Source Water Quality Assessment and the Management of Pathogens inTributaries

摘要

Under southern and eastern Australian conditions, concentrationsrnand loads of watershed pathogens were evaluated in six systems, spanning fully-protect,rnopen grazing country, semi-rural, intensive (dairy) to on-site septic-impacted. Comparedrnto baseflow pathogen concentrations, historically small rainfall run-off events (1 per mornto 1 in 4 y) increased the concentration of microbial parameters up to four orders ofrnmagnitude (I.e. by a factor of 10,000), and the load flux (units of contaminant.sec-1.unit-1rnarea of watershed) by up to seven orders of magnitude. Maximum observedrnconcentrations of contaminants from the most impacted watersheds were ca 1000rnCryptosporidium oocysts.10 L-1; >100 mpn.100 mL-1, Campylobacter spp.; 50,000rnmpn.100 mL-1, E. coli/enterococci; and 5000 ng.L-1, total β-stanols. In contrast, from twornfully-protected watersheds almost no pathogens were detected even during eventrnconditions and only E. coli/enterococci increased in some of the major tributariesrn(unrelated to pathogen occurrence), highlighting the value of watershed protection. Fecalrnsterol/stanol biomarkers provided evidence of sewage impact during event hydrographsrnin otherwise herbivore-dominated fecal contamination, which was not evident from thernabove mentioned microorganism assays, and suggested periods of potential human virusrnimpact. The biomarkers enabled estimates of the equivalent wastewater released fromrnseptic tanks to urban streams (ca 500,000 L per day-event). An overall risk assessmentrnmatrix was produced that linked watershed development, off-take location and level ofrnrun-off event impact. The need to assess watershed pathogen impacts during run-offrnevents can not be overstated, yet few report the hydrological state when sampling forrnmicrobiology, and indeed, typically select against such periods to sample.