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Insect pests pose a significant threat to alpine ecosystems, especially under rapid environmental change conditions. Therefore, it is necessary to explore the effects of environmental factors on insect pest risks and provide methods for pest management in alpine regions. Habitat heterogeneity and topographic variation are the indicators of insect pest risks. However, few studies have explored the effects of habitat heterogeneity and topographic variation on insect pest risks in alpine regions. We used species distribution modeling (i.e., maxent modeling) to project the distributions of insect pests in this alpine region based on occurrence records. Then, we delineated the high-risk areas for insect pests based on the species distributions under a conceptual risk framework using Zonation software for different ecoregional types. We determined the alpine conifer and mixed forests of the Nujiang Langcang Gorge, the conifer forests of the Qilian Mountains, and the shrublands and meadows of Southeast Tibet as the key areas requiring monitoring for insect pests in Qinghai province based on the scoring of insect pest risk rank with >0.7. Habitat heterogeneity and topographic variation could be developed as indicators of risk exposure to insect pests in alpine regions. Our study suggests that the prevention and control of insect pests should be conducted in areas with high habitat heterogeneity and topographic roughness in alpine regions. We provided new insights into the application of species distribution modeling based on habitat heterogeneity and topographic variation. The results of our study indicate that habitat heterogeneity and topographic variation should be considered for improving pest management effectiveness in alpine regions. [ABSTRACT FROM AUTHOR]

The glaciers of the Tibetan Plateau have undergone profound changes due to rapid global warming, but the nature of their response to climate change at various settings remains unclear. This study focuses on the analysis (grain sizes, magnetic susceptibility, and element ratios) of a sedimentary core from a proglacial lake (Qiangyong (QY) Co) at the southern Tibetan Plateau, based upon the 210Pb and 137Cs dating, aiming to unveil the fluctuations of the QY glacier over the recent 500 years and its response to global warming. Four pre-1900s distinct glacier advance/cold intervals (C1: 1560s, C2: 1660s, C3: 1760s and C4: 1860s), a minor advance in the 1950s and an extensive glacier retreat since the 2010s were discerned. There are five glacier fluctuation cycles, each spanning approximately 100 years, correlating generally well with the Northern Hemisphere temperature patterns on a century time scale. The glacier advances align with the cold periods, whereas the retreats correspond to the warm intervals. However, coarse grain sizes indicated a marked glacier shrinkage of the QY glacier since the 1920s owing to global warming, over-shading the inherent 100-years fluctuation cyclic variations intrinsic to glaciers. The reason is that after QY glacier has significantly shrunk to higher altitude, the response of the glacier to climate change is no longer as sensitive as at the lower altitude, even under post-industrial-revolution warming. The QY glacier and even the entire Himalayan region will face the threat of glacier melting during the 21st century, but dynamic patterns of glacier retreats in higher Himalayan regions may differ from that in the low-altitude. [ABSTRACT FROM AUTHOR]

Faithfully tracing sources of sediment and then quantifying the flux of each source are the first-order basis for reconstructing paleoclimate and paleoenvironment using lake sediments. The budget of various sources contributing to lake sediment in Lake Qinghai, the largest lake on the Tibetan Plateau, is controversial. In the previous study, the flux of the dust deposition to the modern lake sediment was obtained through 2-year observations, but estimations of other sources have some uncertainties due to inadequate data. In this study our new estimations for the modern Lake Qinghai sediment using new measured data show (1) that contribution (22.1 ± 5.2 %) of the fluvial particulate matter is of second significance, only about one-third of the dust deposition, to the modern lake sediment, when its quick deposition near river mouths is not considered, (2) that lacustrine organisms contribute only 5.2 ± 1.1 % of the sediment, but account for ~70 % of the organic matter in sediment, and (3) that authigenic carbonates contribute 21.0 ± 8.6 % of the sediment and 63.6 % of the total carbonates in the lake sediment, respectively, which is due to a direct precipitation of both Ca and Mg in the modern Ca-limited lake. These quantifications are instructive to understand the particulate fluxes to sediment pools in Lake Qinghai under the present conditions and to reconstruct paleoclimate and paleoenvironment via physical and geochemical proxies using past sediments. [ABSTRACT FROM AUTHOR]

