Current Research

We study the chemicals that make up life on earth and how they change in freshwater ecosystems.

What's in the water? Why is it there? How does it change? What does that mean for things that live in the water or the water we drink?

Freshwater ecosystems (streams, wetlands, ponds, rivers, lakes, and reservoirs) provide many important services, including drinking water, fisheries production, pollutant removal, flood control, and recreation. Changes in the environment (for example: storms/droughts, pollution, landscape development, climate change, and flow modifications) can disrupt or enhance the services provided by freshwaters, often through alterations in freshwater ecology (the interactions between living things and their environment).

As freshwater ecosystems expand and contract across landscapes and merge together at confluences, they connect and disconnect different sources of water and chemicals. The chemicals entering water from land and confluences can serve as food resources or pollutants, and thus alter the ecology of freshwater ecosystems. When the living things within freshwaters (algae, bacteria, fungi, plants, and animals) breathe, eat, grow, reproduce, and die, they respond to and change the chemistry of the water around them. 

We study the chemicals that make up life on earth and how they change in freshwater ecosystems. We investigate the connections between freshwater chemistry and ecology using environmental sensors, water chemistry analyses, experiments, and ecosystem models. Our research provides new knowledge about how freshwater ecosystems function as well as how changes in the environment alter freshwater chemistry, ecology, and ecosystem services.

Technical descriptions of our current research collaborations are provided below.

Photo from the air of boreal forest, meadow, and stream

Linking terrestrial-aquatic fluxes and stream carbon cycling to inform meta-ecosystem carbon balance

The movement of carbon (C) across land-water boundaries is a critical factor for metabolism in freshwater ecosystems and the net C balance of watersheds. Because streams are a primary interface between terrestrial and freshwater ecosystems, they are ideal test beds to advance understanding of land-water C transfers and meta-ecosystem ecology (i.e., the study of multiple ecosystems linked by energy and material transfers). Our research seeks to answer: (1) What is the magnitude and variability of land-to-water C transfers and stream C emissions? (2) How does meta-ecosystem C cycling vary within and among paired terrestrial-aquatic National Ecological Observatory Network (NEON) research sites across the United States? (3) What controls C form, cycling, and fate in meta-ecosystems? Our research will advance a predictive understanding of the daily, seasonal, and annual processes controlling watershed C cycling through measurements and models that cross land-water boundaries and approaches that integrate biology, geology, and chemistry across space and time. Collaborators: D Butman (University of Washington), W Wollheim (University of New Hampshire), J Jones (University of Alaska Fairbanks), K Cawley & K Goodman (NEON). "Collaborative Proposal: MRA: Linking land-to-water transport and stream carbon cycling to inform macrosystem carbon balance" - funded by NSF DEB. Funding period: 2020-2023.

DelVecchia, A.G., S. Rhea, K.S. Aho, E.H. Stanley, E.R. Hotchkiss, A. Carter, & E.S. Bernhardt. 2023. Variability and drivers of CO2, CH4, and N2O concentrations in streams across the United States. Limnology & Oceanography 68: 394-408.
Battin, T.J., E. Bernhardt, E. Bertuzzo, L. Gómez Gener, R.O. Hall, E.R. Hotchkiss, R. Lauerwald, T. Maavara, T. Paveksly, L. Ran, P. Raymond, P. Regnier, & J. Rosentreter. 2023. River ecosystem metabolism and carbon biogeochemistry in a changing world. Nature 613: 449-459.
Conroy, H., E.R. Hotchkiss, K.M. Cawley, K. Goodman, R.O. Hall, J.B. Jones, W.M. Wollheim, & D. Butman. 2023. Seasonality Drives Carbon Emissions along a Stream Network. Journal of Geophysical Research – Biogeosciences 128: e2023JG007439. 
Iannucci, F.M., K. Olson, M.E. Muscarella, E.R. Hotchkiss, & J.B. Jones. Temperature and flow control organic matter metabolism in boreal headwater streams. In Preparation.

Hydrologic connectivity and carbon fluxes in wetland-dominated catchments

Worldwide, low-lying areas once rich in forested wetlands have been converted to agricultural production after draining and filling. Prior to their loss, the wetlands reduced flooding through water storage, provided downstream environments with an important energy source in the form of dissolved organic carbon, and played a critical role in regional carbon budgets. This research will test how spatiotemporal changes in surface and subsurface hydrology govern carbon dynamics in wetland-rich landscapes. Using coupled empirical and modeling components, we will quantify: (1) dynamics of surface water connections and surface-subsurface exchange at wetland and catchment scales; and (2) consequent hydrologic influences on wetland- and catchment-scale carbon dynamics. The study sites are on the Delmarva Peninsula of Maryland. Our research will integrate hydrologic sciences, ecosystem ecology, biogeochemistry, and restoration science; and ultimately, help inform wetland restoration and land management across the coastal plain region. Collaborators: DL McLaughlin, ER Hotchkiss, DT Scott, K Wardinski, C López Lloreda, & N Corline (Virginia Tech); CN Jones (University of Alabama); MA Palmer, J Maze, M Williams, & M Gonsior (University of Maryland). "Collaborative Research - Hydrologic Connectivity and Water Storage as Drivers of Carbon Export and Emissions from Wetland-Dominated Catchments" - funded by NSF DEB. Funding period: 2019-2023.

