Ecology of the Avon-Heathcote Estuary: Comparative Salt Marsh Survey 2006-2007. Estuarine Research Report 34

摘要

Executive Summary: 1. As cities cope with increasing populations, salt marshes around the world areon the decline due to negative effects of high levels of development, drainingand reclamation. Due to high levels of disturbance in estuaries, monitoring isessential to ensure that salt marshes are preserved for future generationsthrough sustainable management.2. During the summer of 2006/07, salt marsh vegetation surveys were undertakenin the Avon-Heathcote Estuary, Christchurch, New Zealand using the samestudy areas as in McCombs and Partridge (1992). Global Positioning Systems(GPS) were used to capture each of 14 study sites to enable a high degree ofaccuracy. GPS were also used to create a detailed map of the margins of theestuary and to determine the locations of salt marsh vegetation.3. The main aims of the study were to evaluate the current area of salt marshvegetation in the Avon-Heathcote Estuary, to describe the community typesand assess if these have changed since 1991/92.4. A total of 12 vegetation types were found in 2006/07 compared with 15 in1991/92. Oioi Rushland (Type 1) with 340 sites and Sea Rush Rushland (Type2) with 205 sites were the dominant community types in the Avon-HeathcoteEstuary.5. Salt marsh vegetation in the Avon-Heathcote Estuary has changed since1991/92. Salt tolerant plants, such as New Zealand Musk (Mimulus repens)and Suaeda (Suaeda novae-zelandiae) have been replaced by less tolerantplants, such as sea rush (Juncus krausii) and Oioi (Apodasmia similis). This ismost likely due to increased sedimentation of finer sediments fromdevelopments around areas such as the Heathcote River. Of the original 495sites, 27 had no vegetation in 2006/07.6. The salt marsh near the Avon River had the most stable vegetation, dominatedby Oioi Rushland (Type 1) and Sea Rush Rushland (Type 2). They shared anindex of stability of 0.83, that is 83% of the survey sites remained the samefrom 1991/92 to 2006/07. In contrast, Sandy Point and the study area aboveFerrymead were the most unstable areas and had changed the most.7. The GPS map confirmed a high proportion of built structures compared tonatural substrates around the margins of Avon-Heathcote Estuary. The totalarea of salt marsh in the Avon-Heathcote Estuary, determined from GPSmeasurements, was 372163 m2 (0.37 km2). The largest area contiguous of saltmarsh was on the Avon River (Study area 1), with the smallest area at SandyPoint (Study area 8).8. To encourage protection of the salt marsh vegetation in the Avon-HeathcoteEstuary the survey should be completed again within 8 to 10 years. Thepresent study forms a baseline for future comparative research which focuseson changes to the estuary and its salt marshes, this may be particularlyimportant after 2008 with removal of the treated wastewater from the estuary.