News & Updates

2024-12-06 - Hotchkiss Lab and collaborators at AGU

We're looking forward to seeing lots of amazing science and scientists at the American Geophysical Union (AGU) annual meeting in Washington, D.C. next week! The list of events and presentations our group is affiliated is below. Please reach out if you're attending and would like to connect.

2024-12-04 - Hotchkiss co-authors article on modeling stream nutrient cycling

A new article led by Ahmed Monofy suggesting a modeling framework that can move us "Toward a Universal Model of Hyporheic Exchange and Nutrient Cycling in Streams" was recently published in AGU Advances. This paper was selected by AGU Advances editors for an article highlight in EOS: 'Physics and Biology as Likely Stream Bedfellows'.


Key Points:


Citation: Monofy, A., Grant, S. B., Boano, F., Rippy, M. A., Gomez-Velez, J. D., Kaushal, S. S., Hotchkiss, E. R., & Shelton S. 2024. Toward a universal model of hyporheic exchange and nutrient cycling in streams. AGU Advances 5: e2024AV001373.

Fig 1. Conceptual and mathematical model for the uptake velocity of nutrients and other reactive contaminants in streams. (a) Conceptual model. (b) Nutrient transport across the concentration boundary layer by stream turbulence (Step 1) is coupled to nutrient transport into the streambed by hyporheic exchange (Step 2) and biotic (or abiotic) reactions in the streambed (Step 3). These three steps are indicated in the figure by bold red numbers. (c) Transport of nutrients into the streambed by hyporheic exchange is modeled by an effective diffusivity that declines exponentially with depth into the sediment (see Equation 3).
Fig 6. Previously published LINX II measurements of (a) total and (b) denitrification uptake velocities in streams draining agricultural (AGR), urban (URB), and reference (REF) land-use types. (c, d) When these measured uptake velocities are normalized by the convective mass transfer coefficient, km, the resulting ratios are generally less than unity (horizontal dashed line), consistent with the idea that in-stream mixing across the concentration boundary layer sets an upper limit on nitrate uptake. (e,f) Values of the in-sediment first-order reaction rate constants, ktot and kden, inferred from measurements of vf,tot and vf,den at the LINX II sites. Circles are rate constants inferred from Equation 6 and triangles are approximate lower limits (see main text).
Fig 7. (a) Inferred reaction timescales for nitrate removal by both assimilation and denitrification (“Total Uptake”), denitrification alone (“Denitrification”), and assimilation alone (“Assimilation”) (gray diamonds denote median values). Typical timescales for oxygen consumption (gray box) and denitrification (black arrow) in streambed sediments are also shown. (b and c) Performance of the top regression models for ktot and kden (see Equations 14a and 14b); solid line is a perfect correspondence, dashed lines are 90th percentile prediction intervals. The coefficient of determination for these relationships are also shown. 

2024-11-20 - Photos from the field: Post-dredging sampling of Stroubles Creek above and below Virginia Tech's Duck Pond

Our research characterizing water quality in Stroubles Creek continues with a new team of undergraduate collaborators! This semester we are sampling above and below the Duck Pond to assess the impact of sediment dredging on short-term water quality disturbances and (hopefully) longer-term water quality improvements. Pictured above: members of the Fall 2024 undergraduate research team sampling Webb Branch of Stroubles Creek in November 2024. From left to right: Jialin Huo, Brooke Vaughn, Carter Offhaus, Emma Lucier, Andie Flota, Katherine Campo, & Erin Walters. We will share results from our before/during dredging comparisons on our project website later in the year.

2024-11-15 - López Lloreda leads new article on headwater wetland CO2 & CH4

Carla López Lloreda recently published the first chapter of her dissertation in Ecosystems: 'CO2 and CH4 concentrations in headwater wetlands influenced by morphology and changing hydro-biogeochemical conditions'. This research was supported by our "DelmarvaDisco" NSF research grant as well as Carla's NSF GRFP award.


Key Points:


Citation: López Lloreda, C., J. Maze, D. McLaughlin, C.N. Jones, D. Scott, M. Palmer, K. Wardinski, N. Corline, & E.R. Hotchkiss. 2024. CO2 and CH4 concentrations in headwater wetlands influenced by morphology and changing hydro-biogeochemical conditions. Ecosystems 27: 999-1019.

