By Bev Clarkson
New Zealand wetlands sustain indigenous biota, improve water quality, abate floods, lock up carbon, and provide cultural, recreational, and educational resources. Despite their multiple values, more than 90% of pre-settlement wetlands have been lost. Remaining wetlands are under increasing pressure through too little water, too much nutrient, and too many weeds and pests, and many require urgent action to prevent further loss and degradation.
Landcare Research and its research partners NIWA, DOC, University of Waikato, and Waikato Raupatu River Trust have worked to deliver scientifically based guidelines, techniques, and tools to improve the management and guide the restoration of wetlands. These improve the likelihood of success in repairing complex physical–biological processes, and thus reduce the risk of wasted time or resources. Publication of our wetland restoration handbook (Peters & Clarkson 2010) represents the culmination of many years of research that involved development of best practice techniques from restoration experiments, case studies, and collaboration with wetland partners and the wider community.
Restoration techniques were developed through field experiments in wetlands that have been drained, burnt, mined, invaded by weeds, or otherwise modified. These experiments include restoration of a rare and threatened bamboo rush (Sporadanthus ferrugineus) bog type at a site that is being mined for horticultural peat. When the bogs are restored using our patch creation approach, nutrient balances are improved, leading to faster growth rates, improved decomposition patterns, and increased storage of carbon. Under our technical guidance, wetland managers and community groups have introduced populations of bamboo rush and rare invertebrates to three new wetland projects at sites where the bog type once occurred – Lake Serpentine, Lake Komakorau, and Waiwhakareke Natural Heritage Park, in the Waikato. The bamboo rush bog at Lake Serpentine will be showcased as part of the soon-to-be-built National Wetland Trust’s wetland interpretation centre.
Our current research focuses on determining hydrological and nutrient thresholds to maintain indigenous biodiversity and functioning. This research includes a nutrient enrichment experiment across a swamp-fen-bog wetland gradient, which indicates that high inputs of phosphorus (e.g. from fertiliser drift) can threaten our unique bog ecosystems by inhibiting the formation of peat-forming roots. Another experiment on litter decomposition shows even a small lowering of the water table in wetlands can exponentially increase litter decomposition rates. This indicates the integrity of wetlands, particularly those in extensively developed landscapes, is being threatened by on-going regional lowering of water tables. On-going drainage can also lead to significant increases in the release of carbon, thus contributing to global warming.
The goal of our research is to increase the number and success rate of wetlands being restored by providing a sound foundation for their management, monitoring, and restoration. By working alongside DOC, local authorities, iwi, and the wider wetland community we will help achieve New Zealand’s high-level goals of protecting wetland biodiversity values.
Peters M, Clarkson BR eds 2010. Wetland restoration: a handbook for New Zealand freshwater systems. Lincoln, Manaaki Whenua Press. 273 p.
Dr Bev Clarkson is a plant ecologist at Landcare Research, Hamilton, and leads the MBIE-funded Restoring Wetlands programme under contract C09X1002.