Wetland edge delineation

Abstract

Wetlands are an important but diminishing natural resource in New Zealand. With the growing demand for protection of wetland areas, wetland edges need to be accurately delineated. Uncertainty over the best method to delineate wetland edges is a problem facing wetland managers in New Zealand. Internationally, wetland edges are delineated using three types of indicators, namely; hydrology, soil and vegetation. In this study, the usefulness of three delineation methods for New Zealand managers was examined. A pilot survey of four wetlands in Canterbury was undertaken. The study compared the wetland edges delineated with the following methods; 1) presence and absence of hydric soils, 2) prevalence of hydrophytic vegetation, and 3) presence and absence of wetland vegetation indicator species. The hydric soils investigations showed that the edge delineated by soil indicators can differ from that delineated by vegetation indicators. Comparison of the two vegetation edges delineated showed that these edges were within 0.51 m of one another. The edge based on prevalence of wetland vegetation was, in most cases, positioned closer to the visible water edge. The three methods of delineation were evaluated against five practicality criteria for wetland management. The findings of this study have a number of management implications. It was concluded that an indicator species method is the most useful delineation method when using vegetation parameters. However, managers must understand that any delineation method based on vegetation indicators has a number of limitations in certain situations. Finally, soil and vegetation delineation methods measure different temporal aspects of the wetland hydrology and site history. Consequently, when choosing a delineation method, managers should consider; the characteristics of the individual wetland being delineated, the management goals strived towards, and the type of management that will occur in conjunction with delineation.