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No description available.

The growth of environmentally persistent biofilms in cooling towers causes several associated problems, including microbiologically-induced corrosion (MIC) and biofouling. Current chemical control methods are not only ineffective against biofilms and costly to procure, they also have downstream environmental impacts when released untreated, or incur additional treatment costs. Bacteriophages are alternative biofilm control agents that have the potential to be more effective, cheaper to produce and yet have a more benign effect on the environment. In this study, biofilms grown under conditions simulating seawater fed cooling towers were characterized and the differences in growth and community make-up across time and different substrates were assessed. An MIC associated bacterium common in cooling tower water, P. aeruginosa, was chosen. Seven bacteriophage strains found to be effective against the chosen bacterium were isolated from wastewater influent. The relative effectiveness of these strains was measured against P. aeruginosa across different salinities. Separate biofilms fed with P. aeruginosa enriched seawater were characterized and the effectiveness of the isolated strains, singly and in cocktails, against the enriched biofilms was measured.

The shallow waters west of Scotland feature strong variability in water properties on a variety of temporal scales. While the region is known to be subject to both coastal and oceanic influences, the causes of variability are poorly understood. The limited characterisation of changes in coastal waters impacts our ability to explain the behaviour of coastal ecosystems, and predict their resilience to future climate scenarios. This thesis uses historical data in conjunction with recent cruises and a coastal mooring to investigate the causes of variability in the waters west of Scotland. Two new inter-annual salinity time series on the European shelf are developed. The spatial variability in salinity in shallow waters is greatest during winter and increases by a factor of four between the shelf edge and the coastline. At the shelf edge, new observations of the along-slope current suggest that it is stronger but less stable during winter, leading to a greater availability of oceanic water on the outer Malin Shelf. However unlike other documented shelf regions, shelf edge processes do not directly influence Scottish coastal water properties. A baroclinic current originating in the Irish Sea is the main influence near the Scottish coast during quiescent periods, but wind forcing dominates shelf processes during most winters, with prevailing winds tending to drive oceanic water towards the coast. While salinity in the Sea of the Hebrides is moderately correlated to wind, coastal salinity is sensitive to both advective processes and freshwater runoff. On inter-annual time-scales, salinity on the Malin Shelf is higher when the North Atlantic Oscillation (NAO) is positive, whereas the northern Irish Sea is fresher during a positive NAO state. Salinity and flow pathways in Scottish coastal waters appear to be resilient both to changes in the Rockall Trough and a warming climate on decadal time-scales.

There has been a growing concern of water scarcity in recent years as global water shortages are increasing. The concrete industry consumes about 2 billion tons of potable water annually. For this reason, seawater has drawn attention as a potential substitute for mixing and curing water for concrete if certain challenges can be addressed. One of the main problems associated with the use of seawater in concrete is the risk of corrosion of internal steel reinforcement. Fibre-reinforced polymer (FRP) bars have been shown to be a viable reinforcement alternative in aggressive environments due to their corrosion-resistant properties. Glass FRP (GFRP) bars, due to their acceptable mechanical properties and reasonable price, are currently the most widely used in industry. GFRP bars are manufactured with a variety of surface configurations having different bond performance in concrete, which influences structural behaviour in concrete flexural elements. Therefore, the viability of GFRP bars with sand coated and spiral deformations in seawater concrete is an important topic for research. In this study the bond behaviour is investigated using two different test methods: 1) pullout specimens, and 2) beam anchorage specimens. The results suggest that there is no significant difference between the short-term bond strength of GFRP bars in seawater concrete compared to normal concrete. Additional research is recommended to explore possible long-term issues.

This study used an energy budget approach to record changes in the biology of the Antarctic sea urchin Sterechinus neumayeri in relation to environmental seasonality (i. e changes in chlorophyll standing stock and seawater temperature) over an unbroken two year period. Chlorophyll standing stock showed a brief but intense bloom each austral summer which contrasted with prolonged winter minima. Benthic chlorophyll standing stock, as recorded from sediment cores showed a similar cycle. Seawater temperature varied between -1.8°C and +1.2°C. Feeding activity was highly seasonal and closely correlated to chlorophyll standing stock. Feeding ceased during the austral winter of 1997 and 1998 for 6 and 4 months respectively. Metabolism, as measured by oxygen consumption and also ammonia excretion showed strong seasonality, with relatively brief 3 to 4 month periods of elevated activity in the austral summer contrasting with prolonged winter dormancy. Laboratory studies indicated that only 10-15% of the 3 fold seasonal rise in metabolism was caused directly by temperature (Q10=2.5) and that 80- 85% was related to increased physiological activity associated with feeding. Growth rate was measured over one year and was very slow. Comparison with other studies indicated that echinoid growth rate is strongly dependent on food availability, but that maximal growth rate is limited by seawater temperature, or by a co-varying factor. S. neumayeri is an annual spawner and histology was used to describe both the vitellogenic cycle and also to calculate reproductive output. Comparison with other published studies worldwide indicated that reproductive output is highly dependent on food availability, and that maximal reproductive output is not limited by temperature. Although the overall P: B ratio was low, the ratio of reproductive production to total production was higher than expected. These results indicated that due to the low metabolic rate only 12-16% of total body energy levels were used to endure the prolonged non-feeding polar winter. The overall annual growth efficiency was greater than for warmer water species, due to the larger relative contribution to reproductive output.

