Diwata-1 images being used to monitor Manila Bay rehabilitation

Researchers from the Department of Science and Technology (DOST) are using images from the Diwata-1 microsatellite to conduct remote sensing processing and analysis of Manila Bay .

Figure 1. A portion of Manila Bay as captured by Diwata-1 on 3:24 PM using its Spaceborne Multispectral Imager (SMI)

On February 19, 2018, Diwata-1 was able to capture an image of Manila Bay using its Spaceborne Multispectral Imager – nearly a year before the rehabilitation project. Satellite data, such as in the form of images yielded by the microsatellite, can help track changes in water quality.

An analysis of turbidity, using the Formazin Nephelometric Unit (FNU) to measure water clarity, shows unmistakably turbid murky waters at the mouth of Pasig River appearing to flow out from inside the river.

Using a baseline of less than 5 FNU based from Figure 2, which generally indicates clear waters, more than 25 FNU units are shown to move out from the mouth of the river even extending inside the river.

Figure 2. Turbidity Map (February 2018) of Manila Bay using Diwata-1

Figure 2 shows that the extent of water pollution extends inland, which may point to the built-up areas inside the river as a source of pollutants. This means that residential and industrial runoffs, such as wastewater from factories, are dumped onto the river.

It is important to note that for the successful long-term rehabilitation of Manila Bay, the sources of pollution that enter the river, as well as other river systems that drain to the bay, should be identified and regulated as well.

Figure 2 also helps identify that turbid waters are also present at the shores of Bulacan and Pampanga. These turbid waters have a different origin: aquaculture.

In the figure, we can see the environmental impact of the growing demand for food to supply the growing Philippine population. To keep up with supply, masses of aquaculture farms have to be set up for intensive fish farming which is an activity commonly associated with using fish feed and fertilizers.

Unfortunately, unregulated usage of fish feed and fertilizers contaminate water resulting to the milky blue waters at the area as shown in Figure 1. These also contaminate the waters of Manila Bay.

Diversifying and promoting alternative ways for aquaculture should be explored, as limiting aquaculture activities in this area — a possible  effect of the Manila Bay Rehabilitation Project — which may lead to a food supply crisis.

Overall, it can be observed from Figure 2 the multitude of sources of the bay’s pollution. Restoring the natural environment of the bay will require efforts to reduce waste material from point sources. These sources can be easily identified by satellite images such as those provided by the Diwata microsatellites.

What exactly are the effects of water pollution in Manila Bay? For one, there is evidence of bioaccumulation of lead in fish muscles as well as deterioration in muscle fibers of the fish captured from the bay.

Mamon et al. (2016) found growth impairments to Perna viridis (green mussel), a bioindicator of water quality, due to pollution in Manila Bay. Heavy metal pollution is bad for both the ecosystem and humans as these metals are transferable when eaten. Manila Bay is one of the sources of food for many individuals who live in the area and their health may be impaired from consumption of contaminated fish captured by fishermen.

Interestingly, applying the analysis to earlier images obtained through other satellites (Landsat), showed that high turbidity reaching above baseline levels occurred at the same general areas at same month.

Figures 3 and 4 show that turbidity is not a unique event captured by Diwata-1; it is an event that is most likely have been part of the bay for a long time. The use of satellite images gives more dimension to the gravity of the rehabilitation project aimed to improve the coexistence of the environment and humans.

Figure 3. Turbidity Map (February 2016) of Manila Bay using Landsat-8 data
Figure 4. Turbidity Map (February 2017) of Manila Bay using Landsat-8 data

Satellite images, such as those provided by Diwata-1, and their capability to provide timely and periodic information are invaluable tools to help the rehabilitation project.

In ideal conditions, satellite images can help track the temporal changes of turbidity within Manila Bay helping the efforts of the government to rehabilitate the bay. With Diwata-2’s revisit capability, the government can better monitor certain high-priority areas — such as Manila Bay — to compare water quality changes over time.

Also, remote sensing is a cost-effective way to conduct large-scale assessments of water quality at the bay as both Diwata-1 and Diwata-2 can capture a large area of the bay to be used for water quality assessments.

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