The rise and fall of ancient cultures and civilizations is a hotly debated topic that has generated disagreements and disputes. In this paper we summarize some case studies on the abandonment of ...ancient sites, the prosperity and collapse of ancient cultures, and demographic changes, as well as the influence of environment and technology during the prehistoric and historic periods. We then suggest that the dominant influencing factors for the evolution of ancient societies vary by spatial scale.At the local scale, sudden disasters are critical factors leading to the destruction and abandonment of large settlements. On a regional scale, climatic variations（e.g., droughts or cold events lasting for decades or centuries） are important factors that induce the collapse of ancient civilizations and mass migrations, while an enduring and stable optimal climate facilitated the prosperity of ancient civilizations. On a global scale, major technological innovations and their dispersion lasting for centuries and even millennia are major catalysts for population growth and social development. Lastly, we illustrate a possible mechanism under which environmental and technological factors played a critical role in ancient human survival and social evolution on different spatial scales.
In northwestern China, many historical nomadic kingdoms and Chinese dynasties sought to control the Heihe River basin, an important location on the eastern part of the ancient Silk Road. ...Archaeologists have argued that changes in material culture are tied to the frequent turnover in polities in the area, but no published evidence supports these claims. In this paper, we evaluate the relative importance of environmental and political factors in determining the spatiotemporal pattern of archaeological sites in the middle and lower reaches of the Heihe River basin by using previously published high-resolution paleoclimate records and a variety of historical documents. Our results indicate that humans intensively exploited the Heihe River basin during Han dynasty (202BC–AD 220). Following the Han dynasty, during the Wei-Jin (AD 222–589) and Sui-Tang (AD 581–907) periods the number of archaeological sites. In the Western Xia-Yuan period (AD 1038–1368), people mainly settled in the lower reaches of the Heihe River basin and only returned to the middle reaches of the Heihe River basin during the Ming and Qing dynasties (AD 1368–1912). Although climate change and the local environment affected human activities in Heihe River basin, geopolitical events, such as forced mass migrations, are more responsible for influencing the distribution of archaeological sites over the past 2000 years.
Human settlement and agricultural development are closely linked to local geomorphological and climatic environments. However, the variation in agricultural systems in different environmental and ...prehistoric contexts remains unknown. We report new archaeobotanical and radiocarbon dates from 34 Neolithic and Bronze Age sites in the Hutuo River Valley (HTRV) in north-central China and compare them with updated archaeobotanical studies in the Sushui River Valley (SSRV) and Henan Province (HNP), to explore the similarities and differences of agricultural patterns under different geomorphologic and climatic environments in north-central China. Our results reveal that humans consistently cultivated foxtail and broomcorn millet in the HTRV from the Miaodigou (6000–5700 cal. a BP) to the Shang-Zhou (3600–2256 cal. a BP) period, despite the introduction of wheat and barley into the area around 4000 a BP. Climate conditions and hilly landforms in the HTRV, SSRV and some parts of the HNP led people to develop foxtail and broomcorn millet dry land farming practices between 7000 and 3000 a BP. Alternatively, in other areas of the HNP, the climate conditions and alluvial plains enabled people to develop a mixed agriculture of millets, soybeans, and rice from 7000 to 4000 a BP, with the addition of wheat between 4000 and 3000 a BP. Farmers’ different agricultural technologies and interactions with foreign cultures may have also influenced the formation of different agricultural patterns in the three regions between 7000 and 3000 a BP. Population growth during 7000–3000 a BP can explain the overall propensity of the higher-yield foxtail millet rather than broomcorn millet as the main cultivated crop. In the HTRV, however, higher proportions of broomcorn millet (as compared to the SSRV and HNP), may reflect the greater drought and heat tolerance of broomcorn millet, representing an adaptive agricultural strategy in the river valley.
