<str<strong>on</strong>g>Proceedings</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> <str<strong>on</strong>g>Third</str<strong>on</strong>g> <str<strong>on</strong>g>Internati<strong>on</strong>al</str<strong>on</strong>g> <str<strong>on</strong>g>C<strong>on</strong>ference</str<strong>on</strong>g> <strong>on</strong> <strong>Invasive</strong> SpartinaChapter 3: Ecosystem Effects <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>Invasive</strong> SpartinaASSESSMENT OF THE POTENTIAL CONSEQUENCES OF LARGE-SCALE ERADICATION OFSPARTINA ANGLICA FROM THE TAMAR ESTUARY, TASMANIAM. SHEEHAN 1 AND J.C. ELLISON 21Department <str<strong>on</strong>g>of</str<strong>on</strong>g> Primary Industries, PO Box 3100, Bendigo DC, Victoria, Australia; mat<str<strong>on</strong>g>the</str<strong>on</strong>g>w.sheehan@dpi.vic.gov.au2School <str<strong>on</strong>g>of</str<strong>on</strong>g> Geography and Envir<strong>on</strong>mental Studies, University <str<strong>on</strong>g>of</str<strong>on</strong>g> Tasmania, Locked bag 1376, Launcest<strong>on</strong>, Tasmania;Joanna.Ellis<strong>on</strong>@utas.edu.auSpartina anglica is a vigorous exotic perennial salt marsh grass typically inhabiting <str<strong>on</strong>g>the</str<strong>on</strong>g> upperintertidal z<strong>on</strong>e <str<strong>on</strong>g>of</str<strong>on</strong>g> temperate estuaries. Following its introducti<strong>on</strong> into <str<strong>on</strong>g>the</str<strong>on</strong>g> Tamar Estuary, Tasmania,patterns <str<strong>on</strong>g>of</str<strong>on</strong>g> sediment depositi<strong>on</strong> and erosi<strong>on</strong> have been significantly altered. This paper presents <str<strong>on</strong>g>the</str<strong>on</strong>g>background to an interdisciplinary approach used to determine <str<strong>on</strong>g>the</str<strong>on</strong>g> potential impacts <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> widescale eradicati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> S. anglica, from what is now Australia’s largest infestati<strong>on</strong>. Analysis <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>seinterdisciplinary lines <str<strong>on</strong>g>of</str<strong>on</strong>g> inquiry have provided a greater understanding <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> biogeomorphologicalresp<strong>on</strong>ses to restorati<strong>on</strong> attempts within intertidal z<strong>on</strong>es and have provided a sound basis <strong>on</strong> whichto formulate and implement future management <str<strong>on</strong>g>of</str<strong>on</strong>g> Spartina.Keywords: Spartina anglica, Estuaries, salt marsh, intertidal z<strong>on</strong>e, geomorphology, sward, sedimentati<strong>on</strong>,erosi<strong>on</strong>, accreti<strong>on</strong>, eradicati<strong>on</strong>, surveyingINTRODUCTIONSpartina anglica, (rice grass or cordgrass) is a vigorousexotic perennial salt marsh grass typically inhabiting<str<strong>on</strong>g>the</str<strong>on</strong>g> upper intertidal z<strong>on</strong>e <str<strong>on</strong>g>of</str<strong>on</strong>g> temperate estuaries. Spartinaanglica influences marsh development through <str<strong>on</strong>g>the</str<strong>on</strong>g> ability <str<strong>on</strong>g>of</str<strong>on</strong>g><str<strong>on</strong>g>the</str<strong>on</strong>g> canopy to promote sediment depositi<strong>on</strong> (Shi et al. 1995),and <str<strong>on</strong>g>the</str<strong>on</strong>g> ability <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> dense rhizomes and roots to increase<str<strong>on</strong>g>the</str<strong>on</strong>g> erosi<strong>on</strong> resistance <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> substrate (Brown 1998a; Brownet al. 1998b; Van Eerdt 1985). These properties, al<strong>on</strong>g withits ability to establish and spread rapidly are largely <str<strong>on</strong>g>the</str<strong>on</strong>g>reas<strong>on</strong> for its deliberate introducti<strong>on</strong> to temperate estuariesthroughout <str<strong>on</strong>g>the</str<strong>on</strong>g> world (Chapman 1960; Lee and Partridge1983; Ranwell 1967).Accelerated accreti<strong>on</strong> rates following <str<strong>on</strong>g>the</str<strong>on</strong>g> establishment<str<strong>on</strong>g>of</str<strong>on</strong>g> S. anglica have been observed in <str<strong>on</strong>g>the</str<strong>on</strong>g> Ne<str<strong>on</strong>g>the</str<strong>on</strong>g>rlands (VanEerdt 1985), China (Chung 1990), New Zealand (Lee andPartridge 1983) and in Poole Harbour, United Kingdom(L<strong>on</strong>g et al. 1999). However, compacti<strong>on</strong> and settling havebeen found to be important comp<strong>on</strong>ents <str<strong>on</strong>g>of</str<strong>on</strong>g> sedimentati<strong>on</strong>that may, in some instances result in negligible change intopographic height <str<strong>on</strong>g>of</str<strong>on</strong>g> mudbanks (Lee and Partridge 1983).Fur<str<strong>on</strong>g>the</str<strong>on</strong>g>rmore, studies <str<strong>on</strong>g>of</str<strong>on</strong>g> Louisiana marshes suggest that rootgrowth and below-ground accumulati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> organic matter,ra<str<strong>on</strong>g>the</str<strong>on</strong>g>r than inorganic matter governs <str<strong>on</strong>g>the</str<strong>on</strong>g> maintenance <str<strong>on</strong>g>of</str<strong>on</strong>g> saltmarshes in <str<strong>on</strong>g>the</str<strong>on</strong>g> vertical plane (Hatt<strong>on</strong> 1983; Nyman 1995;Turner 2004).This paper provides <str<strong>on</strong>g>the</str<strong>on</strong>g> background to an interdisciplinaryand precauti<strong>on</strong>ary study that was c<strong>on</strong>ducted between 2002and 2007 as part <str<strong>on</strong>g>of</str<strong>on</strong>g> a PhD research project aimed at assessing<str<strong>on</strong>g>the</str<strong>on</strong>g> impacts <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> wide scale eradicati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> S. anglica from<str<strong>on</strong>g>the</str<strong>on</strong>g> Tamar Estuary, Tasmania. Methodology and results <str<strong>on</strong>g>of</str<strong>on</strong>g>this study have been reported elsewhere (Sheehan & Ellis<strong>on</strong>,2007; Sheehan, 2008).BackgroundThe Tamar Estuary (Fig. 1) extends some 71 kilometers(km) inland from Bass Strait through to its tidal extent at<str<strong>on</strong>g>the</str<strong>on</strong>g> city <str<strong>on</strong>g>of</str<strong>on</strong>g> Launcest<strong>on</strong>. The Tamar is a semi-diurnal mesotidalsystem with tides ranging from 1.3 meters (m) at LowHead, to 4 m at Launcest<strong>on</strong>. The Tamar is well supplied withsediment from <str<strong>on</strong>g>the</str<strong>on</strong>g> South and North Esk Rivers, which, in <str<strong>on</strong>g>the</str<strong>on</strong>g>narrow and poorly flushed estuary, tend to accumulate as finegrainedsilt deposits in <str<strong>on</strong>g>the</str<strong>on</strong>g> upper reaches <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> system bothwithin <str<strong>on</strong>g>the</str<strong>on</strong>g> channel and <strong>on</strong> adjacent mudflats and shoals. Theaverage rate <str<strong>on</strong>g>of</str<strong>on</strong>g> siltati<strong>on</strong> has been estimated at 30,000 cubicmeters (m 3 ) per year, though this may vary between 10,000and 90,000 depending <strong>on</strong> variati<strong>on</strong> in river flow (Foster etal. 1986). Sedimentati<strong>on</strong> in <str<strong>on</strong>g>the</str<strong>on</strong>g> Tamar’s upper reaches hasbeen an issue <str<strong>on</strong>g>of</str<strong>on</strong>g> l<strong>on</strong>g standing c<strong>on</strong>cern, both for reas<strong>on</strong>s <str<strong>on</strong>g>of</str<strong>on</strong>g>shipping channel maintenance and envir<strong>on</strong>mental quality.Introducti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> SpartinaSpartina anglica was introduced in 1947 at Windermere(Fig. 1) in an attempt to stabilize sediments and safeguardagainst fur<str<strong>on</strong>g>the</str<strong>on</strong>g>r siltati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> shipping channel at a timewhen commercial water traffic travelled <str<strong>on</strong>g>the</str<strong>on</strong>g> length <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>estuary (Phillips 1975; Pringle 1993; Ranwell 1967). Mudflatsand shoals in <str<strong>on</strong>g>the</str<strong>on</strong>g> upper Tamar were pr<strong>on</strong>e to severe erosi<strong>on</strong>during <str<strong>on</strong>g>the</str<strong>on</strong>g> combinati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> flood tide and north-west winds.It was thought that stabilizing <str<strong>on</strong>g>the</str<strong>on</strong>g> mudflats would promotevertical accreti<strong>on</strong>, defining <str<strong>on</strong>g>the</str<strong>on</strong>g> channel to enhance scour, andhence reducing <str<strong>on</strong>g>the</str<strong>on</strong>g> likelihood <str<strong>on</strong>g>of</str<strong>on</strong>g> fur<str<strong>on</strong>g>the</str<strong>on</strong>g>r siltati<strong>on</strong>.In 1997, surveys showed that S. anglica covered some420 hectares (ha) (4.2 km 2 ) <str<strong>on</strong>g>of</str<strong>on</strong>g> intertidal z<strong>on</strong>e within <str<strong>on</strong>g>the</str<strong>on</strong>g>- 129 -
