Xingyun Lake Research Articles

Water quality change and humanities driving force in Lake Xingyun, Yunnan Province

Water quality change and humanities driving force in Lake Xingyun, Yunnan Province

A probabilistic method to enhance understanding of nutrient limitation dynamics of phytoplankton

Determination of the limiting nutrient of phytoplankton is critical to the lake eutrophication management. The average value of total nitrogen/total phosphorus (TN/TP) ratio is widely used to determine the limiting nutrient; while it suffers from the risk of the incorrect description of data and neglecting dynamics of the nutrient limitation. A probabilistic method was thereby proposed in this study to explore dynamics of nutrient limitation, including (a) indicator definition as the probability of TN/TP ratio failing in Redfield ratio line (PFR), indicating the possibility of TN limitation, to improve a probabilistic measure for the nutrient limitation; (b) Bayesian ANOVA analysis for posterior distributions of different treatments; and (c) dynamics determination as PFRs to show dynamics of nutrient limitation. Lake Xingyun in Southwestern China was taken as a case to explore the interannual and seasonal dynamics of the nutrient limitation. According to modeling results, we deducted that (a) for the interannual dynamics, the limiting nutrient shifted from TP to TN; and (b) for the seasonal dynamics, TN and TP were co-limiting. Deductions were further confirmed by the observed data. With the proposed probabilistic method, the co-limitation of TN and TP was identified for the seasonal dynamics; while using the average ratio solely denied the possibility of co-limitation. The current study also revealed that, due to neglecting the interannual and seasonal dynamics of nutrient limitation, the average ratio might mislead the eutrophication management strategy by recommending reducing TN and TP concentration together. The proposed probabilistic method demonstrated that TN was the limiting nutrient during the growing season of the phytoplankton in recent years and actions should focus on the TN concentration reduction.

An 8,600 year lacustrine record of summer monsoon variability from Yunnan, China

Interactions between the Indian Summer Monsoon (ISM) and East Asian Summer Monsoon (EASM) are complex, yet needed to provide a long-term perspective of precipitation patterns in southeast Asia. Here we present an 8600-year sediment record from Xingyun Lake in Yunnan, China, a transitional zone that receives inputs of precipitation from both the ISM and EASM. Analysis of stable oxygen isotopes (δ18O) from authigenic calcite yields a semi-quantitative estimate of the timing and magnitude of lake level change that reflects changes in effective moisture from monsoon variability. Between 8600 and 6900 years BP, δ18O values are stable and low, indicating high lake levels and overflowing conditions resulting from a strong ISM. After 6900 years BP, δ18O values shift to higher values, which we suggest reflects a weakening of the ISM caused by declining summer insolation. The most substantial positive shift in isotopes occurs from 5000 to 4300 years BP and is coincident with aridity in India and the Tibetan Plateau. Other proxy records indicate increased ENSO variability and a southward shift in the ITCZ, which has an effect on the strength and onset of the ISM and may account for this change in hydrologic balance. After 4300 years BP, δ18O values continue to increase reflecting a gradual drying trend, but increases are smaller than prior periods, in part due to lake bathymetry that limits the potential for isotopic enrichment driven by evaporation. The relative influence of the ISM and EASM in the Yunnan Province of China during the Holocene remains a topic for future study, but our results suggest the predominance of the ISM and a possible connection to ENSO patterns on centennial to millennial timescales.

