Impact of Glyphosate Use on Agricultural Lands Upstream of the Oudahay, Goloza and Tada Water Retention Dams on Aquifer Biodiversity in the Mayo-Tsanaga in the Sahelian Mountainous Zone of Cameroon

Abstract

The intensive use of glyphosate in agriculture raises concerns about its impacts on aquatic ecosystems, particularly upstream of water retention dams. This study analyzes the consequences of glyphosate use on the aquifer biodiversity of the Oudahay, Goloza, and Tada dams, located in the Mayo-Tsanaga region of Cameroon. Physicochemical analyses of the water show that glyphosate concentrations are high upstream (20-21 µg/L) but decrease downstream (5.8-6.0 µg/L), indicating significant agricultural leaching upstream of the dams and progressive dilution downstream. Water temperatures are higher upstream (29.5-30.0°C during the day and 24.2-24.5°C at night) than in the downstream parts of the dams (27.5-27.8°C during the day and 22.8-23.0°C at night), indicating a thermal impact linked to changes in vegetation cover revealed by the Shannon index (H') lower upstream (1.4-1.5) than downstream (2.7-2.8), indicating a reduced species diversity under the effect of glyphosate. The total abundance of macroinvertebrates follows the same trend: it is lower upstream (160-180 individuals/m²) and higher downstream (450-460 individuals/m²). The lethal concentration 50 (LC50), which indicates the dose of glyphosate that kills 50% of exposed individuals, is lower for Daphnia magna (0.8-1.5 mg/L) and freshwater shrimp (2.8-4.2 mg/L), revealing their greater sensitivity. Fish such as Oreochromis niloticus show higher tolerance (6.2-9.8 mg/L), although sub-lethal effects have been observed. Total bacterial density is higher in Goloza (4.5 × 10⁵ CFU/mL), which may be attributed to increased organic contamination and the presence of glyphosate. Further studies are needed to analyze the long-term bioaccumulation of glyphosate in sediments and aquatic fauna.

Keywords: Glyphosate, aquifer biodiversity, reservoir dams, agricultural pollution, Mayo-Tsanaga