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Review Article
Macroinvertebrates as Potential Indicators of Environmental Quality M. Muralidharan*, C. Selvakumar, S. Sundar and M. Raja Sri Paramakalyani Centre for Environmental Sciences, Manonmaniam Sundaranar University Alwarkurichi – 627412,Tamilnadu, India Corresponding Author email:
[email protected] Received:19.07.2010; Revision:28.11.2010; Accepted:30.11.2010; Published:01.12.2010. Abstract Macroinvertebrate species owing to their wide variation of response to pollutants have been extensively utilized to evaluate quality of aquatic systems. Seasonal samples of the macroinvertebrate community can indicate the effects of pollutant sources which may not have been detected by either physico-chemical sampling or continuous monitoring of a restricted range of parameters. The aim of this paper is to summarize aspects of biomonitoring, utility of macroinvertebrates in predicting condition of aquatic systems and the need for research with emphasis on recent advances. Keywords: Aquatic ecosystem, benthic macroinvertebrates, indicators, pollution
Introduction Biological monitoring, or biomonitoring, is the systematic use of living organisms or their responses to determine the quality of the aquatic environment (Barbour and Paul, 2010). The method is based on the principle that different aquatic invertebrates have different tolerances to pollutants. The presence of mayflies or stoneflies for instance indicates the watercourse as clean. The number of different macroinvertebrates is also an important factor, because a better water quality is assumed to result in a higher diversity. Early efforts to monitor and control aquatic pollution were motivated by the desire to protect human health and in nineteenth century German aquatic ecologists established a protocol for using macroinvertebrates to identify zones of habitat degradation, recovery and clean water downstream of sewage outflows (Peckarsky, 1997). These zones were designated on the basis of indicator species – the type of macroinvertebrates that dominated the benthic fauna. Tubificid worms and aquatic insect midge were associated with the most polluted water, due to their ability to withstand exceedingly low levels of dissolved oxygen. Thus ecologists recognized the importance of taxonomic composition of the community as well as its diversity to monitor water quality. Biological monitoring has an advantage over physicochemical monitoring systems that it gives an indication of past conditions as well as current conditions whereas chemical and physical measurements used to evaluate water quality provide data that primarily reflect © Gayathri Teknological Publication
conditions that exist when the sample is taken. However, physical/chemical measurements and biomonitoring are not mutually exclusive; an optimal water quality monitoring program involves both approaches. The biological assessment of water quality in the field may involve a number of levels of effort – survey, surveillance, monitoring or research. Survey is a program of measurements that defines a pattern of variation of a parameter in space. Surveillance is repeated measurement of a variable in order that a trend may be detected. The research function will be to examine the pollution process in more detail, using experimental and analytical techniques. Observations on performance in relation to standards are known as monitoring. From the surveillance and research program, and taking into account economic considerations, a policy for managing pollution might be decided. The health of bottom-dwellers is threatened by pollutants introduced into streams and rivers by sources such as mining, agriculture, fossil fuel combustion, and household and industrial wastewater treatment facilities. These human activities can add nitrogen and phosphorus to the water, which lead to algal blooms and low dissolved oxygen in slow-moving streams. Mining, agriculture, and development also can add fine sediment to streams, which smothers benthic organisms and contributes to low dissolved oxygen (Foreman et al., 2008). Furthermore, thermal and radioactive pollution can also occur. In this paper, we discuss the 1
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role and importance of macroinvertebrates in biomonitoring, the need for research, highlighting several categories for fields of research that appear to be particularly important for future studies. Three broad categories are: Importance of macroinvertebrates, selection of organisms for biological monitoring and index developed to monitor freshwater ecosystems. How macroinvertebrates qualify as indicators? Stream ecologists have long recognized that macroinvertebrate species composition and abundance can be excellent monitors of ecosystem health. The abundance and diversity of these organisms are good indicators of local stream health because they have more limited movement than fish and they respond quickly to pollutants such as nutrients and sediment and other environmental stressors. Macroinvertebrates