Spatiotemporal evolution of the physicochemical parameters of the waters of the Oum Errabiaa watershed dams (Morocco)

Abstract

This study was conducted to determine the characteristics of the physicochemical parameters of the water of the dams of the Oum Errabiaa watershed during flood and low water periods. Data were collected by water sampling and measurements performed in the various dams from 2016 to 2021. The results showed that the water temperature varied from 11.77 °C to 30.20 °C, depending mainly on the sunshine. The water was alkaline with an average pH of 8.23 and had a weak to high electrical conductivity (143-3180 µS/cm). The water was relatively well oxygenated at the surface and oxygen depleted in depth (1.44 – 15.04 mg/L). The average concentration of suspended solids (SS) was 19.76 mg/L, indicating that the dam water is relatively unpolluted. The average values of nutrients, NH 4 + , NTK and NO 3 - of 0.18 mg/L, 0.53 mg/L and 3.51 mg/L, respectively, were in compliance with the WHO guidelines for drinking water production. The average concentration of SO 4 2- was 90.60 mg/L, which is considered high, exceeding the World Health Organization (WHO) water quality standard of 50 mg/l. The average chlorophyll a was 5.51 µg/L, which is considered to be low to moderate in dams. Overall, the Oum Errabiaa’s water dams of watershed have good physicochemical quality, except for the high concentration of sulfates. This pollution is likely due to agricultural and industrial activities in the watershed. The use of multivariate techniques (ACPN) enabled us to define the origin of nutrients through surface inputs, on the one hand, and through the photosynthetic activity of cyanobacteria, on the other hand.