3.1. Physicochemical Characteristics
The temperatures in the Nador Canal varied seasonally. In summer, they spanned from 27 °C to 39 °C, averaging around 29.92 °C, just below the Moroccan standard of 30 °C. However, the temperatures in winter varied from 17.6 °C to 25.6 °C, with an average temperature of approximately 19.76 °C (
Figure 2a). The temperatures in summer were significantly higher, approaching the maximum standard (<30 °C). This could affect aquatic life during the summer due to higher metabolic rates and lower oxygen solubility. However, in winter, temperatures were well within the norm, indicating a cooler environment that is likely more conducive to aquatic life. Water temperature significantly enhances chemical activity, bacterial activity, and water evaporation [
36,
37]. The pH values in the Nador Canal varied from 7.79 to 8.72, with an average of 8.09 in summer, and from 7.75 to 8.43, with a mean of 7.9623 in winter (
Figure 2b). The pH values for both seasons fell within the Moroccan standard of 6.5 to 8.5. The measured pH values for the Nador Canal waters categorize them as excellent to good according to surface water quality standards, suggesting that in most sampling stations, the water is suitable for irrigation, with a pH falling within the range of 6.5 to 8.5, according to Moroccan water quality standards. Yet, it is worth noting that one station appeared to be moderately polluted. The pH level has a significant impact on water quality, indicating whether the water is acidic or alkaline (basic). It also represents water’s neutrality and is a critical parameter for both drinking and irrigation purposes. Moreover, pH influences the solubility of minerals in water, as well as factors such as alkalinity and water hardness [
36,
38]. Dissolved oxygen (DO) levels varied from 1 to 2.82 mg/L in summer and increased to 4.2 to 9.6 mg/L in winter, both under the Moroccan norm of 5 mg/L (
Figure 3a). All samples showed low levels of dissolved oxygen across all locations in the Nador Canal, indicating pollution, during the summer, while in winter, higher DO levels were measured, with the maximum exceeding the standard, suggesting better water quality during this season [
39]. Electrical conductivity (EC) values in summer (S) ranged between 960 and 2720 μS/cm, which is close to the Moroccan standard of 2700 μS/cm. In winter (W), it was lower, ranging from 860 to 2235 µS/cm. The conductivity in summer exceeded the Moroccan standard of 2700 µS/cm (
Figure 3b). However, there was a noticeable increase in the content of ions associated with pollutants such as agricultural residues and sewage effluents. It is noteworthy that water samples showed a wide range of variations in electrical conductivity values [
40].
Bicarbonate (HCO
3−) levels ranged from 94.7 to 531.2 mg/L in the summer and 92.9 to 512.6 mg/L in the winter. Compared to the Moroccan standard of 400 mg/L, five stations in summer were above the Moroccan standard and ten stations in winter were above the Moroccan standard, and the stations were at the end of the Nador Canal (
Figure 4a). Elevated bicarbonate levels in the Nador Canal can stem from agricultural runoff, industrial effluents, domestic wastewater, natural geological sources, evaporation, seasonal variations, urbanization, and algal blooms [
41]. Sulfate (SO
42−) concentrations ranged from 68.18 to 133.65 mg/L in summer and increased to 176.78 to 305.2 mg/L in winter. Most samples in both seasons were below the standard level of 250 mg/L (
Figure 4b). Sulfate sources included organic matter breakdown, fertilizers, and microbial oxidation [
42,
43]. Sulfate is a nonmetallic element naturally found in soils and rocks in both organic and mineral forms [
44]. Chloride (Cl
−) concentrations ranged from 184.3 to 907.6 mg/L in summer and from 114.6 to 542.5 mg/L in winter (
Figure 4c). The high chloride levels in summer suggest contamination from various sources, while winter levels were significantly lower. The elevated chloride concentration in the Nador Canal is attributed to discharges from human activities, agricultural waste, and excessive fertilizer use. Nitrate (NO
3−) concentrations ranged from 0.28 to 37.09 mg/L in summer and from 1 to 92 mg/L in winter (
Figure 4d). High nitrate levels at the Nador Canal’s end indicate agricultural and human waste accumulation from improper disposal and fertilizers [
45].
Calcium (Ca
2+) concentrations in summer were 50.78 to 111.77 mg/L, and in winter, they were higher, at 74.97 to 164.2 mg/L (
Figure 5a). Calcium levels in summer exceeded the Moroccan standard limit of 100 mg/L at only two stations, while calcium levels exceeded most stations in winter, which may indicate natural mineral leaching or anthropogenic effects. Magnesium concentrations ranged from 21.1 to 45.1 mg/L in summer and from 34.61 to 72.96 mg/L(
Figure 5b). in winter, which can be compared to the normal range of 50 mg/L. Values in both seasons exceeded the Moroccan standard, especially in winter, which may contribute to the overall hardness of the water. The concentrations of sodium (Na
+) ranged from 122 to 343.9 mg/L in summer and 107.7 to 290.2 mg/L(
Figure 5c). in winter. Summer maximum concentrations were higher than winter levels but within the Moroccan standard of 150 mg/L. Mean concentrations in both seasons exceeded the standard. Sodium sources include geological weathering, agricultural runoff, industrial discharges, and wastewater effluents. The concentration of potassium (K
+) in water samples was 3.1 to 5.79 in summer and 8.68 to 16.212 mg/L in winter (
Figure 5d). Potassium levels were well within the norm in summer but were substantially higher in winter, with mean levels almost reaching the standard. This could be influenced by seasonal agricultural runoff or other inputs [
38]. The concentrations of ammonia ranged from 0.32 to 0.62 mg/L in summer and 0.1 to 0.23 mg/L in winter (
Figure 5e). According to Moroccan standards, all samples were within the permissible range [
40]. The concentration of phosphate (PO
43−) was from 0.02 to 1.97 mg/l in summer and 0.36 to 3.87 mg/L in winter (
Figure 5f). Phosphate concentrations in both seasons were below the norm, with winter having higher levels, potentially from runoff or wastewater.
