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The bottom fauna inhabiting two types of ecotones: 1) the transition zone between land and lake water, and 2) the border of a macrophyte bed and open water, situated in different types of littoral, distinguished mainly according to the structure and distribution of macrophytes was studied. The investigations were carried out in five harmonious lakes (from mesotrophic to highly eutrophic) and in one disharmonious (humoeutrophic) in July and September of 1996 and 1997. Both the species composition of zoobenthos and the relative abundance of the most numerous taxa (Tubificidae and larvae of Chironomidae) in ecotones did not seem to depend much on the type of littoral but rather upon the nature of the bottom sediments. The influence of lake fertility in harmonious lakes was clearly expressed mostly in the land-water ecotones where it was demonstrated by the drop of chironomids and increase in tubificids and predators in total faunal abundance with a rise of lake. trophism. The clear pattern in vegetation bed-open water ecotones concerned solely predators which contribution to the total faunal abundance tended to increase with a rise of lake trophic status. The ecotones of the disharmonious lake did not show much differences in comparison with the harmonious lakes except extremely low faunal density in vegetation-open water ecotone, being totally predominated by chironomids. In both harmonious lakes and in disharmonious one the highest faunistic similarities were found within the same types of ecotones, while the two types differed greatly.
The influence of submerged macrophytes on composition, abundance and distribution of epiphytic and benthic chironomids was investigated in five lakes differing in the development of vegetation cover. Studied lakes represented three types, classified according to the concept of Alternative Stable States as: macrophyte dominated MD (dense vegetation), phytoplankton-macrophyte dominated PMD (sparse, patchy vegetation) and phytoplankton dominated PD (lack of submerged vegetation). Both zoocenosis responded differently to the changes in macrophyte cover. The density and biomass of benthic midges (density and biomass per m² of bottom surface) were visibly higher in the patchy vegetated lakes; the abundance of epiphytic chironomids did not show any regularity. The species composition of epiphytic chironomids differed visibly between particular lake types, changed with the decrease of macrophyte cover. The composition of benthic midges was similar in all lake types. The studies showed a strong dependence of the proportion of epiphytic to benthic chironomids on the cover of macrophytes. In MD lakes the phytophilous midges were more abundant than benthic; in PMD lakes we observed the opposite pattern.
The investigations were carried out in the lacustrine-fluvial system of the Lizhma river (the Ladoga lake basin) in its natural condition (until 1993) and during the exploitation of its trout complex. The authors show the water bodies to increase their content of biogenic elements at the expense of the organic form. They mark some changes in the structure of algoflora. The abundance of alkophylic species of periphytone was found to increase, likewise the concentration of chlorphyll and the numbers of blue-green algae. The zooplankton community undergoes some restructurization in lakes; the role of predators in total biomass is growing. The biomass and numbers of zoobenthos have considerably enlarged. The structure and distribution pattern of invertebrates in the benthic community have changed in the pool part within the region of water discharge from the fishery farm. The ichthyofauna of the water bodies so far proves to remain stable.
The chemical composition and biotic structure were studied in ecotonal zones of six trophically differentiated lakes in the region of Polesie Lubelskie (Eastern Poland). High qualitative and quantitative differentiation of zoocenoses (zooplankton and zoobenthos) usually occurred in each ecotonal zone of every lake studied. The highest diversity occurred among microinvertebrates (zoopsammon and zooplankton).
This overview presents in detail the state of knowledge of the abilities of various components of the Baltic Sea environment to accumulate trace elements and radionuclides. Particular components of the Baltic ecosystem (abiotic and biotic) are considered as potential monitors of pollutants. The use of seaweeds, e.g. Fucus vesiculosus or Zostera marina is recommended, also molluscs, e.g. Mytilus edulis, for biomonitoring surveys of metal pollutants and radionuclides in the Baltic Sea. However, several requirements need to be met if results are to be reliable. Since metal levels and radionuclide activities in the growing tips of F. vesiculosus reflect exclusively the levels of their dissolved species in the ambient seawater, this alga is very useful for monitoring dissolved species of metal pollutants and radioisotopes in the Baltic ecosystem. In contrast, M. edulis, a filter feeder is an appropriate tool for monitoring trace elements occurring in both chemical forms, i.e. dissolved and suspended species. Therefore, full information on the bioavailability and toxicity of heavy metals (depending on their chemical speciation) as pollutants of the Baltic Sea can be obtained if at least two biomonitoring organisms are applied simultaneously, e.g. F. vesiculosus and M. edulis. Moreover, the data matrix can be interpreted more accurately if not only trace element but also macroelement concentrations (Ca, Mg, Na, K) in these two representatives of Baltic phytoand zoobenthos are taken into consideration; this point requires special attention. Two coastal species of fish, i.e. Zoarces viviparus and Perca fluviatilis, are good biomonitors of metallic contaminants, so their use as sentinels is recommended. The budgets of chemical elements and the ecological status of the Baltic Sea are presented. Several ‘blacksp ots’, e.g. large estuaries and seaport towns, heavily polluted by trace elements, are identified in the Baltic Sea and other enclosed seas such the Mediterranean and the BlackS eas. Of these seas, the Baltic is the most heavily loaded with trace elements and organic pollutants. The overview identifies gaps in our environmental knowledge of the Baltic Sea, and sets out possible priorities, key areas or strategies for future research.
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