It is critical to accurately estimate carbon (C) turnover time as it dominates the uncertainty in ecosystem C sinks and their response to future climate change. In the absence of direct observations ...of ecosystem C losses, C turnover times are commonly estimated under the steady state assumption (SSA), which has been applied across a large range of temporal and spatial scales including many at which the validity of the assumption is likely to be violated. However, the errors associated with improperly applying SSA to estimate C turnover time and its covariance with climate as well as ecosystem C sequestrations have yet to be fully quantified. Here, we developed a novel model‐data fusion framework and systematically analyzed the SSA‐induced biases using time‐series data collected from 10 permanent forest plots in the eastern China monsoon region. The results showed that (a) the SSA significantly underestimated mean turnover times (MTTs) by 29%, thereby leading to a 4.83‐fold underestimation of the net ecosystem productivity (NEP) in these forest ecosystems, a major C sink globally; (b) the SSA‐induced bias in MTT and NEP correlates negatively with forest age, which provides a significant caveat for applying the SSA to young‐aged ecosystems; and (c) the sensitivity of MTT to temperature and precipitation was 22% and 42% lower, respectively, under the SSA. Thus, under the expected climate change, spatiotemporal changes in MTT are likely to be underestimated, thereby resulting in large errors in the variability of predicted global NEP. With the development of observation technology and the accumulation of spatiotemporal data, we suggest estimating MTTs at the disequilibrium state via long‐term data assimilation, thereby effectively reducing the uncertainty in ecosystem C sequestration estimations and providing a better understanding of regional or global C cycle dynamics and C‐climate feedback.
Underestimated ecosystem carbon turnover time and sequestration under the steady state assumption (SSA) written summary: Considerable biases may arise when improperly invoking the SSA to estimate carbon turnover time at realistic dynamic disequilibrium state. This issue has not yet been carefully examined. Our finding provides a better understanding of the SSA‐induced uncertainty and the global carbon cycle dynamics and carbon‐climate feedback for future research. The SSA significantly underestimates the carbon turnover time by 29% and its sensitivity to temperature and precipitation by 22% and 42%, respectively, thereby leading to a 4.83‐fold underestimation of NEP in China's monsoonal forests, a principal C sink globally. These biases are negatively associated with forest age.
•Spatial relationship between rainstorms and NDVI was determined using statistics.•The total number of rainstorms tended to increase sharply in coastal China.•NDVI overall decreased by 0.002% with ...every 1% increase in rainstorm frequency.•Rainstorm has positive impacts on NDVI in northern parts of the study area in spring.•The responses of vegetation to rainstorm show significant spatio-temporal variations.
Within the context of global climate changes, rainstorms have increasingly become one of the important ecological interferences limiting plant growth and population turnover. However, due to the significant spatial and temporal variability of rainstorms, determining their quantitative relationships with plant growth at some longer temporal and larger spatial scales is challenging. In this study, the relationships between rainstorm changes and vegetation activities are explored by analysing the spatial and temporal correlations between the normalized difference vegetation index (NDVI) and rainstorm frequency on the coast of China during the period of 1982–2015. Our results show that: (1) Both rainstorm frequency and vegetation activities tend to increase gradually over the study period. The impact of rainstorms on vegetation in the northern part of the study area is greater than that in the southern part. (2) Overall, rainstorms have a significant (p < 0.1) negative impact on vegetation activities in the northern parts of the study area, especially during the summer months. Furthermore, the negative impact of rainstorms on vegetation in autumn tends to be strengthened into the future. (3) Rainstorms overall have significant and negative impacts on shrub, coniferous forest, broad-leaved forest during the growing season. The strong-impact seasons and locations of rainstorm on vegetation activities identified by our study can dramatically benefit future ecosystem and water resource management in coastal China.
The large and rapid climate change event that occurred around 4200 years ago (hereafter the 4.2-kyr event that marks the onset of the Meghalayan stage) is one of the most significant climatic ...anomalies in the Holocene. It may have exerted profound societal impact globally; however, its triggering mechanism remains uncertain. Here we present a high-resolution, well-dated pollen record covering this interval from the Tianluoshan archaeological site in East China. Our results show that the hydroclimatic conditions in the study area across this event strikingly resembled the regional expression of modern El Niño-Southern Oscillation (ENSO) and exhibited interdecadal ENSO-like variability from ca. 4.50 to 4.00 cal kyr BP. Also, our pollen data indicate a marked shift toward an overall increased intensity and frequency of ENSO-like climate variability from ca. 4.50 to 4.30 cal kyr BP, which was immediately followed by a decline of rice-based agriculture, providing direct evidence for the causal link between climate deterioration and the collapse of Neolithic civilization in East China some 4200 years ago. This observation is in accord with the enhanced ENSO variability reconstructed from proxy records in the tropical Pacific Ocean. As ENSO is intimately coupled with the Asian summer monsoon and the Intertropical Convergent Zone (ITCZ), we suggest that the enhanced ENSO-like climate variability may have triggered the 4.2-kyr event.
