Research

Study Sites

Research Interests and Projects

Three fisherman aboard a small boatInland Fishery Systems

Freshwater fisheries and aquaculture are critical food resources and are drivers of economic growth, particularly for poor and developing countries of Asia and Africa.  In Southeast Asia over 60 million people rely on the Mekong River and Tonle Sap Lake fisheries for nutrition, income, and cultural identity.  Current proposals for hydroelectric dam projects threaten the long-term sustainability of the fishery by potentially removing the annual flood dynamics believed to be important for fish growth and reproduction.  Despite their importance of the river and its fishery, there is little ecological information about the ecosystem, and many scientific questions about the fishery remain unanswered.  A very basic but currently unanswered question is: what are the unique ecological processes that support this unusually large and productive fishery?

The long-term goal of our research in the lower Mekong is to quantify the socio-ecological links within the Mekong-Tonle Sap ecosystem to understand the combination of factors that maintain this highly productive fishery.  Initially this means firmly establishing the energetic base to the Mekong-Tonle Sap food web.  Combining stable isotope analysis of consumers and their prey with data-driven ecosystem models of primary productivity, we will be able to better understand which fish species and aquatic communities are most likely to be negatively affected by the removal of seasonal flooding with construction of dams.

Taking samples in the fieldBiogeochemical Cycles from Local to Global Scales

Understanding how elements, such as nitrogen and carbon are cycled and transferred among ecosystems is central to understanding the causes and consequences of global environmental change.  Previously this work has involved both field measurement and large-scale data analysis.  In the Puget Sound regions there is significant opportunity to advance the science of watershed-aquatic coupling and how terrestrial organic matter influences the biogeochemical cycles in stream and lake ecosystems, particularly in the context of agriculture, forestry, and urbanizing landscapes.  We are partnering with NOAA and Washington Department of Ecology on two projects.  The first is considering the effects of dam removal on the Elwah River for ecosystem-scale carbon accumulation and losses.  The second is quantifying human and natural sources of N to major US rivers entering the Puget Sound.

Infographic of energy within ecosystemsEnergetic Support of Food Webs

A major focus of the lab is to develop and employ methods and models for understanding how  carbon and energy cycle through through food webs.  This includes both bottom-up drivers of primary production and heterotrophic respiration and top-down drivers such as fishing impacts on trophic structure.  We are actively developing methods and models for quantifying aquatic ecosystem metabolism, including Bayesian methods to estimate metabolic parameters (BaMM, for Bayesian Metabolic Model).  These models use day-night (diel) cycles of oxygen concentration, water temperature, and irradiance data to estimate probability distributions of ecosystem metabolic rates, such as gross primary productivity, community respiration, and air-water gas exchange.  We are also using a suite of tracer tools (stable isotope and fatty acids) to understand the food web pathways through which these materials flow.

Bear eating salmonBiophysical Drivers of Ecosystem Functions

I am keenly interested in how animals interact with each other and their environment to control critical ecosystem functions, such as carbon flow and nutrient cycling. To date most of this work has involved Pacific salmon. Because of their size, large spawning densities, and intense physical activity, salmon are the archetypal example of how migratory animals can often control important ecological functions.

 

Isotope heatmap of North American continentStable Isotope Ecology

Stable isotopes are one of our favorite tools for understanding how ecosystems function and change.  Previous work has used H, C, N, O, and S  isotopic systems in a variety of contexts and settings.  Currently we are using triple isotopes of nitrate (15/14N, 17/16O, 18/16O) to understand sources and sinks of N in Puget Sound rivers.  We are also using oxygen isotopes in wine to look at microclimate variations in the Willamette Valley, Oregon using isoscapes and how this might relate to recent climate change.  Finally, we are working to establish compound specific isotope analysis of fatty acids and amino acids to better understand bacterial metabolic pathways and trophic dynamics in food webs.