Figure 1. Map of the Delmarva Peninsula and location and physical characteristics of our study wetlands. Map of the Eastern Shore, USA (a), with an inset of the Delmarva Peninsula and the Greensboro Watershed (b). We also show the location of the different wetland complexes c with a zoomed in view of each wetland complex and their corresponding wetlands at maximum inundation (d–g). Darker-colored wetlands indicate the wetlands in our study (d–g). Water level average and wetland area of our study wetlands, which are generally small, shallow wetlands (h).
Figure 2. Concentrations of dissolved CO2 (a) and CH4 (b) in wetland surface water (pink circles) and groundwater (blue triangles) across 11 sampling dates and 20 wetlands. Horizontal lines in the boxplots represent the surface water and groundwater CO2 and CH4 medians; lower and upper box boundaries are the 25th and 75th percentile, respectively. Vertical lines are the 95% confidence interval. Letters above each boxplot note a significant difference between surface and groundwater based on a Tukey honest significant difference test (p < 0.05). There was a significant positive relationship between CH4 and CO2 in both surface water (pink circles) and groundwater (blue triangles) (c). Linear regression lines, shading which represents the 95% confidence interval, and corresponding linear model statistics are shown. Note that the CH4 axis is log-transformed.
Figure 5. Relationships of average CO2 and CH4 concentrations with different wetland morphological variables across 18 of our wetland sites and their corresponding statistics. a–c CO2 concentrations and d–f CH4 concentrations with wetland area (a, d), perimeter:area ratio (b, e), and height above drainage network (c, f). Lines are the best-fit linear model for each relationship and shading around the lines is the standard error. Panels with statistics but no lines represent non-significant linear relationships (p > 0.05).

2024-11-01 - Iannucci leads new article on carbon metabolism in boreal streams

A new article led by Frances Iannucci describing how "Temperature and Flow Control Organic Metabolism in Boreal Headwater Streams" was recently published in the Journal of Geophyisical Research: Biogeosciences.


Key Points:


Citation: Iannucci, F.M., J.B. Jones, K.L. Olson, M.E. Muscarella, & E.R. Hotchkiss. 2024. Temperature and flow control organic carbon metabolism in boreal headwater streams. Journal of Geophysical Research: Biogeosciences 129: e2024JG008281. https://doi.org/10.1029/2024JG008281 

Figure 1. Map of study sites in the Caribou-Poker Creeks Research Watershed. Darker shading denotes estimated permafrost extent. Sampling locations for C1-C4 are at the outlet of each catchment. Inset shows the location of the CPCRW in Alaska.
Figure 4. Metabolism and stream chemistry vary with permafrost extent. Center lines, boxes, whiskers, and points indicate the median, interquartile range (IQR), 1.5 × IQR, and outliers (n = 57–119 per site per year). ER = Ecosystem Respiration, GPP = Gross Primary Production, SUVA254 = specific ultraviolet absorbance at 254nm scaled by DOC, DOC = dissolved organic carbon.
Figure 5. Carbon (C) and phosphorus (P) co-limit respiration in laboratory incubations. Center lines, boxes, whiskers, and points indicate the median, interquartile range (IQR), 1.5 × IQR, and outliers of O2 demand (μmol O2 L−1 h−1) across all sites.

2024-10-15 - Hotchkiss co-authors article on the phenology of leaf litter breakdown in stream networks

Our new article in Limnology and Oceanography Letters led by Danielle Hare characterized current and future organic matter dynamics in stream networks driven by interactions between stream temperature and leaf litter phenology. This work was part of an NSF-funded stream warming experiment at the Coweeta Hydrologic Laboratory in North Carolina, USA. 

From our published significance statement: "Stream temperature controls the rate at which leaf litter, the dominant energy input to forest stream food webs, breaks down in streams. Yet, there is a temporal mismatch between the highest stream temperatures and maximum leaf inputs, and how this timing affects seasonal patterns in litter breakdown is unknown. Using stream network models, we show that shifts in-stream thermal regime modify the seasonal phenology of litter breakdown fluxes, but that the response depends on litter species. When we evaluated the effects of future climate warming, streams fed by shallow or minimal groundwater had strongly depleted leaf litter during summer, emphasizing the importance of deep groundwater thermal inputs for the stability and resilience of forest stream ecosystems."

