SFS Annual Meeting

6/03/2024  |   13:30 - 13:45   |  Freedom Ballroom H/G

SPATIAL DYNAMICS OF NITROGEN AND PHOSPHORUS IN A NON-PERENNIAL AGRICULTURAL STREAM Agriculture negatively impacts water quality via changes in land cover, increased nutrient inputs, and alterations in hydrology. For example, the widespread use of synthetic fertilizers and manure can increase nitrogen (N) and phosphorus (P) runoff into nearby streams, resulting in eutrophication in critical downstream systems. Moreover, non-perennial headwater streams are key sites for nutrient transport and processing and are some of the most impacted by land use change. However, few studies explore the interacting effects of stream intermittency and agriculture on downstream nutrient loss. Thus, we sampled Brush Creek, a non-perennial tributary of Beaver Lake Reservoir, the primary drinking water source for Northwest Arkansas. In Brush Creek, ~45% of the land cover is dedicated to animal agriculture, including chicken and cattle production. Additionally, the middle of the watershed is intermittent, and many of the tributaries in Brush Creek are ephemeral. We collected biweekly samples for nitrate and soluble reactive P (SRP), as well as discharge measurements, beginning in June 2023. Preliminary results suggest nitrate increases moving downstream, whereas SRP is low throughout the watershed. However, SRP concentrations are higher in pools, presenting a risk for downstream transport of P during storm events when pools reconnect at high flows. Our results indicate that as stream intermittency and extreme weather events increase with climate change, it is critical to understand the interactions between stream drying and agriculture to maintain downstream water quality and mitigate eutrophication risks.

Kathleen Cutting (Primary Presenter/Author), University of Arkansas, kjcuttin@uark.edu;

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

Alana Strauss (Co-Presenter/Co-Author), University of Arkansas, alanas@uark.edu;

Caroline Anscombe (Co-Presenter/Co-Author), University of Arkansas, anscombe@uark.edu;

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6/03/2024  |   13:45 - 14:00   |  Freedom Ballroom H/G

THE ROLE OF HYDROLOGIC CONNECTIVITY, TEMPERATURE, AND SOLUTE CHEMISTRY ON NITROGEN DYNAMICS IN A FORESTED NON-PERENNIAL HEADWATER STREAM Headwater streams make up the majority of stream miles in the US, especially in the Southeast, serving as important sites of nitrogen removal and influencing downstream water quality. However, headwater flow regimes are becoming increasingly non-perennial, resulting in changes in connectivity across the network that disrupt the timing and magnitude of nitrogen processing. Therefore, we examined factors driving nitrogen removal and export in a forested Piedmont non-perennial stream in the Southeastern US. We asked: What drives nitrate (NO3-) removal and export during seasonal dry down and across the stream network? We predicted network drying and higher temperatures would result in higher NO3- removal via denitrification and lower NO3- export. We used a combination of continuous water quality monitoring and synoptic sampling campaigns across the stream network and at the watershed outlet. We measured dissolved organic carbon, NO3-, temperature, dissolved oxygen, and dissolved gases (N2) at seven sites and complemented our sampling with dilution gauging for discharge (Q). At the outlet, we leveraged the continuous water quality data with concentration (C)-(Q) metrics (e.g., slope of the logarithmic C-Q relationship) to characterize NO3- dynamics. The C-Q relationships demonstrated NO3- source limitations in the summer, suggesting high demand for nitrogen. At the reach scale, net denitrification conditions were higher in the summer, coinciding with warmer water temperatures and lower flow. Our findings reveal consistent patterns of nitrogen removal during summer dry down, indicating the potential impact lower flow conditions will have on nitrogen dynamics given the increased frequency of droughts.

Kaci Zarek (Primary Presenter/Author), University of Alabama, kacizarek10@gmail.com;

Nate Jones (Co-Presenter/Co-Author), University of Alabama, cnjones7@ua.edu;

Delaney Peterson (Co-Presenter/Co-Author), University of Alabama, dmpeterson2@crimson.ua.edu;

Stephen Plont (Co-Presenter/Co-Author), The University of Alabama, plontste@gmail.com;

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

Corianne Tatariw (Co-Presenter/Co-Author), Rowan University , tatariw@rowan.edu;

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

Amy Burgin (Co-Presenter/Co-Author), University of Kansas, burginam@ku.edu;

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6/03/2024  |   14:00 - 14:15   |  Freedom Ballroom H/G

