No description available.

No description available.

No description available.

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No description available.

The significant contribution of infaunal mediated particle movement to depth of the mixed layer, the subduction rates of phytodetritus, the recycling of nutrients and the flux of materials from the sediment to the water column as well as the diversification of marine life and the global extent of bioturbation, makes it a key process in the marine ecosystem, which is well recognized.  The present thesis investigates specifically the links between bioturbation (ecosystem process) and ecosystem function (the depth of sediment mixing, trace metal cycling) through the development of novel <i>in situ </i>methodology and analytical techniques. It is clear that a standardisation and validation of current proxies used for benthic habitat quality assessments are necessary to inform the management of habitat frameworks and that these must consider the influence of a multitude of environmental processes on bioturbation function relations.  The simultaneous use of multi-disciplinary techniques allows biogeochemical processes to be interpreted in light of recent infaunal activity, facilitating a better understanding of underlying mechanisms of species-function relations.  <i>In situ </i>studies highlight the inherent heterogeneity in marine sediment environments, as well as the scale and context dependant nature of species-function relations.  Together, this thesis highlights the need for simultaneous acquisition of high resolution spatio-temporal data under natural environmental conditions to understand underlying mechanisms of how different processes influence and interact with each other.  An immediate challenge for linking in situ species-function-environment relations is to reconcile the difference in spatial and temporal scales of the different processes in question.

No description available.

Absorption and scattering by dissolved and particulate materials in shelf seas influence the attenuation of light in the water column. These effects are most pronounced in coastal regions where the light available for phytoplankton absorption may be limited by the presence of sediment and coloured dissolved organic matter.

No description available.

A series of physical oceanographic investigations were carried out in Swansea Bay to assess the hydrodynamics, circulation processes and the diffusion and dispersion characteristics of the area. The study was designed to describe effluent dispersion in the embayment using various measurement techniques. Current-meter stations were established using either long or short period observations, and existing data from various sources was reanalysed. Vertical current and density fields were measured at various locations, and current shear and stratification parameters, and the related Richardson Number were described. A series of surface salinity surveys were conducted over varying environmental conditions. 18 instantaneous point sources of Rhodamine W.T. dye were released in the Bay, to determine the diffusion characteristics prevalent in the area. These experiments were designed specifically to examine two-dimensional horizontal diffusion processes at two levels in the water column, over relatively short time intervals (maximum 6 h). All releases except the Rivers Neath and Tawe utilized a neutrally buoyant source, the exceptions used a buoyant source. The concentration distributions were measured using continuous recording fluorometric instrumentation. Swansea Bay may be divided into 6 regions, each exhibiting distinct flow regimes. Diagrams are presented depicting the generalized circulation patterns at varying stages of the tidal cycle. Residual current analyses indicate a variable residual system. Logarithmic linear velocity profiles are observed throughout the Bay. The embayment is stratified throughout with values of the mean stratification parameter, ranging between 0.26 x 10'3 to 2.36 x 10-1 (S-2 ). The mean vertical current-shear parameter ranges between 9.5 x 10"3 and 2.11 x 10-t (S -1 ). Computed Richardson Numbers are in excess of the critical value, suggesting that vertical turbulence is surpressed by the density structure observed in the region. The dye experiments were analysed using rotationally symmetrical and two-dimensional techniques. Diffusion diagrams were constructed and diffusion relationships computed such that the behaviour of variance with time, and diffusion coefficient with length scale is described. Horizontal variances in the range 105 to 1010 cm2, and horizontal diffusion coefficients in the range 102 to 109 cm2 are observed for time periods of 103 to 104 s. Vertical diffusion coefficients, determined from dye distributions, are in the range 2 to 20 cm s-) and are comparable with those estimated from vertical current data. The experiments carried out in the western and north-eastern sections of the embayment can be characterised by the Joseph and Sender (1958) P-class solution, diffusion velocities in the range 0.42 to 1.14 cm s'( and 0.22 to 0.51 cm s-( were observed in each area respectively. Shear diffusion characteristics are described by a series of relationships between the longitudinal diffusion coefficients and various current velocity parameters.