# 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

Alexis Dzokom, Ezechiel Kodji, Jules Balna, Esther Laurentine Nya, Sébastien

Vondou, Felix Zieba Watang, Roger Djouldé Darman

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Alexis Dzokom, Ezechiel Kodji, Jules Balna, Esther Laurentine Nya, Sébastien Vondou, et al. 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. Sahel Nature Consulting Revue, In press, Waste Water and Pollutions, 05 (13), pp.1-24. hal-05071840

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## 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

Scientific-Article May 2025, Volume 05, Issue 13

### 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.
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Sahel Nature Consulting Revue (ISSN : 1401-0006 March 2025)

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# 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

Alexis DZOKOM<fnref n="1" />,<fnref n="2" />, Ezechiel Kodji<fnref n="3" />, Jules BALNA<fnref n="2" />, Esther Laurentine NYA<fnref n="2" />, Sebastien Vondou VONDOU<fnref n="4" />, Felix Zieba WATANG<fnref n="2" />, Roger Djouldé DARMAN<fnref n="5" />

## 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/m<fnref n="2" />) and higher downstream (450 - 460 individuals/m<fnref n="2" />). 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

## 1. Introduction

The use of glyphosate-based herbicides in agricultural practices raises major concerns regarding their environmental effects, particularly on the aquifer biodiversity of ecosystems located downstream of cropland (Benbrook, 2016; Dzokom et al., 2025a,b; Dzokom et Darman, 2025; Dzokom et Kodji, 2025a,b; Dzokom, 2025a,b; Dzokom, 2025). Glyphosate, the active ingredient in many commercial herbicides, is widely used for weed control in intensive and semi-intensive agriculture. Its excessive use in areas upstream of the

Oudahay, Goloza, and Tada reservoir dams in Mayo-Tsanaga, a Sahelian mountainous region in the Mandara Mountains of Cameroon, raises questions about its ecotoxicological consequences on aquatic environments (Duke & Powles, 2008a,b). Water retention dams play a fundamental role in drinking water supply, irrigation, and the preservation of local aquatic ecosystems. However, contamination of these waters by glyphosate residues and its metabolites, particularly aminomethylphosphonic acid (AMPA), can have adverse effects on aquatic flora and

<footnote n="1">¹SAHEL NATURE CONSULTING</footnote>

<footnote n="2">²Department of Geography, Faculty of Arts Letters and Social Sciences, University of Maroua, Cameroon</footnote>

<footnote n="3">³Département de Sciences environnementales, École Nationale Polytechnique de Maroua, Université de Maroua, Cameroun</footnote>

<footnote n="4">⁴Institut de Recherche Agricole pour le Développement de l'Extrême-Nord, Kousseri, Cameroun</footnote>

<footnote n="5">⁵Department of Agriculture Animal Husbandry and By-Products, Faculty of Sciences, University of Garoua, Cameroon</footnote>
fauna (Annett et al., 2014). Several studies have demonstrated direct toxicity of glyphosate on aquatic organisms, including fish, amphibians, and aquatic invertebrates, as well as indirect effects through disruption of food chains (Relyea, 2005).

In the Sahelian context, particularly in mountainous areas, where the resilience of aquatic ecosystems is already severely tested by arid climatic conditions and marked hydrological variations, intensive use of glyphosate could exacerbate the degradation of aquatic biodiversity (Battaglin et al., 2014; Dzokom et al., 2025a,b; Dzokom et Darman, 2025; Dzokom et Kodji, 2025a,b; Dzokom, 2023a,b; Dzokom, 2025). It is therefore crucial to assess residual glyphosate concentrations in these reservoirs and their impacts on aquatic communities in order to better regulate its use and limit its harmful effects on the environment and human health.

This study therefore aims to analyze the impact of glyphosate use on the aquifer biodiversity of the Oudahay, Goloza, and Tada dams by highlighting the direct and indirect effects on aquatic ecosystems, while proposing ecologically viable alternatives for sustainable water resource management in the Mayo-Tsanaga region.

## 2. Materials and Methods

### 2.1. Study Area

The study was conducted in the Mayo-Tsanaga department, in the Far North region, located in the mountainous Sahel region of Cameroon. The Oudahay, Goloza and Tada water retention dams constitute essential hydraulic infrastructures for irrigation, drinking water supply and the preservation of local aquatic ecosystems (Folegot et al., 2018; Folegot et al., 2019). These reservoirs are located downstream of agricultural areas where glyphosate is commonly used for weed control in food and cash crops.

<figure><img src="image_8.png" /><figcaption>Figure 1: Study Area</figcaption></figure>
The Sahelian climate is characterized by a prolonged dry season and a short rainy season, influencing the hydrological dynamics of watersheds (Lienou, 2007). The hydrology of the dams studied is highly dependent on rainfall and upstream agricultural activities, making them sensitive to pesticide contamination.

## 2.2. Glyphosate Sampling and Analysis

### 2.2.1. Water Sample Collection

Water samples were collected monthly over a 12-month period (January to December 2024) to assess seasonal fluctuations in glyphosate residues. Three sampling points were defined at each dam:

* Upstream Zone: Entry point for agricultural flows,

* Central Zone: Middle of the dam,

* Downstream Zone: Dam outlet.

Samples were collected using high-density polyethylene bottles previously rinsed with ultrapure water, following the recommendations of Meyer *et al.* (2009). Samples were transported on ice and stored at 4°C before analysis.

<figure><img src="image_9.png" /><figcaption>Photo 1: Sampling</figcaption></figure>

### 2.2.2. Glyphosate Detection and Quantification

The concentration of glyphosate and its main metabolite, aminomethylphosphonic acid (AMPA), was measured using high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS), a widely used method for pesticide detection in natural waters (Battaglin *et al.*, 2014). The detection limit was 0.1 µg/L.

