Marine pollution includes a range of threats including from land-based sources, oil spills, untreated sewage, heavy siltation, eutrophication (nutrient enrichment), invasive species, persistent organic pollutants (POP’s), heavy metals from mine tailings and other sources, acidification, radioactive substances, marine litter, overfishing and destruction of coastal and marine habitats (McCook 1999, Nyström et al. 2000, Bellwood et al. 2004). Overall, good progress has been made on reducing Persistent organic pollutants (POP’s), with the exception of the Arctic. Oil discharges and spills to the Seas has been reduced by 63% compared to the mid-1980’ies, and tanker accidents have gone down by 75%, from tanker operations by 90% and from industrial discharges by some 90%, partly as a result of the shift to double-hulled tankers (UNEP, 2006; Brown et al., 2006). Some progress on reducing emissions of heavy metals is reported in some regions, while increased emissions are happening in others. Electronic waste and mine tailings are included amongst the sources of heavy metal pollution in Southeast Asia. Sedimentation has decreased in some areas due to reduced river flows as a result of terrestrial overuse for agricultural irrigation, while increasing in other regions as a result of coastal development and deforestation along rivers, water sheds and costal areas, and clearing of mangroves (Burke et al., 2002; McCulloch et al., 2003; Brown et al., 2006; UNEP, 2004, 2006).
A major threat beyond overexploitation of fisheries and physical destruction of marine coastal habitats by dredging, is undoubtedly the strong increase in coastal development and discharge of untreated sewage into the near-shore waters, resulting in enormous amounts of nutrients spreading into the sea and coastal zones. This, together with changes in salinity, melting sea ice, increased sea temperatures and future changes in sea currents may severely affect marine life and their ability to recover from extreme climatic
Together with agricultural run-off to the Sea or into major rivers and eventually into the ocean, Nitrogen (mainly nitrate and ammonium) exports to the marine environment are projected to increase at least 14% globally by 2030 (UNEP, 2006). In Southeast Asia more than 600,000 tons of Nitrogen are discharged annually from the major rivers.
These numbers may become further exacerbated as coastal populations are depicted to increase from 77 people/km2 to 115 people per km2 in 2025. In Southeast Asia, the numbers are much higher and the situation more severe. Wetlands and mangroves are also declining rapidly, typically by 50-90% in most regions in the past 4 decades (UNEP, 2006). All of the above, together with changes in salinity, melting sea ice, increased sea temperatures and future changes in sea currents may severely affect marine life and its ability to recover from extreme climatic events.
Also, it will severely exacerbate the effects of extreme weather and the productivity of coastal ecosystems to supply livelihoods and basic food to impoverished. Hence, the poor management of sewage not only presents a dire threat to health and ecosystems services, it may increase poverty, malnutrition and security for over a billion people.