Degradation of Dissolved Organic Matter Non-Perennial, Prairie Stream The composition of dissolved organic matter (DOM) is a driver of many biogeochemical processes within flowing waters, impacting microbial processing, food webs, and water quality. However, how DOM composition varies within non-perennial streams remains to be determined. We conducted a synoptic surface water sampling campaign followed by two years of seasonal sampling within the headwaters of a non-perennial, prairie watershed during a period of above average hydrological surface connectivity. We tested how nutrient and DOC concentrations and DOM composition vary spatially across a non-perennial watershed. We hypothesized that: (1) Increased connectivity throughout the watershed will lead to an allochthonous and humic-like DOM signature across the network, driven by the intensified transport of terrestrially-derived DOM, and (2) higher connectivity within the network will alleviate transport-limitation of in-stream microbial processing, resulting in increasingly microbially-derived DOM signature moving from upstream to downstream. PeakT:PeakC, HIX, BIX, and FI all indicated more humic-like, terrestrially-derived DOM throughout the network. Overall spatial variability of solute concentrations and DOM composition was low, but signals of increasing microbially-derived DOM (insert what indices told you this) were still found with increasing drainage area. Although the composition tended toward being more allochthonous and humic overall, we still see signals that the extent of microbial degradation of DOM increased as we move down the watershed. These studies are imperative to understand the subsequent impacts of non-perennial streams on the carbon processing and functioning of stream ecosystems, aquatic food webs, and water quality.

Sarah Flynn (Primary Presenter/Author), University of Kansas, s.m.flynn@ku.edu;

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

Stephen Plont (Co-Presenter/Co-Author), The University of Alabama, plontste@gmail.com;

Connor Brown (Co-Presenter/Co-Author), University of Kansas, connor.brown@ku.edu;

Michelle Busch (Co-Presenter/Co-Author), University of Kansas, m.h.busch@ku.edu;

Erin Seybold (Co-Presenter/Co-Author), Kansas Geological Survey, University of Kansas, erinseybold@ku.edu;

Alexi Sommerville (Co-Presenter/Co-Author), University of Kansas, alexi.sommerville@ku.edu;

Amy Burgin (Co-Presenter/Co-Author), University of Kansas, burginam@ku.edu;

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6/03/2024  |   14:15 - 14:30   |  Freedom Ballroom H/G

Rejecting advection, or doing ecosystem science in rivers when they stop flowing Flow permanence is a vital assumption in quantifying the ecosystem function of lotic waterbodies. Recent attention identified the extent and effects of non-perennial streams, but knowledge gaps remain in perennial streams that cease flowing seasonally. In this talk, we explore a perennial 3rd order stream, New Hope Creek, NC, that stops flowing during the late summer and early fall, determining the effects of flow on dissolve gas variability across pool-riffle sequences and the consequences in determining ecosystem function. Across three pool-riffle sequences, we deployed paired O2 and CO2 sensors from June – December 2023 to 1) describe the variability in gas concentrations over short (~100 m) heterogeneous reaches, 2) evaluate implications in gas exchange, 3) and discuss methods of estimating gross primary production and ecosystem respiration. As flows decline and riffles dry, gas exchange in the increasingly hydrologically isolated pools becomes dominated by wind rather than flow dynamics. This requires more sophisticated modeling approaches for continuous metabolism as the assumptions of one-station models are increasingly violated as connectivity declines. We use oxygen and CO2 budgets between multiple sampling stations to better refine our estimates of metabolism and to determine the extent to which one station models fail under these conditions. In determining GPP and ER for each reach, we describe differences in using each station as independent and contrast with methods that integrate sensor deployments across the pool-riffle sequence. Our approach is data-intensive but aims to decrease uncertainty across heterogenous stream reaches and the spectrum of perennial flow conditions.

Nick Marzolf (Primary Presenter/Author), Jones Center at Ichauway, nick.marzolf@jonesctr.org;

Adam Rok (Co-Presenter/Co-Author), Duke University, adam.rok@duke.edu;

Emily Bernhardt (Co-Presenter/Co-Author), Duke University, emily.bernhardt@duke.edu;

Amanda DelVecchia (Co-Presenter/Co-Author), University of North Carolina at Chapel Hill, amanda.delvecchia@unc.edu;

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6/03/2024  |   14:30 - 14:45   |  Freedom Ballroom H/G

