Effect of changing flushing rates on development of late summer Aphanizomenon and Microcystis populations in a shallow lake, Müggelsee, Berlin, Germany

Müggelsee is a shallow lake in the suburban region of Berlin, Germany and included in the lake-river system of the river Spree, having an average annual retention time of 42 days which increases to > 100 days in the summer period. The summer equilibrium phase of phytoplankton results in the development of an Aphanizomenon flos-aquae dominated assemblage which, in some years, progresses towards a Microcystis dominated assemblage. Continuously high flushing (in range of 1%-2% of lake volume day (-1) does not prevent Aphanizomenon development but its biomass remains at low levels as compared to other summers with smaller average flushing. In such years (flushing remains < 1% of lake volume day (-1)) a flushing pulse of 1%-2% of lake volume day (-1) has been effectual to break development of cyanoprokaryotes and to decrease their biomass to low levels. The major reason of the decrease is not the dilution effect of flushing pulses but the intolerance of cyanoprokaryotes to sudden environmental changes. Considering the case of Müggelsee from the point of view of reservoir ecology it can be concluded that reservoirs with pulsed use are less exposed to development of cyanoprokaryotes if pulses occur in a sufficient frequency (20-30 days) and their intensity falls to the range of 1%-2% of reservoir volume day(-1). Reservoirs with continuous take off of water are more exposed to cyanoprokaryota development with all the consequences for water use

Sudden and gradual responses of phytoplankton to global climate change: case studies from two large, shallow lakes (Balaton, Hungary and the Neusiedlersee Austria/Hungary)

This paper analyses two phytoplankton long-term datasets; both are from large, temperate shallow lakes. The main difference between them is that phytoplankton growth in Lake Balaton remained severely P-limited despite P-driven eutrophication during the last 30 years, whereas extremely high turbidity causes a permanent light limitation in Neusiedlersee and therefore an increase in P-loadings did not result in a similar increase in phytoplankton biomass. Neusiedlersee is a (slightly) saline inland lake. In Lake Balaton, the blue-green alga Cylindrospermopsis raciborskii blooms invariably if the July-august temperature deviates positively from a 30-year average by ca. 2 °C. A supposed global warming is predicted to cause a higher frequency (but not intensity!) of these blooms. Neusiedlersee is very shallow and therefore regulation techniques cannot prevent water levels sinking in successive dry years. Annual averages of phytoplankton seem to follow quite a regular, wave-like cyclicity. Such cycles can be recognised in the population records of the characteristic species. Similar changes were seen in changes of water level, conductivity, inorganic-P, inorganic N-forms and nutrient ratios. How phytoplankton species can follow a climatic cycle that covers 200 to 500 generations has not yet become clear. Because of reasons discussed in the paper, neither of the two cases can be generalised; each is quite individual

Recent occurrence of Cylindrospermopsis raciborskii, in Waikato lakes of New Zealand.

Cylindrospermopsis raciborskii is a toxin-producing species of cyanobacteria that in autumn 2003 was recorded for the first time in three shallow (max. depth ≤5 m) Waikato lakes and a hydro-electric dam on the Waikato River, New Zealand. It formed water blooms at densities >100 000 cells/ml in Lakes Waahi and Whangape. Net rates of population growth >0.2 day-1 were recorded for C. raciborskii in Lakes Ngaroto, Waahi, and Karapiro, based on comparisons of low numbers (detection of cells/ml) from initial samples and its presence at bloom densities (>15 000 cells/ml) in the subsequent sample "x"-"y" days later. C. raciborskii may be well adapted to rapid proliferation in the Waikato lakes, which are eutrophic to hypertrophic, with high light attenuation, and where nitrogen (N) fixation may provide it with a competitive advantage over non-nitrogen fixing algae under N-limited conditions

Silica-scaled chrysophytes (Chrysophyceae and Synurophyceae) from the Kis-Balaton Reservoir, Hungary

Eight species of silica-scaled chrysophytes were identified by electron microscopy of phytoplankton samples from the newly opened Kis-Balaton Water Protecting Reservoir, Hungary. The composition of this flora of silica-scaled chrysophytes is charachteristic for eutrophic to hypertrophic localities. Most of the species are common and widely distributed, even cosmopolitan. The record of Chrysosphaerella annulata, which was recently described from Austria and has been recorded from widely separated places in the world, is interesting. This and three further species (Spiniferomonas trioralis, Synura petersenii and S. curtispina) are new to Hungary, while the others (Paraphysomonas vestita, Mallomonas acaroides, M. alpina, M. tonsurata) were recorded before mainly on the basis of light microscopy. Electron micrographs of the above species are presented in the paper. A checklist of all the previous records of scaled chrysophytes in Hungary is added as an Appendix. With 10 figures

Disturbance and stress - different meanings in ecological dynamics?

There is an increasing frequency of papers addressing disturbance and stress in ecology without clear delimitation of their meaning. Some authors use the terms disturbance and stress exclusively as impacts, while others use them for the entire process, including both causes and effects. In some studies, the disturbance is considered as a result of a temporary impact, which is positive for the ecosystem, while stress is a negative, debilitating impact. By developing and testing simple theoretical models, the authors propose to differentiate disturbance and stress by frequency. If the frequency of the event enables the variable to reach a dynamic equilibrium which might be exhibited without this event, then the event (plus its responses) is a disturbance for the system. If frequency prevents the variable’s return to similar pre-event dynamics and drives or shifts it to a new trajectory, then we are facing stress. The authors propose that changes triggered by the given stimuli can be evaluated on an absolute scale, therefore, direction of change of the variable must not be used to choose one term or the other, i.e. to choose between stress and disturbance

New, old and evergreen frontiers in freshwater phytoplankton ecology: the legacy of Colin S. Reynolds

This paper offers a brief overview of the contributions provided by widely recognised phytoplankton ecologists to honour the memory of an undisputed leader in the field of aquatic sciences: Colin S. Reynolds. Colin passed away quite unexpectedly in December 2018 causing a wave of sorrow that rapidly circulated among friends and colleagues all over the world. The 14 review papers collected in this Special Issue form a tribute to Colin’s scientific thinking, which survives the man and represents a legacy to all the scientists in the field, especially to young generations. Although authors and editors carefully selected 14 different topics, a certain degree of overlap exists among the collected contributions. This, far from being a limit, further underlines the holistic nature of Colin’s vision about phytoplankton and shows the need to develop a comprehensive cultural framework when analysing this complex ecological group of organisms