AWWA WQTC60720

Under southern and eastern Australian conditions, concentrationsand loads of watershed pathogens were evaluated in six systems that spanned a wide range of conditions consisting of fully-protected,open grazing country to semi-rural, intensive (dairy), to on-site septic-impacted. Comparedto baseflow pathogen concentrations, historically small rainfall run-off events (1 per moto 1 in 4 y) increased the concentration of microbial parameters up to four orders ofmagnitude (i.e. by a factor of 10,000), and the load flux (units of contaminant.sec^-1.unit^-1area of watershed) by up to seven orders of magnitude. Maximum observedconcentrations of contaminants from the most impacted watersheds were ca 1000Cryptosporidium oocysts.10 L^-1; >100 mpn.100 mL^-1, Campylobacter spp.; 50,000mpn.100 mL^-1, E. coli/enterococci; and 5000 ng.L^-1, total â-stanols. In contrast, from twofully-protected watersheds almost no pathogens were detected even during eventconditions and only E. coli/enterococci increased in some of the major tributaries(unrelated to pathogen occurrence), highlighting the value of watershed protection. Fecalsterol/stanol biomarkers provided evidence of sewage impact during event hydrographsin otherwise herbivore-dominated fecal contamination, which was not evident from theabove mentioned microorganism assays, and suggested periods of potential human virusimpact. The biomarkers enabled estimates of the equivalent wastewater released fromseptic tanks to urban streams (ca 500,000 L per day-event). An overall risk assessmentmatrix was produced that linked watershed development, off-take location and level ofrun-off event impact. The need to assess watershed pathogen impacts during run-offevents can not be overstated, yet few report the hydrological state when sampling formicrobiology, and indeed, typically select against such periods to sample. Includes 16 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

11/15/2004

Number of Pages:

8

File Size:

1 file , 1.1 MB