Reduction of human fecal markers and enteric viruses in Sydney estuarine waters receiving wet weather overflows

The current microbial source tracking (MST) study tracked the reduction of the culturable fecal indicator bacteria en-terococci, four human fecal markers (Bacteroides HF183, Lachnospiraceae Lachno3, cross-assembly phage (CrAssphage) and pepper mild mottle virus (PMMoV)) along with four enteric viruses -human adenovirus 40/41 (HAdV 40/41), en-terovirus (EV), human norovirus GI (HNoV GI) and GII (HNoV GII) post wet weather overflows (WWOs) at two estu-arine water sites from two depths under separate six-day sampling campaigns over seven and 12 days in Sydney, NSW, Australia. Neither HNoV GI nor GII was detected, while 13.9 % (10/72) of estuarine water samples had detections of EV. Quantifiable concentrations (0.64 to 2.00 log10 gene copies (GC)/100 mL) for HAdV 40/41 were returned from 65.2% (47/72) of samples collected across the two sites and two depths with 30 quantifications recorded in the surface layer samples. In contrast the presence of HF183, Lachno3, CrAssphage, and PMMoV markers was observed in all 36 (100 %) estuarine water samples collected from the surface layer from both sites. Detection frequencies of these markers were slightly lower at 1 m above the bottom surface. The concentrations of the human fecal markers were compared to established gastrointestinal (GI) risk benchmarks. The concentrations of HF183, Lachno3 and CrAssphage marker only exceeded the GI risk benchmark until day 3, while concentrations of PMMoV marker were indicative of exceedance of the GI risk benchmark on day 7 post WWOs that was much longer than indicated by culturable entero-cocci concentrations that were within this GI risk benchmark by day 2 and day 4 for the two sites, respectively.

Automated summary

This study tracked the reduction of fecal indicator bacteria and enteric viruses in estuarine water after wet weather overflows in Sydney, Australia. The results showed that human fecal markers were detected in all surface water samples, while the detection frequency was slightly lower at the 1-meter depth. In contrast, culturable enterococci concentrations were within the gastrointestinal risk benchmark by day 2 and day 4 for the two sites, respectively.