Environmental Changes During Last 1500 Years In Johnville Peatland,Quebec,Canada

As the most vivid record of paleo-geographical environment change and a good natural geological information carrier,peat plays an important role in the study of palaeo-climate environmental evolution.There are vast and diverse peatlands in Canada,where is an important peat distribution area in the mid-high latitudes of the Northern Hemisphere.In this study,the timescale of peat profile was constructed with AMS¹⁴C dating method.Using the testate amoeba and charcoal indicators to analyze the 96 cm peat profile taken from Johnville peatland restore and reconstruct the environmental changes in the past 1500 in Johnville peatland in southeastern Quebec,Canada.A total of 30 species of testate amoeba were observed in 96 samples,which contains 17649 shells.Among the species with relative abundance greater than 1%are:Arcella arenaria,Archerella flavum,Assulina muscorum,Heleopera petricola/sphagni,Hyalosphenia papilio,Hyalosphenia subflava,Hyalosphenia elegans,Nebela militaris,Trigonopyxis arcula.According to constrained cluster analysis,the history of Johnville peat profile can be divided into four phases:1)1520⁹14 cal yr B.P.?96 cm⁷3 cm?.The testate amoebae assemblage was relatively monotonous and less categories,which dominated by some relative wet taxa.And the species indicating a dry environment are relatively few.The depth to water table increases rapidly,and then gradually decreases.At this stage,the water table of Johnville peatland is relatively high,and the peat habitat is relatively humid;2)914⁵04 cal yr B.P.?73cm⁵3 cm?.The diversity of testate amoeba increased at this stage,and the relative abundance of species indicating the dry environment has decreased.The depth to water table firstly increased and then decreased,but the depth to water table was still larger than the previous stage.The water table was low,and the habitat of Johnville peatland became dry.3)504 to 111 cal yr B.P.?53 cm to 25 cm?.the testate amoeba assemblage indicating humid environment has increased.The depth to water table decreased firstly,then increased,and finally decreased.Overall,the depth to water table has become smaller the previous stage.This indicates that the water table of Johnville peatland was high,and the habitat became wet.4)111 cal yr BP to present?25 cm to 0 cm?,the diversity of testate amoebae assemblage increased comparing with the previous three stages.The depth to water table firstly increased and then gradually decreased,the depth to water table is larger than the previous stage,and the water table decreases.At this stage,the environment of Johnville peatland became dry.To sum it up,the environment of Johnville peatland experienced two alternating wet and dry conditions,but the overall environmental change evolved towards the trend of humidification.And the factor that caused this change were attributed to temperature changes in this region.Charcoal is a black inorganic carbon compound produced by incomplete combustion of a plant under appropriate temperature conditions.There is a positive correlation between the concentration of charcoal and the intensity and frequency of fire events.The charcoal concentration of Johnville peat profile shows that the variation trend of the concentration of charcoal in different particle sizes was consistent.The concentration of charcoal?>120?m?have obvious peaks and valleys,and the fluctuation is more obvious,while the concentration of charcoal?>300?m?fluctuates relatively slowly and the amplitude is relatively small.The peak of charcoal concentration is mainly due to the frequent human-made fire incidents caused by large-scale human economic activities since the end of the 18th century and the beginning of the 19th century.However,whether or not is related to other reasons still needs further discussion.Based on the above studies,we have concluded that the environment of Johnville peatland has become wet in the past 1500 years.The results of this study are similar to those in the neighboring regions,indicating the general applicability of the biological indicators of the testate amoeba in the study of paleohydrological reconstruction in the peatlands.It further demonstrates the environmental significance of testate amoeba in peatland paleo-environment research.Although the regional climate and vegetation conditions revealed by the charcoal deficiencies index have not been well explained,the significance of climate and environment is obvious,and it is consistent with the peatland environmental change trends reflected by the testate amoeba.