Peatland development and environmental change during the past 1600 years in Baijianghe Mire of Changbai Mountains, China

Accepted Manuscript Peatland development and environmental change during the past 1600 years in Baijianghe Mire of Changbai Mountains, China Yang-Yang Xia, Hong-Chun Li, Hong-Yan Zhao, Sheng-Zhong Wang, Hong-Kai Li, Hong Yan PII:

S1040-6182(18)30994-7

DOI:

https://doi.org/10.1016/j.quaint.2019.03.012

Reference:

JQI 7797

To appear in:

Quaternary International

Received Date: 26 August 2018 Revised Date:

7 February 2019

Accepted Date: 13 March 2019

Please cite this article as: Xia, Y.-Y., Li, H.-C., Zhao, H.-Y., Wang, S.-Z., Li, H.-K., Yan, H., Peatland development and environmental change during the past 1600 years in Baijianghe Mire of Changbai Mountains, China, Quaternary International (2019), doi: https://doi.org/10.1016/j.quaint.2019.03.012. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Yang-YangXia1,2,3, Hong-Chun Li1,4*, Hong-Yan Zhao1,2,3*, Sheng-Zhong Wang1,2,3, Hong-Kai

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Li1,2,3, Hong Yan5 1 Institute for peat & Mires Research, Northeast Normal University, Changchun, Jilin 130024, China 2 State Environmental Protection Key Laboratory of Wetland Ecology and Vegetation Restoration, Northeast Normal University，Changchun, Jilin 130024, China 3 Key Laboratory of Vegetation Ecology, Ministry of Education, Northeast Normal University, Changchun, Jilin 130024, China 4 Department of Geosciences, National Taiwan University, Taipei 106, Taiwan, ROC 5 Jilin Provincial Academy of Forestry Sciences, Changchun, Jilin 130033, China

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Peatland development and environmental change during the past 1600 years in Baijianghe Mire of Changbai Mountains, China

*Corresponding authors (equally contributed): [email protected]; [email protected]

Abstract

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A 1.8 m long core was retreated from Baijianghe mire in the west flank of Changbai 14

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Pb/137Cs

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Mountains of China in 2016. The peat sequence was dated by AMS

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methods, showing a 1600-y depositional history. Based on the measured porosity, dry bulk

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density (DBD), TOC%, absorbance and plant macrofossil, we discuss the mire development

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and environmental change during the last 1,600 years. The basin of Baijianghe Mire was a

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water-logged bottomland between 330 and 660 CE. A strong drought occurred during

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530-600 CE caused lowering of water table which provided hydrological condition to form a

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peatland. Wet climate during 660-800 CE led to enhanced primary productivity and

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accumulation of plant remains, resulting rapidly development of the mire. Warm but

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fluctuating wetness conditions during the Medieval Warm Period (MWP, 900-1150 CE) in the

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study area kept moderate development of the mire. Baijianghe Mire had the fastest

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development during 1200-1370 CE under relatively wetter and probably warm conditions.

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Low carbon accumulation of the mire appeared during the Little Ice Age (LIA, 1500-1850

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CE) under cold and dry climates. From 1850 CE to 1945 CE, the climate turned to warm and

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wet. However, the peatland had experienced strong influence by human activity since 1945

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CE. The peatland has gradually recovered from artificial drain since 1990s.

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Keywords: AMS

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change; Baijianghe Mire; NE China

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1. Introduction

C dating; Plant macrofossil; Physicochemical property; Environmental

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Using original self-deposition mode in peatland ecosystems, peat sequences are not

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easily disturbed after deposition under natural conditions, yet easily to be dated with high

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resolution multiple techniques (Chambers and Charman, 2004). Hence, peat sequences

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(especially from peat bogs) are considered as a good geological archive for reconstructing

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vegetation changes and depositional processes under climatic influence of a peatland during

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the past (Aaby, 1976; Barber, 1982; Barber et al., 2003; Ortiz et al., 2011; Amesbury et al.,

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2013).

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Factors such as climatic conditions, plant compositions, redox boundaries, bacterial

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activities, mineral and nutrient concentrations, geomorphologic features, and etc. can affect

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peat formation and preservation, resulting various physical and chemistry processes of peat

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development and complicated interpretation of peat properties (e.g., pH, humification, TOC,

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δ18O and δ13C, elemental content, carbon accumulation rate, etc.) (Blackford, 2000; Hong et

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al., 2000, 2001; Fairbridge, 2001; Oldfield, 2001; Sheoran and Sheoran, 2006; Parviainen et

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al., 2014; Stebich et al., 2011, 2015; Yang et al., 2017). Every peatland, even every sampling

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site of a peatland, may have special features, so that interpretations of some physicochemical

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parameters from a peat study may be only suitable for its own system because local-scale

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factors can act as principal controls on peatland dynamics and C accumulation (Turunen and

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Turunen, 2003; Magnan and Garneau, 2014; Shiller et al., 2014). For instance, rate of carbon

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accumulation (RCA) that is a function of peat composition, formation and preservation, is

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ACCEPTED MANUSCRIPT thought to be an indicator of changes in carbon storage and climatic condition in peatlands

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(Bernal, 2008; Chimner, 2008; Chimner and Karberg, 2008; Yu et al., 2009; Frolking and

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Roulet, 2009; Wania et al., 2009; Yu, 2011; Loisel et al., 2014; Xing et al., 2015). However,

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the influence of detrital content (affecting dry bulk density and peat composition) and

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depositional rate on RCA often obscure the relationship between RCA and climatic influence

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(Yang et al., 2017; Sun et al., this issue). Normally, a young peat profile from a Sphagnum

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spp. hummock of an ombrotrophic bog contains abundant Sphagnum mosses with very low

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dry bulk density (DBD, typically <0.1 g/cm3), high total organic carbon (TOC, typically >40

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wt.%) and relatively high linear depositional rate. Changes in TOC% due to variation of plant

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composition (i.e., percentage of moss, herb, and wood respectively) can be balanced (or

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adjusted) by variation of DBD. But, in many peat fens (minerotrophic mire) detrital content

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of peat is relatively high. DBD in such a peat profile can vary several times (e.g., from 0.05

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to 0.5 g/cm3). Under this circumstance, changes in DBD are largely caused by detrital

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contents rather than plant compositions. This situation will result in a positive correlation

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between detrital content and RCA, and a negative correlation between TOC content and RCA

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(Sun et al., this issue). In addition, influence of peat depositional rate on RCA may be caused

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by non-climatic reasons such as human disturbance, or dating uncertainties. Thus, using RCA

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of a peat sequence as an indicator of climatic change should be caution. Understanding of the

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relationship between RCA and responsive climates is needed more studies of multiple proxies

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from well-dated, high-resolution peat sequences in different environments.

