Blog - Patrick Robson – CHERISH Palaeoenvironmental Researcher (Aberystwyth University)

With the weather set so fair at the moment it has been doubly frustrating not to be carrying out fieldwork in Ireland and Wales as we had planned, but the even great science isn’t as important as staying home at the moment. However, the lockdown has enabled me to count pollen grains samples that I processed in January from our Llyn Maelog core (Rhosneigr, Anglesey). Over the last year, we’ve been reconstructing the palaeoenvironmental history of Llyn Maelog and it has been a fantastic sequence to work on with some really exciting changes.

Llyn Maelog, Anglesey with Rhosneigr on the higher ground to the west.  Image courtesy of Toby Driver

Figure 1 Llyn Maelog, Anglesey with Rhosneigr on the higher ground to the west. Image courtesy of Toby Driver

We have obtained 6 radiocarbon dates which show that the sedimentary record is well over 12,000 years old! So far, we have looked at the physical composition of the core, looked at the geochemistry in minute detail with the aid of our x-ray fluorescence scanner, and analysed the diatom record (microscopic algae that are present in all aquatic environments). Like plants in your garden, different diatoms species have varying tolerance for light, water depth, temperature salinity and nutrient availability and therefore they can reflect physical and chemical changes in the lake.

The evidence reveals the lake evolved through the early Holocene at least in part to a waterlogged wetland habitat. Then around 7,000 years ago the sea invaded the woodland, immediately killing off the vegetation and forming a saline lagoon which may have persisted for 500 to 1,000 years. Eventually, the sea became separated from the lake and it returned to a freshwater environment which persists to the present day.

I am investigating the pollen record trapped in the lake to better understand the vegetation changes around the lake particularly the response to the inundation of the site by the sea. Pollen counting is a slow process – I need to identify (not always an easy task!) and count at least 300 individual grains from each sample. Depending on the abundance and preservation of the sample I aim for at least 2 slides a day, with over 60 slides from the sequence that’s about a calendar month staring down my microscope!

Counting pollen at home - essential items include countless cups of coffee

Figure 2 Counting pollen at home - essential items include countless cups of coffee

Pollen grains range in size from 10 to 130µm, so we use a binocular microscope to see the sample we have mixed with dyed glycerine jelly and mounted onto a glass slide. Most of the species at Llyn Maelog are around 30µm in diameter with ash, oak, alder, birch, hazel, and various grass species the most common. We use reference books and image databases to help identify the different species of pollen, which is not always easy as although it is remarkable resistant to decay, it can be degraded by bacteria, crumpled, obscured behind background debris or just lying awkwardly making identification difficult. 

Selection of Llyn Maelog pollen grains  Scotts Pine, Hazel, Birch, Red Campion, Dandelion, Alder

Figure 3 Selection of Llyn Maelog pollen grains (top-left to right) Scotts Pine, Hazel, Birch, (bottom row) Red Campion, Dandelion, Alder

It’s really exciting progressing through the sequence seeing the proportions of different pollen fluctuating, but it is not until all the samples are counted and the data processed, that the full scale of the changes can be seen – hopefully, this will be early May for Llyn Maelog.