tailieunhanh - Statistics for Environmental Science and Management - Chapter 5

Giới thiệu mối quan tâm ngày càng tăng trên toàn thế giới về mối đe dọa đến môi trường tự nhiên trên cả hai địa phương và quy mô toàn cầu đã dẫn đến sự ra đời của chương trình giám sát nhiều dự định để cung cấp một cảnh báo sớm về các hành vi vi phạm của các hệ thống kiểm soát chất lượng, để phát hiện các tác động của chính các sự kiện như sự cố tràn dầu do vô tình hay xử lý chất thải bất hợp pháp, và nghiên cứu các xu hướng dài. | CHAPTER 5 Environmental Monitoring Introduction The increasing worldwide concern about threats to the natural environment both on a local and a global scale has led to the introduction of many monitoring schemes that are intended to provide an early warning of violations of quality control systems to detect the effects of major events such as accidental oil spills or the illegal disposal of wastes and to study long-term trends or cycles in key environmental variables. Examples of some of the national monitoring schemes that are now operating are the United States Environmental Protection Agency s Environmental Monitoring and Assessment Program EMAP based on 12 600 hexagons each with an area of 40 square kilometres the United Kingdom Environmental Change Network ECN based on nine sites and the Swedish Environmental Monitoring Program based on 20 sites. In all three of these schemes a large number of variables are recorded on a regular basis to describe physical aspects of the land water and atmosphere and the abundance of many species of animals and plants. Around the world numerous smaller scale monitoring schemes are also operated for particular purposes such as to ensure that the quality of drinking water is adequate. Monitoring schemes to detect unexpected changes and trends are essentially repeated surveys. The sampling methods described in Chapter 2 are therefore immediately relevant. In particular if the mean value of a variable for the sample units in a geographical area is of interest then the population of units should be randomly sampled so that the accuracy of estimates can be assessed in the usual way. Modifications of simple random sampling such as stratified sampling may well be useful to improve efficiency. The requirements of environmental monitoring schemes have led to an interest in special types of sampling designs that include aspects of random sampling good spatial cover and the gradual replacement of sampling sites over time Skalski 1990 .