The Health of Auckland’s Natural & Constructed Urban Wetlands
Maiyor, Adrian Michael
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I analysed data from 31 Auckland urban wetland monitoring plots within the Auckland metropolitan urban area. These plots were initially established from 2010 – 2014 by the Auckland council as part of a wider program to provide representative, region-wide monitoring of wetland health and biodiversity values. Data comprised two measures: the first baseline measurement and the 1st re-measurement after 5 years. It is planned to continue measuring these plots every five years, but only two measures were available for analysis in this study. The plots were selected using a 4km x 4km ‘wetland grid’ superimposed across the Auckland region to ensure representative spatial coverage. Each plot used a smaller grid setup of a square 15m x15m plot in which a 10m x 10m square and nine 2m x 2m plots were established within. This study aimed to assess the ‘health’ of Auckland’s urban wetlands using this data through the calculation and analysis of multiple indicators of ‘environmental condition’. These indicators were also evaluated through their usefulness towards the overall assessment of ecosystem ‘health’. The first indicator was the analysis of plant species richness in the plot. Indicator 2 was ‘naturalness’ which compares native vs exotic plant species richness. The third indicator was naturalness (biomass) which provided more information on the growth and proliferation of native plant species in the plots. Indicator 4 was based on the Shannon Diversity index which incorporates aspects of species richness and the relative abundance of those same species (using biomass). Indicator 5 represented Weed Dominance, in which the level of weedy plant species biomass was evaluated over the plot to determine the plots resistance to invasions. Indicator 6 was the proportions of dryland plants, which shows the proportionate value of Dryland plant biomass across the whole plot in order to ascertain the level of ‘drying out’ or changes in hydrological regimes. Indicator 7 was based on the Dieback of plant species, where dead biomass of native and exotic plant species is measured over the total biomass and expressed as a proportion. Prior to analysis, the wetland plots were classed into four different wetland types, Coastal wetlands – Induced, Coastal wetlands -Natural, Freshwater wetland -Natural and Freshwater – Restored. Using statistical tests, no significance differences were found between the baseline measures and 5-year re-measurement across all the indicators. However, there were some significant differences between wetland types in indicators 1, 3 and 4. The lack of significance may be due to the low amount of datapoints as the lack of a 2nd re-measurement would have provided more data over a longer period (of 10 years). At Kohuora Park, four replicate plots were re- measured after 9-years as to compare indicator values and predict the change in ‘health’ of Auckland urban wetland plots after a 9-year period. However, due to the low sample size, no significant differences were detected.