Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1986. / "July 1986." Includes bibliographical references (p. 208-215).

Thesis (Ph. D.)--University of Washington, 1986. / Vita. Bibliography: leaves [192]-199.

The structural properties of surficial sedimentary deposits strongly influence exchange processes across the benthic boundary layer, and hence are important factors controlling sedimentation and biogeochemical cycling. They are governed by a complex combination of hydrodynamic, chemical and biological controls, and therefore exhibit significant spatial and temporal heterogeneity. Geophysical techniques have great potential as tools for investigation of these structural properties. Techniques for determining in situ Electrical Formation Factor (FF) and acoustic shear-wave velocity (Vs) in the upper few centimetres of saturated intertidal deposits were developed: FF was measured by a Wenner electrode array at the sediment surface; Vs was measured by piezoelectric bender transducers inserted to a depth of 40mm. Geophysical properties, porosity, and textural and biological characteristics were determined in situ at a variety of locations, predominantly in sands. The highest variability in all parameters was obtained over large spatial scales, with primary variation in bulk textural composition and benthic infaunal community. Within-location variability was significant over medium spatial scales of tens to hundreds of metres, controlled by local variation in tide-averaged hydrodynamic environment and duration of tidal exposure. In sands, bulk textural variability was of secondary importance over these scales, and was interpreted as due to admixture of relatively small proportions of coarse and fine sub-populations into a uniform sedimentary framework. Localised geophysical variability, while significant, was also of secondary importance, being influenced primarily by properties of this framework. Seasonal variability was also significant, controlled by temporal variation in hydrodynamic environment and temperature. Structural parameters (porosity, FF, Vs) were more responsive than textural parameters to temporal variation in hydrodynamic or biological activity. Porosity was controlled by grain shape and size distribution, and by the depositional environment. It was not apparently directly affected by benthic macrofaunal activity. FF was controlled by porosity, and additionally by factors affecting tortuosity. Tortuosity was increased by increasing both carbonate and mud contents. Burrowing organisms (Arenicola marina and Corophium) and tube-building organisms (Lanice conchilega) reduced FF. Vs was controlled by porosity, and additionally by factors which control intergranular friction. This was increased by increasing carbonate content, and reduced by increasing mud content. Burrowing organisms (Arenicola marina and Corophium) reduced Vs, while tube-building organisms (Lanice conchilega and Pygospio elegans) increased it.

Magister Scientiae - MSc / This study examined the relationship between sediment structure and infaunal polychaete communities off the southern coast of Namibia from two separate sets of data, and a total of ninety-two samples. It also examined whether a selected group of organisms (polychaetes) could provide the same level of information regarding community structure, as the entire fauna, at a number of taxonomic resolutions. A total of 44 samples were collected by De Beers Marine (Pty) Ltd in 1999 off the southern coast of Luderitz from depths between 40 m and 90 m. The sediments varied from soft muds (45 μm) to gravel (> 710 μm). Forty-three morpho species of polychaetes were distinguished, of which only 28 known species of polychaetes could be positively identified, which suggests that more information on the diversity of polychaetes in the region is needed. The fauna was dominated by species in the Ampharetidae, Capitellidae, Maldanidae, Spionidae, Lumbrineridae, Flabilligeridae, Nephtyidae, Pectinariidae and Onuphidae. Multi-variate analyses using PRIMER indicated that communities were structured by mud (45 μm) and very fine sand (45 - 63 μm) and gravel (> 710 μm). Mud and gravel, although selected by the BIOENV procedure as accounting for some of the variation in the polychaete assemblage structure, explained no more of the data (in combination) than did mud on its own. As similar clustering of samples was observed when the data were analysed at both the family and species-level, suggesting that the same level of information was being gained at the two taxonomic levels. The results of the BIOENV analyses were also broadly similar for both taxonomic levels of analyses, in terms of both the proportion of the variation in assemblage structure explained by the selected environmental variables and the choice of selected variables. These results suggested the information gathered at the polychaete family-level were equally clear when they are collected at the family-level for the entire infauna. The use of polychaetes (to the family-level) as surrogates, using sediment structure and depth was independently investigated from a total of 48 samples that were collected by De Beers Marine (Pty) Ltd in 2001, from depths between 20 m and 110 m. The sediment varied from mud (< 63 μm) to gravel (> 710 μm). Twenty-two families of polychaetes were distinguished, the fauna showing an abundance of Capitellidae, Cirratulidae, Flabilligeridae, Lumbrineridae, Magelonidae, Nephtyidae, Paraonidae, Pilargiidae, Onuphidae, Syllidae and Spionidae. Striking differences were found in the amount of variation accounted for in the biological samples by the environmental data. Interestingly, depth in combination with a particular sediment size fraction featured very strongly in structuring both sets of communities. The biotic patterns in the family-level total infauna were not similar for the polychaetes (at the same taxonomic resolution). These results suggested that one group of organisms (polychaetes at the family-level) may not be useful as a proxy for the entire infauna (at the family-level). Because of the contrasting results that were obtained in 1999 and 2001, the biological data in 1999 were pooled and the environmental data (sediment size fractions) were adjusted accordingly (i.e. some of the differences in the results may reflect differences in the methods used to collect data). Consequently the results still did not adequately explain why there was a low level of similarity between the total infauna and polychaete family-level biotic patterns in 2001. It seemed that pooled data improved the taxonomic resolution (amount of variation obtained), but when the sediment size fraction data were adjusted, it lowered the amount of taxonomic resolution. The results suggest that comprehensive and standardized samples must be collected to fully understand the relationships between biotic patterns and environmental variables. This is potentially important given the costs involved and the potentially long lasting value of the material collected. These sediment and biological samples were collected by industry (for baseline biological monitoring in the mining industry, and not academic purposes). Proper protocols need to be established which allow industry-related monitoring programs to make a real contribution to our understanding of the biodiversity and ecology of the area. / South Africa

