Small scale macrophyte-environment relationship in an oxbow-lake of the Upper-Tisza valley (Hungary)

We tested the relationship between water chemical variables and macrophyte vegetation in an oxbow-lake of the Upper-Tisza, Hungary. There were 42 relevés in random plots of 2 m by 2 m and 20 chemical variables (Ca, Fe, Hydrogencarbonate, K, carbonate, Kjeldahl-nitrogen, chloride, COD(Cr), Mg, m-alkalinity, Mn, Na, NH4, NO2, NO3, dissolved orthophosphate-P, total phosphorus, pH, sulphate and conductivity) and a biological one (chlorophyll a) were measured. Detrended canonical correspondence analysis was used to explore the species-vegetation-water chemical variables relationship. Our results revealed that there were pronounced differences both in the vegetation and the chemical variables among the different kinds of vegetation patches. According to the DCCA, Trapetum natantis, Glycerietum maximae, Ceratophyllo-Nymphaeetum albae and Typhetum angustifoliae associations could be separated based on the relevés and environmental variables. Kjeldahl nitrogen and carbonate were found to be the most important variables. Our results suggest that water chemical variables had strong influence on vegetation development. The groups of relevés identified by the DCCA were coherent with classical phytosociological categories

Importance of acidic phosphatase activity in P supply and Gonyostomum semen Ehrenbergh (Raphidophyta) occurrence in a Hungarian peat bog, Keleméri Kis-Mohos (Ne Hungary)

Phosphatase enzymes are capable of releasing phosphate through cleavage of phosphoester bonds. The seasonal importance of this process was examined by using a model substrate paranitrophenylphosphate and the Michaelis-Menten equation to estimate the release rate of PO4-P from phosphomonoesters. The seasonal occurrence of phosphomonoesters and acid phosphatase activity was used to estimate the velocity of phosphate release from these compounds. Filter fractionation of phosphatase activity demonstrated that most activity (>60%) was in size fractions less than 0.45 μm. The release rates were highest in May and June (15 to 25 nmol L–1 min–1) during the Gonyostomum semen (Raphidophyta) bloom and decreased to less than 2 nmol L–1 min–1 in two weeks and remained low throughout the summer and the fall. Fractionation of 32P-H3PO4 labelled dissolved organic phosphorus showed this fraction to vary considerably through the year. Potential phosphate release declined through the summer and into the fall. Significance of the co-occurrence of phosphomonoesters and acid phosphatase activity maxima and Gonyostomum semen (Raphidophyta) bloom is discussed

Population dynamics and food of bleak (Alburnus alburnus L.) in the littoral zone of Lake Balaton, Hungary

Intra- and interspecific effects together with changing environmental conditions regulate the dynamics of the fragile bleak populations in Lake Balaton. Size- and age-structures, length-weight relationships and mortality were studied on 1493 individuals and growth history were determined using scales from 703 specimens. The population growth rate was slow and the basic population parameters showed area variations along the longitudinal axis of the lake. Gut contents were analyzed in 224 individuals. The bleak stocks are trophically strongly related to the littoral zooplankton and benthos; and they play a significant energy-mediating role in the food-webs between the periphytic communities and fish assemblages in the littoral zone of Lake Balaton