engleski

Interactions between microphytoplankton of the Danube, its sidearms and wetlands (1426 - 1388 r. km, Croatia)

Background and Purpose: The Danubian flood area in northeastern Croatia (Baranja Region) covers approximately 53 000 ha, of which the protected area of the Nature Park Kopački rit includes approx. 23 000 ha. Phases of floods and droughts are the main characteristic of floodplain aquatic environments. The aim of this paper is to compare the microphytoplankton compositions of the Danube (sections 1426-1388 r. km) with the microphytoplankton of Danubian sidearms and wetland area of Kopački rit in order to establish the interactions between them. Materials and methods: Samples for hydrobiological analyses were taken in September 2002, November 2002 and March 2003. The investigated area was divided into three groups: the main arm (the Danube River), the Danube sidearms and the wetlands of Nature Park Kopački rit. The phytoplankton samples were taken with a 10-liter sampler from the whole vertical profile. The "tubular-chamber" method was used for the quantitative analyses of microphytoplankton. Results: In September and November 2002, the quantitative composition (7.63x106-18.14x106 ind./L) and total biomass of microphytoplankton (11.53x13.79 mg/L) of the Danube was less than in March 2003 (26.85x106-44.06x106 ind./L, biomass 25.70-46.83 mg/L). Bacillariophyceae had predominance in microphytoplankton composition (up to 95% of the total number of individuals) in November and September, while in March the dominant community was Bacillariophyceae-Chrysophyceae. Biomass of microphytoplankton of side arms system was higher than in the Danube (12.21-44.41 mg/L). Bacillariophyceae-Chlorophyceae was the dominant community in November and September. In March, the Chrysophyceae was a supplement to the Bacillariophyceae community (20-50% of the total number of individuals), except at arms d3 in November and March (Bacillariophyceae had absolute predominance up to 98% of the total number of individuals). Microphytoplankton biomass of the wetland area was in the range 23.43-58.88 mg/L. The developed communities were: Bacillariophyceae-Euglenophyceae (in September), Bacillariophyceae-Chrysophyceae (in November) and Bacillariophyceae-Chrysophyceae-Chlorophyceae (in March). Conclusions: The structure and composition of microphytoplankton of the investigated sidearms and wetland area of Kopački rit were influenced by the hydrological regime of the Danube. Lower biomass of microphytoplankton and predominance of Bacillariophyceae were characteristic for the flooding period (the potamophase). During the dry period (the limnophase), qualitative and quantitative composition of microphytoplankton was the result of specific environmental conditions in each microlocality. The very abundant phytoplankton of the sidearms and wetlands, flowing back to the main arm can affect the increase in the microphytoplankton biomass and trophic level of the Danube.

microphytoplankton; Danube; sidearms; wetland

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