“Lake Bant”: A five year project to solve cyanobacterial problems Peter Lücking and Jürgen Michele*, Jade University of Applied Sciences, Wilhelmshaven, Germany ___________________________________________________________________________

Abstract In the summer of 1990, a bloom of toxic cyanobacteria (nitrogen fixing species) was detected in Lake Bant – a brackish lake close to Wilhelmshaven, Germany – for the first time (Nehring (1993)). These problems occurred several times – but not every year. Free jets are well known in chemical engineering and other technical fields for mixing low viscosity fluids in large environments. In the literature the advantages can be found. Details for an application in a lake are given in Michele, J. and Michele, V. (2002). There, the various methods are discussed which may mitigate the related problems. Destratification was considered as a reasonable solution to overcome harmful algal blooms (HAB´s). Especially the aspect of delivering oxygen to the hypolimnion was recognized to be very helpful – thereby expanding the range for the fauna. Biomass would be transferred from phytoplankton to daphnia and up the food chain to a healthy fish population. In the literature the destratification is done by the recommended technique of a bubble curtain. This method is believed to be the most effective and also the most economical way to destratify a large lake. But this method and also vertical jet mixing are relatively ineffective. In a poster presentation Michele, J. (2009) showed why this is the case. Vertical jets and also bubble curtains entrain themselves, quickly creating a short circuit. Some successful results reported in the literature are generated in a lake due to some cross flow which helps mixing. Opposed to vertical jets, inclined jets have a long way to accumulate oxygen rich water and feed it downwards into the wind driven backflow. There is no short circuit! A YouTube video is available (Michele, J. (2012)), which shows how to do mixing in a stratified environment. The results of the project are discussed. Two inclined propellers were installed in 2008 (only one 1.5kW and the second 2.5kW energy consumption in a lake with a volume of 11.5*106m3) – a minimal-invasive attempt. Destratification was accomplished, oxygen level was brought down to the lake ground at 10m depth, species changed – HAB´s were considerably reduced, oxygen levels made decomposition (odor problems) of accumulated wind driven algal masses a minor problem, phosphorus was reduced, and the lake was on a way to recover. The propellers were removed from the lake in 2013 providing an “off – on – test” for the destratification project. This showed the effectiveness of the applied minimal-invasive method. Just recently a new look at phosphorus revealed that 5.4t were “removed” from the water column during the project. Literature points to an effect of satisfactory oxygen concentration at the sediment surface. Keywords: Cyanobacteria, blue green algae, destratification, aeration, oxygen, lake flora and fauna, biodiversity __________________ *Corresponding author: Tel.: +49 4461 83043, E-mail address: [email protected]

1.

Introduction

1.1. The “very special lake” Lake Bant is a very special lake. It was separated from Jade Bay and made a military harbour. After the war it became a brackish water lake by closing it off from the harbour by a dam. These days it is close to a fresh water lake with the flora and fauna adapted to the newly established water system. Because there is no flow-through, the lake is only fed by groundwater and rain, yielding a long holdup time. There is some communication with the salty sea. The lake orientation and depth can be seen in fig. 1.

Fig.1 Lake Bant – lake orientation and depth (taken from Manzenrieder, H., 2014) The former harbour has a rectangular cross section. Only less than 10% of the water is below the average water depth of 10m (a hole for a swimming dock and excavations for sand). The maximum length is 2650m, the width about 370m, maximum depth 20m. Total water volume is 11.5*106m3. The lake has steeply sloping shores – this means that there are very few flat regions with hydrophytes. Wilhelmshaven is also called “Schlicktown” - the fine grain of the former

wadden sea causes a low water visibility in the lake, if mixed to the ground.

