July 28, 2021, by Lexi Earl

Diversity of duckweed sites in Elgin, Scotland: Part four in a botanical tale of exploring natural variation around us

This post is written by Kellie Smith. 

After a successful duckweed hunt in the South East and West of England, featured in my previous blog posts, we then made our way north. We were headed to Scotland to see whether duckweed coverage was equally dense as in southern England and if different species compositions prevailed. We picked the North/South to give us the greatest diversity in latitude and prevailing UK climates.

For the last part of the spring collection trip we find ourselves in Elgin (near Inverness) on the north coast of Scotland, the northernmost point of our trip. Duckweeds had been reported there in the previous two years making it a hotspot! Our hypothesis asked: are overwintering duckweeds more frequent here? Are they more able to establish early in the season after surviving winter on the bottom of the water as seeds? Interestingly, invasive lesser duckweed, Lemna minuta, which was densely reported in the south, has only once been reported in the north of Scotland in databases. The invasive duckweed is suggested to be invading the UK in migration waves spreading south to north. Therefore in Elgin, we sought to check distributions, and establish if the invasive species was interfering with the balance of habitat diversity.

Coincidently it was also Invasive Species Week between 24-30^th May, which aims to increase awareness of invasive species and the problems caused by them. During the hunt, the public and landowners tended to be very helpful and engaging in the duckweed research. Arable and pastoral farming sites were both of interest due to their associated nutritional profiles, as they are suspected to contain high volumes of leached nitrates, phosphates and potassium. An alpaca farm in Moray is situated at the meeting point between Mosstowie canal and Swanstree burn, has a pond and potential agricultural run-off from alpacas, so seemed like a great spot for duckweed diversity. We found two species inhabiting the waters there and we also found a population of duckweeds in a ditch connected to the sea at Spey bay, Elgin and as such was expected to have high salt content.

We are collecting duckweeds and water samples from each site to build a consensus panel to assess duckweed tolerance ranges to minerals of interest. To do this, all water samples are taken in triplicate from the top surface of a waterbody and filtered to remove any mud and plant debris. The filtered water is then mixed into weak acid and stored at 4 degrees. This is used for short term storage to release dissolved ions ready for measurement at the Ionomics facility.

Other sites of interest in northern Scotland included numerous golf courses with streams and ponds to be checked. Estates such as Innes House were of interest. We spoke to a lord who allowed us to check the 5000 acres of land, making up a large area on the map on the west side of Elgin. This site showed dense overgrowth of ivy-leaved duckweed, Lemna trisulca, thriving in a pond not usually accessible to the public. This wasn’t the only incidence of ivy-leaved duckweed, in fact it seemed a relatively common species populating Scottish ponds, lochs and waterways, and even more so than in English waters.

Visiting Scotland proved fruitful for our understanding of duckweed migration as only 8% of sites had invasive Lemna minuta present, relative to 49% in the southern sites, and 14% of sites containing Lemna trisulca in the north relative to only 7% in the south.  Other species such as the overwintering seed-producing species require extended lab phenotyping and genotyping to better confirm their identities. So far there seems to be some interesting compositional differences between North and South and I’m sure there is much variety between sites as well.

This concludes the final part to the duckweed blog series. Look out for the Future Food Beacon biannual briefings to find out more about the results from the spring collection hunt.

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