A Velencei-tó bevonatlakó algáinak tér- és időbeli változása, kapcsolata a tó ökológiai állapotával | Spatial and temporal change of epiphytic algae and their connection with the ecological condition of shallow lake Velencei-tó (Hungary)

Ács, Éva (2007) A Velencei-tó bevonatlakó algáinak tér- és időbeli változása, kapcsolata a tó ökológiai állapotával | Spatial and temporal change of epiphytic algae and their connection with the ecological condition of shallow lake Velencei-tó (Hungary). Hidrobiológiai Monográfiák; Acta biologica Debrecina. Supplementum oecologica Hungarica, 1.; 17 . Magyar Ökológusok Tudományos Egyesülete, Debrecen.

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Abstract

The shallow lake Velencei-tó is the second largest sodic (alkaline) lake in Hungary. Except for its western part, the lake is characterized by high concentration of dissolved salts (conductivity is about 3000 μS cm-1), dominant ions are sodium, magnesium, sulphate and hydrogen-carbonate, typical value of pH in the soda part of the lake is 8.8-9. From the point of view of the epiphytic algae, the water of the lake is rarely limited in terms of phosphorus, however limitation in terms of nitrogen occurs relatively often. This fact, as well as the sodic character of the lake and its precipitation-dependent water level fun-damentally determines the algae composition of the epiphyton. Based on ana-lyses made by Self Organizing Map (SOM) method, epiphyton samples on the one hand taken from different water level periods and on the other from the two parts of the lake with different chemical and biological qualities (the western, reedy part and the rest of the lake, the open water areas) segregated from each other. In summer, samples taken from the same place, at the same time, from dead and alive reed did not differ from each other significantly.Forthewaterqualificationofthelake,amodelwasdevelopedbyweightedaveragingmethod,which was based on the conductivity optimum and tolerance of the algae in the epiphyton. By the application of the transfer function, the optimum- and tolerance values of the species were calculated by means of which indicator species were defined.Theseindicatethegoodecologicalstateofthesodicpartofthelake.By the use of the optimum- and tolerance values, a sodic index (SCIL = Sodic Conductivity Index for Lakes) was created that can be calculated on the basis of the ZELINKA & MARVAN formula, which was found suitable for the assessment of the ecological condition by means of the investigation of the epiphytic algae in Lake Velencei. Besides the IBD index calculated by the OMNIDIA software was also in good agreement with the results of the quali-ficationperformedonthebasisofphytoplankton. In those standing waters where the quantity of non-diatoms is significantintheepiphyton, result that is more precise can be obtained if all algae are considered during the assessment. For this, the SCILall index developed by me can be a good starting-point. When only diatom investigations are performed, suitable ones can be found among the indices calculated by the OMNIDIA, as the IBD proved to be so in the case of Lake Velencei. Although the IBD index was developed for watercourses, it is duly robust so that it can be used well for standing waters too.

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