engleski

Nitrate concentration in alluvial aquifer of the Drava River in correlation with toxic algal bloom

Nitrogen is one of essential elements limiting growth of autotrophic organisms in terrestrial and aquatic environments. Increase of nitrate concentrations through agriculture, industry and domestic wastewaters became a significant environmental issue with a strong impact on eutrophication. Availability of nitrogen compounds influences algal growth and assemblages, often favouring blooms of potentially toxic genera. Temporal dynamics, fate and sources of nitrate at the alluvial aquifer of Drava River were investigated in the present study. The main aims were to develop multi-parametric approach to characterize hydraulic, chemical, isotopic and microbiological properties of groundwater systems and to define the role of algal community in surface water on aquifer recharge and nitrogen cycle. Sampling was performed monthly from June 2017 to March 2018 at Šijanec gravel pit. During the investigated period algal community showed variation in taxonomic composition, abundance and biomass. Summer of 2017 was characterized by a high abundance of Cyanobacteria, specifically the bloom-forming Microcystis aeruginosa Kützing (biomass of 5.11 mg/L), which resulted in the sharp decrease of nitrate concentrations (50.1 mg/L to 2.5 mg/L). Cyanobacteria have the capacity for increased uptake of nutrients, especially nitrates, which allows them to outcompete other algal species in eutrophic conditions. Following the breakdown of M. aeruginosa in October, nitrate concentrations increased from 9.4 mg/L to 38.4 mg/L in March 2018 and in colder winter period, Bacillariophyceae become dominant group. Changes in algal composition indicated strong correlation between N forms and algal community. According to the origin and transport of nitrate in the alluvial aquifer of the Drava River it is possible to predict succession of algal groups and blooms of toxic species, thus allowing local communities to react on time. In addition, modelling the fate of N compounds in the alluvial aquifer can provide results helpful in preventing the occurrence of algal blooms.

nitrogen compounds ; alluvial aquifer of Drava River ; algal toxic bloom ; Microcystis aeruginosa Kützing

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