The first assessment of surface water quality in Lksob river (Essaouira, Morocco): Physico-chemical parameters and nutrients distribution

Abstract

Rivers play a critical role in the hydrological-cycle, by transporting organic and inorganic materials to the oceans. Despite their importance, the processes driving the distribution of physicochemical parameters and nutrients in rivers, as well as the factors affecting water quality, are not fully understood, especially in semi-arid regions as Essaouira city located in the southwest of Morocco. This work is the first study conducted on the assessment of the surface water quality in Lksob River and aims to understand the functioning of this ecosystem through a spatio-temporal distribution of physicochemical parameters and nutrients. Weekly water samples were collected from March 2022 to March 2023 at seven stations from upstream station (S1) to the downstream (S7). temperature, salinity, pH, electrical conductivity, dissolved oxygen, orthophosphate, ammonium, nitrite and nitrate were measured. Our results showed spatial variations in key parameters along Lksob river. The highest water temperature (25.8 ± 0.45 °C) occurred at station S3 in summer 2022, while the lowest (14.57 ± 1.46 °C) was in winter 2023. Dissolved oxygen varied significantly and reached the highest levels (15.15 ± 0.22 mg/L) at station S1 in winter 2022 and the lowest (5.78 ± 0.82 mg/L and 6.64 ± 0.20 mg/L) at stations S5 and S2 in summer 2022. Electrical conductivity (1766 ± 998.08 μS/cm to 4211.5 ± 143.53 μS/cm) indicated moderate to high pollution according to Moroccan standards. Ammonium concentrations ranged from (10.70 ± 1.39 to 61.46 ± 2.01 μmol/L). The highest values were recorded at S2, S7, S6 during summer, and S5 during spring-winter, highlighting significant seasonal and spatial variations. Lksob River was well-oxygenated and relatively rich in nutrients compared to other studies in Morocco such as Loukkos, Tiflet and Oum Er-Rabia Rivers. These study results provide the first data on physicochemical and nutrient concentrations, enabling researchers to understand the functioning of this small river ecosystem.