• Daily to seasonal river sediment transport has been investigated in Tibetan area. • The freeze–thaw increased loose sediment generation. • The freeze–thaw cycles enhanced surface erosion in pre–monsoon period. • NE Tibetan Plateau showed max. ∼ 2 °C warming over the past 30 years. Global warming and intensified climate variability have greatly affected Earth's surface processes and continental sediment evacuation. River suspended sediment is a sensitive indicator for tracing seasonal surface erosion, but details of the rates of sediment generation and evacuation, and their connections with nowadays warming climate are not entirely clear, particularly in Tibet and other high–altitude areas where field observations remain scarce. Here, we investigate daily to seasonal river sediment transport dynamics between the cold, permafrost–dominated northeastern Tibetan Plateau and warm, non–permafrost Sichuan and Taiwan regions. Our results show that at a given river water discharge, greater river suspended sediment was evacuated during the pre–monsoon season (April–Mid June) relative to other seasons in the cold NE Tibetan catchments. In contrast, no such phenomenon was observed in the warm, non–permafrost regions. These comparisons likely indicate a center role of freeze–thaw processes on loose sediment generation, which enhanced sediment output. Hydrometeorological records show up to ∼2 °C warming in the NE Tibetan Plateau since the past 30 years, coupled with an 8-fold increase in sediment transport. We suggest that continuous warming climate may further accelerate sediment and soil carbon release in the Tibetan Plateau and other global permafrost–dominated areas, which in turn influences climate feedback. [ABSTRACT FROM AUTHOR]

Abstract: Water samples from the Buha and Shaliu Rivers, located on the semi-arid northeastern Tibetan Plateau, were collected weekly over a one year period. The major ionic compositions of water samples were measured and the daily contents of suspended particulate material (SPM) were monitored in both rivers in order to investigate the influence of lithology, climate and physical erosion on seasonal silicate weathering. In the Shaliu River, weathering of trace amounts of calcite contributes more than 50% of the Ca2+ and to the river water. Through high-resolution variations of Ca2+ concentrations and elemental ratios, the signal of carbonate precipitation is captured at the end of monsoon in this river. The measured physical erosion rate is only 8.7–16.0mm/kyr in this semi-arid region, which is 2–3 orders of magnitude lower than that in the Himalaya and nearby regions. In contrast with several orders of magnitude in seasonal variations of silicate weathering rates in both catchments, the distinct lithology between the catchments only leads to a 15 times difference of annual net CO2 consumption. The correlation analysis shows that seasonal silicate weathering is strongly dependent on water discharge in the semi-arid area. The most important observation is that, unrecognized by the previous studies, both physical erosion rate and air temperature exhibit two distinct trends with silicate weathering rates (and net CO2 consumption) during the years. The two trends might suggest that temperature plays a more important role on the CO2 consumption rate before the mid-monsoon under a condition of low water discharge than that after the monsoon with a high water discharge. During the period before the mid-monsoon, the relationship between temperature and silicate weathering rate exhibits higher activation energy than after the mid-monsoon, suggesting a greater dissolution of uneasily weatherable minerals from groundwater, frozen soil, and/or dust input. The relationship between erosion and weathering during the period before the mid-monsoon indicates a faster increase of silicate weathering rate, because freezing erosion produces large amount of high surface area minerals. [Copyright &y& Elsevier]

Conventional hydrochemical techniques and statistical analyses were applied to better understand the solute geochemistry and the hydrochemical process of shallow groundwater in the Qinghai Lake catchment. Shallow groundwater in the Qinghai Lake catchment is slightly alkaline, and is characterized by a high ion concentrations and low water temperature. The total dissolved solids (TDS) in most of the samples are <1,000 mg/L, i.e. fresh water and depend mainly on the concentration of SO, Cl and Na. Groundwater table is influenced directly by the residents' groundwater consumption. Most of the groundwaters in the Qinghai Lake catchment belong to the Ca(Na) -HCO type, while the Qinghai Lake, part of the Buha (BHR) and the Lake Side (LS) samples belong to the Na-Cl type. The groundwater is oversaturated with respect to aragonite, calcite and dolomite, but not to magnesite and gypsum. Solutes are mainly derived from strong evaporite dissolution in Daotang, BHR and LS samples and from strong carbonate weathering in Hargai and Shaliu samples. Carbonate weathering is stronger than evaporite dissolution with weak silicate weathering in the Qinghai Lake catchment. Carbonate weathering, ion exchange reaction and precipitation are the major hydrogeochemical processes responsible for the solutes in the groundwater in the Qinghai Lake catchment. Most of the shallow groundwaters are suitable for drinking. More attention should be paid to the potential pollution of nitrate, chloride and sulfide in shallow groundwater in the future. [ABSTRACT FROM AUTHOR]

