Mangrove removal trial - Whangamata

The monitoring programme included sampling of benthic infauna and grain size and organic content of the surficial sediments in the trial sites. Four treatment plots and a control plot were established at the trial site: Plot A – all mangrove material (above and below-ground material, including seedlings) removed. Plot B – seedlings and all above-ground mangrove material (e.g., stumps, shoots, pneumatophores) removed. All underground material (e.g., roots, rhizomes) left intact. Plot C – seedlings, stumps and all green leaf-bearing shoots and branches removed. All pneumatophores and underground roots and rhizomes left intact. Plot D – Seedlings and all green leaf-bearing shoots and branches removed. All stumps, pneumatophores, underground roots and rhizomes left. Control Plot – no mangrove material removed Purpose: In May 2000 a resource consent was granted to Whangamata Harbour Care Inc. to undertake a trial removal of mangroves in the coastal marine area in Patiki Bay, Whangamata Harbour (Resource Consent No. 102475). As a condition of this consent, an environmental monitoring programme was to be undertaken to examine the sediment release from the different trial areas following mangrove removal.

Sediment grain size information and organic matter content available for three samples at each plot for each of three sampling dates. Results of statistical analysis on changes in the fine fraction of the sediment, and on changes in the organic content.

Trial sites in Whangamata Harbour:

Patiki Bay T12: 643-417

July 2002-February 2001

5 replicate surficial (top 10-20 mm) sediment samples were collected from haphazardly located positions throughout each of the plots. Sediments were frozen until analysis. Sediment samples were analysed from each treatment and control plot on each sampling occasion, using a Galai particle-size analyser. The organic matter content of three sediment samples from each treatment and control plot on each sampling occasion, was determined using combustion and infra-red detection (with acid pre-treatment to remove carbonates). Frequency of collection: All plots were sampled pre-mangrove clearance in July 2000, and re-sampled post-clearance in October 2000 and February 2001.

There is no monitoring of the effects of the clearance on existing neighbouring habitats. An initial pre-treatment transect goes as far as identifying habitat types in the vicinity of the treatment plots but then does not monitor these habitats for effects from the clearance activity. Sampling is not replicated both in time and space, before and after an impact occurs. Replication and controls are missing. There is no 'before' bird surveys within the mangroves. Gaps in collection: Not reported

report, maps, spreadsheet Digital Format: MS Word, MS Excel

Freely available Sensitivity/Confidentiality: None

Study completed.