Tasman District is home to several internationally and nationally significant estuaries and sand flats, including Wanganui Inlet, Waimea Inlet and Farewell Spit. They are significant because of the rich life they support, including several threatened and migratory birds and many fish species.
Over the last century or more, many of our estuaries have been subject to various discharges from industry or the river catchments feeding them and from disturbances such as reclamation. In some cases, these activities have compromised the health of the ecosystem. To determine the health of our estuaries Tasman District Council began an estuary monitoring programme in 2002.
Estuaries are valued by many people for their aesthetic appeal, natural character as well as a recreation venue. Another use of estuaries is waste assimilation. Ecologically, estuaries are particularly valued for their remaining important habitats e.g. saltmarsh, seagrass and extensive shellfish beds. Seagrass beds are a very important source of biodiversity and are very productive feeding areas for wading birds.
Tasman District Council undertakes education and advocacy via workshops and events to promote successful estuarine habitat restoration, and workshops on reducing sediment discharges from site developments. Additional tools include the use of regulation to place controls which ensure sustainable development and where necessary exclusion.
Learn about estuarine restoration and consider re-establishing the natural sequence of vegetation from the inter-tidal area to well above the high tide mark. Join a CoastCare group – it is more fun and there is a better result with the combined expertise. Consider building hides for bird-watching.
Approximately 30% of saltmarsh in Golden and Tasman Bays has been lost, mostly to reclamation (this excludes Abel Tasman area). The Moutere and Ruataniwha estuaries have suffered the largest loss at 50% and 40% respectively. Saltmarsh is one of the most productive environments on earth and serves as an important nursery ground and wildlife habitat. It also provides for flood and erosion control, improvements to water quality and carbon sequestration.
While reclamation of saltmarshes rarely occurs today, they are likely to be threatened by sea level rise.
Restoration of saltmarsh communities is encouraged by Council provided it is appropriate to the site and does not cause any significant adverse effects on neighbouring landowners. Many opportunities exist for restoring biodiversity, landscape and amenity values. While as yet there are no formal restoration plans for our estuaries, the following document has some useful pointers on saltmarsh restoration.
Other useful resources include:
To ensure the community and ecological values of our estuaries are maintained or enhanced, we have to know what condition they are in. The specific aims of Council's estuary monitoring programme are to:
The monitoring programme is made up of four components:
Estuaries are a sink for contaminants that run off the land. If we look after the land well the estuary with be in good health.
Estuaries such as Whanganui Inlet are generally in very good condition, probably similar to that in pre-human times. Over the last century most of our estuaries with greatly modified catchments and intensive land use near to or around them have become highly modified, particularly from fine sediment discharges and habitat loss. In some cases, these activities have compromised the health of the ecosystem. Additionally pests such as stoats and rats, as well as cats and dogs have reduced the number of many bird species.
Sediment discharges from subdivision developments, farming, forestry and roading activities is an on-going issue. The area of soft mud in some estuaries, particularly Waimea and Upper part of Motupipi was elevated (a “poor” rating). It was also elevated in parts of the Ruataniwha, Moutere, and Motueka Delta estuaries and rated “fair”. Low sediment oxygen and lower biodiversity was also apparent in these areas. Sediments can also carry toxins such as heavy metals. Zinc is an example of a heavy metal which is elevated in sediment near urban or industrial areas.
Threat to saltmarsh habitat due to reclamation has reduced in the last two decades. There has been a significant loss of saltmarsh in all the estuaries but particularly the Waimea and Motueka Delta. The rate of loss is much lower than two decades or more ago. Seagrass areas are low in most estuaries except Wanganui estuary. The area of seagrass in the Waimea has declined.
Disease-causing organisms discharged as run-off from intensive agricultural or urban land or sewage discharges can affect the safety of swimming or in-water recreation as well as shellfish food safety. Water quality monitoring shows the Motupipi and Ruataniwha estuaries to have the highest concentrations of enterococci, an indicator disease-causing organism. Moutere and Waimea estuaries are only occasionally unsafe for swimming. All these monitored estuaries are unlikely to regularly contain shellfish that are safe to eat.
Generally less of an issue in Tasman’s estuaries. However parts of the Moutere and Motupipi are nutrient enriched but nuisance macro-algal cover is only occasionally a nuisance issue.
Generally less of an issue in Tasman’s estuaries. Higher concentrations of toxins in estuarine sediment are only found in very isolated areas of Waimea estuary associated with the urbanised streams.
Sediments around slipways used for cleaning of boats in the coastal area are often contaminated with anti-fouling paints containing heavy metals and other chemicals such as try-butyl tin. Further information and the report describing heavy metal contamination of sediments slipways in estuaries in Tasman is available:
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