Environment, Local News

Lagoons report published

0 Comments 14 June 2016

Auckland West Coast Lagoons: Sources of Faecal Contamination

From: Catchments & Incentives | Environmental Services | Infrastructure & Environmental Services

Executive summary

Karekare LagoonsThe west coast beaches at Karekare, Piha, North Piha and Te Henga (Bethells) have excellent water quality based on long-term monitoring information; however, the lagoons at these locations have poor water quality. The lagoons have a history of high faecal indicator bacteria (Escherichia coli) concentrations, since at least 1985. This long-term contamination has remained consistently high since Auckland Council monitoring began in summer 2003–2004 consistent with the Ministry for the Environment’s 2003 guidelines, Microbiological water quality guidelines for marine and freshwater recreational areas. Previous investigations have used microbial source tracking (MST) analysis of water samples from the lagoons to indicate the biological sources of this contamination. This testing revealed a complex mix of sources from a range of animals, including dogs, birds, ruminants and humans.

The lagoons are often unsuitable for swimming

Bethells LagoonWater quality monitoring has shown that the lagoons are frequently unsuitable for recreational activities and during the peak summer holiday season, Auckland Council is often required to place signs advising people not to swim in the lagoons, on occasions for up to two weeks. In order to effectively manage the contamination, it is important to know where in the catchment the source is and from what animal sources any faecal contamination is originating. Therefore, the purpose of this investigation is to develop a more complete understanding of the biological and geographical sources of the microbiological contamination observed through the Safeswim monitoring programme.

Multiple faecal sources identified, but some could not be identified

Piha LagoonsThe investigation has confirmed the presence of a complex mix of microbiological contamination in the west coast lagoons. All of the lagoons had high concentrations of E. coli at times during the 2013-2014 summer and all 49 samples subject to MST analysis tested positive for the general faecal marker, which is a more reliable indicator of faecal contamination. A range of animal faecal sources were contaminating the west coast lagoons and their tributaries, including human, dogs, birds and ruminants, however all of the lagoons had occasions where the faecal source could not be detected.

The Piha Lagoon was the most chronically contaminated, having the highest concentration of E. coli of any of the study lagoons. The Piha stormwater inlet that was sampled had high concentrations of E. coli and tested positive for human markers, indicating that this discharge is one source of human faecal contamination to the lagoon. Human faecal contamination was consistently detected in the lagoon and further up Piha Stream, with 43 per cent of the MST samples from this catchment having evidence of human contamination, although in addition bird and dog markers were consistently detected in the lower parts of the catchment.

The samples from the Karekare Lagoon catchment had moderate concentrations of E. coli, but despite the detection of the general faecal marker in all five MST samples, a reliable source could be detected in only one of these. A human marker was detected in a single sample from the Company Stream, which is potentially a consequence of a large rain event overwhelming on-site wastewater systems.

Lagoon pollution PihaThe North Piha catchment sample sites had moderate levels of E. coli, but this was accompanied by strong evidence of human contamination at the Marawhara Lagoon site as five (of six) MST samples tested positive for human markers. The geographic source of this contamination was unclear and it is likely that there is a currently unknown contribution of wastewater to the lagoon requiring further investigation.

The results from the Te Henga Lagoon catchment provided very strong evidence of faecal contamination by ruminant animals, suggesting that improved livestock management could reduce the level of contamination in this catchment. However, bird and dog sources were also common in this catchment.

Managing contamination sources should help to minimise the faecal contamination

The report provides a number of recommendations aimed at reducing the level of faecal contamination in the lagoons. They include fencing riparian areas to exclude stock, investigations of and improved management of on-site wastewater systems, practical steps to manage faecal contamination from dogs and birds, and installing permanent warning signs about the public health risk of swimming in the lagoons.

Full Report  2016012awestcoastlagoonssourcesfaecalcontamination

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