Brigitte Nixdorf

Phytoplankton assemblages and steady state in deep and shallow eutrophic lakes - an approach to differentiate the habitat properties of Oscillatoriales

Ecological conditions and phytoplankton succession in two shallow hypertrophic lakes (Langer See and Melangsee) and a dimictic, eutrophic lake (Scharmützelsee) in a lake chain in Eastern Germany were analyzed from 1999 to 2001 in order to find situations of phytoplankton steady state assemblages and variables controlling the phytoplankton composition according to Reynolds et al. (2002). Long term background data from 1993 to 2001 suggest steady state conditions in shallow lakes, whereas the deep lake exhibited irregular fluctuations between various phytoplankton stages. Since the phytoplankton composition in the shallow lakes was similar in all the 3 years, it was highly predictable. Steady state conditions dominated by different species of Oscillatoriales were detected during the summer period 1999 and 2000 in Langer See and in Melangsee (see Mischke & Nixdorf, this volume). This dominant assemblage found in both lakes (group S1 acc. to Reynolds et al., 2002): Planktothrix agardhii (Gom.) Anagn. et Kom., Limnothrix redekei (Van Goor) Meffert, Pseudanabaena (Lauterb.) is typical in turbid mixed layers with highly light deficient conditions, but it is also regularly dominant in the dimictic lake Scharmützelsee as observed in 1999 and 2001 (Pseudanabaena limnetica (Lemm.) Kom. The Nostocales Cylindrospermopsis raciborskii (Wolz.) Seenayya et Subba Raju and Aphanizomenon gracile (Lemmerm.) Lemmerm. were important in the shallow lakes as well as in lake Scharmützelsee. Nevertheless, the occurrence of filamentous cyanobacteria in the dimictic lake was not regular and an unpredictable change in phytoplankton development was observed in 2000. It is discussed, whether this phenomenon of regular succession in shallow hypertrophic lakes is caused by adaptation to a resilient and an extreme environment or by the pool of species that can live or survive in that environment. This was checked through comparison of the depth of the mixed layer, the mean daily irradiance within this layer and the nutrient resources. Although the nutrient resources in both types of lake are near threshold levels, indicating growth inhibition by dissolved nutrients (DIP, DIN, TIC, DSi), the under water light supply seems to be the key factor favoring the dominance of filamentous cyanobacteria belonging to the functional group S1.

Microcystins (hepatotoxic heptapeptides) in german fresh water bodies

In 1995 and 1996 a total of 55 German water bodies with different trophic states were investigated for the presence of potentially microcystin‐producing cyanobacteria. The seston biomass of over 500 samples was analyzed by HPLC to assess microcystin content. The highest microcystin content per dry weight was found when Planktothrix rubescens was dominant, followed by Planktothrix agardhii and Microcystis spp. The microcystin to chlorophyll‐a ratio mostly varied between 0.1 and 0.5, with maxima of 1–2. In over 70% of the samples from pelagic water, particulate microcystin concentrations were below 10 μg L−1. By contrast, spatial and temporal concentrations varied by 4 orders of magnitude (2–25,000 μg L−1) at bathing sites in 1997 during a mass development of Microcystis spp. The seasonal peak of development of Microcystis spp. occurred from June to September and of Planktothrix agardhii from September to November. Planktothrix rubescens, however, was almost perennial. The seasonal levels of these cyanobacteria were clearly reflected by microcystin concentrations in the water bodies. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 13–22, 1999

Distribution of three alien cyanobacterial species (Nostocales) in northeast Germany: Cylindrospermopsis raciborskii, Anabaena bergii and Aphanizomenon aphanizomenoides