## 2.3. Aquatic Biodiversity Analysis

### 2.3.1. Macroinvertebrate Inventory and Aquatic Bioindicators

The impact of glyphosate on aquatic biodiversity was assessed through the study

of benthic macroinvertebrates, which are bioindicators sensitive to chemical contaminants (Bélanger *et al.*, 2013). Sampling was carried out using the Kick Sampling method (Rosenberg & Resh, 1992), using a net over a 10-meter length per sampling site. The collected organisms were identified using the identification keys of Wessell *et al.*, 2008

### 2.3.2. Fish and Amphibian Toxicity Assessment

Ecotoxicological tests were conducted on Oreochromis niloticus fish and Xenopus laevis tadpoles under controlled laboratory exposure to glyphosate. The following parameters were measured:

* Survival rate,

* Developmental abnormalities,

* Oxidative stress enzyme activity (catalase, glutathione peroxidase), according to the protocols of Glusczak *et al.* (2006).

## 2.4. Statistical Data Analysis

The results were processed using R software (version 4.1.2). A one-way ANOVA was used to compare glyphosate concentrations between the three sampling areas, and a Pearson correlation test was applied to assess the relationships between glyphosate concentrations and aquatic biodiversity (Zuur *et al.*, 2009).

## 3. Results and Discussion

### 3.1. Glyphosate and Residues Concentrations in Dam Waters

Glyphosate negatively impacts water quality, with acidification, decreased dissolved oxygen, and elevated conductivity upstream. The impact on aquatic biodiversity is evident through a reduced Shannon index, confirming major ecological stress. Ecological recovery downstream shows that glyphosate reduction is essential for preserving biodiversity. The table below presents the
environmental data collected upstream, in the center, and downstream of the Oudahay, Goloxa, and Tada dams.

<figure><img src="image_10.png" /><figcaption>Figure 2: Environmental parameters of dam water</figcaption></figure>

**3.1.1. Glyphosate concentration and its impact on water quality**

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. According to de Castilhos et al., 2020, concentrations above 10 µg/L are toxic to aquatic ecosystems, particularly affecting biodiversity and water oxygenation. Upstream, high concentrations disrupt aquatic fauna, reduce microbial activity, and impair the natural
degradation of organic matter. Downstream, glyphosate biodegradation and sedimentation contribute to improving water quality.

### 3.1.2. pH and Dissolved Oxygen: Signs of Pollution

The upstream pH (6.7-6.9) is slightly acidic, which could be attributed to glyphosate residues and herbicide breakdown products (ammonium and AMPA). Downstream, the pH is more neutral (7.4-7.5), indicating ecological recovery.

Dissolved oxygen is lower upstream (4.0-4.2 mg/L) and higher downstream (6.6-6.8 mg/L), consistent with the trends observed by Peruzzo et al. (2008), who showed that glyphosate causes secondary eutrophication and increased oxygen consumption due to the degradation of organic matter. Low dissolved oxygen upstream limits the survival of sensitive aquatic organisms. Increased dissolved oxygen downstream demonstrates better ecological recovery with lower toxic pressure.

### 3.1.3. Temperature and Conductivity: Indicators of Aquatic Stress

Water temperatures are higher upstream (29.5-30.0°C during the day and 24.2-24.5°C at night) than downstream of the dams (27.5-27.8°C during the day and 22.8-23.0°C at night), indicating a thermal impact related to changes in vegetation cover caused by intensive agriculture. Conductivity is higher upstream (350-360 µS/cm) than downstream (250-260 µS/cm), suggesting an increased presence of dissolved salts and agricultural contaminants upstream. Higher temperatures promote the volatilization of toxins and alter the metabolism of aquatic organisms. High conductivity is an

indicator of organic and inorganic pollution, confirming the influence of agricultural activities.

### 3.1.4. Shannon Index: Alteration of Aquatic Biodiversity

The Shannon Index (H') is lower upstream (1.4-1.5) than downstream (2.7-2.8), indicating reduced species diversity due to glyphosate. According to Pesce and Wunderlin (2000), an H' below 2 is synonymous with serious ecological disturbance. Here, the gradual increase in the index downstream suggests that aquatic biodiversity is gradually recovering thanks to the reduction in glyphosate concentrations.

Ban the use of glyphosate near dams and adopt sustainable agricultural practices. Implement continuous water monitoring to assess the impact of pesticides. Promote reforestation programs to limit erosion and diffuse pollution.

## 3.2. Harmful and Beneficial Chemical Elements in Dam Waters

### 3.2.1. Glyphosate

Glyphosate concentrations are high upstream of dams, gradually decreasing in the center and downstream. This indicates accumulation and leaching of agricultural chemicals, particularly upstream of dams, which can cause long-term pollution of aquatic environments. High glyphosate concentrations can disrupt aquatic flora and fauna, particularly algae and macroinvertebrates, which are sensitive to chemicals (Gauthier et al., 2008). The concentrations observed upstream (over 20 µg/L) are above the toxicity thresholds recommended by WHO (2016) for safe water quality.
<figure><img src="image_11.png" /><figcaption>Figure 3: Harmful and beneficial chemical elements in dam waters</figcaption></figure>

### 3.2.2. Ammonium ($NH_4^+$)

Ammonium concentrations are higher upstream of dams, which can be attributed to organic pollution (fertilization residues May 2025, Volume 05, Issue 13

and biomass decomposition). This concentration decreases downstream, suggesting natural water dilution. Ammonium is an element that can lead to eutrophication and a decrease in aquatic
biodiversity. According to Schindler (2006), concentrations above 0.5 mg/L can cause a sharp decrease in dissolved oxygen and disrupt biological cycles in aquatic ecosystems.

### 3.2.3. Nitrates ($NO_3^-$)

Nitrates follow a similar pattern to other pollution parameters, with higher concentrations upstream and a decrease downstream. Nitrates mainly come from agricultural fertilizers used on cultivated land upstream of dams. High nitrate concentrations in water can promote excessive algae growth (eutrophication), which disrupts water quality and can cause dead zones where oxygen is depleted. Critical thresholds for aquatic biodiversity are often above 1 mg/L (WHO, 2003).