Changes in moisture conditions or precipitation in the SE Tibetan Plateau during the Holocene have been studied using various environmental archives and proxies. However, due to different ...interpretations of the proxies and records, the pattern of Holocene precipitation/moisture variations in the region remains unclear. A lake-sediment-based reconstruction of runoff variations, which can directly and sensitively reflect changes in precipitation, provides the opportunity to reconstruct the evolution of moisture conditions in the SE Tibetan Plateau during the Holocene. In this study, we used a well-dated sediment core (LGH2) from Lake Lugu, a deep alpine lake charged mainly by precipitation on the lake surface and by runoff from the watershed, to reconstruct variations in runoff during the Holocene. In addition, 70 lake surface sediment samples were collected to examine the spatial variation of grain size. Endmember modeling analysis of the grain-size data was used to characterize the processes of sediment transport and runoff fluctuations. The carbonate content of core LGH2 shows that the lake level was generally high during 11,600–3100 cal years BP, and that the lake basin was closed after 3100 cal years BP and semi-closed since 90 cal years BP. Grain-size endmember EM 3, which represents the runoff input clastic materials, is used to reconstruct runoff fluctuations in the Lake Lugu watershed. The record indicates a gradual increase in runoff during 11,600–9000 cal years BP, stable and high runoff during 9000–2000 cal years BP, and weak runoff and a low lake level since 2000 cal years BP. Our reconstruction of runoff fluctuations tracks changes in regional temperature and tropical SSTs rather than in boreal summer insolation. This finding supports the hypothesis that increasing tropical SSTs strengthened ITCZ convection which enhanced the flux of water vapour from the ocean to the air, and hence the moisture supplies to SW China.
Purpose
Lake sediment is an important carbon reservoir, and knowledge of organic carbon distribution and its controlling factors can provide insights into the effects of natural processes and ...anthropogenic pressures on carbon dynamics in drainage basin.
Materials and methods
Here, we combined total organic carbon (TOC), total nitrogen (TN), and their stable isotopes (δ
13
C and δ
15
N) with a Bayesian isotope mixing model to identify the origin of organic matter (OM) and the key factors influencing OM accumulation in surface sediments from Lake Yangzong (YZ) and Lake Chenghai (CH), located on the Yunnan Plateau, SW China.
Results and discussion
The δ
13
C values in surface sediments from YZ showed a gradual increase from south to north, with an asynchronous decrease in δ
15
N, suggesting an increasing contribution of pollutants originating from the Yangzong River. In contrast, CH was characterized by a rapid decrease in δ
13
C and an increase in δ
15
N values occurring in the deepest part of the lake, indicating that water depth may play an important role in OM accumulation in the lake. Allochthonous OM (C3 plant and soil OM) was the dominant sediment OM source for surface sediments in YZ, while substantial contributions of OM originated from plankton, soil OM, and sewage in CH.
Conclusions
These findings suggest that trophic state and terrestrial input may exert large impact on OM accumulation in deep lakes, which results in different distribution patterns of OM sources.
•Quantitatively study charring progress with multi-indicators;•Analyzing the microstructure changes of wood/charcoal by measuring the thickness of tracheid cell wall and the lumen area during the ...charring process for the first time;•Comparing the essential indexes of experimental charred wood with archaeological charcoal fossil;•Providing key physical and chemical parameters in the wood charcoalification process.