Table 2 shows the concentrations of heavy metals in the water of the Nador Canal across two different seasons, summer and winter. In the summertime, the concentration of copper in the water was quite stable, oscillating between 0.01 and 0.02, and averaging out at 0.02. Come winter, however, there was a noticeable broadening in the range of copper concentrations, which stretched from 0.10 to 0.50, with the average increasing to 0.19. This highlights a more pronounced variability in copper levels compared to the summer season (
Figure 6a). During summer months, iron levels in the water spanned from a minimum of 0.04 to a maximum of 0.21, with an average concentration of 0.12. In the winter, however, the variability in iron concentrations was more pronounced, with values extending from 0.14 to 0.29 and an increased average value of 0.22. This suggests a tighter clustering of values around the mean compared to the summer, despite the overall higher winter concentrations (
Figure 6b). Throughout the summer, manganese concentrations hovered between 0.02 and 0.04, with an average resting at 0.02, displaying minimal variation, as evidenced by a standard deviation of 0.01. When winter arrived, the manganese levels experienced a slight increase, with a range from 0.04 to 0.06 and a median value of 0.05 (
Figure 6c). In summer and winter, zinc statistics were the same in both seasons and ranged from 0.01 to 0.02, with a constant average of 0.01 (
Figure 6d). The concentration of lead ranged from a minimum of 6.66 to a maximum of 16.56, with an average (mean) of 10.49. In the winter, the lead concentration ranged from a higher minimum of 10.45 to a maximum of 22.75, with an increased average of 15.19, indicating a greater spread of values around the mean than in the summer. This means that the lead concentrations were not only higher on average but also more varied in winter than in summer (
Figure 6e). Cadmium levels in the summer were between 2.25 and 28.60, with a mean of 11.49. The coefficient of variation for cadmium is quite high at 14.83, indicating significant variability in its concentrations during the summer months. The winter data showed an increased minimum level of cadmium at 10.45, a maximum of 22.75, and a mean value that matches the mean for lead at 15.19. The standard deviation is the same as for lead, at 6.62, suggesting a similarly wide range of values around the mean for cadmium in the winter (
Figure 6f). The comparison makes it clear that the concentrations and fluctuations of these minerals and elements in the water of the Nador Canal change between summer and winter. It is worth noting that the levels of copper, iron, and lead were higher on average in winter, with varying degrees of increased variation. Cadmium showed particularly high variability in both seasons but to largely different extents. It is important to note that for some variables, such as boron and lead, there are potential inconsistencies or errors in the presentation of data for the winter season.
3.4. Water Quality Assessment Using Water Quality Index
The water quality index (WQI) classifies water quality into five categories: excellent (WQI < 50), good (50 ≤ WQI ≤ 100), poor (100 < WQI ≤ 200), inferior (200 < WQI ≤ 300), and unsuitable (WQI > 300). This index is a simple measure to convey water’s overall health and suitability for various uses [
46]. The WQI is a numerical indicator that integrates multiple criteria to represent the overall quality of water in a single value. The WQI of the surface waters in the Nador Canal shows marked seasonal variation; in summer, values ranged from 69.06 to 196.60, with an average of 113.19, and in winter, values ranged from 114.09 to 325.63, with an average of 165.84 (
Table 6 and
Figure 10). In summer, the minimum WQI value was 69.06 at station S22, classified as “good”, indicating the highest observed water quality. The maximum value was 196.60 at station S16, classified as “poor”, denoting the poorest quality during the summer. In winter, the maximum WQI value increased to 325.63 at station S16, which is classified as “unsuitable”, highlighting this station as having the most problematic water quality. The summer minimum suggests a potential decline in water quality, reaching levels that may necessitate additional water treatment or selective irrigation strategies to protect crops and soil health. Furthermore, the winter WQI indicates an overall degradation in quality. Seasonal variations in the WQI may be influenced by factors such as precipitation patterns, agricultural runoff, and other seasonal dynamics that impact water quality. It is crucial for farmers who rely on this water for irrigation to stay informed about these fluctuations to adjust their agricultural practices and ensure crop viability. Continuous monitoring of water quality throughout the year is essential to maintain standards suitable for irrigation. When examining individual monitoring stations, the summer season typically recorded “poor” ratings at most stations, except for six stations (S17, S18, S19, S20, S21, and S22) that received a “good” rating due to their proximity to the Espoo River, which is consistent with the results of the principal component analysis (PCA). However, the winter season presented a consistent pattern: most stations were rated “poor”, except two (S15 and S17) that fell into the “very poor” category, and one station (S16) that fell into the “unsuitable” category. Notably, stations S15, S17, and S16 exhibited alarming pollution levels during the winter, reaching the “unsuitable” category, the worst possible rating. This indicates significant contamination that renders the water unfit for almost all types of use without substantial remedial measures. The Nador Canal water quality index readings underscore the critical importance of seasonal monitoring, the development of responsive irrigation practices, and a consistent water quality assessment framework to ensure sustainable agricultural productivity. The occurrence may result from factors such as ion discharge, coastal zone development, seawater intrusion, agricultural input contamination, human waste, or sewage from homes and septic tanks, among other causes [
47].