The Recreational Swimming Water Quality Programme is a joint project, administered by the Northland Regional Council (NRC), in partnership with the Northland District Health Board (DHB), and the Far North District Council (FNDC), Whangārei District Council (WDC) and Kaipara District Council (KDC).
Under this programme, a number of the region’s most popular coastal and freshwater swimming sites are sampled once a week throughout the summer months. The samples are analysed for illness causing bacteria and the results distributed to key stakeholders and the general public. Sites are graded each week according to the level of bacteria recorded at each site – green ‘considered suitable for swimming’, orange ‘considered potentially unsuitable for swimming’ and red ‘unsuitable for swimming’.
The aim of the programme is to provide information on water quality at popular freshwater and coastal swimming sites in Northland, to allow the public to make an informed decision about whether a site is suitable or not for swimming.
As a result of water quality testing undertaken through this programme, a number of freshwater and coastal sites in Northland have been identified as having poor, or ‘unsuitable for swimming’, water quality. Some sites have consistently poor water quality with high levels of bacteria recorded on most sampling occasions. Other sites have generally good water quality but occasional, extreme spikes in levels of bacteria.
In most cases, the source of bacterial contamination at these sites is not immediately obvious. Over the previous summers, NRC investigated several sites with consistently poor water quality to try and identify the source(s) of contamination. The results from this work is used, where possible, to improve water quality at these sites.
Investigative work undertaken includes taking samples for microbial source tracking; catchment profiling and undertaking sanitary surveys, where septic tanks are suspected as being a source of contamination.
Microbial Source Tracking
There are several scientific techniques used to assist in identifying the source of bacterial contamination in water. These include faecal sterol analysis, fluorescent whitening agents (FWAs) and polymerase chain reaction (PCR) markers. The science behind this analysis is quite new and therefore still evolving.
Sterols are lipids that relate to both plants and animals, for example, cholesterol. The sterol profile in faeces depends on the animal’s diet, internally produced sterols and the bacteria in the animal’s gut. Consequently, analysis of the sterol composition of animal faeces can generate distinctive faecal sterol fingerprints. The ratio of different sterols in a water sample can be used to narrow down the potential source(s) of bacterial contamination to either humans, herbivores (animals whose main diet consists of vegetation, including cattle, sheep, deer and goats), and plant decay and/or run-off from vegetation.
Fluorescent Whitening Agents
Fluorescent whitening agents (FWAs) are common ingredients of washing powders and only one is used in New Zealand. In most households, the effluent from toilets is mixed with grey water from washing machines and therefore FWAs are usually linked to human faecal contamination in both septic tanks and community wastewater systems.
Polymerase chain reaction (PCR) markers show the difference between closely related bacteria using DNA sequencing. In some cases, this bacterium is highly host specific (i.e. only associated with the faecal material of one animal or animal group). Therefore the type of animal that the bacteria came from can sometimes be identified. PCR markers for the following host groups have been developed - human, ducks (wildfowl), ruminants (includes sheep, cattle, deer and goats), possums and pigs, as well as a general indicator for faecal contamination.
Catchment profiling involves mapping catchment land-use around problem sites so that potential sources of contamination can be identified, such as pastoral farming or septic tank soakage fields.
Once catchment land-use had been mapped for each site, microbiological samples were collected from key locations within each catchment to identify where bacterial levels were at their lowest and highest. This information provides an indication of where contamination is originating from, and in some cases, can point to a specific source of pollution.
Sanitary survey involves inspecting the septic tank and associated soakage field of each property in order to identify any failing or poorly maintained systems, which could be contributing contaminants to the water body.