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Plant macrofossils represent plant remains to reflect vegetation grown at the sample

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location in a mire (Birks, 2001). Compared with pollen record, plant macrofossil record can

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reflect more directly the vegetation change in a mire, so that the use of macrofossil in

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peatland ecosystems is a common method for reconstruction of paleo-vegetation (Barber et

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al., 1994; Birks and Birks, 2000; Mauquoy and Van Geel, 2007; Novenko et al., 2015;

ACCEPTED MANUSCRIPT Parducci et al., 2015; Väliranta et al., 2015; Waller and Early, 2015). Although plant

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macrofossils are mostly autogenic, selective decomposition of plant species and non-linear

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response of plant communities to changes in water-table depth often make complications of

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climatic reconstruction based on plant macrofossils (Blackford, 2000; Barber et al., 2003;

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Mauquoy and van Geel, 2007). Hence, although plant macrofossils are still frequently used to

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reveal the climate variability on annual-to-decadal scales, more comparison studies are

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needed to improve the use of plant macrofossil for climate reconstructions.

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With a temperate continental monsoonal climate, northeast China has abundant

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peatlands (Chen, 2000). For example, Changbai Mountains contain nearly 92.162 km2 in area

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with 38.92 million tons of peat storage (Chen, 2000). Previous studies on peat sequences in

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Northeastern China for paleoclimate and paleoenvironment were mainly carried out in a few

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mires, including Hani Mire (Hong et al., 2005, 2010), Jinchuan Mire (Hong et al., 2000, 2001;

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Makohinienko et al., 2008), Gushantun Mire (Liu, 1989) and Hanlongwan Mire (Fu, 2006) in

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Changbai Mountains, Motianling bog in Great Hinggan (Zhang et al., 2014), and Shen

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Jiadian (SJD) peatland in the Sanjiang Plain (Zhang et al., 2015). Most of these records used

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stable isotopes (cellulose δ18O and δ13C) and lipid biomarkers (n-Alkane concentration and

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distributions) as major proxies for paleoclimate reconstructions. However, the use of those

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isotopes and biomarkers for climatic reconstruction have been debated for long time, as

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effects of changing species composition on the isotopic compositions are not easy to be

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separated climatic influence (Van Geel and Middeldorp, 1988; Blackford, 2000; Fairbridge,

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2001; Oldfield, 2001; Stebich et al., 2011, 2015). For instance, based on n-Alkane

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concentration and distributions of SJD record, Zhang et al. (2015) concluded a warmer and

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wetter climate prevailed during 6~8 ka corresponds to the monsoon maximum and Holocene

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climate optimum in northeast China; and a cold and wet period from 6 to 4 ka. However, this

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core contained very low sedimentation rate (SR = ~0.005 cm/yr) with very low TOC content

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ACCEPTED MANUSCRIPT (<8%) during 4~8 ka (the 1.6~2 m part out of the 2 m core) compared with the upper section

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(SR = ~0.09 cm/yr and TOC ranging 15-40%) which referred relatively cooler and drier

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climates. The material and environment represented in the core were totally different during

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different periods, e.g., before 4 ka (lake deposits) and after 1.5 ka (peat deposits). Changes in

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temperature, hydrology, vegetation composition and sedimentary source, etc. all could affect

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the n-Alkane concentration and distribution. Construction of paleoclimate based on these

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proxies in peat sequences needs more supportive evidence from physical and chemical

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properties of the core. High-resolution (
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paleoenvironmental change during the past 2000 years in NE China is not common.

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On the other hand, there are a few studies on maar lakes in the northeast China, which

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are all close to our study site. Based on a multiproxy (δ13Corg, δ15N, C/N, Dinocyst

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concentration) record of a 110-cm long sediment profile from Lake Xiaolongwan, Chu et al.

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(2009) interpreted the climatic variations over the past 1600 years: drought periods during

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490–570 CE, 780–990 CE, 1360–1450 CE, 1590–1670 CE and the last 150 years. They

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concluded that these drought periods were corresponding to the weakening of solar activity

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(sunspot minimal periods). In a nearby maar lake, Sihailongwan, Stebich et al. (2015)

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retrieved several long sediment cores up to 39 m. Using pollen assemblages in the upper

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4.4-m varved sediments, they reconstructed precipitation and temperature during the past 12

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ky based on the method of biomization and weighted averaging partial least squares

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regression (WA-PLS) technique. The reconstructed temperature record agreed with the

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insolation trend, but the precipitation record was not consistent with wetness change in other

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monsoonal regions of eastern China, showing relatively low precipitation during 7~10 ka.

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The Sihailongwan record does not agree with the SJD record too. Although Sihailongwan and

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Xiaolongwan are the two adjacent maar lakes with accurate (varve counting) chronologies,

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their records for the last 1.6 ky exhibit significant differences (See comparison in this paper).

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Thus, more paleoclimate records from the study area will help us to understand not only

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climatic variability, but also response of peat properties.

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In this study, a 1.8-m peat core retrieved from Baijianghe Mire in Northeast China has 14

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been studied. The core was dated by AMS

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1600-year deposition history. Plant macrofossil, DBD, TOC% and humification of the peat

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core have been analyzed. The measured results and calculated RCA will be used for

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interpreting development of Baijianghe Mire and corresponding climatic conditions and

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human activities during the past 1600 years.

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2. Background of the study site

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Pb dating methods, showing a

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Under the management of Sanchazi Forestry Bureau, Baijianghe Mire (used to be called

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Sandaolaoyefu mire) (42°10’1.1” N, 126°44’02.4” E) is located at Jingyu County, Jilin

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Province, northeast China (Fig. 1). With an elevation of 777 m, Baijianghe Mire is

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surrounded by Longgang mountain range where belongs to the west flank of Changbai

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Mountains. The mire is about 0.7 km2 in size with a maximum depth of about 3~4 m. This

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mire is about 10 km and 20 km southeast of the well-studied Hani Mire and Jinchuan Mire,

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respectively (Hong et al., 2000, 2001, 2010; Makohinienko et al., 2008; Yang et al., 2017;

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Sun et al., this issue) (Fig. 1).

