Coastal blue carbon in China as a nature-based solution toward carbon neutrality.

To achieve the Paris Agreement, China pledged to become "Carbon Neutral" by the 2060s. In addition to massive decarbonization, this would require significant changes in ecosystems toward negative CO2 emissions. The ability of coastal blue carbon ecosystems (BCEs), including mangrove, salt marsh, and seagrass meadows, to sequester large amounts of CO2 makes their conservation and restoration an important "nature-based solution (NbS)" for climate adaptation and mitigation. In this review, we examine how BCEs in China can contribute to climate mitigation. On the national scale, the BCEs in China store up to 118 Tg C across a total area of 1,440,377 ha, including over 75% as unvegetated tidal flats. The annual sedimental C burial of these BCEs reaches up to 2.06 Tg C year-1, of which most occurs in salt marshes and tidal flats. The lateral C flux of mangroves and salt marshes contributes to 1.17 Tg C year-1 along the Chinese coastline. Conservation and restoration of BCEs benefit climate change mitigation and provide other ecological services with a value of $32,000 ha-1 year-1. The potential practices and technologies that can be implemented in China to improve BCE C sequestration, including their constraints and feasibility, are also outlined. Future directions are suggested to improve blue carbon estimates on aerial extent, carbon stocks, sequestration, and mitigation potential. Restoring and preserving BCEs would be a cost-effective step to achieve Carbon Neutral by 2060 in China despite various barriers that should be removed.

The timing and magnitude of anthropogenic mercury pollution: A 200-year record from multi-lake sediment cores in northeast China.

The recent substantial expansion of human activities in northeast (NE) China has resulted in increased emission of environmental pollutants. Longer-term records of such environmental pollutants provide a benchmark against which it is possible to evaluate the nature, extent and timing of anthropogenic environmental changes. Based on measurements of mercury (Hg) concentrations and accumulation rates in 11 lake sediment cores from the Songnen Plain in NE China, we here present a reconstruction of the historical deposition of Hg as an indicator of the changing scale of human impact. The results demonstrate an increasing trend of Hg concentration, concurrent with elevated anthropogenic emissions, beginning from the early 1900s, accelerating through the mid-1950s and slightly decreasing from the late 1990s onwards. The increase in anthropogenic Hg coincides with the reform and opening up of China, which precipitated social and economic transformation, and rapid industrial and economic growth. Measurements of the Hg enrichment factor in all the cores enables identification of the anthropogenic contribution to Hg accumulation. The geoaccumulation index indicates that the lakes are in general moderately polluted by Hg. The historical trend of Hg accumulation rate parallels the temporal progression of biomass burning and fossil fuel consumption in the region. The findings elucidate the extent of anthropogenic pollution in the Anthropocene and underline the importance of identifying Hg sources to reduce emissions and guide the implementation of effective mitigation strategies.

Black carbon and mercury in the surface sediments of Selin Co, central Tibetan Plateau: Covariation with total carbon.

Tibetan Plateau (TP) is an important geographical region for investigating the long-range transport of pollutants as limited emission sources exist in this region. In this study, based on analysis of 61 surface samples, we report the spatial distribution and concentrations of BC, Hg, total organic carbon (TOC) and inorganic carbon (IC) in surface sediments of Selin Co, the largest lake in central Tibet. The mean BC and Hg concentrations were 0.62 ± 0.34 mg/g and 32.03 ± 9.88 ng/g (range: 0.03-1.47 mg/g and 13.83-51.81 ng/g respectively), which were lower than the values from other lakes in the Himalayan-Tibetan Plateau (HTP). BC and Hg exhibited similar spatial distribution in the surface sediments. Similarly, the mean TOC and IC were 2.19 ± 1.46% and 3.13 ± 1.07% (range: 0.0007-7.78% and 0.30-5.30% respectively). BC/TOC ratio, as well as char/soot ratio, suggests biomass burning as a major source of BC in the sediments via the influence of long-range transport. The positive correlation between the concentrations of BC and Hg suggests similar emission sources or transport pathway. Concentrations of BC and Hg were higher in fine grain particles (size <~50 µm) which were capable of transport and deposit in the deeper part of the lake, as suggested by a significant relationship between water depth and particle size. This study elucidates the extent of pollution in very recent ages and also could serve as the basis for paleo-environmental studies in future.

Chemical composition of inorganic and organic species in snow/ice in the glaciers of western China.

Recent studies have revealed the abundance of dissolved organic matter (DOM) in snow/glaciers of the Tibetan Plateau (TP). Here, we present a comprehensive study on the chemical compositions of snowpit samples collected from widely distributed eight glaciers in the western China (six from the TP) to investigate the spatial variation of deposited atmospheric aerosols. An Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was used to chemically characterize the DOM in snow samples which can offer chemical properties of DOM. Highest mass concentration of dissolved species mass was observed in Tienshan Baishui No 1 glacier (TS, 6.55 ± 0.85 mg/L) close to Takalamagan Desert, whereas lowest (0.89 ± 0.18 mg/L) was observed in Zadang Glacier (ZD) in the central TP. DOM (8-40%) and calcium as well as magnesium (9-67%) were generally the most abundant chemical species. Average DOM concentration in the TP glaciers among the investigated sites were comparable. DOM was found highly oxidized with an oxygen to carbon ratio (O/C ratio) ranging from 0.82 to 1.03. Highly oxidized DOM could have related with aerosol aqueous processes as illustrated by observed organic acids. This study provides insights into the spatial variations of the DOM and dissolved inorganic matter, as well as oxidized organic aerosol, were most likely due to local and regional contribution.

Historical Black Carbon Reconstruction from the Lake Sediments of the Himalayan-Tibetan Plateau.

Black carbon (BC) is one of the major drivers of climate change, and its measurement in different environment is crucial for the better understanding of long-term trends in the Himalayan-Tibetan Plateau (HTP) as climate warming has intensified in the region. We present the measurement of BC concentration from six lake sediments in the HTP to reconstruct historical BC deposition since the pre-industrial era. Our results show an increasing trend of BC concurrent with increased anthropogenic emission patterns after the commencement of the industrialization era during the 1950s. Also, sedimentation rates and glacier melt strengthening influenced the total input of BC into the lake. Source identification, based on the char and soot composition of BC, suggests biomass-burning emissions as a major contributor to BC, which is further corroborated by open-fire occurrence events in the region. The increasing BC trend continues to recent years, indicating increasing BC emissions, mainly from South Asia.