NIWA nutrients and mangrove expansion

This study aims determine if there is any evidence of anthropogenically derived nutrient additions enhancing the rate of spread of mangroves.This study aims to establish the role of nutrients in contributing to mangrove expansion in different estuaries as well as in specific areas within each of those estuaries. Case study estuaries were Whangamata, Whangapoua and Tauranga, with the inclusion of additional information from a previous study by NIWA for the Whitford embayment.

46 sites including salinity, organic matter and nutrient content of sediments, Leaf PN:PP, mangrove density and height data.

Tauranga, Whangamata and Whangapoua Harbours.

Whangamata – E2764538 N6442493, NZMG, 20000, AREA Whangapoua Harbour – E2745181 N6493816, NZMG, 20000, AREA

March – May 2002 (Whitford March – May 2001).

9 sites in Whangapoua and Whangamata and 20 sites in Tauranga were chosen from aerial photos to cover a gradient of likely nutrient inputs from the head to the mouth of the estuary. A 10 m x 10 m plot was established at each site in mangroves on the tidal fringe at the interface with the estuary. Total number of trees, total number of saplings, number of seedlings in four 2 m x 2 m sub plots, and the height of 10 haphazardly chosen trees were measure in each plot. Salinity of subsurface water was measured in a shallow pit. Leaf nutrients and sediment characteristics (organic matter, grain size, total N, total P) were also measured. Frequency of collection: One off study

Not yet sufficient information available on New Zealand mangroves to state definitively from the N:P ratio whether mangroves at a given site are nutrient limited. However can look at the range of N:P ratios and establish whether there are any patterns. Data quality: sampling based on the experiences from other NIWA mangrove monitoring protocols (Craggs et al., 2001) and standard protocols developed for the Caribbean coastal marine productivity programme (CARICOMP, 2001).

report, spreadsheet, graphs, electronic

Catchment management.

Sensitivity/Confidentiality: See NIWA

Complete

Continuing NIWA research funded by FRST is addressing some of the longer-term nutrient cycling processes occurring in the sediments of mangrove stands and the effects of adding nutrients to sediment, on mangrove growth.