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In 1986/1987, Baijianghe Mire had experienced serious human impact (Schröder et al.,

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2007). Large drainage ditches were made for forestry (Fig. 1). After the drainage, the

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peatland was strongly degraded and the surface vegetation was dominated by Potentilla

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fruticosa L. Since late 2000s, drainage activity of the peatland has been stopped and the

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surface vegetation has been recovered with Larix olgensis A. henry, Betula fruticosa Pall. var.

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ruprechtiana Trautv., Pot. fruticosa, Carex appendiculata Kukenth., Polytrichum strictum and

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Sphagnum palustre. In early 2000s, a detailed investigation of modern vegetation and it

ACCEPTED MANUSCRIPT distribution in Baijianghe Mire had been carried out. At the present, the vegetation of

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Baijianghe mire is mainly divided into at least five kinds of plant communities. The Larix

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olgensis – ledum palustre L. – Carex–Sphagnum covers the south and northeast marginal

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areas of the mire. Salix grows on the south edge of the mire. Betula fruticosa is dominated in

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the northwest and west marginal areas, and gradually followed by Carex communities and

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Pot. fruticosa – Rhododendron parvifolium Adams in the western and Pot. fruticosa – Rh.

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parvifolium in the eastern part of the mire. Pot. fruticosa grows in the central area of the mire,

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and occupies nearly 1/4 of the total area of the mire. The part standing with Pot. fruticosa had

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seriously been influenced by the drainage event while the other parts were slightly influenced.

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Figure 2 exhibits the vegetation distribution in the mire at the present.

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Like the Hani and Jinchuan mires, climate of this study area is belong to temperate

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continental monsoon climate with four distinctive seasons. The mean annual temperature is

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2-6°C with a minimum of -16.9°C in January and maximum of 19.9°C in July (Fig. 3). The

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average annual precipitation is 630 mm/yr which is mostly concentrated from May to

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September. Geologically, this area is in the Longgang volcano field which had several

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eruptions during Holocene-to-late Pleistocene (Fan et al., 2002; Frank, 2007; Liu et al., 2009).

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The youngest eruption of the Longgang Volcano was about 1700 years age (Liu et al., 2009).

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Eight maar lakes formed in late Pleistocene exist in the area, in which Xiaolongwan and

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Sihailongwan have been studied for paleoclimate reconstructions (Chu et al., 2009; Stebich et

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al., 2015).

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3. Materials and methods

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3.1 Sampling method and description of the peat profile

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A 1.8-m long peat profile was combined from two cores taken on August 26, 2016 in a

ACCEPTED MANUSCRIPT selected site of Baijianghe Mire. This sampling site was far away from the drainage ditches

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and might have minor influence due to the drainage impact. The site has the deepest peat

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sequence in the area with no drainage influence. The upper 80 cm part of the profile was

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retrieved by a 10 cm×10 cm×80 cm Wardenaar surface sampler (Vleeschouwer et al., 2010).

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The core was subsampled with a stainless steel knife and a pair of scissors at 1 cm intervals

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on site. A total of 77 samples were from this part. The deeper part of the peat profile came

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from the second core which was taken by a Russian borehole corer in a 50 cm deep pit dug

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beside the first core. The second core was 130 cm long covering deposits from 50 cm to 180

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cm depth. Both the upper 80-cm core and the 130-cm Russian core of the profile were

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subsampled at 1 cm intervals in the field using the same method. All of the samples were

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packed in plastic bags and stored at 4°C in a refrigerator in the School of Geographical

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Sciences, Northeast Normal University (NENU).

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The profile can be briefly divided into several zones as following: (1) below 145 cm

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depth: Black color, mainly silt and clay with some sands. Plants are well decomposed and

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contain mainly shrub and herb remains. Relatively low water content. (2) 145-115 cm depth:

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Dark color. Peat content and porosity increase rapidly, but the plant structures are difficult to

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be recognized. Very low moss%. (3) 115-47 cm depth: Brown color. Peat plants are

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moderately decomposed. Plant structure is not clear. Squeezing water is dark and dirty. (4)

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47-23 cm depth: Yellow color. Peat plants are moderately decomposed. About 1/3 of plant

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remains are woody species. (5) 23-15 cm depth: Light brown color. Weak decomposition of

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plants with loose spaces. Squeezing water is light yellow. (6) 15-2 cm depth: Yellow color.

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Very weak decomposition. Plant structures are clear. Squeezing water is clean. (7) 2-0 cm.

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Light yellow color. Modern plants without decomposition.

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3.2 Porosity and Dry bulk density

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One cubic centimeter (1 cm3) of the original subsample in the field by a scale mark

ACCEPTED MANUSCRIPT injection syringe that has a 1 cm2 section area (1 cm2 × 1 cm) was weighed, and dried at 90oC

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for 8 hours in an oven. The dried sample was weighed again to calculate the porosity (weight

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loss divided by original sample weight) and dry bulk density (DBD) (dry weight divided by

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original sample volume) (Givelet et al., 2004).

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3.3 TOC content and LOI

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Total organic carbon (TOC) contents were obtained by an Aurora 1030W TOC Analyzer

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made in USA which equips with an 88-position rotary autosampler. The dried sample was

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grinded and weighed about 2 mg for measurement. Heated sodium persulfate solution

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(Na2S2O8) was added into the sample reaction vessel to oxide organic carbon and to produce

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CO2 for measurement. For each batch of samples, the analyzer was calibrated by organic

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standard. For every 10 samples, three replicated measurements were made. Repeatability of

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the method is 2.0% with detection limit of 2 ppb.

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When the upper 50 cm part conducted DBD measurement for the second time, TOC of

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these samples were also measured by Loss of Ignition (LOI) (Raymond et al., 1987; Leishvan

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and Koroli, 1989; Chambers et al., 2011). The dried sample was weighed and placed into a

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furnace at 550oC for 4 hours. The residue was weighed to calculate ash content. The

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percentage of weight loss multiplied by 0.5 yields TOC content, marked as TOC by LOI.

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Figure 4 shows strong corrections of the two TOC measured results, indicating reliability of

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the TOC results. However, the LOI results are about 11% higher than the results measured by

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the TOC Analyzer. The TOC overestimation of the LOI measurement may be caused by the

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relatively high detrital content of the peat samples.