are regarded as bioindicators for the following reasons i. The macroinvertebrate community is extremely diverse, represented by a number of species falling in a variety of tropic groups. ii. The pollution tolerance levels of macroinvertebrates range from very high, being able to withstand considerable pollution levels, to very low meaning sensitive to even mild variations. iii. Sampling macroinvertebrates can be performed easily by a single individual with simple equipment, say a kicknet. The methods for collecting, subsampling and preserving are easier hence facilitates comparison between sites. iv. The aquatic life spans of macroinvertebrates range from several weeks to several years. This long life span provides an indication of stream quality over a period of time. v. Macroinvertebrates can be found in any aquatic habitat as long as the water quality is high enough to sustain them. vi. Macroinvertebrates communities can recover rapidly from repeated sampling events, providing the ability for repeated sampling. Selection of macroinvertebrates for biological monitoring A monitoring program must be based on those organisms that are most likely to © Gayathri Teknological Publication
provide the right information to answer the questions being posed. The use of a single species as a water-quality indicator is generally avoided because individual species show a high degree of temporal and spatial variation due to habitat and biotic factors and these confuse any attempt to relate presence, absence or population level with water quality. Similar constraints will limit the value of ratios of species or groups such as the ratio of chironomids to total insects. For indicator species to be worthwhile, they must be able to register subtle, rather than gross and obvious effects of pollution. The use of communities of organisms allows this more subtle approach. To be suitable for a broad survey or monitoring program, a biological system requires the following features (Bonada et al.,2006): √ The presence or absence of an organism must be a function of water quality rather than of other ecological factors. √ The system must reliably assess water quality, be reliably expressible in a simplified form, yet be sufficiently quantifiable to allow for comparisons. √ The assessment should relate to water quality conditions over an extended period, rather than just at the time of sampling. √ It is often important that the assessment should relate to the point of sampling rather that to the watercourse as a whole. √ Sampling, sorting, identification and data processing should be as simple as possible, involving the minimum of time and manpower. √ Numerical abundance at some sites, widespread distribution and a welldocumented ecology are also important factors to take into account in selecting a group of organisms for water-quality assessment. Hellawell (1986) and Metcalf (1989) give number of reasons for preferring benthic macroinvertebrates to other groups. The sampling procedures are relatively well developed, can be operated by someone working alone and there is identification keys for most groups. Macroinvertebrates are reasonably sedentary, with comparatively long lives, so that they can be used to assess water quality at a single site over a long period of time. The group is heterogenous and so a single sampling technique may catch a 2
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considerable number of species from a range of phyla. It is likely, therefore, that at least some species or groups will respond to a particular environmental change. Macroinvertebrates are also generally abundant. They have some disadvantages. Their aggregated distribution means that, to obtain a representative sample of a site, many samples must be taken. The muddy, depositing substrata of the lowland reaches of rivers, or of lakes, are often dominated by chironomids and tubificid worms, which are difficult to identify, while the water in these situations is frequently deep, making difficult. The insect members of the community may be absent for part of the year, so that care needs to be taken in interpreting the results of monitoring. Furthermore, benthic macroinvertebrates are not sensitive to some perturbations, such as human pathogens and trace amounts of some pollutants. However, advantages do outweigh disadvantages. In contrast to subcellular, individual, and population-level analyses involving macroinvertebrates, community measures attempt to summarize the magnitude, ecological consequences, or significance of a particular stress on the system being examined (Johnson et al.,1993). For this reason, the analysis of macroinvertebrate communities, including aquatic insects, has received more detailed attention than any other level. Community-level biomonitoring involves both traditional quantitative approaches and rapid assessment procedures which reduce the intensity of site-specific study required and enable a greater number of sites to be examined, providing a cost-effective tool for evaluating the biological status of the aquatic habitats under study. The methodology involves the procedures to (1) conduct physical habitat assessments of aquatic habitats and their surrounding riparian zones and (2) use benthic macroinvertebrates in evaluating water quality. This is done by assessing selected physical features an aquatic habitat, collecting and identifying benthic macroinvertebrates, and using this latter information to calculate a biotic index scores has emanated from the fact that benthic macroinvertebrates may be influenced by habitat quality (e.g. bank stability) as well as water quality (e.g. a pollutant present in the water). © Gayathri Teknological Publication