1.2. The Problems In the summer of 1990, a bloom of toxic cyanobacteria (nitrogen fixing species) was in Lake Bant detected for the first time (Nehring (1993)). These problems occurred several times – but not every year. Because the lake is “very special” and eventual solutions to its problems therefore would not be generally applicable, there was no research money from the European Union and German public organizations. Jade University of Applied Sciences proposed to use an inclined jet to destratify and oxygenate the lake. Engineering experience in mixing low viscosity fluids and waste water treatment led to a project proposal. The theoretical background can be found in Michele, J. and Michele, V. (2002), Michele, J. (2009), and in a youtube video by Michele, J. (2012). We consider oxygen to be a very important factor for a lake ecological system. Hupfer, M. and Lewandowski, J. (2013) stressed the importance of oxygen. The German LAWA (2003) organization also connects the trophic state with the resulting oxygen level: oligotrophic: oxygen also at the end of stagnation period above 4mg/l, mesotrophic: also in the hypolimnion there may be a deficiency in O2, eutrophic: at the end of summer: oxygen deficiency in hypolymnion, polytrophic: degradation problems because of zero oxygen, hypertrophic: already shortly after stratification – no oxygen in hypolimnion.

2

Present authors are sure that the oxygen level can be kept above zero down to 10m yearround at very little cost.

departments of the city of Wilhelmshaven were involved. The installations were of different design:

The most crucial results of eutrophication are harmful algal blooms and odor developments during degradation of wind-accumulated algae. If enough oxygen is above the sediment, at least the odor problems are reduced. In Lake Bant in the years before the project, frequently strong blooms and odor problems would last almost for a week. Destratification is an inexpensive technology used worldwide to overcome the problems. So far, limnologists saw destratification only as an emergency method to mitigate these problems. Reduction of phosphorus input was considered the preferred method. Hupfer and Lewandowski discussed several methods of lake internal technologies to overcome the problems.

1.3. The Project The town of Wilhelmshaven intended to solve the lake problems and was looking for a solution at reasonable cost. Jade University offered a five year project, aiming at destratifying the lake with two inclined propeller jets. The project was initiated in 2007. The project was also intended to give our students an inside view of such a research program. At least five years were thought necessary to observe the shift of the ecological system, since self-reproduction of fish and the establishment of benthic life (fauna and bacteria) takes even longer. The realization was accomplished with the help of our students: design, construction supervision, assembling, installation, measurement equipment installation, and maintenance. Also, technical service

Fig. 2 „Bant 1“ on the hook and „Bant 2“ design and realization System details: “Bant 1” “Bant 2” diameter: 1.3m 1.5m angle to horizon: 37.5° 30° speed: 110 rpm 40 rpm exit speed: 0.95m/s 0.95m/s speed at 10m depth *: 0.35m/s 0.33m/s *Speed calculated with equations for a free jet in water of homogeneous density See Lücking, P. et al. (2013) „FreistrahlAnlagen im Banter See – Abschlussbericht Technik“ .

3

Larger impeller diameters make sense, but the fabrication cost is much higher. Operational cost will be lower. The installation was in the positions shown in fig. 3.

Fig. 3 Positions of the two pontoons with the propeller installations In the first year, only one system (“Bant 1”) was ready and in operation with a power consumption of 1.5kW. In the following years both systems were in operation with an additional power consumption of “Bant 2” of 2.5kW. Because the main wind direction is from the west, the inclined jets were pointing to increase the back flow. The position had to be fixed because the power supplied was by cable. Operations were scheduled from the time before stratification developed (mid of April) until the autumn overturn (mid of September). The jet speed was kept on the low side, avoiding stirring up sediments. Higher speeds would have only a local effect. Sediment stir-up would be only the same as during total recirculation in spring and autumn, when higher wind speeds create higher speeds at the lake bottom.

1.4. Normal stratification of Lake Bant Lake Bant is a dimictic lake. Dimictic lakes mix from the surface to bottom twice each year. The metalimnion is usually located in midsummer at a depth of about 5m. A number of people did not believe that only 1.5kW would be able to help the lake to overcome the cyanobacteria problems and would destratify the big lake. But our project proved the effect, as theoretically predicted in Michele, J. and Michele, V. (2002). Data of normal stratification development in summer are not available for Lake Bant for the time before project start. Eichbaumsee in Hamburg is a lake of similar size. Fig. 4 shows the development of a stratification there in July 2011. The lake is strongly stratified and after the first strong algal bloom, the oxygen level below 7m is already zero. This diagram also shows that it is not necessary to have three measuring stations installed. Data are the same at the three stations (west, middle, east). This proves the wind mixing in the lake and the density convection, which equalizes also the nutrient distribution in the same depth.