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3.4 Absorbance

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Humification degree of the peat sample was determined by the alkali extraction solution

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absorptiometry (Chambers et al., 2011; Payne and Blackford, 2008). Take 0.1g of the grinded

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absorbance of the solution was measured by a 721S spectrophotometer manufactured by

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Shanghai No.3 Analytical Instrument Factory at a wavelength of 540 nm. The average value

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of three replicates was used to characterize the humification degree of the samples. Figure 5

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reveals all measured physicochemical properties of the Baijianghe profile.

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3.5 210Pb and 137Cs dating

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The half-lives of

Pb and

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Cs are 22.3 years and 30.2 years, respectively. These two

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radionuclides are often used for determining chronology of peat sequences within 200 years.

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Total

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the atmospheric fallout. The excess

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an anthropogenic radionuclide related to thermonuclear weapon tests and nuclear power

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plants (Davis et al., 1984). The 1964 CE peak of 137Cs profile can be used as a time marker.

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In some cases, another peak of

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Chernobyl may also be recorded in some peat sequences (Ali et al., 2008).

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Pb and excess

Pb, the later comes from

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Pb is obtained by total

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Pb subtracting supported

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Pb which is determined by 214Bi and 214Pb activities (Appleby and Oldfield, 1992). 137Cs is

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Cs at 1986 CE caused by the catastrophic explosion of

The upper 14 cm part (every 1 cm) of the peat profile were subjected to

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Pb/137Cs

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dating using a high-purity helium gamma spectrometer at the Key Laboratory of Wetland

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Ecology and Vegetation Restoration at NENU. The measured 210Pb, 214Bi, 214Pb and 137Cs are

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plotted in Fig. 6. The 137Cs peak is at the depth of 8 cm, indicating this depth represents 1964

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CE. The calculated excess

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from the

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an age of 120 years at 13 cm depth.

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3.6 AMS 14C dating

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210

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Pb and estimated age are also plotted with depth. Chronology

Pb profile was used constant flux model (Appleby and Oldfield, 1992), resulting

Plant remains such as leaves or stems of the peat mosses or herbaceous species from

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Baijianghe profile were selected for AMS

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aboveground plant material, especially pure Sphagnum spp. should be used for

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(Nilsson et al., 2001; Blaauw, 2003; Goslar et al., 2005; Clarke et al., 2012; van der Plicht et

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al., 2013; Satu Räsänen, 2005). However, from the strongly decomposed peat samples of

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Baijianghe profile it is difficult to pick up aboveground Sphagnum spp. In order to have at

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least 1 mg of carbon, about 4 mg of plant remains are needed for the AMS 14C dating.

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C dating

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C dating. Previous studies suggest that only

Dry and clean plant remains were put into a 9 mm quartz tube with pre-combusted CuO 14

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powder. The tube was placed on the graphitization line in the

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NENU. Then, the tube was sealed under vacuum of 10-5 mbar, and heated for 6 h at 850°C in

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a muffle furnace for combustion of organic carbon into CO2. The produced CO2 was then

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purified cryogenically on the graphitization line and transferred into a combination tube with

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a 9 mm glass tube containing Zn+TiH2 and an inner 6 mm center tube containing Fe powder

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(Xu. et al., 2007). The tube was sealed under vacuum of 10-5 mbar and placed into the muffle

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furnace for graphitization of the CO2 at 550°C for 6 h.

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C dating preparation Lab at

The graphite samples were sent to the NTUAMS laboratory at the National Taiwan

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University (NTU) for AMS measurement with a HVE 1.0 MV Tandetron Model 4110

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BO-Accelerator Mass Spectrometer (AMS). Each batch of samples will run together with

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three international standards (OXII), three backgrounds (BKG) and two known age

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inter-comparison samples. Radiocarbon ages are determined with a half-life of 5568 years

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and corrected the isotopic fractionation with measured

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measured

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using CalPal Online Radiocarbon Calibration of

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1986, 1993). Age uncertainties are in 1σ error. All 14C results are listed in Table 1. Four ages

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in Table 1 are apparently not in stratigraphic sequence, probably due to coring process. Since

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the peat profile contains mainly herb and shrub plants with abundant roots, penetration of the

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C/12C ratio by the AMS. The

C ages are converted to calibrated calendar ages (a BP = years before 1950 CE) 14

C and CALIB 7.0 (Stuiver and Reimer,

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used for chronological construction. The 66 cm depth was dated twice, showing similar

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results. This similarity indicates that the dating results are reliable.

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3.7 Plant macrofossil

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The macrofossil analysis followed the Quadrat and Leaf Count Macrofossil Analysis

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technique (QLCMA) developed by Barber et al. (1994) and Mauquoy et al. (2010). About 1

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cm3 of each sample was washed by 5% NaOH solution to remove humic and fulvic acids.

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Then, the samples were sieved through a 125 µm sieve. The sieved sample was scanned using

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a low power (×10-80) stereozoom microscope. Moss leaves and small seeds are examined at

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high magnifications (×100-400). Fifteen random view on the sample slide under the

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microscope were counted for each sample to calculate the average percentage of the plant

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components. The percentages of three plant macrofossil groups: moss, herb and wood species

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were calculated first. For each individual group, subspecies were further identified and their

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percentages were estimated. Once the power of magnification is selected, the view size is

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fixed for the entire slide counting. The results are plotted in Fig. 7. Based on the

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characteristics of the plant macrofossils using Tilia 1.7.16, we classify three major zones A, B

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and C and 9 subzones in Zone C for the peat profile (Table 2).

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4. Results and Discussions

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4.1 Chronology construction

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In Table 1, the uppermost two

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C dates show nuclear bomb

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peat deposition of these layers after 1950 CE. Although the

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support the modern

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horizons. For example, the

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C signal, reflecting the

Pb and

C dates, their age estimations are older than the 14

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Cs dating results

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C ages at the same

C age at 24 cm depth is 30±30 a BP (1920±30 CE), but

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Pb

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estimated age at 13 cm depth is 120 years (~60 a BP or ~1900 CE). This phenomenon is often

299

observed in the comparison of 14C and 210Pb dating of peat studies because of upward shifting

300

of 210Pb and 137Cs in peat sequences (van der Plicht et al., 2013; Li et al., this issue). Thus, we

301

do not use the chronology based on 210Pb dating alone for the upper 14 cm shown in Fig. 6. AMS 14C dating, on the other hand, also reveals some outliers (Table 1). Bacon program

303

is a common age model to construct age-depth relationship for 14C dated sequences (Blaauw

304

and Christen, 2011). Using 13 available 14C date and two points constrained by

305

cm depth) and 137Cs (at 8 cm depth) (Fig. 8a), we apply Bacon age model for the chronology

306

of Baijianghe profile. Figures 8a and 8b show the Bacon model results. We adopt the Bacon

307

mean age-depth model for the chronology of Baijianghe profile. The Bacon program provides

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age of every sampling depth. Using the age-depth relationship, we calculate the

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sedimentation rate (SR, cm/yr) by age difference in each cm.

