Macroinvertebrates of Serbian streams and their significance as bioindicators in estimation of water quality

Despite the fact that it represents only a small part of the total amount of water on the planet (1.2%), land-based water is very significant for man. The demographic explosion that marked the 20th century on the one hand caused constant growth of the need for pure water and on the other hand increased the extent of water pollution due to development of industry, intensification of agriculture and expansion of urban regions. Human action leads to greater or lesser changes of ecological factors in aquatic ecosystems (amount of dissolved oxygen, pH, heavy metal concentration, etc.), regulation of watercourses, disruption of communication between biocoenoses and disturbance of the natural water regime (through the creation of reservoirs). All of this brings about changes in biocoenoses that can be very pronounced, going even so far as to the virtual destruction of life in an aquatic ecosystem or in less severe cases to replacement of an existing biocoenosis by a new one that due to greater homogeneity of ecological factors is characterized by lower diversity. In order to conserve the water resources of the Republic of Serbia, it is necessary to monitor them closely. Biomonitoring is an obligatory part of this task because it is a simple, fast and economical way to follow the state of ecosystems of land-based water. Of all groups of aquatic organisms used in biomonitoring: bacteria, protozoans, zooplankton, phytobenthos, macrophytes and fish, macroinvertebrates are the most widely employed, especially in streams, where they are absolutely the most significant community of bioindicatory organisms. Modern biomonitoring of streams both in the world at large and in Serbia is based to the greatest extent on the use of macroinvertebrates as bioindicators of water quality owing to their many advantages over other aquatic organisms. Macroinvertebrates are widely disseminated organisms that inhabit various types of aquatic ecosystems, from little temporary (ephemeral) stagnant pools, small springs and creeks to large lakes and rivers. The great diversity of macrozoobenthic organisms and extremely complex structure of their communities on the one hand make them very sensitive to anthropogenic action causing changes of ecological factors, and on the other hand enable them potentially to respond with changes in the composition of their biocoenoses that are proportional to intensity of the anthropogenic action in question. Such organisms are characterized by the ability to persist in conditions of fast flowing water because they live attached to the bottom, possess long life cycles and have limited mobility. Their low mobility and sedentary way of life enable the investigator to establish the state of ecological factors on a given area. The relatively long life cycles (lasting 2-3 years) of these organisms make it possible to investigate changes occurring over the course of time. Apart from biological considerations, there are also numerous practical reasons why these organisms are considered good indicators of water quality: samples are taken with relatively inexpensive equipment; the taxonomy of most groups has been thoroughly elaborated; keys for their identification are available; methods that employ macrozoobenthic organisms have been used for many years and are highly reliable; and the responses of certain organisms to different types and levels of pollution have been precisely defined. Macrozoobenthic organisms can be used to test the influence of anthropogenic stress on aquatic. biotopes at all levels of biological organization, from molecular to ecosystematic. The effects of pollution on these organisms under natural conditions are most often analysed on the level of their populations or communities, using structural attributes (measured by indexes of diversity and similarity, biotic indexes, etc.) or functional characteristics, including, for example, primary production, respiratory processes, biomass (secondary production) and circulation of elements, but also aspects of the organisms' life history such as functional guilds in the feeding of a taxon. Investigation of macrozoobenthic communities has been and will be a central part of the ecology of land-based water, partly due to the fact that streams for them represent a crucial link between resources in the form of organic matter (for example, fallen leaves, algae, detritus, etc.) and fish in food webs, and partly due to the diversity and wide dissemination of the organisms involved. In view of these facts, it is unsurprising that systematic research on the fauna of macroinvertebrates in land-based water of Serbia was initiated almost a century ago and has been carried out in continuity with varying intensity up to the present day. More intensive use of macroinvertebrates in biomonitoring of the ecosystems of land-based water in Serbia, as in the world at large, began around the middle of the last century, at which time they started to be included in monitoring of water quality by the Hydrometeorological Institute of Serbia. As