Limnological data were collected by Liebezeit, G. (2013) - MarChemConsult.

4

Fig. 5 Temperature and oxygen content development in Hamburgs Eichbaumsee ( July 15th, 2011) as a function of lake depth

destratification system is usually designed for long time operation. Infinite time mixes a well-defined closed system completely.

The slide is taken from the city of Hamburg’s internet homepage (prepared by Spieker, J. (2014)). A similar situation is expected for Lake Bant without free jets running in the same weather situation. In longer strong wind periods the epilimnion may be deeper. Destratification is discussed below.

Here, the jets were not designed to mix the lake in a short time as required e.g. in waste water treatment. Primary flow through the propellers corresponds to a theoretical turnover of the lake total volume in 12 weeks. But jet entrainment, waves, and wind driven currents (also seiches) would help the lake to mix in a much shorter period.

1.5. The objectives The main goal was to solve the cyanobacteria problems. Destratification helps green algae to be mixed and prevented from sedimentation. Cyanobacteria generally prefer stagnant water. Destratification also lowers the epilimnion and helps to avoid fish kills. Oxygen is distributed in the water column. This increases the habitat for the fauna at the cost of algae reproduction - in addition phosphorus is removed from the water column. When more sediment is oxygenized, benthic fauna may develop and bacteria for algae destruction will become available at the bottom. Phosphorus will be permanently bound to the sediments. Fish eggs may survive at the bottom of the lake – bringing fish selfreproduction.

2.

Divers noticed a water movement at the bottom in the influence zone at a speed of more than 5 cm/s. There were small potholes in the direct influence zone of the jets at the lake bottom (10m depth). Sediments were carried away. This influence was only local and only for a short time. The propellers were removed from the lake at the end of 2012 providing an “off – on – test” for the destratification project. This showed the effectiveness of the applied minimal invasive method.

Results and discussion

2.1. Was the lake destratified? Modeling of a free jet in a realistic stratified environment is a difficult task and requires expensive software and longtime modeling experience. There are a number of attempts reported in the literature. These usually lack a longer running time of the mixers. But a

Fig. 6 Water temperature in the summers of 2012 and 2013 (slide of Manzenrieder, H. (2014))

5

In 2013, with no jets running the thermocline was reported at 6m. This is the quite normal situation at Lake Bant - whereas in 2012 even the deep holes were partially mixed! Practically speaking, the lake had no thermocline and no hypolimnion.

Manzenrieder also measures the temperatures below 10m depth. These temperatures are only of minor importance for the ecological evaluation. Liebezeit, G. (2013) did not measure these.

2.2. A short summary of main results Fig. 7 shows the monitored temperatures in 2012 and 2013 – these continuous measurements were not available during the Jade University project years because of cost.

The results are reported in two publications, which are available online. Lücking, P. et al. (2013) gave a detailed closing report of the “Free Jet Project 2007 – 2012”. It covers mainly the design calculations, the construction, operation, and cost (about half of the money funded was spent for the ecological measurements) - but also the different views of engineers at the outcome of the project. Liebezeit, G. (2013) collected the ecological data and reported the results. Both reports are in German. Here we present only the main results with diagrams taken from Liebezeit, G. (2013).

Fig. 7 Temperatures and temperature differences (difference surface - 8.8m depth) in 2012 and 2013 – (diagrams Manzenrieder, H. (2014) - modified)) The data of 2012 show that the difference (usually named stratification index) is mainly given by surface heating in a warmer period without wind mixing. In a week’s time (see especially in the second half of May 2012) the difference is again back to zero. The 2013 data clearly show the strong stratification from June to September – quite normal for Lake Bant without jets running.

Temperature data are given in fig. 8. These measurements show that during the whole project run time the lake was destratified. The lake had only small temperature differences all the way to the depth of 9m.