Indicators and scores in development of indices Biotic indices are based on the premise that pollution tolerance differs among various benthic organisms. Tolerance scores for each taxon are intended for a single type of pollution; usually these are for organic pollution but tolerance scores for acidification have also been developed (Johnson et al., 1993). In most biotic indices, the tolerance of the taxa that comprise a macroinvertebrate community and the numbers (or their proportion of the total) of each taxon are used to calculate a single score. A comprehensive index developed to monitor organic pollution in freshwater systems was designed by Hilsenhoff (1977, 1982;1987) in U.S.A. Equally comprehensive Biotic Index developed in Britain is the Biological Monitoring Working Party (BMWP) Score (Chesters,1980) and its modified version to produce the Average Score Per Taxon (ASPT). Modified BMWP were followed in biomontoring studies in Yamuna and Kaveri rivers (Sivaramakrishnan et al., 1998). These indices rely on the differential ability of aquatic macroinvertebrates (primarily insects) to survive under specific levels of dissolved oxygen availability, which directly reflects levels of organic wastes in a system. In BMWP identification of taxa is to the family level only and no account is taken of the abundance. Each family is given a score, between 1 and 10, depending on their perceived susceptibility to pollution. Those taxa that are least tolerant, such as families of mayflies and stoneflies, are given the highest scores (Table-1). Following collection of a sample from a water body, all the organisms are picked out, identified, and assigned values. The BMWP score is the sum of the individual scores. This total score can then be divided by the number of taxa to produce the Average Score Per Taxon (ASPT), which is independent of sample size. Armitage et al., (1983) found that the ASPT was less influenced by season and sample size than the BMWP score. Physical and chemical data, and physical data alone, were used to predict BMWP scores and ASPT respectively using multiple regression techniques. The authors suggested that the ratio of observed to predicted ASPT could be used to indicate the possible influence of pollution on the macroinvertebrates (Mason, 1991). 3
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Table- 1: The Biological Monitoring Working Party (BMWP) score Group Mayflies Stoneflies River bug Caddisflies
Families Siphlonuridae, Heptageniidae, Leptophlebiidae, Ephemerellidae, Potamanthidae, Ephemeridae Taeniopterygidae, Leuctridae, Capniidae, Perlodidae, Perlidae, Chloroperlidae Aphelocheiridae Phryganeidae, Molannidae, Beraeidae, Odontoceridae, Leptoceridae, Goeridae, Lepidostomatidae, Brachycentridae, Sericostomatidae
Crayfish
Astacidae
Dragonflies
Lestidae, Agriidae, Gomphidae, Cordulegasteridae, Aeshnidea, Corduliidae, Libellulidae Psychomyidae, Philopotamiidae Caenidae Nemouridae Rhyacophilidae, Polycentropidae, Limnephilidae Neritidae, Viviparidae, Ancylidae Hydroptilidae Unionidae Corophiidae, Gammaridae Platycnemididae, Coenagriidae Mesoveliidae, Hydrometridae, Gerridae, Nepidae, Naucoridae, Notonectidae, Pleidae, Corixidae Haliplidae, Hygrobiidae, Dytiscidae, Gyrinidae, Hydrophilidae, Clambidae, Helodidae, Dryopidae, Elminthidae, Chrysomelidae, Curculionidae Hydropsychidae Tipulidae Simuliidae Planariidae, Dendrocoelidae Baetidae Sialidae Piscicolidae Valvatidae, Hydrobiidae, Lymnaeidae, Physidae, Planorbidae Sphaeriidae Glossiphoniidae, Hirudidae, Erpobdellidae Asellidae Chironomidae Oligochaeta (whole class)
Caddisflies Mayflies Stoneflies Caddisflies Snails Caddisflies Mussels Shrimps Dragonflies Waterbugs Water beetles
Caddisflies Craneflies Blackflies Flatworms Mayflies Alderflies Leeches Snails Cockles Leeches Hoglouse Midges Worms
Biotic indices are one of several types of measures that are routinely used in biological monitoring. Most contemporary survey approaches rely on multiple measures, also referred to as metrices, of community structure and function. These measures can be grouped into several categories (Resh et al., 1996): (1) taxa richness (e.g., family-level, generic-level, species-level), (2) enumerations (e.g., number of all macroinvertebrates collected, proportions of selected orders such as Ephemeroptera, Plecoptera and Trichoptera (EPT)) (3) community diversity indices (e.g., Shannon’s index), (4) community similarity indices (e.g., the Pinkham-Pearson index), (5) functional feeding group ratios (e.g., percentage of the “shredder” functional group © Gayathri Teknological Publication
