Current Research

Carbon cycling and the metabolic regime of an east Texas stream

Although less than 1% of the Earth's surface, inland freshwaters are active components of global carbon (C) cycling. Streams and rivers receive C from the terrestrial landscape, where over half is buried or emitted as carbon dioxide (CO2) to the atmosphere, before being exported to the ocean. It is this tie of C cycling in freshwaters to regional and global budgets that drives our interest in understanding metabolic processes in streams and rivers.

Using high-frequency temporal data collected using sensors deployed in Harmon Creek, we are working on quantifying the particulate and dissolved organic C fluxes and standing stocks in addition to quantifying ecosystem metabolism.

This work is in-part funded by SHSU COSET Undergraduate Research awards that were co-led by Makayla Mcilhaney and Katrina Stephen (SHSU undergraduates) in Summer & Fall 2021 and Makayla Hernandez and Danielle Grabert in Spring 2022.

RAPID: Quantifying the response of stream ecosystems to a punctuated cold-stress disturbance across a semi-arid to sub-humid gradient

National Science Foundation funded (NSF-DEB-2128280) project studying the effect of the 2021 Polar Vortex on Texas Coastal Streams

Collaborators: Drs. J. Derek Hogan (Lead, TAMUCC), Chris Patrick, Bradley Strickland (VIMS), Hannah Vander Zanden, Matt Whiles (University of Florida)

TERRG: Thresholds in ecosystem responses to rainfall gradients

National Science Foundation funded (NSF-DEB 1927639) project linking stream ecosystem metabolism to higher trophic levels in streams that span the precipitation gradient along the Texas coast.

Collaborators: Dr. Chris Patrick (VIMS), Dr. J. Derek Hogan (Texas A&M University Corpus Christi), Dr. Matt Whiles (University of Florida)

Response of Ecosystem Metabolism to Hurricane Harvey

National Science Foundation RAPID funded project to look at the effects of Hurricane Harvey, which hit the Texas Coast in fall of 2017. Amber is a collaborator of the project working up the oxygen data to estimate daily gross primary production and ecosystem respiration fluxes pre- and post-Harvey from streams along the precipitation gradient. The project also entails microbial, macroinvertebrate, and fish production from the same time span!

Collaborators: Dr. Christopher Patrick (Texas A&M Corpus Christi), Dr. J. Derek Hogan (Texas A&M Corpus Christi), Dr. Brandi Reese (Texas A&M Corpus Christi)

Past Research

Quantifying gas-exchange in Alpine streams

In order to quantify greenhouse gas (e.g. carbon dioxide, methane) and metabolic fluxes (e.g. ecosystem metabolism) in aquatic ecosystems, estimating the gas exchange across the air-water boundary is a key component. We are using argon as a tracer gas to estimate gas-exchange in high-gradient streams in the Swiss Alps. Our goal is to quantify gas-exchange across several streams varying in slope, channel geomorphology, and across various stream discharges. Our aim is to be able to predict gas-exchange in these high-gradient streams in order to quantify biogeochemical fluxes and ecosystem metabolism.

Ulseth, A.J., R.O. Hall Jr., M. Boix Canadell, H.L. Madinger, A. Niayifar, T.J. Battin. 2019. Distinct air-water gas exchange regimes in low- and high-energy streams. Nature Geoscience. doi:10.1038/s41561-019-0324-8

Press release by EPFL:

Collaborators: Dr. Tom Battin (EPFL), Dr. Bob Hall (Flathead Biological Station, University of Montana), Marta Boix Canadell (PhD student, EPFL), Dr. Hilary Madinger (Concordia University Wisconsin ), Dr. Daniel McGinnis (University of Geneva), and Dr. Amin Niayifar (former PhD student, EPFL)

Carbon cycling in Alpine streams (Switzerland)

While both high elevation and high latitude ecosystems are particularly susceptible to climate change, we know little of the contribution of C-cyling in alpine stream ecosystems. It is predicted that precipitation patterns in mountain ecosystems will shift from snow to rain as temperatures warm and snowpack is reduced. Furthermore, warming temperatures have led to a decrease not only in snowpack, but in glaciers as well. SBER at EPFL (led by Dr. Tom Battin) has several projects investigating ecosystem metabolism and carbon dioxide dynamics in these unique stream ecosystems.

Here is a video clip highlighting some of this work on C-cycling in Alpine streams.

Horgby, Å., P.L. Segatto, E. Bertuzzo, R. Lauerwald, B. Lehner, A.J. Ulseth, T.W. Vennemann, T.J. Battin. 2019. Unexpected large evasion fluxes of carbon dioxide from turbulent streams draining the world’s mountains. Nature Communications,

Boix Canadell, M., N. Escoffier, A.J. Ulseth, S.N. Lane, T.J. Battin. 2019. Alpine glacier shrinkage drives shift in dissolved organic carbon export from quasi-chemostasis to transport-limitation. Geophysical Research Letters.

