USES OF DIATOMS AS BIOINDICATORS OF URBANIZATION

The biota of rivers and lakes within heavily populated reaches of aquatic catchments are greatly affected by the effects of urbanization. Such impacts are observed to influence primary producers (e.g., algae) through to top predators (e.g., fish). Urbanization effects on aquatic systems include the delivery of industrial and domestic effluents (e.g., organic, metal and thermal pollution), siltation as well as the introduction of exotic species, to name a few. Each of these can cause detrimental changes to the ecosystem. Thus aquatic monitoring programs are important in order to track environmental conditions and to ensure the health and viability of the ecosystem. A number of chemical, physical and biological monitoring programs exist. However, biological monitoring programs based on fish, algae and macroinvertebrates are advantageous and effective because they integrate the physical and chemical conditions of their ambient environment.

Diatoms are a class of algae that are increasingly being used as bioindicators for environmental monitoring. These single-celled organisms reproduce quickly and are sensitive to a number of environmental pressures including changes in salinity, metals, pH, saprobrity, turbidity, current strength, water depth, substrate availability and so forth. Sampling for diatoms is a simple and relatively inexpensive procedure although it requires a degree of taxonomic expertise. A variety of indices based upon diatom community structure have been developed to assess and track the environmental health of rivers. By evaluating the health of an ecosystem across various reaches of a river over a time series, it is possible to assess and identify the effects of urban impacts over the course of seasons and years. From these data it is possible for effective environmental stewardship of those particular watersheds. This presentation focuses on the uses of epilithic diatoms as bioindicators in rivers that are heavily impacted by the effects of urbanization.