Biological responses to recent eutrophication and hydrologic changes in Xingyun Lake, southwest China

The synergistic influence of multiple environmental stressors on lake ecosystems has typically been evaluated paleolimnologically, through examination of a single biological indicator. Aquatic organisms, however, may display heterogeneous responses because of differences in their ecological sensitivity, and/or because of ecological consequences caused by strong interactions among multiple stressors. We applied paleolimnological methods to compare patterns of algal and invertebrate response to multiple stressors in a large, shallow lake in southwest China over the last two centuries. Our multi-proxy records show a clear trajectory of lake eutrophication (greater total nitrogen) and increasing lake productivity (greater sediment Chlorophyll-a concentration) during the last century. Nutrient enrichment and lake productivity played significant, but different roles, in structuring diatom and cladoceran assemblages, accounting for 31.4 and 77.3% of the total variance in the communities, respectively. Furthermore, there was a pronounced influx of the endemic diatom species Cyclotella rhomboideo-elliptica Skuja, which was strongly associated with the second axis of a diatom PCA (Principal Component Analysis). This occurred synchronously with a documented reversal of hydrological connectivity with a downstream, nutrient-poor lake during the early twentieth century, suggesting a role for species dispersal in modulating community reorganization. There are also strong differences between the two organism groups in their sensitivity to hydrological fluctuations, as hydrodynamics, indicated by sand content, was a significant driver for cladocerans (>25%), but showed only minor influence on diatom assemblages in our selection of minimum adequate models. The proportion of the total variance explained by our measured variables (<30%) was much lower for diatom assemblages than for both cladoceran assemblage and accumulation data (~77%), reflecting differences in community reorganization between the two biological indicators. The sediment-based evaluation of community responses revealed the differential impact of eutrophication and hydrological fluctuations on the biota of this large, shallow lake. Therefore, multiple biological indicators should be evaluated in limnological surveys to assess the full scope of ecological changes in highly stressed lake systems targeted for conservation or restoration.

Modern pollen assemblages in topsoil and surface sediments of the Xingyun Lake catchment, central Yunnan Plateau, China, and their implications for interpretation of the fossil pollen record

Modern pollen data from topsoils and surface lake sediments are commonly used as modern analogues and as climate calibration data for reconstructing vegetation and climate history from fossil pollen profiles. However, the potential differences and biases in pollen assemblages from these two sample types, as well as the processes of pollen sedimentation in lake basins, have received relatively little attention. Here we present the results of the analysis of modern pollen assemblages in 10 surface sediment samples and 25 topsoil samples from Xingyun Lake and its catchment, a shallow alpine lake site in the central Yunnan Plateau, southwest China. The modern pollen assemblages from both types of samples are mainly composed of Pinus, evergreen and deciduous oaks, Alnus, Poaceae, Artemisia, Brassicaceae and Amaranthaceae, and are consistent with the modern vegetation. Although the pollen assemblages of topsoil samples vary with the type of modern local vegetation, in general they are representative in term of the composition of the main pollen taxa, with some significant differences in the case of some vegetation types. With regard to the surface lake sediment samples, the pollen assemblages are relatively constant with no significant changes with sample location and water depth. The main pollen taxa are Pinus (around 40%), Alnus (around 18%) and Poaceae (around 11%), with relatively high percentages of evergreen and deciduous oaks, Betula (2–4%), and low percentages of Ulmus, Rosaceae, Corylus, Cupressaceae, Euphorbiaceae, Myrica and Elaeagnaceae. This composition is a good representation of the main types of catchment vegetation. The relative uniformity of the pollen assemblages from the lake surface samples may partly result from the effect of currents in redistributing the pollen input to the lake by rivers and wind. Therefore, we suggest that it is better to use pollen data from surface lake sediments, rather than from topsoils from the lake catchment, for interpreting fossil pollen assemblages of lake sediment cores. Our results indicate that the pollen assemblages in a sediment core from any part of Xingyun Lake are likely to provide a reliable record of the regional vegetation history and thus climatic change. Our modern pollen results, together with modern pollen data from other surface lake sediment samples along a large altitudinal gradient from Yunnan to southwest Sichuan Province, were used to reanalyze fossil pollen assemblages during the Last Glaciation period at Xingyun Lake. The results show that the vertical vegetation belts decreased in altitude from late Marine Isotope Stage 3 (late MIS3) to the Last Glacial Maximum (LGM) and then increased during the Last Deglaciation.

