Ziel dieses Projektes ist es, zur Klärung der derzeitigen Verbreitung und Variabilität des toxischen Cyanobakteriums C. raciborskii und des Toxins Cylindrospermopsin (CYN) in Gewässern der Berliner Region beizutragen und eine Grundlage zu schaffen, auf welcher deren weitere Entwicklung und das damit verbundene Risiko für Mensch und Umwelt abgeschätzt werden kann. Die Verbreitung von C. raciborskii und CYN wurde in einem Pre-Screening Programm im Sommer 2004 untersucht. Für 142 Gewässer, die sich hinsichtlich Morphometrie, Trophie und Mixistypus unterscheiden, wurde die Zusammensetzung der Cyanobakterien einmalig qualitativ und semi-quantitativ analysiert sowie der CYN Gehalt des Sestons ermittelt. C. raciborskii wurde in 27,5 % der 142 untersuchten Gewässer nachgewiesen. Ihre relative Häufigkeit wurde überwiegend als vereinzelt (21,1 %) oder häufig (6,3 %) eingeschätzt. Massenentwicklungen der Art traten zum Zeitpunkt der Untersuchung nicht auf. Als typisches Habitat für C. raciborskii wurden flache eutrophe Gewässer mit niedriger Sichttiefe, und geringen Zeu/Zmix Verhältnissen analysiert. Entgegen bisheriger Annahmen ist die Art jedoch nicht auf Flachseen beschränkt, sondern kann auch in tiefen dimiktischen Gewässern Populationen etablieren. Darüber hinaus wurden vier weitere bedeutende Arten ermittelt. Raphidiopsis curvata und R. mediterranea, die in 5 von 142 Gewässern detektiert wurden. Von beiden Arten ist bekannt, dass sie CYN produzieren können. Anabaena bergii wurde vereinzelt bis häufig in 14,1 % der Gewässer nachgewiesen. Für diese Art wurde der gleiche Habitattyp wie für C. raciborskii festgestellt. Aphanizomenon aphanizomenoides wurde vereinzelt bis häufig in 13,4 % der Gewässer nachgewiesen. Bei beiden Arten handelt es sich wie bei C. raciborskii um Neo-Cyanobakterien, die bisher nur aus tropischen bzw. subtropischen Regionen bekannt waren. Beide produzieren toxische Substanzen, die im Fall von A. aphanizomenoides noch nicht näher identifiziert werden konnten. Im Fall von A. bergii handelt es sich bei einem der Toxine um CYN. Zusammenfassend kann für die hier relevanten Arten festgestellt werden, dass sie weiter verbreitet sind als bisher bekannt war. Die Tatsache, dass C. raciborskii bisher in verhältnismäßig wenigen und A. bergii sowie A. aphanizomenoides bisher gar nicht für das Untersuchungsgebiet beschrieben wurden, wird u.a. auf taxonomische Unklarheiten zurückgeführt. Bislang wurden 96 Sestonproben aus 80 Gewässern auf CYN untersucht. In 63 % der Proben, bzw. 61 % der Seen wurde CYN in Konzentrationen zwischen 0,1 und 100 µg/g TG nachgewiesen und ist somit in Deutschland weiter verbreitet als bisher angenommen. Ein erster Vergleich der Cyanobakterienzusammensetzung mit dem CYNVorkommen zeigt, dass CYN in den untersuchten Gewässern nicht nur von C. raciborskii produziert wird, da es auch in Proben gemessen wurde, in denen die Art nicht nachgewiesen wurde. Derzeit werden die beiden oben beschriebenen Arten A. bergi und A. aphanizomenoides als weitere potentielle CYN-Produzenten in Betracht gezogen sowie eine Reihe weiterer Arten der Gattungen Anabaena und Aphanizomenon. Eine entgültige Klärung wird nach Abschluss der chemischen und molekularbiologischen Analysen der isolierten Stämme erwartet.