Fig. 8 Temperature distribution from surface to 9m depth – vertical axis is lake depth, temperatures as indicated by colors in the right bar

6

In 2008, only one jet was in operation. The second one was scheduled for the next year. This means that only one jet at a power consumption of 1.5kW can do the destratification.

well above zero. This means that there was a special effect in respect of binding phosphorus – and no resolution of phosphorus.

In the following diagrams – copied from the ecological summary - the ecological outcomes are demonstrated.

Fig. 11 Development of phytoplankton in Lake Bant - number of cells in 2008 - 2012

Fig. 9 Developement of oxygen saturation at the two surface stations from April 2008 to December 2012

In 2008 Chlorophyceae were dominant. From 2009 on cyanobacteria numbers increased. From 2010 on, phytoplancton numbers were conciderably reduced. In 2011 and 2012, the number of cyanobacteria was reduced by a factor of 10.

In 2008 (the first year of jet operation), algal abundance was high with oxygen levels well above 120% saturation for longer periods. There were still strong algal blooms, but the higher oxygen level at the lake bottom reduced the odor problems to a relative short time, even in the zones where wind driven accumulation of algal mass occurred.

Fig. 12 Change in numbers of cyano phytoplankton species in the project years

Fig. 10 Oxygen level during the project years (vertical-axis is depth in m)

In the years before the project started, there were only Nodularia und Anabaena spp. in the lake. In 2009, Microcystis sp.was found. From 2010 on, also other cyano species were existing – especially Oscillatoria species.

Fig. 10 proves that the oxygen level at lake bottom in the five project years was always

7

The salinity profiles in fig. 13 also show that the lake is homogeneous with respect to density.

1.5kW and 2.5kW each presented a minimalinvasive approach. The energy added from wind stresses is more than two orders of magnitude higher. But even high surface winds – also with longer duration – will not create a surface velocity higher than 20cm/s. This low velocity can not bring down lowdensity waters. The backflow will stop the surface flow. For more details, see the literature and especially the Michele, J. and Michele,V. (2002) publication.

Fig. 13 Salinity as a function of depth in July and August 2012

Results shown in the figures above clearly demonstrate that the obtained effects are striking. The ecological report (Liebezeit, G. (2013)) did not cover sediment evaluation, fauna changes and bacteria contributions for decomposing of algal mass at the lake bottom. These were omitted because of lack of funding. Some empirical evidence could be obtained, however: local fishermen are the group of lake users which is most satisfied with the years of lake oxygenation by free jet operation.

Fig. 14 Stratification index (eastern part of the lake) – surface temperature minus temperature at 9m depth The stratification index (temperature difference: surface – bottom) plotted in fig. 14 gives no information about the ecological conditions at the lake bottom. This diagram only tells that the air temperatures are changing in level and duration. This difference is determined by intensive solar radiation – usually only of short duration. Bottom conditions are normally not changed. A warmer top layer may develop. The installed jets were not designed to immediately avoid or cure these situations. From an energy point of view, the installations of the mixers with an energy input of only

2.3. Another look at phosphorus in Lake Banter In 2012, the city of Wilhelmshaven’s administration initiated another evaluation of the ecosystem, because the objectives changed to open the lake to the sea. A reason was also the fact that not all cyanobacteria disappeared completely during the free-jet run time – even though improvements were realized. Since the removal of the destratification systems in autumn 2012, time has gone by and the lake was monitored in 2013 by Manzenrieder. Also in 2013, 2014 and 2015 only minor cyanobacteria problems became evident.

8

When the authors of this paper reconsidered the phosphor situation and the comments in the ecological summary report, an interesting fact became evident. We learned that only fishermen are removing phosphorus from a stagnant lake. To check the amount we realized that taking out a 12kg pike one would remove about 36g of phosphorus. This can create already a good mass of algae. When re-inspecting the phosphorus reductions (RDP – reactive dissolved phosphorus) observed in the project years as shown in fig. 16, we realized that this meant a reduction by a factor 4.7 (from 600mg/m3 to 128mg/m3).