MNDWI和NDWI指数提取富营养化湖泊水体边界的对比研究

本研究基于Landsat 8 OLI卫星影像，采用云南省中部地区的5个湖泊，即滇池、抚仙湖、阳宗海、星云湖和杞麓湖作为研究对象，其中滇池、星云湖、杞麓湖是富营养化湖泊，比较了两种水体指数，NDWI和MNDWI提取湖泊水体边界的精确度。结果表明：由于近红外波段能够较好的区分植被和水体，但也带来了藻类覆盖的水域容易被误识别为植被的情况。因此，采用NDWI提取的富营养化湖泊水体面积比实际值偏小，中红外波段对水分含量较为敏感，在富营养化湖泊中采用该指数可以有效的区分陆地和水体，排除藻类的干扰。因此，MNDWI更适合用于富营养化湖泊的水体边界提取。 This study is based on the Landsat 8 OLI satellite images, and uses 5 lakes as sample, which are Dianchi Lake, Fuxian Lake, Yangzonghai Lake, Xingyun Lake and Qilu Lake, there are all located in the central region of Yunnan province, and Dianchi Lake, Xingyun Lake, Qilu Lake are eutrophic lakes. The accuracy of NDWI and MNDWI index for lake water boundary extraction was compared. The results show that the near infrared band can distinguish vegetation and water body better. But it has also brought the algae covered waters that can be mistakenly identified as vegetation. Therefore, the water area of eutrophic lake extracted by NDWI is smaller than the actual value. The infrared band is more sensitive to moisture content. Using this index in eutrophic lakes can effectively distinguish between land and water, eliminate algal interference. Therefore, the MNDWI index is more suitable for water boundary extraction in eutrophic lakes.

星云湖季节性水质变化及影响因素

依据实地监测数据，本文分别对旱季和雨季末星云湖水体在垂向和空间分布上的水质变化特征进行了分析，探讨了季节性水量变化对星云湖水质的影响。监测结果显示：星云湖丰水期水质空间差异较小，枯水期水质空间差异较大，主要表现在丰水期溶解氧含量高于枯水期。同时，丰水期水体的比电导明显高于枯水期。星云湖水体的pH值在8.9~9.4之间变化，且有枯水期高于丰水期的特征。在垂向上，星云湖丰水期水温、pH值与溶解氧含量具有相似变化趋势，整体上均随深度的增加而呈现下降的变化，这可能与浮游藻类的呼吸作用有关；丰水期水体中叶绿素含量在整个湖泊较低且趋于一致，而枯水期具有由表层向下增高的变化。营养盐分析结果显示，丰水期的总磷(TP)含量平均为0.43~0.48 mg/L，枯水期平均为0.29~0.39 mg/L；而丰水期的总氮(TN)含量平均为2.1557~2.5225 mg/L，枯水期1.9388~2.875 mg/L，指示丰水期河流物质输入作用明显增加，人类活动影响明显增强。计算分析结果显示，星云湖水体全湖全年为重富营养水平，且具有枯水期水质富营养水平南部 >中部 > 北部水体、底层 > 中层 > 表层水体、丰水期北部 > 南部 > 中部水体，中层 > 底层 > 表层水体的特点。认识这些特点及时空变化规律，对于有的放矢、高效的开展星云湖富营养化治理具有一定的指导作用。 Based on field monitoring data, the characteristics of water quality changes, in both vertical and spatial distributions in the end of dry and wet seasons in Xingyun Lake were analyzed. The monitoring data shows that the water temperature has seasonal changes and on the vertical profile, the water temperature almost always below 1 m in depth. In wet season, the lake water mixture condition enhanced, and the water quality shows slight changes in spatial pattern, but it displays a significant difference in dry season. In vertical profile, the pH value of lake water shows a high uniformity from the surface to 7 m in depth, with an average value of 8.9~9.4. And it shows that a higher value in wet than in dry season. The chlorophyll content in Xingyun Lake shows a weak seasonal change in wet season, but the content increases with the increasing of water depth in dry season. The dissolved oxygen content is higher in wet season than that in dry season. The SpCond is significantly higher in wet season than that in dry season. We found that the water temperature, pH value and dissolved oxygen content possess a similar change tendency in vertical profile. Our analysis results reveal that the average TP content in the wet season is 0.43~0.48 mg/L, while that in dry season is 0.29~0.39 mg/L. The average TN content is 2.16~2.52 mg/L in wet seasons, and 1.94~2.88 mg/L in dry seasons, showing the TP and TN input increased significantly in the wet season. The calculation results demonstrated that the whole lake possess a heavy nutrient level, and the nutrient level distribute a pattern of in the south > in the central > in the north, the bottom > the surface > the middle in dry season, and the north > the south > the central, the middle > the bottom > the surface in wet season.