### 3.2.4. Phosphorus ($PO_4^{3-}$)

Phosphorus is generally present in small amounts but remains a key parameter in agricultural pollution. Concentrations decrease from upstream to downstream, suggesting a natural dilution process as water flows. Phosphorus is a crucial element for the growth of aquatic plants and algae. However, excessive levels of phosphorus can cause algal blooms, thereby reducing aquatic biodiversity and affecting ecosystem balance (Carpenter, 2008). The figure below presents data on harmful and beneficial chemical elements in the waters of the Oudahay, Goloz, and Tada dams, collected upstream, in the center, and downstream of the dams.

### 3.2.5. Calcium and Magnesium

Calcium and magnesium concentrations are relatively constant, but there is a slight downward trend downstream of the dams, which could indicate a dilution phenomenon or mineral precipitation in the water. These elements are essential for the formation of shells and skeletons of aquatic organisms. A significant decline could affect populations of mollusks and other calcareous organisms (Yang et al., 2023).

### 3.2.6. Sodium ($Na^+$)

Sodium is primarily influenced by agricultural waste and fertilization practices. Concentrations are higher upstream, which could affect water salinity. High sodium concentrations can adversely affect water quality by disrupting the osmotic systems of aquatic organisms and affecting aquatic flora and fauna (Brown et al., 2012).

## 3.3. Comparison of chemical element concentrations in dam water

### 3.3.1. Glyphosate and AMPA contamination

Glyphosate concentrations significantly exceed the WHO recommended standard (0.7 mg/L) in all study areas, particularly upstream of the dams. The table below presents data on the concentration of glyphosate and its residues in the waters of the Oudahay, Goloz, and Tada dams.

<table><caption>Table 1: Chemical element concentrations (mg/L) in dam waters</caption><thead><tr><th>Chemical Element</th><th>Dam</th><th>Upstream</th><th>Middle</th><th>Downstream</th><th>WHO Standard (mg/L)</th></tr></thead><tbody><tr><td rowspan="3">AMPA (metabolite)</td><td>Oudahay</td><td>1.6 ± 0.4</td><td>1.2 ± 0.3</td><td>0.8 ± 0.2</td><td rowspan="3">0.5</td></tr><tr><td>Goloz</td><td>1.9 ± 0.5</td><td>1.4 ± 0.4</td><td>0.9 ± 0.3</td></tr><tr><td>Tada</td><td>1.7 ± 0.4</td><td>1.3 ± 0.3</td><td>0.8 ± 0.2</td></tr><tr><td rowspan="3">Dissolved Oxygen (O<sub>2</sub>)</td><td>Oudahay</td><td>5.2 ± 0.8</td><td>6.1 ± 0.7</td><td>7.3 ± 0.6</td><td rowspan="3">6.0 - 8.0</td></tr><tr><td>Goloz</td><td>4.8 ± 0.7</td><td>5.9 ± 0.6</td><td>7.1 ± 0.5</td></tr><tr><td>Tada</td><td>5.0 ± 0.7</td><td>6.0 ± 0.6</td><td>7.2 ± 0.5</td></tr></tbody></table>
These values are comparable to the results of Battaglin et al. (2014), who demonstrated that intensive agriculture contributes significantly to glyphosate pollution of surface waters.

The metabolite AMPA, although generally less toxic than glyphosate, remains a concern, with concentrations reaching 1.9 mg/L upstream of the Golozan dam. This confirms the results of Meyer et al. (2009), who observed high persistence of AMPA in aquatic environments. The decrease in glyphosate and AMPA concentrations from the center to downstream suggests a dilution and biodegradation process in the reservoir. However, the high AMPA levels indicate that glyphosate degradation is slow, which may prolong its ecotoxicological effects on aquatic fauna.

### 3.3.2. Impact on Water Quality and Aquatic Biodiversity

The results show that glyphosate use upstream of the Oudahay, Golozan, and Tada dams has a significant toxic impact on aquatic organisms, with more pronounced effects in Golozan. The most affected species are *Daphnia magna* and *Macrobrachium rosenbergii*, which play a key role in the aquatic food chain. These results suggest the need to regulate glyphosate use and adopt more sustainable agricultural practices to protect aquatic biodiversity.

#### 3.3.2.1. Glyphosate Toxicity and LC50

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 tilapia (*Oreochromis niloticus*) show higher tolerance (6.2–9.8 mg/L), although sub-lethal effects have been observed

<table><caption>Table 2: Glyphosate toxicity to aquatic organisms in the Oudahay, Golozan, and Tada dams</caption><thead><tr><th>Organism</th><th>Sampling Site</th><th>LC<sub>50</sub> (mg/L)</th><th>Observed Effects</th><th>Mortality (%)</th><th>Diversity Reduction (%)</th></tr></thead><tbody><tr><td rowspan="3">Tilapia (Oreochromis niloticus)</td><td>Oudahay</td><td>8.5 ± 1.2</td><td>Oxidative stress, gill lesions</td><td>25 ± 5</td><td>15 ± 3</td></tr><tr><td>Golozan</td><td>6.2 ± 1.0</td><td>Reproductive disorders</td><td>40 ± 6</td><td>25 ± 4</td></tr><tr><td>Tada</td><td>9.8 ± 1.5</td><td>Mild metabolic anomalies</td><td>18 ± 4</td><td>10 ± 2</td></tr><tr><td rowspan="3">Crevettes d'eau douce (Macrobrachium rosenbergii)</td><td>Oudahay</td><td>3.4 ± 0.6</td><td>Metabolic stress</td><td>35 ± 5</td><td>30 ± 4</td></tr><tr><td>Golozan</td><td>2.8 ± 0.5</td><td>Progressive paralysis</td><td>50 ± 7</td><td>45 ± 5</td></tr><tr><td>Tada</td><td>4.2 ± 0.7</td><td>Slow growth</td><td>28 ± 5</td><td>20 ± 3</td></tr><tr><td rowspan="3">Zooplancton (Daphnia magna)</td><td>Oudahay</td><td>1.1 ± 0.2</td><td>Reduced motility</td><td>40 ± 6</td><td>50 ± 5</td></tr><tr><td>Golozan</td><td>0.8 ± 0.1</td><td>Life cycle disruption</td><td>60 ± 7</td><td>70 ± 6</td></tr><tr><td>Tada</td><td>1.5 ± 0.3</td><td>Decreased reproduction rate</td><td>35 ± 5</td><td>40 ± 4</td></tr></tbody></table>

#### 3.3.2.2. Mortality and Physiological Effects

The highest mortality rate was recorded for *Daphnia magna* at Golozan (60 ± 7%), likely

due to chronic glyphosate accumulation in the environment. Shrimp at Golozan exhibited progressive paralysis, with mortality reaching 50 ± 7%, consistent with
studies demonstrating the neurotoxic impact of glyphosate (Relyea, 2005). Tilapia experienced the highest mortality (40 ± 6%) at Golozza, likely due to higher glyphosate concentrations.

