The Center for Ecological Health Research (CEHR) is located at the University of California, Davis. It is one of four environmental research centers established in 1991 by the U.S. Environmental Protection Agency (R819658 & R825433). The University of California, Davis is in the center of a region experiencing one of the most rapid population growth rates in the nation thus producing a high rate of urban encroachment in areas that include highly sensitive ecosystems, including the nation's most diverse and productive agricultural lands. Within a few hundred miles of UC Davis are several well known ecosystems that Center researchers are using as long-term case studies to investigate basic science questions in an applied context.

What do we do? The central goal of the Center is to understand how multiple stresses interact to affect biological and ecological processes in aquatic and terrestrial systems. Natural stresses such as drought, salinity, and climate change and anthropogenic stresses such as toxic compounds, nutrients, species introductions and habitat destruction are cumulative impacts on ecosystems. An important product of the Center's activities will be a toolkit of inexpensive methods. With these methods we expect to be able to reduce the theoretical complexity of a multiply-stressed ecosystem to a manageable level. The Center provides a forum and a structure that identifies significant issues, designs assessment strategies, and integrates research efforts relevant to assessing risks on selected ecosystems. The Center has formulated four overall objectives:

• Maintain and intensify interdisciplinary research on complex ecosystem processes

• Develop and verify new data management, risk analysis, and modeling techniques

• Develop and apply new sensitive and reliable biomarkers based on a mechanistic understanding of toxic processes

• Use new methodologies to effectively characterize and develop cost-effective strategies to manage ecological risks and communicate them to users and managers

Why do we do it? Environmental policy makers must cope with the fact that ecosystems are exceedingly complex. The complexity, uniqueness and diversity of ecological systems are critical impediments to the practical analysis of problems resulting from multiple stresses. The Center provides a mechanism for university researchers and outside scientists, engineers, policy makers and managers to work together to focus research and remediation on the most important elements impacting a particular ecosystem.

How do we do it? The Center is a group of 36 faculty and 50 graduate students from four colleges and schools at UC Davis. It brings together scientists from many disciplines to study transport and fate, ecology and toxicology in specific watersheds. The combining of disciplines to focus on a specific geographic area provides an infrastructure to promote long-term multi-process environmental studies that more closely reflect the ways ecosystems function. Combining disciplines leverages the tools, methods, and perspectives of classic academic disciplines to provide new insights into data collection, synthesis and analysis. Studies of the molecules, cells and behaviors of individual organisms are being coupled with models of population dynamics in communities and models of transport and fate in air, water and soil to explore the relationship between physical and biological processes. Together Center researchers are working to answer six general scientific questions:

1. Which parameters provide the best early assessment of ecological risk in specific ecosystems and what features of specific ecosystems are likely to be most informative?
2. What quantity, precision, and accuracy are required of environmental, ecological and biochemical data to insure their usefulness in specific monitoring programs?
3. How can chemically derived risks be studied separately and in combination with other environmental risk factors such as drought, urbanization, and other anthropogenic activities?
4. What are the expected transit times, exposure levels, and fate of toxic materials in soil, air, and water of selected ecosystems, and how can such information be used to predict long-term effects?
5. How do multiple stresses interact at the watershed scale?
6. How can we best provide information to public agencies and individuals to better manage the environment?

The Center is using three important and representative aquatic and terrestrial environments in Northern California to evaluate new approaches for addressing multiple stresses: Sacramento River Watershed, Clear Lake Watershed, Sierra Nevada Watershed. There are also three Core projects whose primary function is to do general basic research on developing tools and techniques that researchers can apply to specific watersheds: Analytical and Biomarkers Core, Transport and Fate Core, Data Integration and Decision Support Core.