Characterization and sources of sedimentary organic matter in Xingyun Lake, Jiangchuan, Yunnan, China

Xingyun Lake plays a particularly important role in the retention and processing of organic matter in Yuxi City, China. In this study, geochemical analyses (grain size, OC, N, δ13C) were carried out. The April 2014 sediment was finer than the October 2013 sediment. OC content was in the range of 1.07–2.68 % showing a increasing OC content with decreasing percent sand from the October 2013 sediment to the April 2014 sediment. TN distribution in surface sediments followed a similar distribution and was commonly correlated with OC. The correlation of δ13C values and N/C ratios in sediment reflected a mixing of soil-derived and terrestrial organic matters. The Ali/Aro ratios from the solid-state 13C-NMR spectra exhibited more aliphaticity for April 2014 sediments. The isotopic analyses on the fatty acids of sediments from twenty sampling stations in Xingyun Lake indicated that terrigenous components can be assigned as the major sources of the organic matters in the lake sediments. The low yields in lignin in sediment pointed to nontypical terrigenous inputs to the lake sediments. Ratios of p-hydroxyacetophenone to p-hydroxyl phenols (Pon/P) in the surface sediments (0.08–0.22) over the all sampling stations in Xingyun Lake further demonstrated a contribution from soil-derived organic matters. It was observed a plot of the ratio of S/V versus C/V exhibited an organic input attributed to angiosperm nonwoods. The reworking of surficial sediments may result in a difference in organic input between the October 2013 sediment and the April 2014 sediment. Furthermore, the associated ratios of (Ad/Al)v, P/(V + S) in sediment indicated that the April 2014 sediments had experienced the lower degree of oxidation of lignin than the October 2013 sediments. This can be attributed to the higher fine particle content in the former sediments protecting organic matter than in the latter sediments, as revealed by the lower alkyl C/O–alkyl C ratio (A/O–A) in solid-state 13C NMR spectra of April 2014 samples.

A preliminary investigation of relationship between modern &amp;lt;italic&amp;gt;Pediastrum&amp;lt;/italic&amp;gt; and the level of Xingyun Lake, central Yunnan, and its implications for the interpretation of the fossil record

