Human impacts overwhelmed climate as the dominant factor controlling lacustrine organic matter accumulation in Erhai Lake 2000 years ago, Southwest China.

Climate and human activity are two important factors in regulating organic matter (OM) accumulation in the lake environment. However, when and how anthropogenic impacts have affected lacustrine OM accumulation in southwest China during the late Holocene have not yet been well defined. Here, a 16.3-kyr n-alkane record derived from Erhai Lake was used to trace OM sources and explore their connections to climate and human activity. The n-alkane distributions indicated that the dominant sediment sources shifted from terrestrial and aquatic plants to algae in the late Holocene. OM accumulation was closely related to catchment soil erosion, sediment transport, and deposition processes regulated by climate conditions before 5.0 cal. kyr B.P., following the patterns that stronger monsoon precipitation favoured more terrestrial and less aquatic OM input, and vice versa. From 5.0 to 2.0 cal. kyr B.P., the synchronous downwards trends in terrestrial OM input and precipitation intensity indicated that climate remained a major driving force for OM accumulation. However, sediment sources experienced large-magnitude and centennial-scale oscillations between allochthonous and autochthonous inputs, reflecting early human impacts appeared and lake ecosystems retained the self-regulated ability to recover from the basin-wide early moderate human disturbances. Afterwards, the increased (decreased) OM contributions from terrestrial (aquatic) plants contradicted the weakening monsoon precipitation since 2.0 cal. kyr B.P., indicating a dominant effect of human activities on OM accumulation. This change was accompanied by highly improved algae productivity and gradually elevated lacustrine trophic status, and the lake ecosystem eventually shifted into another state largely deviating from its climate-driven background due to intensified deforestation and agricultural cultivation. Regional comparison indicated that anthropogenic disturbances have temporal differences in southwest China. This study will further improve our understanding of past climate-human-environment interactions in southwest China.

Anthropogenic activities altering the ecosystem in Lake Yamzhog Yumco, southern Qinghai-Tibetan Plateau.

Lakes on the Qinghai-Tibet Plateau (QTP) have been subject to multiple environmental pressures from rapid climate change and intensified human activity in recent decades. However, their ecological effects on the lake ecosystem remain largely unclear due to the lack of long-term monitoring data. This study presented the environmental and ecological changes of the lake Yamzhog Yumco (Southern QTP) over the past three decades based on multi-proxy analysis (geochemistry and sedaDNA) on a high-time resolution sediment core. The result showed that the lake exhibited a continuous eutrophication process from 2004 CE, which has accelerated since 2014 CE. The nutrient enrichment was mainly attributed to anthropogenic emissions from the catchment. The sedimentary ancient DNA (sedaDNA) metabarcoding data registered a sensitive response of aquatic communities to the additional nutrient supply. Eukaryotic algae and aquatic invertebrate communities exhibited similar temporal dynamics, characterized by the increase in eutrophic taxa and the decrease in oligotrophic taxa. Change points analysis suggested that lake ecosystems underwent a slight ecological shift in 2003 CE and an abrupt shift in 2012 CE driven by nutrient enrichment. Quantitative analysis revealed that nutrients and human activity accounted for 27.9 % and 21.7 % of the temporal variation in aquatic communities, whereas climate change only explained 6.9 % of the total variation. From a paleolimnological view, our study supported that regional human activity could distinctly alter the nutrient level and aquatic community structure of lake ecosystems in the QTP. Considering that anthropogenic disturbance will continuously increase, it is crucial to strengthen the field monitoring of the lakes on the plateau and make effective management measures to avoid irreversible ecological consequences.

Spatiotemporal patterns of organic carbon burial over the last century in Lake Qinghai, the largest lake on the Tibetan Plateau.

