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Black carbon (BC), ubiquitous in soils, plays an important role in global carbon cycles, the radiative heat balance of the Earth, pollutant fate, emissions of greenhouse gas, soil fertility, soil microbial community, and ecosystem stability. However, information on BC in topsoils of the northeastern Qinghai-Tibet Plateau is limited. Therefore, this study performed field sampling and analyzed contents of total BC and soot BC in topsoils. The results indicated that the contents of total BC in all soil samples ranged from 0.504 to 74.381 g kg−1 with an average value of 5.152 g kg−1, whereas those of soot BC were in the range of 0.400–15.200 g kg−1 with a mean value of 1.719 g kg−1. Contents of BC were significantly correlated with those of total carbon and total organic carbon. Soil types affected the distribution of soil BC. The contents of total BC in the loam soils were larger than those in the clay soils, whereas soot BC was more easily enriched in the clay soils. Total BC was negatively correlated with Ca, and soot BC was negatively correlated with Ti. The contents of soil BC in functional areas, such as agricultural and pastoral areas, industrial areas, and mining areas, were significantly higher than those in other areas, illustrating that anthropogenic activities drastically affected the distribution of soil BC. This study exhibits the fundamental information on soil BC in the northeastern Qinghai-Tibet Plateau to provide important knowledge on global soil carbon sink.

Da Qaidam Salt Lake, northern Qaidam Basin, is known for its liquid and solid boron resource. More than that, pinnoite-bearing sediments, occurring in this lake, are rare in the world. However, little attention has been paid to the hydro-climate change and brine evolution correlation with the formation of pinnoite deposit. According to the multi-proxy records, as well as AMS 14C dating, the sediment profiles DCD02 and DCD03 from Da Qaidam Salt Lake were studied. The results revealed that the ore-forming age of three pinnoite deposits are 7.83–8.62 cal ka BP, 6.74–7.07 cal ka BP and 4.66–5.41 cal ka BP. The sedimentary evolution of Da Qaidam Salt Lake along with the pinnoite formation during the past 13,000 years can be divided into four stages, i.e., (1) relatively fresh and deep paleo-lake with low salinity during 12.98–9.00 cal ka BP; (2) seasonal variations between fresh and brackish paleo-lake during 9.00–8.62 cal ka BP; (3) salt lake stage with relatively high salinity and alkalinity during 8.62–4.66 cal ka BP, and (4) relatively shallow lake with high salinity since 4.66 cal ka BP. Under favorable sedimentologic and hydrogeochemical conditions, a series of boron deposits including pinnoite ore formed in different zones of Da Qaidam Salt Lake due to the different ore-forming mechanisms. Finally, under the differential effect of climate warming condition between the high mountain catchments and arid basin, the boron ore-forming model was established as a higher mountain–lower basin–shallower water model.

Environmental changes influenced by human activities were recorded in the sediment cores from Xingyun lake. Based on the 137Cs and 210Pb dating, multi-proxy records, enrichment factor (EF), and geoaccumulation index (Igeo) methods, the history of human–environment interactions in Xingyun lake catchment during the past 140 years was studied. The results showed that the total heavy metal pollution in Xingyun lake followed the decreasing order: the northwestern > the middle > the southwestern > the southern > the north easterly. These distributions were controlled by regional geochemical background values, pollution load, and the lake current driven by prevailing southwesterly winds. The total EF value of heavy metals followed the decreasing order: EF (Zn) > EF (Cr) > EF (Pb) > EF (Cd) > EF (Cu). The total Igeo value of heavy metals also followed the decreasing order: Igeo (Zn) > Igeo (Cr) > Igeo (Pb) > Igeo (Cd) > Igeo (Cu). Consequently, the total pollution level of heavy metals followed the decreasing order: Zn > Cr > Pb > Cd > Cu. Before 1910 AD, the natural erosion caused by climate changes was the key factor for the heavy metals accumulated. After 1910 AD, the heavy metal concentrations were mainly controlled by anthropogenic impacts, the dominant sources were from industrial pollution, agricultural pollution, mining, and organic degradation. Finally, the sedimentary evolution history of Xingyun lake can be divided into four stages, i.e., (1) natural evolution stage during 1862–1910 AD, (2) anthropogenic disturbance stage during 1910–1953 AD, (3) anthropogenic reconstruction stage during 1953–1984 AD, and (4) eutrophication stage after 1984 AD.