Effects of light pollution (and brownification) on lake ecosystem structure and function in response to altered zooplankton diel vertical migration: a large-scale enclosure experiment. Project lead: Mark Gessner, Franz Hölker, 01/08-31/10/2018.
Timing of the experiment: The large-scale mesocosm experiment will be about three months starting at the beginning of August and run until the end of October. There will be a hot phase of 4-6 weeks for intensive experiment preparation before the actual start of the experiment (in addition to more long-term preparation).
Users for TA: We plan to observe whole-systems responses; everyone with expertise in plankton communities or pelagic processes is welcome. We specifically invite experts in fish-labelling, sensor deployments on fish, researchers and trainees to work with the FlowCam, experts on mixotrophs, blue-greens and theirs toxins, cell stress (e.g. oxidative stress), near remote sensing experts, physicists interested in artificial light sources, trainees for preparations. A total of at least 240 person days will be allocated to external users through Transnational Access provided under AQUACOSM for 2018. It is anticipated that AQUACOSM will support stays of at least 4 persons for 60 days or other constellations.
Introduction to the project: Light is key in structuring ecosystems and biological communities. During the last decades globally averaged artificial light emissions increased by 3 to 6 percent per year, occasionally even up to 20 percent. The “loss of the night” affects all industrialised regions in the world and is thus an additional element of global environmental change caused by humans.
Also lakes can be disturbed by light pollution – the riparian areas through direct lighting, the open water by a diffusely illuminated night sky. This phenomenon of skyglow is mostly driven by clouds back-scattering artificial lighting above, for example, towns and greenhouses. Although the intensity of skyglow compared to direct light is low, it can extend over very large areas and therefore also affect lakes and aquatic organisms. The influence of the loss of the night for lake ecosystems, their functioning and biodiversity are largely unknown.
Potential effects of skyglow may be modulated by another element of global environmental change: the increase of coloured dissolved organic matter in freshwaters. Such “brownification” leads to changes in water column light climate and general darkening during day and night, besides potential effects via increased organic energy availability.
Description of the experiment: We want to study the ecological consequences of skyglow (i.e. diffuse artificial lighting at night) and the underlying mechanisms. The experiment will be performed in the LakeLab, where skyglow is simulated in 6 enclosures using a specially developed light system. We expect that the new lighting conditions will influence the physiology and behaviour of key species. Our special focus is on Daphnia and other zooplankton. They usually show a diel vertical migration pattern: While during the day they hide in the darkness of the deep water to avoid predation by planktivorous fish, they migrate up to the surface water in order to feed on algae at night. However, an altered migratory behaviour would also change the interactions between organisms in the food web and thus the material flows in the lake. The two-level skyglow treatment (control vs. skyglow) will be crossed with the addition of highly coloured humic substances to study interactions of skyglow with a changed underwater light environment. The resulting experimental design is 2-factorial with two levels per factor and a sampling size of 6 enclosures for each factorial combination. Even though the humic treatment will be rather low, this design also offers the possibility to study the light effects of brownification in isolation.
Our results promise both fundamental new insights into the effects of nocturnal lighting on lakes modulated by brownification and will provide important information for future water management.
Leibniz-Institute for Freshwater Ecology and Inland Fisheries (IGB)
Outdoor – pelagic/benthic – freshwater
24 large lake mesocosms, each 9 m diameter, 20 m depth, reaching into the sediment, water volume 1,270 m3 per mesocosm, one additional central unit 30 m diameter, volume 14,000 m3
e.g. thermocline depth, stratification, extreme wheather events, browning, nutrients
Responses of the planktonic food web, biodiversity patterns, and biogeochemical processes and fluxes under climate change scenarios
Lake Stechlin, Stechlin, Germany, 80 km north of Berlin
The IGB LakeLab in north-eastern Germany is located in Lake Stechlin, a deep clear-water lake representing the extensive southern Baltic lake district. The facility consists of 24 cylindrical mesocosms (Fig. 6.1.1) enclosing water volumes of 1270 m3 (9 m diameter, 20 m depth). A large central mesocosm (30 m diameter, 14,000 m3 volume) serves as water reservoir and can also be used for experimentation (e.g. deployment of mobile mesocosms as described in WP9). Flexible curtains attached to sturdy aluminium floats extending into the sediment enable experiments on benthic-pelagic coupling – a unique feature of mesocosms in deep waters. Continuous operation during winter is possible under ice. Water is renewed by high-throughput impeller pumps (100 m3/h) that minimize disturbance of plankton. The same pumps have proved excellent to manipulate mixing regimes and stratification patterns. Furthermore, perforated stainless steel rings can be connected to a compressor to aerate the mesocosms at any given depth. Other gases (e.g. N2, CO2, CH4) and solutes could be injected as well, whereas application of xenobiotics or introduction of foreign species is precluded. Thus, the physical structure and chemical composition of the water can be conveniently manipulated in multiple ways, despite the large size and large number of replicate experimental units. This combination of large number and size of mesocosms is unmatched worldwide, enabling multiple experimental designs involving more than a single factor and yet ensuring adequate replication. This opens entirely new research perspectives, ranging from hydrological, chemical and biological replicated experiments to testing of large instruments and calibration opportunities for remote sensing.
