Contemporary and pre-human wetland area in New Zealand

Wetlands: New Zealand’s freshwater wetlands include areas that are permanently or intermittently wet, shallow water, or margins of land and water that support a natural community of plants and animals adapted to living in wet conditions (Resource Management Act, 1991). Wetlands occur in many locations, ranging from estuaries to mountaintops.

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The contemporary and estimated pre-human extent of wetlands were mapped at 1:50,000 to a minimum size of 0.5ha. Seven classes of wetlands were mapped according to their function. Wetlands were categorised as bog, fen, inland saline, marsh, pakihi/gumland, seepage, and swamp, based on Johnson and Gerbeaux (2004). Ephemeral wetlands, saltmarsh, and shallow water wetlands were not mapped.
The historic extent was estimated from the national Fundamental Soil Layers (FSL) database, and refined using a 15m digital elevation model derived from 20m digital contours. Geographic Information System (GIS) rules were used to identify wetland soils, based on soil survey descriptions that included drainage properties and the presence of peat and wetland vegetation. Soil drainage is divided into five classes in the FSL, from poorly drained (class 1) to well-drained soils (class 5). Soils in classes 1 to 3 were considered to have a high probability of having been wetland.
The contemporary extent was mapped using 26 Landsat Enhanced Thematic Mapper (ETM+) satellite imagery, and wetland point and polygon data. The data were collated from recent surveys, field work, or photo-interpretation held by local and central government. Point and polygon data were checked against the satellite imagery, and the wetland boundaries were corrected or delineated using the imagery (Ausseil et al, 2008).