## 3 Results  
### Physicochemical Parameters of Waters  
Table 1 presents the values of temperature, pH, conductivity, salinity, and orthophosphate of the water. The obtained temperature (T\({}^{\circ}\)C) values are homogeneous all over the hydrosystem (CV = 1.64) with an average value of 29.33 \({}^{\circ}\)C. A total of 75% of these values are between 28.49 and 29.50 \({}^{\circ}\)C (3 rd quartile = 29.50 \({}^{\circ}\)C). All these values are higher than the WHO standards for drinking water quality. The pH values also present a homogeneous distribution (CV = 4.21) with an average value of 6.99. The majority of pH values are between 6.43 and 7.22 and comply with the WHO standards. The average values of conductivity (EC), TDS, salinity (Sa), and orthophosphate (PO\({}_{4}\)\({}^{3-}\)) are, respectively, 15.51 mS/cm, 127.12 mg/L, 8.52 g/L, and 0.80 mg/L. These parameters show more variation in their values in the hydrosystem. According to the third (3 rd) quartile values (Table 1), it can be concluded that 75% of these parameters values vary from 8.24 to 18.80 mS/cm for EC, 43.60 to 205.39 mg/L for TDS, 4.20 to 10.49 mg/L for Sa, and 0.48 to 0.94 mg/L for PO\({}_{4}\)\({}^{3-}\). All these parameter values do not comply the WHO guidelines (Table 1) for drinking water except that of pH ([PERSON], 1975; [PERSON], 1976; [PERSON], 1976). Globally, it can be concluded that the waters from the hydrosystem are not good for human consumption according to the WHO guidelines as far as the physicochemical parameters are concerned. In aquatic ecosystems, temperature is a very important factor in the physicochemical and biochemical reactions occurring in the biotope and living organisms ([PERSON], 1976; [PERSON], 1976). The variogram parameters recorded for physicochemical variables showed two different models describing the spatial variability (Table 2). They were Exponential (T\({}^{\circ}\)C, pH, and PO4) and Spherical (EC, Sa, and TDS) models that produced the most accurate data prediction based on their mean error (ME) closer to 0 and the lowest root mean square error (RMSE) values obtained [25,38]. Spatial dependence of the distribution of physicochemical parameters was observed for all the variables, with nugget-sill ratios varying from 0% (T\({}^{\circ}\)C) to 22.33% (pH). Indeed, high spatial dependence was recorded for all the physicochemical variables (T\({}^{\circ}\)C, pH, PO4, EC, Sa, and TDS) according to their nugget-sill ratios (SD = \(C_{0}\)/(\(C_{0}\) + C)) comprised between 0 and 25% [42,68]. There was a great similarity of spatial variability pattern between EC, TDS, and Sa, confirmed by the highest correlation coefficients (0.96-1) obtained between them. Similar spatial distribution of pH, conductivity, salinity, total dissolved solids (TDSs), and orthophosphate (PO\({}_{4}\)\({}^{3-}\)) was observed (Figure 2). This similarity is stronger between EC and Sa with regard to their nugget-sill ratios and ranges (Table 2). These values increase from upstream to downstream, with the highest values obtained in the lagoon of Aneho. This trend of spatial variation can be due to the influence of seawaters. Indeed, these waters are more mineralized with higher pH values and contain phosphoric liquid waste discharged into the sea by the phosphoric processing plant at Kpeme [52]. The spatial variation in temperature values shows a slight decrease in values from upstream to downstream. The highest values in Lake Togo can be due to a shallow depth, which allows the easy traversing of solar rays associated with regular mechanical mixing. However, the slight decrease at the downstream is related to the influence of seawaters, which are often colder [39,52,53].