Assessment of seasonal variations in physico-chemical indicators of irrigation water affected by macroalgae-induced eutrophication

To identify the factors responsible for eutrophication of the waters of two irrigation basins by the macroalgae Cladophora glomerata, present in a covered basin, and Chara vulgaris, present in an open basin, a novel periodic monitoring program was implemented in Morocco. A comparative analysis of the concentrations of different chemical elements in the water of the two basins was carried out within this framework. In order to account for the spatiotemporal variability of the measured parameters, the monitoring campaign, carried out from March 1, 2021, to March 1, 2022, relied on rigorous surveys and monthly sampling. The results indicated that nitrate concentrations in the first basin ranged from 3.08 ppm in winter to 4.72 ppm in summer, while in the second basin they ranged from 3.09 ppm in winter to 4.05 ppm in summer. Phosphorus concentrations in the first basin reached 6.78 ppm during winter and increased to 11.42 ppm during summer. By contrast, phosphorus levels were lower in the second basin, at 2.048 ppm in autumn and 3.5 ppm in summer. High concentrations of potassium were recorded in both tanks. In the Cladophora glomerata basin, potassium levels reached 146.16 ppm in winter and 191.66 ppm in summer. Concentrations were significantly higher in the Chara vulgaris basin, reaching 278.6 ppm in winter and 463.33 ppm in summer. The sustained presence of nutrients at high and relatively constant concentrations, combined with optimal sunlight conditions and poor maintenance practices, has encouraged the annual growth and persistence of these two species of macroalgae. Consequently, it is essential to implement pre-treatment measures before using this water for irrigation. It is also necessary to intervene at the source of these ponds and control the proliferation of harmful macroalgae to mitigate their negative impact on aquatic ecosystems.