Framework for system understanding (DPSIR)

Practical Applications

Within the BwN programme, the DPSIR tool was applied to a Singapore case to structure information on environmental risks and impacts ensuing from various activities in the coastal zone (other than dredging). Here we focus on water quality aspects, with the emphasis on pressures, state and impacts.

The marine ecosystems of Singapore are exposed to pressures resulting from a large number of human activities, such as land reclamation and coastal protection works. Around Singapore, marine ecosystems such as sea grass meadows, coral reefs and mangroves are in decline, possibly as a result of altered hydrodynamic, sedimentation and turbidity patterns in the coastal waters. Ecodynamic infrastructure development, aimed at maximising the potential of the local ecosystems, are taken to improve the status of these ecosystems.

Furthermore, the quality of the marine waters around Singapore is key to the ecosystem health. Poor water quality may hamper the recovery of ecosystem elements, and reduce or annihilate the effectiveness of ecodynamic infrastructure development. The actual water quality is therefore important to put BwN-measures in the right context. Water quality factors considered in Slijkerman et al. (2011) are contamination and nutrient status. The DPSIR framework was used to structure information on water quality for each aspect by structuring the information via the DPSIR elements. By doing this, the most relevant relationships between activities and ecosystem impacts could be designated through water quality aspects.


Singapore has a highly developed and successful free-market economy. The economy depends heavily on exports, particularly in consumer electronics, information technology products, pharmaceuticals, and on a growing service sector (CIA 2009). The Port of Singapore, one of the world’s largest in terms of shipping tonnage, is key to Singapore’s prosperity and economic health (EIA 2007). All these activities will exert pressures on the environment (see Table below). Drivers in Singapore affecting water quality can be onshore or offshore based. Land-based activities responsible for nutrient emissions are e.g. sewage treatment plants, but indirect emissions from agricultural activities, entering the coastal waters via Singaporian or Malaysian rivers, are important to consider. Aquaculture and shipping are the main activities for nutrient emissions offshore. The input of contaminants to the environment relates to many activities. Depending on the compound, specific sources can be identified.

Oil refineries and petrochemical industryX 
Desalinitation facilitiesX 
Port activityX 
Wastewater treatment plantsX 
Coastal reconstruction & Land reclamation, including land fillsX 
Construction of dams (and causeways)X 
Land based activity (includes various activities that contribute via run off and atmospheric deposition) XX
Overview of activities in Singapore and (potential) related pressures on water quality.


Pressures are defined here as the stresses human activities exert on the environment. Pressures can be described in terms of habitat damage or loss, due to e.g. smothering, underwater sound, marine litter, contamination or nutrient enrichment. In Slijkerman et al. (2011) only pressures related to chemical water quality are addressed, the aim of the study being to assess the impact of water quality deterioration due to human activities on the local coastal ecosystems. The main pressures known to determine the quality of the marine environment of Singapore are listed in the Table below and described in chapter 3 of Slijkerman et al. (2011). It should be noted that information on pressures, thus the actual emissions to the environment per activity, is limited and a comprehensive overview is therefore not provided in the report.

PressuresNutrient levelHeavy metalsPhenolsPOPsPAHsAntifouling compoundsEcosystemsContaminants in biota
Nutrient enrichmentxx
Antifouling compounds inputxxx
Heavy metals inputxxx
PAH’s inputxxx
POP’s inputxx
Petrochemical inputxxxx
Table showing the effect of different Pressures on the different State parameters that influence water quality and ecosystem health. POP’s stand for Persistent Organic Pollutants such as pesticides, PAH’s stand for Polycyclic Aromatic Hydrocarbons


 The state of Singapore’s marine environment can be described by several state descriptors. A number of such state descriptors and the related impacts are presented in the table below. Extensive information of the state of the marine environment of Singapore regarding nutrient levels, contaminant concentrations (in water, sediment and biota) and ecosystems can be found in Slijkerman et al. (2011). As studies on state and contamination are relatively recent and isolated, no historical trends could be deduced. Note that most reported studies were performed in 2000-2006, so the actual water quality may differ from the reported one.

StateImpact eutrophicationImpact Contamination*Impact biota**
Heavy metals XX
Phenols XX
Antifouling compounds XX
Ecosystems X 
Contaminants in biota** X 
State descriptors for Singapore waters, including the related Impact. *Contaminations of water and sediment (i.e. state descriptor) could lead to contamination effects and/or contaminants in biota (i.e. impact). ** Contaminants could be measured in water, sediment and/or biota as State descriptors. In Slijkerman et al., (2011) indicators are provided.


Nutrient influxes may stimulate primary production that in turn may lead to an increase in phytoplankton biomass and sustain elevated levels of phytoplankton standing crop. Further nutrient increase can lead to the formation of Harmful Algal Blooms (HABs) and subsequent oxygen depletion. The magnitude and extent of the impacts of nutrient enrichment in Singapore’s coastal waters is usually determined by complex local factors. Toxicity effects observed in the marine environment of Singapore could be attributed to different contaminants, such as heavy metals, petroleum compounds and organotin compounds.

Due to the limited availability of local information on impacts of water quality aspects, additional evaluations were performed to fill in data gaps. Interviews with local experts were held and an environmental risk assessment for both nutrient state and contaminant state was carried out. Interviewed experts generally agreed that turbidity and sedimentation are the most important factors affecting the viability of coral reefs and sea grass meadows, but water quality may also be an important factor. So far, the latter has not been considered extensively, by lack of data. Chemical water quality aspects (nutrients, heavy metals and other toxic compounds ) are considered less important, but an overview of concentrations of pollutants and their effects is lacking and conclusions cannot easily be drawn.

In Slijkerman et al. (2011) the evaluation of possible impacts of nutrients enrichment in the Singapore marine environment was performed using two approaches: ASSETS and OSPAR. Both assessments were strongly hampered by the limited data availability, but it was concluded that for the entire Johor Strait the susceptibility to eutrophication remains high. The analysis indicates that the situation in Singapore Strait is likely to worsen. A relative increase in nutrients originating from a much larger region and numerous river inputs is to be expected. This may increase the impact of eutrophication. Only if pressures (over a much wider area than the Singapore region alone) are reduced and natural biological communities have the opportunity to recover, the situation may improve.

The evaluation of the impact of contaminants is performed using the PEC/PNEC approach . This methodology is commonly used as a first tier in ecotoxicological studies. This first-tier environmental risk assessment leads to the conclusion that the marine environment of Singapore faces a high risk to be affected by water quality, as reported in various scientific references. Especially the alkylphenol concentrations are of serious concern, as calculated risk factors are extremely high. No risk of heavy metals is to be expected, and PAHs are of minor concern. TBT risk factors are high, but due to the ban on TBT-containing paints, this risk will phase out with time.

Since the lack of data made it impossible to assess the water quality impacts very well, the Response element in the DPSIR framework is not addressed in Slijkerman et al. (2011). The Response element deals with questions such as “What are we doing about it, or what can be done about it?” and reflects the societal and political response to the previous element in the framework. One societal response to the issue of water quality in the Singapore coastal waters would be better regulation, but this requires much more information than presently available.