Both globally and locally on the island of Curaçao, coral reef degradation is a pressing issue. These ecosystems are threatened by climate change and pollution due to human activities. The latter mostly occurs through pollution of groundwater, elevating the groundwater concentration of nutrients such as Nitrogen (N) and Phosphorus (P). A possible route of this polluted groundwater towards the coastal areas is through submarine groundwater discharge (SGD). One of the main groundwater polluting factors in Curaçao is the leakage of N and P from onsite sewage disposal systems (OSDS). Limited data is available on these leakage processes, and how the increased nutrient concentrations reach the sea through SGD. With the reef degradation furthering, it is of high importance to gain insight into this pollution process.

The goal of this thesis was to determine the behaviour of nutrient fluxes towards the sea and the bays through SGD on Curaçao. This was done by creating a numerical model in MODFLOW6, which first determined the groundwater head distribution and flow field on Curaçao based on a variable-density model. In this model, simplifications were done and fractured flow was ignored. A nutrient model was used to simulate the current state of the nutrient levels of N and P in the groundwater resulting from leakage from OSDS, and their progression towards the coastal area. The current state and three future scenarios were performed, consisting of a pollution increase due to population growth, a pollution stop and constant pollution similar to the current state.

The scenario simulations highlighted the immediate and delayed impacts of population growth and stopped pollution on nutrient fluxes. While N-fluxes responded quickly to changes in input, P, due to its sorptive behaviour, showed a delayed response. Although the SGD is equally distributed between the bays and the sea, the nutrient fluxes are relatively higher towards the bays for the current situation (83% for N and 61% for P). In both current and future states, N-concentrations were higher than P-concentrations, due to a higher N-input rate and the sorptive behaviour of P. If leakage from OSDS stops, N as decaying is almost completely flushed out within 25 years. For N with conservative behaviour, the N flux will be reduced by 75% in 2050. For P, it will take much longer to flush out, as after 30 years the outflow is still increasing. If current pollution increases due to population growth, the N-flux increase by 13% and 12% for respectively the conservative and decay simulations. In 2050, or quickly after, the flux will reach a new constant level. Contrarily, the P-flux will continue to increase for the foreseeable future, decreasing the N:P mass ratio.

The model results provided first insights into nutrient fluxes, current pollution, and future scenarios. However, the results are subject to uncertainties because fractured flow and dual-porosity were not included, requiring careful consideration of the results. In addition, future research should refine parameters and include an uncertainty analysis. Despite these limitations, the model offered valuable insights into nutrient behaviour and the model could be employed in more realistic simulations, allowing assessment of the future of groundwater pollution and its effect on Curaçao’s coral reefs.

Curaçao's coral reefs are subjected to a deteriorating momentum risking the health and therefore sustainability of this vital ecosystem. Despite the dependency of the Island's prosperity on the condition of the ecosystem, research suggests that wastewater management is likely to be a significant contributor to this effect. Incorporating both open literature results and information obtained from an extensive constructed research network, this study demonstrates essential aspects of the urban wastewater management system of Willemstad regarding the quantity and quality of the urban wastewater fluxes and their potential environmental implications. The system, which merely connects 33\% of Curaçao's population, is concluded to be outdated and insufficient with respect to capacity as well as treatment efficiency. Although it is solely designed for pure domestic wastewater, this study concluded and demonstrated the significant impact of illegal discharge onto this system by industrial sectors leading to both high contamination loading and increased wastewater volumes. The combination of these features is the major cause of wastewater discharge pathways into marine environments. Arising from the constructed urban wastewater flux model, which visualizes the wastewater management system, 14 discharge locations correlated to significant environmental contamination pathways are identified with Piscadera Bay, Rif Mangrove area, Playa Kanoa and Shut concluded as the utmost importance. Furthermore, the model revealed that the urban wastewater is predominantly directed towards the treatment plant Klein Hofje via either the northern trajectory (Bonam - Suffisant F - Garipitoweg - Argentianweg - Klein Hofje) or the southern one (SVB - Klein Hofje). Also, the quantity and quality of the fluxes are estimated based on the connected area and the potential industrial activities within it. However, validation of these estimations is recommended since no water quantity and quality analysis was performed or available for conducting the modelled estimations. Furthermore, since the system is partly a combined sewage system, hence harvesting stormwater fluxes as well, its effect is recommended to incorporate in the model and estimations for accuracy purposes. Lastly, the government reports that at least 90\% of all industrial wastewater is discharged either directly into the ocean or onto the sewer system. Since the actual ratio as well as the water quality remains unknown this is recommended for future research. Overall, this study enables tailored future research programs to overcome the discussed limitations and with that significantly contribute to eliminating the current existing white spot concerning the effect of urban wastewater fluxes on the marina ecosystem of Curaçao.