News & Updates

2021 Archive

2021-12-16 - Bretz presents research at #AGU21

Kristen Bretz contributed a virtual talk in the "Non-perennial Streams: An Interface Between Hydrology, Ecology, Biogeochemistry, and Society" special session at the 2021 American Geophysical Union conference this week. Her talk shared new results from the final chapter of her dissertation, in which she is comparing water quality and metabolic consequences of stream fragmentation and reconnection in a pair of non-perennial mountain streams near Blacksburg, VA, USA:

Bretz, K.A., J.P. Gannon, & E.R. Hotchkiss. 2021. Metabolic patterns of non-perennial temperate forest streams. American Geophysical Union Conference. Virtual Talk.

2021-12-13 - López Lloreda contributes to Puerto Rico NEON Data Jam

Carla López Lloreda was part of a recent STEM outreach and education program, "Puerto Rico NEON Data Jam", where Carla and other professionals worked with 6 teachers and 50 students in Puerto Rico on projects using real-world scientific data from the National Ecological Observatory Network's (NEON) Guánica Dry Forest site to test research questions of interest to the students. Carla, her collaborators, and several of the students and instructors who were part of the project shared their experiences in this video:

2021-12-10 - Photos from the field: Slavkov Forest, Czech Republic

Katherine X. Pérez Rivera has been in the Czech Republic for over 3 months now as part of her Fulbright Research Grant. She is studying stream metabolism and collaborating with the Czech Geological Survey (CGS) on their over 30 year monitoring of small catchments in the Slavkov Forest, a place that is well-known for its mineral waters and contrasting lithology. She has been visiting field sites on a monthly basis to check on sensors and download data as well as assist with regular sampling. She will continue to work there until June 2022 and is excited about this collaboration with CGS and all the different experiences she is having as part of this educational and cultural exchange.

Check out the wonderful photos and annotations below from Katherine!

2021-12-09 - Co-authored paper featured in Eos Editor's Highlight

A recent paper led by Lluís Gómez Gener and co-authored by Erin Hotchkiss (Gómez-Gener et al. 2021 Water Resources Research) was selected for featuring as an Editor’s Highlight in the American Geophysical Union’s science news magazine:

van Meerveld, I. “Export of Different Carbon Types from a Boreal Catchment”.
Eos. 2 December 2021.

2021-11-22 - Photos from the field: Coweeta, NC

Erin recently returned from our final Coweeta field campaign of 2021! We're monitoring an experimentally warmed and a 2nd reference stream to test how increasing temperatures alter carbon fluxes, metabolism, and fate in headwater networks. This trip happened at the perfect time to appreciate the significance of annual leaffall inputs to Coweeta streams every autumn - the small streams were covered! This project is an NSF-funded collaboration with folks at University of Alabama, University of Georgia, Coastal Carolina University, and University of Connecticut.

2021-11-12 - Hotchkiss co-leads first #VTBioWalk

Earlier this week, Erin Hotchkiss co-led a nature walk with Ignacio Moore (Professor, Biological Sciences) as part of our department's "Building Belonging in Biology" efforts led by Meg Emori (Instructor, Biological Sciences). We walked with undergraduate students from Derring Hall to Stroubles Creek and the Duck Pond while making observations and sharing knowledge about the environment around us. It was a great chance to connect/reconnect with students, facilitate in-person interactions among students and faculty beyond the classroom, and watch otters! A short video from our outing can be viewed here:

November 2021 #VTBioWalk on Virginia Tech's Blacksburg, VA campus led by Hotchkiss & Moore. Photo credits: Steven Mackay (all but the otter photo) & Gavriel Cambridge (the otters!).

