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Groundwater Interception Potential Impacts on Migratory and Threatened Shorebird Communities in Botany Bay October 2004 Report prepared by: Avifauna Research & Services Avifauna Research & Services Groundwater Interception - Potential Impacts on Migratory and Threatened Shorebird Communities in Botany Bay Contents Executive Summary …………………………………………………………………….. 1 Shorebird habitat at Penrhyn Estuary and Foreshore Beach ……………………………… 2 Availability of prey ………………………………………………………………………. 4 Changes in groundwater flows 4 Changes to invertebrate populations ………………………………………………………4 Changes to saltmarsh communities ………………………………………………………. 5 Likelihood of impact ………………………………………………………………………4 Avifauna Research & Services ii Groundwater Interception - Potential Impacts on Migratory and Threatened Shorebird Communities in Botany Bay Executive Summary Shorebird species that were once abundant in the north of Botany Bay have declined over the past 60 years as a result of habitat loss and are now restricted to a small area of intertidal habitat at Penrhyn Estuary. Most shorebird species feed on invertebrates found in tidal mud and sand flats on the falling tide and to a lesser extent on the rising tide. During high tide when feeding habitat is covered shorebirds roost (rest) at suitable locations. Little is known about the influence on invertebrates as a result of alterations to groundwater flows, and therefore indirect impacts on shorebird populations, however it is likely that species diversity and abundance will change with changes in salinity. Any changes to the number of invertebrates or species composition of invertebrates at Penrhyn Estuary may have an effect on shorebirds in the estuary, however it is known that shorebirds are readily able to switch prey due to their migratory nature. Invertebrate populations are currently under severe stress as a result of contaminants in the mudflats at Penrhyn Estuary. The proposed groundwater interception will reduce the risk of further contamination and risk to the estuary and its fauna and flora allowing the levels of contaminants to decline over time. Roost sites used by shorebirds are usually areas that have an open aspect to allow an all-round view for potential predators either saltmarsh habitat with low vegetation or open sand spits or beaches. The level at which saltmarsh grows depends on a number of factors including tide heights and freshwater runoff, including groundwater flows. Cessation of groundwater flows may result in a change in saltmarsh distribution, influenced by tide heights alone. The proposed expansion of Port Botany will to some extent override the effect of groundwater interception in that that proposal includes the establishment of additional saltmarsh habitat, much larger than the that currently existing. If the port expansion proceeds the remediation measures planned by SPC would complement those of Orica in providing and improved roosting and foraging habitat for migratory and non-migratory shorebirds within the estuary. Foreshore Beach currently provides very little shorebird feeding habitat. However the proposed port expansion would result a modification of the beach and protection from wave action. This is likely to increase the area of shorebird feeding habitat if the slope of the beach is lowered. This would also be compatible with the Proposal by Orica, providing a wider area of tidal flats and minimising the effect of groundwater interception. Key issues The retention of the existing mudflats at Penrhyn Estuary is essential to the long-term survival of shorebirds currently using the site. Actions to prevent toxic chemicals entering the estuary should be taken to protect shorebirds, their habitats and prey at the earliest opportunity. Regular, monthly, monitoring of the site will be essential to determine in any changes to the nature of the foreshore as a result of the proposal. Although it is likely that invertebrate populations and saltmarsh would adjust, it may be advantageous to carry out landscaping, Avifauna Research & Services 1 Groundwater Interception - Potential Impacts on Migratory and Threatened Shorebird Communities in Botany Bay including the addition of appropriate soils to enhance and expand the area of saltmarsh and therefore shorebird habitat. Recent successes in the establishment or enhancement of saltmarshes in Sydney have clearly demonstrated the feasibility to manage saltmarsh in modified habitat. Ongoing management of the site may be necessary to prevent invasion shorebird habitat by mangroves including the ‘weeding’ of mangrove seedlings on an annual basis. Avifauna Research & Services 2 Groundwater Interception - Potential Impacts on Migratory and Threatened Shorebird Communities in Botany Bay Shorebird habitat at Penrhyn Estuary