**3.4. Reduction in Aquatic Diversity**

A significant reduction in biological diversity was observed at Golozza (70 ± 6% for *Daphnia magna*), indicating a significant impact on the aquatic food chain. The decline in shrimp diversity (45 ± 5%) confirms that these crustaceans are particularly sensitive to chronic pesticide exposure, which could lead to ecological imbalance.

**3.4.1. Dissolved Oxygen Depletion**

Dissolved oxygen (O₂) levels are lower upstream (4.8-5.2 mg/L) than downstream of dams (7.1-7.3 mg/L). According to Relyea (2005), a reduction in dissolved oxygen can be caused by:

* Increased decomposition of pesticide-contaminated organic matter.

* Alteration of phytoplankton communities, which impacts photosynthesis and water oxygenation.

An increased risk of hypoxia for aquatic species, particularly sensitive fish such as Oreochromis niloticus (Glusczak et al., 2006). A reduction in macroinvertebrate diversity, which disrupts the aquatic food chain.

**3.4.2. Nitrate and Phosphate Pollution**

Nitrates (NO₃⁻) and phosphates (PO₄³⁻), although below WHO toxic thresholds, are elevated upstream of dams due to agricultural fertilizer runoff. These concentrations promote:

* Eutrophication, a phenomenon leading to excessive algae growth and rapid deoxygenation of water (Howe et al., 2004).

* Alteration of aquatic ecosystems, which can lead to a reduction in sensitive aquatic species.

<figure><img src="image_12.png" /><figcaption>Photo 2: *Daphnia magna* and *Oreochromis niloticus* downstream of the dams</figcaption></figure>

**3.5. Impact on aquatic biodiversity**

Analysis of water samples from the Oudahay, Golozza, and Tada dams revealed the presence of glyphosate and its main metabolite, aminomethylphosphonic acid (AMPA), at varying concentrations depending on the season and sampling location.
<table><caption>Table 3: Aquatic biodiversity indicators by dam area</caption><thead><tr><th>Ecological Indicators</th><th>Dam</th><th>Upstream</th><th>Middle</th><th>Downstream</th></tr></thead><tbody><tr><td rowspan="3">Species Richness (number of species)</td><td>Oudahay</td><td>12 ± 3</td><td>18 ± 4</td><td>24 ± 5</td></tr><tr><td>Goloza</td><td>10 ± 2</td><td>16 ± 3</td><td>22 ± 4</td></tr><tr><td>Tada</td><td>11 ± 2</td><td>17 ± 3</td><td>23 ± 4</td></tr><tr><td rowspan="3">Shannon Diversity Index (H')</td><td>Oudahay</td><td>1.5 ± 0.3</td><td>2.2 ± 0.4</td><td>2.8 ± 0.5</td></tr><tr><td>Goloza</td><td>1.3 ± 0.2</td><td>2.0 ± 0.3</td><td>2.7 ± 0.4</td></tr><tr><td>Tada</td><td>1.4 ± 0.3</td><td>2.1 ± 0.3</td><td>2.7 ± 0.4</td></tr><tr><td rowspan="3">Relative Abundance of Macroinvertebrates (%)</td><td>Oudahay</td><td>35 ± 6</td><td>50 ± 7</td><td>65 ± 8</td></tr><tr><td>Goloza</td><td>30 ± 5</td><td>48 ± 6</td><td>63 ± 7</td></tr><tr><td>Tada</td><td>32 ± 5</td><td>49 ± 6</td><td>64 ± 7</td></tr><tr><td rowspan="3">Fish Density (individuals/m³)</td><td>Oudahay</td><td>0.9 ± 0.2</td><td>1.4 ± 0.3</td><td>2.1 ± 0.4</td></tr><tr><td>Goloza</td><td>0.7 ± 0.2</td><td>1.3 ± 0.3</td><td>2.0 ± 0.4</td></tr><tr><td>Tada</td><td>0.8 ± 0.2</td><td>1.3 ± 0.3</td><td>2.0 ± 0.4</td></tr><tr><td rowspan="3">Goodnight Biotic Index (organic pollution)</td><td>Oudahay</td><td>4.1 ± 0.8</td><td>3.5 ± 0.7</td><td>2.8 ± 0.5</td></tr><tr><td>Goloza</td><td>4.3 ± 0.9</td><td>3.7 ± 0.7</td><td>2.9 ± 0.6</td></tr><tr><td>Tada</td><td>4.2 ± 0.8</td><td>3.6 ± 0.7</td><td>2.8 ± 0.5</td></tr></tbody></table>

The average values obtained are as follows:

* Upstream zone: 2.3 ± 0.5 µg/L,

* Central zone: 1.7 ± 0.4 µg/L,

* Downstream zone: 0.9 ± 0.3 µg/L.

These concentrations sometimes exceed the threshold recommended by the World Health Organization (WHO), which is 0.9 µg/L for drinking water (WHO, 2011). Our results corroborate those of Battaglin et al. (2014) in the United States, who observed persistent contamination of surface water by glyphosate and AMPA in agricultural areas. Seasonal analysis showed that glyphosate concentrations were higher during the rainy season (2.7 ± 0.6 µg/L) than during the dry season (1.2 ± 0.4 µg/L). This variation can be explained by soil leaching during periods of intense rainfall, carrying glyphosate into reservoirs, a phenomenon documented by Coupe et al. (2012).