The Secchi disk is one of the simplest and least expensive instruments for measuring the rate of attenuation of light in natural water bodies. Because this rate of attenuation is often closely related to the concentration of suspended sediment in the water, disk measurements may, in some situations, provide a useful and inexpensive alternative to the standard gravimetric methods for determining sediment concentration. Published empirical studies indicate that satisfactory relationships between Secchi disk transparency and concentration can be established but that these relationships differ from area to area and become more complex as turbidity increases. Results presented in this paper based on data from the Mackenzie delta, N.W.T. support these conclusions. These results cover a range of turbidities which extends well above those previously examined. Physical interpretation of these empirical results is made difficult by the large number of uncontrolled variables associated with Secchi disk readings. This interpretation is facilitated by the introduction of objective attenuation coefficients (more variables controlled) as variables intermediate between transparency and concentration. The two coefficients most commonly used are the volume attenuation coefficient α and the diffuse attenuation coefficient for downwelling irradiance Kd. Empirical relationships between either of these objective attenuation coefficients and disk transparency are reciprocal in form but depart from the simple reciprocal model at high sediment concentrations. Tyler (1968) has shown theoretically that transparency is dependent upon both α and Kd. Since the ratio α/Kd increases with turbidity, the observed departures from the simple reciprocal model can be explained. Burt (1954, 1955) has developed a theoretical expression relating α and sediment concentration in which he shows that α and thus Secchi disk transparency are dependent upon total particle surface - ie., on particle size as well as concentration. This dependence on particle size provides an explanation for the increasing complexity of empirical transparency-concentration relationships as the turbidity range considered widens and for the change in relationships with location. Tyler's and Burt's expressions have been combined in this paper to enable estimations of particle size to be made given only an empirical transparency-concentration relationship and knowledge of the ratio α/Kd. The resulting equation has been applied to the Mackenzie delta data and, considering the large number of untested assumptions made, the particle size estimations are remarkable close to those obtained using Postma's (1961) purely empirical relationship. Secchi disk measurements, then, can provide a surprising amount of information about sediment concentration and particle size. There are, of course, many limitations to the method and the theory associated with it is largely untested. Within the context of these limitations, however, the disk can be very useful. It is simple to use in the field, is remarkable insensitive to changes in the underwater light field and is not greatly influenced by observer bias / Arts, Faculty of / Geography, Department of / Graduate

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Thesis (M.Sc.)--Memorial University of Newfoundland, 2006. / Bibliography: leaves 162-184. Also available online.

Univ., Diss.--Göteborg, 2007. / Enth. außerdem 5 Zeitschriftenaufsätze.

Thesis (Ph.D.)--Memorial University of Newfoundland, 2001. / Bibliography: leaves 259-275. Also available online.

No description available.