can be seen from the above, Serbian science actively followed world trends in biomonitoring of land-based water from the very start, although the intensity of these investigations was highly variable. Intensification of research on macroinvertebrates and their use in biomonitoring of land-based water occurred during the 1990s, with the formation in Novi Sad, Belgrade and Kragujevac of several independent teams of investigators that laid a solid foundation for further progress, as is evident in a series of studies introducing new and modern methods of biomonitoring, methods such as employment of biomarkers, recording of morphological asymmetries and deformities and use of artificial neuron networks. To be specific, the work of these teams has greatly advanced available knowledge about biology of the macroinvertebrates of land-based water in Serbia and continued to keep pace with world trends in their use for biomonitoring. A good example is the development of BNBI and incorporation of a number of EU standard methods into norms for regulation of biomonitoring in Serbia. Despite this positive trend, it must be stated that the use of macroinvertebrates as bioindicators of the quality of land-based water in Serbia is relatively limited because in the majority of cases it is done within the framework of saprobiological analyses, whereas biotic indexes are for the most part unjustifiably ignored, while multimetric indexes and the multivariant approach have not even begun to be employed. For these reasons, the state of biomomitoring in Serbia still cannot be considered satisfactory. To be specific, if the extent of land-based water biomonitoring in Great Britain where it is continuously conducted at more than 6000 localities is compared with the state of affairs in Serbia where about 90 localities out of a planned 500 are continuously monitored it can be seen that the level of biomonitoring in our country is disproportionally lower. Moreover, a comparison of stream quality in Great Britain, despite that country's significantly more advanced industrial development and greater population density, with the situation in Serbia shows that the quality of streams in our country is conspicuously far worse. It is clearly necessary to expand the volume and content of biomonitoring because only in that way will it be possible to make correct decisions in the management of water resources and thereby improve their quality. Meanwhile, at the existing level of macroinvertebrate studies in Serbia, that is not simply a question of political willingness, but also a task limited by the quality and quantity of fundamental research. As has been stated before, successful use of macroinvertebrates in biomonitoring demands an exceptionally good knowledge of the base reference state. That at the present time calls for additional faunistic, taxonomic, biogeographic and toxicological research, as well as studies on the typization of watercourses. It will be possible to define groups of reference localities in Serbia, as has been done in Great Britain, only if the inventory of species in our country is known in detail, if taxonomic problems are resolved, if keys for the identification of species are available, if their range has been clarified and if the types of watercourses and their ecological status (condition) are known. This in turn will make it possible to apply some highly organized system of biomonitoring like RIVPACS or to develop a multimetric index like the ones elaborated in the EU's AQEM program. That the path to this goal is long is clearly indicated by the fact although acknowledged experts today exist for the taxonomy of macroinvertebrate groups such as Chironomidae, Oligochaeta, Heteroptera, Trichoptera, Amphipoda and Gastropoda, research on a number of very important groups such as Ephemeroptera and Plecoptera has only just begun, a situation that has a significant effect on the quality and reliability of determination of these groups, knowledge about their distribution and awareness of their ecological preferences, as well as on the typization of land-based water habitats in Serbia vis-a-vis other countries in the world. Progress in this area largely depends on politics of the state, that is on the measure in which it is ready to support studies, finance the necessary increase in the number of researchers and through selection of programs and projects guide investigative efforts in an appropriate direction. It is also necessary to widen the network of localities at which sampling is prescribed by law, since only by sampling in an organized and planned manner will it be possible to collect an adequate number of data in a procedurally uniform way permitting the drawing of comparisons, development of new biomononitoring methods in Serbia and improvement of ones already in existence. That is the only way to form a standardized database of information about the ecosystems of Serbian streams. Such a database will be the foundation needed for the standardization of reference localities, which represents a key step toward the implementation of both multivariant and multimetric methods in biomonitoring