2021-10-29 - Photos from the field: Tom's Creek network, VA

Stephen Plont recently completed the second of two multi-week sampling campaigns throughout the Tom's Creek network in Blacksburg, VA. Plont is tracing the biogeochemical consequences of stream confluences as part of his dissertation research; data from October sampling will be compared with measurements from the same sites during summer 2021 to explore seasonal changes in water quality and ecosystem function. We're excited to see what we learn about metabolism and nutrient fluxes above/below confluences and throughout the fluvial network!

2021-09-16 - Bretz leads new article published in JGRB

Kristen Bretz recently published the first chapter of her dissertation, "Integrating Ecosystem Patch Contributions to Stream Corridor Carbon Dioxide and Methane Fluxes" in the Journal of Geophysical Research - Biogeosciences! Kristen's paper was co-authored with three former undergraduate researchers in our lab, Alexis Jackson, Sumaiya Rahman, and Jonathon Monroe, as well as Erin Hotchkiss.

Summary: Carbon dioxide and methane emissions from freshwaters can be very different depending on where they are measured in a watershed. As distinct areas near a stream become connected by water moving through the watershed, stream greenhouse gas emissions may change in response to new carbon inputs from these connections. We found that CO2 and CH4 emissions were spatially variable within streams. CO2 emissions were different between our two study summers while CH4 emissions were more stable. We also found that the presence of vernal pool wetlands near a stream elevated total stream corridor carbon emissions.

Citation: Bretz, K.A., A.R. Jackson, S. Rahman, J.M. Monroe, & E.R. Hotchkiss. 2021. Integrating ecosystem patch contributions to stream corridor carbon dioxide and methane fluxes. Journal of Geophysical Research – Biogeosciences 126: e2021JG006313.

2021-09-02 - Hotchkiss co-authors article in Advances in Water Research

Hotchkiss and colleagues working on freshwater salinization research and management recently published an article in The Water Research Foundation's magazine, Advances in Water Research. From the article: "Inland freshwater salinity is rising globally, a trend that threatens water and food supplies, civil infrastructure, and freshwater ecosystems. There is an urgent need to reverse freshwater salinization by engaging practitioners, scientists, policy makers, entrepreneurs, and the public."

Citation: Grant, S.B., H. Zhang, S.V. Bhide, T. Birkland, E. Berglund, A. Dietrich, J.L. Druhan, M. Edwards, S. Entrekin, J. Gomez-Velez, E. Hester, E.M.V. Hoek, E.R. Hotchkiss, D. Jassby, S.S. Kaushal, P. Kumar, K. Lopez, A. Maile-Moskowitz, K. McGuire, S. Mohanty, E.A. Parker, G. Prelewicz, M.A. Rippy, E.J. Rosenfeldt, T. Schenk, K. Schwabe, & P. Vikesland. 2021. Reversing Freshwater Salinization: A Holistic Approach. Advances in Water Research 31(3): 24-29.

2021-08-31 - Pérez Rivera and López Lloreda receive ASLO Global Outreach Initiative Grant

Graduate students Katherine X. Pérez Rivera and Carla López Lloreda are co-PIs on a recently awarded Global Outreach Initiative Grant from the Association for the Sciences of Limnology and Oceanography (ASLO): "Bringing Limnology and STEM careers to the classroom: Engaging with underrepresented high school students". Their project will implement a hybrid program to expose underrepresented minority high school students in Puerto Rico to limnology and STEM fields. The program will consist of online workshops focused on teaching students about different watershed compartments and exploring related data sets. Students will also develop and lead their own short-term research projects aided with common research tools used in limnology that will be made available to them. The program will culminate with a symposium where they will merge science and art by sharing their final projects and creating a community art project about what they've learned throughout the program. They will also have the chance to interact with Puerto Rican professionals in limnology and related fields during the program.

Congratulations, Carla and Katherine! We're excited to follow the progress of this collaboration!

