SFS Annual Meeting

6/04/2024  |   15:30 - 15:45   |  Freedom Ballroom H/G

A LOTIC EMERGENT MACROPHYTE SPECIES (AMERICAN WATER WILLOW) MODIFIES HYPORHEIC BIOGEOCHEMICAL CONDITIONS IN AN URBAN STREAM Emergent freshwater stream macrophytes form a rhizosphere in the hyporheic zone. This ecohydrological interface is a key component of stream ecosystems and the global biogeochemical flux of nitrogen, but the role of lotic emergent macrophytes in this system remains poorly understood. We investigated the effect of American water willow (Justicia americana) on surface-subsurface exchange and biogeochemical conditions in the hyporheic zone of an urban stream. Justicia is flood-resilient and unique among lotic macrophytes for its capacity to generate massive root systems, which comprise a significant portion of the streambed. We expected these plants to modify the hyporheic zone through physical (change in hyporheic flow paths, increased water residence time) and biological processes (root system exudates and biological nutrient uptake). Finally, we expected these modifications to vary across seasons, responding to differences in plant phenology and environmental flow conditions. We installed 21 hyporheic wells within and near two elongated Justicia beds and sampled surface and hyporheic water roughly biweekly over 9-months. We measured specific conductivity, dissolved oxygen, and temperature, and we took water samples for analyses of chloride, nitrate, ammonium, and total dissolved nitrogen. We observed significant biogeochemical differences between control and macrophyte bed hyporheic samples relative to surface water. These biogeochemical differences persisted across time, through seasonal plant flowering and senescence, and through changes in stream flow. Justicia beds appear to insulate the hyporheic zone beneath them from changes in surface water chemistry, while driving accumulation of high inorganic nitrogen concentrations, particularly ammonium, in hyporheic water among the roots.

Jacob Moore (Primary Presenter/Author), University of Missouri, jam4k4@umsystem.edu;

Alba Argerich (Co-Presenter/Co-Author), University of Missouri-Columbia, argericha@missouri.edu;

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6/04/2024  |   15:45 - 16:00   |  Salon 3/4

HOW DO RIPARIAN TREES BY INTERMITTENT STREAMS MOVE WATER ACROSS THE SURFACE-GROUNDWATER INTERFACE? Intermittent streams, those that temporarily cease to flow or dry completely, comprise about 60% of global river miles. Although intermittent rivers are the rule rather than the exception, fundamental knowledge gaps exist around the role riparian trees play in the ecohydrology of these environments. This study addresses (1) What are the sources, magnitude, and timing of water uptake and redistribution by riparian trees? And (2) How do these vary across space (i.e., an intermittency gradient) and time (i.e., the wet and dry seasons) in an intermittent stream? We used Chalone Creek--an intermittent stream in Pinnacles National Park, CA where 90% of the network dries for part of the year--as a model ecosystem. We instrumented a riparian Salix laevigata (red willow) to monitor its sap flow dynamics, collected stable isotope source water data (hydrogen ?D and oxygen ?18O), and developed time-series analysis on five years of groundwater levels from 3 wells spanning the intermittency gradient. We found that riparian trees rely on groundwater during the dry season (May to November), switching to other sources during the wet season. We also documented the hydraulic descent (“banking”) of shallow soil moisture down to deeper soils or groundwater via tree roots during the wet season, and the hydraulic lift (“withdrawing”) of groundwater up to shallow soils during the dry season. Because hydraulic lift by trees may offer moist refugia when it matters most to drought-stressed organisms and resistance forms, these results may have implications for the invertebrate “seedbank” that persists in the hyporheic zone.

