Rather like a Farrow and Ball paint chart, however 'Microcystis Green' or 'Anabanea Green' is far more exciting than 'Ball Green' and 'Ground Green'. If this doesn't turn out well I could change careers to be a paint colour consultant, they have 'Arsenic' as an option so I think they could be interested in some more toxic varieties.
The pots contain samples from each of the tanks (sampled this morning) and will be fixed with Lugols so that I can look at the community composition and also the bio-volume of the most dominant taxa in each tank at a later date.
The experiment is a two factorial block design; factorial meaning that each treatment is cross-matched with all other possible treatment combinations giving eight stressor combinations (heated, unheated, heated + nutrients, unheated + nutrients, heated + flushing, unheated + flushing, heated + nutrients + flushing and unheated + nutrients + flushing), block meaning that each of these eight treatments are randomly assigned to one tank in each block (or row) of eight tanks. We have four blocks (see below) which makes four replicates of each stressor combination and 32 tanks in total.
What you see in the first picture are samples from each tank ordered from number 1 - 32; because the treatments are randomly assigned to tanks within each block this means that treatments are not placed together. Shuffling them around to place them in their treatments looks like this:
The colour gives quite a good indication of the relative amount of algae in each tank, green ones have more algae than clear ones. Here are some chla concentrations to convince you of this (for those unacquainted, chlorophyll a is a pigment used in photosynthesis and is used widely as a proxy for biomass, it is measured in micro grams per litre (μg L-1) in this case using an instrument with fluorescence):
Heated + Nutrients (average): 295 μg L-1
Unheated (average): 60 μg L-1
Here comes the time to make some sweeping generalisations from one sampling date based on some colour charts (and some data too): nutrients support higher algal growth (the 16 tanks to the left) than tanks without nutrient enrichment. It is already generally accepted that nutrients are a strong driver for increased algal growth, especially cyanobacteria; this makes sense, as nutrients are essential for growth. It is also thought that warming also increases algal growth again especially cyanobacteria, the reasons for this are far more complex but it can be seen here that heated tanks seem to have more growth than unheated tanks (without nutrients). But do these single treatments and multiple treatments favour cyanobacteria over other algae? Time at the microscope and some data crunching will soon tell.
The real crux of the matter (of the experiment) is to understand how cyanobacteria respond to combinations of these stressors (treatments) because real lakes can be subjected to nutrient enrichment, warming or changes in flushing rates all at the same time. In the past research has focused on the response of cyanobacteria to individual stressors, and so this experiment along with other the other factorial mesocosm experiments, time series analysis and European scale analysis of the MARS project will contribute to our limited knowledge of how aquatic systems will respond to multiple stressors.
I have managed to turn my rather unhealthy obsession with plankton in to my day job. Things don't get much better than this! This blog documents my PhD research and the plankton delights I encounter along the way.