Chapter 3: Ecosystem Effects <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>Invasive</strong> Spartina<str<strong>on</strong>g>Proceedings</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> <str<strong>on</strong>g>Third</str<strong>on</strong>g> <str<strong>on</strong>g>Internati<strong>on</strong>al</str<strong>on</strong>g> <str<strong>on</strong>g>C<strong>on</strong>ference</str<strong>on</strong>g> <strong>on</strong> <strong>Invasive</strong> SpartinaFig. 2: Physiographic units <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> Tamar Estuary intertidalz<strong>on</strong>e.Fig. 1: Tamar Estuary, Tasmania.Tamar; however, recent surveys indicate that it c<strong>on</strong>tinues tospread throughout <str<strong>on</strong>g>the</str<strong>on</strong>g> lower estuary (Hedge 1998).Although <str<strong>on</strong>g>the</str<strong>on</strong>g> introducti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> S. anglica has improvednavigability in <str<strong>on</strong>g>the</str<strong>on</strong>g> Tamar Estuary (Pringle 1993; Wells 1995),it is now c<strong>on</strong>sidered a pest species as <str<strong>on</strong>g>the</str<strong>on</strong>g> current generati<strong>on</strong><str<strong>on</strong>g>of</str<strong>on</strong>g> natural resource managers and land-holders c<strong>on</strong>sider itsprogressive invasi<strong>on</strong> to be a major threat to <str<strong>on</strong>g>the</str<strong>on</strong>g> integrity <str<strong>on</strong>g>of</str<strong>on</strong>g>inter-tidal coastal ecosystems and wetlands <str<strong>on</strong>g>of</str<strong>on</strong>g> internati<strong>on</strong>alimportance (Doody 1990; Wells 1995).The present management strategy for S. anglica within<str<strong>on</strong>g>the</str<strong>on</strong>g> Tamar is <strong>on</strong>e <str<strong>on</strong>g>of</str<strong>on</strong>g> c<strong>on</strong>tainment ra<str<strong>on</strong>g>the</str<strong>on</strong>g>r than eradicati<strong>on</strong> dueto <str<strong>on</strong>g>the</str<strong>on</strong>g> complex nature <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> Estuary as outline above. Thereis, however, community and industry pressure to eradicate S.anglica from <str<strong>on</strong>g>the</str<strong>on</strong>g> banks <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> Tamar.GEOMORPHOLOGY OF THE INTERTIDAL ZONEThe intertidal z<strong>on</strong>e within <str<strong>on</strong>g>the</str<strong>on</strong>g> Tamar c<strong>on</strong>sists <str<strong>on</strong>g>of</str<strong>on</strong>g> fourdistinct physiographic units (Fig. 2):1) Narrow mudflats <str<strong>on</strong>g>of</str<strong>on</strong>g> recent alluvial deposits largely <str<strong>on</strong>g>of</str<strong>on</strong>g>terrestrial origin entering <str<strong>on</strong>g>the</str<strong>on</strong>g> system via <str<strong>on</strong>g>the</str<strong>on</strong>g> North Esk and <str<strong>on</strong>g>the</str<strong>on</strong>g>South Esk Rivers. These have accumulated predominantly in<str<strong>on</strong>g>the</str<strong>on</strong>g> upper estuary, however this unit can also be found in <str<strong>on</strong>g>the</str<strong>on</strong>g>mid and lower intertidal z<strong>on</strong>es <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> mid estuary or in largerembayments that receive sediment from minor tributaries;2) A laterally extensive area <str<strong>on</strong>g>of</str<strong>on</strong>g> outcropping substratewhich has wea<str<strong>on</strong>g>the</str<strong>on</strong>g>red in situ to form a narrow boulder beachthroughout <str<strong>on</strong>g>the</str<strong>on</strong>g> mid and some parts <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> lower Tamar. Thisformati<strong>on</strong> c<strong>on</strong>sists largely <str<strong>on</strong>g>of</str<strong>on</strong>g> Dolerite but also some Miocenebasalt shorelines at Whirlpool reach;3) Extensive beaches within <str<strong>on</strong>g>the</str<strong>on</strong>g> mid Tamar c<strong>on</strong>sisting<str<strong>on</strong>g>of</str<strong>on</strong>g> a thin veneer <str<strong>on</strong>g>of</str<strong>on</strong>g> Tertiary sands and gravels underlain byclays. The clays are likely to be lacustrine deposits <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>Miocene while <str<strong>on</strong>g>the</str<strong>on</strong>g> sand and gravel are indicative <str<strong>on</strong>g>of</str<strong>on</strong>g> highenergyfluvial envir<strong>on</strong>ments, which would have been presentduring <str<strong>on</strong>g>the</str<strong>on</strong>g> Pleistocene; and- 130 -
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