Evaluation du T90 des coliformes et streptocoques fecaux d'un effluent urbain dans les eaux de surface du lagon de Mayotte (ocean Indien)

摘要

Decrease rate (T90) of fecal bacteria from an urban sewage was estimated in the surface waters of the Mayotte lagoon using 2% urban sewage - lagoon water mixtures, in situ incubated between 0,5 and 4 meters depth in clear or black one liter flasks. T90 values, which were longer for fecal streptococci (FS) than for thermotolerant coliforms (TTC), appeared to be strongly related to light intensity. The higher T90 were found in the dark (30 to 48 hours for TTC and 80 to more to 200 hours for FS). In the daylight, weather conditions encountered during the experiments allowed to define 3 different meteorological cases: rainy days (confidence interval at 0.05 for TTC T90 ranging from 10 to 50 hours), sun and clouds (TTC T90 from 8 to 20 hours), sunny days (TTC T90 from 3 to 5 hours). In the daylight, regression analysis showed a good correlation between T90 and surface light intensity, attenuation light coefficient and depth, leading to operational multilinear regression models. These models can explain a good percentage of variance, especially for TTC (explained variance : 82%), but lesser for FS (58%).