Assessment of water quality with emphasis on trophic status in bathing areas from the central-southern coast of Cuba

Abstract

Bathing water quality has become a matter of concern due to health risks. This study sought to assess water quality in bathing areas from the southeastern coast of the Cienfuegos province, Cuba. Certain physical, chemical, and biological parameters (salinity, temperature, pH, oxygen saturation, N-NH₄⁺, N-NO₂^-, N-NO₃^-, P-PO₄^3-, COD, BOD₅, fats and oils, chlorophyll-a, thermotolerant and total coliforms, and phytoplankton) were measured on five beaches during 2019-2020 in both rainy and dry seasons. A water quality index (WQI) was calculated using the the results of an eutrophication index (EI) and subsequently analyzed. Cluster analysis (CA) and principal components analysis (PCA) were conducted to interpret water quality variations. The WQI values ranged between fair and good, with significant differences between seasons. Multivariate analyses demonstrated the influence of river contributions on water quality indicators based on the results of the CA and the first principal component (PC1) correlated with Sal, DO, total and thermotolerant coliforms, and certain nutrients. PCA also reflected the increase in BOD₅ levels during the summer based on PC2, while the PC3 correlated with COD and response parameters (chlorophyll-a and phytoplankton) were linked to the trophic status. The assessment of trophic status showed non-eutrophic conditions. The abundance and diversity of phytoplankton in these beaches was low (128.5 x 10³ cells L^-1, total mean value), following the normative definitions of the water framework directive. Harmful algal species occurred in low numbers (1.88 x 10³ cells L^-1, total mean value), but certain species could represent a risk of dermatitis to bathers. The application of different classification schemes allowed for a comprehensive assessment of water quality in this coastal zone, helping to identify the need for monitoring and further ecological study on harmful algae species.

Descriptors: Beaches; Eutrophication; Phytoplankton; Indices; Season