Wardinski, K.M., E.R. Hotchkiss, C.N. Jones, D.L. McLaughlin, B.D. Strahm, & D.T. Scott. 2022. Water soluble organic matter from soils at the terrestrial-aquatic interface in wetland-dominated landscapes. Journal of Geophysical Research – Biogeosciences 127: e2022JG006994.
López Lloreda, C., J. Maze, D. McLaughlin, C.N. Jones, D. Scott, M. Palmer, K. Wardinski, N. Corline, & E.R. Hotchkiss. Wetland CO2 and CH4 concentrations and variability in a hydrologically dynamic landscape. In Preparation.
Corline, N.J., E.R. Hotchkiss, D. Scott, J. Maze, B. Badgley, B. Strahm, & D. McLaughlin. Tadpole aggregations create biogeochemical hotspots in wetland ecosystems. In Preparation.

Ecology and management of salty freshwater ecosystems

Increased salt loading to inland waters is a "wicked environmental problem" with unknown consequences for freshwater ecosystem function. We are involved with collaborations focused on different aspects of freshwater salinization impacts and solutions, including two NSF-funded collaborations:

Past salinization-related collaborations include:

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.
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.
Grant, S.B., M.A. Rippy, T.A. Birkland, T. Schenk, K. Rowles, S. Misra, P. Aminpour, S. Kaushal, P. Vikesland, E. Berglund, J.D. Gomez-Velez, E.R. Hotchkiss, G. Perez, H.X. Zhang, K. Armstrong, S. Bhide, L. Krauss, C. Maas, K. Mendoza, C. Shipman, Y. Zhang, & Y. Zhong. 2022. Can common pool resource theory catalyze stakeholder-driven solutions to the freshwater salinization syndrome? Environmental Science & Technology 56: 13517-13527. doi:10.1021/acs.est.2c01555.
DeVilbiss, S.E., B.D. Badgley, E.R. Hotchkiss, & M.K. Steele. In Press. Subsidy-stress response of ecosystem functions along experimental freshwater salinity gradients. Biogeochemistry.
Bhide, S.V., S.B. Grant, S. Kaushal, K. McGuire, J. Gomez-Velez, E.R. Hotchkiss, M.A. Rippy, P. Vikesland, S. Saksena, T. Schenk, J. Webber, J. Jastram, & A. Sekellick. Stream water age drives patterns of inland freshwater salinization. In Revision.
Google Earth image of interconnected streams, forests, wetlands, ponds, and river that make up a boreal river discontinuum

Biogeochemical consequences of river network discontinuities

While flow discontinuities within river networks (e.g., wetlands, reservoirs, confluences, intermittent surface waters) are ubiquitous, we rarely account for ecosystem heterogeneity in network-scale measurements or simulations of water quality and ecosystem processes (e.g., carbon metabolism, nutrient uptake). Indeed, much of our current understanding of freshwater ecosystem function is still informed by predicted physical, chemical, and biological shifts from upstream to downstream ecosystems along a simplified stream-river continuum (i.e., the river continuum concept). Ongoing research is measuring biogeochemical consequences of discontinuities within river networks, including work led by graduate students working with me on NSF-funded projects who have developed dissertation research chapters addressing discontinuity knowledge gaps in addition to the core objectives of our NSF collaborations. A working group funded in 2019 is interested in "Ecosystem Mosaics and Broad-Scale Biogeochemistry".  Collaborators K Bretz, S Plont, KX Pérez Rivera (Virginia Tech), AM Helton (University of Connecticut), CT Solomon (Cary IES), SE Jones (Notre Dame), and others.

Hotchkiss, E.R., S.Sadro, & P.C. Hanson. 2018. Towards a more integrative perspective on carbon metabolism across lentic and lotic inland waters. Limnology & Oceanography Letters 3: 57-63. doi: 10.1002/lol2.10081
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.
Plont, S., D. Scott, & E.R. Hotchkiss. 2023. Biogeochemical processes are altered by non-conservative mixing at stream confluences. Water Resources Research 59: e2022WR034224.
Bretz, K.A., N.M. Murphy, & E.R. Hotchkiss. 2023. Carbon biogeochemistry and export governed by flow in a non-perennial stream. Water Resources Research 59: e2022WR034004.
Bretz, K.A., J.P. Gannon, & E.R. Hotchkiss. Metabolic patterns of non-perennial stream pools. In Preparation.
Monroe, J.M., K.A. Bretz, & E.R. Hotchkiss. Stream intermittency and fragmentation alters microbial metabolic potential. In Preparation.
Plont. S., C. Hemphill, J.E. Riney, & E.R. Hotchkiss. Carbon and nutrient cycling are suppressed downstream of a stream confluence. In Preparation.
Pérez Rivera, K.X., S. PlontG, & E.R. Hotchkiss. Longitudinal patterns in carbon cycling in a stream draining a heterogenous landscape. In Preparation.
Forested creek in VA

Dynamics of carbon and nutrient transport and fate

Time series of water chemistry, climate, hydrology, and ecosystem processes (carbon metabolism, nutrient cycling, food web dynamics) can identify changing patterns and controls of carbon and nutrient variability, transport, and fates within and among ecosystems. Considering the spatial and temporal dynamics of linked nutrient, carbon, and water cycles will help us better understand how the efficiency of ecosystem- and catchment-scale carbon and nutrient transformations may respond to environmental change. Ongoing research with KX Pérez Rivera (Virginia Tech). Additional collaborations with members of the Stream Resiliency RCN Working Group, Heterotrophic Regimes working group, and others.