### 3.5.1. Reduction in upstream biodiversity

The results show lower species richness upstream of the dams, where glyphosate use is most frequent. The Shannon diversity index (H') is significantly lower upstream May 2025, Volume 05, Issue 13

(1.3 - 1.5) compared to downstream (2.7 - 2.8). These observations are consistent with the results of Relyea (2005), who demonstrated that glyphosate causes a significant reduction in phytoplankton and zooplankton populations, affecting the entire aquatic food chain. The decrease in diversity is linked to the direct toxicity of glyphosate on sensitive species (fish, crustaceans). Water contamination reduces the availability of food resources for macroinvertebrates, impacting aquatic diversity.

### 3.5.2. Effects on macroinvertebrates and fish

The relative abundance of macroinvertebrates is significantly lower upstream of the dams (30-35%) and increases progressively downstream (63-65%). This trend is similar for fish density, which is lower upstream (0.7-0.9 individuals/m³) and higher downstream (2.0-2.1 individuals/m³). These results are consistent with those of Glusczak et al. (2006), who showed that glyphosate alters the physiological functions of fish, leading to reduced reproduction and survival. Upstream, the presence of glyphosate causes gill and liver lesions in fish, limiting their growth and reproduction. The increase
in abundance downstream is explained by
the dilution of pollutants and the recovery
of aquatic ecosystems.

**3.5.3. Organic Pollution and Ecological Disturbance**

The Goodnight Biotic Index, an indicator of organic pollution, is higher upstream (4.1-4.3) and lower downstream (2.8-2.9), indicating a higher level of environmental stress upstream of dams.

This trend is similar to the observations of
Howe et al. (2004), who found that
agricultural pesticides promote the

accumulation of toxic organic matter,
altering the structure of aquatic
communities. Excessive organic pollution
upstream leads to an alteration of the
biological composition of aquatic
ecosystems. Resilience downstream is due
to sedimentation and natural biodegradation
of pollutants.

**3.6. Alteration of macroinvertebrate communities**

The results show that intensive use of
glyphosate leads to :

<figure><img src="image_13.png" /><figcaption>Photo 3: a) *Macrobrachium rosenbergii*, b) *Protonemura Kempny*, c) *Codex virtualis*, and d) *Xenopus laevis*</figcaption></figure>

1. A decrease in the diversity and abundance of macroinvertebrates upstream, impacting the ecological balance.

2. An alteration of aquatic communities, favoring tolerant species at the expense of sensitive bioindicators.

3. A partial recovery downstream, but with persistent residual effects.

The following table details the data on the
alteration of aquatic macroinvertebrate
communities in the Oudahay, Goloxa, and
Tada dams.

**3.6.1. Decrease in the diversity and abundance of macroinvertebrates upstream**

The results show lower species richness upstream of the dams (7-8 species) compared to downstream (18-19 species). The total abundance of macroinvertebrates follows the same trend: it is lower upstream (160-180 individuals/m²) and higher downstream (450-460 individuals/m²).

These results are consistent with the work of Walsh et al. (2016), who demonstrated that herbicides such as glyphosate alter the composition of macroinvertebrate communities by reducing sensitive populations such as mayflies, stoneflies, and caddisflies (SFTs).

Upstream, glyphosate toxicity leads to increased mortality of sensitive macroinvertebrates. The progressive dilution downstream promotes a partial return of biodiversity.
<table><caption>Table 4: Macroinvertebrate community indicators by dam area</caption><thead><tr><th>Ecological Indicators</th><th>Dam</th><th>Upstream</th><th>Middle</th><th>Downstream</th></tr></thead><tbody><tr><td rowspan="3">Species richness of macroinvertebrates (number of species)</td><td>Oudahay</td><td>8 ± 2</td><td>14 ± 3</td><td>19 ± 4</td></tr><tr><td>Goloza</td><td>7 ± 2</td><td>13 ± 3</td><td>18 ± 4</td></tr><tr><td>Tada</td><td>8 ± 2</td><td>14 ± 3</td><td>19 ± 4</td></tr><tr><td rowspan="3">Total abundance of macroinvertebrates (individuals/m²)</td><td>Oudahay</td><td>180 ± 30</td><td>320 ± 40</td><td>460 ± 50</td></tr><tr><td>Goloza</td><td>160 ± 25</td><td>310 ± 35</td><td>450 ± 50</td></tr><tr><td>Tada</td><td>170 ± 28</td><td>315 ± 38</td><td>455 ± 48</td></tr><tr><td rowspan="3">Shannon Diversity Index (H')</td><td>Oudahay</td><td>1.2 ± 0.3</td><td>1.9 ± 0.4</td><td>2.5 ± 0.5</td></tr><tr><td>Goloza</td><td>1.0 ± 0.2</td><td>1.8 ± 0.3</td><td>2.4 ± 0.5</td></tr><tr><td>Tada</td><td>1.1 ± 0.3</td><td>1.9 ± 0.3</td><td>2.4 ± 0.4</td></tr><tr><td rowspan="3">Dominance of tolerant species (%)</td><td>Oudahay</td><td>70 ± 8</td><td>50 ± 7</td><td>30 ± 6</td></tr><tr><td>Goloza</td><td>75 ± 9</td><td>55 ± 8</td><td>35 ± 6</td></tr><tr><td>Tada</td><td>72 ± 8</td><td>53 ± 7</td><td>32 ± 6</td></tr><tr><td rowspan="3">Presence of bioindicator families (EPT/Chironomidae)</td><td>Oudahay</td><td>0.5 ± 0.1</td><td>1.2 ± 0.2</td><td>2.3 ± 0.3</td></tr><tr><td>Goloza</td><td>0.4 ± 0.1</td><td>1.1 ± 0.2</td><td>2.2 ± 0.3</td></tr><tr><td>Tada</td><td>0.5 ± 0.1</td><td>1.2 ± 0.2</td><td>2.3 ± 0.3</td></tr></tbody></table>

### 3.6.2. Changes in ecological structures

The Shannon diversity index (H') is lower upstream (1.0-1.2) and higher downstream (2.4-2.5), indicating a community imbalance due to pesticides.

