Name: Relative Wetness Gradient Lowlands

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Description: <DIV STYLE="text-align:Left;"><P STYLE="margin:0 0 0 0;"><SPAN STYLE="font-weight:bold;">1 Overview </SPAN></P><P STYLE="margin:0 0 0 0;"><SPAN><SPAN>Approximately 95% of Northland’s original wetlands have been lost. Northland Regional Council </SPAN></SPAN><SPAN><SPAN>(NRC) have been working to improve knowledge of existing wetlands, to better understand how best to prevent further loss, to identify suitable restoration sites, and to provide landowners with better advice for wetland protection and management. </SPAN></SPAN></P><P STYLE="margin:0 0 0 0;"><SPAN><SPAN>This document details the associated metadata for the mapping of hydric soils and wetlands integrating radiometric and satellite (Sentinel) imagery for the Northland Region. Background information on the theory, method, validation and outputs can be found within Rissmann et al. (2019; Envirolink Grant: 1955-NLRC214 and 1956-NLRC215). The GIS layers that were integrated to produce Northland</SPAN></SPAN><SPAN><SPAN>’</SPAN></SPAN><SPAN><SPAN>s Relative Wetness Gradient Layer (NRWGL) classification included: </SPAN></SPAN></P><P STYLE="margin:0 0 2 0;"><SPAN><SPAN>• </SPAN></SPAN><SPAN><SPAN>Percentage gamma-ray attenuation derived from Radiometrics </SPAN></SPAN></P><P STYLE="margin:0 0 2 0;"><SPAN><SPAN>• </SPAN></SPAN><SPAN><SPAN>Normalised Differential Wetness Index (NDWI) derived from Sentinel Satellite </SPAN></SPAN></P><P STYLE="margin:0 0 0 0;"><SPAN><SPAN>• </SPAN></SPAN><SPAN><SPAN>Topographic </SPAN></SPAN><SPAN><SPAN>domain, ‘upland’ and ‘lowland,’ derived from NASA’s MERIT Digital Elevation </SPAN></SPAN><SPAN><SPAN>Model </SPAN></SPAN></P><P /><P STYLE="margin:0 0 0 0;"><SPAN><SPAN>The gamma-ray attenuation layer, 50 x 50 m resolution (0.25 Ha), forms the basis of a perennial wetness gradient layer for the Northland Region that also identifies the existence of peat deposits and hydric soils. Importantly, gamma-ray attenuation mapping identifies peat deposits and hydric soils independent of vegetative cover, providing insight over the extent of former wetland complexes that have been cleared for productive purposes. Sentinel satellite derived Normalised Differential Wetness Index (NDWI) appears most relevant to land cover gradients and MERIT based terrain analysis provides an objective basis for evaluating the association between geology, topography, and perennial wetness gradients derived from gamma-ray attenuation. </SPAN></SPAN></P><P STYLE="margin:0 0 0 0;"><SPAN><SPAN>The resultant NRWGL provides a classification of wetness gradients as a function of gamma-ray attenuation, wetness index, and topographic pos</SPAN></SPAN><SPAN><SPAN>ition. Across the ‘lowland’ domain there are 3 main </SPAN></SPAN><SPAN>families that define a wetness continuum from wettest (Family 1) to driest (Family 3). Within each of the 3 families the relative wetness gradient is defined by each class (high to low). Family 1 encompas</SPAN><SPAN><SPAN>s most of Northland’s known wetlands (Wetlands 1000, Top 150 and L</SPAN></SPAN><SPAN><SPAN>UCAS) and/or areas of likely former wetlands that are now associated with productive land cover. There is also a strong association between this family and the QMAP geological classification of peat deposits and the NZLRI classification of organic and poorly