N loads

Landscape Nitrogen Attenuation Index (LNAI)

LNAI derived from an unsupervised classification between land unit redox probability, rock type and soil drainage.

Land use typologies

Land use typologies by Srinivasan et al. (2021). Land use data by Manaaki Whenua (2020), slope data from NZ LRI, irrigated areas from 2020 data set (Aqualinc/MFE), moisture classified from average annual rainfall 1972-2016 (NIWA).

Map

‘Attenuated (t/y)’ and ‘Unattenuated (t/y)’ loads are calculated based on the land use typology multiplied by 1 - LNAI score (at the landscape unit scale) to provide the Nitrogen Attenuation Factor (NAF) for each subzone.

LNAI scores have been assigned as:

  • Very low: 0.1
  • Low: 0.25
  • Medium: 0.5
  • High: 0.75
  • Very high: 0.9

Monitoring sites are included in the map and are either consistent with the subzone results (where a monitoring site covers just a single subzone e.g. Mangatoro at Mangahei Road) or are cumulative of several subzones (e.g. Manawatu at Weber Road)

Tables and maps for comparison

Snelder et al. (2020) estimated river loads based on xx methodology at select monitoring sites in the region…

… and the attenuation coefficient based on the difference