COROMANDEL WATER PROBLEMS
BY GEOFFREY ROBINSON

A Waikato Regional Council report on coastal stream mouth water quality released last week has uncovered serious problems involving faecal bacteria and nutrient loads, with implications for both the ecological health and recreational suitability of popular Coromandel spots.

The study, conducted in January and February 2015, sampled water eight times at weekly intervals at each of 18 sites around the peninsula. Water was tested for three faecal bacteria indicators -- enterococci bacteria, e coli, and faecal coliforms – to gauge suitability for contact recreation like swimming. Samples were also tested for turbidity and nutrient concentrations, including several nitrogen and dissolved reactive phosphorus parameters, as measures of stream ecological condition.

According to the WRC report, median enterococci concentrations over the two months exceeded Ministry for the Environment guidelines for marine and freshwater recreation at five of the 18 locations. Those locations were Graham’s Creek (Tairua), Stewart Stream (Opito Bay), Tarapatiki and Taputapuatea streams (Whitianga) and the Kuaotunu River. Tarapatiki Stream exceeded the NZ enterococci guideline of 280cfu (coliform forming units) per 100ml in each of the eight weekly samples. The WRC report states, “an exceedance of the recommended guideline indicates an elevated potential health risk.”

Water quality was noticeably better at all four west coast peninsula sites, as well as the Otahu River (Whangamata), with median enterococci counts below the Ministry for the Environment guideline and only one outlying sample above. The Purangi River (Cooks Beach) was the only location within the recommended limit on every week of the study.

Because enterococci is the “preferred indicator” in the marine environment, according to the report, no guideline was supplied by WRC to help evaluate e coli and faecal coliform test results. However, US Environmental Protection Agency beach and river guidelines for e coli do provide an indication, with no sample to exceed 235cfu/100ml and a 30-day mean concentration to be below 125cfu/100ml, according to that agency, for water to be considered “swimmable”.

Research in the US indicates a concentrations of 235cfu/100ml e coli is associated with an expected eight cases of gastroenteritis per 1000 swimmers.

According to WRC’s “snapshot” study, e coli levels in the Purangi and Otahu rivers were the lowest on the Coromandel by far. Median e coli levels over the summer were less than five percent of the EPA guideline level in both waterways, with no sample coming anywhere close to the limit.

Results for other Coromandel locations, however, showed notably higher e coli levels, with seven streams and rivers exceeding the 235cfu guideline in three or more of the eight weekly samples. Two streams, the Whangarahi (Coromandel Town) and Pitoone, exceeded 235cfu/100ml e coli in all except one test. As for median e coli levels over the full study period, sixthe Kuaotunu River was more than triple (790cfu) the EPA guideline, and the Tarapatiki Stream more than quadruple (955cfu).

The 18 peninsula waterways were also assessed for nutrient concentrations against guidelines of the Australian and NZ Environment and Conservation Council (ANZECC). Although exceeding the ANZECC guidelines “does not imply any adverse environmental effects”, according to WRC, the test parameters “are indicative of the ecological health of the stream mouth”. Waterways notable for testing in excess of the guidelines for either phosphorus, nitrate and nitrite, total nitrogen, or total ammoniacal nitrogen parameters included the Kuaotunu, Whangarahi, Purangi, and Wigmore Stream (Hahei).

Test results for nutrients were again more positive at west coast locations, whereas individual samples elsewhere on the peninsula exceeded guidelines by as much as 100 times in some cases.

According to WRC, further studies are being planned for the coming summer season, with regional council liaising with TCDC and the Waikato District Health Board regarding implications for public health and “better communication of results to the public”. A water quality monitoring programme for “open-coast beaches” is also being developed, according to WRC.

Coromandel residents can find complete nutrient and bacterial test details for each of the 18 streams and rivers atwww.waikatoregion.govt.nz/tr201607/ and following the link to “snapshot of coastal stfream mouth water quality”.

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