•Increasing intensity and frequency of ENSO-like climate variability ocuurred from ca. 4.50 to 4.30 cal kyr BP.•The enhanced ENSO-like climate variability may have triggered the 4.2-ka event.•4.2-ka were likely the ultimate trigger of the collapse of Neolithic civilizations.•The observed climatic and societal changes represent the Northgrippian-Meghalayan transition in E China
Alluvial fan-lake complexes are common in the piedmont zone of mountains on the southern Alxa Plateau, NW China. Interconnected by the erosional and depositional processes, they can be treated as a ...typical source-to-sink system. Yet the dynamics of these coupled sedimentary systems during the Late Quaternary is poorly understood. For example, radiocarbon dating of alluvial fans and elevated shoreline features of megalakes in this area usually yields numerical ages in radical contradiction to those obtained using the optically stimulated luminescence (OSL) method. Resolving this controversy of timing of the alluvial fan-lake systems is important for understanding the driving mechanisms of climatic and environmental changes in this ecological vulnerable area. The Yabulai alluvial fan-lake system is an exceptional example for tackling this issue. Here we provide numerical ages from three sites to better understand the dynamics of this sedimentary system during the last interglacial-glacial cycle. Our results, when compared with palaeoclimate proxy records, suggest that the fan-lake system was highly regulated by the East Asian summer monsoon and it has experienced four stages of remarkable changes. Debris flow processes were active and lake level was ~30 m higher than that of today during Marine Isotope Stage (MIS) 5. A gradual decrease in the aggradation rate of the alluvial fan along with lake-level fall occurred during MIS 4–3, which was followed by a period of intensive wind erosion corresponding to the Last Glacial Maximum. Postglacial growth of the alluvial fan slowed down substantially and small-scale lake-level fluctuations occurred in the foreland basin. The desiccation of megalakes during recent times suggests that the East Asian summer monsoon may have retreated from this area as semi-arid climate emerged.
•The Yabulai alluvial fan-lake system is highly regulated by the East Asian monsoon.•Debris flow processes were active under monsoonal climate condition during MIS 5.•Megalakes with a 30–50 m highstand existed in several foreland basins during MIS 5.•Enhanced wind erosion over the fluvial fan and playa occurred during the LGM.•Arid climate emerged on the southern Alxa Plateau during the late Holocene.
Recently, engineering metal-organic frameworks (MOFs) into metal oxides by solid state thermal decomposition has attracted wide attention for photocatalytic applications. Here, a series of C-doped ...ZnO materials decorated with Au nanoparticles (Au/C-ZnO) were constructed
via
controlled pyrolysis of ZIF-8 adsorbing different amounts of HAuCl
4
·4H
2
O. In this pyrolysis process, ZIF-8 was transformed into C-doped ZnO according to the EDX and XPS analysis. Meanwhile, HAuCl
4
·4H
2
O was transformed into Au nanoparticles that were uniformly dispersed on the surface of C-ZnO as seen in TEM images. The photocatalytic activity of as-prepared catalysts was evaluated by the degradation of methyl orange under UV-vis light irradiation. It was found that the photocatalytic activity of Au/C-ZnO was better than C-ZnO and pure ZnO. Furthermore, Au/C-ZnO exhibited high photocatalytic stability. After three consecutive cycles, there was no noticeable deactivation in the reaction. This unusual photocatalytic activity was attributed to the synergistic effect of C-doping and Au NPs.
C-doped ZnO decorated with Au nanoparticles (Au/C-ZnO) were prepared
via
one step pyrolysis of ZIF-8 adsorbing HAuCl
4
.
The Yellow River floodplain represents a fertile landmass that contributes significantly to human welfare and thus has been colloquially known as the birthplace of Chinese civilization. The ...sediment-laden nature of the Yellow River gave rise to a super-elevated channel belt, which is prone to failure particularly in the summer months when excessive precipitation occurs, resulting in cataclysmic floods traditionally regarded as “China’s Sorrow.” Therefore, a deeper understanding of levee breach frequency in this area is especially important for the assessment of socio-economic risk of levee breaches associated with future climate changes. To better understand the nature, evolution, and driving mechanisms of levee breaches on the lower Yellow River, it is necessary to place the instrumental data within a longer time framework. Here, we retrieve past information about levee breaches on the lower Yellow River since AD 11 from various documentary sources such as official histories of China. We evaluated each line of descriptions and narratives about the location, timing, and nature of each event in these documents, ending up with a detailed timeline of levee breaches on the lower Yellow River during the last 2000 years on an annual time scale. Our results reveal remarkable variations in the frequency of levee breaches superimposed on a long-term increasing trend. In addition to climate changes, the iterative embankment-siltation-breaching process caused a feedback: more breaches result in much more channel siltation, which in turn leads to even more breaches. The enhanced farming in the Loess Plateau played a pivotal role in the formation and operation of this positive feedback. Our findings may not only help improve the assessment of socio-economic risk of levee breaches associated with future climate changes, but also provide consulting information for hydraulic engineering and infrastructural designs in the lower Yellow river area.
