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Browsing by Author "Woodward, C"

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Evidence against early nineteenth century major European induced environmental impacts by illegal settlers in the New England Tablelands, south eastern Australia.
(Pergamon-Elsevier Science Ltd, 2011-12-01) Woodward, C; Chang, J; Zawadzki, AW; Shulmeister, J; Haworth, R; Collecutt, S; Jacobsen, GE
Paleoenvironmental reconstructions from Little Llangothlin Lagoon have been used to argue for early European impact on the eastern Australian landscape. In particular, these studies have argued for European arrival on the New England Tablelands at about 1800 AD, with significant impacts including the clearance of one species of Casuarina before 1820 AD and significant erosion by 1836 AD (Gale et al.. 1995: Gale and Pisanu, 2001; Gale and Haworth, 2002, 2005). We have re-cored the lagoon, dated the cores using (210)Pb and radiocarbon, and counted pollen and other proxies. Our (210)Pb results indicate that (210)Pb background was achieved stratigraphically later than the erosion event and we have three early Holocene radiocarbon ages in the erosion event interval. We conclude that the 'erosion event' predates European settlement. The (210)Pb results indicate much less erosion in response to European settlement than suggested by these earlier studies. We also find no notable decline in Casuarina in the pollen record spanning the time of initial European impact, and in fact we find very little Casuarina in the record. Instead of a Casuarina dominated vegetation we conclude that the area was dominated by open Eucalypt forest prior to European settlement. Rather than changes in the regional vegetation in the early 19th century, we attribute changes in the palynoflora spanning the 'erosion event' to changes within the lake/wetland and in particular to changes in the dominance of different species of Myriophyllum; most likely due to water depth fluctuation. This site has stood out as indicating an earlier European impact than other localities in eastern Australia, beyond the original limits of settlement near Sydney. Our findings suggest that a more traditional interpretation of this site is warranted and that no very early impact is discernable. (C) 2011 Elsevier Ltd. All rights reserved.
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
Fire and fuel in Holocene northern Australian tropical savannas
(International Union for Quaternary Research (INQUA), 2019-07-26) Rehn, E; Bird, MI; Rowe, C; Ulm, S; Woodward, C; Jacobsen, GE
Fire has a long history of interaction with Australian ecosystems but poses a growing risk as future climate change is predicted to lengthen fire seasons and increase extreme fire weather. Tropical savannas cover almost one quarter (1.9 million km2) of the Australian land mass, and fire occurs here almost annually. A greater understanding of past fire regimes, and their environmental context, is essential for management and planning in an increasingly fire-prone landscape. Despite the central importance of fire in savanna ecosystems, the region remains understudied in Australian palaeofire research. In light of this knowledge gap, this study combines established and emerging optical and chemical methods for charcoal analysis in the context of northern Australian tropical savannas. This study presents three new Holocene palaeofire records from tropical savanna wetland sites in far northern Australia, each with diverse land-use histories. Three methods were applied to achieve a more comprehensive understanding of fire and fuels over time in tropical savannas. Charcoal abundance is presented for four size classes covering a local signal (>250 µm and 250-125 µm) and surrounding regional signal (125-63 µm and <63 µm). Particle morphology and aspect ratio are proposed indicators of fuel type (e.g. grass, leaf, wood). However, this technique derives primarily from temperate environments, notably from experimental burns and sites in the Northern Hemisphere. Our study tests methods developed in temperate, Northern Hemisphere settings on charcoal from the Australian tropical savanna. Fuel type data are discussed using a morphotype classification system, and a length-width ratio of ≥3.6 is used to identify macroscopic grass particles. We demonstrate the application of chemical quantification of pyrogenic carbon (PyC) as well as isotopic identification of fuel type. PyC abundance determined using hydrogen pyrolysis and δ13C composition (contribution of C3 versus C4 plants) are presented for the three sites and combined with the data generated using optical methods. All records are supported by 210Pb and 14C chronologies and XRF core scanner data on elemental composition. Preliminary results show negligible variations in fuel composition through time at each site, with broad correspondence between fuel type determined by morphology and isotope composition. Variations are apparent between different charcoal size classes (macroscopic and microscopic) in both abundance and fuel composition at all sites, reflecting differences in local and regional fire signals and highlighting the importance of size differentiation during analysis. This study is a step towards filling the palaeofire knowledge gap represented by northern Australia and is an important assessment of the application of existing palaeofire techniques to this unique context. © The Authors.