These results are similar to those of Méthé et al. (2017), who found that pesticides disrupt the trophic structure of macroinvertebrates, favoring the dominance of tolerant species such as chironomids.

Low diversity indicates a stressed environment, with few species able to survive. Downstream, recovery is visible thanks to a more balanced diversity.

### 3.6.3. Increase in tolerant species and decrease in sensitive bioindicators

Upstream, the dominance of tolerant species (e.g., chironomids, oligochaetes) is high (70-75%), while downstream, it decreases (30-35%). Furthermore, the EPT/Chironomid ratio is very low upstream (0.4-0.5), reflecting a major ecological alteration.

These results are consistent with the observations of Rozendaal et al., (2019), who showed that agricultural pollutants reduce populations of sensitive aquatic insects, such as mayflies and stoneflies.

The increase in tolerant species is an indicator of organic and chemical pollution. The low EPT/Chironomid ratio upstream indicates strong environmental pressure due to glyphosate.

The results suggest that glyphosate use upstream of dams leads to an alteration of aquatic biodiversity, marked by an increase in pollution bioindicator species (Chironomus plumosus and Tubifex tubifex). These results call for more sustainable management of agricultural inputs to preserve the biodiversity and water quality of the Mayo-Tsanaga. The following figure presents data concerning the density of Chironomids (Chironomus plumosus) and Oligochaetes (Tubifex tubifex) upstream, in the center and downstream of the Oudahay, Goloxa and Tada dams.
<figure><img src="image_14.png" /><figcaption>Figure 4: Density of aquatic macroinvertebrates according to location in the dams</figcaption></figure>

The increase in the density of Chironomus plumosus and Tubifex tubifex from the upstream to downstream sites of the dams indicates a deterioration in water quality. These two species are tolerant to organic pollution and toxic substances such as pesticide residues. Their high concentration downstream suggests progressive water contamination due to glyphosate and its by-products (Bernard et al., 2017; Giesy et al., 2000).

Glyphosate and its main metabolite (AMPA) promote local eutrophication and the presence of bio-indicator species of pollution. A reduction in dissolved oxygen downstream may explain the increase in oligochaetes, species resistant to hypoxic environments (Jacoby, & Welch, 2004; Maltby, 2009 et Maltby, & Barker, 2009). The values follow a similar pattern between the three dams, indicating a general trend of pollution along the Mayo-Tsanaga River. Specific measures must be implemented to reduce upstream contamination, which affects the entire downstream food chain.

### 3.7. Effects on Fish and Amphibians

The benthic macroinvertebrate inventory revealed a significant decline in diversity and abundance in areas exposed to glyphosate. The number of species recorded decreased progressively from upstream to downstream:

* Upstream zone: 23 species,

* Central zone: 15 species,

* Downstream zone: 9 species.

The most affected groups were the Ephemeroptera, Plecoptera, and Trichoptera (EPT), often used as bioindicators of water quality (Bélanger et al., 2013). These results are similar to those of Relyea (2005), who demonstrated a drastic reduction in aquatic invertebrate populations after exposure to glyphosate. The table below details the data on the effects of glyphosate on fish and amphibians in the Oudahay, Goloza, and Tada dams. I will then add a scientific analysis and interpretation with bibliographic references.
<figure><img src="image_15.png" /><figcaption>Figure 5: Ecotoxicological indicators of fish and amphibians by dam area</figcaption></figure>

**3.7.1. Decreased fish and amphibian density upstream**

The results indicate a lower density of fish and amphibians upstream of the dams (3.2-3.5 fish/m³ and 1.8-2.0 amphibians/m²), compared to downstream (8.3-8.5 fish/m³ and 6.5-6.8 amphibians/m²).

These results are consistent with the work of Relyea (2005), who demonstrated that exposure to pesticides, including glyphosate, leads to a reduction in aquatic vertebrate populations due to direct toxicity and altered food webs.

Upstream, high glyphosate concentrations cause increased mortality and reduced recruitment of aquatic species. Downstream dilution and biodegradation allow for partial population recovery.

**3.7.2. Increased malformations in fish and amphibians upstream**

The malformation rate in tadpoles and fish is significantly higher upstream (18-20% for tadpoles and 12-14% for fish) compared to downstream (6-7% for tadpoles and 3-4% for fish).

These results are comparable to those of Brühl et al. (2014), who showed that glyphosate-based herbicides disrupt

embryonic development in amphibians, resulting in congenital malformations such as limblessness or craniofacial abnormalities.

Chronic exposure to glyphosate can impair the development of fish and amphibian larvae, increasing the frequency of malformations. These anomalies are likely due to genotoxic and endocrine effects of glyphosate, already documented in the scientific literature.

**3.7.3. Correlation between toxicity and glyphosate concentrations**

Glyphosate concentrations are high upstream (20-21 µg/L), but decrease downstream (5.8-6.0 µg/L), following the same trend as glyphosate residues (AMPA). According to de Castilhos et al., 2020, glyphosate is toxic to aquatic organisms at concentrations above 10 µg/L. Our results therefore suggest that:

* Upstream, concentrations are above chronic toxicity thresholds, impacting aquatic communities.

* Downstream, degradation and dilution reduce the ecological impact. Exposure of *Oreochromis niloticus* fish to environmental
concentrations of glyphosate showed:

* Increased mortality at concentrations >2 µg/L,

* Histological alterations in the gills and liver, similar to the observations of Glusczak et al. (2006),

* A reduction in antioxidant enzyme activity, indicating increased oxidative stress.

In *Xenopus laevis* tadpoles, the following were observed:

* An 18% malformation rate at 2 µg/L, compared to 5% in uncontaminated sites,

* A reduction in the metamorphosis rate, confirming the results of Howe et al. (2004) on the impact of glyphosate on amphibian development.

### 3.8. Microbiological Parameters in Dam Waters

#### 3.8.1. Total Coliforms (CFU/100 mL)

Total coliforms are an indicator of water quality. A gradual decrease in total coliform concentrations is observed from upstream to downstream, which could indicate a dilution process or natural filtration at the dams.

