Introduction

For many years, environmental variables and indices have been used to monitor pollution, changes in biotic communities and so-called ‘environmental standards’ or ‘quality of the environment’. Environmental indices include those that are based on physical and chemical parameters, those based on biological parameters and also those based on perceived aesthetic qualities of the environment. The aim of this chapter is to provide an introduction to a selection of indices, their calculation, uses and limitations. Applications of some of these indices in monitoring programmes are described in later chapters.

Number of species, species composition, abundance and diversity

Perhaps the simplest variable that could be used in biological and ecological monitoring is the number of species. In addition to that there is the species composition and also the proportional abundance of species. The difference between the number of species, species composition and proportional abundance of species in a hypothetical community may be illustrated as shown in Fig. 6.1. Sample 1 or the ‘baseline’ contains four species. Samples 2, 4 and 5 also contain four species (the species richness is the same for each sample) but there are differences in species composition and total biomass. In sample 2, there are also four species but the species composition has changed. There is a difference between the relative abundance of each group of species in samples 1 and 4. The species richness of sample 3 is greater than found in the other samples.