Lakes are important carbon sinks in terrestrial environments. However, the estimation of the global lake carbon sink has large uncertainty. Data from plateau and remote lakes are rare, and most studies of carbon sequestration in large lakes have been based on single or a few sediment cores. Here, twenty-five sediment cores were collected by grid sampling covering Lake Qinghai, the largest lake on the Tibetan Plateau. Age models were established by combining radionuclide 210Pb137Cs dating with magnetic susceptibility chronostratigraphy of sediment cores. Furthermore, the spatiotemporal variations of the organic carbon burial rate (OCBR) over the past century were investigated. The OCBR of Lake Qinghai has increased significantly since the 1990s in association with warm-humid climates, increased nutrient supply and, enhanced land-use changes. The spatial distributions of OCBR were insignificant during the 1900s-1960s and 1960s-1990s and then shifted to a pattern of high values occurring in the southwestern lake areas during the post-1990s period. The spatial distribution of OCBR was mainly determined by sediment mass accumulation rate, primary production, and potential mineralization. The average OCBR in the all sediment cores showed no correlation with water depth (12-30 m) and was within one standard deviation of the whole-lake average value for most cores. These results suggest that the average OCBR of a sediment core in a relatively flat lakebed can generally represent the whole-basin level of Lake Qinghai. The average OCBR was 22.5 ± 5.5 g m-2 yr-1, which is close to those values reported previously for lakes of boreal forest and taiga but significantly higher than those reported for tundra lakes. Our findings highlight that the remote lakes on the Tibetan Plateau have great carbon sequestration potential in sediments and may act as a significant natural carbon sink.

A Chironomid Record of Early-Middle Holocene Environmental Evolution in the Darhad Basin, Northern Mongolia.

Under the influence of various circulation systems, the Holocene humidity conditions on the Mongolian Plateau are spatially heterogeneous and the underlying mechanism is still ambiguous. The complexity of climate change may affect the accuracy of assessing lake ecosystem evolution. In this study, based on the precise chronology, a chironomid assemblage sequence from the Darhad Basin in northern Mongolia is analyzed to elucidate the hydroclimate variation during the early-middle Holocene. The results show that the chironomid communities changed suddenly from littoral taxa to sublittoral/profundal taxa at about 9 cal kyr BP, reflecting an environmental transition from a river or shallow lake condition to a deep lake environment. Thereafter, most parts of the paleolake remained at a relatively high level until 4.5 cal kyr BP. This hydrological pattern resembles the typical humidity variations in the Westerlies affected regions, except that the onset of wetter conditions occurred one thousand years earlier as reflected in our results. The melting of glaciers and permafrost in the basin resulting from the early increased summer solar insolation could be a feasible explanation for these time advances.

[Source and Optical Dynamics of Chromophoric Dissolved Organic Matter in the Watershed of Lake Qinghai].

Lake Qinghai is the largest lake in China and is of great significance to maintain the ecological security of the Qinghai-Tibet Plateau. Few studies have been carried out to investigate the optical composition and source of chromophoric dissolved organic matter (CDOM) in large lakes on the Qinghai-Tibet Plateau. It is of great significance to study the source and optical dynamics of CDOM in Lake Qinghai watershed for water quality protection and filling in the gaps in the knowledge of CDOM variability in a remote area. Two sampling campaigns in the Lake Qinghai watershed were carried out, and excitation-emission matrices coupled with parallel factor analysis (EEMs-PARAFAC) were used to unravel the optical composition and the sources of CDOM. Our results indicated that the mean dissolved organic carbon (DOC) concentration, a250:a365, and the spectral slope of CDOM absorption S275-295 in the lake were significantly higher than that in the inflow river (P<0.0001, t-test), whereas the mean absorption coefficient of CDOM a350, humification index (HIX), fluorescence peak integration ratio IC:IT, and specific ultraviolet absorbance at 254 nm SUVA254 of CDOM were shown to be lower in the lake than in the inflow river (P<0.0001), indicating that compared with the lake itself, CDOM in the inflow was humic-rich and highly aromatic. Four fluorescent components were obtained using PARAFAC, including a terrestrial human-like component C1, a microbial human-like component C2, a tyrosine-like C3, and a tryptophan-like C4. The mean DOC concentration, S275-295, and a250:a365in the headwater streams of the Lake Qinghai watershed were lower than those in the downstream estuary, indicating that the CDOM abundance increased, and the molecular weight decreased, from the headwaters to the downstream river mouths. The mean of SUVA254, C1, and the first axis of principal component analysis were positively related to terrestrial input (i.e., the PC1 values were significantly higher in rivers than in lakes (P<0.001)), indicating that the aromaticity of CDOM in rivers was higher than that in lakes. Particularly, the contribution of terrestrial humic-like C1 was higher in the Quanji River, Shaliu River, and Khargai River compared with that in other tributaries due to an intensified cultivated land use at the downstream estuary of these rivers.