Holocene ecosystem change in Little Llangothlin Lagoon, Australia: implications for the management of a Ramsar-listed wetland
(Springer Nature, 2016-01-01) Woodward, C; Shulmeister, J; Zawadzki, AW; Child, DP; Barry, LA; Hotchkis, MAC
We present new chironomid and stable isotope (δ13C and δ15N) data from Little Llangothlin Lagoon, Australia that provides more detail on changes in this wetland since European settlement ca. 1840 AD. We also examine how the updated Holocene paleoecological record provides insights for management of this Ramsar-listed wetland. The current management strategy for Little Llangothlin is to restore the wetland and catchment to its natural state. This strategy is intended to protect the values that allowed it to be listed as a Ramsar wetland; i.e. its role as a drought refuge for waterbirds and to preserve or enhance threatened ecological communities. There are clear conflicts between the Ramsar listing criteria, management objectives and the management strategy in light of information provided by the palaeoecological record. In particular, restoration of terrestrial ecosystems through reforestation may jeopardise the wetlands role as a drought refuge. Some activities, such as artificial raising of the water level in 1989 are intended to restore, but actually introduced a state that did not exist prior to human settlement. We recommend a more integrated management approach that heeds the information provided by the palaeoecological record and focuses more on maintenance or enhancement of ecosystem services and biodiversity. © 2016, Springer
A Holocene record of climate and hydrological changes from Little Llangothlin Lagoon, south eastern Australia
(Sage, 2014-06-30) Woodward, C; Shulmeister, J; Bell, D; Haworth, R; Jacobsen, GE; Zawadzki, AW
We present a new well dated Holocene record of environmental change from Little Llangothlin Lagoon in eastern Australia derived from aquatic plant macrofossils, macroscopic charcoal flux, and sediment stratigraphy from multiple cores. Little Llangothlin was an ephemeral freshwater wetland exhibiting frequent dry phases between 9800 and 9300 calendar years before present (cal. yr BP). There was a switch to a more positive water balance after 9300 cal. yr BP, and by 8000 cal. yr BP, there was a lake that persisted until 6100 cal. yr BP. The period between 6100 and 1000 cal. yr BP was much drier, and there is no evidence for a permanent lake during this period. The Little Llangothlin record provides evidence for a wet phase during the Early to Middle Holocene (9000–6000 cal. yr BP) from the boundary region between temperate and tropical influences in eastern Australia. We propose that generally enhanced circulation after 9000 cal. yr BP explains the pattern of increasing moisture at the site at this time. The later Holocene climate at the site is consistent with other sites in south east Australia with a switch to generally drier conditions after 6000 cal. yr BP. © 2020 by SAGE Publications
The hydrological legacy of deforestation on global wetlands
(American Association for the Advancement of Science (AAAS), 2014-11-14) Woodward, C; Shulmeister, J; Larsen, JR; Jacobsen, GE; Zawadzki, AW
Increased catchment erosion and nutrient loading are commonly recognized impacts of deforestation on global wetlands. In contrast, an increase in water availability in deforested catchments is well known in modern studies but is rarely considered when evaluating past human impacts. We used a Budyko water balance approach, a meta-analysis of global wetland response to deforestation, and paleoecological studies from Australasia to explore this issue. After complete deforestation, we demonstrated that water available to wetlands increases by up to 15% of annual precipitation. This can convert ephemeral swamps to permanent lakes or even create new wetlands. This effect is globally significant, with 9 to 12% of wetlands affected, including 20 to 40% of Ramsar wetlands, but is widely unrecognized because human impact studies rarely test for it. © 2014, American Association for the Advancement of Science.
