APRIL 2016 TORO ENERGY EXTENSION TO THE WILUNA URANIUM PROJECT RESPONSE TO EPA SUBMISSIONS TECTICORNIA GROUNDWATER DEPENDENCY Toro Energy Pty Ltd Extension to the Wiluna Uranium Project Response to EPA Submissions Tecticornia Groundwater Dependency Document status Approved for Issue Rev Author Reviewer/s Date Name Distributed To Date 1 S. Grein S. Grein/L.Chandler 1/4/2016 A. Worland Toro Energy 1/4/2016 2 S. Grein S. Grein/L.Chandler 19/04/2016 A. Worland Toro Energy 19/04/2016 3 S. Grein S. Grein/L.Chandler 21/4/2016 A. Worland Toro Energy 21/04/2016 ecologia Environment (2016). Reproduction of this report in whole or in part by electronic, mechanical or chemical means including photocopying, recording or by any information storage and retrieval system, in any language, is strictly prohibited without the express approval of the Toro Energy and ecologia Environment. Restrictions on Use This report has been prepared specifically for the Toro Energy. Neither the report nor its contents may be referred to or quoted in any statement, study, report, application, prospectus, loan, or other agreement document, without the express approval of the Toro Energy and ecologia Environment. ecologia Environment 1/224 Lord St PERTH WA 6000 Phone: +61 8 6168 7200 Email: [email protected] 2 Toro Energy Pty Ltd Extension to the Wiluna Uranium Project Response to EPA Submissions Tecticornia Groundwater Dependency TABLE OF CONTENTS KEY POINTS ..................................................................................................................................... 4 1 TECTICORNIA GROUNDWATER DEPENDENCY .................................................................... 5 1.1 TECTICORNIA ............................................................................................................................ 5 1.2 SOIL PROFILES AND SALINITY AT MILLIPEDE, LAKE MAITLAND AND FORTESCUE MARSH ...... 7 1.3 GROUNDWATER DEPENDENCY IN VEGETATION COMMUNITIES ............................................ 7 1.4 TECTICORNIA DOMINATED VEGETATION COMPLEXES AND UNITS AT THE MILLIPEDE AND LAKE MAITLAND DEPOSITS .................................................................................................... 10 1.5 TECTICORNIA ECOHYDROLOGICAL STUDIES .......................................................................... 12 2 CONCLUSIONS ................................................................................................................. 15 3 REFERENCES .................................................................................................................... 16 FIGURES Figure 1 – Observations of Tecticornia indica subsp. bidens root system at the edge of the Fortescue Marsh (Equinox 2013). ........................................................................................................ 6 Figure 2 – East Shallow Bore groundwater levels and rainfall ................................................................ 8 Figure 3 – North Shallow Bore groundwater levels and rainfall ............... Error! Bookmark not defined. Figure 4 – Locations of North and East Shallow Groundwater Monitoring Bores .................................. 9 Figure 5 – Locations of Tecticornia indica subsp. bidens from Millipede and Lake Maitland Development Envelopes ................................................................................................... 11 Figure 6 – Locations of Tecticornia indica subsp. leiostachya from Millipede and Lake Maitland Development Envelopes ................................................................................................... 11 Figure 7 – Locations of Tecticornia sp. Denny’s Crossing from Millipede and Lake Maitland Development Envelopes ................................................................................................... 12 Figure 8 – Fortescue Marsh ecohydrological conceptualisation (BHPIO, 2016) ................................... 14 3 Toro Energy Pty Ltd Extension to the Wiluna Uranium Project Response to EPA Submissions Tecticornia Groundwater Dependency KEY POINTS • Recent studies of Tecticornia dominated vegetation communities fringing the northern flank of the Fortescue Marsh are relevant to the assessment of impacts associated with the Wiluna Extension Proposal. This includes: o Soil conditions at Christmas Creek/northern fringe of Fortescue Marsh and at Lake Way/Lake Maitland are similar. o Groundwater conditions (including depth to water and salinity) are also similar o Several of dominant Tecticornia species, including Tecticornia indica subsp. bidens, Tecticornia indica subsp. leiostachya and Tecticornia sp. Dennys Crossing (K.A. Shepherd & J. English KS 552) are common to all three locations (ie Fortescue Marsh, Lake Way, Lake Maitland) • The