Three single-filament isolates of Aphanizomenon flos-aquae from two German lakes were found to produce remarkable amounts of the cyanobacterial epatotoxin cylindrospermopsin (CYN). CYN-synthesis of the strains were evidenced both by LC-MS/MS analysis and detection of PCR products of gene fragments which are implicated in the biosynthesis of the toxin. The strains contain CYN in the range of 2.3–6.6 mg gK1 of cellular dry weight. To our knowledge this is the first report of CYN in A. flos-aquae.

A suite of predictive quantitative models of phosphorus (P) dynamics in Lake Tegel and Schlachtensee has been developed. The results, specific to each lake, are set out below, together with general conclusions about management strategies, and some high priority areas for future research. Lake Tegel: 1. The inflow from the Havel to Lake Tegel has been estimated using both a discrete time step box model and a time integrated numerical model. There is good internal agreement between the 2 estimates of the Havel inflow as a mean fraction of the total inflows (~ 40 %) , as well as with the earlier work of Ripl (1993). The estimated residence times agree closely (~ 70 d). 2. There is considerable inter-annual and inter-seasonal variation in Havel inflows. The numerical model can be used to satisfactorily predict these as a function of the Havel discharge, OWA discharge, and water extraction (bank infiltration and recharge, r²=0.76). 3. Over the past 15 years Lake Tegel has been both a net source (1984-1992;2000-2002), and a net sink (1993 – 1999), for phosphorus. The Havel inflow is the most important component in the P budget of Lake Tegel. When the sediment is a source, the modelled internal P load is 2-4 fold of the OWA annual load. 4. The internal P load can be satisfactorily modelled (r²=0.72) as a function of the external P loads, the water works extractions, and the temperature and nitrate concentration in the hypolinmion. The sensitivity analyses indicate that temperature is the major controlling factor for the P release. The significance of nitrate has to be explored further, and identifying thresholds for parameters which trigger release remains to be done in years 2 and 3. 5.The sediment investigations indicate that the sediment P release is dominated by mineralisation, plus desorption at times of high mineralisation and FeS precipitation. 6. Sediment investigations indicate that artificial oxidation of the sediment surface will only impact on P release when the mineralisation is intense and sulphate reduction is prevented. 7. The internal store of mobilizable P in the sediments is small, the rate of mobilisation is high, and the water residence time is short; thus the internal P load will have no long term effects after the external load is reduced sufficiently (< 5 years, assuming an external load of zero). At present, the external P load is high enough to recharge the sediments. Schlachtensee: 1. The water balance of Schlachtensee can be modelled satisfactorily (r²=0.89) by considering precipitation, storm water discharges and a term to reflect groundwater flows, which yet needs to be validated. 2. Groundwater inflows, as unknown parameter, were determined from modelling by a constant groundwater inflow plus other variable components dependent on precipitation, the level of Schlachtensee, the extraction at Well Rehwiese and of the temperature; this still needs to be cross-checked with a more detailed analysis of groundwater data. 3. The long time development of the P concentration is dominated by the reduced external load from the OWA Beelitzhof. The modelled long term steady state is about 0.02 g P m3 (annual mean). Schlachtensee has been a sink for P since 1985. 4. Next to effects of the reduced external load, the P concentration in Schlachtensee is characterised by peaks occurring in autumn and winter. The cause is not conclusively identified, but is suspected to be due to loading from the steep shoreline, e.g. leaching P from fallen leaves or mobilisation of animal/human excreta deposited in the summer. 5. Modelling shows that in Schlachtensee the epilimnion exerts a dominant effect on the P dynamics. Although P accumulation occurs in the hypolimnion, this is only a small fraction of the total lake P content. P release is controlled mainly by temperature and redox conditions, as well as the hydrological regime. Whether or not thresholds for release can be identified from any of these remains to be investigated. 6.The sediment investigations indicate that the sediment P release is dominated by desorption due to FeS precipitation. 