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What are the trends in the ecological processes that sustain the Nation's ecological systems?
Ecological systems are sustained by a number of biological, physical, and chemical processes. Collectively, these processes produce organic matter using energy (photosynthesis and chemosynthesis), transfer carbon and nutrients (through food webs and through decomposition), drive soil formation, and enable the reproduction of organisms (e.g., through pollination of plants by insects). Ecological processes also play an important role in providing ecological services such as the provision of natural resources and regulation of air and water quality.33
Ecological processes influence the extent, distribution, and biodiversity of systems. If primary production declines, energy flow to higher trophic levels is diminished, potentially compromising the sustainability of animal populations dependent on plants for food. Primary production is influenced by the availability of nutrients. Decreases and increases in nutrients can affect the amounts of primary production as well as the types of plants that grow, with subsequent effects on animals. The successful reproduction of plants and animals depends on the physical and chemical regimes of their environment.
Too much primary production can also cause problems, such as those that occur in eutrophic lakes that experience an overload of nutrient inputs. Eutrophic conditions can alter the composition of animal and plant life and result in reduced oxygen levels due to decomposition of organic matter. For these reasons, management of nutrient inputs is commonly driven by the potential for excessive plant growth.
Primary production and associated carbon cycling (which form the base of food webs), nitrogen cycling (e.g., ammonification and nitrification), nutrient cycling (e.g., phosphorous and other essential elements for sustainability of carbon-based life), and hydrogen/oxygen cycles (implicating hypoxic/anoxic conditions) are fundamental ecological processes within systems. Processes related to the production, transfer, and loss of biomass and the reproduction and death rates of individuals within populations are reflected in various “end states” in time, snapshots of the outcomes of integrated processes. The standing stock of a population or the amounts and types of carbon stored within an ecological system are measures of these end states. While not processes themselves, trends in end states provide some insight into the relative balance among processes. Carbon storage in forests, discussed in this section, is an example of such an end state.
EPA has long been concerned with the impacts of human activities that can affect the rates, types, and timing of ecological processes. In particular, activities that upset the balance between primary production and respiration (e.g., biochemical oxygen demand, nutrients from fertilizers and human waste, and the effects of ultraviolet radiation) and activities that affect sediment erosion and transport are important factors in water quality management. Many pesticides, chemicals used in industry, pollutants, and waste products have the potential to interfere with species reproduction (one of the most important of ecological processes). At local and regional scales, changes in land use that alter the extent and distribution of ecological systems directly affect ecological processes within and adjacent to particular areas. Concomitant changes often occur in primary production, nutrient cycling, and erosion and sediment transport. For example, shifts from forested 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.