Euro-limpacs Deliverables

ABSTRACT - DELIVERABLE 34

Report on the analogue matching approach for nutrient enriched lakes

An analogue matching training set was developed comprising 30 UK lakes, 266 diatom taxa and 41 Cladocera taxa. Three subsets of the training set were applied to the reference samples (ca. 1850AD) of three enriched UK lakes to test the value of the analogue matching approach for identifying appropriate reference sites for lakes impacted by eutrophication using, i) the diatom data alone, ii) the Cladocera data alone, and iii) the diatom and Cladocera data combined. The squared chord distance dissimilarity coefficient was employed to determine the best analogues for the reference assemblages of the three test lakes. For Loch Davan, a medium alkalinity, shallow lake, there were no close analogues in the diatom dataset (Black Loch was the closest match), three good matches in the Cladocera dataset (Little Sea Mere, Loch Grogary and Llyn Fanod), and no close matches in the combined dataset (Bayfield Loch, Llyn Fanod and Loch Grogary were the best matches). The lakes with the closest matches are all medium alkalinity waters and are currently mesotrophic with diverse plant populations covering a large proportion of the lake bed. Their selection as potential reference sites for medium alkalinity, shallow lakes such as Loch Davan therefore seems appropriate. For Felbrigg Lake, a high alkalinity, shallow lake, there were no close analogues in the diatom dataset (Frensham Great Pond, Loch Watston, and Oxwich Pool were the best matches), four close matches in the Cladocera dataset (Frensham Great Pond, Loch Watston, Oxwich Pool and Llyn Helyg), and two close matches in the combined dataset (Frensham Great Pond and Oxwich Pool). Loch Watston was also a reasonable analogue using the combined dataset. For Groby Pool, another high alkalinity, shallow lake, there were no close analogues in the diatom dataset (Oxwich Pool, Llyn Llygeirian and Loch Watston were the best matches), six close matches in the Cladocera dataset (Frensham Great Pond, Llyn Helyg, Oxwich Pool, Loch Watston, Broomlee Lough and Loch Ardnave) and no close analogues in the combined dataset, although Oxwich Pool, Frensham Great Pond and Loch Watston were relatively good matches. These three sites were also the closest matches using the combined dataset for Felbrigg Lake. Oxwich Pool and Loch Watston currently support diverse, abundant macrophyte populations, and the latter has been identified as a good example of a reference lake for the high alkalinity, shallow waterbody type. Validation of the choice of reference sites for Felbrigg Lake and Groby Pool using the fuller palaeoecological record suggests that the selected analogues are appropriate for these lakes, although there were few lakes with a present day macrophyte flora similar to that of the Groby Pool pre−enrichment macrophyte assemblage, which was comprised of relatively nutrient−poor taxa. To investigate the application of analogue matching at a wider scale, 14 selected sites spanning the major lake types in the UK's lake typology scheme were selected and close modern analogues were sought for the reference condition samples from each of the study lakes using a 219−lake diatom surface sediment training set from the UK. Close modern analogues were identified for five of the 14 study sites. Felbrigg Lake was one of the 14 study sites, and in this application 2 close modern analogues were identified for this site where no close diatom analogues were identified using the 30−lake training set. In summary, the results suggest that the analogue matching technique does have the potential to be a useful tool for identifying appropriate reference sites for lakes impacted by eutrophication, although a larger training set with a greater number of reference lakes is required to improve the diatom analogues. Future work will include extending the analogue matching approach to lake types across Europe. The EDDI database will initially be explored. This is a harmonised dataset of 1350 modern diatom samples and associated environmental data covering most of Europe and parts of Africa. A harmonised typology for European lakes will be developed and applied to the dataset. The analogue matching approach will be evaluated for a selection of key European lakes, both acidified (from WP4) and enriched (from WP3).

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