Citation: Hare, D.K., A.M. Helton, C.S. Cummins, P.M. Bumpers, N.J. Tomczyk, P.A. Rogers, S.J. Wenger, E.R. Hotchkiss, A.D. Rosemond, & J.P. Benstead. 2024. Leaf litter breakdown phenology in headwater stream networks is modulated by groundwater thermal regimes and litter type. Limnology and Oceanography Letters 9: 532-542. https://aslopubs.onlinelibrary.wiley.com/doi/10.1002/lol2.10423

2024-08-23 - López Lloreda attends ESA

Carla López Llorda recently attended the annual Ecological Society of America (ESA) meeting in Long Beach, CA, where she presented a poster on her dissertation research: "Greenhouse gas dynamics in vulnerable tropical coastal wetlands: Assessing spatial variability and the potential impacts of saltwater intrusion". Carla's poster received an honorable mention award from the Latin American and Caribbean ESA Chapter - congratulations!

Carla's attendance to ESA was supported by a SEEDS program graduate student alumni award and she was able to participate as a mentor to 30 undergraduate SEEDS students as well as reconnect with many SEEDS alumni (group photo below)!

2024-08-21 - Hotchkiss co-PI on new grant award linking river dissolved oxygen dynamics with Eastern hellbender population declines & freshwater biodiversity 

William Hopkins, Erin Hotchkiss, and the Virginia Department of Wildlife Resources will be collaborating on one of 10 projects recently funded by the Partnership to Advance Conservation Science and Practice program supported by the National Science Foundation (NSF) and the Paul G. Allen Family Foundation. Our funded project, "Integrating organismal biology and biogeochemistry to develop science-informed actions to conserve stream biodiversity in a changing climate" will begin in 2025.

You can read more about our award in Virginia Tech's press release: "A watershed moment for the survival of imperiled Appalachian salamanders".

Our lab will be recruiting one Master's or PhD student to focus on the biogeochemistry part of this project and engage in our broader collaboration starting in August 2025. You can read more about that opportunity and how to apply here.


Above image: Research plan spanning ecosystem-level changes in stream biogeochemistry to organismal behaviors and fitness in eastern hellbenders. * indicates research included in the funded proposal. PI Hopkins’ prior work established cannibalism as the cause of population declines and a shift in age structure. Panels on the right depict our predictions supported by preliminary data. (diagram credit: ER Hotchkiss & WA Hopkins; reach cross-section used to generate the geomorphic background in upper panel is from Bonada et al. 2020)

2024-08-05 - Pérez Rivera is a 2024-5 Emerge Fellow!

PhD Student Katherine Pérez Rivera was selected to join the 2024-5 cohort of Emerge Fellows. Funding from the National Science Foundation and Society for Freshwater Science supports the year-long engagement of early career Fellows in activities focused on professional development and community-building in freshwater science. Congratulations, Katherine! 

2024-07-25 - Aquatic Ecosystems workshop for teachers & STEM Governor's School students

Earlier this month, Erin Hotchkiss and Caleigh Meehan joined our NSF-funded "Salty Carbon" collaborators from Virginia Tech Entomology and UVA-Wise to deliver a two-day hands-on Aquatic Ecosystems workshop for high school students attending this year's STEM Governor's School at UVA-Wise as well as a group of middle and high school science teachers from southwest VA enrolled in a professional development biodiversity workshop. We led the students and teachers through a series of data collection and analysis activities to characterize the hydrology and biodiversity of macro-invertebrate communities in the Clinch River and Big Cedar Creek, and discussed our findings in the context of freshwater food webs and watershed dynamics. It was a fun chance to share our knowledge and learn from residents of southwest VA about their local freshwater ecosystems!