Fossil Pediastrum is frequently found in Quaternary lacustrine deposits and has attracted much attention because it can be well preserved and easily identified. However its palaeoenvironmental significance is unclear. Several studies suggest that the occurrence of a large amount of Pediastrum indicates a gradually decreasing lake-level, while others point out that Pediastrum mainly occurs in the deep areas of lakes. Thus clarifying the relationship between Pediastrum and lake levels is of great importance for improving the reliability of palaeoenviromental reconstruction. In this study, we investigated the occurrence of Pediastrum in Xingyun Lake, a semi-enclosed shallow fault and eutrophic lake located in central Yunnan Province, southwest China. We obtained 4 lake surface water samples at water depths of 4, 4.5, 5.2 and 6.5 m; 16 water samples collected at various depths within the water column at the deepest part of the lake; and 10 lake surface sediment samples taken at different water depths from the lake shore to the deepest part using a Grab sampler. We present the results of Pediastrum analysis of samples of both the lake water and surface sediments of Xingyun Lake and discuss the relationship between the Pediastrum distribution and the lake-level/water depth. The variation of the fossil records during the past 3000 years is also reported. The results show that two types of Pediastrum were identified in the water and lake sediment samples, including Pediastrum boryanum and Pediastrum simplex . The concentration of Pediastrum in the water samples is extremely low, varying from 2 to 6 grains mL - 1. Spatially, the concentrations of Pediastrum in the surface lake water samples exhibit little change with increasing water depth. In terms of the depth variation within the water column in the deepest part of the lake, the Pediastrum concentration of the bottom sample is the highest, which may be related to the effects of resuspension and redeposition of lake sediments caused by wind-induced turbulence in shallow water. With respect to the lake surface sediment samples, the Pediastrum content is relatively high. The concentration of Pediastrum varies from 60700 to 104000 grains g - 1, with an average of 81000 grains g - 1; and the relative percentage abundance ranges from 66%–80%, averaging around 76%. Interestingly, both the concentration and percentage content of Pediastrum in these samples exhibit no significant relationship with water depth. Based on comparison of the results from Xingyun Lake with those of other workers, we conclude that the relationship between the Pediastrum distribution and water depth inferred from the lake sediments of several relatively larger lakes mentioned in previous studies may be caused by depositional processes: turbulence resulting from wave activity in these larger lakes could result in the resuspension of Pediastrum in shallow water and its focusing into deeper areas. However, whether or not there is a large quantity of Pediastrum living in the lake water may be related to the physicochemical status of the lake water, determined by factors such as the river input, nutrient level, temperature, pH and salinity. In addition, these factors may vary between different lakes in different regions. Therefore, the variation of Pediastrum content cannot be used as an indicator of water depth or lake-level without careful consideration of these factors. In addition, it needs to be used in the context of multi-proxy studies. Both the percentage and the concentration of fossil Pediastrum in the sediments of Xingyun Lake exhibit distinct features over the last 3000 years: very low values before 2000 cal a BP followed by a rising trend, and then an abrupt increase after 1500 cal a BP. This is consistent with variations in the intensity of human activity revealed by frequent high-amplitude fluctuations in mean grain-size and by an abrupt increase in magnetic susceptibility. In addition, the abrupt changes in fossil Pediastrum in Xingyun Lake precede those of mean grain-size and magnetic susceptibility, suggesting that the Pediastrum from the Xingyun Lake sediments may be a sensitive indicator of the process of lake water eutrophication caused by human activities.

星云湖硅藻群落响应近现代人类活动与气候变化的过程

星云湖硅藻群落响应近现代人类活动与气候变化的过程

Changes in the radiocarbon reservoir age in Lake Xingyun, Southwestern China during the Holocene.

Chronology is a necessary component of paleoclimatology. Radiocarbon dating plays a central role in determining the ages of geological samples younger than ca. 50 ka BP. However, there are many limitations for its application, including radiocarbon reservoir effects, which may cause incorrect chronology in many lakes. Here we demonstrate temporal changes in the radiocarbon reservoir age of Lake Xingyun, Southwestern China, where radiocarbon ages based on bulk organic matter have been reported in previous studies. Our new radiocarbon ages, determined from terrestrial plant macrofossils suggest that the radiocarbon reservoir age changed from 960 to 2200 years during the last 8500 cal a BP years. These changes to the reservoir effect were associated with inputs from either pre-aged organic carbon or 14C-depleted hard water in Lake Xingyun caused by hydrological change in the lake system. The radiocarbon reservoir age may in return be a good indicator for the carbon source in lake ecosystems and depositional environment.