The hydrological legacy of deforestation on global wetlands
(Australasian Quaternary Association Inc., 2014-06-29) Woodward, C; Shulmeister, J; Larsen, JR; Jacobsen, GE; Zawadzki, AW
Catchment erosion and increased nutrient loading are commonly recognised impacts of deforestation on global wetlands. Forest clearance can increase water availability in wetland catchments, but globally, the hydrological effect of deforestation has received little attention. We provide the first unequivocal evidence that historic and prehistoric forest clearance in dryland areas in Australasia increased catchment water yield; creating new wetlands and converting existing wetlands into shallow lakes. We developed a hydrological model to predict the location of global wetland catchments that are susceptible to this effect and demonstrate that hydrological alteration of wetland catchments is a previously overlooked dimension of the cultural landscape. We used a meta-analysis of published papers to demonstrate that the effect is widespread but under-appreciated in the literature. We conclude that artificially enhanced wetlands may be common even in regions with short histories of human settlement. Restoring them to their pre-human impact state may be difficult or even undesirable if we want to protect biodiversity and wetland ecosystem services.
Integrated age modelling of numerical, correlative and relative dating of a long lake sediment sequence from Orakei maar paleolake, Auckland, New Zealand
(Australiaian Quaternary Association Inc., 2018-12-10) Peti, L; Augustinus, PC; Woodward, C; Nilson, A
Accurate and precise chronologies are fundamental for any successful Quaternary paleo-climate/-environment reconstruction. Aside from varved lake sequences, all records depend on sediment core age models developed from a limited number of dated horizons, often with large errors. Hence, it is crucial to combine every piece of available information on the depositional history of the basin with modelling tools used for chronology development such as Bacon, a Bayesian age modelling package. Whilst sediment core chronology development has progressed from linear interpolation between dated horizons to considering uncertainties and Bayesian accumulation models, these age models rarely reach the resolution and precision desired for reliable paleo-climatic interpretations, especially in pre-Holocene sequences as errors increase and radiocarbon dating is not suitable anymore. We address this issue here in the context of Orakei maar paleolake sequence, Auckland, New Zealand. This record spans ca. 120 to 10 cal ka BP and is underpinned by tephrochronology, radiocarbon dating and relative changes in paleointensity of the earth magnetic field. Pre-40 cal ka BP, the age model relies on comparison with and correlation to the global PISO-1500 paleointensity stack through dynamic time warping (DTW in R). The chronology for the time interval ca. 50 to 10 cal ka BP has been estimated in Bacon (rBacon in R) with non-normal error distribution of un-calibrated ages, variable mean accumulation rates and accounting for many “slumps” (horizons of instantaneous deposition).The Orakei maar paleo-lake age model is a work in progress but serves as an example for extended age modelling from lake sediment sequences, particularly beyond the radiocarbon age limit. Furthermore, the Orakei maar sequence offers a high-resolution and continuous record of climatic variations that span much of the last glacial cycle and is one of the few from the mid-latitudes of the Southern Hemisphere. The rarity of records of this type makes Orakei maar a crucial record for development of an improved understanding of the global climate system because of its potential to be tied directly to the polar ice core and tropical lake and speleothem records.
The last deglaciation in New Zealand ; new 10Be production rates from Misery moraines, Arthur’s Pass, Southern Alps
(International Union for Quaternary Research (INQUA), 2019-07-29) Fink, D; Rother, H; Woodward, C; Schulmeister, J; Wilcken, KM; Fujioka, T
Recent debate on mid-latitude New Zealand glaciation has focused on reconstructing paleo-climate conditions leading into the (global) Last Glacial Maximum and subsequent deglaciation dynamics during the last termination. Paleo-environmental evidence coupled with reliable glacial chronologies confirms significant differences from that observed in northern hemisphere signatures of glacial change. The New Zealand glacial record does not show glacial readvance and strong cooling commensurate with Younger Dryas timing (~11.7-12.9 ka) and many lake pollen records suggest a minor cooling or hiatus in warming during the period from ~14.5 – 12.0 ka that is more commonly associated with the Antarctic Cold Reversal (ACR) (~14.7 - 13.0 ka). The Arthur’s Pass Moraine complex at 950 masl, deposited by an alpine glacier advancing out of the Otira Valley splaying east and westward over the divide of the Southern Alps in New Zealand, exhibits a full post-LGM glacial chronology. We have determined paired 10-Be and 26-Al exposure ages from 58 greywacke samples taken from all major moraines. Calculated exposure ages (using accepted local NZ production rates) show that the Arthur’s Pass moraine system spans a period of 19.5 ka to 12.0 ka with mean recessional moraine ages in chrono-stratigraphic sequence. The overall timing of deglaciation after peak LGM conditions is similar to the glacial systems we have dated in the Rakaia, Waimakariri and Rangitata Valleys. The Misery sequence shows ice retreat at the end of the ACR and no major advance during the YD period. Multiple cores from two intermorainal bog (Lances and Misery Tarns), separated by ~1 km and constrained by the terminal Dobson and Misery moraines, have been recovered for paleo-climate study. Basal glacial silts and organic matter have provided radiocarbon ages representing a minimum age for glacial retreat. Combined with the Misery moraine cosmogenic concentrations, new 10Be and 26Al production rate calibrations can be made for New Zealand to improve exposure age accuracy.
