Environmental Monitoring and Modelling

Economic growth has led to significant coastal developments such as land reclamation, port and harbour facilities, urban and industrial townships and aquaculture. To understand the impact of human activities on the marine ecosystem, a monitoring scheme and numerical models have been developed to study eutrophication, sediment transport and the fate and transport of contaminants in tropical marine waters. In addition, complementary studies in collaboration with the Department of Geography are being conducted on land-based inputs into the coastal zone, with particular emphasis on the quantification of pollutant loading from urbanised tropical catchments.

One of the major concerns of coastal ecosystems is the deterioration in water quality arising from anthropogenic inputs. In particular, the discharge of nutrients from sewerage can cause exceptional blooms of algae, which eventually lead to depletion of dissolved oxygen levels, and hence fish kills. Alternatively, some of the dominant algal species may carry toxins, which can accumulate in the food chain and eventually be consumed by humans resulting, for example, in paralytic and diarrhoetic shellfish poisoning. In Southeast Asia, harmful algal blooms (or "red tides" because of the colour imparted to the water by the algae) occur periodically in Manila Bay, the Gulf of Thailand, parts of Indonesia and Hong Kong. Singapore, like all major ports, faces the risk of introduction of new toxic species of algae into its waters via the ballast water of ships passing through the vicinity. To monitor changes in the marine environment, a baseline characterisation of water column properties in the Singapore Straits is under way, in collaboration with the Maritime and Port Authority of Singapore (MPA) (Fig. 1). Particular emphasis is placed on understanding changes in nutrients, suspended material and phytoplankton community structure as a function of environmental disturbances or pollution.

In addition to field monitoring, three-dimensional numerical models have recently been developed to predict the fate and transport of pollutants in the Singapore Straits and adjoining seas. Modelling ecosystem processes help us to conceptualise and integrate scientific knowledge for the purpose of predicting the system response to perturbations. Water quality models dealing with eutrophication and chemical spills are coupled to the hydrodynamic model, the latter providing the necessary flows under various monsoon and tidal conditions. These models serve as a management tool to address the environmental impacts of urban, industrial and vessel discharges into marine waters.

The eutrophication model predicts the fate and transport of nutrients, pathogens and suspended material in response to forcing conditions such as wind, current, temperature and light. Eleven state variables (ammonia, nitrate, phosphate, phytoplankton, zooplankton, CBOD, dissolved oxygen, organic nitrogen, organic phosphorus, coliform bacteria, and total suspended solids) and five interacting systems (nitrogen and phosphorus cycles, phytoplankton and zooplankton kinetics and the dissolved oxygen balance) are simulated (Fig. 2). Several issues are being examined, including the safety of swimming and recreational beaches in the east coast, protection of coral reefs, fisheries and aquaculture farms and the possibility of noxious or algal bloom nuisance, such as red tides.

Figure 2 : Schematic of interactions between nutrients, plankton and dissolved oxygen in the NEUTRO model

The heavy shipping traffic in the Singapore Straits also places it at risk from vessel discharges. Oil spills have occurred frequently in the Straits, with the latest spill of some 28,000 tons of marine fuel oil occurring in October, 1997. The impact of oil spills on our tropical marine environment is an issue of concern to local authorities and the general public. A chemical spill model has been developed to incorporate the interactions of the important physical, chemical and biological processes in tropical marine waters, depending on the nature of the organic chemical that is spilled. This is supported by field measurements of sensitive marine biota, which were affected by the recent oil spill (in collaboration with the Marine Biology and Biotechnology Programme, TMSI).