SFS Annual Meeting

6/04/2024  |   13:30 - 13:45   |  Independence Ballroom D

LAND USE AND STREAM SIZE IMPACT SPATIAL PATTERNS OF WATER CHEMISTRY SIGNATURES ACROSS FOUR MIDWESTERN RIVER BASINS Water chemistry signatures of streams are influenced by a combination of land use, stream size, and other environmental drivers. To understand how water chemistry signatures vary within and among watersheds, we used a synoptic sampling approach to sample N=105 tributary and mainstem sites across four Midwestern river basins spanning a gradient in agricultural land use (as % cover). The basins included the Manistee R. (MAN; 8%), Muskegon R. (MUSK; 20%), St. Joseph R. (JOE; 56%), and the Tippecanoe R. (TIP; 78%). Watersheds with >50% agriculture had the highest nitrate-N (0.2-1.3 mgN/L) and ammonium-N concentrations (18-54 ugN/L; Kruskal-Wallis, p<0.001), whereas soluble reactive phosphorus (SRP) was more similar among basins (15-28 ug/L). Among watersheds, nitrate-N concentrations were an order of magnitude higher than for SRP or ammonium (Friedman, p<0.001). Nutrient concentrations did not differ between tributary and mainstem sites in any watershed (Mann-Whitney U, p>0.05), but we will use estimated discharge to further explore the relationship between size and nutrient loads. Principal component analysis showed significant grouping by land use, where >50% agriculture was distinct from <50% agriculture along PC1, which was primarily explained by dissolved nutrients, conductivity, and temperature. We plan to use membrane inlet mass spectrometry (MIMS) to analyze dissolved N gasses, and the SSN2 R package to summarize spatial stream networks among basins to make predictions at unobserved locations. Our data will refine our understanding of how land use impacts water quality and nutrient loading to downstream ecosystems.

Abagael Pruitt (Primary Presenter/Author), University of Notre Dame, abagaelpruitt@gmail.com;

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

Mitchell Liddick (Co-Presenter/Co-Author), University of Notre Dame, mliddick@nd.edu;

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6/04/2024  |   13:45 - 14:00   |  Independence Ballroom D

SPATIAL VARIATION IN SURFACE WATER BACTERIAL COMMUNITIES ACROSS A LAKE Lakes and reservoirs are important for global carbon sequestration, nutrient cycling, and provide habitat for abundant biodiversity. Microbial communities in lakes are critical for biogeochemical cycling, but studies of microbial community composition in lakes are often limited to fewer than five samples. This makes spatial patterns in lake microbial communities difficult to discern. To determine the extent of spatial heterogeneity in lake microbial communities, we investigated bacterial community composition and diversity, microbial enzymatic activity, and physicochemical variation in surface water across a single lake. We collected 88 water samples from the surface of Puskus Lake, a 96 acre lake in Holly Springs National Forest, Mississippi, USA. For each water sample, the activity of enzymes related to organic carbon (b-glucosidase), nitrogen (NAGase), and phosphorus (phosphatase) mineralization was determined fluorometrically. DNA was extracted from 100 mL of each sample and a portion of the bacterial 16S rRNA gene sequenced. Bacterial communities across the lake were dominated by Cyanobacteria, Actinobacteria, Verrucomicrobia, Bacteroidetes, and Proteobacteria. Species richness varied across the lake with a range of 1,314 to 3,406 ASVs per sample. Microbial enzyme activity and water chemistry were generally more homogenous across the lake than bacterial community parameters.

Jordan Heiman (Primary Presenter/Author), University of Mississippi, jaheiman@go.olemiss.edu;

Colin R. Jackson (Co-Presenter/Co-Author), University of Mississippi, cjackson@olemiss.edu;

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6/04/2024  |   14:00 - 14:15   |  Independence Ballroom D

