Current Research

Headwater stream networks in a warming world

We will test the effects of temperature on organic matter breakdown at the stream reach and stream network scales. We will use data from temperature manipulations at multiple spatial and temporal scales at Coweeta Hydrologic Laboratory, NC to (1) inform ecological theory that uses basic principles to understand how the effects of temperature scale from individual organisms to entire ecosystems, and (2) build a model that simulates the effects of temperature on organic matter processing at the stream network scale. PIs: JP Benstead (Alabama), V Gulis (Coastal Carolina), AM Helton (University of Connecticut), AD Rosemond (UGA), ER Hotchkiss (Virginia Tech). "Headwater stream networks in a warming world: Predicting heterotrophic ecosystem function using theory, multi-scale temperature manipulations and modeling" - funded by NSF DEB.

Metabolic signatures of Swedish streams and rivers

This project will (1) determine how rates of ecosystem metabolism in Swedish rivers are shaped by regional climatic and anthropogenic gradients from hemi-boreal to the arctic, (2) quantify the extent to which streams in the Swedish landscape degrade terrestrial organic carbon and contribute to greenhouse gas evasion, and (3) advance the use of metabolism as a tool for environmental monitoring programs. PIs: R Sponseller, J Karlsson (Umeå University), ER Hotchkiss (Virginia Tech), H Laudon (Swedish University of Agricultural Sciences). "Taking the pulse of Swedish rivers: Using metabolism to monitor ecosystem responses to environmental change" - funded by Swedish Research Council Formas.

Dynamics of carbon and nutrient transport and fate

Time series of water chemistry, climate, hydrology, and ecosystem process (carbon metabolism, nutrient cycling, food web dynamics) data can be used to identify changing patterns and controls of carbon and nutrient variability, transport, and fates within and among ecosystems. Further, 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. Lab projects with S Plont, B O'Donnell, M Gallagher (Virginia Tech). Additional collaborations with members of the Stream Resiliency RCN Working Group.

Changing ice-cover regimes and freshwater ecosystem function

A new collaboration recently funded by the Swedish Research Council Formas will (1) examine seasonal shifts in aquatic carbon metabolism, (2) assess how a shorter ice-covered period will affect whole-system productivity and aquatic CO2 and CH4 emissions on an annual scale, and (3) increase public awareness about climate change effects in northern aquatic ecosystems. With J Ask (Umeå University). 

Advancing real-time monitoring of stream corridor function 

Stream ecosystem processes respond rapidly to physical changes in channels and corridors; quantifying process rates requires good estimates of time- and space-varying physical parameters such as inundated surface area and turbulence at the air-water interface. Uncertainties in channel morphology and gas exchange at time scales compatible with water quality sensor data currently limit our ability to produce high-quality estimates of ecosystem processes. Despite the critical link between watershed perturbations, stream corridor physical characteristics, and biological processes, few ecosystem-level studies are informed by remote sampling data. We will integrate ecosystem process methods with remote sensing model development to enhance ongoing monitoring of stream corridor health. With WC Hession et al. (Virginia Tech)

Biogeochemistry of boreal river networks

We are measuring the sources, transformations, and fluxes of dissolved organic matter and greenhouse gases in a large boreal river network, from soils to the sea. The Romaine River is in the process of being dammed for hydropower, so we will also have the opportunity to identify distinct contributions of river/reservoir sections at varying stages of pre- and post-dam to network- and landscape-scale biogeochemistry. With P del Giorgio, M Gérardin (Université du Québec à Montréal), et al.

Hotchkiss, E.R. & P.A. del Giorgio. Integrating gas exchange rates and carbon emissions along a large boreal river. In Preparation.

Hotchkiss, E.R. & P.A. del Giorgio. Controls on CO2 and CH4 replenishment and loss in a boreal river discontinuum. In Preparation.

Ecosystem production and environmental change

Ongoing collaborations are using experimental ponds and whole-lake manipulations to identify how increases in temperature, nutrients, organic carbon, and/or fish harvest alter ecosystem productivity, food web dynamics, and carbon cycling. With J Karlsson, P Byström, M Klaus, M Jonsson, M Hamdan (Umeå University), et al.

Hamdan, M., P. Byström, E.R. Hotchkiss, M. Haidery, J. Ask, & J. Karlsson. Carbon dioxide stimulates aquatic primary production. In Revision.

Klaus, M., S. MacIntyre, E.R. Hotchkiss, A.-K. Bergström, & J. Karlsson. Depth-integrated metabolism in clear and brown boreal lakes: the importance of accounting for vertical oxygen fluxes. In Preparation.

Byström, P.,  P. Hedström, E.R. Hotchkiss, P. Rodríguez, F. Vasconcelos, & J. Karlsson. Warming decreases fish population densities and biomass. In Preparation.

Sources, uptake, and fate of organic matter in freshwater ecosystems

We are interested in large-scale patterns of dissolved organic matter uptake and fate, how these may shift with environmental change, and the consequences for aquatic food webs. Collaborators from different working groups, workshops, and other projects include: S. Sadro (UC-Davis), P.C. Hanson (UW-Madison), WM Wollheim, MM Mineau (University of New Hampshire), IF Creed (Western University), AK Bergström (Umeå University), 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.