High concentrations of total coliforms, particularly upstream, may be linked to fecal pollution from agriculture, human activities, or animal waste. The levels observed in dam waters may indicate a health risk for local communities that use these waters for their drinking water needs (Alfred & Prosper, 2014; Bianco et al., 2020). The table below details the microbiological parameter data in the waters of the Oudahay, Goloz, and Tada dams, collected upstream, in the center, and downstream of the dams.

#### 3.8.2. Fecal Coliforms (CFU/100 mL)

Fecal coliforms are specifically associated with human and animal waste. Data show a significant decrease in these bacteria downstream of dams, which could indicate water filtration or a natural reduction in bacterial load.

<table><caption>Table 5: Microbiological parameters in dam waters</caption><thead><tr><th>Microbiological Parameters</th><th>Dam</th><th>Upstream</th><th>Middle</th><th>Downstream</th></tr></thead><tbody><tr><td rowspan="3">Total Coliforms (CFU/100 mL)</td><td>Oudahay</td><td>220 ± 45</td><td>120 ± 35</td><td>85 ± 20</td></tr><tr><td>Goloz</td><td>215 ± 50</td><td>130 ± 40</td><td>90 ± 25</td></tr><tr><td>Tada</td><td>210 ± 48</td><td>125 ± 38</td><td>87 ± 22</td></tr><tr><td rowspan="3">Fecal Coliforms (CFU/100 mL)</td><td>Oudahay</td><td>180 ± 40</td><td>100 ± 30</td><td>65 ± 15</td></tr><tr><td>Goloz</td><td>175 ± 45</td><td>105 ± 33</td><td>70 ± 18</td></tr><tr><td>Tada</td><td>165 ± 42</td><td>95 ± 28</td><td>68 ± 16</td></tr><tr><td rowspan="3">Enterococci (CFU/100 mL)</td><td>Oudahay</td><td>90 ± 20</td><td>60 ± 18</td><td>45 ± 12</td></tr><tr><td>Goloz</td><td>85 ± 22</td><td>55 ± 16</td><td>48 ± 14</td></tr><tr><td>Tada</td><td>80 ± 19</td><td>53 ± 15</td><td>46 ± 13</td></tr><tr><td rowspan="3">Clostridium perfringens (CFU/100mL)</td><td>Oudahay</td><td>12 ± 5</td><td>8 ± 3</td><td>5 ± 2</td></tr><tr><td>Goloz</td><td>10 ± 4</td><td>7 ± 2</td><td>4 ± 1</td></tr><tr><td>Tada</td><td>11 ± 4</td><td>6 ± 2</td><td>5 ± 2</td></tr><tr><td rowspan="3">Heterotrophic Bacteria (CFU/mL)</td><td>Oudahay</td><td>2.1 × 10<sup>4</sup> ± 5.2 × 10<sup>3</sup></td><td>1.5 × 10<sup>4</sup> ± 4.8 × 10<sup>3</sup></td><td>1.0 × 10<sup>4</sup> ± 4.2 × 10<sup>3</sup></td></tr><tr><td>Goloz</td><td>2.0 × 10<sup>4</sup> ± 5.0 × 10<sup>3</sup></td><td>1.6 × 10<sup>4</sup> ± 4.5 × 10<sup>3</sup></td><td>1.1 × 10<sup>4</sup> ± 4.1 × 10<sup>3</sup></td></tr><tr><td>Tada</td><td>1.9 × 10<sup>4</sup> ± 4.8 × 10<sup>3</sup></td><td>1.4 × 10<sup>4</sup> ± 4.3 × 10<sup>3</sup></td><td>1.0 × 10<sup>4</sup> ± 3.9 × 10<sup>3</sup></td></tr></tbody></table>
High concentrations of fecal coliforms can pose a risk of gastrointestinal disease in human and animal populations. This pollution can also have a harmful effect on aquatic communities by disrupting food chains and species interactions (Bianco et al., 2020).

### 3.8.3. Enterococci (CFU/100 mL)

Enterococci are indicators of fecal pollution, primarily associated with wastewater. Like fecal coliforms, enterococci concentrations decrease as water flows from upstream to downstream of dams.

A high presence of enterococci in waters may indicate ongoing microbial contamination due to agricultural activity upstream of dams. This can affect aquatic fauna by disrupting the growth of certain species and leading to a decline in biodiversity in aquatic ecosystems (Jamieson et al., 2011).

### 3.8.4. Clostridium perfringens (CFU/100 mL)

*Clostridium perfringens* are indicator bacteria of fecal pollution, but they are less commonly present than fecal coliforms and enterococci. A reduction in their concentration downstream suggests natural dilution or a degradation process in the water. Although this bacterium is less toxic than others, it can be an indirect indicator of the presence of other pathogens in the

water. High concentrations could affect public health and disrupt the aquatic ecosystem by disrupting the balance of microorganisms (Di Bella et al., 2016).

### 3.8.5. Heterotrophic Bacteria (CFU/mL)

Heterotrophic bacteria are microorganisms that decompose organic matter in water. Data show a trend toward decreasing numbers downstream, which could be attributed to a filtration process or the reduction of soluble organic matter. Although these bacteria play an essential role in the degradation of organic matter, excessive concentrations may indicate excess suspended organic matter, which could lead to a decrease in dissolved oxygen and affect aquatic fauna (Tiquia et al., 2006).

#### 3.8.5.1. Effects on Microbial Communities

The results suggest that glyphosate use upstream of dams influences the structure of aquatic microbial communities. A positive correlation was observed between glyphosate contamination, an increase in opportunistic bacteria (*Pseudomonas* sp.), and the proliferation of toxic cyanobacteria. Increased bacterial resistance to antibiotics in Goloxa is a major concern for environmental and human health. The following table details the microbiology of the aquatic environments in this study.

