Sediments from Xinyun Lake in central Yunnan, southwest China, provide a record of environmental history since the Holocene. With the application of multi-proxy indicators (total organic carbon (TOC), total nitrogen (TN), δ13C and δ15N isotopes, C/N ratio, grain size, magnetic susceptibility (MS) and CaCO3 content), as well as accelerator mass spectrometry (AMS) 14C datings, four major climatic stages during the Holocene have been identified in Xingyun′s catchment. A marked increase in lacustrine palaeoproductivity occurred from 11.06 to 9.98 cal. ka BP, which likely resulted from an enhanced Asian southwest monsoon and warm-humid climate. Between 9.98 and 5.93 cal. ka BP, a gradually increased lake level might have reached the optimum water depth, causing a marked decline in coverage by aquatic plants and lake productivity of the lake. This was caused by strong Asian southwest monsoon, and coincided with the global Holocene Optimum. During the period of 5.60–1.35 cal. ka BP, it resulted in a warm and dry climate at this stage, which is comparable to the aridification of India during the mid- and late Holocene. The intensifying human activity and land-use in the lake catchment since the early Tang Dynasty (∼1.35 cal. ka BP) were associated with the ancient Dian culture within Xingyun's catchment. The extensive deforestation and development of agriculture in the lake catchment caused heavy soil loss. Our study clearly shows that long-term human activities and land-use change have strongly impacted the evolution of the lake environment and therefore modulated the sediment records of the regional climate in central Yunnan for more than one thousand years.
The Upper Cibolo Creek (UCC) karst watershed in Central Texas, USA, represents a portion of the drainage area that supplies water to the recharge zone for the Edwards Aquifer. However, the surface water–groundwater interactions along the UCC are not well quantified, and the hydraulic interactions are important for water budget and water quality of the aquifer. In this study, we investigated the evolution of hydrochemical and isotopic signatures (δ18O, δ2H and d-excess) from precipitation, surface water to groundwater in the UCC watershed from 2017 to 2019, and investigated surface water–groundwater interactions using samples from 14 creeks/spring sites. Factor analysis for the observed parameters demonstrates that changes in water hydrochemistry are primarily controlled by human activity, precipitation input, and water–rock interaction. Hierarchical clustering analysis of temporal isotope variations confirms that significant surface water–groundwater interactions occur in the UCC watershed. We identified relationships between nitrate concentrations at creek/spring sites and land-use conditions, and nitrate input sources were determined utilizing the dual-isotope analyses (δ15N and δ18O) of nitrate. This study provides capacity for a more precise assessment of water resources and water quality in Central Texas.
A series of analogs of n-fatty acid amide(n-FAA)have been identified in different late Quaternary sedimentary strata from northwest China by using the gas chromatography-mass spectrometry(GC-MS).Based on the carbon distribution as well as the characteristics of n-FAA and previous studies,we suggest that the n-FAA originates from biogenic sources rather than petrolic residues,or any other potential contaminant.By comparing the distribution of n-FAA in different paleo-lakes and loess strata,we propose that Ejina basin is one of the main source areas of Luochuan loess deposits.Alternatively,the relationship of the material source between the Qaidam Basin and Luochuan Loess deposit is low.The ratios of unsaturated to saturated n-FAA(UFAA)show trends comparable to that of the magnetic susceptibility and grain size variation within the loess,especially the lowest values associated with warm/humid episodes.This phenomenon indicates that the distribution of the n-FAA is influenced by early diagenetic processes,which are controlled by paleoclimatic variations.Our results highlight the variation within n-FAA,which is naturally formed in the physiology of different organisms.n-FAA can also record the paleoclimatic variation,similar to lipids,which originate from the constitutional unit of a cell membrane.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)