Tecticornia species have morphological and physiological characteristics (ie low LAI, low transpiration rate, shallow root architecture) associated with plant drought tolerance and are not typical of groundwater dependent species • Published and unpublished technical literature suggests possible linkages between Tecticornia zonation and submergence tolerance, but not between zonation and drought tolerance • It is likely that the environmental water requirements of Tecticornia species are met by periodic surface recharge of the vadose zone • Other environmental water requirements (related to seedling emergence, for example) are triggered by fresh water inputs from rainfall events and are not influenced by changes in groundwater regimes • Natural variations in the depth to groundwater at Lake Way (and also likely at Lake Maitland) are in the order of more than 0.5m over the annual cycle. Even if Tecticornia species did exhibit a level of occasional groundwater reliance, plants of this genera are likely to be tolerant of natural groundwater fluctuations of at least 0.5m at Lake Way and Lake Maitland and up to 2m at Fortescue Marsh. • Samphire communities within the 0.5m drawdown contour and outside the direct disturbance footprint will be monitored to confirm that possible changes in groundwater hydrology are not affecting vegetation health. 4 Toro Energy Pty Ltd Extension to the Wiluna Uranium Project Response to EPA Submissions Tecticornia Groundwater Dependency 1 TECTICORNIA GROUNDWATER DEPENDENCY 1.1 TECTICORNIA The genus Tecticornia (Amaranthaceae, subfamily Salicornioideae) is a group of stem succulent and perennial halophytes that typically inhabit marshes and margins of inland salt lakes of Australia (Marchesini et al, 2013). They are considered keystone species due to their unique adaptations, and typically dominate the plant communities in these habitats. While some Tecticornia species are widespread, others are restricted to particular habitats and landforms. The distribution of Tecticornia species across ecosystem gradients generally reflects the tolerance of the species to variability in environmental conditions. Ecophysiology studies of Tecticornia communities on the Fortescue Marsh in the Pilbara region of WA by the University of Western Australia (UWA) (Moir-Barneston et al, 2013; Marchesini et al, 2013) demonstrated that the more flood and salinity tolerant Tecticornia species (ie T. medusa) tends to occur in the interior of the Marsh while the more drought tolerant species (ie Tecticornia indica subsp. bidens) occurs on the outer margins of the Marsh fringe where soil conditions were drier and the deeper groundwater was inaccessible to the root system of the species. Tecticornia species, including Tecticornia indica subsp. bidens, are generally found in well-drained soils (Lake Carey Catchment Management Group, 2013). An unequivocal observation that has been made with respect to plant groundwater dependency is that if groundwater is found to be within the rooting depth of the vegetation it is reasonable to conclude that the vegetation is using that groundwater (Eamus, 2009). Baseline groundwater levels at the northern edge of the Marsh averaged 403m AHD with the saturated soil zone virtually never reaching a depth as shallow as 1m, more typically occurring at a depth of about 2m (FMG, 2015). Root studies of plant communities occurring on the fringes of the Fortescue Marsh conducted by UWA in 2012 (Grierson et al, in prep), that included Tecticornia indica subsp. bidens species, found that T. indica subsp. bidens has a woody root system that is predominantly confined to the top 70 cm of the soil profile (Figure 1), with the finer roots confined to the top 50 cm. Between flood events the roots of T. indica subsp. bidens are located within the unsaturated zone (FMG 2015). According to Eamus et al 2006, the inference of dependency on groundwater is based on the subsurface presence of groundwater and the groundwater or capillary fringe above the water table is likely to be within the rooting depth of any of the vegetation. On the basis of the Fortescue Marsh root study field data and photographic evidence in Figure 1, the fact that the roots of T. indica subsp. bidens do not extend into groundwater (at approximately 2m) or the capillary fringe above the watertable, indicates that the taxon has a water use strategy that targets surface water infiltration of the unsaturated soil layer (vadose zone) and is not dependent on groundwater for its survival (Equinox, 2013). 5 Toro Energy Pty Ltd Extension to the Wiluna Uranium Project Response to EPA Submissions Tecticornia Groundwater Dependency Figure 1 Observations of Tecticornia indica subsp. bidens root system at the edge of the Fortescue Marsh (Equinox 2013).