Charcoal is commonly preserved in both natural and artificial sediments, and is intensively used in paleontological, paleoenvironmental, and archaeological studies due to the abundant bio-information it contains. The biochemical properties of charcoal are also used for paleoclimatic reconstruction; however, the reliability of this approach has been challenged due to a lack of clarity on how physicochemical properties change during the charring process, as well as the temperatures required for charcoalification. To address this lack, in this study, Qinghai spruce and Chinese pine wood samples from the northeastern Tibetan Plateau were heated at different temperatures and for different lengths of time under restricted oxygen conditions. The reflectance; carbon, nitrogen, and oxygen content; and tracheid morphology were quantified before and after heating to assess changes related to the charring process. Archaeological charcoal remains were then evaluated to determine the charcoalification temperatures by comparing with the experimental results. The minimum temperature required for wood charcoalification was ∼300°C, while temperatures recorded by archaeological charcoal were concentrated at 400–500°C. During the charring experiments, the tracheid cell walls gradually homogenized, and tracheid cell wall thickness and lumen area decreased by ∼20%. On average, 50% mass losses were observed; the carbon and oxygen content (% wt.) approximately changed from 47% to 60% and 48% to 35% respectively, while the nitrogen content (% wt.) fluctuated around 0.2%. The reflectance increased slightly from 0% to 0.5%. We propose that the charcoalification of wood tissue refers to charring (in restricted air) and carbonization (in the almost absence of air) when the wood is exposed to a heat source, which then finally transforms into a black, inert solid. This quantitative study provided valuable data and a thorough assessment of the process of wood charcoalification, as well as accurately estimated the feasibility of using charcoal physicochemical properties in paleoclimatic research.
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The origin, development and expansion of prehistoric agriculture in East Asia have been widely investigated over the past two decades using archaeobotanical analysis from excavated Neolithic and ...Bronze Age sites. Research on prehistoric agriculture has predominantly focused in the valleys of the Yellow River and the Yangtze River. Agricultural development during the Neolithic and Bronze Age periods in the Yunnan-Guizhou Plateau of southwest China, an important passageway for human migration into Southeast Asia, still remains unclear. In this paper, based on macrofossil and microfossil analysis and radiocarbon dating at the Shilinggang site, we investigate plant subsistence strategies in the Nujiang River valley during the Bronze Age period. Combined with previous archaeobotanical studies in the Yunnan-Guizhou Plateau, we explore agricultural development processes in this area during the Neolithic and Bronze Age. Our results indicate that rice and foxtail millet were cultivated in Shilinggang around 2500 cal a BP. Three phases of prehistoric agricultural development in the Yunnan-Guizhou Plateau can be identified： rice cultivation from 4800–3900 cal a BP, mixed rice and millet crop（foxtail millet and broomcorn millet） cultivation from 3900–3400 cal a BP, and mixed rice, millet crop and wheat cultivation from 3400–2300 cal a BP. The development of agriculture in the Yunnan-Guizhou Plateau during the Neolithic and Bronze Age periods was primarily promoted by prehistoric agriculture expansion across Eurasia, agricultural expansion which was also affected by the topographic and hydrological characteristics of the area.
Accumulations of aeolian deposits in a range of sedimentary environments provide evidence for past changes in atmospheric circulation patterns over a range of spatiotemporal scales. As yet, there ...have been relatively few studies of aeolian records in Southwestern (SW) China, and thus there is hitherto untapped potential of using such records to reveal regional atmospheric circulation. Rare earth element (REE) and grain-size analyses were carried out on a well-dated sediment core from Lake Lugu, SW China, to establish the provenance of aeolian deposits preserved within the lake during the last 32 kyr. The core sediments (LGH2) possess high δEuN values (0.73–0.87) and exhibit a moderate REE abundance (156–274 ppm). The δEuN-∑REE pattern of the Lake Lugu sediments are distinct from those of adjacent geographical areas, but are shown to overlap with the sediments from the Kashmir Valley and northwestern (NW) Deccan Plateau indicating a long-distance dust source. The grain-size endmember for the aeolian deposits shows a gradually increasing trend from 32 kyr B.P. to the onset of the Holocene, followed by a sharp decrease around 9 kyr B.P., with very low values observed during the Holocene optimum (8.3–2 kyr B.P.). Aeolian deposition resumed from 2 kyr B.P. and has continued to the present day. Comparisons with both local and regional palaeoclimate records show that both the local climate and East Asian monsoon (EAM) have not influenced aeolian deposition in Lake Lugu. Rather, changing vegetation cover in the north India and NW Deccan Plateau provided the sediment supply, with entrainment governed by variations in the Southern Winter Westerlies in the dry season (north India), and the South Asian summer monsoon (SASM) in the rainy season (NW Deccan Plateau).