The Last Glacial transition and Holocene ecological change in Arthur’s Pass National Park, New Zealand
(Australian Nuclear Science and Technology Organisation, 2021-11-17) Adams, PM; Fink, D; Shulmeister, J; Woodward, C; Fujioka, T; Simon, KJ
This study improves our understanding of paleo-climate and -environmental change in the high-country South Island New Zealand focusing on formerly glaciated valleys near Arthur’s Pass. The area is of importance being positioned under a steep precipitation gradient on the lee side of the Southern Alps. Be-10 exposure ages (n=37) of ice limits, mapped as terminal moraines deposited during the last deglaciation through to late Holocene, span the past 17 000 years. The glacial record from well-preserved moraine sequences within the valley floor and glacial benches (850 to 1350m) demonstrates an initial post-LGM fast retreat that confirms previous studies (e.g. Shulmeister et al., 2010). Coupled with available in-valley exposure ages from Misery, Dobson and McGrath Moraines (Fink et al, 2017), a comprehensive regional deglacial pattern emerges. The Be-10 ages at Misery Moraines, subject of an early debate supporting a Younger Dryas glacial advance in the Southern Hemisphere (Ivy-Ochs et al. (1999), are re-dated to the Antarctic Cold Reversal (~14-15 ka). The record in headwater valleys of the Bealey and Otira rivers is largely obscured by slope-processes making conclusive observations relating to glaciation difficult. Consequently, early to middle Holocene moraines ages were not recovered in these valleys in contrast to nearby Dart Valley (Dowling et al., 2021). There is strong evidence at Otira headwall for a Little Ice Age glacial moraine limit. Several non-glacial boulders yield ages of 6.7ka, 4.2ka, 2.2ka and 1.7ka in the over steepened upper reaches of Bealey and Otira valleys that may reflect landslides associated with separate seismic events. In addition to our glacial chronology, we report on a well constrained record from Lances Tarn (Pb-210, and 37 radiocarbon dates over 4 m core length), a moraine-impounded bog at the saddle of Arthur’s Pass. This record spans ~13 000 years and displays post-glacial environmental change. The pollen record indicates typical succession from herb field through to closed forest, similar to other regional records (e.g. McGlone et al., 2004). The onset of Holocene like conditions is observed early c12ka, unlike central and lower South Island (~10ka). The area is influenced by persistent westerly flows through the entire record but with a reduction in flow in Early Holocene between 9.5 and 8.5ka, causing drier conditions in agreement with other records in Tasmania (Mariani and Fletcher, 2017 also in Patagonia (Moreno et al., 2020). There is little evidence of burning until c2.2ka when grass pollen rises sharply and charcoal counts increase, indicating a change in evapotranspiration (drying). Increased fires are evident from the onset of human arrival 750 years ago. The largest change in fire history and sediment transport occurs after European settlement ~ 1850’s, when intensive deforestation is evident in the pollen record. © The Authors
Late holocene climate variability In the Australian Alps: can sedimentary and geochemical tracers track fine scale paleo-environment change?