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Pb (at 13

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Although the age-depth relationship provided by the Bacon model exhibits detailed

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variations of the sedimentation rates, this age model basically show four linear sedimentation

312

rates: 0.136±0.05 cm/y in the upper 36 cm; 0.066±0.025 cm/y between 36 cm and 56 cm;

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0.190±0.043 cm/y between 56 cm and 100 cm; and 0.102±0.022 cm/y between 100 cm and

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180 cm. The sedimentation rate was the lowest during 1400~1700 CE corresponding to the

315

Little Ice Age (LIA). An anomaly high depositional rate (1 cm/y) at 11 cm depth (around

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1950 CE) based on the Bacon age-depth model is caused by an artificial effect from

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pre-bomb to post-bomb transection of the Bacon model. Hence, this anomaly high

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depositional rate which will lead to high RCA calculation should be eliminated.

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The bacon age model indicates that the bottom age of the Baijianghe profile is 1625 a BP.

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With the sampling resolution of 1 cm, the record has an average resolution of 10 years. The

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age uncertainty is less than ±100 y over the whole record, and less than ±20 y during

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1270~1670 CE and 1850 CE to the present (Fig. 8b). Hence, we can interpret confidently

ACCEPTED MANUSCRIPT changes in the peatland development on decadal to centennial scales over the past 1600 years.

324

Figure 9 gives all physicochemical properties of Baijianghe profile with age.

325

4.2 RCA in Baijianghe Mire during the past 1600 years

326

The calculation formula of RCA (Ali et al., 2008) is:

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RCA(gC/m2/y) = SR(cm/y) × DBD(g/cm3) × TOC(%) × 100

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(1)

where RCA is the rate of organic carbon accumulation (gC/m2/yr), SR is depositional rate

329

(cm/y), DBD is the dry bulk density (g/cm3), TOC is organic carbon content (%). The results

330

of DBD and TOC are shown in Fig. 5. The calculated RCA is plotted in Fig. 9.

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Since the upper 50 cm samples were from the surface sampler which has an open side,

332

water could lose when pulling out the core during sampling. Therefore, the porosity of the

333

upper 50 cm part could be much underestimated. By the same reason, the DBD of this part

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might be slightly overestimated. Thus, we recently measured DBD of upper 55 cm samples

335

again (8 month after the first run), and got similar results (Fig. 5). Figure 5 also exhibits both

336

TOC measured by the TOC analyzer and by LOI, which show similar trends reflecting

337

reliability of the measurements. However, the TOC measured by the TOC analyzer is

338

systemically lower than the TOC measured by LOI (Figs. 4 and 5). This is probably because

339

the peat materials in this part contain low TOC. The assumption that plant remains contain

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50% TOC may be overestimated when peat is not pure plant remains (Tolonen and Turunen,

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1996). The TOC measured by the TOC analyzer is the measurement of CO2 amount, while

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LOI is organic matter including other organic material except TOC.

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The calculated RCA ranges from 8 to 204 gC/m2/y except the value at 11 cm depth which

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is 367 gC/m2/y due to anomaly high depositional rate. The RCA below 145 cm depth (660

345

CE) might not represent carbon accumulation rate of peatland because of detrital influence.

346

This part does not have characteristics of peat as the TOC is less than 15%, and DBD is

347

greater than 0.3 g/cm3. Porosity of this part is also very low (Fig. 9). The RCA is mainly

ACCEPTED MANUSCRIPT 348

controlled by DBD (or detrital content). Between 660 CE and 1180 CE, the RCA values were relatively low, ranging 30~96

350

gC/m2/y with an average of 61±16 gC/m2/y (n = 50). Carbon accumulation in the mire during

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660~1180 CE was moderately high, with high TOC and porosity, low DBD and abundant

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sphagnum spp. mosses (Figs. 7 and 9).

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From 1180 CE to 1390 CE, the RCA values increased significantly, ranging from 73 to

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204 gC/m2/y with an average of 127±35 gC/m2/y (n = 39). The strong increase of RCA

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reflects largely enhanced primary productivity during this period, probably due to increased

356

temperature and effective moisture. During this period, the mire had good development,

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resulting in abundant sphagnum spp. mosses with high TOC% and porosity, fast deposition

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rate and low DBD (Figs. 7 and 9).

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The lowest RCA appeared between 1440 CE and 1860 CE corresponding to LIA. During

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this period, the RCA had a range of 8~63 gC/m2/y, averaged 26±12 gC/m2/y (n = 28).

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Ericaceae and Polytrichum spp. increased their percentages at the beginning and end of this

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stage although Cyperaceae was dominant at the 1690-1800 CE (Fig. 7). Peat in this part

363

contains TOC contents around 35%, and low depositional rate. The lowest RCA of the mire

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corresponded to the cold and dry climates during the Little Ice Age.

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After 1860 CE, the RCA returned to a normal level, ranging from 41 to 86 gC/m2/y, and

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averaging 56±14 gC/m2/y (n = 11) until 1946 CE. However, since 1950 CE, the mire had

367

experienced strong influence of human activity. The peat composition contained more

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detritus resulting in high DBD and ash content, but low TOC and porosity, especially during

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1950~1964 CE. This situation was also found in Jinchuan Mire (Sun et al., this issue). The

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RCA during this period did not reflect climatic response and natural carbon accumulation.

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4.3 Vegetation development in Baijianghe Mire during the 1600 years

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ACCEPTED MANUSCRIPT Plant macrofossil components of the Baijianghe profile are shown in Fig. 6, and their

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corresponding water table and surface wetness are described in detail in Table 2. The basal

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portion of the peat core (179–160 cm; ~330–500 CE) consists of small quantity of plant

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residues, aquatic micro-organisms (e.g., freshwater sponge, chironomid, acari and amoebae)

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and abundant detritus (clay and silt) (Figures 7 and 9). The herb accounts for ~62% of the

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peat composition, most likely derived from Carex appendiculata (its seed is seen there). The

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other herbaceous plants include Equisetum fluviatile L. and Scirpus spp. The proportions of

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mosses (~16%) consists primarily of Sphagnum spp. (S. palustre and S. section Cuspidata).