Horgby, Å, M. Boix Canadell, A.J. Ulseth, T.W. Vennemann, T.J. Battin. 2019. High-resolution spatial sampling identifies groundwater as driver of CO2 dynamics in an Alpine stream network. Journal of Geophysical Research Biogeosciences.

Flury, S., A.J. Ulseth. 2019. Exploring the sources of unexpected high methane concentrations and fluxes from Alpine headwater streams. Geophysical Research Letters.

Collaborators: Dr. Tom Battin (EPFL), Dr. Nicolas Escoffier (University of Lausanne), Dr. Janine Rüegg (University of Lausanne), Sabine Flury (EPFL), StreamPULSE (NSF Macrosystems), and PhD students (EPFL): Åsa Horgby, Marta Boix Canadell, and Pier Luigi Segatto

Ecosystem metabolism and dissolved organic carbon (DOC) in Austrian streams

Ecosystem metabolism is the combination of gross primary production (GPP) and ecosystem respiration (ER). The balance between GPP and ER within a stream reach is indicative to how that stream reach functions in regards to basal carbon resources. We had several projects focusing on ecosystem metabolism in Austrian streams. One focus was on temporal and spatial dynamics of GPP, ER, and NEP across a subalpine stream network where we measured ecosystem metabolism in 15 streams for over 18 continuous months.

One of our key findings was that we could link ecosystem metabolism as a functional metric to climate change. We illustrated that reduced snowpack, and therefore, residence snowmelt in the spring resulted in NEP to shift from autotrophy to heterotrophy across an elevational gradient. This shift could potentially have effects on the annual metabolic carbon fluxes, resulting in more respiratory CO2 production in a warming world.

Another focus was on the effect of land-use on ecosystem metabolism, where we focused on a 'snap-shot' of metabolism across a land use gradient in stream catchments across the Austrian and Czech Republic border where we were able to link DOC and nutrients to ER fluxes.

Lastly, I was also able to collaborate on a project focusing on the potential effect of light and priming on ecosystem respiration. This approach involved growing phototrophic biofilms under a gradient of light and then introducing those biofilms to terrestrial DOC in microcosms. We found light drove the production of phototrophic biofilms, resulting in a distinct autochthonous fingerprint on the DOC pool. Furthermore, we found that heterotrophic bacteria used algal sources of DOC if they were available, indicating that priming did not occur.

Ulseth, A.J., E. Bertuzzo, G.A. Singer, J. Schelker, T.J. Battin. 2017. Climate-Induced Changes in Spring Snowmelt Impact Ecosystem Metabolism and Carbon Fluxes in an Alpine Stream Network. 2017. Ecosystems. doi:10.1007/s10021-017-0155-7.

Press release by EPFL summarizing the article on Snowmelt and Ecosystem Metabolism: streams-produce-more-co2-after-a-warm-winte/

Fuß, T., B. Behounek, A.J. Ulseth, and G.A. Singer. 2017. Land use controls stream ecosystem metabolism by shifting dissolved organic matter and nutrient regimes. Freshwater Biology. doi:10.1111/fwb.12887.

Wagner, K., M.M. Bengtsson, R.H. Findlay, T.J. Battin, A.J. Ulseth. 2017. High light intensity mediates a shift from allochthonous to autochthonous carbon use in phototrophic stream biofilms. Journal of Geophysical Research Biogeosciences. 10.1002/2016JG003727

Collaborators: Dr. Tom Battin (EPFL), Dr. Gabriel Singer (IGB Berlin), Dr. Jakob Schelker (University of Vienna), Dr. Enrico Bertuzzo (EPFL), Dr. Mia M. Bengtsson (University of Greifswald), Robert. H. Findlay (University of Alabama), Dr. Karoline Wagner

CO2 evasion and dissolved organic carbon (DOC) export from Austrian Alpine streams

As the contribution of inland freshwaters to regional and global carbon budgets has become realized, quantifying the contribution of C sources to C fluxes is essential. I had the opportunity to collaborate on several projects, including quantifying CO2 evasion and DOC fluxes from subalpine streams located in the Ybbs River Network in lower Austria.