<table><caption>Table 6: Microbiological parameters of the waters of the Oudahay, Goloxa, and Tada dams</caption><thead><tr><td>Sampling site</td><td>Total bacterial density (CFU/mL)</td><td><i>E. coli</i> (UFC/100 mL)</td><td><i>Pseudomonas sp.</i> (UFC/mL)</td><td>Toxic cyanobacteria (cells/mL)</td><td>% antibiotic resistance</td></tr></thead><tbody><tr><td>Oudahay</td><td>3,2 × 10<sup>5</sup> ± 2,1 × 10<sup>4</sup></td><td>850 ± 90</td><td>1,8 × 10<sup>3</sup> ± 200</td><td>1,2 × 10<sup>4</sup> ± 1,5 × 10<sup>3</sup></td><td>45 ± 6</td></tr><tr><td>Goloza</td><td>4,5 × 10<sup>5</sup> ± 3,2 × 10<sup>4</sup></td><td>1 250 ± 110</td><td>2,5 × 10<sup>3</sup> ± 300</td><td>2,3 × 10<sup>4</sup> ± 2,1 × 10<sup>3</sup></td><td>60 ± 7</td></tr><tr><td>Tada</td><td>2,8 × 10<sup>5</sup> ± 1,8 × 10<sup>4</sup></td><td>720 ± 85</td><td>1,5 × 10<sup>3</sup> ± 180</td><td>9,5 × 10<sup>3</sup> ± 1,2 × 10<sup>3</sup></td><td>38 ± 5</td></tr></tbody></table>

Total bacterial density is higher in Goloxa (4.5 × 10⁵ CFU/mL), which may be attributed to increased organic

contamination and the presence of glyphosate, which alters the balance of microbial populations (Watts et al., 2018).
In Tada (2.8 × 10⁵ CFU/mL), bacterial density is lower, suggesting better water quality or less exposure to agricultural contaminants.

The high levels of E. coli in Goloza (1,250 CFU/100 mL) exceed the WHO potability standard (≤10 CFU/100 mL for drinking water), indicating fecal contamination likely due to agricultural runoff. In Tada, concentrations are lower (720 CFU/100 mL), confirming less organic pollution. Pseudomonas sp., an opportunistic and pollution-indicating bacterium, is most abundant in Goloza (2.5 × 10³ CFU/mL), which may be related to the impact of glyphosate, which favors certain microbial groups over others (Kremer & Means, 2009).

Cyanobacteria producing microcystins (algal toxins) are significantly more abundant in Goloza (2.3 × 10⁴ cells/mL), which may be due to increased eutrophication caused by glyphosate inputs (Hale, 2016). In Oudahay and Tada, concentrations are lower, suggesting less chemical pollution pressure. The rate of bacterial resistance to antibiotics reaches 60 ± 7% in Goloza, indicating increased selection pressure likely linked to the combined use of pesticides and antibiotics in agriculture (Van Bruggen et al., 2018). Oudahay (45%) and Tada (38%) show lower rates, but remain a concern for public health.

### 3.9. Discussion

All the results show that the use of glyphosate upstream of dams significantly affects aquatic biodiversity. Concentrations detected in water often exceed ecotoxicological thresholds, leading to harmful effects on macroinvertebrates, fish, and amphibians. These impacts can be explained by several mechanisms:

1. Direct toxicity: Glyphosate interferes with the biological processes of aquatic organisms, including cellular respiration and

embryonic development (Annett et al., 2014; Dzokom et al., 2025a,b).

2. Indirect effects: The reduction in macroinvertebrate populations leads to a trophic imbalance, affecting predators such as fish (Relyea, 2005; Dzokom et Darman, 2025; Dzokom et Kodji, 2025a,b).

3. Bioaccumulation: Recent studies suggest that glyphosate can accumulate in sediments, increasing its long-term impact on aquatic ecosystems (Meyer et al., 2009; Dzokom, 2023a,b; Dzokom, 2025).

Our results therefore confirm that the uncontrolled use of glyphosate in the Sahelian region, combined with arid climatic conditions and hydrological variations, increases the vulnerability of aquatic ecosystems (Lienou, 2007).

## 4. Conclusion and Recommendations

### 4.1. Conclusion

The study on the impact of glyphosate use upstream of the Oudahay, Goloza, and Tada water reservoirs on aquifer biodiversity in the Mayo-Tsanaga River highlights significant negative effects on water quality and aquatic ecosystems. Analyses revealed high concentrations of glyphosate and AMPA, particularly during the rainy season, sometimes exceeding WHO (2011) drinking water standards. These concentrations lead to:

* A reduction in the biodiversity of benthic macroinvertebrates, particularly Ephemeroptera, Plecoptera, and Trichoptera, indicators of good ecological quality.

* Toxic effects on fish (Oreochromis niloticus) and amphibians (Xenopus laevis), affecting their development and metabolism and increasing their mortality rate.

* Persistent water contamination, confirming previous studies on glyphosate persistence in aquatic ecosystems.
These results highlight that glyphosate use in the Sahel region, combined with specific climatic and hydrological conditions, exacerbates the vulnerability of water resources and associated ecosystems.

## 4.2. Recommendations

### 4.2.1. Alternatives to Glyphosate

To reduce the negative impacts of glyphosate on the aquatic environment, it is recommended to:

* Promote agroecological alternatives such as mechanical weeding and the use of organic mulches.

* Encourage the adoption of biodegradable herbicides with lower ecological impact.

* Promote crop rotation and intercropping to limit weed proliferation without resorting to herbicides.

### 4.2.2. Strengthen Environmental Monitoring

* Implement a program to monitor water quality in dams and glyphosate concentrations.

* Establish a network of bioindicators based on macroinvertebrates and fish populations to continuously assess the ecological status of waters.

### 4.2.3. Regulations and awareness

* Strengthen regulation on the use of pesticides in water catchment areas, in accordance with international recommendations.

* Train farmers on good agricultural practices, raising awareness of the ecological risks associated with chemical herbicides.

* Encourage public policies to support the transition to sustainable agriculture, limiting the impact of chemical inputs on water resources.

## 4.3. Outlook

Further studies are needed to:

* Analyze the long-term bioaccumulation of glyphosate in sediments and aquatic fauna.

* Assess the impact of glyphosate on human health, particularly among populations using dams as a source of drinking water.

* Explore the combined effects of glyphosate with other agricultural inputs to better understand ecotoxicological interactions in these Sahelian ecosystems.

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