Chapter 5* - the Use of Biological Material
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Water Quality Assessments - A Guide to Use of Biota, Sediments and Water in Environmental Monitoring - Second Edition Edited by Deborah Chapman © 1992, 1996 UNESCO/WHO/UNEP ISBN 0 419 21590 5 (HB) 0 419 21600 6 (PB) Chapter 5* - The use of biological material *This chapter was prepared by G. Friedrich, D. Chapman and A. Beim 5.1. Introduction Natural events and anthropogenic influences can affect the aquatic environment in many ways (see Chapter 2): synthetic substances may be added to the water, the hydrological regime may be altered or the physical or chemical nature of the water may be changed. Most organisms living in a water body are sensitive to any changes in their environment, whether natural (such as increased turbidity during floods) or unnatural (such as chemical contamination or decreased dissolved oxygen arising from sewage inputs). Different organisms respond in different ways. The most extreme responses include death or migration to another habitat. Less obvious responses include reduced reproductive capacity and inhibition of certain enzyme systems necessary for normal metabolism. Once the responses of particular aquatic organisms to any given changes have been identified, they may be used to determine the quality of water with respect to its suitability for aquatic life. Organisms studied in situ can show the integrated effects of all impacts on the water body, and can be used to compare relative changes in water quality from site to site, or over a period of time. Alternatively, aquatic organisms can be studied in the laboratory (or occasionally in the field) using standardised systems and methods, together with samples of water taken from a water body or effluent. These tests, sometimes known as biotests, can be used to provide information on the intensity of adverse effects resulting from specific anthropogenic influences, or to aid in the evaluation of the potential environmental impact of substances or effluents discharged into surface or groundwater systems. Most kinds of biological analysis can be used alone or as part of an integrated assessment system where data from biological methods are considered together with data from chemical analyses and sediment studies. A full appreciation of natural changes and anthropogenic influences in a water body can only be achieved by means of a combination of ecological methods and biotests. Sometimes these studies need to be carried out over a period of many years in order to determine the normal variation in biological variables as well as whether any changes (natural or unnatural) have occurred or are occurring. An example of a continuous programme of biological assessment using a variety of methods is that carried out in Lake Baikal, Russia (Kozhova and Beim, 1993). It is not possible to describe in this chapter, in detail, all the methods and variations that exist for biological analysis of water quality. There are several comprehensive texts and reviews which cover this subject (e.g. Ravera, 1978; OECD, 1987; Newman, 1988; Abel, 1989) and the details of many of the methods are published in appropriate reports and journals. Since many biological methods have been developed for local use and are based on specific species, an attempt has been made in this chapter to give only the basic principles behind the methods. With the help of such information it should be possible to decide whether such methods are applicable to the water quality assessment objectives in question. In many cases, when such methods are chosen, it will be necessary to adapt the basic principle to the local hydrobiological conditions, including the flora and fauna. 5.2. Factors affecting biological systems in the aquatic environment 5.2.1 Natural features of aquatic environments The flora and fauna present in specific aquatic systems are a function of the combined effects of various hydrological, physical and chemical factors. Two of these factors specific to water bodies are: • The density of the water, which allows organisms to live in suspension. Organisms which exploit this are called plankton, and consist of photosynthetic algae (phytoplankton), small animals (zooplankton) which feed on other planktonic organisms and some fish species which feed on other plankton and/or fish. The development of a rich planktonic community depends on the residence time (or retention time) of the water in the water body (see sections 6.4.2 and 7.2.5). Fast flowing water tends to carry away organisms before they have time to breed and to establish populations and, therefore, planktonic communities are more usually associated with standing waters such as lakes and reservoirs. As many fish are strong swimmers they are able to live in rivers, provided there are suitable breeding grounds present (see sections 6.4.1 and 6.4.2). Organisms living permanently in fast flowing waters, require specific adaptations to their body shape and behaviour (see section 6.4.1). • The abundance of dissolved and particulate nutrients in the