Ground-truthing of dominant substrate, saltmarsh, macroalgae, seagrass, and terrestrial margin (200m) was undertaken during 28 November 2021. Features were recorded directly onto 30 cm pixel resolution (0.30 m GSD), 3-band (RGB) uncompressed GeoTIFF colour aerial imagery captured summer 2019-2021 for Otago Regional Council by Aerial Surveys Ltd.

Catchment land cover was sourced from Landcare Research Land Cover Database (LCDB5, 2018).

Each feature was digitised and field codes recorded in a master layer used to produce individual summary output layers using in-house scripting to validate field codes and check for any errors in geometry or typology.

Spatial accuracy for features clearly visible on aerial photos (e.g. salt marsh, cobble fields) is ~2 metres. Spatial accuracy for features difficult to distinguish on aerial photos (e.g. where boundaries represent a habitat transition from mud to sand) is ~10 to 20 metres depending on the extent of ground truth undertaken.

Sand and mud substrate classifications were validated through the laboratory analysis of representative samples from the surface 20mm for sediment grain size.

Macroalgal features were classified based on estimated percent cover, measured biomass (g/sq m wet weight) and presence of entrainment (growing >30mm within sediment).

Areas with High Enrichment Conditions (HECs) - also termed Gross Eutrophic Zones (GEZs) were defined as mud-dominated sediments (>50% mud content, based on expert judgement) with >50% macroalgal cover and with macroalgae entrained and growing as stable beds rooted within the sediment. These areas typically also have an aRPD depth shallower than 10mm due to sediment anoxia and elevated organic content (i.e. >1%).

Salt Ecology Report 102, prepared for Otago Regional Council, August 2022. 49p.