Climate and industrial pollution determine the seasonal and spatial mercury variations in the China's Weihe River.

Natural processes and human activities impact mercury (Hg) pollution in rivers. Investigating the individual contributions and interactions of factors affecting variations in Hg concentrations, particularly under climate change, is crucial for safeguarding watershed ecosystems and human health. We collected 381 water samples from China's Weihe River Basin (WRB) during dry and wet seasons to assess the total Hg (THg) concentration. Results revealed high Hg concentrations in the WRB (0.1-2200.9 ng/L, mean 126.2 ± 335.5 ng/L), with higher levels during the wet season (wet season: 249.1 ± 453.5 ng/L, dry season: 12.7 ± 14.0 ng/L), particularly in the mainstream and southern tributaries of the Weihe River. Industrial pollution (contributing 26.2 %) and precipitation (contributing 33.5 %) drove spatial heterogeneity in THg concentrations during the dry and wet seasons, respectively. Notably, combined explanatory power increased to 47.9 % when interaction was considered, highlighting the amplifying effect of climate change, particularly precipitation, on the impact of industrial pollution. The middle and downstream of the Weihe River, especially the Guanzhong urban agglomeration, were identified as high-risk regions for Hg pollution. With ongoing climate change the risk of Hg exposure in the WRB is expected to escalate. This study lays a robust scientific foundation for the effective management of Hg pollution in analogous river systems worldwide.

Permafrost degradation alters the environmental signals recorded in tree-ring lignin methoxy group δ2H in northeastern China.

Climate warming has profoundly altered the status of permafrost and has caused extensive permafrost degradation in the Northern Hemisphere. However, long-term observations investigating the hydrological dynamics of permafrost and its ecological effects on plant growth are lacking. Previous studies have reported tree-ring stable hydrogen isotope ratios of lignin methoxy groups (δ2HLM) as an archive of hydrological signals. This study sampled tree-ring cores from a Larix gmelinii forest in Nanwenghe Forest Park, Northeastern China, and separately measured the tree-ring δ2HLM for earlywood and latewood from 1900 to 2020. Earlywood and latewood δ2HLM values, as well as the difference between them, showed no significant long-term trend from 1900 to 1987; however, they both exhibited significant increasing trends since 1988 at rates of 2.6 ‰ and 4.9 ‰ per decade, respectively. This variance changes the magnitude of the difference between the two chronologies and can be explained by the shift in source water δ2H values during tree growth. Based on a structural equation model analysis, when the influence of permafrost melting weakened due to permafrost degradation, the growing season temperature was better recorded in latewood δ2HLM through the effects of precipitation δ2H from July to September. Based on the environmental response of tree-ring δ2HLM in the permafrost region, permafrost degradation influences the source water δ2H values of trees, thereby affecting the expression of temperature signals in tree-ring δ2HLM. The novel results in this study provide a new perspective on permafrost degradation based on the dynamic responses of tree-ring δ2HLM to source water δ2H during permafrost degradation.

[Mercury in tree rings: Advances, problems and prospects]. / æ ‘æœ¨å¹´è½®æ±žè®°å½•: 进展、问题和展望.

As a highly biotoxic element, mercury (Hg) can be enriched by the food chain and has negative effect on ecosystems. Changes of Hg flux and reserves in forest have important effects on its biogeochemical cycle in forest ecosystem. Due to limitation of temporal and spatial monitoring, there is not comprehensive understanding on Hg distribution. Widely distributed trees can be used as effective bio-monitors and Hg records in tree rings can be used to study Hg temporal and spatial distribution. Hg accumulated by root, leaf, bark, and other tissues can be detained in bole and record environmental Hg variations. Therefore, historical Hg trends can be restructured by analyzing Hg concentration in tree rings and the biogeochemical characteristics can be understood with Hg isotope ratio. We reviewed the method of measurement of Hg concentration and isotope ratio and application of reconstruction using Hg concentration in tree ring. We suggested the great application potential of Hg isotope ratio in atmospheric Hg construction and biogeochemistry cycle and raised concerns in further studies.

Black Carbon in Surface Soil and Its Sources in Three Central Asian Countries.

Black carbon (BC) aerosol impacts the air quality, public health, agricultural productivity, weather, monsoon, cryosphere, and climate system from the local to the global scale. However, its distribution over vast Central Asia is poorly known, because it is one of the poorly sampled regions of the world. BC in the soil can be resuspended into the atmosphere and transported to downwind regions with sensitive ecosystems and vulnerable populations, such as from Central Asian countries to the cryospheric regions in the Tianshan Mountain and the Tibetan Plateau, which could accelerate the melting of the snowfields and glaciers. We report the distribution of BC and total organic carbon (TOC) in surface soil with samples collected at multiple sites, for the first time, over three countries in Central Asia (Uzbekistan, Tajikistan, and Kyrgyzstan). The mean BC (TOC) concentrations over three countries were 0.06 ± 0.06 (11.86 ± 4.84) mg g-1, 0.15 ± 0.21 (20.35 ± 10.96) mg g-1, and 0.32 ± 0.29 (26.45 ± 20.38) mg g-1, respectively. They were found to be originated from the same or similar sources, at least over Tajikistan and Kyrgyzstan, as indicated by their high and significant correlation (R2 > 0.6, p < 0.001). The char/soot ratio indicated the diesel and gasoline combustion as dominant BC sources over this region. To gain further insights into the soil BC and its implications to air quality, climate, and cryosphere, future studies should include a wider area over Central Asia with different land-use types and other soil parameters combined with atmospheric simulations for this important yet relatively less studied region of the world.