/library/oar/handle/123456789/120826 2025-11-05T23:01:45Z 2025-11-05T23:01:45Z /library/oar/handle/123456789/135048 2025-06-18T07:40:08Z 2023-01-01T00:00:00Z

Title: Rationalising marine space : a multidisciplinary analysis for ecosystem-based marine spatial planning Abstract: This work and its abstract are both under embargo until the restriction is lifted. Description: Ph.D.(Melit.)

2023-01-01T00:00:00Z /library/oar/handle/123456789/121572 2024-05-02T12:40:27Z 2023-01-01T00:00:00Z

Title: A preliminary quantitative and qualitative investigation of microplastics sampled from Maltese nearshore waters Abstract: This study aims to characterize the microplastic pollution of the Maltese nearshore waters from an innovative perspective by targeting to shed more light on the dynamics of microplastic accumulation within the water column around the Maltese Islands over two year (2022 and 2023). This pioneering survey is in fact examining different sea layers in order to determine whether different plastic polymers accumulate with increasing water depth. We have performed an experimental sampling methodology, with the modification of our Manta trawl which has been used for the sampling of the surface water, We executed horizontal tow sampling by maintaining the Manta net at a stable depth (6 ±1m and 10 ±1m) in a parallel position, by setting up the perfect balance between the weighting of the frame of the Manta net and the speed of the tugboat to keep the net tight. The focus of our research was on the examined lower size (50-1000µm) range as the larger pieces (1000-5000µm) were typically not found in the water column samples but rather, almost exclusively in the surface samples; hence, the comparison was out of scope. Most of the particles were made of 27.9% Acrylic, 27.2% PE (Polyethylene) , 23.9% PP (polypropylene) and 11.6% PS (polystyrene). Average between the two years, 60% of the total number of plastic particles found to be distributed within the 50-350μm range. We have observed that the Microplastic pollution level of the surface waters were 0.25-7.363 particles/m3 , while in the sub-surface water column on 10 meters from the surface we found 1.090- 6.60 particles/m3. Description: M.Sc.(Melit.)

2023-01-01T00:00:00Z /library/oar/handle/123456789/121569 2024-05-02T12:39:11Z 2023-01-01T00:00:00Z

Title: A novel approach to groundwater monitoring in the Maltese Islands : analysis of auto- and cross-correlation functions of ambient seismic noise Abstract: The Maltese islands, approximately 315 km2 in area with a high population density, face high levels of water stress due to low amounts of rainfall and a dependence on groundwater abstraction. Up till now, in-situ borehole readings are the only utilised method to monitor the quantitative status of groundwater in Malta. This study investigates an innovative, cost-effective approach to groundwater monitoring in an island environment; by computing cross-correlations and autocorrelations of ambient seismic noise recorded by two types of seismic stations in the Maltese islands: six broadband from the Malta Seismic Network (MSN) and six short-period from the FASTMIT network. Six years of seismic noise data was utilised from the broadband stations, and a year-long dataset was available from the short-period stations. Interstation distances in this study ranged from 3-35 km. The MSNoise program was used for the data management and processing. Seismic velocity changes (δv/v), which are possibly induced by changes in groundwater level, were detected using the Moving-Window Cross-Spectral (MWCS) technique. Both types of stations can provide similar sensitivity to the δv/v when taking into consideration appropriate filters (0.1-1 Hz and 0.3-3 Hz for the broadband and short-period stations respectively). The results demonstrate that seasonal and annual changes in the groundwater levels can be detected by changes in seismic velocity. The method works for both cross-correlation (maximum δv/v variation of ∼0.3%) and autocorrelation functions (maximum δv/v variation of ∼2%) of ambient seismic noise, the latter being an order of magnitude more sensitive. Seasonal and annual variations of the δv/v from autocorrelations of some stations were found to be more pronounced than from cross-correlations. Clear seasonal variations in δv/v were observed as a result of cross-correlations between short-period stations as well as short-period and broadband stations. The quality of the δv/v deteriorates at longer interstation distances when seasonal variations in the δv/v are less obvious. Presumably, this is because longer interstation paths tend to traverse more complex geology, different types of aquifers, or even the sea. Generally, the comparison of the δv/v with groundwater level readings from nearby boreholes show highly encouraging similarities in the seasonal variations, indicating that δv/v may be used as a proxy for monitoring groundwater levels in the Maltese islands in regions where borehole measurements are sparse. Description: M.Sc.(Melit.)

2023-01-01T00:00:00Z /library/oar/handle/123456789/121565 2024-05-02T12:38:16Z 2023-01-01T00:00:00Z

Title: Analysis of the local sea state derived through in-situ, remote sensing, and numerical model Abstract: For this study, the physical ocean data measured remotely from High Frequency Radars (HFR) and the data calculated from the SHYFEM numerical model were analysed against in-situ observations, which was carried out on two geographical scales located on the West side of the Maltese Islands, referred to hereafter as the micro and macro Areas of Study during 2020, 2021 and 2023. Within the micro AoS, the trajectories observed by Lagrangian-type SouthTEK drifters were visually compared to model-simulated trajectories. The comparision carried out is primarily a visual comparison. In terms of magnitude, for the majority of the plot model replicated quite well the magnitude of drifter’s velocity, while for a few, the model either predicted a faster or a slower moving current. In terms of direction, the model replicated quite well the drifters’ trajectory, while a few of the model-simulated trajectories did not replicate the drifters’ trajectory at all. Additionally, the 2-D temperature and salinity profiles for two transects, which were gathered using CTD sonde casts, were compared to the 2-D temperature and salinity profiles generated by the model. The temperature profiles between the two datasets indicated that the model replicated well the insitu measurements throughout each profile, with some exceptions during the seasonal transition period. With regards to the salinity profiles, the observed salinity ranged from 34.4 to 36.6 pss, with the salinity generally decreasing with increasing depth. Meanwhile, the modelled salinity ranged from 37.6 to 37.95 pss, with the salinity generally decreasing with increasing depth, although with some exceptions. Furthermore, CODE-type drifters were deployed for several days within the macro AoS. Their trajectories were then simultaneously compared in terms of surface current vector fields and magnitude. Overall, the radar successfully replicated 8 out of 10 trajectories, while the model replicated 6 out of 13 trajectories. Thus, it can be concluded that the radar replicated the drifters’ trajectories better than the model. This conclusion is based on the assumption that the drifters’ trajectories are a representation of the ground truth data while assuming a radar-simulated trajectory without any data gaps. Within both AoS, the temperature sensor on both the SouthTEK and CODE drifters also provided SST data, which were also compared to the modelled SST data. Overall, the model replicated fairly well the observed SST data however, given the scale difference between the two areas of studies, the comparison within the micro AoS visualised certain outliers, such as overestimation by the model from winter to spring, and underestimations in June and August potential due to seasonal variability and marine heatwave. Description: M.Sc.(Melit.)

2023-01-01T00:00:00Z