NIWA Whangapoua terrestrial sediment experiment

A field experiment was conducted at three sites on the intertidal flats of Whangapoua Harbour to assess the effect of variation of wave climate on the recovery of macrofauna following the deposition of terrestrial sediment. Macrofaunal communities and sediment characteristics were sampled over time to determine recovery rates. Purpose: Determining the rate of recovery of the macrobenthic community following the deposition of terrestrial sediment, and understanding the effect that variations in wave-induced hydrodynamics would have on long-term colonisation of terrestrial sediment deposition on intertidal flats.

Macrofauna (rare taxa, total numbers of taxa and individuals, Shannon-Weiner diversity index), particle size, firmness, shear strength, wave climate and chla data.

Whangapoua Harbour, 3 sites in the western arm (Opitonui) south and south-east of the causeway islands.

Whangapoua Harbour – E2745181 N6493816, NZMG, 1:20000, AREA

Feb 1999-2000

At each of the three sites a single 5m diameter aluminium ring was pushed into the sediment surface and filled with a sediment slurry (~4 cm deep). After one tidal cycle the ring was removed. Two cores (10 cm diam x 15 cm deep) were taken from within each of the 3 sites and 2 cores outside of each of the 3 treatment sites. Deposited terrestrial sediment and natural marine sediment from the cores were separated. Samples were sieved through a 0.5 mm mesh. Photos were taken of 0.25 m2 quadrats and the depth of the deposited sediment and any sand layer present on the surface measured. Sediment 'firmness' and shear strength also measured, and analysis undertaken for chemical and particle size analysis. A DOBIE wave gauge measured hydrostatic pressure a the bed every 30 minutes in bursts, with each burst containing 2048 sampling points separated by 0.2 s. Frequency of collection: At 10, 12, 14, 16, and 20 months.

Only 3 sites were selected (all within the western arm of the harbour) due to the scale of the deposition and the need to simultaneously measure hydrodynamics at all sites. Gaps in collection: None Data quality: Standard coring and sieving techniques used. Attribute accuracy: Not reported Completeness: Not reported

reports, graphs, spreadsheets, electronic Digital Format: MS Word, MS Excel

See NIWA Sensitivity/Confidentiality: See NIWA

Finished