engleski

Changes of phytoplankton community structure in correlation with different concentrations of nitrates in surface water of Varaždin alluvial aquifer system

Nitrate is a compound of nitrogen (N) that occurs naturally in moderate concentrations in aquatic environments. Higher concentrations of nitrate in freshwaters are typically caused by anthropogenic activities. In the project Origin, fate and TRAnsport modelling of NITrate in the Varaždin ALluvial aquifer (TRANITAL) an interdisciplinary approach was developed to study the spatio-temporal dynamics, fate and sources of nitrate in the aquifer systems at the catchment scale of Drava River near Varaždin. The main aims of the research are to: (i) develop multi-parametric approach to characterize alluvial aquifer hydraulic properties and chemical, isotopic and microbiological properties of groundwater ; (ii) define the role of surface waters on aquifer recharge and nitrogen cycle ; (iii) describe algal succession in surface waters in correlation to microbial community and groundwater flow and transport of nitrate in the alluvial aquifer. Sampling of surface waters was performed monthly from June to December 2017 on five study sites: Plitvica stream, gravel pits Šljunčara and Zelendvor, accumulation HE Varaždin (Ormoško Lake) and Drava River near Virje. Samples of phytoplankton and phytobentos were collected for molecular and morphological analyses according to standard methods using water sampler and scratching from substrates, accordingly. Different physical and chemical factors affect the composition of algal communities and one of the main factor is the availability of N compounds, mainly nitrates. Current preliminary results show that in the Plitvica stream, where nitrate concentrations are higher, species from phyla Chlorophyta and Cryptophyta are dominant. In the gravel pit Šijanec, where nitrate concentrations are very low, summer bloom of Cyanobacteria (Microcystis aeruginosa Kützing and Microcystis wesenbergii Komàrek) occurred. Study areas gravel pit Zelendvor, accumulation HE Varaždin and Drava River near Virje showed domination of diatoms (Bacillariopyceae), where nitrate concentrations oscillate. Further results will include molecular and morphological analyses of algae and microbiological community in correlation with nitrate concentrations.

nitrates, alluvial aquifer system, phytoplankton, ecological status assessments, bloom of Cyanobacteria.

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