AVAILABILITY DRIVES NUTRIENT REMOVAL IN HIGH-ARCTIC HEADWATER STREAMS IN NE GREENLAND While high-Arctic landscapes are at the frontlines of climate change, there remain knowledge gaps about how climate-induced warming will modify nutrient availability and cycling in headwater streams, especially in understudied NE Greenland. While nitrogen (N) has been shown to limit stream biofilms in these ultra-low-nutrient systems, deployment of nutrient diffusing substrata across seven headwater streams (1-40 L/s) with differing catchment properties (e.g., lithology, geomorphology and vegetation) in the Zackenberg Basin (74ºN) in Aug 2023 showed significant N limitation (4 of 7 streams) with secondary/co-limitation by phosphorus in half of these. We hypothesized that small changes in inorganic N and P availability, combined with variation in underlying geology, would significantly alter biogeochemical cycling and nutrient export to the nearby fjord. We conducted short-term ammonium-N, nitrate-N, and soluble reactive phosphate (SRP) releases to quantify nutrient spiraling metrics; ammonium-N removal was measurable (n=7/7 releases) and high in all streams, with uptake velocities (Vf) ranging from 0.9-8.1 mm/min, while SRP (n=5/7) and nitrate-N (n=3/7) were more challenging to measure, particularly in streams with higher discharge (SRP Vf=1.0-9.9 mm/min; nitrate-N Vf=0.8-2.8 mm/min). Despite consistently low ammonium-N availability (<5 ugN/L) in all streams, very small increases in background concentration predictably decreased Vf, while streams with highest water column turbidity had lowest nutrient demand for all solutes. Stream spiraling metrics suggest that even small changes in N availability resulting from increased glacial or permafrost thawing can alter biological demand, emphasizing the need to understand solute-specific patterns of stream uptake and implications for sensitive coastal waters.

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

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

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

Emma M. Thrift-Cahall (Co-Presenter/Co-Author), University of Notre Dame, ethrift@nd.edu;

Mitchell Liddick (Co-Presenter/Co-Author), University of Notre Dame, mliddick@nd.edu;

Shannon Speir (Co-Presenter/Co-Author), University of Arkansas, slspeir@uark.edu;

Ada Pastor (Co-Presenter/Co-Author), Institute of Aquatic Ecology, University of Girona, ada.pastor@udg.edu ;

Tenna Riis (Co-Presenter/Co-Author), Aarhus University, Denmark, Tenna.riis@bio.au.dk;

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6/04/2024  |   14:15 - 14:30   |  Independence Ballroom D

Response of stream nitrogen uptake to green and brown energy sources across biomes Streams play a critical role in the nitrogen (N) cycle by retaining a substantial amount of dissolved inorganic nitrogen (DIN). The magnitude of this retention depends on the interaction of several biological processes, which are mostly mediated by two energy sources: light and dissolved organic carbon (DOC). Yet a comprehensive assessment of the relevance of these energy sources as drivers of stream DIN uptake across biomes is missing. To fill this knowledge gap, we compiled published data on ammonium and nitrate uptake velocity (Vf-NH4 and Vf-NO3) from 240 streams across six biomes; thus encompassing a wide range of light (0-131 mol/m2/d), DOC (0.3-30 mgC/L), and DIN (1-1750 µgN/L) availability. We expected light inputs to drive DIN uptake velocity in open-canopy streams dominated by photoautotrophs, and DOC concentration to control DIN uptake velocity in closed-canopy streams dominated by heterotrophs. Results show that, for open-canopy streams, increases in light inputs promote Vf-NH4 (r = 0.38), while no energy source is related to Vf-NO3. For closed-canopy streams, increases in DOC concentration enhance Vf-NO3 (r = 0.46) but reduce Vf-NH4 (r = -0.47), suggesting that DOC availability does not limit heterotrophic ammonium uptake in streams. A subset of 17 streams for which we conducted acetate additions further indicated that DOC composition better predicts Vf-NH4 across biomes than bulk DOC concentrations. Overall, this study highlights that green vs brown energy sources determine the predominant biological processes that ultimately shape the form and fate of N in streams.

Anna Lupon (Primary Presenter/Author), Center for Advanced Studies of Blanes (CEAB-CSIC), anna.lupon@gmail.com;

Dolly Kothawala (Co-Presenter/Co-Author), Uppsala University, dolly.kothawala@ebc.uu.se;

Susana Bernal (Co-Presenter/Co-Author), Center for Advanced Studies of Blanes (CEAB-CSIC), Spain, sbernal@ceab.csic.es;

Xavi Peñarroya (Co-Presenter/Co-Author), Integrated Freshwater Ecology Group, Center for Advanced Studies of Blanes (CEAB-CSIC), Blanes, Girona, Spain., xp.galceran@gmail.com;

Allison Herreid (Co-Presenter/Co-Author), USDA-ARS, Allison.Herreid@unh.edu ;

Ryan Sponseller (Co-Presenter/Co-Author), Department of Ecology and Environmental Science, Umeå University, 901 87 Umeå, Sweden, ryan.sponseller@umu.se;

Lluís Gómez-Gener (Co-Presenter/Co-Author), Centre for Research on Ecology and Forestry Application (CREAF), gomez.gener87@gmail.com;

