Abstract
Abstract. Boracay is a top tourist island in the Philippines known for its 4-km beach with powdery white sand. Recently, abundance of green algae, an indicator of high nutrient discharge, along the coastal waters of the island had led to concerns on its water quality and prompted its closure to allow ample time for rehabilitation. This study examined the algal bloom along the coastal waters of Boracay through the determination of Normalized Difference Vegetation Index (NDVI) and Floating Algae Index (FAI). ENVI and SNAP software were used to process the satellite images of Boracay obtained from its pre-closure to its reopening. Necessary corrections such as scaling to Top of Atmospheric radiance were applied. NDVI was calculated using orthotile images to determine vegetation and FAI was calculated using Sentinel-2A images. Secondary data showed that the coliform level decreased from 1 million to 18.1 MPN per 100 mL after the rehabilitation of Boracay. Lower NDVI and FAI index values were observed during the reopening of the island. The NDVI value decreased while the FAI value slightly increased on the 1st month of closure which was late dry season. Both NDVI and FAI values increased to their maximum during early wet season and eventually decreased during the reopening of Boracay. Results showed that the abundance of algae had lowered after the rehabilitation of Boracay. However, fluctuating NDVI and FAI values showed the possible seasonal effects on the algal bloom in the island. Further studies considering the other factors on algal blooms may be done.
Highlights
1.1 Background of the StudySustainable use of water resources requires water quality monitoring and assessment
4.1 Normalized Difference Vegetation Index (NDVI) Results From the figure below, a fluctuating trend of NDVI mean values can be observed from the four datasets
The presence of algae along coastal waters of Boracay Island after its closure and before reopening was observed using the combination method of Normalized Difference Vegetation Index, an algorithm for detecting vegetation, and Floating Algae Index, an algorithm for detecting floating algae in an aquatic environment. These methods were convenient as a pair due to their common function and proved the correlation of coliform bacteria to the increasing number of algae
Summary
1.1 Background of the StudySustainable use of water resources requires water quality monitoring and assessment. A well-designed monitoring and assessment program defines existing and emerging problems and serves as a basis for formulating water quality management programs. Images from PlanetScope could provide ocean, inland sea and coastal zone color assessments with 3m resolution and multispectral bands of RGB and NIR. These bands are helpful in determining the spectral signature of the area. The amount of reflected solar radiation as a function of its varying wavelength, is considered as the identity of different features types such as water and soil. Different responses of each type can be observed on range of wavelengths using a software called ENVI which can be used to identify on the features types an object fall
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