7. The internal store of mobilizable P in the sediments is small, the rate of mobilisation is moderate, and the water residence time is longer than Lake Tegel. Thus, though its contribution to the lake’s P pool is much smaller, the internal P load will continue to exert an effect for longer than in Lake Tegel after the removal of the external load. Assuming the external load to be zero, the mobilizable P-Pool will be released in about 5 years. Both lakes: Chlorophyll-a data is used to depict the reaction of phytoplankton biomass to reduced in-lake TP concentrations. Chlorophyll-a were recalculated without the phaeophytin correction, and investigations for TP thresholds that govern phytoplankton response were begun. TP thresholds in Lake Tegel appear to be higher (around 100 µg/L) than in Schlachtensee (around 30 µg/L). Further data evaluation, including analysis of monthly means and individual sampling dates, is needed. Management implications: 1. Lake Tegel and Schlachtensee have quite different behaviours and require different management strategies. The various models already developed provide a basis for exploring adapted management scenarios. An initial exploration has identified potentially effective strategies. 2. For Lake Tegel the results strongly point to the continuation of the current management strategy to limit the inflow of P rich Havel water into Lake Tegel, i.e. increasing the OWA discharge during summer, when the P concentration in the Havel, and the extraction by the Water Works, are at their highest. 3. As the P release from the sediment in Lake Tegel is mainly driven by the temperature above the lake bottom the stratification stability should be as high as possible.Therefore, operation of the aerators in a fashion to maintain the maximum possible stratification in summer is proving critically important. 4. The model results confirm that for Schlachtensee the P balance is no longer dominated by the inflows from the OWA Beelitzhof, thus any further efforts to reduce P loading will be more effective if concentrated on the other major external sources. 5. The dominant term in the P balance of Schlachtensee appears to be the autumn and winter deliveries, though the actual mode of delivery is still unclear. Identifying the source(s) is an important future research task. 6. Epilimnetic processes are dominant in Schlachtensee and thus no further measures are required to reduce the internal P loading from the sediments to the water column. Future Research Goals 1. Improving the P models for both lakes, for Lake Tegel particularly for the calculation of the internal loads and for Schlachtensee for calculating the external loads, 2. Developing the P models towards management models for both lakes by improving the calculation of the internal loads for Lake Tegel and the external loads for Schlachtensee, 3. Including model components for biological interactions and interfacing them within a transferable P process model to explain the process of trophic recovery, 5 4. Using the improved models for assessing the relative effects of external and internal measures aimed at modifying the P budget, e.g. seasonality of OWA output, aerator operation and seasonal changes in water residence time, 5. Analysing which responses of the lake components are continuous and which show thresholds, and identifying threshold values for the latter; in a second step including other lakes using literature and data provided by other partners, 6. Conducting specifically targeted field investigations to fill gaps, to validate the models and as supplement of monitoring by ILAT in order to uphold the long-term data series, as detailed in the proposal for continuation of the project; 7. Using the outcomes of 1 – 6 for optimised management scenarios for the two Berlin lakes. Together with the evaluation of literature and data from other lakes undergoing trophic recovery, general guidance on managing restoration and predictions of responses to reduced nutrient loading will be developed.

L'Erdre, rivière de l'ouest de la France, a subi ces dernières années une prolifération massive de cyanobactéries, avec des répercussions négatives sur les activités touristiques étant donné le danger potentiel pour la santé humaine lié au rejet de toxines. A la demande de l'établissement public territorial "Entente pour le Développement de l'Erdre Navigable", E.D.E.N., un consortium de spécialistes (SETUDE, Anjou Recherche, KWB, UBA, Bi-Eau, BCEOM, Eco-Environnement Ingénierie) a participé à une étude détaillée sur l’équilibre écologique de l’Erdre, la croissance des cyanobactéries ainsi que le relargage de toxines, afin de développer des stratégies pour limiter ce phénomène. Au sein de ce consortium, le Centre de Compétence des Eaux de Berlin (KompetenzZentrum Wasser Berlin gGmbH, KWB) et l'Agence Fédérale de l'Environnement d’Allemagne (Umweltbundesamt, UBA) ont réalisé des travaux de recherche en laboratoire. Le projet a été mené de fin 2002 à début 2004 par les partenaires scientifiques français et allemands. Les expériences en laboratoire réalisées par les deux partenaires à Berlin ont pour but d’identifier l’influence de trois facteurs sur le développement des cyanobactéries et la libération de leurs toxines : l’impact d’une limitation en nutriments (azote, phosphore), l’influence de la vitesse d’écoulement, et le rôle des sédiments. L’étude porte sur la cyanobactérie filamenteuse Planktothrix agardhii et la toxine microcystine, qui prédominent dans l’Erdre.