Pictured from top to bottom: Caleigh Meehan (Master's student, VT Biology) gives instructions to workshop participants before starting organic matter retention experiments in the Clinch River; Governor's School  students work with EPA scientist Greg Pond to identify macro-invertebrates sampled from the Clinch River near St. Paul, VA.
Pictured from top to bottom: Workshop participants prepare for whole-stream leaf additions to measure organic matter retention in the Clinch River; students calculate river hydrology and transport variables from measurements they collected; Dr. Sally Entrekin (Professor, VT Entomology) holds up a leaf skeleton while removing macro-invertebrates from leaf packs deployed in the Clinch River with middle and high school science teachers from southwest VA.
Workshop participants prepare to capture leaves experimentally added to Big Cedar Creek to estimate organic matter retention in Pinnacle Area Natural Preserve, VA.

2024-07-11 - Hotchkiss co-authors article highlighting team science strategies used to support a hybrid collaboration-incubator workshop

A new Limnology and Oceanography Bulletin article led by Steve Sadro shares team science activities and the broader framework my collaborators and I used to support working group development and networking during an NSF-funded hybrid workshop "Revisiting the Freshwater Imperative": Sadro et al. (2024)  https://aslopubs.onlinelibrary.wiley.com/doi/full/10.1002/lob.10645


Our hybrid workshop last summer was a whirlwind of science fun with amazing people and I'm very happy to see continued collaboration among attendees!


Citation: Sadro, S., E.R. Hotchkiss, K.L. Cottingham, M.J. Vanni, S.L. Speir, & C.M. O'Reilly. 2024. Revisiting the Freshwater Imperative: Harnessing Team Science to Face Emerging Challenges to Freshwaters. Limnology and Oceanography Bulletin. https://aslopubs.onlinelibrary.wiley.com/doi/10.1002/lob.10645 

2024-06-15 - Hotchkiss co-authors article on ecosystem responses to freshwater salinization

A new peer-reviewed article in Biogeochemistry led by Steve DeVilbiss shares results from a series of experiments testing freshwater ecosystem responses to increased salt inputs. We found both subsidy-stress and salt-specific responses to increased salinity for freshwater microbial respiration, primary production, and nutrient uptake.


Citation: DeVilbiss, S.E., Badgley, B.D., Hotchkiss, E.R., & Steele, M.K. 2024. Subsidy-stress responses of ecosystem functions along experimental freshwater salinity gradients. Biogeochemistry 167, 743–757. https://doi.org/10.1007/s10533-024-01131-5


Abstract: "Human activity is increasing salt concentrations in freshwaters worldwide, but effects of freshwater salinity gradients on biogeochemical cycling are less understood than in saline, brackish, or marine environments. Using controlled microcosm experiments, we characterized (1) short-term (one to five days) biogeochemical responses and (2) water column metabolism along a freshwater salinity gradient of multiple salt types. After one day, microcosms were oxic (4.48–7.40 mg O2 L−1) but became hypoxic (1.20–3.31 mg L−1) by day five. After one day in oxic conditions, microbial respiration in magnesium-, sodium-, and sea salt-based salinity treatments showed a subsidy-stress response, with respiration increasing by over 100% as salinity increased from 30 to 350–800 µS cm−1. Conversely, respiration consistently increased along a calcium-based salinity gradient, peaking at 1500 µS cm−1. By day five, an inverse subsidy-stress response was observed with elevated respiration at upper or lower ends of the gradient except for the magnesium treatment, which had the lowest respiration at the highest salinity. Calcium- and magnesium-based salinity treatments also caused considerable changes in phosphorus concentrations and C:P and N:P. In a separate experiment, microbial respiration and water column primary production also displayed subsidy-stress responses, but imbalances in effect sizes caused consistently declining net community production with increasing salinity. Collectively, our results establish that short-term exposure to different salt ion concentrations can enhance freshwater biogeochemical cycling at relatively low concentrations and alter resource stoichiometry. Furthermore, the nature of effects of freshwater salinization may also change with oxygen availability."

Figure 1 in DeVilbiss et al. (2024). 'Microbial respiration rates along experimental freshwater salinity gradients of CaCl2 (top row), MgCl2 (second row), NaCl (third row), and artificial sea salt (bottom row) under oxic (left column) and hypoxic (right column) conditions. More negative values indicate higher oxygen consumption.'

