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Cores (15 to 40 cm of depth) were collected from 11 lakes of the Songnen Plain in northeastern China to reconstruct changes in potentially harmful trace element (PHTE) inputs as tracers of human activities. In each profile, most PHTE enrichment factors do not differ significantly from the pre-industrial values (EF 1.5), except for Cd (EF = 2-5.5). This shows that detrital material accounts for a large part of the PHTE supply to the Songnen Plain lakes. Radiometric dating of the cores (

Mountain ecosystems are sensitive to environmental changes and are affected by direct and indirect anthropogenic activities. This study sought to understand the impacts of human occupation, environmental and climate change on the Great Hinggan Mountains (GHM) in Northeastern China. The last 200 years of environmental changes are reconstructed by analyzing sediment cores from five small mountain lakes. Cores were dated using ²¹⁰Pb and ¹³⁷Cs radioisotopes, microscopic charcoal identified regional fire activity and fossil pollen analysis reconstructed temporal and spatial changes in vegetation. Peaks in ¹³⁷Cs, ²²⁶Ra and microscopic charcoal flux were found to follow similar trends between sites. The radioisotope records reflect redistribution processes, such as erosion and fire events, which overwhelm the atmospheric fallout signal in the GHM. Microscopic charcoal increased from 1950 CE and peaked at all sites after 2000 CE suggesting that current fire management, coupled with a warmer climate due to global warming, may be leading to more wildfire events in the region. Pinus, Quercus and Betula declined at all sites as human occupation occurred in the early 1900s. Initially, open forest and grassland expanded in response to overexploitation of forests, followed by arboreal pollen reaching maximum values after 2000 CE. This study concludes that the present‐day mixed coniferous broad‐leaved forest dominating the southern region of the GHM is a product of changing fire activity, excessive logging and, more recently, forestry management and vegetation regeneration. Results suggest further management strategies are needed to address land degradation and wildfire events in mountain regions of Northeastern China.

Ombrotrophic bogs are widely used to reconstruct the history of atmospheric metal deposition. Minerotrophic fens are potential archives as well but not much attention has been paid to them. This study examined the accumulation of major and trace elements in a poor fen of Fenghuang Mountain, NE China. Peat cores were dated by 210Pb and 137Cs techniques and elemental analyses were conducted after a two-step sequential digestion with HCl. Results suggest no significant pollution for other trace metals but Pb in Fenghuang Mountain area. Atmospheric soil dust flux (ASD) was calculated from the Ti content in the peat, and its decreasing trend over the last 60 years agrees with the East Asian winter monsoon (EAWM) shift, which suggests that ASD could be a potential climatic proxy for the EAWM variability in the region.

China is one of the fastest-growing economies of the late 20th and early 21st centuries, and heavy metal emissions have increased in parallel with rapid industrialization and urbanization. Over the last decade, several studies of geochemical records from peat have reconstructed changes in atmospheric metal pollution in China. We review the peat records that detail the history of atmospheric metal pollution over the last two centuries in NE China. The ecological risk (ER) of accumulated metals and their potential eco-toxicological effects, through threshold and probable effect concentrations (TEC and PEC), are also evaluated. Peat records of metals show an increase of pollution loads in the environment over the pre-industrial level during the past two centuries, with an unprecedented increase in China over the last 60 years. There is generally good agreement between geochemical peat records from NE China and others records elsewhere in China. However, some discrepancies are observed especially with Hg records from lake sediments. These discrepancies could be explained by several factors, including post-depositional processes or uncertainties arising from dating methods. The ecological risk of heavy metals is found to be relatively weak in the remote and high-altitude environment in NE China. Although, most metals are under the TEC, Pb concentrations usually surpass it and are getting close to the PEC which indicates increasing ecological risks. Some areas of improvement have been highlighted such as the need for more long-term studies on atmospheric metals and a greater number of Pb isotopes records to better capture the long history of human activity and the spatial variability in metal deposition of the region.

Northern peatlands act as archives of environmental change through their sensitivity to water balance fluctuations, while being significant contributors to global greenhouse gas dynamics. Subarctic fens in northeastern Canada are characterized by a dominance of pools and flarks. We aimed to reconstruct the late-Holocene hydrological conditions of these fens to establish the timing of the initiation of pool and flark formation and possible linkages with climate. Testate amoebae and plant macrofossils from five cores, sampled in three fens, were analyzed to infer water tables with chronologies based on 14C and 210Pb dating. All sites showed presence of relatively dry, ombrotrophic conditions with abundant Picea from 5000 cal a BP, followed by a first shift to wet, poor fen conditions with pool and flark development around 3000 cal a BP and a subsequent wet shift after ~800 cal a BP. These trends coincide with previously observed Neoglacial and Little Ice Age cooler and wetter conditions and therefore climate may well have been a dominant factor in the initiation and development of pools and flarks over the late-Holocene. The effect of anticipated climate change on subarctic peatlands remains unclear, although wetter conditions might enhance pool expansion to the detriment of terrestrial components.

Permafrost peatlands contain globally important amounts of soil organic carbon, owing to cold conditions which suppress anaerobic decomposition. However, climate warming and permafrost thaw threaten the stability of this carbon store. The ultimate fate of permafrost peatlands and their carbon stores is unclear because of complex feedbacks between peat accumulation, hydrology and vegetation. Field monitoring campaigns only span the last few decades and therefore provide an incomplete picture of permafrost peatland response to recent rapid warming. Here we use a high-resolution palaeoecological approach to understand the longer-term response of peatlands in contrasting states of permafrost degradation to recent rapid warming. At all sites we identify a drying trend until the late-twentieth century; however, two sites subsequently experienced a rapid shift to wetter conditions as permafrost thawed in response to climatic warming, culminating in collapse of the peat domes. Commonalities between study sites lead us to propose a five-phase model for permafrost peatland response to climatic warming. This model suggests a shared ecohydrological trajectory towards a common end point: inundated Arctic fen. Although carbon accumulation is rapid in such sites, saturated soil conditions are likely to cause elevated methane emissions that have implications for climate-feedback mechanisms.