sess the condition of the environment and identify trends in environmental quality. First, the nation became more aware that the quality of the environment cannot be described meaningfully using trend data related to a single species or a single environmental medium. Rather, the environment consists of complex interactions among multiple species and multiple media occurring over large geographical areas. For example, air pollution not only can cause the decline and death of particular species of trees within a forest ecosystem, but it also can affect a multitude of animal species that rely on those trees for food and shelter. Additionally, more subtle changes, such as an increase in temperature and moisture on the forest floor and rapid leaching of nutrients from the soil, could have far-reaching impacts on the stability and quality of the forest ecosystem. Second, although the ecosystem concept had been understood for many years, it was not until the 1970s that ecosystems like lakes, streams, forests, wetlands, and oceans were recognized as the basic functional units of the environment. Thus, the critical need for environmental monitoring programs that would collect consistent, comparable, quality-assured data at the ecosystem level also was recognized. This emphasis on the ecosystem as a whole was a driving force in the changes that took place in environmental monitoring during the 1980s. Ecosystems include both living organisms (plants, animals, microorganisms) and a nonliving environment (water, air, soil) that are inseparably interrelated and interactive. Furthermore, ecosystems do not exist or function in isolation; the range of ecosystem types found in the United States are closely interrelated. Changes occurring in one ecosystem result in changes in other ecosystems. For example, the widespread application of fertilizers, herbicides, and pesticides in agricultural ecosystems can alter water chemistry and biology in stream, river, and lake ecosystems hundreds of miles away. Therefore, an adequate assessment of the status and trends in environmental quality requires monitoring networks and data collection over multiple ecosystems and on a regional scale. Because changes within ecosystems and the consequent effects on adjacent ecosystems can happen very slowly, they are often subtle and difficult to detect. For example, studies of the recovery of clearcut forests revealed that 20 years was perhaps 1/20 of the time needed by some forests to reach a mature condition. Detecting environmental trends that result from natural or man-induced ecosystem changes requires the continuous collection of a consistent set of environmental data over a long period of time-from years to decades. Although some human activities, such as clearcutting, channelization, or wetland drainage, have very obvious effects on ecosystems, long-term environmental monitoring is necessary to detect long-term trends that result from cumulative impacts. For example, toxic substances can accumulate in stream sediments, and salts can build up in soils because of continuous evaporation in irrigated agricultural fields. While short-term data may be useful to describe short-term impacts, environmental trends revealed through monitoring programs of 2-5 years provide a very different picture of overall trends within an ecosystem than monitoring conducted over a period of 20-30 or more years. For example, growth trends in spruce and pine forests in southern Sweden over a 65-year period clearly indicate a decrease in annual tree ring width. However, data collected between 1960 and 1970 suggest an increase in annual tree ring width. Thus short-term data would lead to very different conclusions regarding overall forest growth than those drawn from 65 years of data collection (Figure 3-1). 6 Because an ecosystem is comprised of many biological organisms, nonliving substances, and the complex interactions among them, it is unlikely that any single organization-public or private would have the expertise or the financial resources to monitor it adequately. Thus assessing status and trends in whole ecosystems often requires the cooperation of local, state, and federal agencies. Multiagency cooperation also is valuable for minimizing the duplication of data collection efforts and ensuring effective, efficient data collection, the use of similar data collection methods, and consistent data quality, so that data can be compared over time and space. Figure 3-1. Comparisons of Forest-Growth Trends in Southern Source: Swedish Ministry of Agriculture, Environment '82 Committee, Acidification Today and Tomorrow, SMA, Stockholm (1982). The ability to anticipate future changes in environmental quality is an essential component of this country's environmental policy. If emerging problems and future changes in the condition of the environment can be projected from environmental trends, then long-term national efforts to protect the environment will be much more effective and less costly to implement. Environmental Data and Trends Today Recognizing the need for adequate monitoring programs that would identify and detect long-term environmental trends within ecosystems and on regional, national, and global scales, the U.S. government improved its monitoring efforts during the 1980s. These improvements are illustrated by the monitoring programs and networks described in the remainder of this chap ter. One example of the progress made during the 1980s is the National Acid Precipitation Assessment Program (NAPAP), a comprehensive, large-scale, multiagency monitoring program established to monitor and study a specific type of environmental problem-acid rain. Because this program integrated the expertise and unique capabilities of many agencies, it was capable of managing and maintaining long-term monitoring networks to detect trends in environmental conditions within several ecosystems and over regional scales. Moreover, during the 1980s several different federal agencies developed new monitoring programs, or improved existing ones, to collect environmental data on regional and national scales. In many cases those programs involved cooperation and coordination with other federal agencies. Finally, a fully integrated, multiagency effort has been established to coordinate U.S. global monitoring and data collection and to cooperate with international global monitoring programs. The U.S. Global Change Research Program demonstrates the nation's commitment to the long-term data collection needed to identify and detect global environmental trends. That program will help generate the scientific information needed to formulate national and international policies to protect the nation's and the globe's-resources for future generations. National Acid Precipitation The acid rain problem illustrates how this nation's approach to the collection of environmental data and identification of environmental trends changed in the 1980s from local to regional and national scales and from short-term to long-term time frames. It also demonstrates the change from a single agency to an interagency approach to data collection. Acid rain, more properly referred to as acidic deposition, is formed when sulfur and nitrogen compounds are released into the atmosphere, usually through the combustion of fossil fuels. In the atmosphere, these compounds are converted to sulfuric and nitric acids, which can be transported hundreds of miles before they return to the ground as acid rain or as dry acidic particles. Lakes and streams, forests, fish and wildlife, monuments and buildings, and human health all can be affected by the deposition of acids from the atmosphere. In the early to mid-1970s, acid rain and its potential environmental effects attracted the attention of the nation. While some lakes and streams were acidified and some forest damage was apparent, very few long-term data were available to test the hypothesis that surface water acidification or changes in forests over time were a result of acidic deposition. Therefore, in 1978 the National Acid Deposition Program was established. It was a volunteer effort by universities and other groups to obtain long-term data on acidic deposition in ecosystems ranging from lakes and streams to forests and agricultural fields. Such long-term measurements were deemed critical, because ecosystem acidification as a result of acidic deposition occurs over decades. Long-term measurements were also needed to identify long-term environmental trends and to distinguish between natural short-term variability and trends in environmental conditions caused by human activities. For example, the natural variability in precipitation chemistry data collected in an experimental forest in New Hampshire (Figure 3-2) indicated an increase in sulfate and nitrate concentrations from 1970-1975.7 The long-term trend over the 15 years of |