Assessment of the effects of seasonal changes, urban discharges and leachates on the parasitological and bacteriological qualities of soil and water from Oued Larbaâ (North-eastern, Morocco).

The objective of this study is to evaluate the parasitological and bacteriological qualities of the soil and water of the Oued Larbaâ, through nine stations covering the part of the Oued crossing the Taza city of Morocco (7 km of length). This study was conducted during two dry periods (2017 and 2018) and one wet period (2018). Soil parasitological studies revealed high contamination by helminths belonging to the species Enterobius vermicularis and Toxocara sp., which recorded the highest concentrations in stations S2 and S8, respectively, with values of 11.41 and 29.26 eggs/g. Concerning water, the majority of stations indicated contamination mainly by Ascaris lumbricoides, which reached concentrations of 56.49, 37.39, and 56.15 eggs/l in stations S3, S6, and S8, respectively. Bacteriological examination of the soil showed very high concentrations of bacteria, especially Streptococcus, due to the high retention of this type of bacteria in the soil. The water analysis indicated that stations S3, S4, and S8 are the most impacted, with total coliform and Streptococcus concentrations in station S3 of 2.45 105 and 0.20 107 CFU/ml, respectively, Fecal coliforms and Staphylococci are detected in high concentrations in station S8 with values of 1.35 104 and 8.92 106 CFU/ml, respectively, and total aerobic mesophilic flora in station S4 with a concentration of 1.89 109 CFU/ml. During the study periods, influences of sampling season, nature of discharge existed (wastewater or leachate) on the parasitological and bacteriological composition of the river were established with high concentrations during the dry period and in the stations in which large amounts of liquid discharge were observed.