Hydrological and ecosystem response to abrupt changes in the Indian monsoon during the last glacial, as recorded by sediments from Xingyun Lake, Yunnan, China

The Indian Summer Monsoon (ISM) is the major moisture source of precipitation in southwest China and plays an important role in regional environmental change and in economic and social development, since abrupt changes of the ISM can cause crop failures and flooding that impact the livelihood of a large population. However, with the exception of speleothem records, abrupt changes of the ISM during the last glacial are not well documented in terrestrial records. Here we present a sediment record from Xingyun Lake in Yunnan Province, southwest China, spanning the interval 36.4kaBP to 13.4kaBP (1ka=1000cala) which documents the occurrence of a series of millennial-scale episodes which may reflect the abrupt weakening of the ISM. Seven AMS 14C dates from terrestrial wood fragments provide a robust chronology. The results demonstrate that increases in the coarse sediment fraction (>30μm) correspond to increases in the concentration of Pediastrum, the grain size of magnetic minerals, carbonate content and C/N ratios, which together indicate episodes of low lake level. In addition, pollen analysis indicates that Quercus (oak) increased and that ferns decreased during intervals of abrupt weakening of the ISM, indicating a drier environment. Nine abrupt shifts to a low lake level are documented for the studied interval and three of them are correlative with Heinrich events 1 to 3. Our study supports the hypothesis that, in response to the cold events in the North Atlantic associated with massive iceberg influxes and the corresponding slowing down of Atlantic meridional overturning circulation, the mean latitudinal extent of the ITCZ shifted southwards. As a result of an atmospheric teleconnection there was a corresponding decrease in precipitation associated with ISM precipitation, which caused reduced fluvial runoff in Yunnan.

抚仙湖和星云湖水质变化趋势分析

国内有关抚仙湖及星云湖的水环境指标的成文调查研究始于1963年。但2008年抚仙湖—星云湖倒流之后的研究几乎空白，对两湖联动机制研究也较少。本文结合1957~2009年的气象数据和两湖水质参数，分析湖泊对全球气候变化的响应，同时探究两者联动影响机制及其空间差异。发现近半个世纪以来，温度有明显的波动上升，降水量有轻微的波动下降趋势，相比夏季，冬季对全球气候的变化有更敏感的响应，云南高原湖泊的抚仙湖和星云湖正向着不利于湖泊良性循环的方向发展；抚仙湖和星云湖均存在时空异质性，受人类活动比较小的地区，水质较好，星云湖东岸水质好于西岸水质；在各项指标中，星云湖几乎均高于抚仙湖，其中，星云湖的电导率(Spcond)约是抚仙湖的2倍，星云湖的藻蓝蛋白约是抚仙湖的21倍，但抚仙湖和星云湖的PH值均偏高。 The domestic written research on water environment of Lake Fuxian & Lake Xingyun has begun since 1963. But after 2008, the research on Lake Fuxian & Lake Xingyun is almost blank, and the research on the linkage mechanism between the two lakes is also insufficient. Based on the me-teorological data from 1957 to 2009 and on the water quality parameters, this paper analyses the situation of lakes in response to global climate change, at the same time explores the mechanism of influence and its spatial difference. It is found that in nearly half a century, the temperature fluctuations increase markedly, and the precipitation fluctuation decline slightly. Compared with summer, the two lakes have more sensitive response to global climate change in winter. Lake Fuxian & Lake Xingyun of Yunnan plateau are developing in the direction unfavorable to a virtuous cycle; Lake Fuxian & Lake Xingyun both have spatio-temporal heterogeneity and areas less affected by human activity. The water quality is relatively good, and the water quality on the east side of Lake Xingyun is better than that in the west; almost all the indicators of Lake Xingyun are higher than those of Lake Fuxian. The conductivity (Spcond) of Lake Xingyun is about twice of Lake Fuxian. The Cynobacteria of Lake Xingyun is about 21 times of Lake Fuxian. However, the PH values of Lake Fuxian & Lake Xingyun are both on the high side.

