Waikato Regional Estuary Monitoring - Intertidal Estuarine Vegetation

The purpose of this dataset is to map the spatial extent of estuarine vegetation in Waikato estuaries and harbours and follow changes in communities over time for state of the environment reporting. Initially, this dataset contained estuarine vegetation maps for eight estuaries on the Coromandel Peninsula (Manaia, Te Kouma, Coromandel, Whitianga, Tairua, Wharekawa, Whangamata, Otahu). More recently, surveys have been completed in the inner Firth of Thames, Port Waikato, Aotea Harbour and Raglan (Whaingaroa) Harbour, Colville Bay Estuary and Purangi Estuary. The vegetation that has been mapped is within the Coastal Marine Area (CMA) and includes the spatial cover of mangrove, seagrass, sea meadow, saltmarsh and estuarine weed communities. The results of the estuarine vegetation surveys are included in Environment Waikato’s Global Information System (GIS) database, and are used for State of the Environment investigations and assessing resource consent applications that may affect estuarine vegetation.

Spatial coverage of esturine vegetation based on aerial photographs and ground-truthing. The baseline inventory of estuarine vegetation identified the following broad vegetation types in Waikato Region estuaries: Mangrove communities (Avicennia marina var. australasica). Seagrass communities (Zostera capricorni). Saltmarsh communities. Within the broad saltmarsh community three sub-communities were identified: The 'Rush/Sedge community' (mid-high tide level) generally monospecific stands determined by site condition (includes, for example, species such as Leptocarpus similis [golden jointed rush], Juncus maritimus var. australiensis [sea rush]); The 'Marsh Ribbonwood community' (high tide level) where the rush/sedge and salt meadow communities intermingle with saltmarsh ribbonwood (includes, for example, species such as Plagianthus divaricatus [marsh ribbonwood], Samolus repens [sea primrose], Silliera radicans [remuremu], Stipa stipoides [silver tussock grass]); The 'Salt Meadow community' (above mid-high tide level) dominated by the prostrate mat-forming plants (includes, for example, species such as Samolus repens [sea primrose], Selliera radicans [remuremu], Sarcocornia quinqueflora [glasswort]. Patches or narrow bands of these species can be found scattered throughout the saltmarsh zone, but are more often found along the inland edge of the 'rush/sedge community'. Also found associated with these three main species, is the Austrostipa stipoides [silver tussock] on coarse or rocky outcrops; and in more brackish areas: Cotula coronopifolia [bachelor's button], Eleocharis acuta [sharp spike-sedge, Isolepis cernua [slender clubrush] and Triglochin striata [arrow-grass]. Invasive exotic plant (weed) communities (e.g., Paspalum vaginatum, Spartina sp.). Estimations are made of the historical extent of wetlands around the estuaries. This is based on a visual assessment only (no review of historical aerial photographs).

Initial dataset included eight estuaries on the Coromandel Peninsula: Manaia, Te Kouma, Coromandel, Whitianga, Tairua, Wharekawa, Whangamata and Otahu. More recently the inner Firth of Thames has been included and three estuaries on the West Coast: Aotea, Port Waikato and Whaingaroa (Raglan).

Manaia (NZMS 260-T11 295810), Te Kouma (NZMS 260-T11 290830), Coromandel (NZMS 260-T11 320870), Whitianga (NZMS 260-T11 505780), Tairua (NZMS 260-T12 635597), Wharekawa (NZMS 260-T12 655500), Whangamata (NZMS 260-T12 645425), Otahu (NZMS 260-T12 660373), Inner Firth of Thames (NZMS 260 - XXXXX), Port Waikato (NZMS 260 - XXXXX), Aotea (NZMS 260 - XXXXXX), Raglan (NZMS 260 - XXXXXX).

Aerial photographs flown: April 1995 - Whangamata, Whitianga; November 1995 - Manaia, Te Kouma; January 1996 - Coromandel; April 1996 - Tairua; May 1996 - Otahu, Wharekawa. Aerials were taken in 2002 for Port Waikato, Raglan, Aotea and the Firth of Thames. 2006 and 2007 aerial photos were used for the second surveys of Raglan, Tairua, Manaia and Wharekawa, and for the first survey of Colville Bay Estuary and Purangi Estuary. Ground survey undertaken: January 1997 - Wharekawa, Whangamata, Otahu; July 1998 – Coromandel, Tairua; August 1998 – Manaia, Te Kouma; January 1999 – Whitianga, April-June 2006 - Thames, January-February 2005 - Kawhia, February 2005 - Aotea, November 2004 - Port Waikato and Raglan, April 2008 - Wharekawa and Tairua, June 2008 - Manaia, December to March 2012 - Raglan, October to January 2012 - Colville Bay. Purangi October - November 2012.

Information on estuarine vegetation was derived from interpretation of aerial colour photographs flown in 1995-1996 (scale of 1:5,000 or 1:10,000) combined with ground survey. Aerial photographs of each estuary were mosaiced and laminated. Vegetation boundaries were drawn (colour-coded lines) by a skilled interpreter, on transparent acetate film overlaid over the mosaics to define the spatial extent and distribution of different vegetation types. These boundary lines were ground surveyed to establish their accuracy. The spatial extent and distribution of estuarine vegetation was documented at the broad assemblage level (e.g., seagrass, mangrove, rush/sedge, marsh ribbonwood, saltmeadow), with ground survey including information at the genus/species level. Traced vegetation boundaries were converted to digitised images which were imported into Geomedia GIS software. The mapped vegetation was registered to the New Zealand Map Grid by overlaying the vegetation and harbour boundaries over a 1:50,000 map sheet and known points on the map were used to adjust the positions of the unreferenced data. For the most recent survey (Inner Firth of Thames), a personal digital assistant (PDA) loaded with 2002/03 aerial maps was used as the primary mapping tool. Colour coded lines were drawn directly onto the PDA to define the spatial extent of wetland vegetation types. Frequency of collection: At this stage it is planned that spatial extent and distribution of intertidal estuarine habitats will be undertaken approximately every 5 years.

Small discrete communities such as seameadow do not show up on aerial photographs and are therefore only surveyed during field inspections. Small populations may still be overlooked in the field and it is likely that the spatial estimation of seameadow communities is underestimated. This may be offset by the thickness of the line used to denote the small populations for digitising which may cause the overestimation of the population size. The error introduced through the thickness of the hand-drawn delineating boundary line is reduced for large communities such as mangroves or rush/sedge. Gaps in collection: None Data quality: Sites located from aerial photographs 1:5,000 and 1:10,000. Note that there is a difference between the date of aerial photography and the date of ground survey. Attribute accuracy: Ground survey undertaken and type specimens collected. Completeness: Vegetation maps only – no reference to other intertidal estuarine habitat types.

Maps, reports. There is also a collection of type specimens, and a large number of site photographs. Digital Format: The data is stored as corporate GIS layers.

Monitoring the spatial extent, distribution and habitat type in estuaries will provide the empirical basis for assessing the state of the Region's estuaries, and to signal any local-scale (e.g., stock trampling, point-source pollution) or broad-scale pressures (e.g., changes in land-use and catchment management practices).

Unrestricted availability – but note that there is an issue of map layout and accuracy. Sensitivity/Confidentiality: None

The database is regularly updated and maintained as information is gathered through the Regional Estuary Monitoring Programme.

Additional comments: The first set of data (eight Coromandel estuaries) was built in ARCView format, which enforces topological consistency (i.e., no overlapping features, complete polygons). More recent survey data has been built in Geomedia software. Related information: MfE - Monitoring Protocol for NZ Estuaries – Whangamata Harbour