8.7 Case study 1: Whangaroa Harbour Study

An investigation was established in the Whangaroa Harbour in 2003 to identify faecal contamination in the harbour and sources of this contamination. Historically the closure criteria for the operation of the marine farms was brought into question as a result of high results during normal sampling by Northland Health on behalf of the oyster farmers and the New Zealand Food Safety Authority. Frequent events of bacterial contamination were occurring when they were not expected, threatening the operating classification of the harbour for commercial growing of oysters.

Whangaroa Harbour.

In July 2003 a sampling programme was developed which included 12 sites around the harbour, five sites in the Kaeo River catchment and five sites at the mouth of other freshwater inputs to the harbour. These are marked with a circle in figure 23 (below). These 22 sites were sampled monthly for physio-chemical and microbiological parameters. The five sites within the Kaeo River catchment were sampled to establish a data profile up the catchment, to determine likely contamination sources.

Map of testing sites in Whangaroa Harbour.

Figure 23: Sampling sites included in the Whangaroa Harbour study.

In October 2005 this data was reviewed and it was found that microbiological water quality deteriorated as you moved down the Kaeo River catchment, as shown in figure 24 (below).

The worst site was below the Kaeo Wastewater treatment plant (site 100671) with a median E. coli level of 932/100ml as shown in table 10 (below). However microbiological water quality was also impacted above the Kaeo township. The most likely source is faecal contamination carried in surface runoff from agricultural farming and where stock have access to the river. Faecal contamination from septic tanks and feral animals is also a possibility.

Median E. coli (n/100mL) results at Whangaroa Harbour study sites.

Figure 24: Median E. coli (n/100mL) results at Whangaroa Harbour study sites. Note: Results also available in table 10 (below).

This highlighted that there are several sources of faecal contamination in the Kaeo River and that the cumulative effects of these different sources as you move down the catchment is leading to elevated bacterial levels entering the Whangaroa Harbour, particularly after heavy rain.

Meetings have been held with key stakeholders to follow up on the findings of this initial sampling, including Far North District Council, Northland Regional Council, Department of Conservation, landowners, Te Rununga O Whangaroa, Federated Farmers, Northland Health and stakeholders from the marine farming industry. Key areas identified as requiring action were the discharge consent for Kaeo's treated wastewater, onsite disposal systems, land management of stock access to waterways and farm dairy effluent discharges, boat pump-out and dumping facilities, pest control and shellfish harvest management.

 

Table 10: Median E. coli (n/100mL), turbidity (ntu), proportion of freshwater (%) and number of samples for all sites in the Whangaroa Harbour study. Note: Median E. coli results also shown in figure 24 (above).

Site Description Median E. coli Median turbidity Median % freshwater Sample number
100765 North of Whangaroa marina 10 3.4 2.0 42
100858 Middle of Waitapu Bay 10 4.0 1.7 42
100928 Midway of Touwai Bay 10 3.2 2.6 42
101620 North corner of marine farm 10 4.8 2.6 42
101701 South corner of marine farm 10 7.1 5.4 42
102231 Totara North jetty 10 4.7 2.9 39
101614 Near Waitaruke drain outflow 31 8.8 4.3 42
102234 Ferguson Point 31 9.8 3.4 42
104993 Middle of Lane Mill Bay 31 5.6 2.9 42
102232 West of Cape Horn 41 8.5 5.4 42
108605 Pupuke River at culvert beside road 68 4.2 99.9 16
102228 Entrance of Waihapa Bay 109 11.4 8.9 43
108689 Headwaters of Anaotehuruhuru Strm 115 7.4 99.9 8
101622 Whangaroa Rd culvert before turnoff 166 6.8 47.4 40
108960 Touwai Strm at Matangirau School Rd 199 4.1 99.9 8
108564 Unnamed trib near Campbell Rd 347 6.1 64.9 18
102224 Mangaiti Stream at Dip Rd 400 6.1 99.7 26
100047 Kaeo River at Green Lane 428 4.3 99.7 25
102237 Near Kaeo River mouth 434 11.3 82.0 26
108959 Headwaters of Te Ahu Stream 472 5.2 99.9 8
108958 Whakare Stream at Huia Road 477 7.5 99.9 8
108603 Pupuke River at Weber Rd footbridge 480 4.6 99.9 16
100431 Touwai Stream near stream mouth 547 4.8 80.0 43
108690 Headwaters of Whakare Stream 552 6.4 99.9 8
101608 Kaeo River at SH 10 bridge 559 8.4 96.0 26
108604 Pupuke River at Mangapa Rd bridge 562 3.4 99.9 16
102199 Touwai Stream at Wainui Rd bridge 594 4.5 98.6 8
100862 Waitapu creek below road bridge 598 7.8 50.3 43
102227 Pupuke River at SH 10 bridge 613 9.2 75.1 43
108565 Unnamed trib at Totara School Rd 635 9.1 20.0 18
101607 Kaeo River below fire station 679 5.3 99.7 26
100436 SH 10 Bridge at Weber Rd 695 10.8 40.3 43
108566 Unnamed trib at Gangway Rd 789 7.6 97.1 18
100671 D/strm of Kaeo Sewage discharge 932 7.7 99.7 25
108602 Unnamed trib at Weber Rd 1308 6.8 34.9 16