Changing intensity of human activity over the last 2,000 years recorded by the magnetic characteristics of sediments from Xingyun Lake, Yunnan, China

We report mineral magnetic measurements (magnetic susceptibility, anhysteretic and isothermal remanence, magnetic hysteresis and thermomagnetic properties) from a 2.46-m-long sediment core taken in Xingyun Lake, Yunnan, China. Results demonstrate that magnetic minerals in the lake sediment are dominated by stable single-domain (SSD) ferrimagnetic minerals derived mainly from in-washed catchment soil. Magnetic susceptibility increases sharply during the period AD ~500–1050, and the grain size of magnetic minerals decreases. These changes are accompanied by increases in the concentrations of Fe, Ti, Zr and Si, and by decreased tree pollen percentages. δ18O measures in speleothems from South China demonstrate that climate was relatively uniform during this interval. Documentary evidence, however, indicates a large increase in the human population of Yunnan Province at that time. We conclude that the late Holocene sediment record from Xingyun Lake reflects a dramatic increase in soil erosion that was caused by a growing human population, which in turn was responsible for increased deforestation and agricultural activity. Our results from Xingyun Lake are consistent with sediment magnetic records from Erhai Lake, located near our study site. We therefore conclude that the interval AD ~500–1050 corresponded to a regional-scale increase in the intensity of human activity on the Yunnan-Guizhou Plateau.

Holocene vegetation history, precipitation changes and Indian Summer Monsoon evolution documented from sediments of Xingyun Lake, south‐west China

ABSTRACTWe present a pollen‐based precipitation reconstruction and multi‐proxy records from a 485‐cm‐long sequence from a sediment core from Xingyun Lake, Yunnan Plateau, south‐west China, which depicts the evolution of the Indian Summer Monsoon (ISM) during the last 8500 years. Pollen and other palaeoenvironmental records document several stages of vegetation history and climate change. The warmest and wettest climate in the Xingyun Lake catchment occurred before 5500 cal a BP, and subsequently the climate became gradually drier. After 2000 cal a BP the regional environmental conditions became unstable, and a wet Medieval Warm Period is probably recorded. Our reconstruction of the ISM is similar to that portrayed by Holocene speleothem δ18O records from southern China, but is distinctly different from the East Asian Summer Monsoon (EASM) evolution, which features a mid‐Holocene maximum. Our results support the hypothesis that the ISM and EASM evolved asynchronously during the Holocene, and imply that the Chinese speleothem δ18O records from southern China may principally reflect changes in moisture source from the Indian monsoon domain, and thus record the history of the ISM rather than the EASM.

Lake sediment records on climate change and human activities in the Xingyun Lake catchment, SW China.

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.

Rapid environmental change during dynastic transitions in Yunnan Province, China

Pollution and eutrophication of Chinese lakes are widely perceived to be 20th century phenomena. However, China has a long history of deforestation, agriculture, mineral resource extraction, and other anthropogenic activities that impact the environment. Here, we present a sediment record from Xing Yun Lake in the Yunnan Province of China that reveals significant alterations to the lake, its ecosystem, and its watershed beginning as early as 500 AD. A comprehensive suite of biogeochemical and isotopic proxies reveal several rapid transitions related to changes in agriculture and lake-level management that coincides with cultural and dynastic transitions. The deterioration of contemporary environmental conditions at Xing Yun arises from a long history of anthropogenic manipulation, eutrophication, and pollution of the lake and its watershed. This study highlights the importance of using historical records of industrial and agricultural activities, including landscape modification, in conjunction with records of climate change, to place present day environmental concerns into a long-term context.

Vegetation history, climatic changes and Indian summer monsoon evolution during the Last Glaciation (36,400–13,400 cal yr BP) documented by sediments from Xingyun Lake, Yunnan, China

