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

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.

Magnetic Particle Induction and Its Importance in Biofilm Research

“…Strong correlations between sediment stability, benthic algal biomass and EPS concentration have been observed in marine systems (Sutherland et al, 1998;Yallop et al, 2000). Although biostabilisation has also been observed in freshwater systems (Droppo et al, 2007;Gerbersdorf et al, 2007& Spears et al, 2007 correlations between the aforementioned parameters are weaker. It is evident that under high electrolyte concentrations the effect of EPS on sediment stability is enhanced (Spears et al, 2008).…”

“…Although biostabilisation has also been observed in freshwater systems (Droppo et al, 2007;Gerbersdorf et al, 2007& Spears et al, 2007 correlations between the aforementioned parameters are weaker. It is evident that under high electrolyte concentrations the effect of EPS on sediment stability is enhanced (Spears et al, 2008). This emphasizes the need for a device, such as the MagPI System, that is sensitive enough to discern subtle changes in sediment stability across freshwater environments where low ionic concentrations generally place sediment stability below the range measurable by other devices (See section 2).…”

“…More recently the influence of benthic microbial assemblages on sediment stability has been proven (Decho, 2000;Gerbersdorf et al, 2008;Spears et al, 2007). Traditionally physicochemical and biochemical processes were considered to be the most important drivers of sediment stability (Calles, 1983;McNeil & Lick, 2004).…”

“…Since then the MagPI System has contributed significantly to advancement in our understanding of biostabilisation. Until recently research into the biostabilisation of sediments focussed largely on the stabilising effect of benthic microalgae and their carbohydrate-rich EPS (Underwood & Paterson, 2003;Spears et al, 2008;Stal, 2003). The contribution of benthic bacteria was for the most part overlooked despite their omnipresence at sediment surfaces and their ability to produce copious amounts of EPS as recognized from medical (Costerton et al, 1999), biotechnology (Wang et al, 2006) and industrial investigations (Kumar & Anand, 1998).…”

Influence of benthic macroinvertebrates on the erodability of estuarine cohesive sediments: Density- and biomass-specific responses

“…The erosion threshold of cohesive coastal sediments is instead under control of biological factors including microphytobenthos activity, macrophyte growth as well as meio-and macrofauna activity Paterson et al, 2000;De Brouwer et al, 2005). Biostabilization is particularly dependent on the formation of a surface film of extracellular polymeric substances (EPS) generated primarily by microphytobenthos (Quaresma et al, 2004;Spears et al, 2008). Thus, EPS films are known increase the critical shear stress 3 fold under replete light conditions (Lundkvist et al, 2007b).…”