Diatom plankton dynamics of shallow lakes along nutrient and macrophyte
gradients
Supervisor: Carl Sayer (Geography, UCL)
Our understanding of diatom records in sediment cores is only as good as our
understanding of contemporary diatom ecology. Yet, few true ecological studies are
ever undertaken whereby diatom population dynamics are quantified in time and
related to changes in their environment. This is particularly so for the small, centric
planktonic diatoms which are often key components of assemblages in shallow lakes.
Sporadic, often anecdotal data suggest that different taxa may have distinct
seasonalities (late winter-spring vs. late summer-autumn bloomers). Furthermore,
along nutrient and macrophyte gradients, the seasonal abundance and occupancy of
the water column by diatom plankton may also alter, along with the relative
importance of planktonic vs. periphytic primary production. If we had a better
understanding of the aforementioned factors then our ability to interpret diatom
sequences in sediment cores from eutrophic lakes would be much improved. In turn
this would permit a much more detailed understanding of diatom
responses/contributions to nutrient enrichment in shallow lakes.
The proposed study will exploit an existing set of planktonic diatom samples (1 x litre
of surface water) collected (but not analysed) from 29 shallow lakes in Norfolk, UK.
The study lakes were selected to cover broad gradients for key nutrients and
macrophyte density. Data from this contemporary dataset, will be used to explore
changes in planktonic diatom abundance with variation in nutrient levels and
“macrophyte-covered period”. The faithfulness of different plankton species to
partcular seasons will also be assessed. In the second phase of the project the degree
to which sediment core assemblages might reflect contemporary diatom plankton
communities will be assessed by making comparisions between the plankton data and
surface sedment diatom assemblages. Finally sediment cores will be collected from a
series of nutrient-enriched sites to investigate changes in plankton, periphyton and
macrophyte relationships before, during and following macrophyte loss. This will be
achieved through a combined analysis of diatom and plant macrofossils. It is hoped
that the linked ecological and palaeoecological approaches utilised in the study will
shed light on both the short-term and longer-term dynamics of plankton and
macrophyte populations in shallow, lowland lakes.