The effect of carbohydrate production by the diatom Nitzschia curvilineata on the erodibility of sediment

Increasing the biomass of bivalve suspensions feeders has been proposed as a means to improve water quality in eutrophic estuaries such as the Chesapeake Bay. However, water quality impacts are likely to be determined by the balance of bivalve feeding and the deposition and sediment regeneration of nutrients from particulate organic matter. In shallow-water environments, benthic and pelagic processes are closely coupled and water flow can regulate the supply of seston to the bivalves. In addition, such flow may regulate benthic-pelagic nutrient fluxes through mass transfer limitation and resuspension. We studied the interacting effects of juvenile oysters Crassostrea virginica and bottom shear velocity on phytoplankton biomass and on nutrient regeneration in a series of three 4 wk long comparative experimental ecosystem experiments. All mesocosms had a 1000 l water volume, a 1 m 2 sediment surface area, and a 1 m water-column depth, and the same realistic water-column mixing (turbulence intensity 1 cm s -1 ). The systems included a multi-component mesocosm with moderate bottom shear velocity (0.6 cm s -1 ) and 2 standard cylindrical tanks with an unrealistically low bottom shear velocity (0.1 cm s -1 ). Oysters shifted processes to the sediments by decreasing phytoplankton biomass without stimulating additional blooms and by increasing light penetration to the bottom. Through complex and indirect relationships, the interaction of oysters and enhanced shear velocity significantly affected microphytobenthos biomass. Light, as enhanced by the oyster feeding on phytoplankton, increased microphytobenthos biomass; a moderate bottomshear velocity eroded the biomass. Microphytobenthos biomass decreased nutrient regeneration from the sediments to the water column and may have implications for water quality in low-energy parts of shallow-water estuaries such as Chesapeake Bay. Enhanced bottom shear in more energetic parts of shallow estuaries negatively affects microphytobenthos biomass and may increase nutrient regeneration from the sediments.

Section: Discussionmentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Effect of oysters Crassostrea virginica and bottom shear velocity on benthic-pelagic coupling and estuarine water quality

Porter

Cornwell²,

Sanford³

2004

“…Benthic algae produce extracellular polymeric substances (EPS, mainly colloidal carbohydrates), which increase the cohesiveness of the sediments, and this is reflected in the significant relationship between U crit (and mass eroded) and the chlorophyll a content of surface sediments (r = 0.54; p = 0.005 for 1996 and 1997 data). Field studies (Sutherland et al 1998b, Austen et al 1999, Paterson et al 2000, Widdows et al 2000a) have consistently demonstrated a significant correlation between sediment stability and the content of chlorophyll a and EPS in the surface sediments. Furthermore, controlled laboratory flume experiments have confirmed that there is a cause-effect relationship between microphytobenthos chlorophyll a (and EPS) and sediment stability (Sutherland et al 1998a).…”

Section: Spatial and Temporal Changes In Sediment Resuspension And Dementioning

confidence: 99%

Role of physical and biological processes in sediment dynamics of a tidal flat in Westerschelde Estuary, SW Netherlands

Widdows

Blauw²,

Heip

et al. 2004

110

This article synthesises a series of studies concerned with physical, chemical and biological processes involved in sediment dynamics (sedimentation, erosion and mixing) of the Molenplaat tidal flat in the Westerschelde (SW Netherlands). Total sediment accretion rate on the flat (sand to muddy sand) was estimated to be ~2 cm yr -1 , based on 210 Pb and 137 Cs profiles. 7 Be showed maximum activity in the surface sediments during summer, reflecting accretion of fine silt at this time of year, and total vertical mixing of sediment to be in the order of 50 cm 2 yr -1 . The extent to which different physical and biological processes (tidal currents, air exposure, bio-stabilisation, biodeposition and bioturbation) contributed towards sediment dynamics was estimated. A sediment transport model based on physical factors estimated sedimentation rates of 1.2 cm yr -1 , but did not account for tidal or seasonal variation in suspended particulate matter (SPM), wind or effects of spring-neap tidal cycles. When the model was run with an increased critical bed shear stress due to the microphytobenthos, net sedimentation rates increased 2-fold. These higher rates were in closer agreement with the rates derived from the depth profiles of radionuclides for the central region of the tidal flat (2.0 to 2.4 cm yr -1 ). Therefore a significant part of the sedimentation rate (~50%) may be explained by spatial-temporal changes in biological processes, including 'bio-stabilisation' by microphytobenthos, together with the enhanced biodeposition of silt by suspension feeders, and offset by processes of 'bio-destabilisation' by grazers and bioturbators. In the centre of the tidal flat there was a shift from high sediment stability in spring-summer 1996 to low sediment stability in autumn 1997, quantified by a significant reduction in critical erosion velocity of 0.12 to 0.15 m s -1 , and accompanied by a 30-to 50-fold increase in sediment erosion rate. The change was associated with a shift from a tidal flat dominated by benthic diatoms and a low biomass of bioturbating clams (Macoma balthica), to a more erodable sediment with a lower microphytobenthos density and a higher biomass of M. balthica. Vertical mixing of sediment and organic matter, studied using a variety of tracers, was rapid and enhanced by advective water flow at sandy sites and by burrowing polychaetes and bivalves at silty sites. The sediment dynamics and biogeochemistry of tidal flats is dependent on the complex interactions between physical, chemical and biological processes/properties, which include tidal currents, river flows, storm waves, air exposure, dehydration in summer, ice-scour in winter, sediment properties (grain size and composition, organic content, nutrient content, redox balance), stabilisation by biota (algal biofilms, mussel beds, salt marsh) and destabilisation by biota (bioturbating bivalves, scouring around clumps of animals and plants). To date, there have been very few multi-disciplinary studies providing an integrated view of the sedim...

“…In the intertidal zone, sediment stability is increased by organisms like microphytobenthos that cause adhesion of grains (e.g. Sutherland et al 1998) and decreased by bioturbators such as deposit-feeding bivalves (e.g. Macoma balthica) and grazers (e.g.…”

Section: Introductionmentioning

confidence: 99%

Effects of sediment source and flow regime on clam and sediment transport

Hunt¹

2005

Erosion and transport of juvenile benthic invertebrates, including bivalves, has the potential to alter patterns of distribution and abundance during the early postsettlement period. Field observations indicate that there is often great spatial variability in rates of transport of juvenile bivalves. Differences in transport among sites may arise from both physical and biological causes, including variation in water flow, sediment grain size, and the local biological community. In this study, an experiment was conducted in a laboratory flume to examine the effect of sediment source (4 subtidal sites in the Navesink River estuary, New Jersey, USA) and flow velocity on rates of transport of juvenile Mya arenaria and Gemma gemma. Rates of erosion of M. arenaria were significantly related to sediment volume eroded, suggesting that dispersal at high flow speeds is linked to bedload transport. Sediment erosion and clam transport was lower for sediment cores from the 2 sites where the sediment was covered by a mat of amphipod Ampelisca abdita tubes. Reduction of the tube mat resulted in a small but significant increase in sediment erosion. The results of this study and comparison of shear velocities between the laboratory and the field suggest that both the presence of an amphipod mat and low shear velocities will result in low rates of transport of sediment and juvenile clams in the field.