WETLANDS AND WATERSHED MANAGEMENT: THE ROLE OF AQUATIC VEGETATION

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Abstract
The single feature which distinguishes wetlands from other aquatic ecosystems is an abundance of aquatic vegetation. This vegetation affects water movements, gas and dissolved chemical exchanges, and sediment transport, and provides a unique microclimate above the water surface. Two roles attributed to wetlands in watersheds are discussed in this review—modification of the hydrology, trapping of sediments and dissolved nutrients. Data provided from studies on a New Zealand stream demonstrate the part played by the aquatic vegetation in these roles. The stream hydrological characteristics followed the seasonal pattern of macrophyte growth. The trapping of suspended sediments and dissolved nitrogen from stream waters was related to macrophyte biomass. It is recognised that quantification of wetland processes can only be done with a knowledge of wetland hydrology, and that wetlands are developmental stages in a hydrosere and thus are changing with time. The implications of these concepts are discussed in relation to the long term use of wetlands. However, if wetlands are considered useful in catchment areas then it is recommended that rather than manipulating natural wetlands, consideration should be given to the establishment of artificial wetlands or at the least to the improvement of aquatic plant habitats wherever possible. We now understand the functions of wetlands. Research should be aimed at quantifying the optimum wetland cover in a watershed to make best use of these values without over use of other catchment resources such as potential farm land or water.