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20 Conservation Science W. Aust. 5 (1) : 20–135D.J. Cale (2004) et al. Wetland monitoring in the Wheatbelt of south-west Western Australia: site descriptions, waterbird, aquatic invertebrate and groundwater data D.J. CALE1, S.A. HALSE1 AND C.D. WALKER2 1Science Division, Department of Conservation and Land Management, PO Box 51 Wanneroo Western Australia 6956 Email: [email protected], [email protected] 2GEO & HYDRO Environmental Management, Suite 1, 9 Wygonda Road Roleystone Western Australia 6111 Email: [email protected] ABSTRACT The Wheatbelt of south-west Western Australia contains a range of wetland types with varying salinity, including many naturally saline lakes and playas. The increase in salinity of most wetlands during the last 50 years as a result of land-clearing is a major threat to wetland biodiversity. As part of the State Salinity Strategy, a wetland monitoring program began in 1997 at 25 wetlands from locations throughout the wheatbelt. The aim of the monitoring program was to document trends in biodiversity at the 25 wetlands and relate these trends to physical conditons in the wetlands and patterns of surrounding landuse. This report summarizes existing information on the wetlands and provides, as baseline conditions, results of initial waterbird, aquatic invertebrate and groundwater monitoring. It documents the monitoring methods used and highlights the need for a long-term program. There was a strong negative relationship between aquatic invertebrate species richness and salinity. A negative relationship also existed for waterbird richness, although other factors determined numbers of species in many wetlands with salinity being a constraint on maximum potential waterbird richness rather than a determinant of the actual number of species. Further salinization is likely to change detrimentally both invertebrate and waterbird communities. Such changes are apparent in historical waterbird data from some wetlands. The ultimate cause of increased salinity in wetlands is rising groundwater, although sometimes wetlands are more directly affected by the increased surface run-off that results from high watertables in the catchment than by groundwater beneath the wetland. INTRODUCTION However, Pinder (2000; 2003) review what is known about species in granite rock pools and hypersaline lakes, The Wheatbelt region of south-west Western Australia Halse et al. (2000a) provide information about Toolibin contains many different types of wetlands with a range of and Walbyring Lakes, Geddes et al. (1981) provide a list water salinities (Lane and McComb 1988). Land-clearing, of crustaceans for many wetlands in the eastern Wheatbelt, grazing and rising watertables have altered the and Brock and Shiel (1983) provide a list of rotifers and characteristics of many wetlands over the last 150 years other invertebrates. but the physiognomic and chemical diversity of Wheatbelt Over the next few years, considerably more information wetlands remains considerable and they contain a on the biodiversity of wetlands should become available corresponding diversity of plants and animals. The most as the results of the recent State Salinity Strategy biological comprehensive summary of waterbird use of Wheatbelt survey of the Wheatbelt are published (Lyons et al. 2002; wetlands is that of Jaensch et al. (1988). Information on Blinn et al. 2003; Halse et al. 2003). The biological survey wetland plants is more scattered but Halse et al. (1993b) began in 1997 and 232 wetlands were surveyed for aquatic provide an overview of vegetation structure and the main invertebrates, waterbirds and wetland plants. A range of species. Aquatic invertebrates were largely overlooked until physico-chemical parameters were also measured. The recent years and there is little published information State Salinity Strategy is intended to combat the available about their occurrence in most lake types. detrimental effects of increasing secondary salinization on Wetland monitoring in the Wheatbelt of south-west Western Australia 21 biodiversity, agricultural production and rural effect of salinization on aquatic invertebrates in rivers is infrastructure (Government of Western Australia 1996). somewhat contradictory (see Kay et al. 2001 for a review). Secondary salinization is a global phenomenon but is Work by Pinder et al. (2000 and unpublished data) particularly acute in the Wheatbelt of south-west Western suggests only a small proportion of the species in Wheatbelt Australia, where > 70 % of Australia’s secondary wetlands, often occurring in granite rock pools and other salinization occurs (Williams 1987; Williams 1999). In specialised habitats, are restricted to very fresh water. Most the Wheatbelt, increased salinity