Abstract
Seawater turbidity due to suspended particulate material (SPM) is an important property of a marine ecosystem, determining the underwater light environment and many aspects of biological production and ecology. SPM concentrations are largely determined by patterns of sediment resuspension from the seabed due to shear stress caused by waves and currents. Hence planning for the construction of large scale offshore structures which will alter regional hydrodynamics needs to consider the consequences for SPM concentrations. Here we develop a one-dimensional (vertical) model of SPM dynamics which can be used to scope the effects of changes in wave and tidal current properties at a site. We implement the model for a number of sites off the east coast of Scotland where we have extensive data sets to enable numerical parameter optimisation. The model performs well at simulating fluctuations in turbidity varying from flood-ebb tidal cycles, spring-neap cycles, storm wave events, and an annual cycle of SPM concentration which is attributed to seasonal consolidation of seabed sediments. Sensitivity analysis shows that, for the range of seabed sediment types in the study (water depth 16–50 m; mud content 0.006–0.380 proportion by weight), relatively large (50%) attenuations of tidal current speed are required to produce changes in water column turbidity which would be detectable by observations given the variability in measurements. The model has potential for application to map the large scale sensitivity of turbidity distributions to the installation of wave and tidal energy extraction arrays.
Highlights
Sea water turbidity due to suspended particulate matter (SPM) determines the depth to which sunlight penetrates below the sea surface
Availability of fine-grained material We assume that water column turbidity is mainly due to suspended mud and silt grains, i.e. particles
The fitted rate equated to a period of around 3 days for a particle to sink from the sea surface to the seabed in still water conditions at most of the sampling sites, justifying the long autocorrelation time-scale of 4.7 days to emerge from the parameter optimisation
Summary
Sea water turbidity due to suspended particulate matter (SPM) determines the depth to which sunlight penetrates below the sea surface This is one of the key factors determining the species composition and productivity of marine ecosystems. 7 sites were selected for approximately monthly measurements of water column turbidity and sediment porosity, permeability, oxygen consumption and nutrient fluxes between mid-2008 and mid-2009 from the RV ‘Temora’. At these sites, undisturbed sediment cores were collected with a Mini Muc k/MT 410 corer fitted with 60 cm acrylic core tubes (Serpetti, 2012). Sediment mud content (proportion by weight of grains
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