Spatial Representation of Aquatic Vegetation by Macrofossils and Pollen in a Small and Shallow Lake |
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| Authors: | Yan Zhao Carl D Sayer Hilary H Birks Michael Hughes Sylvia M Peglar |
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| Institution: | (1) Key Laboratory of Western China’s Environmental Systems (Ministry of Education), Lanzhou University, 730000 Lanzhou, Gansu, P.R. China;(2) Environmental Change Research Centre, Department of Geography, University College London, 26 Bedford Way, WC1H 0AP London, UK;(3) Department of Biology, University of Bergen, Allégaten 41, N-5007 Bergen, Norway |
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| Abstract: | We have explored the contemporary spatial relationship between aquatic vegetation and surficial macrofossil and pollen remains
in a small, shallow, English lake. A detailed point-based (n = 87) underwater vegetation survey was undertaken in the middle of the plant-growing season in July 2000. Then following
plant die-back in November 2000, surface sediment samples (upper 1.5 cm) were collected from 30 of these plant survey points
and analysed for plant macro-remains (all 30 samples), and pollen (4 evenly spaced samples). All data were stored as separate
layers in a geographical information system and spatial relationships between the aquatic vegetation and plant remains were
explored. In contrast to pollen types, plant macrofossils were not evenly dispersed across all parts of the lake and, with
the exception of Chara oospores, higher concentrations of remains (particularly for Potamogeton) were found close to areas of source-plant dominance. The spatial pattern of macrophyte–macrofossil relationships revealed
that vegetative remains (particularly leaf fragments) were probably deposited at source, whereas seeds were recovered close
to the shore suggesting slightly wider dispersal. Overall, however, macro-remains best represented local ‘patch-scale’ vegetation
within 20–30 m of the core site. The macro-remains effectively recorded the dominant plants in the lake with 63% of samples
containing a combination of remains of Chara, Elodea, and Potamogeton. However, relationships between macrophytes and fossils were complex. Some species were significantly over-represented by
macrofossils (e.g., Chara spp., Nitella flexilis agg., and Zannichellia palustris), while others were either under-represented (e.g., Potamogeton spp.), or not represented at all (e.g., Lemna trisulca). Pollen represented macrophyte diversity poorly, but some taxa were found (e.g., Myriophyllum spicatum, Ceratophyllum demersum) that were not recorded by macro-remains. We conclude that macrofossil analysis may be very usefully employed to determine
the dominant taxa in past aquatic plant communities of shallow, productive lakes and that the addition of pollen analysis
provides further information on former species richness. |
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| Keywords: | Aquatic vegetation Plant macrofossils Pollen Representation in surface sediments Shallow lake Taphonomy |
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