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Species of Vaccinium uliginosum L. and Betula fruticosa are dominant components of

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ligneous peat in this portion of the core.

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The Sphagnum spp. is overlain by woody plants (over 43%) (145–160 cm; ~500–660 CE) that are dominated by Larix olgensis (~31%) and Ericaceae. The herbaceous plants decrease

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by ~10% although most of them are still composed by Carex spp. and Equisetum fluviatile.

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The amount of plant residues increase along with disappearance of aquatic micro-organisms

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and clay in this part of the record.

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The wood (~12%) and herb are rapidly replaced by Sphagnum spp. (104–145 cm;

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~660–1100 CE). The proportion of Larix olgensis decreases by 9% and lower than that of

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Ericaceae. Carex spp. and Equisetum fluviatile are still dominant herbaceous plants although

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their content also decrease. The mosses, especially S. palustre suddenly increase to 50% at

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this stage.

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The proportions of Betula fruticosa increase (up to 45%) although woody plants decrease

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at the depths between 104 cm and 41 cm (1100-1600 CE). The concentrations of Carex spp.

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and Equisetum fluviatile also increase after 1100 CE (the greatest proportion is nearly 90%).

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The total concentrations of mosses slightly decrease at these depths. Of them, the

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concentrations of S. section Cuspidata and S. section Subsecunda account for 30% in the first

ACCEPTED MANUSCRIPT 397

part of these depths while Polytrichum strictum and S. palustre are major in the second part

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of these depths. The compositions of plant macrofossils change rapidly in the uppermost 41 cm (since

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1600 CE), marked by the transition of the relative abundance from herb (for example, Carex

401

spp.) to mosses (sphagnum spp.), then herb again and wood (Betula fruticosa and Pot.

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fruticosa) upward along the core.

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4.4 Development of Baijianghe Mire and climate change during the past 1600 years

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Vegetation growth and preservation in peat mires is a response to climatic condition. In

405

general, warm and wet climates may enhance primary productivity in boreal peat mires, and

406

vice versa (Charman et al., 2013). Although local non-climatic factors such as topography,

407

geomorphology, mineral and nutrient conditions may affect plant components, mire

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vegetation assemblages correspond to changes in the water table under influence of climate

409

changes (Mauquoy and Barber, 2002). RCA should be related to climate changes through

410

production and decomposition of plants (Charman et al., 2013). However, topography,

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hydrology, species composition, and disturbance in a peatland can play major roles on

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accumulation and dynamics of carbon (Magnan and Garneau, 2014; Shiller et al., 2014;

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Lacourse and Davies, 2015). In addition, RCA is also influenced by DBD and deposition rate

414

of peat layers. All of these suggest that the relationship between RCA and climatic condition

415

is not simple. Therefore, we will use the plant macrofossil results shown in Table 2 and Fig. 7,

416

combining the physicochemical properties and RCA, to interpret peatland development and

417

responsive climatic conditions. According to the Bacon age-depth model of the Baijianghe

418

profile, we plot the physicochemical properties and plant macrofossils with ages in Figures 9

419

and 10. In Figure 10, we also plot records from Xiaolongwan (Chu et al., 2009) and

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Sihailongwan (Stebich et al., 2015) for comparison. The development of Baijianghe Mire

421

during the past 1600 years can be briefly classified as following stages.

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ACCEPTED MANUSCRIPT 330-660 CE (below 145 cm depth): The deposits in this interval contained mainly silt

423

and clay with well decomposed shrub and herb remains. Very high DBD, low TOC and

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porosity indicate that the coring site was a water-logged bottomland. Although the coring site

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is not the deepest part of Baijianghe Mire, the surface hydrological condition over the entire

426

marsh could be similar. Since there were small amount of aquatic micro-organisms in this

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interval of the coring site, we speculate that Baijianghe Mire probably originated from a

428

small water body, but no evidence to define whether it was a lake or not as Yuan and Sun

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(1990) described before. Very high abundance of wood species, 70% of Larix olgensis and

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10% of Ericaceae, around 575 CE (153 cm depth) reflects that relatively cold and dry climate

431

were prevailed during 530~600 CE. Within age uncertainty, this strong drought seems to

432

agree with the drought events appeared in lakes Xiaolongwan (Chu et al. 2009) and

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Sihailongwan (Stebich et al., 2015) records in early 500s CE (Fig. 10), and relatively cold

434

period happened in lake Sihailongwan (Chu et al. 2011).

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660-800 CE (145-133 cm): In this interval, TOC rapidly increased to 40% with >90%

436

porosity, while DBD dropped to 0.1 g/cm3. Plant remains are mainly Cyperaceae and

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Ericaceae, with very low moss%. The most outstanding feature of this interval is that

438

humification is the highest in the record. Although humification degree has been widely used

439

to infer changes in the peat surface wetness, with higher humification in absorbance

440

reflecting drier surface wetness (drier climatic condition) (Blackford, 2000). However, the

441

humification degree might be affected by the inorganic material incorporated in the peat

442

matrix relate to absolute TOC content (Chambers et al., 2011). Variation of humification also

443

reflects changes in the time passed from the death of plant matter to reach the anaerobic

444

catotelm (zone beneath the water table) (Aaby, 1976; Blackford, 2000). In general, high TOC

445

provides more amorphous humus, resulting in higher humification. When a water-logged

446

bottomland changed to a mire, accumulated plant remains shown by strong increased TOC%

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ACCEPTED MANUSCRIPT and porosity and decreased DBD would enhance the thickness of peat deposits, so that the

448

depth of anaerobic catotelm would increase significantly. The strong increase in humification

449

during this period probably reflected both high TOC decomposition (thus high amorphous

450

humus) and increased depth of anaerobic catotelm. Compared to the proceeding stage at

451

530-600 CE, the climatic condition should be wetter, which agrees with the Xiaolongwan

452

record. Note that the reconstructed wetness records between 600 and 800 CE from

453

Xiaolongwan (Chu et al., 2009) and Sihailongwan (Stebich et al., 2015) are different. The

454

Larix olgensis replaced by Betula fruticosa suggests a trend of warm climate (Jin and Wu,

455

2003; Bu, 2004).

