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 This website is no longer updated and links to external websites and some internal pages may not work.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 »

Report on the Environment

Ecological Processes

What are the trends in the ecological processes that sustain the nation's ecological systems?

Importance of Ecological Processes

Ecological systems are sustained by a number of biological, physical, and chemical processes, including primary production (conversion of the sun's energy into organic matter through photosynthesis), and the associated cycling of carbon, nutrients (nitrogen, phosphorus), hydrogen/oxygen, and other elements from the physical environment (air, water, land) through biological organisms and back into the physical environment.

Collectively, ecological processes produce organic matter, transfer carbon and nutrients, drive soil formation, and enable organisms to reproduce. They also play an important role in providing ecological services—for example, providing natural resources, such as food, fiber, and timber, and regulating air and water quality. 1 Ecological processes, such as primary production, influence the extent, distribution, and biodiversity of systems.

  • Primary producers include everything from microscopic plants of the oceans to the giant redwoods of California.
  • Primary production is influenced by the availability of nutrients.
  • If primary production declines, energy flow to higher trophic levels is diminished, potentially compromising the sustainability of animal populations dependent on plants for food.
  • Too much primary production can also cause problems, such as when lakes experience an overload of nutrients. Such eutrophic conditions can alter the composition of animal and plant life and result in reduced oxygen levels as organic matter decomposes. The “dead zone” in the Gulf of Mexico is an example of the effects caused by excess nutrients and too much primary production.

Top of Page


Ecological processes can be impacted by both natural forces and human activities happening over different temporal and spatial scales. With respect to natural forces, ecological processes are affected by both small-scale natural events such as seasonal changes in temperature, precipitation, and stream flows and large-scale events such as climate change.

EPA has long been concerned with the impacts of human activities—including pesticide use, chemical use, waste generation, land use changes, and water quality management, among others—on the rates, types, and timing of ecological processes.

  • Many pesticides, chemicals used in industry, pollutants, and waste products can interfere with species reproduction, one of the most important ecological processes.
  • Changes in land use that alter the extent and distribution of ecological systems can directly affect ecological processes in particular areas, often causing associated changes in primary production, nutrient cycling, and erosion and sediment transport. For example, changing forested land to urban or agricultural lands influence the amounts and types of primary producers, the infiltration of water into soils, and the storage and cycling of carbon and nutrients.
  • Water quality management is affected by:
    • Activities that upset the balance between primary production and respiration (such as wastewater treatment plant discharge, nutrients from fertilizers and animal manure, and ultraviolet radiation).
    • Activities that affect sediment erosion and transport.

Top of Page

ROE Indicators

Only one indicator that meets the ROE criteria, Carbon Storage in Forests, is available to address this question because ecological processes are difficult to measure directly, particularly at a national scale.

Ecological processes such as primary production, respiration, energy, carbon and nutrient flow through food webs, reproduction, and decomposition are represented as rates of change, which requires repeated measurement over time. This is difficult to achieve for many ecosystems at a local scale and even more difficult at the national scale. For example, remote sensing imagery has been used to obtain "snapshots" of indicators of ecosystem conditions over time, and to infer ecological processes such as terrestrial net primary production.

The Normalized Difference Vegetation Index has been estimated at a national scale using remote sensing. Repeated measures over a season might provide an indicator of net primary production. Indicators for other ecological processes, such as respiration, nutrient cycling, or decomposition have been developed for ecosystems at watershed scales, but have not been developed at the national scale. Developing these indicators at the national scale represents a significant scientific and research challenge.

Top of Page


[1] Millennium Ecosystem Assessment. 2005. Ecosystems and human well-being: Current state and trends. Washington, DC: Island Press.

Top of Page