Ponding in the stream: discontinuities in greenhouse gas dynamics across pool - riffle sequences Although we conceptualize rivers as lotic systems with relatively high rates of gas exchange, lentic reaches are common, whether they be in non-perennial and disconnected rivers, or perennial but low-gradient, longitudinally heterogenous systems. The discontinuity in gas exchange likely affects rates of gas production, retention, and flux, but our methods for understanding riverine greenhouse gas (GHG) emissions are predicated on two assumptions: homogeneity in flow along a given reach length, and gas exchange driven by advective transport. We used three riffle-pool-riffle sequences in a low-gradient, perennial 3rd order stream with minimal groundwater contributions to understand how gas concentrations, flux rates, and contributions vary between pool and riffle sections. Over three sampling periods from July 2023 to February 2024 encompassing a gradient in stream discharge, we compared gas concentrations, flux rates, and departure from atmospheric equilibrium in pool and riffle sections. Differentiation between pool and riffle sections was pronounced in September 2023. During this low-discharge period, CO2 and O2 departures suggested low gas exchange, net heterotrophy and anaerobic metabolism at pool sites. Potential for anaerobic metabolism was further evidenced by mean methane concentrations of 13.8 ± 36 µmol L-1 in pools compared to 0.3 ± 0.2 µmol L-1 in riffles across all sites in September, with consistent differences at the site level. Our results suggest that riffles might be control points for gas evasion, pools locations for methane production, and that reach-scale estimates of total gas production need to account for longitudinal discontinuity.

Amanda DelVecchia (Primary Presenter/Author), UNC Chapel Hill, adelvecc@unc.edu;

Nicholas Marzolf (Co-Presenter/Co-Author), J.W. Jones Ecological Research Center, nmarzolf@jonesctr.org;

Adam Rok (Co-Presenter/Co-Author), Duke University, adam.rok@duke.edu;

Nguyen Tien Anh Quach (Co-Presenter/Co-Author), University of North Carolina at Chapel Hill, tienanhquachnguyen@gmail.com;

Emily Bernhardt (Co-Presenter/Co-Author), Duke University, ebernhar@duke.edu;

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6/03/2024  |   14:45 - 15:00   |  Freedom Ballroom H/G

Variable inundation in river sediments leads to a continuum of neutral to cold biogeochemical moments Variable inundation is the norm in hyporheic zone sediments, with over half of the global river network undergoing wetting and drying cycles. Projected changes to intermittency along river corridors make it increasingly important to understand the biogeochemical response of sediments to variable inundation. Rewetting of dried stream sediments has been shown to produce a pulse of respiration, similar to the Birch Effect seen in soils. However, the mechanisms behind this pulse and its relevance in the context of inundated river sediments has not yet been explored. To understand sediment response to variable inundation, we worked with the WHONDRS consortium to collect hyporheic zone sediment from 56 perennial sites across the United States. A manipulative experiment was conducted over 21 days, whereby sediments were either kept inundated or allowed to air dry. Samples were then inundated with native river water and respiration was measured over two hours using customized optodes before collecting biogeochemical subsamples. Drying and rewetting caused “cold” and “neutral” moments, in which respiration either decreased or stayed the same, respectively, compared to consistently inundated samples. This differs from “hot moments” in soils, whereby rewetting increases respiration. Physical parameters, such as sediment texture, play an important role in this response. Developing a mechanistic understanding of the impacts of intermittency on river sediments is crucial for future predictions in global biogeochemical cycles. Moreover, placing river sediments alongside soils on a variably inundated continuum facilitates comparisons that span the terrestrial-aquatic interface.

Maggi Laan (Primary Presenter/Author), Pacific Northwest National Laboratory, maggi.laan@pnnl.gov;

Kenton Rod (Co-Presenter/Co-Author), Pacific Northwest National Laboratory, kenton.rod@pnnl.gov;

Vanessa Garayburu-Caruso (Co-Presenter/Co-Author), Pacific Northwest National Laboratory , vanessa.garayburu-caruso@pnnl.gov;

Dillman Delgado (Co-Presenter/Co-Author), Pacific Northwest National Laboratory , dillman.delgadoparedes@pnnl.gov;

Laura Coulson (Co-Presenter/Co-Author), Wasser Cluster Lunz, laura.e.coulson@gmail.com;

Lupita Renteria (Co-Presenter/Co-Author), Pacific Northwest National Laboratory, lupita.renteria@pnnl.gov;

Sophia McKever (Co-Presenter/Co-Author), Pacific Northwest National Laboratory, sophia.mckever@pnnl.gov;

Amy Goldman (Co-Presenter/Co-Author), Pacific Northwest National Laboratory, amy.goldman@pnnl.gov;

Brieanne Forbes (Co-Presenter/Co-Author), Pacific Northwest National Laboratory, brieanne.forbes@pnnl.gov;

James Stegen (Co-Presenter/Co-Author), Pacific Northwest National Laboratory, james.stegen@pnnl.gov;

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