Abstract
The last few decades have witnessed a tremendous increase in nutrient levels (phosphorus and nitrogen) in coastal water leading to excessive algal growth (Eutrophication). The presence of large amounts of algae turns the water’s color into green or red, in the case of algal blooms. Chlorophyll-a is often used as an indicator of algal biomass. Due to increased human activities surrounding Dubai creek, there have been eutrophication concerns given the levels of nutrients in that creek. This study aims to map chlorophyll-a in Dubai Creek from WorldView-2 imagery and explore the relationship between chlorophyll-a and other eutrophication indicators. A geometrically- and atmospherically-corrected WorldView-2 image and in-situ data have been utilized to map chlorophyll-a in the creek. A spectral model, developed from the WorldView-2 multispectral image to monitor Chlorophyll-a concentration, yielded 0.82 R2 with interpolated in-situ chlorophyll-a data. To address the time lag between the in-situ data and the image, Landsat 7 Enhanced Thematic Mapper Plus (ETM+) images were used to demonstrate the accuracy of the WorldView-2 model. The images, acquired on 20 May and 23 July 2012, were processed to extract chlorophyll-a band ratios (Band 4/Band 3) following the standard approach. Based on the availability, the 20 May image acquisition date is the closest to the middle of Quarter 2 (Q2) of the in-situ data (15 May). The 23 July 2012 image acquisition date is the closest to the WorldView-2 image date (24 July). Another model developed to highlight the relationship between spectral chlorophyll-a levels, and total nitrogen and orthophosphate levels, yielded 0.97 R2, which indicates high agreement. Furthermore, the generated models were found to be useful in mapping chlorophyll-a, total nitrogen, and orthophosphate, without the need for costly in-situ data acquisition efforts.
Highlights
Anthropogenic activities have a direct and indirect impact on the environment [1]
The results indicate that the approach used for chlorophyll-a estimation using the WorldView-2 image can be reliable
Based on the obtained R-squared values shown in Table 2, the developed spectral chlorophyll-a model with three-band ratios; (Coastal blue + Near infrared 1)/Near infrared 2 was found to be most accurate
Summary
Anthropogenic activities have a direct and indirect impact on the environment [1]. One such type of water pollution is eutrophication, a case of algal bloom caused by increasing levels of nutrients [2,3].As part of the water pollution management, it is important to detect and manage pollution sources [4,5].Traditional means of monitoring nutrients and algal growth monitoring are often point based, requiring large amounts of effort in the laboratory analysis, in addition to a mathematical approach in analyzing the data [4,6]. Anthropogenic activities have a direct and indirect impact on the environment [1]. One such type of water pollution is eutrophication, a case of algal bloom caused by increasing levels of nutrients [2,3]. As part of the water pollution management, it is important to detect and manage pollution sources [4,5]. Traditional means of monitoring nutrients and algal growth monitoring are often point based, requiring large amounts of effort in the laboratory analysis, in addition to a mathematical approach in analyzing the data [4,6]. This study examines the role of nutrient pollution on algal growth in a coastal lagoon.
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