An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

About EPA

About the Pacific Ecological Systems Division (PESD)

The Center for Public Health and Environmental Assessment (CPHEA) provides the science needed to understand the complex interrelationship between people and nature in support of assessments and policy to protect human health and ecological integrity. Within CPHEA, sits the Pacific Ecological Systems Division.

On This Page:

What We Do


What We Do

EPA's Pacific Ecological Systems Division (PESD) conducts innovative research on watershed ecological epidemiology and develops tools to assist stakeholders achieve sustainable and resilient watersheds. Research focuses on terrestrial, freshwater and coastal systems and how they are connected.  Scientists develop tools to monitor and predict the condition of these systems and their contributions to human well-being nationwide, with a special focus on the Pacific Northwest.  

PESD leads innovative research and predictive modeling efforts that link environmental condition to the health and well-being of people and society. PESD advances research and tools for achieving sustainable and resilient watershed and water resources. PESD advances systems-based research to predict the adverse effects of chemicals and other stressors across species and biological levels of organization through the development and quantification of adverse outcomes pathways across multiple scales.

Programs and projects managed by PESD:

  • Estuaries are very important ecosystems for coastal communities, producing natural resources that are beneficial for local economies, public health, and recreation.  In Tillamook estuary on the central Oregon coast, PESD researchers are working with federal, state, and local partners to understand how nutrients affect water quality, (such as seagrass beds) and natural resources (such as shellfish, finfish, and wildlife) valued by residents and visitors. 
  • Efforts to control the release of nutrient pollution to air, land and rely on accurate measurement of these releases. Keeping nitrogen in the soil and dollars in the pocket is an important resource objective for farmers in the Willamette Valley in Oregon, and PESD researchers are working with farmers to manage nitrogen in their fertilizer more efficiently to provide for clean and safe water. They have also helped collaborated with universities to create the Institutional N footprint to assist institutions and individuals measure their nitrogen footprint.  Some of PESD’s work on nitrogen and phosphorus release is available through EPA’s EnviroAtlas.
  • Increasing water temperatures are threatening salmon populations in the Pacific Northwest. PESD researchers are developing models to identify the locations and potential importance of cold-water areas or “refuges” that can help salmon persist during periods of warm water temperature. This information is being used to help state, local and tribal managers develop habitat plans for salmon recovery.
  • PESD is working on methods and models to improve water quality in cities by examining how stream restoration, stream daylighting, green roofs, and other green water infrastructure for managing stormwater can help prevent erosion and reduce polluting nutrients.
  • Biochar is a charcoal-like substance created by slowly burning vegetation like agricultural waste. Researchers at PESD are using this substance to revitalize the land and prevent contamination in mines at Superfund sites in Oregon. By mixing biochar in soil at contaminated sites, vegetation grows better and the site can be restored.
  • PESD scientists created models, like VELMA, to help planners and communities identify best watershed management practices to control pollutant loadings to streams and estuaries. VELMA is used extensively at the state and local levels for community forest planning, urban stormwater management, and assisting states and tribes to help improve salmon habitat in working forests.
  • PESD scientists have developed two extensive catchment datasets for the conterminous U.S.: one for streams and one for Lakes. For streams, the Stream-Catchment (StreamCat) dataset is an extensive collection of landscape metrics for 2.6 million streams and associated catchments.  For lakes, the Lake-Catchment (LakeCat) dataset is an extensive collection of landscape metrics for about 378 thousand lakes and associated catchments. The data are summarized both for individual stream or lake catchments and for cumulative upslope watersheds. The two datasets include both natural and human-related landscape features. The data have been used to develop national maps of aquatic condition and watershed integrity.
  • PESD conducts research on the identification, quantification and valuation of final ecosystem goods and services (FEGS) available in the nation, regions, and communities. A classification system, the FEGS-CS guides the development of this information and houses the information. Scientists developed a framework to economically account for the benefits provided by ecosystems. This framework, called the National Ecosystem Services Classification System, analyzes the human welfare impacts of policy-induced changes to ecosystems. It classifies the flows of the ecosystem supply and demand.
  • PESD scientists are studying how release of engineered nanomaterials to terrestrial ecosystems affects human health and the environment. They conduct analyses to identify molecular initiating events (key events directly perturbed by interaction with a chemical) across species. Using these events, they are able to develop Adverse Outcome Pathway (AOP) models to determine common events triggered by engineered nanomaterials. At PESD , researchers are interested in whether nanomaterial release may lead to effects on important ecosystem properties such as nutrient cycling.  Terrestrial plants are critical for ecological function and human provision, and therefore much of the work focuses on important plant species.
  • PESD leads research and technical support for the Office of Water’s National Aquatic Resource Surveys (NARS).  The surveys and assessments provide answers to common questions of the public and Congress such as:  Is there a problem in our Nation’s waters?  How big is the problem?  Is it widespread or localized?  What are the biggest causes of problems?  PESD provides survey design and data analyses for the indicators used in the surveys.  In turn, the data resulting from the surveys are used in national assessments and used as a core portion of the information.
  • Ecoregions, developed by PESD scientists, are a spatial framework used for watershed ecological epidemiological research, assessment, management, and monitoring of ecosystems and their components.



Alan Thornhill, Director


  • Ecology Effects Branch (OR),  Acting Branch Chief Jim Markwiese
  • Freshwater Ecology Branch (OR), Branch Chief Paul Ringold
  • Pacific Coast Ecology Branch (OR), Branch Chief Theodore Dewitt

Top of Page