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800-1100 CE (113-104 cm): This interval is corresponding to the Medieval Warm

457

Period (MWP) (Mann et al., 2009). During this period, Sphagnum mosses in Baijianghe Mire

458

were well developed, whereas both wood% and herb% were largely reduced. In addition,

459

there are five obvious fluctuations in the moss% change during this period, higher moss%

460

corresponding to lower herb%+wood%. According to occurrence of large proportion of the S.

461

palustre and the S. section Cuspidata in combination with gradually decreased Larix olgensis

462

in this part, the temperature in the study area during MWP gradually increased with relatively

463

wet conditions and fluctuating water table.

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1100-1200 CE (104-93 cm): This was a wet period reflected by high herb% (Cyperaceae

465

is dominant), and both low moss% (<20%) and wood% (<10%). Wet climate might lead to

466

rapidly increased water table which is not suitable for development of Sphagnum spp. and

467

tree species.

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1200-1370 CE (93-60 cm): During this period, RCA strongly enhanced and reached the

469

highest values in the whole record, reflecting very good mire development under warm and

470

wet conditions. Abundant S. section Cuspidata in this interval indicates relatively high water

471

table under wet climates. Increased percentage of Betula fruticosa and disappearance of Larix

ACCEPTED MANUSCRIPT 472

olgensis probably denotes warm temperature (Jin and Wu, 2003; Bu, 2004). The wet climates

473

agree reasonably with Xiaolongwan and Sihailongwan records (Fig. 10). 1370-1520 CE (60-45 cm): Although moss% was still high, the dominant moss species

475

was Polytrichum. The Betula fruticosa was gradually substituted by Ericaceae. This indicates

476

decline of water table due to dry climate. RCA dropped quickly to low level due to low

477

primary productivity. This dry interval was coincident with the drought in Xiaolongwan

478

record (Fig. 10).

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1520-1860 CE (45-24 cm): This interval corresponds to the period of Little Ice Age

480

(LIA) (Mann et al., 2009). Baijianghe Mire had the lowest RCA during this time. The moss%

481

in the plant macrofossils reduced dramatically. Although Cyperaceae was the dominant plant

482

species during 1690-1800 CE., abundance of Ericaceae increased significantly in two time

483

intervals (1560-1660 CE and 1800-1890 CE). The two wood% increased intervals reflect dry

484

climates, which agree with the Xiaolongwan record (Fig. 10). The apparent increase in

485

Polytrichum spp. during 1830-1860 CE provided another evidence of dry climate during

486

1800-1890 CE. According to the Baijianghe record, climatic condition in the study area

487

should be cold and dry.

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1860-1945 CE (24-12 cm): Both herb% and wood% dropped to minimal, whereas moss%

EP

488

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479

was usually >90% during this period. The abundance of S. section Cuspidata increased

490

apparently, which indicate wet climates. Increase in RCA in this interval also reflected warm

491

and wet climatic conditions. This wetness increase can also be seen in the Xiaolongwan

492

record (Fig. 10).

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1945-2016 CE (12-0 cm): The mire had experienced human influence since 1945,

494

shown strong decreases in TOC% and porosity, and increases in DBD and ash content.

495

Sphagnum mosses were almost diminished. Hydrological drainage in 1986/87 led to further

496

damage of the peatland. No climatic information should be interpreted from the

ACCEPTED MANUSCRIPT 497

physicochemical properties and plant macrofossils of this interval.

498

5. Conclusions

The peatland development and responsive climate in Baijianghe Mire during the past

500

1600 years have been studied throughout analyses of physicochemical properties and plant

501

macrofossils on the well-dated sequence. Changes in wood%, herb% and moss%, as well as

502

Sphagnum spp. species provide useful information in terms of water table variation under

503

climate changes. Changes in RCA and humification, however, can only sometimes help us to

504

understand peatland development. Their relationships to climatic signal are rather

505

complicated, due to influence of local non-climatic factors. Before 660 CE, the basin of

506

Baijianghe mire was a water-logged bottomland. A strong drought during 530-600 CE caused

507

water table decline which provided hydrological condition for mire initiation. Relatively wet

508

climate during 660-800 CE enhanced primary productivity and accumulated plant remains,

509

and finally the water-logged bottomland changed to a mire. Baijianghe mire development was

510

poor during LIA (1400-1850 CE). Climatic conditions in the study area during LIA were cold

511

and dry, whereas warm and wet conditions were prevailed during the MWP (900-1150 CE).

512

However, the best development of Baijianghe Mire appeared during 1200-1370 CE wet and

513

probably warm conditions. After the LIA ended at 1850 CE, climate in the study area became

514

warm and wet. Since 1945, the mire had been disturbed by human activity. The peatland has

515

gradually recovered after 1990. The climatic interpretations based on our Baijianghe record

516

agree with the climate reconstructions from the Xiaolongwan maar lake study.

517

Acknowledgments

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The authors would like to thank Dr. Yanmin Dong at NENU for his help in the fieldwork,

519

and Ms. Shasha Liu and Ms. Xinhua Zhou at NENU for their assistance in the laboratory

ACCEPTED MANUSCRIPT chemical analysis. This work was financially supported by the National Key Research and

521

Development Program of China (2016YFC0500407), National Natural Science Foundation of

522

China (No. 41471165), Yanbian Korean Autonomous Prefecture Wetland Conservation &

523

Development Center (No. 2017220101000913) and The Education Department of Jilin

524

Province (No. 2016506). The AMS 14C dating was supported by grants from the Ministry of

525

Science

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106-2116-M-002-012 and MOST 106-2923-M-002-002-MY3) to H.-C. Li.

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(5), 579-586. Novenko, Y.E., Tsyganov, A.N., Volkova, E.M., Babeshko, K.V., Lavrentiev, N.V., Richard J. Payne, R.J., Mazei, Y.A., 2015. The Holocene paleoenvironmental history of central

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Yuan, S.M., Sun, X.J., 1990. The vegetational and environmental history at the west foot of Changbai Mountain, Northeast China during the last 10,000 years. Acta Botanic Sinica, 32, 558-567. (In Chinese) Zhang, Z.Q., Xing, W., Wang, G.P., Tong, S.Z., Lv, X.G., Sun, J.M., 2015. The peatlands

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developing history in the Sanjiang Plain, NE China, and its response to East Asian monsoon variation. Sci. Rep. 5(5), 11316, 1-10. Zhang, Y., Liu, X.T., Lin, Q.X., Gao, C.Y., Wang, J., Wang, G.P., 2014. Vegetation and climate change over the past 800 years in the monsoon margin of northeastern China

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reconstructed from n-alkanes from the Great Hinggan Mountain ombrotrophic peat bog. Org. Geochem 76 (76), 128–135.