Katherine X. Pérez Rivera & Carla López Lloreda

2021-08-27 - Hotchkiss co-authors new paper in Water Resources Research

A new paper led by Lluís Gómez-Gener, "Integrating discharge-concentration dynamics across carbon forms in a boreal landscape", was recently published in Water Resources Research! From the paper's summary: "Carbon transferred from soils to streams plays an important role in aquatic ecosystems and is relevant for carbon budget estimates at broader scales. The consequences and fate of carbon exported from land to water is influenced by the form of that carbon (e.g., dissolved organic carbon (DOC) or gases like carbon dioxide and methane). Yet, we still know little about what factors regulate the makeup of carbon that enters streams, including how it is influenced by the different “interface zones” that lie between soil sources and stream channels. We used seven years of data from a well-studied boreal research site to characterize the composition of carbon flux from three small streams dominated by different types of interfaces, including riparian forests, a large wetland, and a lake. Our results demonstrate that snowmelt periods are dominated by DOC and downstream transport, whereas high flow events in summer and autumn promote relatively greater carbon gas evasion to the atmosphere [Fig 5 below]. DOC dominated export at all sites, but the relationships between water flow and the concentration of different carbon forms varied among sites and over time, reflecting differences in how interface zones regulate, store, and transform carbon before it reaches streams [Fig 6 below]."

Citation: Gómez-Gener, L., Hotchkiss, E. R., Laudon, H., & Sponseller, R. A. (2021). Integrating discharge-concentration dynamics across carbon forms in a boreal landscape. Water Resources Research, 57, e2020WR028806.

2021-08-01 - Photos from the field: National Ecological Observatory Network streams!

Our NSF-funded Macrosystems Project, "Linking land-to-water transport and stream carbon cycling to inform macrosystem carbon balance", is characterizing terrestrial carbon inputs to and ecosystem metabolism within streams across the United States. In addition to leveraging the terrestrial and aquatic data collected by the National Ecological Observatory Network (NEON), we installed in situ sensors to record high-frequency changes in stream carbon dioxide concentrations. We will use these data to support ecosystem metabolism, groundwater input, and stream network carbon flux modeling and analyses.

Collaborators recently shared photos from two of our five core study streams: Martha Creek, WA (lefthand photo) and Caribou Creek, AK (righthand photo). We are excited to learn more from these and other sensor datasets as part of our collaborative project!

2021-07-30 - Murphy and deToll share their science at summer research symposium

Undergraduate researchers Natalie Murphy and Felicity deToll presented updates from their research projects at Virginia Tech's 2021 Summer (Virtual) Research Symposium this week!

Natalie shared results from her GCC-supported project, "Spatial Variability of Microbial Metabolism in Mining-Impacted and Reference Streams", which she conducted with mentor Kristen Bretz.

Felicity presented the work she completed this summer as a Fralin Summer Undergraduate Research Fellow, "Similar carbon uptake rates among wetlands with different development histories", which she completed with mentors and collaborators Stephen Plont, Katherine Pérez Rivera, Kristen Bretz, Carla López Lloreda, and Morgan Wood.

Congratulations to Felicity, Natalie, and collaborators! Great work!

2021-06-02 - Congratulations to Dr. Mohammed Hamdan!

Mohammed Hamdan successfully defended his Doctoral thesis in Ecology at Umeå University! The title of his thesis was "Effects of temperature and terrestrial carbon on primary production in lake ecosystems", which included two chapters already published in peer-reviewed journals:

  1. Hamdan, M., P. Byström, E.R. Hotchkiss, M.J. Al-Haidarey, J. Ask, & J. Karlsson. 2018. Carbon dioxide stimulates lake primary production. Scientific Reports 8: 10878. doi:10.1038/s41598-018-29166-3

  2. Hamdan, M., P. Byström, E.R. Hotchkiss, M.J. Al-Haidarey, & J. Karlsson. 2021. An experimental test of climate change effects in Northern lakes: Increasing allochthonous organic matter and warming alters autumn primary production. Freshwater Biology 66: 815– 825. doi: 10.1111/fwb.13679

Mohammed was co-supervised by Jan Karlsson (UmeåU), Pär Byström (UmeåU), and Erin Hotchkiss (VT). Congratulations, Dr. Hamdan! I (Erin) hope we can celebrate your success in person soon!