Schelker, J., G.A. Singer, A.J. Ulseth, S. Hengsberger, and T.J. Battin. 2016. CO2 evasion from a steep, high gradient stream network: importance of seasonal and diurnal variation in aquatic pCO2 and gas transfer.Limnology and Oceanography. doi:10.1002/Ino.10339

Fasching, C., A.J. Ulseth, J. Schelker, G. Steniczka, and T.J. Battin. Hydrology controls dissolved organic matter export and composition in an Alpine stream and its hyporheic zone. 2015. Limnology and Oceanography. doi:10.1002/lno.10232

Collaborators: Dr. Tom Battin (EPFL), Dr. Gabriel Singer (IGB Berlin), Dr. Jakob Schelker (University of Vienna), Dr. Christina Fasching (University of Vienna)

Colorado River, Grand Canyon: Sources and Loss of DOC

Dissolved organic carbon (DOC) is a major flux of carbon in rivers. Quantifying the sources and fate of DOC is key to understanding how carbon is processed in these freshwater ecosystems.

The Colorado River, Grand Canyon is an ideal ecosystem to model sources and fates of DOC. The construction of Glen Canyon Dam has essentially cut off the Colorado River from upstream reaches, resulting in a distinct boundary of the ecosystem.

Part of my dissertation research focused on modeling the processes that drive DOC concentration along the 360+ km reach of the Colorado River, Grand Canyon.

Ulseth, A.J., R.O. Hall Jr., and T. Kennedy. Quantifying sources and loss of dissolved organic carbon in a large, desert river using a Bayesian modeling approach.Resubmitted, following major revisions, JGR Biogeosciences.

Collaborators: Dr. Robert O. Hall Jr. (Flathead Biological Station, Montana), Dr. Ted Kennedy and Kate Behn (Grand Canyon Monitoring and Research Center, USGS), Dr. Emma Rosi (Cary Institute of Ecosystem Studies), Dr. Colden Baxter (Idaho State University), Dr. Wyatt Cross (Montana State University)

Reservoirs & Tailwaters impact organic carbon export

Impoundments and their respective tailwaters have altered riverine flow regimes. In order to quantify the effect of altered flow regimes on dissolved organic carbon (DOC) in arid Western Rivers, I quantified the export of organic carbon in regulated and non-regulated reaches of the Yampa and Green Rivers in the upper Colorado River basin.

I quantified the concentration and quality of DOC along the hydrograph above and below Flaming Gorge and Fontenelle Reservoir and their respective tailwaters on the Green River, as well as the Yampa River. I found reservoirs impact organic carbon export by reducing and transforming terrestrial organic carbon while likely producing algal-derived DOC. Furthermore, tailwater ecosystems produced similar amounts of algal-derived organic carbon as trapped behind the dams, thus further altering organic carbon export to downstream ecosystems.

Ulseth, A.J. and R.O. Hall Jr. 2015. Dam tailwaters compound the effects of reservoirs on the longitudinal transport of organic carbon in an arid river. Biogeosciences 12: 4345-4359. doi:10.5194/bg-12-4345-2015.

Collaborator - Dr. Bob Hall, University of Wyoming, now at the Flathead Biological Station, University of Montana

The role of migratory fish on nitrogen cycling in Venezuelan streams

Subsidies to stream ecosystems can be an imperative component to biogeochemical cycles. As a research technician, I managed a NSF funded project investigating the role of a migratory fish, Prochilodus mariae, on the nitrogen (N) cycle in N-limited Venezuelan streams.

Collins, S.M., N. Bickford, P.B. McIntyre, A. Coulon, A.J. Ulseth, D.C. Taphorn, and A.S. Flecker. 2013. Population structure of a Neotropical migratory fish: contrasting perspectives from genetics and otolith microchemistry. Transactions of the American Fisheries Society 142: 1192-1201.

Solomon, C.T., E.R. Hotchkiss, J.M. Moslemi, A.J. Ulseth, E.H. Stanley, R.O Hall, & A.S. Flecker. 2009. Sediment size and nutrients regulate denitrification in a tropical stream. Journal of the North American Benthological Society, 28: 480-490.

Taylor, B.W., C.F. Keep, R.O. Hall, B.J. Koch, L.M. Tronstad, A.S. Flecker, & A.J. Ulseth. 2007. Improving the fluorometric ammonium method: matrix effects, background fluorescence, and standard additions. Journal of the North American Benthological Society, 26: 167-177.

Collaborators - Dr. Alex Flecker (Cornell University), Dr. Bob Hall (University of Wyoming, now at the Flathead Biological Station, University of Montana)

Tracing anthropogenic N and C into urban stream food webs

For the research I conducted for my MS in NC, we were able to show that the natural abundance of 13C and 15N could be used to trace the incorporation of anthropogenic nitrogen and carbon into urban stream food webs from point sources. This was a proof of concept paper, which has implications towards many of the other chemical constituents that are released into our waterways today.

Ulseth, A.J. and A.E. Hershey. 2005. Natural abundances of stable isotopes trace anthropogenic N and C in an urban stream. Journal of the North American Benthological Society, 24: 270-289. Recommended by Faculty of 1000.

Collaborator - Dr. Anne Hershey (University of North Carolina Greensboro)