Ada Pastor (Co-Presenter/Co-Author), Institute of Aquatic Ecology, University of Girona, ada.pastor@udg.edu ;

Matthew Cohen (Co-Presenter/Co-Author), University of Florida, mjc@ufl.edu;

Eugènia Martí (Co-Presenter/Co-Author), Center for Advanced Studies of Blanes (CEAB-CSIC), eugenia@ceab.csic.es;

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6/04/2024  |   14:30 - 14:45   |  Independence Ballroom D

WATER COLUMN NITROGEN UPTAKE DURING STORMS IN A LOW-ORDER WATERSHED Water column uptake in streams and rivers is a nitrogen (N) cycling pathway that has been historically overlooked, with focus placed on the increasing role of water column N uptake role in mid-to-large order rivers with significant loads of suspended sediment. We contend that smaller streams and rivers may provide comparable loads of suspended sediment during and after storm flow events, creating favorable conditions for water column N uptake. To assess the presence, magnitude, and governing controls of water column N uptake during storm events in low-order watersheds, we measured water column denitrification and assimilatory N uptake rates at three locations in a Mid-Atlantic watershed during 5 storm events of varying flow dynamics, sediment load and properties, and nutrient availability. We found large variation in water column denitrification (0 – 5.56 mg N g-1 d-1) and assimilatory uptake (0 .003– 1.67 mg N g-1 d-1) among all storm events, with generally higher rates of water column N uptake during flow recession, and a positive effects of sediment organic matter content on denitrification but not on assimilatory uptake rates. Water column rates of denitrification and assimilatory uptake were higher on average when low intensity and flashy storm events occurred and appear to be more closely associated with heterotrophic pathways. Our study showed rates of water column N uptake during storm events that are comparable to others measured during baseflow conditions in larger rivers, highlighting the overlooked role of biological N retention during and after high-flow periods in small streams.

Eva Bacmeister (Primary Presenter/Author), University of Delaware, embac@udel.edu;

Erin Peck (Co-Presenter/Co-Author), University of Massachusetts Amherst, ekpeck@umass.edu;

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

Shreeram Inamdar (Co-Presenter/Co-Author), University of Delaware, inamdar@udel.edu;

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

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

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6/04/2024  |   14:45 - 15:00   |  Independence Ballroom D

MISMATCHES BETWEEN AMMONIUM AND NITRATE SIGNATURES AT THE FIELD AND WATERSHED-SCALE SUGGEST DIFFERING CONTROLS ON NITROGEN LOSS FROM TWO AGRICULTURAL WATERSHEDS Nitrogen (N) fertilizers enhance crop production in agricultural lands, but N runoff impacts water quality in adjacent streams. Planting cover crops reduces nitrate losses during the fallow period, but less is known about ammonium dynamics. We sampled biweekly from the Shatto Ditch (SDW) and Kirkpatrick Ditch Watersheds (KDW) in Indiana to compare N losses and the impact of cover crops at the field- and watershed-scales. From 2016-2023, we measured soil N, biomass, and organic matter in fall/spring, and we quantified tile drain losses biweekly from fields with/without cover crops, and export from watershed outlets. Both soil ammonium and nitrate were lower in cover cropped fields (ANOVA, p<0.01), but there was no relationship between cover crop biomass and soil ammonium. Tile losses and watershed-scale yields were consistently two orders of magnitude lower for ammonium relative to nitrate. At SDW, cover crops reduced field-scale losses of ammonium and nitrate by 17-98% and 35-87%, respectively, but the impact of cover crops was more variable at KDW. Tile flow controlled interannual variation in nitrate losses, but not ammonium, suggesting field-scale N dynamics were decoupled and influenced by different drivers. At the watershed-scale, ammonium and nitrate yields showed different patterns. Nitrate yield mirrored runoff, while ammonium yield followed a step-function suggesting that storms are an important driver of ammonium loss. Given the linkage between ammonium availability and nitrification rates, understanding controls on field- and watershed-scale losses of both inorganic N species will be critical for managing water quality in agricultural landscapes.

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

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

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

Shannon Speir (Co-Presenter/Co-Author), University of Arkansas, slspeir@uark.edu;

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

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

Lienne Sethna (Co-Presenter/Co-Author), St. Croix Watershed Research Station, lsethna@smm.org;

Lindsey Rasnake (Co-Presenter/Co-Author), Indiana University Bloomington, lrasnake@iu.edu;

Todd V. Royer (Co-Presenter/Co-Author), Indiana University Bloomington, troyer@iu.edu;

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