This is back dated, it actually happened at the start of August but I have been super busy with other field work, courses and writing literature reviews.
The aim of this mesocosm experiment is to explore the response of lake ecosystems to multiple climate change and nutrient stressors. One of the effects of climate warming is a change in the water cycle, it is predicted that northern European countries will have more rainfall annually with an increase in rainfall during the winter, overall summers will be drier but with an increase in extreme rainfall events lasting 1-5 days during the later summer (July to September) whilst southern European countries will experience a reduction in annual rainfall (Christensen and Christensen 2003). Modelled changes in precipitation patterns will result in 10-30% decreases in run-off in southern European countries whereas northern countries will experience a 10-30% increase in run-off (Milly et al 2010). So as well as a 'warming' treatment we also have an 'extreme rainfall event' treatment. Water (1500 litres) is pumped into each tank to mimic the increase in in-flow that will happen as a result of a high intensity rainfall event. The tanks hold 3000 litres so this is similar to displacing half of the water in the tanks, although this is not direct displacement as just like in a lake the water will mix with the inflowing water and so the water lost from the tank will be a mix of the water from the mesocosms and the water pumped in. This event happens once every 12 weeks, 4 events in total over the duration of the experiment.
For each extreme rainfall event we need 24,000 litres of water - at the top of the site we have two large tanks which we fill up with filtered water from a nearby reservoir (this does not contain algae but does contain nutrients which we adjust for at the next nutrient addition). The tank is open to the elements so after 12 weeks of being exposed to rainfall, leaves and what not the tanks need to be cleaned out until they are spotless. This involves lots of buckets, a step ladder and a pair of waterproof overalls.
Now the taps get switched on, it takes 24 hours to fill both up so we leave them running overnight ready for the event the next day.
We place one pump in each large tank and attach a long hose pipe that will reach to all of our smaller experimental tanks. Each pump has a different flow rate so first we time how long it takes to fill up 50 litres in marked buckets and multiply this to work out the time needed to pump 1500 litres into each tank for the different pumps. Then we place the hose end in a bucket so that the force of the water hits the bottom of the bucket instead of churning up the sediment and switch on the pumps. Easy peasy, no stress involved at all! It's like a rocket launch for each tank - five, four, three, two, one, GO - but probably less exciting. The end of the video below shows a short clip of a tank being treated with this treatment, to get an idea of the magnitude of the event the duration of the treatment is 15 minutes for one pump and 21 minutes for the other pump.
Carvalho, L., C. Miller, et al. (2012). "Water quality of Loch Leven: responses to enrichment, restoration and climate change." Hydrobiologia 681(1): 35-47.
Christensen, J. H. and O. B. Christensen (2003). "Climate modelling: Severe summertime flooding in Europe." Nature 421(6925): 805-806.
Milly, P. C. D., K. A. Dunne, et al. (2005). "Global pattern of trends in streamflow and water availability in a changing climate." Nature 438(7066): 347-350.
Reynolds, C. S., S. C. Maberly, et al. (2012). "Forty years of monitoring water quality in Grasmere (English Lake District): separating the effects of enrichment by treated sewage and hydraulic flushing on phytoplankton ecology." Freshwater Biology 57(2): 384-399.