A. Stüken, J. Rücker, T. Endrulat, K. Preussel, M. Hemm, B. Nixdorf, U. Karsten and C. Wiedner. 2006. Distribution of three alien cyanobacterial species (Nostocales) in northeast Germany: Cylindrospermopsis raciborskii, Anabaena bergii and Aphanizomenon aphanizomenoides. Phycologia 45: 696–703. DOI: 10.2216/05-58.1 Cylindrospermopsis raciborskii is considered a cyanobacterium of tropical origin and an alien species to temperate waters. However, it has been detected as far north as northern Germany. While previous studies have shown that all isolated German C. raciborskii strains are hepatotoxic, little is known about the spatial occurrence and relative frequency of this species in temperate Germany. The aim of this study was to investigate the spatial distribution and relative frequency of C. raciborskii close to its northernmost distribution limit, to characterise the habitat in which it is most likely to occur in this climatic zone and to search for any other neocyanobacterial species that might be present in German waters but has so far been overlooked. One hundred forty-two water bodies in northeast Germany were sampled from June until September 2004. All cyanobacteria species were analysed qualitatively and semiquantitatively. Besides C. raciborskii, two additional neocyano-bacterial species were detected: Anabaena bergii and Aphanizomenon aphanizomenoides. For both taxa, these findings represent their northernmost occurrence and their first report from German waters. Cylindrospermopsis raciborskii was present in 27%, Anabaena bergii in 9% and Aphanizomenon aphanizomenoides in 7% of the samples. The occurrence of each species was analysed in relation to maximum lake depth, Secchi depth, lake volume and lake surface area. All three species were present in a wide range of habitats, but C. raciborskii and Anabaena bergii occurred significantly more often in shallow, turbid waters than in deep, transparent water bodies. None of the parameters investigated were significantly correlated with the occurrence of Aphanizomenon aphanizomenoides. In conclusion, alien thermophilic cyanobacterial species are much more widely distributed in temperate Germany than previously known. The results are discussed with respect to the possible mechanisms that enable these organisms to expand northwards.

Chrysophytes and chlamydomonads: pioneer colonists in extremely acidic mining lakes (pH <3) in Lusatia (Germany)

Twenty-three extremely acidic (pH between 2.5 and 3.5) mining lakes in Lusatia (Germany) were analysed in order to classify their hydrochemistries and to assist the understanding of phytoplankton colonization of these extreme environments. Neither morphometric nor physical parameters influence phytoplankton composition but determine the extent to which the nutrient supply supports the mass development of Chrysophyceae and Chlorophyceae in certain layers of the water (hypo- or epilimnetic chlorophyll maxima and short mass developments). Conventional trophic classification is not readily applicable to these lakes but a chemical classification on the basis of hydrogen, total iron and acidity is proposed. Species of Ochromonas and Chlamydomonas dominate the phytoplankton in fourteen of the most acid lakes; dinoflagellates occurre additionally in four; a more diverse algal assemblage with diatoms and cryptophytes is found in lakes with moderately acidic (pH 5.7–7.0) or alkaline conditions (pH 7.0–9.4). The lake chemistry is the main determinant for the planktonic composition of the water bodies whereas the trophic state mainly determines the level of algal biomass.

Dynamics of planktonic food webs in three mining lakes across a pH gradient (pH 2–4)

Acidic mining lakes (ML) in Lusatia (Germany) are characterised by their geogenically determined chemistry. The present study describes the structure, main components and relationships within the food webs of three acidic mining lakes with different pH values (ML 111: pH 2.6; ML 117: pH 2.8; ML Felix: pH 3.6) in order to show their typical characteristics. The investigation covered the period 1995–1997. The number of species and the biomass are both low, but increase with increasing pH. Planktonic components in the most acidic ML 111 (pH 2.6–2.9) comprise bacteria, Ochromonas spp. and Chlamydomonas spp. and a few rotifers (E. worallii, C. hoodi). Heliozoans are the top-predators. In ML 117 (pH 2.8–3) Gymnodinium sp., ciliates, the rotifer B. sericus and the pioneer crustacean Chydorus sphaericus join the pelagial community. Heliozoans were not found in ML 117 or ML Felix (pH 3.4–3.8). ML Felix had the most taxa. The benthic food chain of all three lakes includes phytobenthic algae as producers, chironomids as primary consumers and corixids as top predators in the profundal. Corixids predate on small cladocerans inhabiting the pelagial in lakes with a pH above 2.8 such as ML Felix. They invade the pelagial and act as a connecting link between the benthic and the pelagic food chains, which are isolated in lakes with a lower pH. Occasionally primary producers and consumers were abundant in all three lakes. These organisms do not depend on the degree of acidity, but on the availability of essential ressources. Mass variations covered up any seasonal variation in the extremely acidic ML 111 (0.9 mm3 l−1), while in the other two lakes seasonal patterns of biomass were found.