Low CO2 levels of the entire Pleistocene epoch.

Quantifying ancient atmospheric pCO2 provides valuable insights into the interplay between greenhouse gases and global climate. Beyond the 800-ky history uncovered by ice cores, discrepancies in both the trend and magnitude of pCO2 changes remain among different proxy-derived results. The traditional paleosol pCO2 paleobarometer suffers from largely unconstrained soil-respired CO2 concentration (S(z)). Using finely disseminated carbonates precipitated in paleosols from the Chinese Loess Plateau, here we identified that their S(z) can be quantitatively constrained by soil magnetic susceptibility. Based on this approach, we reconstructed pCO2 during 2.6-0.9 Ma, which documents overall low pCO2 levels (<300 ppm) comparable with ice core records, indicating that the Earth system has operated under late Pleistocene pCO2 levels for an extended period. The pCO2 levels do not show statistically significant differences across the mid-Pleistocene Transition (ca. 1.2-0.8 Ma), suggesting that CO2 is probably not the driver of this important climate change event.

Assessment of atrial electromechanical coupling and influential factors in nonrheumatic paroxysmal atrial fibrillation.

BACKGROUND: Sequential analysis of atrial electromechanical coupling (P-A) by Doppler tissue imaging (DTI) might provide important insight into the mechanisms of paroxysmal atrial fibrillation (PAF). HYPOTHESIS: The purpose of this study was to evaluate P-A and the dispersion of P-A, and to analyze the influential factors of P-A. METHODS: One hundred and ten patients with PAF and 87 normal controls were enrolled. Using DTI, the time intervals from the beginning of P-wave to the onset of atrioventricular ring motion related to atrial contraction were measured. RESULTS: Atrial electromechanical coupling at the interventricular septum atrioventricular annulus (P-A1), left lateral mitral annulus (P-A2) and right lateral tricuspid annulus (P-A3) in PAF group were significantly longer than those in control (p < 0.001). The difference between P-A2 and P-A1 (T1), P-A2 and P-A3 (T3) in PAF group were greater than those in control before age correction (p < 0.05). The linear regression analysis showed that the duration of PAF episodes and age were the greatest influential factors of P-A1 (r = 0.564). Left atrial anterior-posterior dimension (LAD) and age were the greatest influential factors of P-A2 (r = 0.459). The LAD was the greatest influential factors of T1 and T3 (r = 0.408, 0.542). CONCLUSIONS: The atrial electromechanical coupling was significantly longer and the dispersion of P-A at left lateral mitral annulus was greater in PAF patients. The prolongation of P-A may be related to left atrial enlargement, long episodes of PAF and aging and the dispersion of P-A at left lateral mitral annulus to LAD.

Left and right atrial size and the occurrence predictors in patients with paroxysmal atrial fibrillation.

The purpose of the present study is to evaluate left and right atrial volume in patients with paroxysmal atrial fibrillation (PAF) and to select the best clinical variables to predict the occurrence of PAF. 157 patients and 106 normal subjects were enrolled. In patients with PAF, right atrial volume and dimension were all significantly greater (P<0.001 approximately 0.05). Left atrial (LA) volume were obviously higher (P<0.01) before correction for age. Atrial dilation and right atrial shape remoding are evident compared to normal controls. Patients are more prone to PAF occurrence if they have increased LA anterior-posterior diameter, greater P maximum and advancing age.