The salinity of the ocean is inherently linked to the global hydrological cycle by net evaporation. The surface salinity, however does not just act like a 'rain gauge', ocean dynamics are vital in shaping the sea surface salinity (SSS) distribution. Here I investigate the effect of unsteady motions on scales of several hundred km and smaller - mesoscale eddies - on the water masses in the saltiest regions of the surface oceans. These water masses are eventually subducted equatorward and contribute to the shallow overturning circulation by transporting surface signals from the subtropics to the tropics, making them important components of the variable climate system. Towed CTD measurements in March/April 2013 (a component of the NASA SPURS process study) within the North Atlantic SSS maximum (SSS-max) reveal several relatively fresh and warm anomalies, which deviate strongly from climatological conditions. These features introduce a large amount of freshwater into the subtropical region, exceeding the amount introduced by local rain events. The scales and evolution of the features strongly suggest a connection to mesoscale dynamics. This is supported by high-resolution regional model output, which produces an abundance of features that are similar in scale and structure to those observed, confirming the importance of eddy mixing for the near surface salinity budget of the North Atlantic SSS-max. Observations from the Aquarius satellite and the Argo array in the global SSS-max revealed marked differences in the mean shape and variability of the SSS-maxima. These results motivated an investigation of the role of eddy mixing in setting the regional characteristics of SSS maxima. Observed surface velocities from altimetry are used to stir salinity fields in high-resolution idealized model experiments. Using a water mass framework (salinity coordinates) temporal variability in eddy mixing can be quantified, using diagnostics for the total diffusive flux into the SSS-maxima (transformation rate; TFR) as well as the estimated cross-contour diffusivity(effective diffusivity,$K_{eff}$). Both diagnostics reveal distinct variability in the different ocean basins. In the North Atlantic, both $TFR$ and $K_{eff}$ are dominated by changes in the velocity field while the North Pacific shows high sensitivity of the temporal variability in eddy mixing with respect to the initial conditions used, which represent seasonal/interannual change of the SSS-max shape and position. This implies that temporal variability of eddy mixing and diffusivities must be taken into account when constructing salinity budgets in these regions. Furthermore, the translation of results from one SSS-max region to the other might not be possible, particularly when considering a changing climate, which might influence the mechanisms responsible for temporal variability differently. Lastly evidence is presented for large scale diffusivity variability (particularly in the Pacific), connected to large scale climate fluctuations (ENSO). The evidence presented here suggests a significant modulation of surface diffusivities by climate variability, which represents a feedback mechanism not commonly recognized nor included in modern climate simulations.

This project aimed to characterise the organic speciation of iron in various oceanic waters associated with the New Zealand marine environment, and to examine the possible production of natural organic Fe-binding ligands by the Southern Ocean phytoplankton Phaeocystis antarctica. The location of New Zealand at the edge of the Southern Ocean provides a natural laboratory for studying ocean processes in a variety of oceanic conditions. A time series of a surface transect across the Otago Continental Shelf was undertaken between April 2002 and January 2005 to measure the organic complexation of iron, hydrographic parameters and macronutrient concentrations. The study area contains three distinct water masses: 1) neritic water; 2) the Southland Current, derived from the Subtropical Surface Water (STW); 3) Subantarctic Surface Water (SASW). Hydrological measurements outlined the positions of the three water masses as being fixed within predictable boundaries. Variations in nutrient concentrations in the study area indicated that SASW is the predominant source of nitrate and phosphate to the shelf. Dissolved iron concentrations dropped sharply seaward from several nanomolar to sub-nanomolar levels. The dissolved iron was fully complexed with strong organic ligands in all three water masses, and the ligand concentrations also showed a slightly seaward decreasing trend. Trends in dissolved iron and the iron-binding ligand concentrations related to season were only obvious in neritic waters. Concentration maxima occurred during late spring and summer months, and concentration minima occurred in the middle of each year (winter months). Dissolved iron concentration was low (~0.1 nM) in SASW year round. Data from the present study are in support of that the SASW as a whole is classified as a high nitrate low chlorophyll (HNLC) water body and has an iron-limited phytoplankton population. East of the New Zealand landmass, the Subtropical Convergence (STC) is topographically locked to the Chatham Rise. This is a dynamic region of enhanced primary production (Bradford-Grieve et al., 1997), which separates macronutrient-depleted STW from macronutrient-replete SASW. Dissolved iron concentrations were low (~0.1-0.2 nM) in SASW, while elevated dissolved iron concentrations were observed at the north flank of the Chatham Rise. The iron data imply that the regional currents may be an important vehicle for transporting the elevated iron across the front. Total dissolved iron-binding ligand concentrations were consistently higher (~0.5 nM) in the STW and STC waters than in SASW. The discrepancy in the ligand concentrations between STW and SASW may reflect a different contribution to the ligand pool from the local planktonic community. The organic complexation of iron in the oligotrophic subtropical water columns in the Tasman Sea was also studied and comparison of waters to the north and south of the Tasman front were reported. The iron speciation data imply the potential biological origin for the iron-binding ligands, and the difference in ligand concentrations across the Tasman Front may represent slight differences in algal biomass. A limited investigation to examine the production of natural organic iron-binding ligands by the Southern Ocean phytoplankton Phaeocystis antarctica was undertaken in laboratory culture experiments. Release of nanomolar levels of a strong iron-binding ligand was detected by cathodic stripping voltammetry (CSV) even under relatively high iron concentrations (> 1nM). The estimated iron binding strength for the ligands was similar to those observed in the open ocean. Moreover, the kinetic data suggested the presence of another weaker ligand class, which had a higher Fe concentration (>2 nM) and was not detectable by the CSV ligand titration technique. Our field observations and culture experiment results suggest that the Fe-binding ligands are biologically produced. It appears algae engineer their environment to make Fe more available/accessible for longer by producing these ligands. Therefore, the organic speciation of Fe plays a very important role in the sustained nutrition of ocean primary productivity and must be accounted for in geochemical modelling.

Graduation date: 1967