Name: 2016 Low O2

Display Field: Estuary

Type: Feature Layer

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Description: 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 Serivce. 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. Areas with a mud content >25%, sediment oxygen (aRPD) depth 50%, and elevated organic content >1% were defined as representing Gross Eutrophic Zones (GEZ).

Copyright Text: Salt Ecology

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Last Edit Date: 12/9/2025 3:29:38 AM

Schema Last Edit Date: 12/9/2025 3:27:43 AM

Data Last Edit Date: 12/9/2025 3:27:43 AM

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