Phytoplankton structure in the tropical port waters of Singapore

Abstract

Singapore is an island located at the confluence of the Malacca Straits, the South China Sea and the Java Sea (Figure 1). Its unique geographical position and deep waters have enabled it to grow as a thriving port city and it is currently one of the busiest ports in the world. The challenge which Singapore and other coastal cities face is how to effectively manage the coastal impacts in such a way that sustainable development can be pursued. One of the concerns is the occurrence of cultural eutrophication and harmful algal blooms. Cultural eutrophication is caused by excessive nutrient inputs which lead to the proliferation of phytoplankton. Several problems may arise, including the depletion of dissolved oxygen as the plant biomass decays and/or the production of toxins from harmful algal blooms (HABs). The incidence of eutrophication of coastal waters in South East Asia has increased dramatically in recent years, coinciding with increases in loading from domestic and industrial effluents. For example, occurrences of harmful algal blooms have been reported in Hong Kong (Lam and Ho, 1989, Ho and Hodgkiss, 1995), Philippines (Estudillo et al., 1984, Bajarias and Relox, 1996), Brunei (Jaafar et al., (1989), Papua New Guinea (Maclean, 1989), Sabah in East Malaysia (Ting and Wong 1989) and possibly the Malacca Straits of West Malaysia (Usup et al., 2002) and Indonesia (Azanza and Taylor, 2001). The need to establish baseline characteristics and to understand the potential for eutrophication is particularly important for Singapore as it continues to expand its coastal developments. The control of nutrient inputs to the coastal environment is a key factor in determining the extent of eutrophication. For Singapore, the main anthropogenic (figure presented) inputs into the coastal zone include wastewater effluents, storm runoff and vessel discharges. 100% of Singapore's population is served by modern sanitation; all wastewater (both domestic and industrial) is required to be discharged into the public sewerage system where it undergoes secondary treatment. Industrial wastewater, however, can be discharged into a watercourse (if a public sewer is not available), but it must be treated to a specified standard before discharge. Singapore has six water reclamation plants which not only treat wastewater but also reclaim water for non-potable use. However, to meet Singapore's long-term needs for the 21st century, the construction of a Deep Tunnel Sewerage System has been initiated. This consists of replacing the existing sewerage systems with two centralized, stateof-the-art, water reclamation plants to be located at either end of the island. The treated effluents from these plants will then be pumped through 5 km long outfall pipes 30 m below the sea surface, into the Straits of Singapore where they will be diluted and dispersed by currents. Another major source of nutrients into the coastal zone is storm runoff. Singapore has a land area of 650 km2 and sustains a population of about 4 million people. Most of Singapore's catchments are highly urbanized and channelized. However, to date there are few studies quantifying the amount of nutrient loading through the catchments. Major changes in the future are also anticipated given that existing estuaries will be converted to freshwater reservoirs to increase Singapore's water supply. This will have an impact on the nutrient loads from river and estuaries. In this chapter, we present an overview of the phytoplankton composition in Singapore coastal waters and their relationships with nutrient and environmental conditions. A variety of techniques were employed to determine the structure of the phytoplankton community, in addition to overall biomass levels. These include sophisticated methods, such as flow cytometry and high performance liquid chromatography (HPLC) but also traditional methods, such as microscopy and extracted chlorophyll measurements. While field measurements are important for understanding baseline conditions and explaining past trends, they are not as useful for prediction. Thus, a numerical model was also developed to serve this purpose and to assist coastal managers in the assessment of eutrophication issues.