2021-05-28 - Photos from the field: Stroubles Creek network, VA

PhD student Katherine Pérez Rivera will be measuring solute dynamics in different locations across the Stroubles Creek watershed in Blacksburg, VA. These are great sites to test questions about the interactions between landscape heterogeneity and stream network biogeochemistry; the Stroubles watershed includes town, campus, agricultural land cover, rural development, parks, and forests.

2021-05-28 - Hotchkiss Lab at #2021SFS

Members of our research group contributed to several talks and posters at the 2021 Society for Freshwater Science (SFS) annual conference. We enjoyed opportunities to engage with other freshwater scientists across the globe on the virtual platform this year. We’re also looking forward to a hopefully in-person Joint Aquatic Sciences Meeting in 2022!

Presentations as lead authors or co-authors:

Lab members in bold; *=graduate student; **=undergraduate student

Bretz. K.A.*, N. Murphy**, & E.R. Hotchkiss. Stream fragmentation disrupts carbon emissions and transport. View talk.

Plont, S.*, J. Riney**, & E.R. Hotchkiss. Integrating perspectives on dissolved organic carbon removal and metabolism. View talk.

C. López Lloreda*, A. Herreid, & W.H. McDowell. The future of stream greenhouse gas dynamics in a stormier and drier tropical landscape.

Hotchkiss, E.R., C. Braswell**, K.A. Bretz*, A. Gray, C. López Lloreda*, L. Morris**, N. Murphy**, B. Onozuka**, K. Pérez Rivera*, & S. Plont*. A global assessment of organic carbon metabolism and spiraling in running waters. You can learn more about this collaboration (and contribute to our database!) at

Hall, R.O., M.A. Baker, E.R. Hotchkiss, & S. Plont*. Modelling delayed respiration of labile DOC in a stream.

Tomczyk, N., A. Kaz, E.R. Hotchkiss, V. Gulis, J. Benstead, & A. Rosemond. Temperature effects on nutrient uptake in heterotrophic streams.

Cross, W., K. Anderson, A. Benke, T. Brey, E.R. Hotchkiss, A.D. Huryn, J. Jones, L. McGill, C. Patrick, P. Saffarinia, E. Scholl, M. Troia, J.B. Wallace, & M. Whiles. Investigating energetic scaling predictions for stream invertebrate communities.

James, A., E.R. Hotchkiss, D. McLaughlin, G. Pond, S. Schoenholtz, T. Timpano, C. Zipper, & S. Entrekin. Insect biomass and emergence sustained despite mayfly declines in mini-induced salinized Appalachian headwaters.

Other contributions to #2021SFS:

  • Carla co-convened a special session, "Greenhouse gases in tropical streams, rivers, lakes and wetlands" (with primary convener N Marzolf and co-conveners D Riveros-Iregui, C Duvert, & M Ardón), and was a graduate student mentor in the Instars-Emerge program.

  • Kristen hosted a virtual coffee break, “Show Me Your Pets!”, and co-organized the Student Resources Development Committee’s annual Student-Mentor Mixer.

  • Stephen helped put together two pre-meeting workshops with the Student Resources Development Committee’s Undergraduate Affairs subcommittee to prepare undergraduate attendees for the virtual SFS meeting. Stephen also co-moderated the live discussion for presentations in “Hydroecology” with D Wynne.

  • Erin co-convened two special sessions: (1) "Beyond lentic or lotic: Integrating the science of inland waters" (with primary convener M Fork and co-conveners J Gardner, S Jones, & C Solomon) & (2) "Exploring freshwater ecosystems under a changing climate via storm-driven nutrient, carbon, and sediment transport and biogeochemical cycling" (with primary conveners A Hounshell & SL Speir and co-conveners M Bieroza, J Hosen, & JL Tank). Erin also co-moderated the live discussion for presentations in “Lentic Ecology” and “Beyond lentic or lotic…” with R Brown.

