engleski

Alternation of factors affecting bacterioplankton abundance in Danube river floodplain (Kopački rit, Croatia)

The purpose of this investigation was to determine influence of different phases of hydrologica cycle on abundance of colony-forming units in Kopački rit floodplain and to record temporal and saptial variations in proportion of eutrophic and oligotrophic bacteria (r and K-strategists) as biological reflectors of avalibility of dissolved organic carbon (DOC). Explanation of bacterial abundance was performed with abiotic variables (water temperature, depth, Secchi disc transparemcy, dissolved oxygen, pH, conductivity, ammonia, nitrates, nitrites, total nitrogen and total phosphorous) and one biotic (Chl-a) variable. Their dimensionality was reduced with PCA analysis. Produced principal component scores were used as indipendent variables in multiple regression by which examination of relationship between scores (indirectly variables) and bacterial abundance was performed. Elevated bacterial abundance was established during limnophase (floodplain isolation from river) and potamophase (flood). During limnophase it was positively correlated with Chl-a ; and in Sakadaš lake in September 2003 significatly higher number of eutrophs versus oligotrophs emerged (P=0, 026). During potamophase opposite was the case. Bacterial abundance was negatively correlated with Chl-a ; and during July 2004 in Čonakut Channel significantly higher number of oligotrophs versus eutrophs emerged (P=0, 000). Differentiation in the number of eutrophs and oligotrophs suggest existence of higher concetration of labile DOC in September 2003 and July 2004. In multiple regression analysis, significant contribution to explanation of variation in eutrophs abundance (54%) gives first and fourth axis (with loadings of Chl-a, ammonia, transparency, depth and pH) while for oligotrophs neither axsis contributes significantly. These results suggest existence of two different mechanisms of bacterioplankton control in Kopački rit flooplain. In addition, there are two sources of DOC, which differentiate the quality of organic matter. They predominate under very different hydrological regimes. Under these conditions eutrophic bacteria are manily bottom-up controlled. However, it is not clear which mechanism controlled the abundace of oligotrophs.

bacterioplankton; eutrophic bacteria; oligotrophic bacteria; Danube; Kopački rit

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