Hydrothermal processes and the regimes of frozen soil formed in alpine regions with glaciers and lake area are complex and important for ecological environment but have not been studied in Tibet. Based on soil temperature and moisture data from October 2005 to September 2006 collected in the Nam Co lake basin, Tibetan Plateau (TP), those questions were discussed. The mean annual air temperature was –3.4°C with 8 months below 0°C. Air and soil temperature varied between –25.3~13.1°C and –10.3~8.8°C, respectively. Soil moisture variations in the active layer were small with the minimum value of 1.4%, but were influenced greatly by snowmelt, rainfall and evaporation, varying up to 53.8%. The active layer froze later, thawed earlier and was thinner, however, the lower altitude limit of permafrost is higher than that in most areas of TP. The effects of soil moisture (unfrozen water content) on soil temperature, which were estimated through proposed models, were more significant near ground surface than the other layers. The surface soil temperature decreased with snowcover, the effect of cold snow meltwater infiltration on soil thermal conditions was negligible, however, the effect of rainfall infiltration was evident causing thermal disruptions. [ABSTRACT FROM AUTHOR]

The lake state and chemistry are sensitive to climate change at short timescales, but it is unclear how lake hydrochemistry responds to monsoonal climate, especially over glacial-interglacial cycles, owing to lack of well-dated and continuous sedimentary records. The types and geochemical compositions of authigenic carbonates from lacustrine sediments can be used to reconstruct past hydrochemistry. Yet, little is known about the significance and influencing factors of the Mg/Ca and Sr/Ca ratios of authigenic carbonates over glacial-interglacial cycles. Here, trace-element data of a 666 m long sediment sequence from the Heqing basin, a paleo-lake situated at the southeastern margin of the Tibetan Plateau, provide detailed glacial-interglacial hydrochemical conditions and their association with Indian summer monsoon (ISM) evolution during the entire Pleistocene. In interglacials, variation in both Mg/Ca and Sr/Ca ratios can serve as proxies for salinity as a result of precipitation of low-Mg calcite, constrained by enhanced ISM intensity and catchment weathering product. Instead, in glacials, high Mg/Ca and Sr/Ca ratios reflect high-Mg calcite and aragonite precipitation under low lake level conditions. There is a nonlinear response of the Sr/Ca ratio of lacustrine sediment to salinity variation when high-Mg calcite and aragonite precipitate in a hydrologically closed and evaporative lake. Based upon the sedimentary Sr/Ca and Mg/Ca ratios in the Heqing paleo-lake, the lake hydrochemistry during the Pleistocene experienced obvious glacial-interglacial ISM cycles at the life span of the lake itself: (1) in the old interval (2640–1840 ka), the salinity was low with cycles at the early stage of lake development owing to strong ISM; (2) in the middle interval (1840–920 ka), the lake was at a balance state and its salinity was more constrained by weathering solute, rather than ISM; and (3) in the young interval (920–130 ka), the salinity fluctuated with large amplitude over glacial-interglacial cycles and subsequent increase paced the weakened ISM. This study highlights the sensitivity of the types of lacustrine authigenic carbonates and lake chemistry to ISM changes over glacial-interglacial cycles. • In the monsoon-impacted areas, sedimentary Mg/Ca and Sr/Ca ratios controlled by ISM intensity and catchment weathering. • Mg/Ca ratios of lacustrine sediment reflect the types of authigenic carbonates over glacial-interglacial cycles. • Sr/Ca ratios of lacustrine sediment record salinity linearly in the interglacials, but nonlinearly in the glacials • Through time, lake hydrochemistry response to catchment weathering gradually decreased. [ABSTRACT FROM AUTHOR]