Figure 2 in DeVilbiss et al. (2024). 'Effects of different chloride salts on microbial respiration at four distinct salinities. The left column shows respiration after a 1-day incubation and the right column after a 5-day incubation that started in oxic conditions but became hypoxic during the 5 days. More negative values indicate greater oxygen consumption. Significant differences in respiration among salt types are shown with letters (p < 0.05).'

Figure 3 in DeVilbiss et al. (2024). 'Net fluxes of dissolved organic carbon (DOC, top row), NH4+ (second row), NO3− (third row), and PO43− (bottom row) along experimental salinity gradients of CaCl2 (first column), MgCl2 (second column), NaCl (third column), and artificial sea salt (last column) in oxic (A) and hypoxic (B) conditions. Positive values indicate net release, negative values indicate net uptake. Dashed lines are at 0, indicating the transition from release to uptake.'

Figure 5 in DeVilbiss et al. (2024). 'Response of community respiration (CR), gross primary production (GPP), and net community production (NCP) along experimental salinity gradients of two salt profiles including a combination of calcium, magnesium, and potassium chloride salts (Ca:Mg:K) and sodium chloride (NaCl). Panel A shows measured oxygen flux values and panel B shows percent change from unaltered reference water. Positive values indicate oxygen production, negative values indicate oxygen consumption.'

2024-06-13 - Pictures from SFS in Philadelphia

Thanks to all attendees for contributing to a great Society for Freshwater Science annual meeting! Pictured above: 

Left column, top-bottom: (1) Tiffany Meadows (VT undergraduate) and Ally Kaelin (VT 2024 grad) presenting their poster on "Assessing terrestrial and aquatic resource dynamics in streams across biomes";  (2) Evie Dana and Isabella Korobow-Velez (VT undergraduates) presenting their poster on "Species abundance and food web structure across biomes"; & (3) the five current undergraduates and spring 2024 VT grads in our lab who attended SFS at the Swann Memorial Fountain in Logan Square (Emily Mulcahy, Ally Kaelin, Tiffany Meadows, Evie Dana, & Isabella Korobow-Velez).

Middle, top-bottom:  (1) Group photo of current members, affiliates, and recent graduates of the lab: Evie Dana, Frances Iannucci, Ally Kaelin (BSc, VT BIOL 2024), Isabella Korobow-Velez, Tiffany Meadows, Erin Hotchkiss, Katherine Pérez Rivera, Stephen Plont (PhD, VT BIOL 2023), Caleigh Meehan, & Emily Mulcahy (BSc, VT BIOL 2024). (2) Katherine Pérez Rivera (PhD student) giving her presentation on "Longitudinal patterns in carbon cycling along a stream continuum draining a heterogeneous landscape".

Right column, top-bottom: (1) Caleigh Meehan (Master's student) presenting her poster on "Consequences of freshwater salinization on stream carbon cycling"; (2) Emily Mulcahy (VT 2024 grad) presenting her poster on "Assessing the role of phytoplankton on the biogeochemistry in geographically isolated wetlands"; (3) lab collaborator Kristin Olson (PhD Candidate, University of Alaska Fairbanks) presenting her poster on "In the boreal forest net carbon exchange puzzle, how big of a piece are stream CO2 emissions?"; and (4) lab affiliate / Stream Team Analytical Laboratory Manager and Data Scientist, Frances Iannucci, presenting her poster on "Contrasting roles of discharge on shaping headwater stream CO2 regimes".

2024-05-31 - Learn about our ongoing research at the Society for Freshwater Science Conference in Philadelphia, PA

We're looking forward to sharing our science, reconnecting with collaborators/friends, & meeting new freshwater scientists next week! https://sfsannualmeeting.org/

2024-05-15 - Congratulations, Spring 2024 graduates!

We are celebrating the graduation of three undergraduate researchers in the lab this year: Emily Mulcahy, Allyson Kaelin, and Caroline Brickner. We're sorry to see you leave, but excited for all that you'll accomplish. 

We also celebrate past undergraduate researchers in the lab who graduated this year: Carmen Curry, Cleo Orlando, & Gavriel Cambridge.

Congratulations, everyone!