Phytoplankton of the extremely acidic mining lakes of Lusatia (Germany) with pH ≤3

Most of the flooded, open-cast lignite mining lakes of Lusatia (Germany) impacted by the oxidation of iron sulphides (pyrite and marcasite) are extremely acidic. Of 32 lakes regularly studied from 1995 to 1998, 14 have a pH <3 (median pH 2.3–2.9). These lakes are typically buffered by high concentrations of Fe (III) and have high conductivity (1000–5000 μS cm−1). Concentrations of dissolved inorganic carbon (DIC) and phosphorus are typically extremely low. These factors result in a very different environment for algae than found in neutral and acid-rain impacted lakes. The planktonic algal flora is generally dominated by flagellates belonging to genera of Chlorophyta (Chlamydomonas), Heterokontophyta of the class Chrysophyceae (Ochromonas, Chromulina), Cryptophyta (Cyathomonas) and Euglenophyta (Lepocinclis, Euglena mutabilis). Near-spherical non-motile Chlorophyta (Nanochlorum sp.), Heterokontophyta of the class Bacillariophyceae (Eunotia exigua, Nitzschia), Dinophyta (Gymnodinium, Peridinium umbonatum), other Chlorophyta (Scourfieldia cordiformis) and Cryptophyta (Rhodomonas minuta) are also found.

Why ’very shallow‘ lakes are more successful opposing reduced nutrient loads

There are different approaches for classifying deep and shallow waters using physically and ecologically derived parameters. Nevertheless, transition states make it difficult to define border crossing points between the two types of limnetic ecosystems and to distinguish more precisely between different types of shallow, especially highly eutrophicated lakes. We contribute a detailed analysis of different characteristics of shallow waters from lakes in the Berlin/Brandenburg-region. In the catchment area of the river Dahme in Eastern Brandenburg (Scharmutzelseeregion) we find mainly shallow and highly eutrophicated lakes, dominated by Cyanobacteria. ‘Very shallow’ lakes of different morphometry and topography are compared with ‘medium shallow’ or deeper lakes in the region with similar loading characteristics for the following properties: morphometry, topography, theoretical retention time, mixing intensity, nutrient dynamics, external and internal loading, underwater light climate, zeu/Zmix, phytoplankton development and oxygen budget. We found that ‘very shallow’ lakes in the region are more efficient in converting the available phosphorus into phytoplankton biomass because of the constant and sufficient underwater light climate due to the favourable relation of zeu and Zmix We conclude that the regular mixing regime guarantees a stable and near optimum light/dark rhythm as well as higher heterotrophic activities, stimulating primary production up to the upper limit of algal development.

