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Snapshot of coastal stream mouth water quality in the Coromandel area (January/February 2015)

TR 2016/07

Report: TR 2016/07

Author: Pete Wilson

About this report

This report presents the findings from a one-off survey carried by WRC, of 18 small coastal stream mouths around the Coromandel region in January and February 2015. The main purpose of this survey was to provide a snapshot of coastal stream mouth water quality in the Coromandel region to assess ecological health and concentration of faecal bacteria that, at high levels, can create a health risk over the time of the survey. A secondary purpose was to trial a new approach to investigate potential sources of faecal bacteria such as humans, possums, dogs, pigs, gulls, ruminant animals, and more specifically, cows. 

This study has shown that the water quality in coastal stream mouths can be extremely variable. Nutrient concentrations were within guideline values most of the time at most sites. The median enterococci (faecal bacteria) concentration over the eight sampling weeks was within the guideline value at 13 out of the 18 sites.

The low flow and frequent blockages of the stream mouth can make these locations particularly susceptible to contaminants washed from the land, most notably during spring tides and following heavy rainfall. This highlights the importance of understanding the environmental processes that may lead to compromised water quality in stream mouths so that community can be better informed and management actions identified.

The trial of faecal source tracking provided some useful information on the potential sources of faecal contamination at the study locations. It identified one of the most common sources of faecal bacteria to be ruminant animals. Additionally, possum and gull sources were identified at most locations most of the time. Human sources were detected at few sites but only on some occasions. Due to the nature of the faecal source tracking technique, direct comparisons could not be made between the different sources to determine the relative contributions from each source. As a result, it cannot yet be used to make reliable statements on the exact causes of coastal water quality degradation.

It is important to note that this report does not make specific comments on public health, such as whether a location is deemed safe to swim or not, as this is out of scope and outside of regional councils’ expertise. 

Read or download the report

Snapshot of coastal stream mouth water quality in the Coromandel area (January/February 2015) [PDF, 4.6 MB]
Summary document [PDF, 799 KB]

Contents
1 Introduction 1
2 Methods 2
2.1 Locations 2
2.2 Sample collection 3
2.3 Water quality parameters 3
2.3.1 Microbial source tracking 4
2.4 Data analysis 5
3 Results 5
3.1 Ecological health
3.2 Faecal indicators  9
3.2.1  Microbial source tracking 11
3.3  Influence of rainfall, river flow, tide height, and catchment land use on stream mouth water quality 14 
3.3.1 Rainfall 15
3.3.2 Tide height 16
3.3.3 Land use 17
4 Discussion 18
4.1 Microbial source tracking 18
4.2 Recommendations for further development and implementation of microbial source tracking 19
  References 21