drained (hydric) soils. </SPAN></SPAN></P><P STYLE="margin:0 0 0 0;"><SPAN><SPAN>Although the work was unable to define wetland by vegetative species, when combined with the LUCAS land cover layer and Northland Regional Councils 1000+ wetlands, it provides a basis for: </SPAN></SPAN></P><P STYLE="margin:0 0 2 0;"><SPAN><SPAN>• Better defining wetness and vegetative cover gradients within recognised wetland areas. </SPAN></SPAN></P><P STYLE="margin:0 0 2 0;"><SPAN><SPAN>• Identifying the location and extent of former wetland areas that have been modified for productive purposes. </SPAN></SPAN></P><P STYLE="margin:0 0 2 0;"><SPAN><SPAN>• Discrimination of perennially and intermittently wet wetlands. </SPAN></SPAN></P><P STYLE="margin:0 0 2 0;"><SPAN><SPAN>• Identifying areas of wetland with or without wetland vegetation that have not formerly been recognised, and; </SPAN></SPAN></P><P STYLE="margin:0 0 0 0;"><SPAN><SPAN>• Evaluating the relationship between topography, geology, land cover, soils and wetness gradients. </SPAN></SPAN></P><P /><P STYLE="margin:0 0 0 0;"><SPAN /><SPAN /></P><P STYLE="margin:0 0 0 0;"><SPAN STYLE="font-weight:bold;"><SPAN>5 Northland Relative Wetness Gradient Layer (NRWGL) </SPAN></SPAN></P><P STYLE="margin:0 0 0 0;"><SPAN STYLE="font-weight:bold;"><SPAN>5.1 Raw data and rationale </SPAN></SPAN></P><P STYLE="margin:0 0 0 0;"><SPAN><SPAN>To produce an integrated picture of the landscape and land cover factors governing perennial wetness gradients, topography, gamma-ray attenuation and MNDWI layers were integrated to produce a classification for Northland of Relative Wetness. Integration also provides a basis through which a single image layer can be interrogated against existing classifications, such as </SPAN></SPAN><SPAN><SPAN>Northland’s </SPAN></SPAN><SPAN><SPAN>ecological districts, </SPAN></SPAN><SPAN><SPAN>LUCAS (land cover), Northland’s Top 1,000 wetlands, geological</SPAN></SPAN><SPAN><SPAN>, soil and property layers. </SPAN></SPAN></P><P STYLE="margin:0 0 0 0;"><SPAN STYLE="font-weight:bold;"><SPAN>5.2 Method </SPAN></SPAN></P><P STYLE="margin:0 0 0 0;"><SPAN><SPAN>Gamma-ray attenuation and MNDWI rasters were weighted and indexed relative to each other before being normalised and standardised for phylogenetic classification. Phylogenetic assessment revealed a total of 10 meaningful </SPAN></SPAN><SPAN><SPAN>classes or ‘clusters.’ </SPAN></SPAN><SPAN><SPAN>The 10-class layer was then subdivided into </SPAN></SPAN><SPAN><SPAN>‘lowland’ </SPAN></SPAN><SPAN><SPAN>(100) </SPAN></SPAN><SPAN><SPAN>and ‘upland’ </SPAN></SPAN><SPAN><SPAN>(200) domains from which zonal statistics were generated for each class within each domain (Table 3). Lakes (300) and Towns (400) were also added to the raster layer. The resulting Relative Wetness Gradient Layer (NRWGL) was then polygonised and combined with </SPAN></SPAN><SPAN><SPAN>Northland Regional Council’s Known Wetland lay</SPAN></SPAN><SPAN><SPAN>er and Heathland layer and the latest LUCAS land cover layer (MfE, 2019). </SPAN></SPAN></P><P STYLE="margin:0 0 0 0;"><SPAN /><SPAN /></P><P STYLE="margin:0 0 0 0;"><SPAN>For a more detailed explanation please refer to the Mapping of Northland’s Wetness Gradients utilising Radiometric and Satellite imagery report - GIS Metadata (Land and Water Science 12/11/2019)</SPAN></P></DIV>

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