Allyson Kaelin

Biological Sciences

After graduation: Ally will be working as a Scientist at the Naval Surface Warfare Center, Dahlgren Division

Emily Mulcahy

Biological Sciences, Wetland Science, & Green Engineering

After graduation: Emily will be starting a Master's program in Biology at the University of Louisiana at Lafayette

Caroline Brickner

Biological Sciences

After graduation: Caroline is taking time to explore different careers in Biology

2024-04-26 - Spring 2024 Undergraduate Research Conference

Several undergraduate researchers collaborating with members of the Hotchkiss Lab shared their science at this year's Dennis Dean Undergraduate Research and Creative Scholarship Conference at Virginia Tech. Congratulations on fantastic posters presentations - we've enjoyed collaborating with all of you!

Emma Lucier & James Logan

Lucier*, Logan*, Hotchkiss, Campo, Flota, Huo, Penland, & Pérez Rivera. 2024. Differences in Water Quality Above and Below a Retention Pond: Implications for Ecosystem Health and Predicted Effects of Dredging. Dennis Dean Undergraduate Research and Creative Scholarship, Virginia Tech, Blacksburg, VA, USA.

Collaboration Team: Spring 2024 Ecology Research in Local Waterways

(BIOL 2984)

*Awarded 3rd place out of all posters evaluated by the College of Natural Resources and the Environment* (congrats, team!)

Emily Mulcahy

Mulcahy*, López Lloreda, Wardinski, Corline, & Hotchkiss. 2024. Assessing the Role of Phytoplankton on the Biogeochemistry in Geographically Isolated Wetlands. Dennis Dean Undergraduate Research and Creative Scholarship, Virginia Tech, Blacksburg, VA, USA.

Collaboration Team: Delmarva Disco 

(NSF DEB 1856560)

Isabella Korobow & Evie Dana

Dana*, Korobow-Velez*, Rasmussen, Rowe, Brickner, Kaelin, Masters, Meadows, & Hotchkiss. 2024. Assessing Macroinvertebrate and Primary Producer Populations and Their Habitats Across Biomes. Dennis Dean Undergraduate Research and Creative Scholarship, Virginia Tech, Blacksburg, VA, USA.

Collaboration Team: Macrosystems Ecology Research Team 

(NSF DEB 1926426)

Jared Rasmussen & Peyton Rowe

Rasmussen*, Rowe*, Brickner, Dana, Kaelin, Korobow-Velez, Masters, Meadows, & Hotchkiss. 2024. Observing changes in macroinvertebrate density and evenness across biomes. Dennis Dean Undergraduate Research and Creative Scholarship, Virginia Tech, Blacksburg, VA, USA.

Collaboration Team: Macrosystems Ecology Research Team 

(NSF DEB 1926426)

2024-02-22 - Photos from the field: Ecology Research in Local Waterways Class

Erin Hotchkiss and Katherine Pérez Rivera are conducting research with a team of undergraduates this semester through a new course developed by Hotchkiss: Ecology Research in Local Waterways. The course is open to all students with sophomore standing or higher; no prior experience in research or freshwater science is required for enrollment. We aim to provide students with real-world freshwater science knowledge, research experience, and team science best practices through a semester-long collaboration; the research goals will change each semester to reflect ongoing freshwater research needs and opportunities on Virginia Tech's Blacksburg campus and/or the surrounding area. This spring, our research collaboration is testing the downstream water quality effects of the Duck Pond, a large retention pond on Virginia Tech's campus that is part of the Stroubles Creek stream network. In addition to testing the current capacity of the Duck Pond to reduce downstream sediment, nutrient, and salt pollution, we will also monitor upstream and downstream water quality during a contracted dredging project that will remove built-up sediments from the Duck Pond and increase its future retention capacity. Below are a few photos of our collaboration team collecting samples to measure stream flow and water quality above and below the Duck Pond; stay tuned for more updates on what we learn this semester! The next section of this class will be offered in Fall 2024.

2024-01-12 - López Lloreda presents at BIOGEOMON 2024

Carla López Lloreda recently gave a presentation at the 11th BIOGEOMON International Symposium on Ecosystem Behavior in San Juan, Puerto Rico. Her talk was titled "Disturbances drive stream greenhouse gas changes and increased heterogeneity at the reach-scale" and was co-authored by Allison Herreid, Tatiana Barreto Vélez, Jesús Gómez, Pablo Gutiérrez-Fonseca, and William H. McDowell.