Key points
This indicator measures the levels of trace elements and organic compounds in sediments in the Firth of Thames and Whaingaroa (Raglan) Harbour. Trace element and organic compound levels are compared to the guidelines derived by the Australian and New Zealand Environment and Conservation Council (ANZECC). For each trace element and organic compound, ANZECC has derived a low and a high interim sediment quality guideline (ISQG-Low and ISQG-High). The ISQG-Low is the level below which adverse effects are very unlikely. The ISQG-High value is the level which is known to have adverse effects on some animals. Between the ISQG-Low and ISQG-High values is a grey area where effects of trace elements and organic compounds are unknown.
- On average, all sediment trace elements, total polycylic aromatic hydrocarbons (PAHs) and dieldrin were at levels less than the lower level of the interim sediment quality guideline values (ISQGs) in both estuaries. No dieldrin was detected in either estuary.
- Total DDT levels exceeded the lower level of the ISQGs in both estuaries. However, levels were less than 15 per cent and 10 per cent of the higher level of the ISQGs in the Firth of Thames and Whaingaroa (Raglan) Harbour, respectively. DDT was applied to pasture in the past and a small proportion has washed down into the estuary. Use of this chemical has now been banned. It is degrading and levels are expected to decrease over time.
- There were differences in trace element, total PAH and total DDT levels between the two estuaries in October 2003. Levels of most (8 out of 10) of the trace elements, total PAHs and total DDT were higher in sediment in the Firth of Thames than in Whaingaroa (Raglan) Harbour sediments.
- The potential for contaminant-related problems for all trace elements, total PAHs and dieldrin is very low. Total DDT levels are in the range where some adverse effects may occur.
- The higher levels of lead, mercury, zinc and arsenic in the Firth of Thames are likely to be related to the mining history of the area. Average mercury levels are close to the lower level of the ISQGs. This lower level is a trigger level for further investigation, so monitoring will continue in the estuary.
Source: Environment Waikato
What agencies are doing
- Environment Waikato regularly monitors trace element and organic compound levels in the sediments of our region's estuaries to update this indicator and assist with policy making and resource consent decisions.
- We manage and require resource consents for activities that affect our coastal marine areas.
- We promote catchment management activities that protect estuarine and coastal ecosystems. This includes Environment Waikato's Clean Streams project. We provide information including practical land management guidelines.
- We support voluntary guidelines and codes of practice such as the New Zealand Fertiliser Manufacturers' Research Association Code of Practice for Fertiliser Use - aimed at minimising fertiliser runoff.
- We support care groups. Their riparian management work, such as planting and fencing helps decrease sediment and nutrient runoff to estuaries and the coast from streams and rivers.
- We have a 'Coasts and Us' school resource kit.
What you can do to help
- Boat owners should dispose of rubbish and sewage from boats onshore, and maintain bilge pumps to reduce oil leaks.
- Prevent pollutants from getting into stormwater drains and flowing into our estuaries and coastal areas by:
- washing your car, boat keels, motors and trailers on the grass, not on paved surfaces
- fixing any oil leaks from your car or boat
- not putting petrol, paints, solvents or garden chemicals down stormwater drains.
- Reduce the effects of land management practices on our estuaries by:
- planting or leaving a buffer strip along streams and at the edge of estuaries to help stabilise the banks and trap nutrients - these act as a filter between land and waterways
- managing farm effluent and grazing to prevent runoff into waterways.
- forming a caregroup to discuss and carry out better catchment management practices to protect our estuaries. A good example of a community group working to protect their harbour is the Whaingaroa Harbourcare Group at Raglan.
More information
More detail on this indicator, including how and where this information is collected, is available here.
What we want to achieve
The community outcome we are seeking to achieve by monitoring pollutants in coastal sediments is:
- Our coastal and waterway environments are restored and preserved and access to them is maintained.