Title slides for talks presented by members of the lab at SFS 2021

Flyer for "Show me your pets!" coffee break hosted by Bretz; Breakout group during the Student-Mentor Mixer co-organized by Bretz

2021-05-18 - Congratulations to our VT 2021 graduates!

Cameron Braswell (Biological Sciences) and Bryce Onozuka (Biological Sciences & Economics) graduated with their Bachelor's degrees from Virginia Tech this month! Bryce and Cameron collaborated with our research group on the development and analysis of a global database of ecosystem metabolism estimates from streams and rivers, which will be presented at the Society for Freshwater Science's annual meeting this month. Congratulations on your graduation! We're excited to see what comes next for you!

Cameron Braswell
Image from

2021-05-12 - Carla López Lloreda receives 2021 SWS Grant

Carla López Lloreda was awarded research funding through a Society of Wetland Scientists (SWS) Biogeochemistry Section 2021 Summer Research Grant! Her proposal was titled "Wetland greenhouse gas dynamics in a changing world: the influence of land use in tropical coastal wetlands." Carla will explore differences in greenhouse gas dynamics between forested and emergent Puerto Rican wetlands. Her research will also test the influence of land use on wetland carbon dioxide and methane emissions and contribute to a broader effort developing wetland health assessments in Puerto Rico.

2021-05-10 - Kristen Bretz receives 2021 VWRRC Grant

Kristen Bretz was awarded research funding through the 2021 Virginia Water Resources Research Center's (VWRRC) Student Competitive Grant Program! Her proposal was titled "Biological Controls on Water Quality in Contracting and Expanding Headwater Streams". Kristen will test how in-stream metabolism of terrestrial-derived materials differs within and among two neighboring intermittent mountain streams with unique valley and channel characteristics, and the degree to which differences in metabolism influence the downstream transport of carbon and nutrients.

2021-04-16 - Hamdan & Hotchkiss co-authors on new paper in Freshwater Biology

Mohammed Hamdan, a Ph.D. student at Umeå University in Sweden who is co-supervised by Erin Hotchkiss, recently published a chapter of his dissertation: Hamdan, M., P. Byström, E.R. Hotchkiss, M.J. Al-Haidarey, & J. Karlsson. 2021. An experimental test of climate change effects in Northern lakes: Increasing allochthonous organic matter and warming alters autumn primary production. Freshwater Biology 66: 815– 825. doi: 10.1111/fwb.13679.

This work tested the effects of warming (+ 3℃) and increased colored dissolved organic matter (cDOM) inputs on gross primary production (GPP) in experimental pond ecosystems during autumn months. cDOM inputs decreased GPP at ambient temperature conditions, while warming increased GPP at all levels of cDOM. Warming delayed autumn ice cover formation by 2 weeks but did not affect light availability in the water column compared to ambient ice‐covered treatments. GPP during the ice-on period was still affected by warming and cDOM. Climate change may shift whole‐ecosystem GPP through different habitat‐specific responses of GPP to increasing cDOM inputs and warming. Our findings stress the importance of accounting for multiple climate drivers and habitats when predicting how lake GPP will respond to climate change.

2021-04-01 - Hotchkiss interviewed for "Women in Ecology" spotlight

Thanks to the folks at the National Ecological Observatory Network (NEON) for the opportunity to share a bit about myself, my science, and some of my perspectives as a mentor and woman in ecology!

