Analysis of the Evolution of Sea Water Quality in the Spanish Coast from Satellite Images before and during a Confinement Period

Abstract

Satellite imaging, a form of remote sensing, can be used to analyse water quality, which must be monitored for proper and sustainable environmental management. This paper studies the effect of a sea traffic reduction in the Alboran Sea (Spain), analysing the changes in water quality before (from February 3rd, 2020) and during (until June 22nd, 2020) a confinement period. This was an unprecedented event in modern times and brought an interesting opportunity to study dynamics when the human impact is reduced. The study of these dynamics and the concentration levels with little human effect is important for environmental conservation purposes. We applied already existing indices using ArcGIS and ACOLITE to determine the following environmental parameters: colored dissolved organic matter (CDOM), suspended particulate matter (SPM), chlorophyll-a (Chl-a), and harmful algal blooms (HABs). Prequarantine concentration levels can reach up to 4 a(CDOM)440 (CDOM), 18 g/m3 (SPM), and 100 μg/L (Chl-a). Most prequarantine days presented an increment in either concentration level or distribution from the day before. The effects a sudden human impact has on an ecosystem which experimented reduced human influence for months were shown. On the day before the said impact (June 12th), three of the parameters were barely detected with concentration levels of mostly 2 a(CDOM)440 (CDOM), 6 g/m3 (SPM), and 25 μg/L (Chl-a), and sparse distribution. Afterwards (June 22nd), their levels went up to 4 a(CDOM)440 (CDOM), 14 g/m3 (SPM), and 1000 μg/L (Chl-a) and were distributed near the ports. The results presented in this study show that the main drivers of change when human impact was reduced were climatologic events (such as storms). Nevertheless, the importance of the human facto can be seen through the CDOM, SPM, and Chl-a plume near port areas observed the day after port activity was reactivated, June 22nd.