(Australasian Quaternary Association Inc., 2018-12-10) Stromsoe, N; Vernon, J; Marx, SK; Woodward, C; Saunders, KM
The Australian Alps have experienced some of the most dramatic change in any Australian landscape over the last glacial cycle, i.e. shifting between cold-climate conditions, glacial growth and dominance of periglacial processes and present day (warm) conditions. While these large scale changes are well documented, less is known about how the Alps have responded to more minor palaeo-climate change during the Holocene. Minor temperature changes may result in a measurable landscape response because they would be expected to manifest in changes to the occurrence of cold-climate processes, such as freeze thaw or solifluction, or conversely, increased vegetation cover and landscape stability. Sedimentary records from cirque lakes, therefore offer the potential to examine palaeo-environmental change in the alpine region during the late Holocene. In this study we examine recent (late Holocene) changes in the Alpine region of Kosciuszko National Park using cores extracted from Blue Lake and Club Lake. The two short cores date from 3,500 and 1,900 cal. yr BP, respectively. At Blue Lake, there is relatively little change recorded over most length of the core with the exception of a minor period of changing sedimentation rates and increased charcoal at 2,200-2,800 cal. yr BP, implying possible increased fires and associated landscape instability. Similarly, the Club Lake core also records little variability, although a change in sediment geochemistry implies the addition of less weathered material to the lake during the Little Ice Age, implying a potential increase in physical weathering. The most substantial change in both cores occurred within the last 200 years, with the addition of finer, less organic and significantly more chemically weathered material to the lakes. This coincides with the onset of grazing in the alpine region. This change implies that there has been increase in the contribution of sediment derived from soil to the lakes and, in particular, an increased contribution from subsoil (which in the case of the Australian Alps are more weathered). Finally, there is evidence of recovery in the top few centimetres of the cores implying conditions in the Alps have recovered from the dramatic grazing era perturbation, with conditions now similar to those over most of the late Holocene. © Author(s)
Major disturbance to aquatic ecosystems in the South Island, New Zealand, following human settlement in the Late Holocene
(Sage Publications Ltd, 2014-06-01) Woodward, C; Shulmeister, J; Zawadzki, AW; Jacobsen, GE
Lake sediment records from three lakes in the South Island of New Zealand were examined to determine the effects of human (Maori and European) impacts on the lake catchments during the Late Holocene. Major changes in lake biota occurred in the Early to Middle Holocene (11,000-6000 cal. yr BP), but there were no major changes between c. 6000 cal. yr BP and the time of human impact. Intensive Maori forest clearance occurred here between c. ad 1200 and 1600, which is consistent with other New Zealand records. Catchment erosion and increased sedimentation probably occurred in all of the studied lakes, but the most obvious changes occurred in Lake Clearwater and the Maori Lakes. There was evidence for gravity-induced slumping of the littoral sediments in Lake Clearwater due to increased sediment loading, and the outflow from the Maori Lakes was blocked by a migrating alluvial fan. The erosion of sediment (and nutrients) from the lake catchments led to eutrophication, but increases in lake depth were just as important in two of the lakes. Increased water depth was caused by damming of the Maori lakes outflow by a migrating alluvial fan. Reduced evapotranspiration following deforestation would also have led to increased water yield in lake catchments. European impacts were minor compared with the impacts of Maori deforestation, and all lakes display different levels of recovery towards pre-human impact conditions. Complete recovery is prevented by permanent changes in catchment hydrology and probable internal feedback mechanism such as wind-induced sediment re-suspension in the larger lakes. © 2014, SAGE Publications.
Orakei maar paleolake (Auckland, NZ):A multi-method approach to the composite stratigraphy of a long sediment core
(Australiasian Quaternary Association Inc., 2018-12-10) Peti, L; Augustinus, PC; Woodward, C
The development of records of Quaternary environmental and –climatic changes relies largely on long, complete sediment sequences. However, coring techniques do not allow extraction of one continuous record of sedimentation to be recovered from a single drill hole. In order to reconstruct a complete record, it is common practice to drill two or more overlapping cores with a depth offset to overcome coring-induced loss and disturbance and then stitch these records together using stratigraphic markers to produce a master stratigraphy. However, details of the process used and critical uncertainties are rarely reported despite the fact that spurious correlations may alter subsequent paleoenvironmental interpretations. Here we detail the procedure employed to build a composite stratigraphy from three overlapping long lake sediment cores from Orakei maar paleolake (Auckland). Orakei maar was created by a phreato-magmatic eruption to forming a lake basin of a low surface-to-depth ratio and virtually no catchment. The accumulated sediment can be considered a direct recorder of