Cyanobacteria proliferation and the potential health risk related with the release of the associated toxins have lead the local association EDEN to initiate a comprehensive study on cyanobacteria in the river Erdre. Within the consortium in charge of the project, the Berlin Centre of Competence for Water (KWB) realised lab-scale research in cooperation with the German Federal Environmental Agency (UBA), on the species Planktothrix agardhii which predominates in the river Erdre, and the associated toxin microcystin. The objective was to determine the influence of key factors such as nutrients (nitrogen, phosphorus), light, flow velocity and sediments on cyanobacteria growth and competition as well as microcystin release from the Planktothrix population in the river Erdre. Results from the lab-scale cultures proved that nutrient-limited conditions lead to a decrease of cyanobacteria biomass and may favour some genotypes with reduced needs among the Planktothrix population. Given the current state of scientific knowledge, no differences in competition between toxic and non-toxic Planktothrix strains can be established. Nutrient limitation favours microcystin release from cells, however the global decrease of cyanobacteria biomass induces a decrease of the total quantity of released toxin. These results can be applied in a water body where nutrients concentrations are very low (below 50 µg/L for total phosphorus). In the river Erdre, as long as external nutrients inputs remain considerable, light is the limiting factor. Internal nutrient recycling from the sediments is globally negligible in comparison with external inputs. Culture experiments in a flow simulation flume proved that flow velocity had substantial impact neither on Planktothrix growth nor on microcystin release. Only a short transition phase with negative effects was observed. Overwintering of Planktothrix in Erdre-sediments could be proved by the detection of a substantial population using fluorescence analysis. This inoculum should be large enough for initiation of Planktothrix development in the next vegetation period. However, the high adsorption capacities of the analysed sediments from the river Erdre allow to put aside a potential risk of microcystin release from sludge. While providing innovative results on the species Planktothrix agardhii, this project contributes to the comprehensive study initiated by the EDEN association in order to preserve the values associated with environment, health and tourism in the river Erdre.

The present report characterizes the field sites Lake Tegel and Lake Wannsee as well as the artificial recharge site GWA Tegel in terms of their clogging layer, sedimentary, hydraulic and hydrochemical properties. As a result, a solid basis for the interpretation of specific compounds evaluated within NASRI and for subsequent modeling and quantification of the data is given. Major problems or difficulties where identified, in order to focus investigations on aspects not fully understood to date in the next project phase. The combination of different tracers enables the interpretation of the flow regime. With the help of T/He analysis, ages of different water bodies can be estimated. The analysis of tracer showing distinct seasonal variations is used to estimate travel times while water constituents which are either mainly present in the bank filtrate or the background water are used for mixing calculations. The proportions of treated wastewater in the surface water were estimated in front of the transects. The surface water composition varies largely both in time and space, which is a problem at Wannsee, where the surface water sampling point is not representative for the bank filtration input. Estimates for travel times of the bank filtrate to individual observation and production wells are given and vary between days and several months. The production wells are a mixture of bank filtrate and water from inland of the wells and deeper aquifers, proportions of bank filtrate are given where possible to differentiate between contaminant removal and dilution. They vary between < 20 and > 80 %. The new observation wells enable a vertical differentiation of the infiltrate. It becomes clear that at Tegel and Wannsee, there is a strong vertical succession towards larger proportions of considerably older bank filtrate with depth. At the Wannsee transect, the observation wells deeper than the lake do not reflect the surface water signal at all. It will be important to combine the new information with hydraulic information of existing flow models (mainly of the IGB “model” group). The evaluation of the redox conditions shows that redox successions proceed with depth rather than (only) in flow direction. In addition, the redox zoning (as characterised by the appearance or disappearance of redox sensitive species) is very transient. The zones are much wider in winter than in summer, in particular at the artificial recharge site GWA Tegel, probably due to temperature effects. This poses a challenge for the desired modelling and the interpretation of data from redoxsensitive substances.