 - 11:30   |  Independence Ballroom D

From the Endosymbiont to the Ecosystem: Tripartite Symbiosis Drives Phenology of River Carbon and Nitrogen Cycling Microscale symbioses can be critical to ecosystem functions, but the nutrient dynamics of these interactions in nature are often cryptic. We used stable isotopic tracers and nanoSIMS imaging to quantify the phenology of nitrogen and carbon dynamics as related to natural succession in a three-member symbiotic relationship that supports a summertime salmon-bearing river food web. After winters with riverbed-scouring flooding, the macroalga Cladophora glomerata uses nutrients in spring runoff to grow streamers up to 11 meters long. During summer flow recession as nitrogen inputs wane, Cladophora becomes densely epiphytized by photosynthetic algae, including three species of Epithemia, a diatom with nitrogen-fixing endosymbionts descended from the free-living cyanobacterium Crocosphaera sp. (formerly Cyanothece sp.). While total carbon fixation rates of assemblages declined during epiphyte succession on Cladophora, nitrogen fixation rates increased as Epithemia spp. became dominant, enhancing food web productivity. At the microscale, Cladophora C-fixation declined to near zero, while Epithemia C-fixation increased. In response to demand for nitrogen, the diatom allocates high levels of newly fixed C to its diazotrophic obligate endosymbiont, which results in these proto-organelles having the highest rate of C and N accumulation in this tripartite symbiotic relationship during the biologically productive season, and one of the highest rates of nitrogen fixation reported for any river ecosystem.

Jane Marks (Primary Presenter/Author), Northern Arizona University, jane.marks@nau.edu;

Mary Power (Co-Presenter/Co-Author), University of California, Berkeley, mepower@berkeley.edu;

Steven Thomas (Co-Presenter/Co-Author), University of Alabama, sathomas16@ua.edu;

Michael Zampini (Co-Presenter/Co-Author), Northern Arizona University, mcz39@nau.edu;

Saeed Kariunga (Co-Presenter/Co-Author), Northern Arizona University, shk45@nau.edu;

Peter Weber (Co-Presenter/Co-Author), Lawrence Livermore National Lab, weber21@llnl.gov;

Ty Samo (Co-Presenter/Co-Author), Lawrence Livermore National Lab, samo1@llnl.gov;

Bruce Hungate (Co-Presenter/Co-Author), Northern Arizona University, bruce.hungate@nau.edu;

Jennifer Pett-Ridge (Co-Presenter/Co-Author), Lawrence Livermore National Lab, pettridge2@llnl.gov;

Raina Fitzpatrick (Co-Presenter/Co-Author), Northern Arizona University, rmf273@nau.edu;

Victor Leshyk (Co-Presenter/Co-Author), Northern Arizona University, victorleshyk@esedona.net;

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6/05/2024  |   11:30 - 11:45   |  Independence Ballroom D

MARSH MADNESS: ASSESSING COMPLEX STREAM SOLUTE PATTERNS IN A LOW-RELIEF, WETLAND-DOMINATED CATCHMENT IN SOUTHWESTERN MICHIGAN In low-relief, spatially-heterogeneous catchments, the distribution of wetlands creates distinctive, complex hydro-biogeochemical processes that influence stream biogeochemistry. However, understanding biogeochemistry at the catchment scale for wetland-dominated landscapes is limited due to methodological limitations and a historical research emphasis on steeper upland catchments. Consequently, we address this unique knowledge gap by investigating solute patterns across the Augusta Creek catchment, in southwestern Michigan. Augusta Creek is a third-order, groundwater-fed stream with a stable flow regime and large wetlands distributed throughout the entire catchment. We used a combination of in situ high-frequency sensors and repeated synoptic sampling to assess patterns of stream, wetland, and overall catchment biogeochemistry throughout different hydrologic and seasonal conditions. To assess the influence of short-term hydrologic variability on solute processes, we used high-frequency dissolved organic carbon (DOC) and nitrate (NO3-) data to construct concentration-discharge (C-Q) relationships for multiple wetland and stream sites. Overall, the C-Q analyses of the stream-dominated site showed that the concentration of DOC consistently increased concurrently with discharge, while NO3- decreased. However, at the outlet of the wetland-dominated site, the C-Q relationships were more complicated, with a lagged positive response of DOC as flow increased, while NO3- C-Q was more stable with a slight negative relationship. Meanwhile, synoptic data revealed that biogeochemical conditions from groundwater contributions may be the most significant control on solute export patterns at the catchment scale. Therefore, using both sampling strategies may be necessary to understand how spatial heterogeneity and hydrologic complexity influence C-Q relationships in these “maddeningly” complex wetland-dominated catchments.

Caroline Weidner (Primary Presenter/Author), Michigan State University, weidne11@msu.edu;

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

Arial Shogren (Co-Presenter/Co-Author), University of Alabama, ashogren@ua.edu;

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6/05/2024  |   11:45 - 12:00   |  Independence Ballroom D

Seasonal effects of urbanization on dissolved carbon quality and quantity in the Johnson Creek Watershed (Oregon, USA) Dissolved organic carbon (DOC), a major flux of carbon in streams, is a vital yet often overlooked parameter in urban stream ecology, even though it is an important factor for aquatic food webs and other key biogeochemical processes. Urban development impacts the quantity and quality of DOC in streams, and this influence likely varies seasonally with changes in hydrologic and DOC inputs. Johnson Creek watershed, in the Portland, Oregon, metro area, provides an excellent setting to study the effect of urbanization on changes in DOC quantity and quality. Urban land use increases in the watershed from upstream to downstream, from around 20% developed upstream to around 60% near the mouth. We hypothesize that DOC quantity will increase, and that sources will change longitudinally as impervious surface cover and urban inputs (sewer and runoff) increase. To quantify DOC quantity and quality changes, surface water samples were collected weekly from three Johnson Creek locations co-located with USGS gaging stations. In summer and fall, DOC concentrations were higher at the upstream stations (3-4 mg L-1) than at the lower, more urban station (1 mg L-1), while samples taken in winter months showed no significant difference. Additionally, fluorescence data indicated more autochthonous organic matter in the urban site compared to the upper watershed sites, which increased through the fall. Changes in water chemistry along this gradient of increasing imperviousness and development suggest an urban effect that differs between seasons. During winter, homogenization of water quality parameters likely occurs due to increases in stream flow.

Jacob Rudolph (Primary Presenter/Author), Smithsonian Environmental Research Center, rudolphjc@icloud.com;

Jennifer Morse (Co-Presenter/Co-Author), Portland State University, jlmorse@pdx.edu;

Kristina Hopkins (Co-Presenter/Co-Author), U.S. Geological Survey, khopkins@usgs.gov;

Rebecca Hale (Co-Presenter/Co-Author), Smithsonian Environmental Research Center, haler@si.edu;

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