climatic and environmental changes over the Last Glacial Cycle in the Southern Hemisphere mid-latitudes, a crucial but under-studied part of the global climatic system. Finely laminated sediment in the Orakei record can be aligned and correlated along visually distinct marker horizons, as well as tephra layers (Fig. 1), with sub-cm to mm resolution, supplemented by μ-XRF core scanning elemental and X-ray density variability. Complications arise from lateral inhomogeneities in sedimentation along the lake bottom and hence, larger differences between the three cores. These sections, usually of coarser grain size, likely caused by local landslides from the crater rim, are correlated based on: visual logging, common pattern in μ-XRF elemental and Xray density variation, and typical depth offset between the observed debris flows in the cores. Figure 1: Composite stratigraphy and lithology of Orakei maar paleo-lake record built from three overlapping sediment cores. © The Authors
The potential power and pitfalls of using the x-ray fluorescence molybdenum incoherent: coherent scattering ratio as a proxy for sediment organic content
(Elsevier, 2019-04-30) Woodward, C; Gadd, PS
Changes in organic matter concentration in sediment cores from natural archives such as lakes and wetlands can be a valuable tool in paleoenvironmental studies. The molybdenum incoherent: coherent scattering ratio (moly ratio) from the Itrax core scanner offers the potential to measure down core changes in sediment organic content. The analysis is rapid, high resolution and does not destroy samples. We built upon previous studies of the power and potential pitfalls of using the moly ratio as a proxy for organic content in sediments. An important difference between our study and previous work is that we accounted for the total mass of moisture and organic content in the sediment using loss on ignition. This had the advantage over total organic carbon measurement of being able to account for all light elements (H, C, N, and O) that would affect the moly ratio. We used redundancy analysis to determine that both organic and moisture content can have large, independent, and variable effects on the moly ratio. It is therefore critical that moisture and organic content have a constant relationship with each other in a core. Samples with higher moisture to organic content ratios can over predict organic content and vice versa. The effect of moisture only accounted for 30% of the prediction error for the moly ratio in our study. We argue that a large part of remaining error reflects sample heterogeneity. XRF core scanning and organic content determination from sub-samples can show different results because the mean sediment composition is different. We recommend that calibration sub-samples are large (≥2 cm3) in potentially heterogeneous sediments, authors should report the sample size used for calibration purposes, and multiple scans of the core may be needed. If organic content is an important proxy for an environmental reconstruction, we recommend calibration of the moly ratio and confirming a constant relationship between moisture and organic content. Thoughtful selection of sub-samples for this purpose could mean that calibration can be performed with a minimum of extra effort. Crown Copyright © 2018 Published by Elsevier Ltd.
Sediment records suggest post British-invasion declines in diversity of wetland plant communities in the Koondrook-Perricoota Forest, Murray River, NSW
(Australasian Quaternary Association, 2022-12-06) Reid, M; McIntosh, L; Woodward, C
Floodplain wetlands support enormous biodiversity and range of other vital ecosystem services. However, these wetlands are threatened by a range of processes. In the Murray-Darling system of southeast Australia, these processes include altered wetting regimes, cropping, grazing, invasive species and even forestry. Detecting and monitoring changes to these systems is limited by poor benchmark data, which would otherwise provide the basis for establishing the degree and nature of changes as well as possible drivers. This study sought to establish benchmark conditions and temporal patterns of change in wetland plant communities by examining stratigraphic changes in preserved plant and animal remains. Sediments from 12 wetlands in the Koondrook-Perricoota Forest were sampled at 2 cm intervals to depths of 30 cm to 40 cm. Lead-210 dating of the sediment profiles suggest the upper 10 to 16 cm of these sediment sequences were deposited in the last 100 years. Identified remains included Azolla megaspores, charophyte oospores, bryozoan statoblasts, chironomid head capsules, cladoceran ephippia and orobatid mites. The preserved remains assemblages of the pre and post-invasion period were generally distinct, though the degree of change varied among wetlands. In general, the post-invasion period is characterised by declining richness and diversity and to a lesser extent abundance in charophyte oospores in several of the wetlands. While there is no compelling evidence as to a specific cause of these changes, they are likely a response to declining frequency of flooding of the wetlands as a result of flow regulation and water abstraction. In the case of the apparent declines in charophytes, the impact of introduced grazers such as cattle could well have been a factor given that trampling and increased turbidity arising from their presence in and around the wetlands is likely to have been detrimental to the persistence of these submerged plants.

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