•Northwest India is the principal source of aeolian input to Lake Lugu, southwest China.•Aeolian is transported to southwest China via the Southern Winter Westerlies and the South Asian summer monsoon.•The East Asian Monsoon and local climate have few influences on the aeolian deposition in Lake Lugu.
Purpose
The effects of anthropogenic activity and climate change on lake ecosystems for nine large plateau lakes in Yunnan Province have recently received much attention; however, most studies have ...focused on the deepest lake sediments and ignored the lake sediments adjacent to the populated area.
Materials and methods
To evaluate the sedimentation rates and ecological changes, four
210
Pb- and
137
Cs-dated sediment cores were collected along the long axis of Yangzong Lake, a fault-controlled north-south strike lake located in Yunnan Plateau in July 2006 and July 2016, respectively. We combined a biological indicator (diatom assemblage) with geochemical indicators (total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP)) for core S0 in the southern part of the lake to examine the ecological changes in response to anthropogenic disturbances within the lake over the last 60 years.
Results and discussion
The results showed that the sedimentation rate in the southern part of the lake (S1) was significantly higher than that in the central (S2) and northern (S3) parts of the lake. Redundancy analysis (RDA) and Pearson correlation analysis identified significant correlations between TP and
Aulacoseira granulata
,
Cyclotella ocellata
, and
Cyclotella rohomboideo-elliptica
(correlation coefficients: − 0.66, − 0.63, and 0.81, respectively,
p
< 0.01). There was a clear shift in the diatom community from oligotrophic to eutrophic species becoming dominant after the 1990s, coinciding with the intensifying human activities around the lake. Furthermore, there were two periods of diatom absence in core S0, which was associated with two periods of rapid depositional events. These are likely associated with the intensification of industry, mining, road construction, and agriculture within the lake catchment.
Conclusions
These findings highlight the sensitivity of freshwater ecosystems in the shallow-water area of a lake to human activities, with implications for future water quality in fault-controlled lakes.
Eutrophication remediation is an ongoing priority for protecting aquatic ecosystems, especially in plateau lakes with fragile ecologies and special tectonic environments. However, current strategies ...to control the phosphorus (P) and nitrogen (N) levels in eutrophication sites have been mainly guided by laboratory experiments or literature reviews without in-field analyses of the geochemical processes associated with the hydrological and eutrophic characteristics of lakes. This study analyzed the water quality parameters of 50 sites at Lake Jian in May 2019, a moderate eutrophication shallow plateau lake, based on dissolved/sedimentary nitrogen, phosphorous and organic matter, grain size, C/N ratios and stable isotope ratios of δ13C or δ15N in sediments. The results showed that the average total nitrogen (TN) and total phosphorus (TP) concentrations in the lake water were 0.57 mg/L and 0.071 mg/L, respectively. The TN and TP contents of surface sediment ranged from 2.15 to 9.55 g/kg and 0.76 to 1.74 g/kg, respectively. Stable isotope and grain source analysis indicated that N in sediments mainly existed in organic matter form and P mainly occurred as inorganic mineral adsorption. Endogenous pollution contributed to >20% of TN. Furthermore, our findings showed that phosphorus was the nutrient that limited eutrophication at Lake Jian, unlike other eutrophic shallow lakes. In contrast, the nutrient levels in the sediment and input streams belonged entirely to the N-limitation state. The distinctness in release intensity of N and P could modify the N/P limitation in the lake, which affects algae growth and nutrient control. These results demonstrated that reducing exogenous nutrients might not effectively mitigate lake eutrophication due to their endogenous recycling; thus, detailed nutrient monitoring is needed to preserve aquatic ecosystems.
