Η εργασία αυτή φιλοδοξεί να εκτιμήσει την περιβαλλοντική κατάσταση στο στενό Ψυττάλειας -Κερατσινίου,όπου ο κεντρικός αποχετευτικός αγωγός απέριπτε αστικά λύματα και βιομηχανικά απόβλητα του νομού Αττικής. Προσδιορίσθηκαν οι συγκεντρώσεις των βαρέων μετάλλων του οργανικού άνθρακα, των φυσικών ραδιονουκλιδίων και του Cs-137. Έξι δειγματοληπτικές πυρηνοληψίες που εκτελέσθηκαν σε επιλεγμένα σημεία οδήγησαν στον καθορισμό του στρώματος της οργανικής λάσπης, ενώ διαπιστώθηκαν οι υψηλές συγκεντρώσεις των βαρέων μετάλλων που περιέχονται σε αυτή. Οι τιμές της ειδικής ραδιενέργειας των φυσικών ραδιονουκλιδίων είναι αντίστοιχες με αυτές των φυσικών ιζημάτων ενώ αυτές του Cs-137 ήταν σχετικά υψηλές παρουσιάζοντας σαφείς κατανομές με το βάθος. / The present research estimates the environmental situation in the Psittalia – Keratsini strait, where the outfall sewer of Athens discharged untreated sewage to the sea. The concentrations of heavy metals, organic carbon, natural radionuclides and Cs-137 were determined. Six sample cores were collected. The geochemical analysis determined high concentrations of heavy metals and Corg in the layer of organic mud. The concentrations of natural radionuclides were similar of those in natural sediments while those of Cs-137 were relatively high presenting explicit distributions with depth.

No description available.

No description available.

This dissertation focussed on the Mvoti River system in KwaZulu-Natal, an important resource for the numerous towns and villages along its course. Catchment activities are varied with agriculture being the predominant activity, and industrial activities common in the lower catchment. The Mvoti River is intensively utilized, especially in its lower reaches, to the extent that it is referred to as a ‘working river’. Modifications of the chemical and physical characteristics of the system, and consequently the biological characteristics, have led to degradation of the system such that the functioning of the lower river has deteriorated in comparison to that of its pre-disturbance condition. There are three main aspects of the Mvoti system around which this dissertation is based, namely, water quality, geochemistry, and conservation of the system. The results of the water quality survey of the estuary revealed that the system is presently experiencing water which is of an inferior quality. Compared against the South African water quality standards, a majority of the parameters exceed acceptable limits and are likely to present negative impacts on aquatic health and potentially human health. Comparison of current results, and water quality data for the system dating back to 1964, revealed that this degradation is not new to the system, and the Mvoti Estuary has in fact been experiencing continued deterioration over the years. The second part of this study investigated heavy metal presence in the sediments of the lower system and elemental presence and distribution in the surface sediments of the middle and lower River respectively. Results indicated that even though selected heavy metals are present, they are of concentrations lower than those of two other South African and two other international systems they were compared with. Enrichment and contamination assessments reveal that contaminants are in all probability present as a result of anthropogenic sources. However, distribution patterns which show highest levels just after effluent disposal sites suggest that the contamination is presumably human-induced and, the predominance of larger grained sediments that do not have high adsorption capacities, suggest that contaminants are readily remobilized into the water column. The final part of this research investigates other environmental problems, and causes, both natural and anthropogenic, experienced by the estuary system. These stresses include poor water quality, reduced water quantity, sedimentation, alien vegetation invasions and loss of biodiversity. Strategies to address these issues are proposed, with the intention of improving the condition of the estuary. This is an attempt at ecological restoration, to restore the estuary to a condition as close to as possible, to its pre-disturbance condition. These strategies include controlling abstraction and discharge, eradicating alien vegetation, controlling sandmining, and improving the overall quality of the system. Also proposed is an estuary management plan (EMP) for the Mvoti system, as there is currently no plan of such a nature in place. The EMP will aid restoration attempts, increase public awareness, and via post-project monitoring and evaluation ensure the success and sustainability of any future projects. Significantly, the adoption of an EMP will be a major step towards the rehabilitation, conservation and protection of this already degraded system. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2010.

The marine gas hydrate stability zone (GHSZ) is sensitive to climatically driven temperature changes at the seafloor. This thesis reviews past studies of the GHSZ response to climate change, and presents the results of a numerical analysis of a marine gas hydrate stability model forced by an intermediate complexity climate model. Potential future climate scenarios are simulated. resulting in realistic predictions of seafloor temperature change over variable bathymetry. The average continental margin seafloor temperature increase is greater than the global seafloor average. and it is determined that even for CO2 concentrations held below present-day levels. the global GHSZ will decrease significantly. The experiments carried out here indicate that after 40 kyr the GHSZ volume will shrink by between 1% and 29%. based on various CO2 scenarios and parameterizations of thermal diffusivity and geothermal gradient. Regions which exhibit 100% GHSZ loss range from 1% to 9% of the prescribed continental margin. Results of this study suggest that the effects of future GHSZ loss may be felt by the exogenic carbon cycle within centuries and last for tens of thousands of years.

