Potential sources of faecal contaminants in four Coromandel catchments

TR 2017/25

Report: TR 2017/25

Authors: Marguerite Nakielski (4Sight Consulting), Pete Wilson, Eloise Ryan (Waikato Regional Council)

About this report

In January and February 2015, Waikato Regional Council investigated the water quality at several stream mouths throughout the Coromandel. Some of these water bodies were found to be particularly susceptible to contaminants (excess nutrients and faecal bacteria) that are washed from the surrounding land, particularly 24–48 hours after heavy rainfall (see our technical report, TR2016-07)

A more comprehensive follow-up study was carried out during January and February 2017 in four catchments (Opito Bay, Kuaotunu, Whitianga, and Tairua) to further identify potential causes of contamination. This study was designed to identify the source of faecal contamination within the catchment, linked to land use where possible, and whether it was from humans or animals. It also investigated how the concentration and source of contamination changed during dry and wet weather and during spring and neap tides.

The study showed that in general:

Faecal contamination was highest after heavy rainfall.
Faecal contamination was highest at pastoral and stream mouth sites and lowest at the native/exotic bush sites.
Faecal contamination was most likely to be elevated at the stream mouth during spring tides.

The findings from this study increase our understanding of the range and source of contamination at these locations following different weather and tide events. This will help us to develop targeted investigations and responses to coastal water quality issues throughout the Waikato region. It may also inform the development of catchment management initiatives if there are opportunities to reduce contamination into these streams.