Factors Influencing the Cyanobacterial Dominance in Lakes: Analysis of Lakes in Central Germany

Abstract

This study aimed to identify the key factors influencing the phytoplankton development in twenty- eight lakes located in Central Germany (state of Sachsen-Anhalt). A multivariate analysis of biological (phytoplankton), physicochemical, morphological, and hydrometeorological variables of the lakes collected between 2005 and 2021 is presented here. This analysis is the first approach for this dataset to summarize the statistics and to explore trends and patterns of evolution from a multivariate perspective to improve understanding of the conditions that favor the emergence of different phytoplankton classes and taxons. Correlation analysis of the data showed that both, the biovolume of the phytoplankton and chlorophyll-a were positively correlated with, total nitrogen and phosphorus, and negatively correlated to the depth to epilimnion, residence time and conductivity. The thresholds for total nitrogen, phosphorus and average depths are investigated for cyanobacterial genera of 'Aphanizomenon', 'Anabaena', 'Microcystis' and 'Planktothrix'. Higher chlorophyll-a concentrations (>100 mu g/l) are observed when TN>2 mg/l, P>0.1 mg/l and the average depth was less than 1 m. These thresholds are also valid for higher biovolume values (>5 cm(3)/m(3)) of these cyanobacterial taxons observed in all lakes. The nonlinear equations proposed for chlorophyll-a and biovolume of the phytoplankton derived by the genetic algorithm greatly improved the goodness of fit with respect to the linear models. When all data is considered R2 values are calculated as 68% for chlorophyll-a concentrations and 55% for the biovolume suggesting that these models can be applied for future studies.