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Table 1 AMS 14C dates of the samples from BJH core. The errors for pMC (percent of

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modern carbon) and measured 14C age are 2σ error. The calibrated 14C ages with 1σ error are used Calpal program (http://www.calpal-online.de/) which uses IntCal13 database (Stuiver

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and Polach, 1977; Stuiver and Braziunas, 1993; Reimer et al., 2013; Niu et al., 2013). BJH-5 BJH-15 BJH-24h BJH-35 BJH 40** BJH-45h BJH-56 BJH 66** BJH-66-2 BJH-77 BJH-100 BJH-125 BJH-135 BJH-153 BJH-160 BJH-170 BJH-180

Type of plant mosses mosses herb herb mosses herb herb/woody mosses herb herb/few moss moss/few herb mosses mosses herb herb/woody herb/woody herb/woody

pMC (%) 101.49±1.40 99.39±1.40 99.22±1.37 95.02±1.31 98.01±0.68 95.15±1.33 94.18±1.31 91.48±0.68 89.89±1.24 92.85±1.27 89.85±1.27 95.00±1.39 86.10±1.25 82.84±1.17 84.10±1.17 91.68±1.33 86.77±1.22

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Calibrated 14C age (a BP)

-119±2 50±1 63±1 410±6 162±1 399±6 482±7 716±5 856±12 596±8 860±12 412±6 1202±17 1512±21 1391±19 698±10 1140±16

modern -15±10 30±30 500±5* 185±40 495±10 525±5 675±5 765±15 600±35 770±15 500±5* 1130±35 1390±20 1310±10 670±5* 1035±30*

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ACCEPTED MANUSCRIPT Description of Zone Small quantity of plant residues and relatively rich in clay and mud, occurrence of aquatic micro-organisms suggest a water-logged status.

Zone B (160 -145 cm, 500-660 CE)

Macrofossils of Larix olgensis make up to 60% of the peat matrix, indicating low water table and relatively low temperature. Very high abundances of Carex spp. point to a gradual transition from non-peatland to peatland. The Baijianghe mire began to develop rapidly after this time.

Zone C-1 (145-135 cm, 660-800 CE) Zone C-2 (135-104 cm, 800-1100 CE) Zone C-3 (104-85 cm, 1100-1250 CE)

The Larix olgensis is overlain by Betula fruticosa, Ericaceae, Equisetum fluviatile, indicating an accretion in local water table and temperature. S. palustre is the major peat component, which in combination with the S. section Cuspidata suggests a continuous accretion in water tables. Cyperaceae, especially Carex spp. is dominant. Decreases in S. palustre and increases in S. section Cuspidata and Betula fruticosa suggest a slight increase in mire surface wetness. Mire surface wetness is higher than the preceding zone since there are high values of S. section Cuspidata. Water tables decline first and then increase in this zone, as there are decreases in the abundances of S. section Cuspidata, and increases in Betula fruticosa and S. palustre, followed increases in Cyperaceae and disappearance of mosses. Water tables continue to decline, since the abundance of mosses, especially Polytrichum spp. dramatically increase, then gradually replaced by Cyperaceae plants. Cyperaceae dominates. The presence of S. section Cuspidata suggests water levels have slightly raised. S. palustre formed a large part of the plant macrofossil assemblage. Increased Ericaceae and Polytrichum spp. during 1820-1860 CE point out a possible recurrence of drier conditions. However, Strongly increased S. section Cuspidata and S. section Acutifolia during 1900-1920 CE suggest a wet climate. Cyperaceae form up to 90% of the peat matrices, then is gradually substituted by Betula ovalifolia (40%) and Potentilla fruticosa L. (40%) in this zone. All of them indicate local water tables have declined.

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Zone C-9 (11-0 cm, 1950-2015 CE)

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Table 2 Summary of the plant macrofossil zonations for the Baijianghe profile

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ACCEPTED MANUSCRIPT Figure captions Fig. 1 Location maps of the study area. The upper left map shows the study area in northeast

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China and modern summer monsoon boundaries. EASM and ISM denote the East Asian Summer Monsoon and Indian Summer Monsoon, respectively. The upper right map shows the locations of Baijianghe, Hani and Jinchuan mires, as well as Xiaolongwan and Sihailongwan maar lakes. The lower right map exhibits the topography of Baijianghe

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Mire. The lower left picture reveals the hydrological drainage in Baijianghe Mire in 1986/87 (Picture source from Schröder et al., 2007) Fig. 2 Distribution of modern vegetation in Baijianghe Mire. Fig. 3 Climatic pattern of the study area (Data source: China Climate Center).

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Fig. 4 Correlation between the TOC measured by the TOC analyzer and the TOC measured by LOI. Fig. 5 The measured physicochemical properties vary with depth of the Baijianghe profile. Fig. 6 210Pb and 137Cs dating of Baijianghe profile. Total activities of 214Bi, 214Pb, 210Pb and 137 Cs were measured by a gamma spectrometry. The estimated age is based on constant

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supply model of excess 210Pb. Fig. 7 Plant macrofossil distribution of the Baijianghe sequence. The interpretation of each zonation is summarized in Table 2. Fig. 8 Age-depth model constructed by Bacon program. A. Output of Bacon modeling result.

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B. Dating results plotted with Bacon model result for discussion of chronology. Changes in sedimentation rate in four segments are shown. Fig. 9 Variations of the measured physicochemical properties in the Baijianghe peat sequence during the past 1600 years. MWP and LIA denote Medieval Warm Period and Little Ice

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Age, respectively (Mann et al., 2009). The depths of the profile and AMS (circles) are shown in the top of the plot.

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Fig. 10 Plant macrofossil variations of the Baijianghe profile compare with the reconstructed climates from Xiaolongwan study (Chu et al., 2009), Sihailongwan study (Stebich et al.,

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2015) and the decadal spring drought index during AD 1011–1980 derived from historical documents from Korea (Kim and Choi, 1987). The reconstructed T and P by Stebich et al., (2015) are mean warmest month (July) temperature (Mtwa) and mean annual precipitation (Pann), respectively. Their modern values are 20.7oC and 775 mm/y, respectively.

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