Fig. 15 RDP-concentration in the water column per square meter (gray month of October - Dezember)

Fig. 16 Trophic state of Lake Bant according to LAWA (1999) - criterion of total phosphorus Probability of trophic state as a function of total phosphrus concentration (Liebezeit, G. (2013)) The value of 76mg/m3 P was inserted in fig. 16 based on Manzenrieder´s measurements in 2013. The values taken from the graph are: 2010/11 600mg/m3 P 2011/12 300mg/m3 P 2012/13 128mg/m3 P Manzenrieder: End of 2013 76mg/m3 P These data are replotted in a linear diagram – fig. 17.

Liebezeit discussed the importance of sedimentation and the reduction of phosphorus - but when looking at the concentration in mg/m3 , the really amazing fact was not realized. Also the logarithmic plot shown in fig. 16 is not appropriate to appreciate the main result of our project. Fig. 17 Concentration reduction of Total Dissolved Phosphorus (TDP) in the years 2011 - 2013

9

If the amount of phosphorus reduction is calculated, this means for the project years 2010 - 2012 that the water column had lost 5.4t of phosphorus. To visualize the order of magnitude of this quantity, one can calculate the cost of a chemical reduction method for binding the phosphorus to the sediments, e.g. by aluminum sulfate, Lanthanum, et ct. With figures for the calculation which may be found in the literature, more than one million Euros would have had to be spent for a similar result. In Hamburgs Eichbaumsee, money in this height was spent. The chemical precipitation project was no succes and was therefore stopped. The interesting fact is that a further reduction was achieved to 76mg/m3 P in 2013, after the free jets had actually been removed. This was another 590kg of total phosphorus reduction, rendering the free-jet technique sustainable beyond its immediate effects. With these facts in mind, we checked the literature for information. Finally, we found research by a number of authors who concerned themselves with sediment and bentic fauna research. Communication with B.E. Beisner and A. Stigebrandt led to their groups publications, where Beisner published research on “Effects of thermocline deepening on lake plankton communities”, Gauthier, J., et al. (2014). B.G. Gustavsson and A. Stigebrandt (2007), and A. Stigebrandt and B.G. Gustavsson (2007, 2013, 2014) published results on oxygenation of the Baltic Sea. In chapter 4 of A. Stigebrandt and L. Rahm (2013), numbers are given: “

… Mechanical oxygenation of the deep water It was described above that the sediments in the Baltic Sea immediately can bind 3 tonnes

of phosphorus per km2 when oxygenated. If the bottoms are kept oxygenated, it is most likely that they can bind another 0.05-0.1 tonnes of phosphorus per km² and year (longterm sink). If oxygenated bottoms again are subdued to hypoxia, the reversed scenario is expected: the binding of phosphorus to the sediments will stop and the bottoms will release 3 tonnes of phosphorus per km². … ” Lake Banter has an area a little larger than one km2. The reduction of phosphorus was in the same order of magnitude. Liebezeit presented some reasons for the reduction of phosphorus in his closing report, but he did not mention the importance of increased bentic fauna and bacteria and the increase in fish population as reasons for a phosphorus reduction. However, the main reason should be the high oxygen level at the sediment boundary. During the project years, there was sufficient oxygen available. Also, flow conditions at the ground resulted in a small boundary layer – the path length for oxygen diffusion was small. Therefore, because in our area there is enough iron in the lake and the sediments, phosphorus can be permanently bound to the sediments - which is a natural process. In the literature, sediment cores show the retention. The literature reports re-solution of phosphorus if there is no oxygen and the temperaures are high. Higher temperatures mean only faster reactions. If there is enough oxygen, also the reaction towards binding of phosphorus is faster. Jeppesen, E. et al. (2011) stress the importance of also monitoring zooplankton as indicators in lakes in a scientific-based ecological quality assessment. Hölker,F. et al. (2015) discuss the effects of tube-dwelling

10

invertebrates on the oxygen level in sediments. These “tiny ecosystem engineers have large effects in lake ecosystems”.

3.

Conclusions

Before we installed the jets in Lake Bant, we tested the method in a small nearby lake – “Accumer See”. The small system was running for three years only. No algal blooms were observerved ever since to this day.

