Answer:
Please see below.
Step-by-step explanation:
Pollution in the environment may come from a variety of sources and in a variety of ways. Most notably pollution may be in the form of the chemicals in the exhausts from factories and cars and it affects terrestrial ecosystems, or it may come from organic matter that is poured into water bodies. The decomposition of this organic matter by bacteria consumes the dissolved oxygen that is needed by the organisms that live in that water body, such as fish and invertebrates. This is measured as Biochemical Oxygen Demand (BOD) and is an indicator of the health of the ecosystem. If the BOD shows there is little oxygen available, the biodiversity in the water body will decrease and only species that are able to live in low-oxygen environments will be present. For example catfish vs. trout. Aquatic invertebrates may also be used as indicator species. Mayflies indicate a good health in the environment whereas worms that live buried in mud indicate poor environmental conditions. In terrestrial ecosystems, an abundance of crustose lichens normally indicates pollution. Plants can also be used as indicator species. An abundance of weedy plants indicate areas with human activity whereas in more pristine plant communities these weeds will be absent or not very abundant. In tropical ecosystems, the presence of some types of bromeliads and cacti indicate the area has a period of drought. Conversely, the presence of tank-forming bromeliads indicate there is some rainfall throughout the year.