Score
10
8
7
6
5
4
3 2 1
etc.). Thus, although calculation of a biotic index is an important and commonly used component of a biomonitoring program, an approach that uses several different measures is likely to be of greater value (Plafkin et al., 1989). Bonada et al.,(2006) have made a critical and comparative review of different biomonitoring approaches using aquatic insects as tools, addressing the rationale, implementation and performance of a method. Recently a macroinvertebrate based biotic index has been proposed to evaluate water quality in freshwater river streams of Sikkim in Eastern Himalaya (Bhatt and Pandit,2010). The proposed index was calibrated and evaluated against various biotic indices such as 4
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water quality index (WQI) of National Sanitation Foundation (NSF), USA. This new index has been found to be better in assessing the health of rivers compared to the existing abiotic and biotic indices for : (i) it takes into account the abundance of taxa and reflects even the minor changes in abundance and community structure of the river ecosystem; (ii) it is flexible and gives freedom to select any pollution sensitivity score system based on family, generic or specific levels and (iii) it is universally applicable and is not affected by the geographic location of the river. Palaeolimnological techniques in biomonitoring Palaeolimnological techniques involve the reconstruction of the history of aquatic systems that have been exposed to impacts such as eutrophication, acidification, industrial pollution or climatic change (Luoto, 2009). As with the use of living aquatic insects in biomonitoring, each species of fossil organism is characteristic of certain environmental conditions present during the period in which it lived. The most commonly used invertebrate remains in palaeolimnology are the cladocerans (Rautio,2007) the dipteran families Chaoboridae (phantom midges) and Chironomidae (Walker,2001). The remains of other aquatic insects such as Ephemeroptera, Plecoptera, Trichoptera, and Heteroptera (true bugs) are less abundant but they are equally informative about past environmental conditions (Klink,1989, Tolonen et al.,2003, Luoto, 2009). Palaeolimnological studies offer biologists a way to reconstruct long-past biotic responses to anthropogenic environmental change, but given suitable conditions they also offer means for detecting very recent limnological change (i.e., events of the past ten years). Moreover, because of the importance currently being attached to rehabilitation of aquatic ecosystems, palaeolimnology should play an increasingly important role indefining what natural conditions existed, and thereby serve as a realistic goal for rehabilitation efforts (Rosenberg and Resh,1996;Luoto,2009). Conclusion Aquatic insects offer an excellent way to examine biological aspects of water quality and scientists in many countries are increasingly using water quality criteria based on macroinverterbrates. Implementation of © Gayathri Teknological Publication
bioassessment into water resource programs requires the collaboration among scientists, resource managers, and other people interested in the sustainability of the systems. Knowledge of the ecological status based on true aquatic indicators is fundamental to addressing the balance between landuse and cultural applications of the water with ecological integrity towards attaining the objective of environmental protection and restoration. Lessons learnt from the success stories in the European Union (EU) and USA as well in some developing Asian and African countries serve as a good foundation for countries in their infancy of developing protective Water Law for their aquatic resources. A solid monitoring and assessment program is vital to the ability of any nation to fundamentally regulate the health of its waters. Using biological indicators to achieve that objective is vital to initiate a comprehensive biomonitoring program. The importance of accuracy in taxonomic identification, the use of new multivariate techniques and the predictive modelling, the pressing need for toxicity testing to address ecosystem concerns, the expansion of ecosystem-level biomonitoring, an improved understanding of the natural variability in response to pollution at all spatial and temporal scales and a sound understanding of macroinvertebrate ecology are essential prerequisites at present and in future to the implementation of a biological approach to ecosystem management.
Acknowledgements We are thankful to Dr. M. Arunachalam, Professor and Head of the Centre for his interest and encouragement. We acknowledge Dr. K. G. Sivaramakrishnan for motivating us and for providing literature support in preparation of this article. We also thank S. S. Mariappan for the illustration.
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