AbstractRegular water quality monitoring is required for protecting the physiochemical and bacteriological quality of surface water and to ensure water is meeting beneficial use criteria. This study investigated the effect of the time of sample collection on bacterial abundance and physicochemical parameters in an urban stream influenced by wastewater effluent but no rain events over 5 days on 3-h intervals. Temperature, discharge, pH, and conductivity were monitored onsite and they varied significantly (P<0.05) hourly. Total coliform and E. coli were measured in the stream water, sediments, and the treatment plant effluent. Over a day, microbial abundance varied eightfold to 21-fold upstream and twofold to 22-fold downstream of the discharge point for total coliform and E. coli, respectively. Compared with the regulatory 206 colony forming units (CFU)/100 mL coliform limit, stream samples exceeded safe limits in 70% of observations at 08:00, 50% at 11:00 and 14:00, and 10% at 17:00. Sediment samples from the upstream and downstream locations showed no significant variation in the microbial abundance based on time of sample collection, although the wastewater effluent effect was clearly seen. These results suggest repeated sampling of streams should be conducted at the same time of day to accurately inform risk-based sampling plans.

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