Faecal Source Tracking at Recreational Bathing Locations in Northland

Investigation was carried out at eleven freshwater sampling sites in Northland to try to establish the source of elevated bacterial levels. Environmental Science and Research (ESR), with support from Envirolink, analysed and reported on samples collected on three occasions in February and March 2008.

Recreational bathing sites

Nine of the eleven sites investigated in this study are popular swimming spots that are sampled every summer as part of the recreational bathing water quality programme. The nine sites investigated have had consistently high bacterial levels and include:

  • Raumanga Stream (site 103246)
  • Above Whangarei Falls (site 105972)
  • Langs Beach Stream below the toilets (site 100686)
  • Langs Beach Stream in the middle of the beach (site 104539)
  • Ocean Beach Stream (site 102077)
  • Otamure Bay Stream (site 108859)
  • Waiharakeke Stream (site 108921)
  • Wairoa Stream at Ahipara (site 105053)
  • Otiria Stream below falls, near Moerewa (site 105376)

As these sites have consistently poor bacterial water quality four were removed from the recreational bathing programme before the 2007/2008 summer.

Refer to the following page on the Regional Council website for more information:
http://www.nrc.govt.nz/Living-in-Northland/At-the-beach/Swimming-water-quality/Previous-results/Sites-removed/

Other sites with consistently high bacterial levels

One of the eleven sites investigated was the Mangere Stream at Knight Road (site 101625), which is sampled monthly as part of the River Water Quality Monitoring Network.

The other site is Ruahuia Stream at the viaduct (site 106991), the headwaters of the Otarao Stream, which is where an integrated catchment project has been carried out over the last six years. These two sites also have consistently poor bacterial water quality.

Methods used by ESR

The samples were tested using a range of scientific techniques by ESR to assist in identifying the source of bacterial contamination, including faecal sterols, fluorescent whitening agents and polymerase chain reaction (PCR) markers.

Sterols are lipids that relate to both plants and animals such as cholesterol or the plant sterol, stigmasterol. 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. Therefore, 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 – members of the ruminant group are a subset of herbivores and include cattle, sheep, deer and goats) and plant decay and/or runoff from vegetation.

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 basically show the difference between closely related bacteria using DNA sequencing. In some cases this bacteria 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 are from can sometimes be identified using PCR markers. PCR markers for the following host groups were used in this investigation: human, ducks (wildfowl), ruminants (includes sheep, cattle, deer and goats), possums and pigs, as well as a general indicator for faecal contamination.

Key findings


The key findings from this research are:

  • None of the samples from any of the sites showed the source of bacteria to be humans.
  • There were several sites which showed one of the sources of faecal contamination to be herbivores, in particular ruminants on one or more sampling occasions, including Whangarei Falls, Langs Beach Streams (at both the south end below toilets and in the middle of the beach), Otamure Bay Stream, Waiharakeke Stream, Wairoa Stream at Ahipara and Otiria Stream.
  • The results from some sites suggested a source of faecal contamination could be water fowl, including Raumanga Stream, Whangarei Falls, Langs Beach Stream (middle beach only), Otamure Bay Stream, Waiharakeke Stream, Wairoa Stream at Ahipara, Otiria Stream and Mangere Stream. However the tools for identifying bird faecal contamination need more development, as it is currently only based on ducks and therefore some sites which did not show birds as a source, could still in fact be contaminated by gulls.
  • There are preliminary (unconfirmed) results that suggest pigs could be a source of faecal contamination at Langs Beach Stream (middle only) and Otiria Stream. The tools for indentifying faecal contamination from pigs need further development.
  • There are preliminary (unconfirmed) results that suggest that plant decay or runoff from vegetation could be contributing to the high bacterial levels in the two Langs Beach Streams (below toilets and middle of beach). This requires further work.
  • There are also preliminary (unconfirmed) results that suggest possums could be a source of faecal contamination at Whangarei Falls, Ocean Beach Stream, Waiharakeke, Wairoa and Otiria Streams. The tools for indentifying faecal contamination from possums need further development.

Summary

The sources of bacterial contamination at each site confirmed by this investigation are summarised in the table below with a tick.

 

Site

Human

Herbivores

Water fowl

Unconfirmed results

Raumanga Stream

x

?

ü

x

Whāngārei Falls

x

ü

ü

? (possum)

Langs Beach Stream (below toilets)

x

ü

X

? (plant decay or runoff)

Langs Beach Stream (middle of beach)

x

ü

ü

? (plant decay or runoff and pig)

Ocean Beach Stream

x

?

?

? (possum)

Otamure Bay Stream

x

ü

ü

x

Waiharakeke Stream

x

ü

ü

? (possum)

Wairoa Stream (Ahipara)

x

ü

ü

? (possum)

Otiria Stream

x

ü

ü

? (possum and pig)

Ruahuia Stream

x

?

x

x

Mangere Stream

x

x

ü

x

Note the results marked with a question mark were either very weak results, questionable or unconfirmed results (i.e. in most cases the tools used by ESR need more development).

 

Although this investigation has ruled out human faecal pollution as the source of elevated bacterial levels, it is important to note that there is still a human health risk associated with the elevated bacterial levels at these sites if the source is herbivores or birds.

The faecal material from herbivores and birds can contain pathogens such as Salmonella sp. and Campylobacter sp., which can cause illness in humans.