Anthropogenic Activities Generate High-Refractory Black Carbon along the Yangtze River Continuum.

Combustion-driven particulate black carbon (PBC) is a crucial slow-cycling pool in the organic carbon flux from rivers to oceans. Since the refractoriness of PBC stems from the association of non-homologous char and soot, the composition and source of char and soot must be considered when investigating riverine PBC. Samples along the Yangtze River continuum during different hydrological periods were collected in this study to investigate the association and asynchronous combustion drive of char and soot in PBC. The results revealed that PBC in the Yangtze River, with higher refractory nature, accounts for 13.73 ± 6.89% of particulate organic carbon, and soot occupies 37.53 ± 11.00% of PBC. The preponderant contribution of fossil fuel combustion to soot (92.57 ± 3.20%) compared to char (27.55 ± 5.92%), suggested that fossil fuel combustion is a crucial driver for PBC with high soot percentage. Redundancy analysis and structural equation modeling confirmed that the fossil fuel energy used by anthropogenic activities promoting soot is the crucial reason for high-refractory PBC. We estimated that the Yangtze River transported 0.15-0.23 Tg of soot and 0.15-0.25 Tg of char to the ocean annually, and the export of large higher refractory PBC to the ocean can form a long-term sink and prolong the residence time of terrigenous carbon.

Historical records and contamination assessment of potential toxic elements (PTEs) over the past 100 years in Ny-Ålesund, Svalbard.

Ny-Ålesund has been significantly impacted by anthropogenic activities (e.g. coal mining, scientific research, tourist shipping) over the past 100 years. However, the studies of potential toxic elements (PTEs) contamination in Ny-Ålesund currently mainly focus on surface soil or surface fjord sediments, and little is known about the history and status of PTEs contamination over the past 100 years. In this study, we collected a palaeo-notch sediment profile YN, analyzed the contents of six typical PTEs (Cu, Pb, Cd, Hg, As, Se) in the sediments, and assessed the historical pollution status in Ny-Ålesund using the pollution load index, geo-accumulation index and enrichment factor. The results showed that the contents of PTEs over the past 100 years increased rapidly compared with those during the interval of 9400-100 BP. In addition, Pb, Cd and Hg showed a clear signal of enrichment and were the main polluters among the PTEs analyzed. The contamination was likely linked to gas-oil powered generators, coal mining, research station, tourist shipping and long-range transport of pollutants.

Atmospheric mercury accumulation rate in northeastern China during the past 800 years as recorded by the sediments of Tianchi Crater Lake.

An evaluation of the history of anthropogenic mercury (Hg) emissions is needed to quantify total atmospheric Hg emissions since the Industrial Revolution. Thus more long-term records of Hg accumulation rate from natural archives are needed. In the present study, a sediment core from Tianchi Lake, a crater lake in northeastern China, was used to reconstruct atmospheric Hg accumulation rates during the past 800 years. The results show that both Hg concentration and Hg accumulation rate began to increase from 29.5 to 40.2 ng g-1 and from 1.44 to 2.26 µg m-2 yr-1, respectively, at ~ 1750 AD, synchronous with the initiation of the Industrial Revolution. The Hg accumulation rate and Hg concentration increased significantly at ~ 1850 AD, and subsequently, there were two prominent peaks, at ~ 1940 AD and ~ 1980 AD, which are temporally consistent with the Second World War and the peak in commercial usage of Hg, respectively. The Hg accumulation rate and Hg concentration decreased after ~ 1980 AD, possibly because of the decrease in the global Hg background at that time. Differences in regional Hg emissions and atmospheric circulation may be responsible for the different trends in Hg accumulation rate after ~ 1980 AD in the Tibetan Plateau and northeastern China. Our results provide new data for evaluating natural and anthropogenic Hg emissions to the atmosphere in China.

Phosphorus fractions in sediments and their relevance for historical lake eutrophication in the Ponte Tresa basin (Lake Lugano, Switzerland) since 1959.

Lake Lugano is one of several deep lakes in Switzerland that have not yet recovered from eutrophication after large reductions of external phosphorus (P) loadings. Persistent eutrophication has been attributed mainly to internal P loadings from sediments. To achieve the restoration goals, it is critically important to evaluate the sediment P availability and release risk in this lake. In this study, we combined sequential P extraction (four fractions) with enzyme hydrolysis to assess distribution characteristics of P forms and potential bioavailability of organic P in an anoxic sediment profile from the Ponte Tresa basin of Lake Lugano, southern Switzerland. Labile P forms, i.e. mostly redox-sensitive iron bound P and metal oxides bound P (Al/Fe-P), comprised ~70% of total P in the sediment profile (1959-2017 CE), suggesting a high potential for P release from the anoxic sediment. Potentially bioavailable organic P forms (determined by addition of substrate specific enzymes) were considerably higher in the surface sediments (top 5 cm), which is very likely to release P in the near future with early diagenesis. The net burial rates (NBR) of redox sensitive Fe-P fraction and total P in sediments both showed significant decreasing trends from 1959 to 2017 CE, when trophic levels of the lake increased from mesotrophic to hypertrophic status. We suggest that, in the Ponte Tresa basin, higher eutrophication conditions led to enhanced sediment P release (mainly from redox sensitive Fe-P fraction), thus reducing P-NBR in sediments. This study highlights the concern that in deep monomictic lakes, eutrophication restoration might be hindered by extensive internal P cycling and reduced capacity of sediment P-trapping.