The present study focused on the chemical characterization of the watercourse of the Togbadji Lake wildlife ranch. The methodological approach followed is as follows: Bibliography review, Sampling campaign. The results obtained were the subject of descriptive statistics, the two-sample Wilcoxon test to determine the impact of different localities on the abundance of microbiological contaminants, a Principal Component Analysis (PCA) with the software R version 3.5.0, in order to group the pollution parameters according to the different levels and sources of contamination. From our results, it is found that the respective average values in dry and rainy seasons for ammonium ions are 0.38 ± 0.16 mg/L and 0.22 ± 0.03 mg/L; for nitrite ions 0.20 ± 0.25 mg/L and 0.02 ± 0.01 mg/L; for nitrate ions 3.72 ± 2.52 mg/L and 7.84 ± 4.91 mg/L; for total Kjeldahl nitrogen 1.27 ± 1.44 mg/L and 1.19 ± 1.49 mg/L; for orthophosphate ions 0.20 ± 0.25 mg/L and 0.02 ± 0.01 mg/L; for total phosphorus 0.04 ± 0.01 mg/L and 0.11 ± 0.23 mg/L; the chemical oxygen demand 93.36 ± 61.73 mg/L of O2 and 89.93 ± 66.11 mg/L of O2 and the biochemical oxygen demand over 5 days 25.50 ± 18.22 mg/L of O2 and 37 ± 33.15 of O2. It emerged that the main sources of pollution in Lake Togbadji are runoff water, discharges of various wastewater from artisanal activities, livestock farming and open defecation.
Water is a precious natural resource essential to the life and socio-economic development of people. It is unevenly distributed across the surface of the globe. In certain places on earth, access to water resources is very difficult because of its geolocation and/or reservoir rocks. Added to this unequal distribution are the threats of alteration of water resources. They are threatened by both natural and anthropogenic processes [
Located in the southwest of Benin, precisely in the Mono delta, Lake Togbadji is a vast expanse of stagnant water with an area of approximately 9.1509 km2 and a depth ranging from 4 m to 14 m. It is located between latitude 6˚44'36 north and longitude 1˚42'9 east and near the localities of Agbodranfo, Adrogbodji, Adjakomey, Bakpohoué, Kpolédji, Takon and Togbadji. With a sword shape oriented south-north, it is a natural water source shared by the communes of Dogbo and Lokossa in the departments of Mono and Couffo. Lake Togbadji constitutes the main source of water for the Ayomi district in the commune of Dogbo. It is one of the most important lakes on the periphery of the alluvial valley of the Mono and Sazué basin characterized by a degraded and complex hydrographic network. It is fed by runoff water coming from several horizons.
The documentary research consisted of browsing articles, dissertations and theses on the internet and in libraries dealing with the physico-chemical and microbiological pollution of bodies of water and courses, its environmental and health impacts, research and dosage techniques parameters for monitoring the quality of natural waters based on environmental matrices. This literature review allowed us to deepen our knowledge of our theme and to clearly understand all its contours.
Prospective field visits allowed us to familiarize ourselves with the realities of the sampling areas. Two prospective visits (one in the dry season and one in the rainy season) were organized to identify sampling sites and target groups to survey. We also took advantage of this field visit to raise awareness among local residents about the work to be carried out in order to obtain their support for the continuation of the work.
There are four sampling campaigns, taken twice each year, one in the dry season and one in the rainy season. All water samples were collected in previously emptied 1.5 L plastic bottles of mineral water, soaped without detergent, rinsed with tap water and then three times with distilled water. Before any sampling, the bottles thus conditioned are rinsed three times with the water to be sampled. Samples are collected in duplicate in the water column approximately 10 cm from the surface. After sampling, the bottles are labeled and stored in a cooler equipped with a cold accumulator and sent to the laboratory for analysis.
In the laboratory, the water samples are kept at 4˚C in the refrigerator until the analyzes start to slow down the degradation of the samples. The standardized methods for determining the different parameters are recorded in
From
| The settings | Principle of the method | Method reference |
|---|---|---|
| NH 4 + | Formation in an alkaline medium of an indophenol type compound by reaction of NH 4 + ions with phenol and ClO − in the presence of nitroprusside Na2[Fe(CN)5NO]∙2H2O as catalyst gives a blue indophenol coloring. spectrophotometric measurement at λ = 630 nm | NFT90-015-2 |
| NO 2 − | The method is based on the reaction of NO 2 − ions with 4-aminobenzene sulfonamide at pH = 1.9 in the presence of H3PO4 to form a diazo salt which complexes with N-(1-Naphthyl)diamino-Dichlorohydrate. 1,2-ethane to give a pink color whose intensity is proportional to the NO 2 − content and measurable at 540 nm | NF EN 26777 |
| NO 3 − | The nitrate content is obtained by the sodium salicylate method | AFNOR T90-012 |
| Total Kjeldahl nitrogen | The total nitrogen content (NT) was determined by mineralization in a sulfuric medium in the presence of copper II | ISO 7150/1 |
| NO 2 − | Nitrite content by the Zambelli method | AFNOR (T90-013) |
| Ion PO 4 3 − | The reaction of phosphate ions with an acidic solution containing molybdate and antimony ions to form an antimonyl-phosphomolybdate complex which is reduced by ascorbic acid to the brightly colored molybdenum blue spectrometer measurable at 700 nm. | NF EN ISO 6878 |
| Total P | The reaction of H3PO4 ions with an acidic solution containing molybdate and antimony ions formation of an antimonyl-phosphomolybdate complex reduced by ascorbic acid to brightly colored molybdenum blue measurable at 700 nm. | NF EN ISO 6878 (T90-023) |
| COD | Oxidation in an acidic medium of organic matter by excess K2Cr2O7 in the presence of AgSO4 as catalyst and HgSO4 to complex the Cl− ions and determination of the excess oxidant with a Mohr’s salt solution (NH4Fe(SO4)2∙6H2O ) | NF T90-101 |
| BOD5 | Oxidation of biodegradable organic matter contained in a water sample by natural microorganisms in the dark in amber vials saturated with O2 placed in a thermostatic incubator at 20˚C ± 2˚C for 5 days | NF EN 1899-2 |
(Source: This study).