Originally domesticated in southwestern Asia, bread wheat represents an exotic element that eventually broadened the subsistence strategies in more than one area of China. Notwithstanding a growing ...body of data, its timing, pace, and pathway of dispersal as well as social impact in China continue to be debated. Here, we present one more line of direct evidence for early occurrence of bread wheat at the coastal site of Sujiacun in the Rizhao area of southeastern Shandong Province, China. Our results by direct dating of a mixed crop cohort consistently show that bread wheat was first introduced into the eastern Chinese coast about 2460–2210 BC. The directly dated wheat grain at Sujiacun is coeval with those found at the Zhaojiazhuang site. Our finding implies that there may have been more than one possible route for wheat transmission to China, including the Eurasian Steppe route. Given the coastal location of the two Shandong sites yielding early wheat remains, however, a trans-Asian dispersal including ocean travel cannot be excluded. Comparison with existing data suggests that, upon arrival on the coast of eastern Shandong, bread wheat quickly dispersed inland and arrived in the Central China Plain and North China Plain by about 2000 BC. It appears that bread wheat was not cultivated extensively in Shandong until hundreds of years later, perhaps due to limitations of climatic, technological, and/or social factors.
Efficient C–ZnS/ZnMoO4@MoS2 and C–ZnS/MoS2 nanocomposite photocatalysts, using ZIF-8 derived C–ZnO as a precursor were successfully synthesized using a simple one-pot procedure. This is the first ...application that involves transforming ZIF-8 into C–ZnMoO4 for photocatalysis. The C–ZnS/ZnMoO4@MoS2 and C–ZnS/MoS2 heterostructures were characterized by X-ray diffraction, UV-vis, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, photocurrent measurements, scanning electron microscopy and transmission electron microscopy. The ZM2 sample of C–ZnS/ZnMoO4@MoS2 exhibited enhanced photocatalytic activity of about 2.9 times as high as that of ZIF-8 derived C–ZnO in the reduction of tetracycline hydrochloride, and also showed obvious photocatalytic activity 1.81 and 3.33 times as high as that of a ZM3 sample of C–ZnS/MoS2 and ZIF-8 derived C–ZnO in the degradation of RhB, respectively. The improved photodegradation activity is a result of the heterogenous structure and the tighter contact between C–ZnS and C–ZnMoO4 compared with the physical contact of general heterogenous photocatalysts. The C–ZnS/ZnMoO4@MoS2 heterostructure photocatalyst is expected to be a new type of nanomaterial for the degradation of pollutants from wastewater.
Paleoclimate proxy records reveal a pervasive cooling event with a Northern Hemispheric extent approximately 9300 years ago. Coeval changes in the oceanic circulation of the North Atlantic imply ...freshwater forcing. However, the source, magnitude, and routing of meltwater have remained unknown. Located in central North America, Lake Superior is a key site for regulating the outflow of glacial meltwater to the oceans. Here, we show evidence for an approximately 45-meter rapid lake-level fall in this basin, centered on 9300 calibrated years before the present, due to the failure of a glacial drift dam on the southeast corner of the lake. We ascribe the widespread climate anomaly approximately 9300 years ago to this freshwater outburst delivered to the North Atlantic Ocean through the Lake Huron-North Bay-Ottawa River-St. Lawrence River valleys.
The radiocarbon concentration of the dissolved inorganic carbon (DIC) pool of most freshwater bodies such as lakes and rivers tends to be depleted with respect to that of the contemporaneous ...atmosphere, resulting in an apparent radiocarbon age of inorganic carbon therein known as freshwater reservoir effect. This phenomenon of radiocarbon age offset is usually site specific and varies over time. By radiocarbon dating pairs of twigs and gastropod shells preserved in an ancient lake, as well as gastropod shells in pre-bomb flooding sediments of known age, we are able to determine the freshwater radiocarbon reservoir effect in the lower Yellow River floodplain during the late Holocene. The regional freshwater radiocarbon reservoir age ranges from 1081 to 233 years with an average of 575 ± 317 years, slightly older than that obtained from Lake Dongping by radiocarbon dating of live submerged aquatic plants. Our results show that the freshwater radiocarbon reservoir age is much older than its marine counterpart of the Yellow Sea and Bohai Bay. A source inversion using dual carbon isotopes (i.e. 14C and 13C) and a linear mixing model revealed that the DIC in the surface water bodies was mainly from shallow groundwater and the Yellow River. Our results have broad relevance to the geological and archaeological chronologies based on the radiocarbon method for this area.
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