Women In Ecology Spotlight:

2021-03-31 - Photos from the field: Coweeta, NC

Erin took a quick solo trip down to Coweeta Hydrologic Lab, NC (~4.5 hour drive from Blacksburg, VA) to check on sensors deployed for our NSF-funded whole-stream warming project. It's been challenging to maintain ongoing projects during the pandemic and we're still nowhere close to being back to "normal", especially for fieldwork where we need to travel to and stay overnight at further away sites. That said, it was nice to be back at Coweeta for the start of spring and remember the joy of sitting by streams while dreaming up new research questions! We're thankful for project extensions and support from NSF to keep this work moving forward while prioritizing the health, safety, and continued support of our project team. Next up: additional data collection to support metabolism modeling through summer/fall!

Carla was also able to get permission from our college to visit field sites for our NSF-funded wetland connectivity project in Maryland recently. Check out a few of Carla's photos here!

2021-03-03 - Bretz & Hotchkiss co-authors on new paper in ES&T Water

Kristen Bretz and Erin Hotchkiss co-authored a recent paper on "Salt Dilution and Flushing Dynamics of an Impaired Agricultural–Urban Stream" in Environmental Science & Technology | Water. This paper emerged from a multi-year collaboration, led by Ph.D. students in Virginia Tech's Interfaces of Global Change interdisciplinary graduate program, using multi-year high-frequency sensor data collected at Virginia Tech's StREAM Lab (managed by Cully Hession, a professor in Biological Systems Engineering and the other faculty mentor of this project).

Lakoba, V.T., L.L. Wind, S.E. DeVilbiss, M.E. Lofton, K.A. Bretz, A.R. Weinheimer, C.E. Moore, C. Baciocco, E.R. Hotchkiss, & W.C. Hession. 2021. Salt Dilution and Flushing Dynamics of an Impaired Agricultural-Urban Stream. ES&T | Water 1: 407-416. doi: 10.1021/acsestwater.0c00160

Congratulations to the student team who led this project! I'm excited to see how this inspires future research on salinization and solute dynamics in streams draining complex landscapes.

2021-02-18 - Kristen Bretz recognized for creative science communication at AGU 2020

Kristen Bretz's haiku submitted to the American Geophysical Union (AGU) Water Quality Technical Committee's #HaikuYourResearch competition received 2nd place:

little streams flow down

visit wetlands on the way

release more carbon

- Kristen Bretz (2020)

This competition was part of the December 2020 virtual AGU meeting. Kristen also shared her science in a more "traditional" poster format: Bretz, K, A.R. Jackson*, S. Rahman*, J. Monroe*, & E.R. Hotchkiss. 2020. Integrating Ecosystem Contributions to Stream Corridor Carbon Dioxide and Methane Fluxes. American Geophysical Union. Virtual Meeting. Poster. Congratulations, Kristen!

* undergraduate alumni of the our lab group

2021-02-17 - Stephen Plont receives 2020 AGU Outstanding Student Presentation Award

Stephen Plont received an Outstanding Student Presentation Award for his virtual talk at the American Geophysical Union's (AGU) annual meeting in December 2020. His talk was titled "Mixing Downstream of Stream Confluences Alters Carbon and Nutrient Cycling in Freshwater Networks", and was given as part of a special AGU Hydrology session on "Frontiers in Water Quality Science". Co-authors on the talk were Jacob Riney (undergraduate, VT 2020), Caitlin Miller (undergraduate, VT 2019), and Erin Hotchkiss. Congratulations, Stephen!

You can view a copy of Stephen's slides here. The video of his presentation is embedded below for your viewing pleasure!

2021-01-19 - Natalie Murphy receives GCC Undergraduate Research Grant

Natalie Murphy, an undergraduate researcher in our lab mentored by Kristen Bretz, was awarded a research grant from Virginia Tech's Global Change Center (GCC)! Natalie is a junior at Virginia Tech majoring in Biochemistry with a Chemistry minor. The GCC award will fund Natalie's proposed research quantifying the spatial variability of microbial metabolism in mining-impacted and reference streams near Blacksburg, VA. Congratulations, Natalie!

Update 2021-02-09: GCC article announcing 2021 research grants!