Meeting papers

                                                                                      Burgess Creek
                                                 Receiving Environment Monitoring Program
                                                                                 Annual Review 2022
levels of E.coli were observed upstream at B8, alongside elevated levels of E.coli and faecal
coliforms upstream of the STP outfall. In general, if the treated wastewater is of good quality
and the creek has a high flow rate and good mixing, the microbiological indicators shouldn’t
add to the natural load downstream due to natural degradation processes and ultraviolet (UV)
disinfection. The presence of dense fringing riparian vegetation and longitudinal distance
indicates that natural UV disinfection is limited and suggests that a local point source may be
responsible for driving the higher microbiological concentrations downstream of B3. Thus,
continued monitoring and investigation of potential sources of microbiological contamination
in the catchment are necessary. Moreover, temporal plots have revealed higher
microbiological indicator concentrations at all sites, except for B3, which remained consistent
during peak periods of rainfall. Enterococci concentrations at B3 and thermotolerant coliform
concentrations at B2 and B3 were the only sites to meet 100% compliance with the biological
indicator guidelines set out by ANZECC. Many factors, including water temperature, rainfall,
natural UV irradiation and flow rate, can affect the growth and survival of enterococci bacteria
in waterways, and the relative contribution of different sources can vary depending on these
factors. Some notable potential factors that could contribute to poor water quality in Burgess
Creek include stormwater runoff, agricultural runoff, local wildlife and septic systems.

Nutrient concentrations were elevated in the vicinity of the STP outfall where water flow was
highest. The greatest concentrations of ammonia, NOx, total nitrogen, filter reactive
phosphorous and total phosphorous follow a similar trend with the highest concentrations
recorded at either B3 or B6 immediately downstream of the STP outfall. The concentration of
chlorophyll a at B8 suggests that this location has either had higher availability of nutrients to
sustain high levels of algae growth than measured during the sampling events or upstream of
there is more surface water into which higher concentrations of nutrients and algae growth
has occurred. The consistent low chlorophyll a: pheophytin ration tends to support the later
reason for the higher algae growth: that there is another source of nutrients upstream and by
the time the water reaches monitoring site B8 the nutrients have been exhausted and the
algae is unable to sustain the growth and more pheophytin is present within algae. Pheophytin
is a breakdown product formed when chlorophyll a within the algae ages and is unable to
support growth. The other supporting evidence is that monitoring during 2019 occurred with
gaps of 3, 4, 5 & 6 weeks between sampling events. These differing gaps should have been
able to detect change in nutrients concentrations present at monitoring site B8 to support the
algae growth if it was occurring at monitoring site B8. This supports the interpretation that
there is a source of nutrients from either stormwater or groundwater expression into Burgess
Creek.

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