Saltmarsh of the Parramatta River-Sydney Harbour: determination of cover and species composition including comparison of API and pedestrian survey

摘要

In 2004 coastal saltmarsh was listed as an Endangered Ecological Community under the New South Wales Threatened Species Conservation Act, but more information on the ecology of saltmarsh species as well as accurate maps of the cover of saltmarsh are needed. Large scale maps produced in the early 1980s and the mid 2000s were based on air photo interpretation with follow-up field checks, but to determine the ability of air photos to detect small patches of coastal saltmarsh, a pedestrian survey along the foreshore of the Parramatta River-Sydney Harbour estuary (33 degrees 53'S; 151 degrees 13'E) was commissioned. Ground-truth activity was partitioned into three levels of intensity. At the greatest level of intensity, many small patches obscured in the air photos by (mainly mangrove) canopy cover were resolved and joined to reveal larger patches of saltmarsh. Compared to the earlier maps these areas are considered to increase the total area of existing saltmarsh, but they also may in fact be areas of saltmarsh that have been recently invaded by mangroves, and ultimately, through shading and competition result in the loss of the saltmarsh species at these sites. Another 609 patches not seen on the air photos were located.The pedestrian survey located 757 saltmarsh patches (70% of these were less than 100 m(2) in area) with a total area of 37.3 ha. Parramatta River, relative to the Lane Cove River, Middle Harbour Creek and Sydney Harbour, supports the most numerous and extensive patches: 461 patches (61% by number), 29 ha (78% by area). Most of the patches of saltmarsh (60%), as well as most of their area (76%), are located in the most upstream Riverine Channel geomorphic zone of the Parramatta River, followed by downstream zones Fluvial Delta and Central Mud Basin. The fewest patches (14) and smallest area (0.04ha) were in the Marine Tidal Delta. The 'conservation 'sensitive' species as well as some of the weed species also appeared to be restricted to the upper and middle parts of the estuary.API is useful for broad assessments of estuarine saltmarsh, but pedestrian survey is needed to provide the finer scale detail necessary to locate small patches and to identify species composition especially for rare or weed species.