SFS Annual Meeting

6/03/2024  |   13:30 - 13:45   |  Salon 5/6

MODELING RIVERINE MACROPHYTE GROWTH TO IMPROVE ECOLOGICAL OUTCOMES OF RIVER MANAGEMENT Macrophytes play diverse ecological roles in rivers, from supporting local biodiversity and intercepting nutrients, sediment, and pollutants, to shading out other primary producers, growing invasively, and interfering with human water use. Because of these varied environmental impacts, it is often useful to model macrophyte growth numerically, but riverine macrophytes have received relatively little modeling attention compared with plants in many other aquatic habitats, despite the unique geophysical conditions in rivers. To address this, we performed a systematic literature review of riverine macrophyte growth models, and developed a new model as a case study. Our objectives were to compile existing approaches and highlight future directions for model development, create a conceptual framework to guide formulations of macrophyte growth, and use our case study to produce a generalizable, broadly applicable modeling tool. Our literature review identified 12 published models or model families simulating riverine macrophyte growth over time. Almost all of them included light availability, nutrient and temperature limitation of photosynthesis, and mortality; however, processes such as dispersal, herbivory, scour, burial, and desiccation were scarce. In our case study, simulating the growth of Podostemum ceratophyllum in the Middle Oconee River in Georgia, we show that the conceptualization of growth, herbivory, and scour can have strong impacts on model outputs. These results highlight both the importance of detailed natural history data on study species, and the power of models to help address questions in macrophyte ecology.

Lee Dietterich (Primary Presenter/Author), Haverford College; US Army Engineer Research and Development Center, Environmental Laboratory, lee.dietterich@gmail.com;

Suhey Ortiz Rosa (Co-Presenter/Co-Author), US Army Engineer Research and Development Center, Environmental Laboratory, suhey.ortiz@upr.edu;

Kyle McKay (Co-Presenter/Co-Author), Environmental Laboratory, U.S. Army Engineer Research and Development Center, kyle.mckay@usace.army.mil;

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6/03/2024  |   13:45 - 14:00   |  Salon 5/6

What is the role of aquatic plants in nitrogen assimilation? In streams, assimilatory uptake accounts for most nitrogen (N) removal. In many streams, assimilatory uptake principally includes epilithic algae, but plants sometimes dominate N uptake. Because plants are larger and longer-lived, they can potentially store N for longer than algae, with consequences for the food web and for downstream water quality. We present a conceptual model for plant N assimilation, based on data from the lower Yakima River (Washington, USA). This lowland agricultural river has abundant water stargrass (Heteranthera dubia), a submergent aquatic plant native to North America. We measured the N content of aboveground tissues via combustion on an elemental analyzer and then scaled those N values to the reach under various biomass scenarios based on data from quadrat samples. Under high biomass conditions (1760 g/m2), aboveground plant tissues store 242,077 kg of N, while under low biomass conditions (219 g/m2), aboveground plant tissues store 30,122 kg of N. This translates to 2 to 8% of the incoming N load. The fate of plant-assimilated N remains unclear, but we hypothesize that rhizomes and roots potentially store N for multiple years, whereas leaves and stems are more likely to move downstream during senescence and high flows. Plant-assimilated N is less likely to move into the food web than algal-assimilated N, given the paucity of herbivores on aquatic plants. Abundant plants potentially drive assimilatory N uptake in some streams and function as a potential N sink, reducing loads to downstream ecosystems.

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

Aaron Pelly (Co-Presenter/Co-Author), Washington State University, aaron.pelly@wsu.edu;

Maryam Akhlaghi Ghanbari (Co-Presenter/Co-Author), Washington State University, m.akhlaghighanbari@wsu.edu;

Jimmy Clifford Oppong (Co-Presenter/Co-Author), Charles University, oppongj@natur.cuni.cz;

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6/03/2024  |   14:00 - 14:15   |  Salon 5/6

Limitation of submerged aquatic vegetation growth by fish in a eutrophic wetland The Everglades Stormwater Treatment Areas (STAs) are large shallow wetlands constructed to remove excess phosphorus (P) from water before it is released to the oligotrophic Everglades. Beds of submerged aquatic vegetation (SAV) are an essential part of P removal, promoting P retention by direct (uptake into plant tissue) and indirect (photosynthetically driven flocculation and settling) mechanisms, facilitating long-term storage in soils, and stabilizing sediments to prevent settled nutrient resuspension. Herbivory and bioturbation by fish, plus wind and water flow can uproot or smother SAV, leading to SAV loss and areas of bare sediment. We manipulated large fish access to areas in the STAs for 12 weeks to evaluate whether fish, particularly tilapia (Orechromis spp.) which are common large bioturbators, limit establishment of SAV (Chara spp., Najas marina, and Najas guadalupensis) or growth of existing beds. Exclosures placed in areas of bare sediment promoted SAV establishment and growth relative to surrounding open controls (mean final SAV cover of 25% in exclosures versus 0.2% in controls). Exclosures placed over existing SAV beds did not affect SAV growth when compared to SAV in control plots. Our results suggest that fish may disrupt the establishment of new SAV propagules in bare areas but do not suggest they are capable of triggering SAV bed collapses (large-scale SAV loss) on their own at typical densities. Limiting fish access to bare areas of the STAs may be a useful management tool to support SAV establishment, but understanding the reasons behind SAV bed loss will require additional study.

