The effect of the introduction of livestock on the erosion of alpine soils: a comparison of five dating techniques applied to sediments of the Australian alpine Blue Lake

Patrick De Deckker; Gary J Hancock; Jon M Olley; Shawn Stanley; Geoffrey Hope

doi:10.1007/s10933-023-00284-x

The effect of the introduction of livestock on the erosion of alpine soils: a comparison of five dating techniques applied to sediments of the Australian alpine Blue Lake

J Paleolimnol. 2023 May 8:1-17. doi: 10.1007/s10933-023-00284-x. Online ahead of print.

Authors

Patrick De Deckker¹, Gary J Hancock², Jon M Olley^{2

3}, Shawn Stanley^{4

5}, Geoffrey Hope⁶

Affiliations

¹ Research School of Earth Sciences, The Australian National University, Canberra, ACT 2601 Australia.
² Formerly of CSIRO Land and Water, PO Box 1666, Canberra, ACT 2601 Australia.
³ School of Environment and Science - Forensics and Archaeology, Griffith University, Nathan, Qld 4111 Australia.
⁴ Formerly of Department of Geology, The Australian National University, Canberra, ACT 2601 Australia.
⁵ Division for Ocean Affairs and the Law of the Sea, Office of Legal Affairs, United Nations, New York, NY 10017 USA.
⁶ Canberra, Australia.

Abstract

²¹⁰Pb and ¹³⁷Cs dating of bulk sediments obtained from the alpine Blue Lake, located in the Snowy Mountains of southeastern Australia, was applied here to date recent lacustrine sediments. In addition, the presence of Pinus pollen (a taxon introduced in Australia about 150 years ago) down to a sediment depth of 56 cm in the core is used to obtain a chronology for the upper part of the core. Accelerated Mass Spectrometry radiocarbon dates obtained from organic muds from the same core do not agree with the chronology constructed using the three other dating techniques. In addition, optically stimulated luminescence (OSL) dating of single quartz grains, from sediment-core samples collected from the same lake, was applied to date recent lacustrine sediments. The optical age of 185 ± 20 years for a sample at 60-62 cm depth, and 470 ± 50 years at 116-118 cm depth are well over 1000 years younger than the ages inferred from radiocarbon dates. We therefore infer that the 'old' radiocarbon ages result from carbon stored for considerable time within the catchment prior to its transport and deposition on the lake floor. As plant decomposition occurs at much slower rates in high altitude environments, these results bring into question the veracity of previously published radiocarbon dates from Blue Lake and alpine lake sediments in general. The deposition ages inferred from the ²¹⁰Pb-¹³⁷Cs and OSL dating, and the first appearance of Pinus pollen, indicate that for the 100-year period after European settlement (from the mid 1800s to early 1900s) the sediment-accumulation rate increased by a factor of about 2, from 0.19 ± 0.01 cm yr^-1 to 0.35 ± 0.02 cm yr^-1. In the 1900s the accumulation rate increased further to 0.60 cm yr^-1. The accumulation rate was particularly rapid in the 20-year period from 1940-1960, reaching a rate 18 times higher than the pre-European rate in the mid-1950s. The increase in sedimentation rate is attributed to changes in land use resulting from European activities in the lake catchment, primarily through sheep and cattle grazing in the Blue Lake catchment.

Keywords: 210Pb and 137Cs geochronology; AMS 14C; Erosion; Land management; Optical dating; Pinus pollen.