Since the 1940s the gradual loss of shorebird habitat has resulted in a substantial decline in the numbers of shorebirds found in the northern part of Botany Bay. Penrhyn Estuary now provides the only shorebird feeding habitat and roosting sites in the north of the Bay. Although shorebird habitat exists along the southern shores of the bay it is not suitable for most of the shorebirds found at Penrhyn Estuary. Twenty four species of resident and migratory shorebirds and seabirds, listed under the Threatened Species Conservation Act (TSC Act) and/or the Environment Protection and Biodiversity Conservation Act (EPBC Act), are known to occur or have previously been recorded at Penrhyn Estuary. Of these seven are listed as Vulnerable and one, the Little Tern, as Endangered under the TSC Act, 22 are listed under international agreements (JAMBA and CAMBA) and 23 under the Bonn Convention of Migratory Animals (see Table 1). The most productive shorebird feeding habitat appears to be the silts in the delta area formed by Springvale and Floodvale Creeks as shown clearly in the airphoto taken at low tide (Figure 1). Figure 1. Penrhyn Estuary at low tide showing silt deltas formed by Springvale and Floodvale Creeks Shorebirds feed almost exclusively on invertebrates found in the substrate of wetlands, especially coastal estuaries. These habitats provide exposed mudflats in a relatively sheltered environment. Estuarine habitats are complex and rely on river flows, daily tidal cycles, groundwater runoff and the presence of organic material which support invertebrate populations. Although groundwater plays an important role in the formation and health of some saltmarsh plant communities it is not known how important groundwater is to maintaining Avifauna Research & Services 3 Groundwater Interception - Potential Impacts on Migratory and Threatened Shorebird Communities in Botany Bay invertebrate populations on tidal mudflats given that frequent freshwater flows occur at Penrhyn Estuary from surface runoff of local catchments. A reduction in groundwater flows into Penrhyn Estuary is likely to result in the change in species composition and numbers of some invertebrates. However it is known that shorebirds are readily able to switch prey due to migratory nature feeding in a variety of habitats from freshwater bogs to hyper saline saltpans and can adjust to a wide variety of invertebrate prey. Figure 2: Available shorebird feeding habitat at Penrhyn Estuary (outlined in orange) Avifauna Research & Services 4 Groundwater Interception - Potential Impacts on Migratory and Threatened Shorebird Communities in Botany Bay Availability of prey Studies of invertebrate populations at Penrhyn Estuary (The Ecology Lab Pty Ltd 2004, Botany Groundwater Clean-up, Aquatic Ecology Component 18/0405A) have indicated that characteristics indicative of this community include reduced species richness, community structure dominated by a few taxa, a paucity of small crustaceans such as amphipods, dominance of a few families of polychaete worms, and dominance by species with small body size and short life spans that retain (by various means) offspring in the immediate vicinity of parents or within the parental habitat. The current population of shorebirds at Penrhyn Estuary have developed in the presence of the current levels of contaminants in the estuary as well as levels of a level of toxins in the tissues of their prey. Any changes to invertebrate populations could influence the species diversity and population density of shorebirds. Improvement in the level of contaminants in the mudflats at Penrhyn Estuary, through the prevention of further contamination of the site, should in the long term provide a healthier environment for shorebirds by improving the diversity and health of their invertebrate prey. The effect of groundwater interception on invertebrates cannot be determined specifically (The Ecology Lab Pty Ltd 2004, Botany Groundwater Clean-up, Aquatic Ecology Component 18/0405A) but may result in a change in species composition. Any such changes may require a switch in prey species by shorebirds, provided the density of available prey is not reduced on the whole, most shorebird species should be able to adapt to these. Changes in groundwater flows The effects of changes to groundwater flows into the estuary as a result of works carried out by Orica are not likely to have any direct impacts on shorebirds as these species frequent a variety of habitats of varying salinity levels in the space of a single day. Any impact on shorebirds is likely to be as a result of changes in vegetation composition and prey (i.e. invertebrates) availability addressed elsewhere in this document. Changes to invertebrate populations Invertebrate populations appear

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