Abstract: Major ions, isotopic ratios of strontium (87Sr/86Sr), hydrogen (δD) and oxygen (δ18O) of groundwater samples were analyzed to decipher spatial variation, controlling factors, solute sources, and the recharge source of shallow groundwaters within the Lake Qinghai catchment. Shallow groundwaters in this area are slightly alkaline, with 97% being fresh water of good quality, though there are high concentrations of nitrate and sulfide in Buha and lakeside groundwaters. Most of the shallow groundwaters are of the Ca2+–HCO3 − type, whereas part of groundwaters surrounding the lake (LS) belongs to the Na+–Cl− type as lake water (QHL). Groundwater geochemistry is controlled by regional lithological association, ion exchange, and mineral precipitation. The dissolved Sr concentrations and 87Sr/86Sr ratios vary from 1.0 to 15.6 μmol/L, and from 0.709859 to 0.715779, respectively. The first quantitative calculation in groundwater using a forward model shows that 40% of dissolved Sr is from carbonate weathering, 33% from evaporite dissolution, 17% from silicate weathering, and the remainder from atmospheric input for the whole catchment. Carbonate weathering dominates groundwater geochemistry in Shaliu (SL), Hargai (HG) and Buha (BH) samples, while evaporite dissolution dominates LS and Daotang (DT) samples. δD and δ18O data show that rain water is the major recharge source of both river water and shallow groundwater within the Lake Qinghai catchment. Qinghai Lake water is characterized by Buha-type water, but its Sr geochemistry is different from the shallow groundwater due to carbonate precipitation. Although shallow groundwater contributes ∼5% of the dissolved Sr to the QHL, groundwater must be taken into account when the chemistry and budget of lake water are characterized. [Copyright &y& Elsevier]

Earthquakes cause widespread landslides that can increase erosional fluxes observed over years to decades. However, the impact of earthquakes on denudation over the longer timescales relevant to orogenic evolution remains elusive. Here we assess erosion associated with earthquake-triggered landslides in the Longmen Shan range at the eastern margin of the Tibetan Plateau. We use the M w 7.9 2008 Wenchuan and M w 6.6 2013 Lushan earthquakes to evaluate how seismicity contributes to the erosional budget from short timescales (annual to decadal, as recorded by sediment fluxes) to long timescales (kyr to Myr, from cosmogenic nuclides and low temperature thermochronology). Over this wide range of timescales, the highest rates of denudation in the Longmen Shan coincide spatially with the region of most intense landsliding during the Wenchuan earthquake. Across sixteen gauged river catchments, sediment flux-derived denudation rates following the Wenchuan earthquake are closely correlated with seismic ground motion and the associated volume of Wenchuan-triggered landslides ( r 2 > 0.6 ), and to a lesser extent with the frequency of high intensity runoff events ( r 2 = 0.36 ). To assess whether earthquake-induced landsliding can contribute importantly to denudation over longer timescales, we model the total volume of landslides triggered by earthquakes of various magnitudes over multiple earthquake cycles. We combine models that predict the volumes of landslides triggered by earthquakes, calibrated against the Wenchuan and Lushan events, with an earthquake magnitude–frequency distribution. The long-term, landslide-sustained “seismic erosion rate” is similar in magnitude to regional long-term denudation rates (∼0.5–1 mm yr −1 ). The similar magnitude and spatial coincidence suggest that earthquake-triggered landslides are a primary mechanism of long-term denudation in the frontal Longmen Shan. We propose that the location and intensity of seismogenic faulting can contribute to focused denudation along a high-relief plateau margin. [ABSTRACT FROM AUTHOR]

An understanding of topsoil geochemistry within a watershed helps to identify the influence of natural processes and anthropogenic activities in the environment. Fifteen elements were measured in 73 topsoil samples (top 30 cm) from the Lake Qinghai catchment, NE Qinghai–Tibetan Plateau (QTP) in 2009, to investigate geochemical patterns, identify possible sources and explore the implications of chemical weathering. Compared with their content in the upper continental crust (UCC), a deficit of Cu and Zn and an enrichment of Pb were identified in the study area. Enriched Ca levels were observed in alpine soil and pedocal, solonchak and aeolian sand soils, whereas there was a loss in hydromorphic and semi-hydromorphic soils. High Na in marsh solonchak indicated the possible presence of evaporites. Cluster analysis (CA) and principal component analysis (PCA) indicated the dominance of carbonate and the accumulation of P, possibly from grassland litterfall in topsoil. Some human activities have exerted an influence on virgin topsoil, as revealed by GIS mapping. The implications for chemical weathering, based on a chemical index of alteration ( CIA ) and an Al 2 O 3 –(CaO* + Na 2 O)–K 2 O (A–CN–K) diagram were characterised by a major carbonate control of the primary weathering stage under cold-dry climatic conditions with Ca and/or Na removal. [ABSTRACT FROM AUTHOR]