Equilibrium phase conditions in shallow German lakes: How Cyanoprokaryota species establish a steady state phase in late summer

In 2000, a field study in two shallow, polytrophic lakes (Langer See and Melangsee) in eastern Germany revealed an equilibrium state assemblage of Cyanoprokaryota in late summer. During 4 successive weeks in Langer See Planktothrix agardhii (Gom.) Anagn. et Kom., Aphanizomenon gracile (Lemmerm.) Lemmerm. and Pseudanabaena limnetica Lemmerm. were more than 80% of the standing biomass of phytoplankton, and their cumulative biovolume was around 33 mm3 l−1 ((±3.2 SD). In Melangsee, the very small Limnothrix species L. amphigranulata (Van Goor) Meffert was the most common species, accompanied by Pseudanabaena limnetica and Planktothrix agardhii. For 3 weeks, their cumulative biovolume was about 23 mm3 l−1 ((±3.4 SD), which represented 75 – 82% of total biovolume. The dominant species all belong to the functional group S1 defined by Reynolds (1997), except for A. gracile, which we suggest to be included in group SN. In both lakes mean light intensities ranged between 2.2 and 8.3 E m−2 d−1. Overall species spectra were very similar in both lakes, but dominance by Limnothrix and by Planktothrix in the respective lakes is observed repeatedly. The success of these species is discussed in the context of the habitat properties in August/September. Summer mixing events represented no disturbances in the sense of Connell (1978), since they do not interrupt the species dominance. More frequent mixing events and higher concentrations of dissolved nitrogen occurred in Langer See than in the more shallow, but wind protected Melangsee. In Langer See light deficient conditions were intensified by an increasing biomass of P. agardhii, and this species probably benefited from nutrient input by more frequent resuspension. The light deficiency also affected the diversity, expressed as Shannon–Wiener Index (H), which was reduced more in lake Langer See (H = 0.51) than in Melangsee (0.74) during steady state periods. Recognizing the important effects of mixing, we suggest an additional variable to describe habitat properties: the number of full mixing days as a proportion of total days of observation should help to discriminate between shallow habitats with intermittent mixing events, and those with more regularly mixing in summer period.

Review: plant life in extremely acidic waters

Abstract In acidic waters, a variety of autotrophic organisms are found including phototrophic bacteria, phytoplankton, filamentous- and micro-benthic algae and macrophytes. To explain the occurrence and distribution of primary producers we must answer the following question. What is acidity and where and how does it influence autotrophic metabolism in aquatic ecosystems? The very low pH per se will have profound effects on the survival and growth of organisms and therefore influence biodiversity. On the other hand, we observed a spatial structuring of phototrophic colonization according to the supply of nutrients at interfaces or specific layers. These are interfaces between sediment and water and the chemocline of meromictic lakes or in the case of planktonic development, chlorophyll maxima in the hypolimnion. Therefore, we attempt to analyze the growth conditions for different types of autotrophic organism in relation to resource demands and the distribution of limiting nutrients in sediments and the water column. Adaptations may be morphological (e.g. size, shape, surface area), physiological (e.g. heterotrophic or mixotrophic metabolism, CO 2 concentrating mechanisms, low intrinsic growth rates), behavioral (e.g. diurnal migration) or ecological (low grazing pressure, low losses through sedimentation).

Comparison of bacterial and phytoplankton productivity in extremely acidic mining lakes and eutrophic hard water lakes

Two types of standing waters are important in Brandenburg (Germany): eutrophic hard water lakes of glacial origin (about 2.800) and several hundred mining lakes, mostly highlyacidic (pH between 2 and 3 and high concentrations of dissolved iron). A trophic gradient can be used, describing the nutrient situation in these lakes from oligo- to mesotrophic mining lakes to eutrophic to polytrophic natural hard water lakes. Bacterial and algal production in some typical lakes of these two types are compared. Whereas bacterial productivity in acidic mining lakes is comparable with eutrophic hard water lakes, primary production is very low. It does not exceed the level of bacterial production considering volume related daily carbon production. Mining lakes are thereby characterised as heterotrophic ecosystems. Reasons for the production differences in both types of lakes can be looked for in the resource availability and top down control. Contrary to the eutrophic natural lakes, phytoplankton productivity in mining lakes is controlled by carbon limitation. Consequences for the structural classification of pelagic bacterial and phytoplankton communities are shown concerning the course of ecosystem succession from pioneer initiation in mining lakes to high-biomass maturation stage in eutrophic hard water lakes.