HYDRODYNAMIC AND TRAJECTORY MODELING TO PREDICT THE DISTRIBUTION OF PLASTIC MARINE DEBRIS AND TO TRACE THEIR RESOURCES IN INDONESIAN WATERS

• Main Author: Andri Kisnarti, Engki
• Format: Dissertations
• Language: Indonesia
• Subjects: Ilmu kebumian
• Online Access: https://digilib.itb.ac.id/gdl/view/65493
• Institution: Institut Teknologi Bandung

Transboundary plastic marine debris is an important problem in Indonesia, considering that the current circulation in Indonesian waters is influenced by the Indonesian monsoon current (Armondo) and the Indonesian throughflow (ITF). Meanwhile, research on transboundary plastic marine debris in Indonesia using ocean currents and trajectory models has not developed much and is still limited. The purpose of this study is to explain the role of density distribution and circulation dynamics of currents in Indonesian waters and examine the movement patterns of plastic marine debris: where it is collected and where plastic marine debris originates. The novelty in this research is the acquisition of understanding and knowledge about the role of dynamics of ocean currents in Indonesia in moving plastic marine debris. The methodology used in this research is the HAMburg Shelf Ocean Model (HAMSOM) numerical modeling and trajectory model. HAMSOM's hydrodynamic model was simulated under neutral year conditions for one year (2013). The simulation results analyze Indonesian waters' density distribution and currents. The current data is then used as input in the path model. The forward model is used to predict the motion distribution of plastic marine debris in the ocean, while the backward model is used to track the source of plastic marine debris in the sea. Plastic marine debris that is simulated is trash on the sea surface with a macro size (2.5 cm –1 m) and has a density smaller than the density of seawater. Plastic marine debris is considered a conservative particle that does not degrade, biodegradation, or mineralization. Chemical processes and the influence of waves on the movement of plastic marine debris are also neglected. The research results on the characteristics of the density and stability of the water column in Indonesian waters show that the density on the surface of Indonesian waters ranges from 1,017–1,023 kg m-3. Brunt Väisälä squared (N2) frequency in Indonesian waters ranges from 0.1–0.8x10-3 s-2. The maximum N2 depth in western Indonesia and the Arafura Sea occurs at 11–62.5 m, while the maximum N2 in eastern Indonesia and the Indian Ocean is 75–100 m. Therefore, the water column layer in the east of Indonesia has more stable characteristics than in the west. The results of the different, forward trajectory models simulated every month for one year show that the movement pattern of plastic marine debris follows the movement pattern of the Indonesian monsoon currents. The eastern monsoon in Indonesia is more dominant and contributes to the transboundary transport of plastic marine debris to the Pacific Ocean, Indian Ocean, and South China Sea (56%). In addition, plastic marine debris in Indonesian waters was found stranded on several Indonesian beaches, especially in May (89%). In contrast, plastic marine debris on the sea surface is also widely seen in September (93%). The forward differential trajectory model simulated for one year shows that more than half of transboundary plastic marine debris originating from Indonesia will remain in Indonesian waters (59.5%). Transboundary plastic marine debris that enters Indonesian waters from the northern border reaches 44%, while plastic marine debris originating from countries on the southern edge of Indonesia only crosses Indonesian waters, and the amount is small (2%). The simulation results of the reverse trajectory model show that the plastic marine debris found in the case study area, apart from originating from the region itself, also came from the other areas, both from Indonesia and from the Exclusive Economic Zone (EEZ) Indonesian. This shows that the dynamics of currents in Indonesian waters have an essential role in distributing the transboundary movement of plastic marine debris. The results show that Indonesia contributes to plastic marine debris in the Pacific Ocean, Indian Ocean, and the South China Sea. In addition, Indonesian waters are also a crossing point and place for plastic marine debris to be collected from Indonesia and neighboring countries.