Rose Mohammadi (Primary Presenter/Author), Department of Environmental Science, Policy, and Management, University of California, Berkeley, rmohammadi@berkeley.edu;

Claire Tiedeman (Co-Presenter/Co-Author), U.S. Geological Survey, tiedeman@usgs.gov;

Todd Dawson (Co-Presenter/Co-Author), Department of Integrative Biology, University of California, Berkeley, tdawson@berkeley.edu;

Albert Ruhi (Co-Presenter/Co-Author), Department of Environmental Science, Policy, and Management, University of California, Berkeley, albert.ruhi@berkeley.edu;

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6/04/2024  |   16:00 - 16:15   |  Salon 3/4

"WETSPOTS' OF BIODIVERSITY: HYPOTELMINORHEIC SEEPAGE SPRINGS IN WASHINGTON, D.C. ARE REVEALED TO CONTAIN UNPRECEDENTED DIVERSITY Groundwater environments are often championed for their unique geology/ecology and the endemic biodiversity which they contain. Despite this, many groundwater systems remain poorly understood. Hypotelminorheic springs are characterized by small flows of water in depressions lined with decaying leaves. Over 150 such springs in the Washington DC metropolitan area host assemblies of stygobitic taxa, some of the most common of which are amphipods in the genus Stygobromus. Several species have been recorded from the DC area, including the federally listed S. hayi; however the most common and widely distributed taxon is Stygobromus tenuis potamacus, which has been recorded throughout the region. Like many amphipod taxa, Stygobromus are highly prone to endemism, and the large range occupied by S. t. potamacus is curious, especially given the patchwork of hypotelminorheic springs, which are likely isolated from each other even at close distances. Stygobromus functions as an ideal model to test the hypothesis of isolation among these habitats. Molecular phylogenetic analyses of springs from the DC metropolitan area reveal surprising levels of diversity, with most springs harboring unique MOTUs, even at remarkably close distances (1-10 km) and within drainage basins. These data suggest hypotelminorheic spring systems act as more prevalent biodiversity hotspots than previously considered. The geographic locations of such springs (in the middle of the developed DC metropolitan area) also highlight conservation concerns for both the habitats and organisms occupying them.

Andrew Cannizzaro (Primary Presenter/Author,Co-Presenter/Co-Author), Miami University, Cannizag@miamioh.edu;

Matthew L. Niemiller (Co-Presenter/Co-Author), The University of Alabama in Huntsville, matthew.niemiller@uah.edu;

Thomas Sawicki (Co-Presenter/Co-Author), Florida Agricultural and Mechanical University, thomas.sawicki@famu.edu ;

David Culver (Co-Presenter/Co-Author), American University, dculver@american.edu ;

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6/04/2024  |   16:15 - 16:30   |  Salon 3/4

: Influence of Ecosystem Engineer Density on Stream Macroinvertebrate Communities Ecosystem engineering can control the structure and function of freshwater communities. For example, limited evidence has shown that the silk-spinning behavior of caddisfly larvae (Trichoptera: Hydropsychidae) might increase population density and biomass of macroinvertebrate beneficiaries associated with caddisfly biostructures. To assess how macroinvertebrate beneficiaries respond to a range of caddisfly biostructure densities, we manipulated caddisflies and beneficiaries in a randomized, controlled field experiment. We installed stream analogue mesocosms (56cm diameter, 0.13m2 surface area) in Cherry Creek, Montana. Mesocosms were filled with natural sediment and then stocked with representative macroinvertebrate communities from the site. We removed net-spinning caddisflies from the community stocked into control mesocosms and treatment mesocosms were stocked with larval Arctopsyche grandis at densities of 1000, 2500, 3500, or 5000 individuals/m2. The mesocosms incubated for four weeks, during which time they could exchange water with the stream, but invertebrates could not enter or exit the flumes. At the end of the experiment, surviving macroinvertebrates were counted and identified. Caddisfly density reached 15% of target goals across treatments, suggesting low carrying capacity in the flumes. We found little evidence of a relationship between caddisfly density and survival of chironomids. Annelid worms showed weak evidence of a negative relationship and lower survival when caddisfly density was high. Our findings demonstrate that density alone may not be driving the ability of ecosystem engineers to provide habitat to macroinvertebrates. Future research should consider how engineer identity and resource availability may drive the strength and direction of interactions between caddisflies and other macroinvertebrates.

