Aquatic macrophytes of the Macquarie and South Esk Rivers, Tasmania

摘要

Aquatic macrophytes are the flowering plants and larger algae growing submerged in orudemerging from water. Macrophytes are an essential component of riverine ecosystems: theyudproduce oxygen, filter out sediments and pollutants and provide habitat and food sources forudinvertebrates, fish and mammals. The Macquarie and South Esk Rivers in Tasmania are theudlargest rivers of the northern central plain, and are unique in Tasmania in having long stretchesudof relatively stable and abundant macrophytic vegetation along their mid- to lower reaches.udThe macrophyte communities of the mid- to lower reaches of the two rivers are described byudclassification into groups with similar species composition. Significant environmentaludvariation between groups is determined. Depth, substrate type and distance upstream are theudenvironmental factors most strongly associated with variation between the distribution ofudindividual species/species assemblages. Distance upstream, percentage shading, river form,udstream width, substrate type and bank height are the factors most strongly associated withudvariation between groups of sites.udBank vegetation type, distance upstream, percentage shading, level of stock damage and streamudwidth are found to be the environmental factors most strongly associated with differences inudrichness and diversity. Percentage shading and bank vegetation type are the factors mostudstrongly associated with differences in cover. The two rivers are found to differ significantlyudin percentage cover and total species richness. The associated environmental factors that varyudsignificantly between the rivers are percentage shading, bank height, bank vegetation type,udlevel of stock damage and stream width. The species rich and abundant macrophyte communities in the mid-reaches of the MacquarieudRiver and in some parts of the South Esk are found to have high conservation value. Audvulnerable marginal species, Persicaria decipiens, is also of high conservation value. Willowudinfestation and changes to flow regimes or water quality are seen as being the greatest threatsudto these communities. The importance of management of stock access to river edges and theudpotential value of buffer zones are discussed.