3.1. Destratification

3.3. Oxygen in water

With only one inclined free jet system, a large lake of one square kilometer and a volume of 107m3 can be destratified. Energy-wise this is a minimal-invasive approach, but results are remarkable. Oxygen was available year- round at the lake bottom, the number of species increased. Also cyanobacteria levels were lowered and other species appeared. Odor problems were significantly reduced, fish population increased. Fishermen did not enjoy fishing here before 2008 but appreciate the present situation. Temperatures were uniform and at surface temperature year-round. The oxygen at the lake bottom makes bentic fauna possible. Bacteria for decomposition of settling algal masses will become available. Nutrients will be recirculated in very short time.

Destratification can oxygenize water. If one adds oxygen to a lake or river, no harm is reported in the literature. Therefore, oxygenation without stirring up the sediments may always help a lake.

Inclined jets should be started before a stratification develops.

3.2. Phosphorus removal The main result is the observed reduction of phosphorus. 5.4t of this algal-growth determining nutrients were removed from the water column over the observed period. If the lake is kept oxygen rich, it is expected that more phosphorus may be bound permanently to the sediment. Destratification is only considered a mitigation technique in the literature. Here, we have presented clear hints that the destratification technique is also a sustainable solution.

Stigebrandt and his coworkers are shooting high. But results are showing that even extremely large water systems as the open Baltic Sea, Lake Erie and the Baltic Sea fjords may be treated to reduce man-made nutrient introductions and overcome worldwide cyanobacteria problems.

4.

Acknowledgements

This research was only possible because the politics required finding a solution for the HAB problem. Jade University of Applied Sciences developed a five-year program. We are grateful for the funds made available for installation, operating, and analyzing the changes by the city of Wilhelmshaven. We are also grateful for the help we got from our coworkers S. Reiche, J. Scheltwort and R. Liesegang. Scheltwort and Liesegang passed their research divers exam during the project, to study the jet in reality. Many groups in the Wilhelmshaven community supported us. Special thanks are due to Technisches Hilfswerk Wilhelmshaven. Also the Wilhelmshaven fishermen reported their findings to the authors.

11

The objectives of the city shifted to open the lake to communicate with the inner harbor – giving sailing ships the opportunity to reach the sea.

5.

The lake will become saltier. New research has to be done. Recommendations are very welcome.

References

Gauthier, J., Prairie, Y. T. and Beisner, B. E. (2014): Thermocline deepening and mixing alter zooplankton phenology, biomass and body size in a whole-lake experiment. Freshwater Biology, 59: 998–1011. doi: 10.1111/fwb.12322 Gustafsson, B. G. and A. Stigebrandt (2007): Dynamics of nutrients and oxygen/hydrogen sulfide in the Baltic Sea deep water JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, G02023, doi:10.1029/2006JG000304, 2007 Hölker, F. et al. (2015) Tube-dwelling invertebrates: tiny ecosystem engineers have large effects in lake ecosystems. Ecological Monographs 85:333–351. http://dx.doi.org/10.1890/14-1160.1 Hupfer, M. et al. (2013): Vorbereitung und Auswahl von Maßnahmen zur Seentherapie Korrespondenz Wasserwirtschaft · 2013 (6) · Nr. 12 Jade University of applied sciences: Project reports - homepage „Projekt Freistrahlanlagen im Banter See Wilhelmshaven” http://evu.jade-hs.de/content/projekt-freistrahlanlagen-im-banter-see-wilhelmshaven Jeppesen, E. et al. (2011): Zooplankton as indicators in lakes: a scientific-based plea for including zooplankton in the ecological quality assessment of lakes according to the European Water Framework Directive (WFD); Hydrobiologia, DOI 10.1007/s10750-011-0831-0) LAWA (2003) Vorläufige Richtlinie für eine Erstbewertung von Baggerseen nach trophischen Kriterien. 1-27. http://www.lawa.de/documents/Vorl_c57_copy_590.pdf , http://www.lawa.de/Startseite.html Lewandowski, J. et.al. (2013): Gewässerinterne Ökotechnologien zur Verminderung der Trophie von Seen und Talsperren; Korrespondenz Wasserwirtschaft · 2013 (6) · Nr. 12 http://www.polyplan-gmbh.de/cms/downloads/49f7b6ed-aa87-4b2f-b3c74c3792360af7/KW_12.113_Gew%C3%A4sserinterne%20%C3%96kotechnologien.pdf Liebezeit, G. (2013): „Abschlußbericht Ökologische Begleituntersuchungen Banter See 2008 – 2012“, MarChemConsult, Altjührdener Straße 6, 26316 Varel (final report in German). http://evu.jade-hs.de/system/files/Banter%20See%20Abschlu%C3%9Fbericht%20%C3%96kologie.pdf