Fig. 6.1.1. Aerial view (left) and schematic (right) of the LakeLab in Lake Stechlin. Photo: P. Casper
The unique value of the IGB LakeLab is further enhanced by vertical profilers recording water-quality parameters in real time (30 min intervals) along high-resolution depth profiles (0.5 m steps) are another outstanding feature of the LakeLab (Fig. 6.1.2). All 24 mesocosms are equipped with automated sensors to record photosynthetically active radiation (PAR), pressure (for accurate depth positioning), temperature, pH, conductivity, O2 concentration and fluorescence-derived biomass estimates of cyanobacteria, diatoms, green algae, cryptophytes and total phytoplankton (bbe fluoroprobes). Four identical additional profilers are deployed in the open lake. The profilers are controlled by industrial computers that also collect and transmit data to a central data base server for routine quality checks and storage. Risk of data loss is minimized by multiple security levels.
Fig. 6.1.2. Bridge over an enclosure for easy access (left), and profiler carrying sensors (right). Photos: IGB.
Key to the operation of the LakeLab is its proximity to well-equipped laboratories of IGB Stechlin, which are located directly on the lake shore (Fig. 6.1.1 left). Boats of various sizes ensure quick access (<5 min) to the laboratories, facilitating prompt analyses of delicate live samples. Laboratories include a radioisotope lab (14C, 3H, 33P, 35S), molecular S1 labs and 3 walk-in climate rooms in addition to standard labs. Analytical instruments include 3 autoanalysers for nutrients (FIAstar), an ion chromatograph, UV-Vis spectrophotometers, 2 fluorimeters, a TOC/TON analyser, a carbon analyser, a CaCO3 analyser, 2 GCs, 3 HPLCs, an ultracentrifuge, 2 flow cytometres, a Color FlowCAM, 2 scanning electron microscopes (SEM), bright-field and epifluorescence microscopes, some of them equipped with image analysis systems, as well as other standard laboratory equipment (autoclave, high-capacity freeze dryer, ovens, clean benches, centrifuges, etc.) and field gear (mutiprobes, plankton nets, sedimentation traps, sediment corers, etc.). Empty lab space can be provided to set up equipment and instrumentation according to specific user needs. A long-term monitoring programme on Lake Stechlin provides background data on water chemistry, phyto- and zooplankton, fish as well as primary and bacterial secondary production. Meteorological and other environmental data are recorded by the German Environment Agency on site.
Each of the 24 mesocosms is equipped with:
- an automatic profiler recordimg PAR, temperature, pH, oxygen, redox potential, conductivity, turbidity, and pigments to distinguish four major algal groups
- an industrial computer recording and transmitting the collected data to servers at IGB
- sediment traps
- a height-adjustable water recirculation system with a perforated ring, rising conduit and pump
A total of at least 720 person days will be allocated to external users through Transnational Access provided under AQUACOSM for 3 years. It is anticipated that AQUACOSM will support stays of at least 4 persons for 60 days in years 2-4. The very large units of the facility means that experiments tend to run longer than in other mesocosm facilities. Consequently, a duration >30 days is typically expected to complete independent projects. Since logistic preparation of experiments at the LakeLab takes at least 6 months, TAs are anticipate to focus initially on integrating external users in activities already in the planning stage, specifically in experiments on brownification and light pollution planned in 2017 and 2018 as part of 2 funded projects. However, in addition to encouraging proposals for large experiments as soon as logistically possible, individuals and smaller groups are invited to apply for AQUACOSM TA support to cooperate at any time within more comprehensive projects, both planned and unplanned at present, resulting in joint publications of results and management recommendations. To maximise synergies, AQUACOSM activities will also be coordinated with long-term monitoring and other projects conducted in the LakeLab and Lake Stechlin.
Services currently offered by the infrastructure: Users will have access to the laboratories and instrumentation at the LakeLab and IGB laboratories. However, to maximize benefit of on-site support and output, scientific cooperation with scientists at IGB Stechlin is strongly encouraged and will be supported by permanent technical IGB staff. Users are also encouraged to engage in scientific activities beyond AQUACOSM (participation in seminar series, journal club, group meetings). Experience from mesocosm experiments at other locations has shown that extended collaborative experiments offer excellent opportunities for networking and creative exchange that produces innovative ideas on scientific questions and industrial and environmental applications. Therefore, users are invited to get involved in social activities organized by both local staff and visitors. The relatively small size and remoteness of IGB Stechlin ensures ample opportunities for such informal exchange. This will be further facilitated by the offered accommodation at IGB’s fully equipped (kitchen, laundry facilities, garden) guesthouse (23 beds) in the nearby village at 20 min walking distance.
Support offered under AQUACOSM: Users will have access to the laboratories and instrumentation at the LakeLab and IGB laboratories. However, to maximize benefit of on-site support and output, scientific cooperation with scientists at IGB Stechlin is strongly encouraged and will be supported by permanent technical IGB staff. Users are also encouraged to engage in scientific activities beyond AQUACOSM (participation in seminar series, journal club, group meetings). Experience from mesocosm experiments at other locations has shown that extended collaborative experiments offer excellent opportunities for networking and creative exchange that produces innovative ideas on scientific questions and industrial and environmental applications. Therefore, users are invited to get involved in social activities organized by both local staff and visitors. The relatively small size and remoteness of IGB Stechlin ensures ample opportunities for such informal exchange. This will be further facilitated by the offered accommodation at IGB’s fully equipped (kitchen, laundry facilities, garden) guesthouse (23 beds) in the nearby village at 20 min walking distance.
IGB guesthouse, 20 beds, kitchen; local B&B