water. The constant supply of these often allows diverse and rich communities of planktonic and benthic (those living in or on the bottom) organisms to develop. An abundance of dissolved nutrients in shallow, slow flowing or standing waters allows the growth of larger aquatic plants (macrophytes), which in turn provide food, shelter and breeding grounds for other organisms. The photosynthetic organisms which depend on the dissolved nutrients and sunlight for their own carbon production are termed the primary producers. These organisms are the food source of the zooplankton and small fish (secondary producers), which in turn are the food source of other fish (tertiary producers). This simplified system is known as the food chain and, together with the processes of decay and decomposition, is responsible for carbon transfer within the aquatic environment. In practice, the interactions between different groups are more complex and may be referred to as the food web. For more detailed information on the fundamentals of biological systems in water bodies see Hutchinson (1967), Hynes (1970), Wetzel (1975), Whitton (1975) and Moss (1980). 5.2.2 Anthropogenic influences on water bodies In addition to natural features, biological communities are often affected directly by human activities (such as inputs of toxins, increased suspended solids, habitat modification or oxygen depletion) or indirectly by processes influenced by anthropogenic activities (e.g. chelating capacity). The variety of effects that can be observed on different aquatic organisms as a result of anthropogenic influences can be demonstrated by the example of domestic sewage. Purely domestic sewage, without the input of modern, synthetic, harmful substances, such as chlorinated hydrocarbons, detergents etc., is characterised by high concentrations of easily biodegradable organic matter. It also contains high concentrations of bacteria, viruses and other pathogens from which water-borne diseases may arise. During the process of biodegradation of sewage in a river there is an initial rapid decline in oxygen concentration in the water resulting from microbial respiration during self-purification. However, microbial activity also leads to an increase in nutrient content and sometimes other harmful substances are formed such as hydrogen sulphide or ionised ammonia (Figure 5.1). Hydrogen sulphide is very toxic, but ionised ammonia is a nutrient which is more easily assimilated than nitrate. However, if the pH value exceeds 8.5, a rapid increase in unionised ammonia occurs (see Figure 3.2) which is very toxic to fish. Phosphate also becomes available following the biological decomposition of domestic sewage. These changes in the chemical composition of the water are followed by significant changes in the structure of the biota, some of which exploit the increased nutrients and others which can tolerate reduced oxygen concentrations (Figure 5.1). Such changes form the basis of water quality assessments using biota as indicators of the intensity of pollution. Figure 5.1 Typical effects on water quality and the associated biota which may be observed downstream of a sewage outlet. A and B. Physical and chemical changes; C. Changes in micro-organism populations; D. Changes in invertebrate populations (After Hynes, 1960) 5.2.3 Physical alterations in the aquatic environment The presence or absence of specific aquatic organisms depends on the physical environment and its associated habitats, such as fast flowing water with large stones or boulders or still waters with fine deposited sediments. Although these environments can easily be modified by human activities, including river damming, canalisation and drainage schemes, natural changes can occur in the physical environment due to local climatological and geographical conditions. Events such as torrential rain storms or prolonged droughts can lead to sudden or gradual modifications of a natural habitat, e.g. by increased siltation or scouring of river beds, which in turn lead to changes in the flora and fauna of the water body. These changes can be quite dramatic, including short term or permanent loss of species. It is important to understand the hydrological regime of water bodies when designing biological assessment programmes so that effects due to natural changes in the environment can be separated from those that may be caused by human activities. 5.2.4 Dissolved oxygen Oxygen is an important factor for aquatic life and the chemical characteristics of the environment. Concentrations less than 100 per cent saturation can occur normally under certain circumstances, e.g. at the bottom of nutrient rich lakes (see Figure 7.8), or at night in slow flowing rivers (see Figures 6.19 and 6.20). In such locations, species may be found which are adapted to low concentrations of oxygen. Under normal conditions these species would be rare, but they can become widespread in association with pollution or nutrient enrichment. However, many species are able to survive a potentially harmful lack of oxygen for a short time, but rarely for days or many hours.