Lücking, P., R. Liesegang, J. Scheltwort (2013): Freistrahl-Anlagen im Banter See – Abschlussbericht Technik http://evu.jadehs.de/system/files/Abschlussbericht%20Freistrahlanlagen%20Banter%20See%20Technik_2.pdf

12

Manzenrieder, H. (2014): Ingenieurbüro Dr .- Ing. Manzenrieder und Partner (12MB) Available from: Büro des Oberbürgermeisters Wilhelmshaven http://www.wilhelmshaven.de/behoerden_dienstleister/9290.htm http://pvrat.de/ratsinfo/wilhelmshaven/Meeting.html?year=2014&month=4&mid=1722#current Banter See: Ergebnisse der Messprogramme 2 0 1 1 - 2 0 1 4 Bericht Nr . 307 – Textband Banter See: Ergebnisse der Messprogramme 2 0 1 1 - 2 0 1 4 Bericht Nr . 307 – Anlagenband Michele, J. and Michele, V. (2002): The Free Jet as a Means to Improve Water Quality: Destratification and Oxygen Enrichment, Limnologica - Ecology and Management of Inland Waters, Volume 32, Issue 4, December 2002, Pages 329–337 http://www.sciencedirect.com/science/article/pii/S007595110280024X Michele, J. (2009): Destratification: Why has this method not been successful in many cases in the past? Destratifikation: Warum war diese Methode nicht erfolgreich in vielen Fällen in der Vergangenheit? - Deutsche Gesellschaft für Limnologie (DGL), Erweiterte Zusammenfassung der Jahrestagung 2009 (Oldenburg), Hardegsen 2010 https://www.researchgate.net/publication/261364449_farbig_Michele_dgl09 Poster available from the corresponding author (in English) Michele, J.: youtube video (2012): Fighting Blue Green Algae (Cyanobacteria), Flow visualization of a free jet to fight cyanobacteria (blue green algae): http://www.youtube.com/watch?v=Bz2MFCbsjps Nehring, S. (1993): Mortality of dogs associated with a mass development of Nodularia spumigena (Cyanophyceae) in a brackish lake at the German North Sea coast. J Plankton Res 15: 867-872. Spieker, J. (2014): Badegewässerprofil Eichbaumsee – Stand: August 2014 KLS-Gewässerschutz http://www.hamburg.de/contentblob/3348608/data/d-profil-eichbaumsee.pdf Stigebrandt, A. and B. G. Gustafsson (2007): Improvement of Baltic Proper Water Quality Using Large-scale Ecological Engineering, Royal Swedish Academy of Sciences 2007 Ambio Vol. 36, No. 2–3, April 2007, http://www.ambio.kva.se Stigebrandt, A. et al. (2013): A New Phosphorus Paradigm for the Baltic Proper, ©The Author(s) 2013. This article is published with open access at Springerlink.com,www.kva.se/en Stigebrandt, A. and L. Rahm (2013): Baltic Deepwater Oxygenation (BOX), http://www.marsys.se/ (2013) Marine System Analysis Group, http://www.marsys.se/lang/se/about-us/research/baltic-deepwater-oxygenation-box/ Stigebrandt, A. et al. (2014): An Experiment with Forced Oxygenation of the Deepwater of the Anoxic By Fjord, Western Sweden, ©The Author(s) 2014. This article is published with open access at Springerlink.com,www.kva.se/en 123, AMBIO, DOI 10.1007/s13280-014-0524-9

13