Assessment of two grainsize methods for peat sediments and their paleoenvironmental significance: the Yueliangwan Peatland in northeast Asia

Abstract

Grainsize is an important indicator in paleoenvironmental research. Over the past few decades, different pretreatment methods have been proposed for grainsize determination of peat sediments. Assessing the reliability of the grainsize measurements is critical to ensure the paleoenvironmental significance represented by different grainsize components. In this study, using peat sediments from the Yueliangwan peatland in northeast Asia, the effects of two pretreatment methods on grainsize measurement were compared. It was found that these two pretreatment methods on peat sediments produced grainsize features with totally different parameters and distribution characteristics. Grainsize method 1, which used a hydrogen peroxide water bath treatment, did not reflect accurate results for grainsize in peat sediments. Grainsize method 2, which used muffle furnace combustion, does reflect the true results because the organic matter, such as plant residues, spores and pollen, is totally removed. The presence of this stubborn organic matter in peat samples greatly disturbs the accuracy of grainsize measurements, and the reliability of grainsize measurements can be affected by the presence of stubborn organic matter. Based on the grainsize grade-standard deviation analysis using method 2, the East Asian Winter Monsoon evolutionary history in northeast Asia during the Little Ice Age (1300–1750 CE) was reconstructed and divided into three stages: the strengthening stage (1346–1425 CE), the strongest stage (1425–1525 CE) and the weakening stage (1525–1725 CE).