Mangrove ecosystem dynamics and clearance impacts

Despite rapid declines in global mangrove ecosystem area, temperate mangrove ecosystems in New Zealand have increased in area in recent decades. Mangrove clearance is increasingly being used as a strategy to manage this expansion. One of the aims of mangrove clearance is to return sandflat habitats which may have been historically present. This thesis provides new insights into the impact of mangrove clearance on sediment characteristics and macrofaunal communities, best practice for mangrove clearance, and the impact of changes in mangrove ecosystem area on carbon and nitrogen stocks and fluxes. Results showed that smaller hand clearances and locations exposed to greater hydrodynamic forces showed more signs of transition to sandflat conditions (decline in mud content, change in macrofaunal communities) than larger mechanical clearances. However, sediment characteristics and macrofaunal communities remained more comparable to intact mangrove than sandflat ecosystems over 3 years following mangrove clearances. Mangrove clearance was also found to have minor impacts on sediment:water column exchange of inorganic nutrients, which was low at both intact and cleared sites. However, clearance increased the amount of CO2 released from the sediment into the atmosphere by more than 2-fold. Lower inorganic nutrient fluxes within cleared and intact mangrove compared to sandflat ecosystems was related to lower abundance of bivalves and other larger burrowing macrofauna, along with a higher fraction of silt and clay content in the surface sediment limiting nutrient exchange. This suggests that expansion of mangroves will be associated with lower sediment:water column fluxes of inorganic nutrients and a decline in the ecosystem value of this service. However, as many of the potential benefits of mangrove clearance rely on a transition to sandflat, which was not observed in this study, mangrove clearance appears unlikely to improve this ecosystem service. In addition, clearance of temperate mangrove ecosystems will likely result in a loss of ecosystem services in the form of carbon and nitrogen stocks, with temperate mangrove ecosystems found to store 117.1 ± 16.8 t C ha-1 and 15.4 ± 1.0 t N ha-1.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Marine Science

Grantor dc:publisher

ResearchSpace@Auckland

Year dc:date.issued

2017

Author dc:creator

• Bulmer, Richard

Advisors dc:contributor.advisor

• Lundquist, C
• Schwendenmann, L

Statement dc:rights

• Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher.

Licence dc:rights.uri

• https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm

Handle dc:identifier.uri

https://hdl.handle.net/2292/32250

OAI identifier oai:identifier

oai:researchspace.auckland.ac.nz:2292/32250