is the result of ‘dryland freshwater species in Wheatbelt wetlands tolerate brackish salinization’, which results from the clearing of deep- or moderately saline conditions (Halse et al. 2000a). It rooted perennial vegetation and its replacement by annual should be noted that some species occur only in naturally crops that evapo-transpire much less soil water (George saline lakes and they may be as much threatened by et al. 1995). As a result of reduced evapo-transpiration, salinization as freshwater species because of the changed watertables rise and salt stored in soil above the previous patterns of inundation, salinity and ionic composition that watertable is dissolved to create more saline groundwater accompany salinization (Pinder et al. 2003). that will cause scalding and death of vegetation as the In this report, we describe the wetlands being watertable approaches the land surface. Secondary monitored as part of the State Salinity Strategy and present salinization can also be caused by irrigation, though this results from the first four years of monitoring. Data for rarely happens in Western Australia. lake chemistry, groundwater, waterbirds and aquatic Not all saline landscapes are the result of anthropogenic invertebrates are presented as an estimate of baseline activity and concomitant secondary salinization. Many conditions and discussed in the context of the inland lakes and river systems in Western Australia are methodology, historical data and future monitoring. The naturally (or primarily) saline and one of the features of overall aim of the monitoring program is to measure the Western Australian environment is the high proportion changes over time in wetland conditions and biodiversity of brackish or saline water in inland water bodies (see to provide information that will lead to better land Schofield et al. 1988 for a summary of nineteenth century management decisions (Wallace 2001). More specific observations). The cause of primary salinity is similar to objectives for the part of the program covered in this report secondary salinization in the sense that it is the result of are: discharge of saline surface or groundwater into a lake, • to monitor trends in water chemistry, groundwater but the time periods involved are orders of magnitude levels and salinity, waterbirds and aquatic invertebrates greater (Johnson 1979). Naturally saline groundwater is at 25 Wheatbelt wetlands representative of a range of produced by the accumulation of marine aerosols over wetland types hundreds of thousands of years (Commander et al. 1994; • to relate trends to patterns of surrounding land-use, Herczeg et al. 2001). Climate, rather than land clearing, management actions and historical data on wetland determines the distribution of primary salinity in inland conditions areas and in Western Australia most naturally saline systems The monitoring program includes two other occur in palaeo-valleys. As a result of the prevalence of components. Vegetation health and plant species diversity this natural salinity, much of the Western Australian biota are monitored at the 25 wetlands (Ogden and Froend is salt-tolerant by comparison with the remainder of 1998; Gurner et al. 1999; Gurner et al. 2000). Bi-annual Australia (Halse 1981; Kay et al. 2001; Pinder et al. 2003). measurement (in September and November) of depth, There are also a few naturally saline lakes in coastal areas salinity and other parameters occurs at 100 wetlands in that reflect previously higher ocean levels, rather than the south-west, including the 25 wetlands where biological groundwater conditions (eg. Moore 1987; Hodgkin and monitoring is occurring (see Lane and Munro 1983 for Hesp 1998). Their biota usually contains a significant historical information on this part of the program). marine component. Information about the detrimental effect of secondary salinization on biodiversity in wetlands of the Wheatbelt is partly anecdotal (Sanders 1991) because there is little METHODS quantified baseline information on biodiversity prior to Locations of the 25 wetlands where biological monitoring salinization. However, a survey of Wheatbelt wetlands by is occurring are shown in Figure 1. Seven criteria were Halse et al. (1993b) suggested significant reduction in used to guide the selection of these wetlands and are listed plant species richness had occurred in secondarily saline below (see also Table 1): sites. Large-scale death of vegetation as a result of increased 1 Wetland listed in Government of Western Australia water level and salinity has been observed at (1996); Toolibin Lake, Noobijup Swamp and Lake Coomalbidgup Swamp (Froend and van der Moezel Wheatfield occur in the 3 original Recovery 1994), Toolibin Lake and surrounding wetlands (Froend Catchments (Toolibin,