Browsing by Author "Barber, E"

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    The benefits of a multidisciplinary team model for groundwater-surface water investigations, Thirlmere Lakes, NSW.
    (National Centre for Groundwater Research And Training, & Australian Chapter International Association Of Hydrogeologists, 2019-11-25) Cowley, KL; Cohen, TJ; Forbes, MS; Barber, E; Allenby, J; Andersen, MS; Anibas, C; Glamore, W; Chen, SY; Johnson, F; Timms, W; David, K; McMillan, T; Cendón, DI; Peterson, MA; Hughes, CE; Krogh, M
    The Thirlmere Lakes Research Program (TLRP) is a four-year collaborative multidisciplinary program designed to gain a whole-of-system understanding of the hydro-dynamics of a complex lake environment. The program was established from concerns that proximal aquifer interference activities were factors in recent lake level declines. Five research teams were established to investigate five adjacent lakes set within an entrenched meander bend located south-west of Sydney. The project involved lithological, geochemical and geochronological analysis from lake beds and surrounding slopes to understand lake evolution and determine potential past lake-drying events. Further geological understanding of the lake area was obtained from resistivity imaging (RI), ground penetrating radar (GPR), and analysis of rock cores that were drilled from two deep bores adjacent the lakes. Development of water balance budgets involved fine-scale on-site meteorological measurements including on-site evapotranspiration monitoring, combined with high-resolution bathymetry from RTK GPS, LiDAR surveying and drone photogrammetry. Groundwater-surface water interactions were measured using lake-bed multilevel temperature and pressure arrays, hydraulic head measurements and fine-scale isotope, major ion and environmental tracer time-series analysis. Preliminary findings indicate that the five lakes have been separated for over ~100,000 years and that the lakes themselves contain sediment that is possibly up to 250,000 years old. Assessing the modern dynamics we show that current lake level declines during a period of low rainfall are largely evaporation dominated. One lake however appears to have greater water storage in adjacent sediments providing compensatory inflows. In a second lake, there are indications of localised connectivity with shallow (≤18m) groundwater, but no evidence of connectivity with deeper aquifers. Geological surveys indicate a clay layer 6-8 m below the lakes and spatial variations in both sediment and rock geology. The influence of these geological features, including structures projecting towards the lakes, on groundwater storage and flow is the focus of ongoing research as is temporal variability and lake interactions at different lake levels. The benefits of the multidisciplinary team model include refining the research targeting areas of uncertainty and to enhance and calibrate each team’s results. This approach will provide a comprehensive whole-of-system model of the evolution and hydro-dynamics of a complex lake system. © The Authors
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    Comparing interglacials in eastern Australia: a multi-proxy investigation of a new sedimentary record
    (Elsevier, 2021-01-01) Forbes, MS; Cohen, TJ; Jacobs, Z; Marx, SK; Barber, E; Dodson, JR; Zamora, A; Cadd, H; Franke, A; Constantine, M; Mooney, SD; Short, J; Tibby, J; Parker, A; Cendón, DI; Peterson, MA; Tyler, JJ; Swallow, E; Haines, HA; Gadd, PS; Woodward, CA
    The widespread formation of organic rich sediments in south-east Australia during the Holocene (Marine Isotope Stage [MIS] 1) reflects the return of wetter and warmer climates following the Last Glacial Maximum (LGM). Yet, little is known about whether a similar event occurred in the region during the previous interglacial (MIS 5e). A 6.8 m sediment core (#LC2) from the now ephemeral Lake Couridjah, Greater Blue Mountains World Heritage Area, Australia, provides insight into this question. Organic rich sediments associated with both MIS 1 and 5e are identified using 14C and optically stimulated luminescence (OSL) dating techniques. Also apparent are less organic sedimentary units representing MIS 6, 5d and 2 and a large depositional hiatus. Sediment δ13C values (−34 to −26‰) suggests that C3 vegetation dominates the organic matter source through the entire sequence. The pollen record highlights the prevalence of sclerophyll trees and shrubs, with local hydrological changes driving variations in the abundance of aquatic and lake-margin species. The upper Holocene sediment (0–1.7 m) is rich in organic matter, including high concentrations of total organic carbon (TOC; 20–40%), fine charcoal and macrophyte remains. These sediments are also characterised by a large proportion of epiphytic diatoms and a substantial biogenic component (chironomids and midges). These attributes, combined with low δ13C and δ15N values, and C:N ratios of approximately 20, indicate a stable peat system in a swamp like setting, under the modern/Holocene climate. In comparison, the lower organic rich unit (MIS 5e-d) has less TOC (5–10%), is relatively higher in δ13C and δ15N, and is devoid of macrophyte remains and biogenic material. Characterisation of the organic matter pool using 13C-NMR spectroscopy identified a strong decomposition signal in the MIS 5e organic sediments relative to MIS 1. Thus the observed shifts in δ13C, δ15N and C:N data between the two periods reflects changes in the organic matter pool, driven by decompositional processes, rather than environmental conditions. Despite this, high proportions of aquatic pollen taxa and planktonic diatoms in the MIS 5e–d deposits, and their absence in the Holocene indicates that last interglacial Lake Couridjah was deeper and, or, had more permanent water, than the current one. ©2020 Elsevier Ltd.
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    The evolution of Thirlmere lakes: a long-term sedimentary record of climate and fire dynamics in the Sydney Basin
    (Australasian Quaternary Association Inc., 2018-12-10) Cohen, TJ; Marx, SK; Barber, E; Forbes, MS; Gadd, PS; Tyler, JJ; Haines, HA; Woodward, C; Zamora, A; Mooney, SD; Constantine, M
    The Thirlmere lakes are located 40 km from the coast and are at ~300 m elevation and fall within the Greater Blue Mountains World Heritage area. The series of five lakes sit within a narrow and sinuous former river valley within the Hawkesbury sandstone with surrounding dry sclerophyll forest. Recent declines in water levels have prompted the NSW Office of Environment and Heritage to fund research about the history of Thirlmere lakes, the sub-surface characteristics and the potential frequency of past drying. This research builds on some existing work and has highlighted the extraordinary potential for the region for a long-term archive for palaeoenvironmental research.To date we have taken multiple vibracores across three lakes to depths of 7 m and we have supplemented this with some preliminary deep drilling to depths of 14 m. Our initial chronology is based on radiocarbon and OSL and we have employed a raft of geochemical and palaeoecological techniques to investigate changes through time. The lakes contain excellent organic preservation with deposition of the ‘modern’ peat environments commencing ~11 ka across two of the lakes investigated. This phase is represented by the upper 2 -3 m of organic rich peat (50% TOC). The underlying sediments are a mix of weakly bedded organic clays and oxidised clay facies that represent lake-wide drying intervals, a sequence that is repeated down profile. All five lakes are separated by alluvial sills that are comprised of medium to well-sorted sands, interbedded with organic ‘marker’ horizons that indicate these separate lakes were once joined, prior to the Last Glacial Maximum. The sandy sills that separate the lakes are derived from tributary alluvial fans accumulating progressively over the Holocene and effectively blocking and separating the lakes into their current configuration. This paper provides a preliminary overview of the chrono-stratigraphic history of Thirlmere lakes. © The Authors