Assessing the relationship between river water pollution and the LULC composition of a basin in the Isthmus of Tehuantepec in Oaxaca, Mexico.

Water pollution originating from land use and land cover (LULC) can disrupt river ecosystems, posing a threat to public health, safety, and socioeconomic sustainability. Although the interactions between terrestrial and aquatic systems have been investigated for decades, the scale at which land use practices, whether in the entire basin or separately in parts, significantly impact water quality still needs to be determined. In this research, we used multitemporal data (field measurements, Sentinel 2 images, and elevation data) to investigate how the LULC composition in the catchment area (CA) of each water pollution measurement station located in the river course of the Los Perros Basin affects water pollution indicators (WPIs). We examined whether the CAs form a sequential runoff aggregation system for certain pollutants from the highest to the lowest part of the basin. Our research applied statistical (correlation, time series analysis, and canonical correspondence analysis) and geo-visual analyses to identify relationships at the CA level between satellite-based LULC composition and WPI concentrations. We observed that pollutants such as nitrogen, phosphorus, coliforms, and water temperature form a sequential runoff aggregation system from the highest to the lowest part of the basin. We concluded that the observed decrease in natural cover and increase in built-up and agricultural cover in the upper CAs of the study basin between the study period (2016 to 2020) are related to elevated WPI values for suspended solids and coliforms, which exceeded the allowed limits on all CAs and measured dates.

Heavy metal bioaccumulation in Oreochromis niloticus from Tenango Dam, Puebla, Mexico.

Oreochromis niloticus was used to determine the effects of heavy metals and their concentration in aquatic environments. Its wide distribution, resistance, and economical importance make it a suitable biomonitor. The present study was conducted in the Tenango Dam (Puebla, Mexico) to determine water quality and its impact on O. niloticus, a species that is cultured and commercialized in this area. Five samples were collected over 1 year to evaluate the water's physicochemical parameters (temperature, dissolved oxygen, pH, and hardness) and metal contents (cadmium, chromium, copper, and lead). Metal concentrations, bioconcentration factors, and metallothionein levels were also assessed in O. niloticus livers and muscle tissues. Water and tilapia quality were estimated according to current Mexican guidelines. Results indicated that the water's physicochemical parameters were within acceptable ranges. Metal concentrations, however, suggested that this resource was not suitable for urban use. Moreover, metal levels in fish tissues exceeded the acceptable limits during two periods, rendering it unsuitable for human consumption. The bioconcentration factor indicated that the metals can potentially accumulate in organisms. Furthermore, metallothionein levels in liver and muscle showed a direct correlation with metal concentrations in these tissues. This is the first study to use tilapia as an indicator of contamination in the Tenango Dam, and also the first to describe the presence of metals in this water body.