Janelle Goeke (Primary Presenter/Author), Casco Bay Estuary Partnership, jgoeke@fiu.edu;

Mark Cook (Co-Presenter/Co-Author), South Florida Water Management District, Mcook@sfwmd.gov;

Sue Newman (Co-Presenter/Co-Author), South Florida Water Management District, snewman@sfwmd.gov;

Sarah Bornhoeft (Co-Presenter/Co-Author), South Florida Water Management District, sbornhoe@sfwmd.gov;

Camille Herteux (Co-Presenter/Co-Author), South Florida Water Management District, cherteux@sfwmd.gov;

Nathan Dorn (Co-Presenter/Co-Author), Florida International University, ndorn@fiu.edu;

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6/03/2024  |   14:15 - 14:30   |  Salon 5/6

Spatial and temporal patterns of filamentous algae and nutrient conditions in the Buffalo National River, 2018-2023 Filamentous algae (FA) blooms and their link to changing water quality, land use, and karst surface-water/groundwater interactions are of increasing concern in the Buffalo National River in Arkansas. From 2018 through 2023, the USGS, in cooperation with multiple partners, investigated patterns of filamentous algae coverage and nutrient concentrations among 12 mainstem sites, 6 spring-fed sites, and 6 gravel-bar sites (temporary shallow wells) along ~112 km of the Buffalo River. The occurrence and coverage of FA blooms varied over time among mainstem sites, where blooms often covered 40% to 80% of the streambed during the growing season (summer/fall) in most years. FA blooms were rare in the more upstream sites, being most common among mainstem sites lower in the watershed. Spatial and temporal relations of FA coverage to other physical habitat features (stream depth, width, substrate, etc.) among sites were not obvious. Direct positive correlation between FA blooms and nutrient concentrations at mainstem sites was also not observed where nutrient concentrations were consistently very low. Nutrient concentrations in spring-fed sites and gravel-bar sites, however, were consistently greater than in mainstem sites and indicate the potential importance of these more complicated, subtle, and sometimes overlooked pathways in influencing nutrient delivery and ecosystem responses. Additionally, aspects of climate and hydrology also likely had strong influence on FA blooms, in which the timing and magnitude of periodic storm events during the 2019 growing season appears to have limited FA compared to other years.

Lucas Driver (Primary Presenter/Author), USGS, Lower Mississippi-Gulf Water Science Center, ldriver@usgs.gov;

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6/03/2024  |   14:30 - 14:45   |  Salon 5/6

DUCKWEED-MEDIATED MOSQUITO SUPPRESSION: MECHANICAL OR CHEMICAL? Mosquitoes (Diptera: Culicidae) vector multiple diseases capable of overwhelming underdeveloped medical systems. Non-chemical control methods are needed to impair populations without off-target effects. Prior research confirms a lethal effect on larval mosquitoes by duckweed (Arales: Lemnaceae), though the mechanism behind such effects is poorly understood. Through an experimental study, I examined if duckweed, a floating aquatic plant found globally, impairs larval mosquito survival through mechanical obstruction (i.e., blocking the siphon from piercing the water surface) or chemical inhibition (i.e., secondary metabolites). To test each possible mechanism, a microcosm experiment was conducted in a laboratory setting. Containers consisted of pondwater, 8 larvae (Culex spp.), zooplankton (Daphnia spp.) and the assigned treatment. To test chemical inhibition, jars were steeped with pulverized duckweed; for mechanical obstruction, jars were populated with duckweed. Both treatments were compared to a control (containing solely pondwater). Larvae were introduced at the second instar and received 5mL of pondwater every three days to ensure microbes were present to act as a food source. Emergence, survival, and time to pierce the siphon above the water surface after a disturbance were tested across treatments in search of an impairing effect. I found no differences in survival, emergence, or time to pierce between the control and the chemical inhibition treatment. Significant differences for all tested metrics were found between the mechanical obstruction treatment and the remaining treatments. The difference in survival suggests that mechanical obstruction may act as an effective cultural control when establishing an integrated pest management system for mosquitoes.

Trevor Rallo (Primary Presenter/Author), Southern Illinois University Edwardsville, trallo@siue.edu;

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