Mineau, M.M., W.M. Wollheim, I.D. Buffam, S.E.G. Findlay, R.O. Hall, E.R. Hotchkiss, L.E. Koenig, W.H. McDowell, & T.B. Parr. 2016. Dissolved organic carbon uptake in streams: A review and assessment of reach-scale measurements. Journal of Geophysical Research - Biogeosciences 121: 2019-2029.
O'Donnell, B. & E.R. Hotchkiss. 2019. Coupling Concentration- and Process-Discharge Relationships Integrates Water Chemistry and Metabolism in Streams. Water Resources Research 55: 10179-10190. doi: 10.2029/2019WR025025.
Plont, S., B.M. O'Donnell, M.T. Gallagher, & E.R. Hotchkiss. 2020. Linking Carbon and Nitrogen Spiraling in Streams. Freshwater Science 39: 126-136. doi: 10.1086/707810.
Gómez-Gener, L., E.R. Hotchkiss, H. Laudon, & R.A. Sponseller. 2021. Integrating discharge-concentration dynamics across carbon forms in a boreal landscape. Water Resources Research 57: e2020WR028806. doi:10.1029/2020WR028806. 
O'Donnell, B. & E.R. Hotchkiss. 2022. Resistance and resilience of stream metabolism to high flow disturbances. Biogeosciences 19: 1111–1134.
Bertuzzo, E., E.R. Hotchkiss, A. Argerich, J.S. Kominoski, D. Oviedo-Vargas, P. Savoy, R. Scarlett, D. von Schiller, & J.B. Heffernan. 2022. Respiration regimes in rivers: Partitioning source-specific respiration from metabolism time series. Limnology & Oceanography 67: 2374-2388. doi:10.1002/lno.12207. 
Tromboni, F., E.R. Hotchkiss, A.E. Schechner, W.K. Dodds, S.R. Poulson, & S. Chandra. 2022. High rates of daytime river metabolism are an underestimated component of carbon cycling. Communications Earth & Environment 3: 270. doi:10.1038/s43247-022-00607-2. 
Tomczyk, N.J., A.D. Rosemond, J.S. Kominoski, D.W.P. Manning, J.P Benstead, V. Gulis, S.A. Thomas, E.R. Hotchkiss, & A.M. Helton. 2023. Nitrogen and phosphorus uptake stoichiometry tracks supply during two-year whole-ecosystem nutrient additions. Ecosystems 26: 1018-1032.
Arial image of experimental ponds with low/high organic matter treatments near Umeå, Sweden

Ecology and environmental change

Widespread changes in land use, climate, hydrology, and species composition are rapidly altering the structure and function of ecosystems. In addition to the whole-stream warming project described above, ongoing research collaborations related to environmental change include: 

In addition to the other ongoing projects related to environmental changes issues listed above, see past research for other examples of environmental change research (e.g., damming rivers, invasive species, and land use change).

Jonsson, M., P. Hedström, K. Stenroth, E.R. Hotchkiss, F. Vasconcelos, J. Karlsson, & P. Byström. 2015. Climate change modifies the size structure of assemblages of emerging aquatic insects. Freshwater Biology 60: 78-88.
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.
Creed, I.F., A.K. Bergström, C.G. Trick, N.B. Grimm, D.O. Hessen, J. Karlsson, K.A. Kidd, E. Kritzberg, D.M. McKnight, E.C. Freeman, O.E. Senar, A. Andersson, J. Ask, M. Berggren, M. Cherif, R. Giesler, E.R. Hotchkiss, P. Kortelainen, M.M. Palta, T. Vrede, & G.A. Weyhenmeyer. 2018. Global change-driven effects on dissolved organic matter composition: Implications for food webs of northern lakes. Global Change Biology 24: 3692-3714. 
Barney, J., T. Schenk, D. Haak, S. Salom, B. Brown, & E.R. Hotchkiss. 2019. Building Partnerships and Bridging Science and Policy to Address the Biological Invasions Crisis. Invasive Plant Science and Management.
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.
García, V.J., E.R. Hotchkiss, & P. Rodríguez. 2022. Ecosystem metabolism in sub-Antarctic streams and rivers impacted by non-native beaver. Aquatic Sciences 84: 54. doi: 10.1007/s00027-022-00876-1. 
Hamdan, M.G, J. Karlsson., E.R. Hotchkiss, & P. Byström. Warming strengthen trophic cascades and top-down control of pelagic and whole-lake primary production. In Revision.