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A Floral Survey, Amoebae,and Bacteria

With palaeoecology being a study of past ecology, we have to decide at what point the past becomes the present. Or do we? In the case of the study at Three Lakes, I decided that the present is just the most recent part of the long timeline, and since I am looking at the fossil pollen and spores in the sediment, and using these to determine the vegetation at the many different times over the past 16,000 years, the vegetation at Three Lakes now is just the latest in that line.

So we undertook a floral survey (Fig 1).

Fig 1 - Surveying the lake margin flora

The first one was done in June, on midsummer’s day in fact. But because different plants flower, seed, live, and die at different times throughout the year, we will probably do a similar survey every month of the year. Added to which there are so many habitat types it just isn’t possible to cover the area without an army of people. A small army. More about the floral survey will be forthcoming later.

I am also taking monthly diatom samples for the same reason - diatom populations rise and fall at different times of the year, and to compare my samples of fossils, that represent what got left behind and preserved, I need a full representative sample from today.

I was surprised, when I paddled in my canoe around to the south eastern wing of the lake, to find blobs of black slime floating like little black jelly icebergs, hanging down in the water. There was an accompanying petrol like sheen and a vile sulphurous smell (Fig 2). The water was warm to the touch following a very warm spring.

Fig 2 - Nasty stinky black effluent

Under the microscope this black slime was not, as I had hoped, a diatom bloom, and all I found were a large number of large amoebae, between 50 and 800 microns across, which it seems are of the genus Pelomyxa (Fig 3) Also see here. Was it these amoebae causing some sort of anaerobic respiration? After contacting two experts in their fields, Wim van Egmond and Ferry Siemensma, both in Holland it seems that this phenomenon is not uncommon in freshwater lakes and ditches of the Netherlands. It was suggested by Ferry that a bloom of cyanobacteria (blue-green algae - but actually bacteria) on the bottom of the lake, amongst the low oxygen environment that Pelomyxa prefers, caused a generation of ?sulphurous? gas that caused rafts of sediment to float to the top; carrying poor oldPelomyxa with it.

Fig 3 - A selection of Pelomyxa amoebae

But after a couple of days, when I looked at the sample again, it was infused by hundreds if not thousands of spirochaete bacteria, all wiggling like little corkscrews (Fig 3). At least, that is what I think they are. But they may be Spirilla bacteria, which are ‘helically curved rod-shaped cells’ (Brock Biology of Microorganisms 16th edition). I do not have the time to go down the bacteria route.

Fig 4 - ?Spirochaete bacteria? Scale bar is 10 microns

Just to top it all off, it was just that part of the lake where I took a sample the previous month (May) of some shoreline sediment. Amongst the diatom community I found some strangely shaped diatoms that defied identification. Experts at the diatom group forum suggested they were teratological forms, that is, diatoms that have grown in deformed shapes (Fig 4). They are most likely of the genus Eunotia. Interestingly, what makes them deformed is likely some condition within the environment that results in aberrant growth. Might this be the action of blue-green algae proliferating? Or was the bloom caused by the same condition that caused Eunotia to deform?

Fig 5 - Various Teratological forms of Eunotia

We are inclined to immediately think of human causes for this 'pollution', but it might equally well be natural causes. There is only one inlet stream to the lake, running through a small number of pasture fields, as well as an inflowing connection from the western lake. These lakes are high up in the watershed and surrounded by either forestry with minimal disturbance, or non-intensively managed pasture. Natural events can have similar effects to human pollution, but it generally fits in with the ecology of the area. An example is just these anoxic and sulphic conditions that occur when large amounts of organic matter accumulate in a wet environment. In extreme, this is known as a euxinic environment, taking the name from the Black Sea, where such an environment occurs at depth, resulting in black mud rich in iron and sulphur. Temperature plays a big part as well, and interestingly when I visited 8 days later, after the weather had turned cool and it had rained, the black slimy rafts had all gone.

A lifetime of study on the occurrence of iron sulphide, also known, when crystalline, as pyrites, has been the work of David Rickard and his book “Pyrite: A Natural History of Fool's Gold” is full of surprises. Not least the fact that pyrites occurs almost everywhere where anoxic and sulphic respiration occurs, resulting in it being one of the most widely occurring minerals, albeit in microscopically small grains, on the planet - and often created by organic action.

Finally, a very in-depth study which yielded fascinating results was undertaken on Lake Vechten in Holland. The resulting paper detailed the variation in 10 different environmental parameters at different depths throughout a full year; temperature, pH, dissolved oxygen, dissolved organic carbon, sulphides, nitrates, sulphates, phosphates, ammonium, and chlorophyll A. The lack of inflow into Lake Vechten is similar to the Middle Lake which has only a small stream flowing in, but Vechten is up to 10m depth, whereas Middle Lake appears to be a constant 2.5 to 3m depth, so possibly the waters of Middle Lake do not get stratified to the same degree. There is room here for some fascinating studies.

See Diao M, Sinnige R, Kalbitz K, Huisman J and Muyzer G (2017) Succession of Bacterial Communities in a Seasonally Stratified Lake with an Anoxic and Sulfidic Hypolimnion. Frontiers in Microbiology. 8:2511. doi: 10.3389/fmicb.2017.02511