West Cork Palaeoecology - Blog
The Environment of West Cork through Time
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These webpages are a series of bimonthly blog posts that will document my work on the Three Lakes Biodiversity project. The original blogsite for West Cork Palaeo, in which I looked at palaeo- (and current) ecology and geography related subjects across West Cork, has now moved to a separate page. Those blogs will continue to be updated when - and if - I have time. They can be accessed here.
The Three Lakes Biodiversity project is a PhD research project that I am undertaking at UCC - University College Cork. I am a postgrad researcher in the School of the Human Environment, in the Department of Geography. My supervisor is Dr Michelle McKeown, and advisor is Dr Aaron Lim.
I have been very generously funded in this project by an Irish Research Council grant for the four year duration of this work.
As part of the dissemination and record of work undertaken, these webpages will document, through a bimonthly blog, the course of the work undertaken and the results that are arrived at.
Having already undertaken some investigation at the Three Lakes site (see here, and here)I started this project off with the prior knowledge that the sediment in the valley basin dates back as far as 16,000 years. With the sediments at the bottom underlying the organic (peat) deposits being a silt, the likelihood is that deposition of sediment on the site dates back to the last glaciation. This is pretty unique for Ireland. Sites further north often underwent a small, minor re-glaciation during the c.1000 year long cold spell known in Ireland as the Nahanagan Stadial, or more widely in Europe as the Younger Dryas. The re-glaciation would have cleared out any organic deposits that had accumulated, and set the sedimentary clock back to zero.
The Nahanagan stadial lasted fromn about 12,500 until 11,700 years ago. Here at three lakes we found a layer of silt that dates to around that time. The deposit being silt rather than organic suggests that the surface of the landscape was exposed to erosion and weathering, with little, if any, plant life. Plants generally act as a protective covering, and roots help to hold the sediment or soil in place. What was probably happening here, making use of prior knowledge and making some assumptions, is that the climate turned cold, and the amount of water increased - either as more heavy precipitation and more often, or as seasonal meltwater, or both. Certainly we can be sure that the ice sheet wiped the face of the land clear of most living things, and this probably happened to some degree with the Nahanagan stadial.
The aim of this project is to understand exactly what happened at Three Lakes. How did the site form, what changes occurred as the climate fluctuated, with a primary focus on the change in biodiversity that occurred. This is of particular interest following the ice age when no living things existed on the landscape of Ireland. As the ice reduced and melted away, exposing the land and creating new river courses, lakes, plains and hills, nature moved in and repopulated the new habitats. Can we understand the sequence, the timing, the successes and failures? That is what we might achieve in this project.
As a brief summary of the project plan, we will be sampling sediment, by taking full depth cores, from both the peatland and the lake. We will look for various fossils within the sediments to help us create a picture of the changing climate. By discovering which species of organisms that are used as proxies for certain factors in the environment, were present at various times in the past, we can see how the climate changed. This will be explained in more detail later. Once we have domne this we will be sampling the sediment for DNA, SEDimentary Ancient DNA - SEDADNA. But the first job was to become familiar with the fossils themselves, learn how to find them in the sediment, and to identify them to species level.
Two fossil organisms are used.
From the peatland, testate amoebae are used as an indicator of water table depth. The fossils we find are the tests, or shells, of these micro-organisms, which remain behind when the organisms die. These tests are generally quite distinctive in shape, although some are very similar to others, so it is not always a simple matter to identify the species. They are quite easily extracted from the sediment by taking a small sample of say 1cc, and filtering first at 350 microns to remove any large particles, and then again at 10 microns, to get rid of the very small particles. This is a lengthy business, but necessary. Testate amoebae tests are of variable size, but within this size range. A micron is one thousandth of a millimetre, or one millionth of a metre, so we are dealing with microscopic material. After filtering out the larger and the smaller particles, a single drop of the sediment is placed, in water, on a slide under a microscope at x200 or x400 magnification. The slide is searched systematically and all tests found are identified, photographed if possible, and a record is kept of all those found. It is quite a simple process, but requires training to recognise the tests.
How we have fared in our search for fossil tests in this project so far is dealt with in a separate blog here posted a while ago. This is something we need to revisit at a later date.
The other organism used is a midge. In fact, the larva of a midge. The head case from the cast off skin of the larva of a midge. These midges are non-biting midges, so named because the adult midges that emerge and fly around do not bite. In fact most of the species do not feed once the adult emerges. The adult form as flying insects purely to mate and lay eggs, though some do seek nectar. The head cases can be from any one of the four stages (called instars) that the larvae grow through. At each change they shed the old skin including the head case. The midges are of the family Chironomidae, otherwise known as Chironomids. Again, the task is to learn how to find these head cases, and how to identify the species. The different assemblages of species have been found to vary largely based upon the summer air temperature of the environment, so changing assemblages over time can suggest changing temperatures. The process in extracting these involves a short warming in an alkali (potassium hydroxide at 10% strength) to break down any clumps of organic matter. This is followed by jet washing (using a wash bottle of deionised water) of the sediment through a 90 micron sieve. The head cases - along with quite a lot of other fossils and bits and pieces - remain, and these need to be sorted through, and the chironomid head cases picked out and placed on microscope slides for later identification. The sorting is done under a stereo microscope to enable easier picking and recognition. Using micro tweezers under a microscope is very difficult - because of the lenses all movements are reversed. But this is not the case with a stereomicroscope.
When the project started I had got to this stage. I was using some five year old sediment cores from Three Lakes, one from the peatland and one from the lakebed at the Middle Lake, for training purposes.
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