Structural and functional characteristics of phytoplankton, algal mats, detritus and water quality under main abiotic factors in urban ponds (case study of urban settlement Hostomel, Bucha District, Kyiv Region, Ukraine). Report ІI. Quantitative indicators, dominant complexes of phytoplankton, detritus and water quality of urban ponds

Abstract

The paper deals with phytoplankton quantitative indicators and dominant complex structure, and dimensional and morphological characteristics of detritus particles in the ponds of Hostomel urban settlement. Water quality has been assessed according to phytoplankton characteristics. The phytoplankton abundance made up 2648.0–113675.0 thousand cells  dm–3, and it was mainly formed by Cyanobacteria. The biomass varied within 3.72–16.53 g  m–3, which is indicative of eutrophic waters. The biomass was dominated by Euglenozoa, Miozoa and Bacillariophyta. The dominant complex according to phytoplankton abundance included small-celled Cyanobacteria, according to biomass – large-celled Euglenozoa, Miozoa and Bacillariophyta with a certain share of Cyanobacteria. Different structures of dominant complexes according to abundance and biomass is an important adaptation mechanism of urban ponds phytoplankton. Phytoplankton’s high primary productivity completely fulfils energetic and trophic demands of aquatic organisms at higher trophic levels, and the unconsumed algal biomass is decomposed and transferred to the water column in the form of organic detritus. The organic detritus particles can be ranged into four classes – from minimal < 30 mcm to maximal > 101 mcm, whose biomass can reach 57.60–62.80 mg  dm–3. It indicates that this biological component is very important in forming energy flow, matter circulation and trophic relations. Water quality assessment according to phytoplankton saprobiological characteristics has shown that χ–ο-saprobic and β-mesosaprobic organisms prevailed in the ponds under study. So, the water bodies can be classified within the range “very clean”–“clean” and “moderately polluted” waters. Unlike most urban ponds, the pond network of Hostomel can be considered a quite safe recreation zone from the ecological point of view and is an attractive green space within the urban landscape.