Testate amoebae: a new indicator of the history of moisture in the swamps of eastern Australia

Key words: Temperate Highland Peat Swamps Sandstone

Introduction. Swamps are an ideal natural archive of climatic, environmental and anthropogenic change. Microbes and plants that once inhabited the swamps are transformed and accumulate in undisturbed anoxic sediments as (sub)fossils and become useful proxies of the past environment. Since these systems are intrinsically related to hydrology, the reconstruction of past moisture availability in swamps allows examination of many influences, including climate variability such as El Nino-induced drought. It can also provide baseline information: long (palaeoenvironmental) records can reveal natural variability, allow consideration of how these ecosystems have responded to past events and provide targets for their restoration after anthropogenic disturbance.

Testate amoebae are a group of unicellular protists that are ubiquitous in aquatic and moist environments. The ‘tests’ (shells) of testate amoebae preserve well and are relatively abundant in organic-rich detritus. Testate amoebae are also sensitive to, and respond quickly to, environmental changes as the reproduction rate is as short as 3-4 days. Modern calibration sets have demonstrated that the community composition of testate ameobae is strongly correlated to moisture (e.g. depth to water table and soil moisture) and this allows statistical relationships to be derived. These relationships have been used extensively in European research for the derivation of quantitative estimates of past depth to water table and hence moisture availability.

Although a suite of different proxies have used to reconstruct aspects of past moisture availability in Australia (e.g. pollen, diatoms, phytoliths) very little work on testate amoebae has occurred to date. This project aims to address this deficiency by examining testate amoebae in several ecologically important mires in eastern Australia including Temperate Highland Peat Swamps on Sandstone (THPSS), an Endangered Ecological Community listed under the Environment Protection and Biodiversity Conservation Act 1999 and as a Vulnerable Ecological Community under the NSW Threatened Species Conservation Act 1995.

The project specifically aims to develop a transfer function linking modern samples to depth to water table in THPSS and to then apply this to reconstruct palaeohydrology over the last several thousand years. Our ultimate aims are to use this research to consider the nature and drivers of past climate change and variability and to also address issues associated with recent human impacts. The analysis of testate amoebae will allow us to consider changes in THPSS state, accumulation and stability over centuries-to-millennia, and this will provide context for recent changes, recommendations for the management of peaty swamps on sandstone and analytic tools for assessing whether remediation is resulting in significant improvement on eroding or drying swamps.

Work Undertaken and Results to Date. Research linking testate amoebae and depth to water table in Europe and North America has mostly been undertaken in ombrotrophic (rain-fed) mires. These are distinctly different to THPSS and related communities of the Sydney Basin, which are often controlled by topography (topogeneous mires). In these environments various sediments are known to build up sequentially through time and the minerogenic-rich sediments of the THPSS have resulted in several challenges in our preliminary work. As an example, standard laboratory protocols do not remove mineral particles and these can obscure and make testate amoebae identification difficult. We have since developed a new laboratory protocol and results are promising. We have also been struck by the distinct Northern Hemisphere bias to testate amoebae research: as an example, the Southern Hemisphere endemic species Apodera (Nebela) vas that has been common in our THPSS samples is not included in the most popular guideline book (https://www.qra.org.uk/media/uploads/qra2000_testate.pdf).

Despite the new laboratory protocols we have found that testate amoebae are relatively scarce in THPSS environments. Table 1 outlines the species we are encountering in modern (surface) samples of THPSS and in the high altitude Sphagnum bogs of the Australian Capital Territory: we are finding greater abundance and species richness in the bogs of the ACT.

This project commenced in 2015 and will run until 2017.

Stakeholders and Funding. This research was funded through the Temperate Highland Peat Swamps on Sandstone Research Program (THPSS Research Program). This Program was funded through an enforceable undertaking as per section 486A of the Environment Protection and Biodiversity Conservation Act 1999 between the Minister for the Environment, Springvale Coal Pty Ltd and Centennial Angus Place Pty Ltd.  Further information on the enforceable undertaking and the terms of the THPSS Research Program can be found at www.environment.gov.au/news/2011/10/21/centennial-coal-fund-145-million-research-program.

Contact information. The project testate amoebae as indicators of peatland hydrological state’ is jointly being undertaken by: A/Prof Scott Mooney (School of Biological, Earth and Environmental Science, UNSW +61 2 9385 8063, s.mooney@unsw.edu.au), Mr Xianglin Zheng (School of Biological, Earth and Environmental Science, UNSW, +61 2 9385 8063, xianglin.zheng@unsw.edu.au) and Professor Emeritus Geoffrey Hope (Department of Archaeology and Natural History, School of Culture, History, and Language, College of Asia and Pacific, The Australian National University, +61 2 6125 0389 Geoffrey.Hope@anu.edu.au).

Table 1. A list of the testate amoebae species found in THPSS environments of the Sydney region and in the high altitude bogs of the ACT. (Those with a ++ are more common.)

Mooney table1

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