Although the phytoplankton indices describing the response of phytoplankton to the eutrophication have been developed and used for many years in the routine lake monitoring programme in some countries, the implementation of the Water Framework Directive (WFD) [EC, 2000] stimulated the development and improvement of quite a number of the current WFD-compliant phytoplankton-based methods. This paper is a review of the current phytoplankton-based methods for assessing the ecological status of European lakes. The particular attention was paid to the ways of solving problems arising from the need to reflect the complex and dynamic plankton algal communities on a numerical scale in order to gain reliable information about the state of the ecosystem.
Hanna Soszka, Agnieszka Pasztaleniec and Agnieszka Kolada
The Water Framework Directive introduces the requirement for ecological status assessment based primarily on aquatic organisms and supporting physico-chemical elements, including oxygen conditions. The criteria for assessing oxygen conditions applied in routine lake monitoring in Poland are based on the mean hypolimnetic saturation with oxygen at the peak of summer stagnation in stratified lakes, and on the oxygen content at the bottom in the summer in polimictic lakes. The currently used oxygen criteria usually cause dismay, particularly if biological elements indicate at least good ecological status and the oxygen conditions are the only reason for lowering status class. The aim of the article is to present the scale of variability of oxygen conditions in selected lakes within the last two decades and to analyse the limitations and conditions of applying this indicator in routine monitoring, assessment and classification of Polish lakes. Data from the years 1999–2015 on oxygen and thermal conditions in a set of nine benchmark lakes in Poland were examined and the reasons for changeability in water oxygenation from year to year were discussed. Alternative oxygen indicators were considered as well as oxygen standards based on fish protection requirements that have been adopted in some European countries. It was suggested that when assessing lake ecological status, data on the oxygen conditions from a number of years must be taken into consideration, e.g., for the analysis of trends in lake trophy changes or for documenting the effects of remedial actions in lake catchment areas in long time frames.
Agnieszka Pasztaleniec, Maciej Karpowicz and Małgorzata Strzałek
The spatial differentiation of the physico-chemical parameters (KdPAR, pH, DOC, nutrient concentrations) and plankton communities (phytoplankton, Crustacea) was considered in the system: the water column without macrophytes, pleustophytes - lemnids (duckweeds) and hornwort Ceratophyllum demersum. It was demonstrated that at the study sites different habitat conditions occurred, which were related to the macrophyte assemblages. The highest values of the phytoplankton biomass and the greatest algal biodiversity were found in the site without vegetation, in both species-specific and functional terms. Zooplankton, dominated by Copepoda, reached the greatest density and species diversity at the Ceratophyllum site. Despite the substantial differentiation of habitats, the plankton diversity was quite low.