Ground-truthing of dominant substrate, saltmarsh, macroalgae, seagrass, and terrestrial margin (200m) was undertaken by Wriggle Coastal Management over December 2016. Features were recorded directly onto rectified ~0.25m/pixel resolution colour aerial photos flown in 2014/15 and sourced from LINZ online data service.

In 2021, Salt Ecology in-house scripting was used to validate 2016 field codes and check for topology errors. In the 2016 master layer, "Orig_Code" is the original 2016 field code and "FieldCode" shows any changes made. Field codes were updated to reflect improvements to the classification of substrate and any mapping errors that were found have been corrected.

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.

Field codes present features in order of their dominance; e.g Lesi Sare = (Lesi (rushland) dominant to Sare (herbfield)). Vegetation height is able to be derived from the structural class of features; e.g. Lesi (rushland) is taller than Sare (herbfield).

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

Sand and mud substrate classifications were validated through the laboratory analysis of representative samples 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).

The primary indicators used to assess sediment oxygenation are aRPD depth and RP measured at 3cm. These indicators were measured at representative sites throughout the dominant sand

and mud substrate types, and from a range of sites with variable macroalgal cover and bio-mass. Results have been used to delineate LowO2 zones where sediment oxygen is depleted to the extent that

adverse impacts to macrofauna (sediment and surface dwelling animals) are expected.

2023 Broad Scale Mapping of the Shag Estuary was undertaken by Salt Ecology on behalf of Otago Regional Council and is described in: O'Connell-Milne S, Forrest BM, Roberts KL, Stevens LM. 2024. Synoptic Broad Scale Ecological Assessment of Shag Estuary. Salt Ecology Report 134, prepared for Otago Regional Council, June 2024. 72p.

Ground-truthing was conducted during November 2023.

Features were mapped onto 30cm/pixel colour satellite imagery captured 15 April 2023 sourced from Apollo Mapping (Colorado).

Generally, at a digitising scale of 1:2000, spatial accuracy for features clearly visible on aerial photos (e.g. salt marsh, cobble fields, dense macroalgae) 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 50 metres depending on the extent of ground truthing undertaken.

Features were digitised and field codes recorded by Salt Ecology in a master layer. Salt Ecology proprietary scripting tools were used to validate field codes, check for topology errors, produce symbolised output layers and create summary data tables.

Macroalgal features were classified based on estimated percent cover, measured biomass (g/m2 wet weight) and presence of entrainment (i.e., stable macroalgal beds rooted >=30mm deep within sediment). PatchIDs identify a macroalgae bed or group of beds that share common classification metrics.

Use with permission of Otago Regional Council and acknowledgment of Salt Ecology.

Data package contains ground-truthed data from 2016 and 2023. Historic salt marsh was assessed from aerial imagery with no ground truthing for 1947, 1967, 1982, 2005. Natural extent was determined from imagery and LiDAR.