Monitoring Tangier (Morocco) coastal waters for As, Fe and P concentrations using ESA Sentinels-2 and 3 data: An exploratory study

Abstract

An exploratory study is presented to investigate human activities pollution in the coastal waters of a popular tourist destination in the west coast of Tangier, Morocco. A series of bathing water samples were examined for arsenic (As), iron (Fe) and phosphorus (P) concentrations in the western coastal waters of Tangier. Additionally, quasi-simultaneous satellite images from Sentinels-2 and 3 were processed to retrieve water leaving reflectances in the same locations. The bathing water samples showed high concentrations of As, P and Fe in the Boukhalef River mouth and in two nearby beaches; Jbila and Sidikacem, which appeared closely correlated with Sentinel-3 reflectances at bands 6 (560 nm) and 7 (620 nm). Since algorithms for Chlorophyll-a and Total Suspended Matter Concentrations rely on these wavelengths, they too were found to be closely related to high As, Fe and P concentrations. Therefore, caution must be taken when analysing these level-2 products in close proximity to the Boukhalef River mouth, since results may be biased due to the presence of significant As, Fe and P concentrations. In this case, Sentinel data proved to be a potentially useful tool with prospects to be used for monitoring environmental hazardous substances such as metals (e.g. As and Fe) spatial distributions in the west coast of Tangier, Morocco.