Following these findings, sampling on the Kaeo River ceased in October 2005 and sampling efforts were shifted to other contributing catchments of the Whangaroa Harbour. This includes 33 sites on the Pupuke River, Touwai Stream, Waitapu Creek and small tributaries in the Totara North area, marked by a triangle in figure 23 (above). The initial results for these sites show there are some areas of concern in terms of faecal contamination. For example the unnamed tributary that flows into the upper Whangaroa Harbour by Weber Road (sites 108602 and 100436), Waitapu Creek (site 100862) and two unnamed tributaries in Totara North (sites 108566 and 108565).

An analysis was carried out to see if there was any relationship between turbidity or salinity and E. coli levels. No relationship was found between turbidity and E. coli as shown in figure 25 (below).

Figure 25: Median turbidity (ntu) against median E. coli (n/100ml) for all Whangaroa Harbour study sampling sites.

However, there appears to be a relationship between E. coli levels and the proportion of freshwater, as shown in figure 26 (below). The trend line in figure 26 has been fitted to the ‘normal sites' dataset (shown in green) which has an equation of y=5.58x0.99 (R2=0.93). This shows that higher E. coli levels tend to be associated with freshwater sites, while lower E. coli levels with saline sites.

There are a few exceptions to this trend, which are shown in red and blue in figure 26. The two sites shown in blue (108605 and 108689) have reasonably low E. coli levels and are both headwater sites. Their surrounding and upstream land use is predominantly native shrub and low intensity farming and therefore there are limited sources for faecal contamination.

At the other end of the scale, the sites shown in red have relatively high E. coli levels considering the low proportion of freshwater at these sites. This includes the unnamed tributary that flows into the upper Whangaroa Harbour by Weber Road (sites 108602 and 100436), Waitapu Creek (site 100862) and an unnamed tributary in Totara North (site 108565).

Figure 26: Median freshwater fraction (%) against median E. coli (n/100ml) for all Whangaroa Harbour study sampling sites.

These problem sites will be investigated further in the future. Other microbial tracking methods will be used to assist with identifying the source of contamination such as testing for fluorescent whitening agents, which originate from laundry detergents and is an indication of the presence of human wastewater, and possibly faecal sterols, which can narrow the source of the contamination to humans, herbivores or other.

In summary, the Whangaroa Harbour sampling to date has shown that the Kaeo River is a significant source of faecal contamination to the Harbour and that the sources of this contamination are varied and cumulative as you move down the catchment. Key stakeholders are currently working together to improve water quality in the Kaeo River. Sampling will continue in other catchments of the Whangaroa Harbour to identify other sources of faecal contamination.

For information on rules for sewage disposal, refer to the ‘Marine pollution regulations' information in our Boating in Northland booklet:

Boating in Northland