Activities of rat brain synaptic plasma membrane (SPM)Na(+)/K(+)-ATPase and Mg(2+)-ATPase were investigated by in vitro individual and simultaneous exposure to ions of the first transition series metals (Cu(2+), Zn(2+), Fe(2+)). All investigated metals produced a larger maximum inhibition of Na(+)/K(+)-ATPase than Mg(2+)-ATPase activity. Metal concentrations causing 50% inhibition of Na(+)/K(+)-ATPase activities were: Cu(2+) 7.1 microM Zn(2+) 19 microM Fe(2+) 25 microM. Simulataneous exposure to metal combinations: Cu(2+)/Zn(2+), Cu(2+)/Fe(2+) and Zn(2+)/Fe(2+) inhibited both the Na(+)/K(+)-ATPase and Mg(2+)-ATPase activity synergistically, i.e., more than the sum of the metal induced inhibitions assayed separately. It is also established that the plot of logarithm IC50 values of Na(+)/K(+)-ATPase activity vs. the ionic radius of (Cu(2+), Zn(2+), Fe(2+)) is a straight line that enables to predict the value IC50 for other metals of the first transition series. The results obtained show that Na(+)/K(+)-ATPase is promising as a biological component of biosensor.

During three years period from 1991 to 1994, investigation of the river Kolubara (Serbia, Yugoslavia) was carried out along 35 km of water course from Valjevo to Lajkovac. The macrozoobenthos community was composed of 117 determined taxa. Of the found taxa Oligochaeta were the most diverse with 40 taxa determined. The greatest diversity of macrozoobenthos community was foound at the river section in Valjevo, upstream the mouth of Gradac (69), while the community was most uniform downstream Valjevo at Bela Stena (24 taxa). A decrease as well as an increase in the macrozoobenthos diversity was not in accordance with similar decrease or increase in saprobic index values since they were in narrow range from 2.37 to 2.59.

According to microbiological parameters, waters of both small rivers of eastern Backa, Serbia (Yugoslavia), are slightly and moderately polluted by organic matter at the most of the investigated localities in summer season. The satisfactory power of water selfpurification has been preserved in these aquatic ecosystems. In order to prevent further eutrophication processes, certain measures of river water protection and conservation should be undertaken, especially in stagnant parts of investigated waters. Also, the regular monitoring of water quality should be established.

In this paper, some data on long term seasonal investigation of hydrography and plankton are presented. The most important fact is that the whole area is exposed to the impact of the freshwater from numerous sources from the coast and submarine springs in Boka Kotorska Bay, as the impact of rivers Bojana and Drim. Exchange of the intermediate water-masses between Adriatic and Jonian basins is of great importance, too. So, basic ecological data, as well as characteristic phytoplankton and zooplankton groups and species are described.

There was investigated potential erodibility of two small experimental watersheds, which belongs to the watershed of Topciderska river, Serbia (Yugoslavia), on the base of geological structure of the watershed area. The investigations of potential erodibility of watersheds were included the analysis of tectonical and every geological formation, as from viewpoint of its possible erodibility as well as of possible sediment type (load, suspended and mixed) which were originated in desintegration processes. The sediment type domination, which was produced from watershed, was confirmed from granulometric composition of sediment in experimental watersteams. The synthesis of results of this analyses is presented with map of potenatial source of sediments from experimental watersheds.

During the summer 1998 the second phase of Cadastre of Water Objects on the Teaching Base Goc, on the Goc mountain, in central Serbia (Yugoslavia) was done. Investigation was carried out on the territory of 20 square km, with serpentine as parent rock. Serpentine is decomposed in the surface layer, with sceletal soil up to 50 cm deep, insignificant retention attributes. Dominate surfaces under bare lands, meadows, pastures and degraded forest stands. 35 springs were registered, small volume yield (up to 0.29 l*/s), with pH=7.5 to pH8.5, electrical conductivity from 80 up to 800 microS*/cm, temperature 7.0-17.0 deg C. Springs are permanent, but on the higher parts could dry up. Water level in the serpentine has small hydraulic gradient, with slope to the zones of out flow, in other words, to the local erosion base. Hydrogeological characteristics of serpentine were analyzed detailed.

The paper presents results of the hydroecological investigations of the Vlasina river basin, Serbia (Yugoslavia). The researches were performed in May and September 1996, as a part an annual investigation cycle. Samples were collected from five localities on the Vlasina river, and on two spots on its main tributaries - the Gradska river and Luznica, just before entering into the Vlasina. Qualitative and quantitative data on composition of phyto- and zooplankton, periphytic and benthic communities together with data obtained from physico-chemical water examinations were analysed to assess water quality of examined water courses. The results of performed monitoring were compared with informations on the sources of pollution, as well as with the data on hydrology, geomorphology, demographic variations, and recent development of tourism and industry in the Region in order to assess environmental quality of aquatic ecosystem and to suggest the conservation strategy.

Determination of total organic carbon content (TOC) and trihalomethane formation potential (THMFP) as well as correlation of those two parameters is recommended for monitoring of water bodies which are considered as drinking water resources. Those parameters would enable a categorization of water bodies from the protection point of view as well as from view of their usage as drinking water sources. Relationship between TOC and THMFP is dependent on the origin and the structure of organic matter in water. In this paper the correlation of TOC and THMFP is given for different kind of resources.

Important differences in the structure of fauna communities of their deepest parts of benthos were found in the investigation of several water reservoirs (Gruza, Grosnica, Barije, Bor, Vlasina and Medjuvrsje) on the territory of Serbia (Yugoslavia) lasting several years. The pronounced alterations of the structure are in the correlation to the pronounced degree of eutrofication was also established according to other indicators, above all according to the concentration of biogenic salts and the amount of organic substances. Characteristic group and taxa of the fauna of benthos which point to certain level of eutrophications were separated.

The investigations of qualitative and quantitative composition of plankton and the bottom fauna of the Tisza river, Serbia (Yugoslavia), were conducted during 1998. According to the analyses of the indicator species of hydrobionts, saprobic index was calculated, and the estimation of the water quality of the lower flow of the dam near Novi Becej on the structure and abundance of the investigated organisms.