Spatio-temporal analysis of algal blooms in a tropical crater-lake from MODIS data (2003-2020)

The crater lake of Santa Maria del Oro in Nayarit State presents Algal Blooms (AB) in a cyclical annual manner. The blooming and subsequent decline of these populations creates color changes in the water, generally in the first half of the year. This work evaluated supervised classification algorithms that allow these changes to be identified using data from the MOD09GQ and MYD09GQ products of MODIS sensor in the period from January 2003 to December 2020. Based on a review of AB recorded in the literature and statistical analysis of dispersion graphs, a database of spectral information and lake color state labels was created to evaluate the different classification algorithms. The best classifier was Random Forest with an accuracy of 83.3%. The temporal analysis and spatial evaluation of the blooms incidence showed that May, April and March are the months with the greatest presence of color changes related to AB in the lake. The spatial analysis found that the highest incidence of blooms occurs in the southeast region of the lake and the the greatest number of events occurred in the years 2011, 2008 and 2012, respectively. The influence of the El Nino-Southern Oscillation (ENSO) phenomenon on the incidence of algal blooms in the crater lake is determined by the temporal pattern between the anomalies in the AB and the Multivariate ENSO Index, where the greater number of AB events occurred in the cold phases of the ENSO.