Using phytoplankton as a tool for evaluating changes in the ecological status of two Bulgarian reservoirs (2020-2021)

Kostadin Dochin

Abstract: The aim of the present research is an attempt to assess the environmental status of two Bulgarian reservoirs by using the assemblage Q index based on the analysis of the data collected from the phytoplankton during 2020-2021.A total of 86 algae belonging to 20 functional groups were identified in Aheloy Reservoir and 61 from 22 groups in Ovcharitsa Reservoir. We found a change in the dominant phytoplankton functional groups compared to previous data published for the same reservoirs. In the Aheloy Reservoir these changes can be ordered as follows from the codons: S1 – H1 – P, trough L0 – W2 – J to D – E – J, and in Ovcharitsa Reservoir from P trough X2 – L0 – M to F – MP – P. The implementation of the assemblage Q index also provides an explanation of these changes by reporting an improvement in the ecological status of the studied reservoirs compared to an earlier publication. The ecological status of Aheloy Reservoir has changed from „poor” to „tolerable”, and of the Ovcharitsa Reservoir from „moderate” to „good” according to the results obtained from the calculation of the Q index. We recognize as controversial the question of the application of the values for the F factor and the possibility of mistakes in establishing ecological status, related to the lack of reliable statistical database concerning the individual characteristics of highly modified water bodies, such as reservoirs. The ecological status assessments obtained using the Q index of these two reservoirs in the period 2020-2021 are relatively close compared to the evaluation based on our unpublished average values for phytoplankton biomass.

Keywords: algae; assemblage index; dominant functional group; F factor; Q index

Date published: 2023-04-27