Graduation date: 1986

Graduation date: 1982

Thesis (Ph.D.)--University of Hawaii at Manoa, 1994. / Includes bibliographical references (leaves 235-249). / Microfiche. / xx, 249 leaves, bound ill., maps 29 cm

The purpose of this study is to present the results of mineralogical and petrochemical analyses of the solid phase components and the inorganic chemistry of the interstitial waters of the Recent anoxic sediments of Kaneohe Bay, Oahu. Nineteen shallow 1-4 meter gravity cores of the lagoonal sediments of Kaneohe Bay were analyzed for pore water chemistry and seven were subjected to detailed mineralogical and petrochemical analyses. The pore waters of the sediment column show depletions in dissolved SO =4, Ca++, Mg++ and Sr++ accompanied by increases in titration alkalinity, NH4 + , PO 4 -3 and Si02 with respect to the overlying seawater with increasing subbottom depth. Na+, Cl-, K+ and Fetot exhibit minor departures from overlying bay waters assuming that depletions of Na+ and Cl- are the result of an influx of meteoric ground water from beneath the bay's floor. The bay may be divided into two parts on the basis of the rates of pore water diagenesis: in the southern part of the bay, S0 =4 is completely depleted within 80cm subbottom depth, whereas in the northern part, complete S0 =4 reduction does not occur at depths to 350cm. The southern sediments are contaminated by raw, high C/N sewage, resulting in an increased metabolic reduction rate of S0 =4 by anerobic bacteria over that observed in the unpolluted northern bay. Calculation of S0 =4 consumed versus alkalinity plus NH=4 produced indicates a relationship in which roughly one-half of the "produced alkalinity" has been consumed in the formation of authigenic minerals, primarily nontronite and aragonite. Quantitative mineralogical and petrochemical analyses of the solid phase components reveal the loss of amorphous iron-oxyhydroxides, biogenic opaline silica, and amorphous aluminosilicate with increasing subbottom depth. Pyrite formation occurs immediately below the sedimentwater interface. Scanning Electron Microscope observations show a hierarchy of morphologies with depth: single l-micron crystals to 30- micron diameter framboids. Pyrite formation accounts for the lack of detectable S= within the pore waters and is dependent on the availability of pore water iron derived from the dissolution of amorphous iron-oxyhydroxides. The amount of pyrite present below 40cm subbottom depth exceeds the amount which could be formed by the complete reduction of buried pore water S0=4 suggesting the importance of bioturbation in the mixing of pore and overlying seawaters. Authigenic nontronite and mixed-layer smectite-illite are being formed as the result of the reaction of amorphous aluminosilicate with pore water Si02 from opal dissolution and pore water Fe and/or other cations. In those cores where sufficent dissolved iron exists in the pore water, nontronite forms, whereas when dissolved iron is not present as evidenced by the presence of dissolved S= in the pore water, a mixed-layer smectite-illite is formed. The amount of smectite formed is limited by the amount of opal which dissolves. For Kaneohe Bay sediments an average of 0.12 weight percent authigenic smectite is added annually to the sediment column. Minor amounts of authigenic plagioclase, phillipsite, clinoptilolite, analcime, sepiolite, siderite and apatite are also being formed within the sediments. The relationship between reduced pore water Fe and smectite formation suggests that reverse weathering reactions resulting in either authigenic nontronite or mixed-layer smectite-illite may occur in all anoxic marine sediments rich in terrigeneously-derived, poorly-crystalline "kaolinite" and containing enriched pore water Si02. Assuming that 10 percent of the total flux of the world river sediments delivered to the ocean is deposited in Kaneohe Bay-type environments and that rates of reaction are similar to those observed in Kaneohe Bay, then approximately 6 percent of the CO2 consumed by rock weathering may be returned annually to the atmosphere by these reactions. / Bibliography: leaves 258-281.

Wave-formed rippled sediment beds are extremely important to the processes that act on or across the sediment-water interface. Ripples increase the exchange of materials between the sediment and the water column, enhance sediment transport rates, and act to increase the dissipation of waves by increasing the hydraulic roughness of the seafloor. Previous research has, however, failed to take into account the substantial spatial and temporal variation rippled beds display when formed under real sea conditions. Based on a set of laboratory experiments a spectral method to predict and model rippled beds has been developed. Through the use of the rippled surface's spectral density function the spatial and temporal variability of the rippled surface can be taken into account with greater efficiency. A prediction method for the equilibrium ripple spectrum was developed based on a nondimensional spectral form, which utilised the peak orbital excursion diameter and the 50th percentile grain size diameter of the sediment bed. The method provided an effective technique to predict ripple parameters with the same degree of accuracy achievable at small scale as more accepted ripple prediction methods. A new method was derived to model the changes a rippled bed undergoes as it actively evolves between two given equilibrium states due to a change in surface wave conditions. The evolution of a rippled bed can be described mathematically in exactly the same way as a rippled bed growing from a flat bed condition. The method allows any bed to be modelled through time if the flow conditions and sediment properties are known. There is little advantage in using the spectral method to predict rippled beds when they are in equilibrium with the flow conditions. The main benefit of the spectral method comes when attempting to model rippled beds evolving under changed flow conditions. In the same way as the parameterisation of surface waves in terms of their spectral density function has increased the ability to model wind generated wave fields, studies of rippled beds would benefit from the increased detail and ease the spectral method brings. / Thesis (Ph.D.)--School of Civil and Environmental Engineering, 2005.