Sediments quality must be considered when evaluating freshwater aquatic environments used for recreational activities

Abstract

Although water quality from freshwater recreational aquatic environments (RAEs) has been long analyzed worldwide, little information is available about their sediments. The aim of this work was to study the physicochemical and bacteriological quality of water and sediment under different seasonal events. For that, Wierna River (WR) and General Belgrano reservoir (GB) were used as freshwater RAEs models. A total of 33 water and 33 sediment samples (15 from WR and 18 from GB from each phase) were collected and analyzed. Physicochemical variables in water (pH, turbidity, dissolved oxygen, temperature, conductivity, alkalinity, hardness) and sediments (organic matter, humidity, ash, and conductivity) were measured. For the bacteriological characterization, total aerobic mesophiles, total and thermotolerant coliforms, E. coli, enteroccocci, Salmonella spp., and Pseudomonas aeruginosa were evaluated using culture-based methods. Universal and human Bacteroides were also quantified by real-time PCR. Univariate (Kruskall-Wallis), bivariate (Spearman correlation), and multivariate (cluster analysis, principal component analysis) statistical techniques were applied for data analysis. All bacterial indicators were almost two-logs higher in sediments than in water, for both RAEs. Also, due to rainfall events and recreational activities, sediments were resuspended in surface water exceeding in most cases the limit values established by international regulation for bacteria. Significant correlation was observed between culturable bacteria and turbidity (p < 0.05) supporting this. We found that while physicochemical variables clustered samples by geographical location in water and sediments, microbiological aggrupation in water was mostly driven by seasonal events. No aggrupation was observed when using microbiological variables in sediments. Thus, geographical location, type of water and sediments, and seasonal events influenced on RAEs quality. Including sediment analysis during RAEs monitoring campaigns is essential as it will allow knowing the real health risk to which bathers are exposed and proposing solutions to mitigate it.