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

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

Anna C. French (Co-Presenter/Co-Author), Montana State University, annafrench.mn@gmail.com;

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;

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6/04/2024  |   16:30 - 16:45   |  Salon 3/4

HOW DOES RIVER-BED COMPOSITION INFLUENCE HYPORHEIC INVERTEBRATES ON A FINE SEDIMENT DEPOSITION GRADIENT? Fine sedimentation (particles < 2mm) and clogging of interstitial pore space is widely considered to be one of the most significant threats to lotic ecosystem integrity and functioning. However, recent research suggests that it isn’t possible to generalise the ecological effects of fine sediment pressure(s) and thus we need to identify the abiotic mechanisms that lead to context dependent effects. To date ecological literature anticipates that greater fine sediment loading will exacerbate ecological effects. However, geomorphological and environmental chemistry research suggest it is more likely that the particle size of the river-bed and vertical hydrological exchange (VHE) pathways will exert a greater control over deposition and thus ecological effects. We sampled hyporheic macroinvertebrates at 19 sites across England and Wales that encompassed a gradient of river-bed particle size (coarse upland through to fine grained lowland streams) and fine sediment pressure. Physicochemical parameters were also recorded including VHE, oxygen content, pH, and mass of inorganic and organic fine sediment. The paper considers the environmental parameters influencing the hyporheic invertebrate communities at the patch scale and especially the role of the river-bed framework in controlling the ecological implications of fine sediment deposition within lotic ecosystems.

Kate Mathers (Primary Presenter/Author), Loughborough University, k.mathers@lboro.ac.uk;

Paul Wood (Co-Presenter/Co-Author), Loughborough University, UK, p.j.wood@lboro.ac.uk;

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6/04/2024  |   16:45 - 17:00   |  Salon 3/4

THE ROLE OF MACROINVERTEBRATES IN BUFFER ZONES: ASSESSING THE KNOWNS, AND EXPLORING THE POTENTIAL OF THE UNKNOWNS. Riparian buffer zones are vegetated strips between agricultural areas and surface waters that can filter the excess diffuse nutrient input from runoff and subsurface flow, preventing further eutrophication. Although the biogeochemical processes in riparian buffer zones that play a role in the retention and removal of nutrients are well known, their reported efficiency is for multiple reasons highly variable. The macroinvertebrate community is an important but often overlooked component of buffer zones. In other ecosystems, macroinvertebrates are important actors in nutrient dynamics, but in buffer zones, their effects remain understudied. Therefore, we aimed to highlight current knowledge and to identify knowledge gaps to provide a roadmap to 1.) clarify the role of invertebrates in buffer zones, and 2.) to implement this knowledge in buffer zone management. To achieve this, based on available literature we categorized known effects of invertebrates on nutrient dynamics in riparian buffer zones, and provided an overview of the nutrient retention and removal processes mediated by invertebrates in comparable ecosystems. Our study showed that little information is available on the role of invertebrates on nutrient dynamics in buffer zones. In contrast, in other ecosystems, this role is broadly assessed. Hence, we hypothesized that macroinvertebrates play a major role in N and P retention and removal processes, such as sedimentation, infiltration, microbial transformation and plant growth, primarily due to burrowing and feeding. Our next step will include field and experimental research to quantify the role of macroinvertebrates in buffer zones, to be able to optimize buffer zone design.

Annalieke M. Bakker (Primary Presenter/Author), Wageningen Environmental Research (WUR)/IBED (UvA), annalieke.bakker@wur.nl;

Tom V. van der Meer (Co-Presenter/Co-Author), Wageningen Environmental Research (WUR), tom1.vandermeer@wur.nl;

Michiel Kraak (Co-Presenter/Co-Author), Institute of Biodiversity and Ecosystem Dynamics, M.H.S.Kraak@uva.nl;

Piet F.M. Verdonschot (Co-Presenter/Co-Author), University of Amsterdam / Wageningen Environmental Research , piet.verdonschot@wur.nl;

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