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RESEARCH ARTICLE
Contents Vol 59(4)

Microalgal sediment biostabilisation along a salinity gradient in the Eden Estuary, Scotland: unravelling a paradox

Bryan M. Spears A B C , James E. Saunders A , Irvine Davidson A and David M. Paterson A
+ Author Affiliations
- Author Affiliations

A Centre for Ecology & Hydrology Edinburgh, Penicuik, Midlothian, EH26 0QB, Scotland.

B Sediment Ecology Research Group, Gatty Marine Laboratory, University of St Andrews, Fife, KY16 8 LB, Scotland.

C Corresponding author. Email: spear@ceh.ac.uk

Marine and Freshwater Research 59(4) 313-321 https://doi.org/10.1071/MF07164
Submitted: 18 September 2007  Accepted: 28 February 2008   Published: 15 May 2008

Abstract

Microalgal biostabilisation of cohesive sediments via the production of extracellular polymeric substances (EPS) has been well documented in intertidal ecosystems and represents a key ecosystem service with respect to the regulation of sediment transport. However, recent ecosystem comparison studies have uncovered a paradox in which sediment stability is commonly observed to be lower in freshwater ecosystems (compared with estuarine ecosystems) even though sediment EPS concentrations and microalgal biomass are high. Using a combination of freshwater and estuarine field and mesocosm techniques, the relative and interactive roles of salinity and the production of EPS (carbohydrate concentration) by benthic microalgae in the mediation of sediment stability in the Eden River catchment (river, mudflat and saltmarsh) were assessed. Sediment stability apparently increased with salinity from river (42.43 N m–2 surface stagnation pressure; salinity 0) to mudflat (98.65 N m–2; salinity 25) to saltmarsh (135.48 N m–2; salinity 46). The opposite trend was observed in sediment chlorophyll a and carbohydrate concentrations, indicating that salinity is the main variable driving sediment stability across the ecosystems under moderate EPS concentrations. Observations from mesocosm experiments highlighted the individual and combined importance of salinity and EPS in biostabilisation, with the largest increase in sediment stability observed following combined additions (25-fold increase compared with the control). The biogeochemical processes responsible, and their role in buffering phosphorus transport across the freshwater–saltwater transitional zone, are discussed.

Additional keywords: ecosystem comparison, extracellular polymeric substances, sediment stability.


Acknowledgements

We appreciate the field and laboratory assistance provided by Fiona Fraser and Ruth Tomlinson. Bryan Spears and James Saunders were funded by Natural Environment Research Council, UK (NERC) PhD studentships (NER/S/A/2003/11324 and NER/S/A/2003/11890 respectively). Mesocosm work was developed with the aid of a NERC award (NER/A/S/2003/00578). We would also like to thank two anonymous reviewers and Professor Andrew Boulton for their helpful and constructive comments.


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