We obtained a 9.74-m-long sediment core (XY08A) from Xingyun Lake in central Yunnan Province, southwest China, and used AMS radiocarbon dating of terrestrial plant macrofossils to provide a chronology. Here we present the results of pollen and grain size analyses of the interval ~36,400–13,400calyr BP and discuss the vegetation history, and record of climate change associated with the evolution of the Indian summer monsoon (ISM). Three stages of regional vegetation change are documented: (i) During the late Marine Isotope Stage 3 (36,400–29,200calyr BP), the study region was occupied by mixed coniferous and evergreen broad-leaved forest dominated by Pinus and evergreen Quercus, with Tsuga, Abies/Picea growing on the surrounding mountains. (ii) During the Last Glacial Maximum (LGM, 29,200–17,600calyr BP), cold-temperate coniferous forest dominated by species of Abies/Picea expanded and reached a maximum extent; and at the same time, the extent of evergreen broadleaved forest increased. (iii) From 17,600 to 13,400calyr BP the hemlock forest and Abies/Picea forest began to decline until they disappeared completely in the early phase of the Last Deglaciation, while pine forest and evergreen broadleaved forest dominated the surrounding areas. The vegetation history indicates a generally drying climate from 36,400 to 13,400calyr BP, suggesting a gradual weakening of the ISM with the weakest ISM influence occurring during the early part of the Last Deglaciation, when the climate was the driest. The regional temperature first decreased intermittently and then increased gradually, being mild and wet during the late MIS3 stage followed by the coldest but not the driest climate during the LGM when the temperature was at least 3˚C lower than at present.

Phosphate-solubilizing capability of microbes in the sediments from different pollution sources in Lake Fuxian

以云南抚仙湖为研究对象,分析了不同污染来源沉积物微生物量、碱性磷酸酶活性(APA)和微生物解磷能力的垂向分布特征和水平分布特征.结果表明,抚仙湖各采样点沉积物微生物生物量与APA垂向分布趋势相似,总体上随着深度增加逐渐降低,微生物作用主要表现在表层.在空间分布上,富营养化星云湖以泄水为主的南岸隔河口微生物生物量和APA最高,其次为以农业面源污染为主的北岸梁王河口和以磷矿开发为污染来源的北岸东大河口,再次为受人类活动影响较小、以自生有机污染为主的湖心和东岸老凹嘴,以自然水土流失为主的西岸尖山河口微生物生物量和APA最低.沉积物微生物生物量和APA体现了不同外源污染对抚仙湖各湖区的影响不同.抚仙湖沉积物微生物对有机磷和无机磷均有解磷能力,并且无机磷解磷能力大于有机磷.沉积物解无机磷细菌数量和APA决定了抚仙湖沉积物磷释放强度,造成了抚仙湖较高强度的内源磷污染负荷.;The vertical variations of microbial biomass, alkaline phosphatase activity (APA) and phosphate-solubilizing ability of microbes were studied in the sediments from different pollution sources in Lake Fuxian, Yunnan Province. The results showed that the microbial biomass and the APA in the sediment cores generally decreased with the depth and the strongest microbial activity was shown in the surface sediment. The microbial biomass and the APA in the sediments of the mouth of Gehe River in the south shore were the highest among the research sites, which was heavily polluted by the discharge from eutrophic Lake Xingyun. The second highest amounts of the microbial biomass and the APA were found in the sediments of the mouth of Liangwan River with agriculture pollution source and the sediments in the mouth of Dongda River with phosphate mining pollution source. However, the lowest amounts of the microbial biomass and the APA were shown in the sediments of the mouth of Jianshan River with the pollution source of soil erosion. The result of incubation experiment showed that the microbes in the sediments had stronger phosphate-solubilizing ability to dissolve inorganic phosphate than to dissolve organic phosphate. The combination of the amount of inorganic phosphate solubilizing bacteria and the APA determined the potential of phosphorus releasing from sediment, which resulted in high interior phosphorus loading in Lake Fuxian.

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofuran concentrations in Xingyun Lake sediment close to the pulp mill region of Jiangchuan (China): a typical case study

Sediment cores from Xingyun Lake close to the pulp mill region of Jiangchuan (China), earlier found to be highly contaminated by pulping at least from the 1990s, were analyzed by HRGC/HRMS for the concentrations of 17 polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). Regarding the contribution of individual congeners, PCDD/F levels ranged from ND (non-detectable) to 82.05 pg g(-1) dw (from ND to 0.16 pg WHO-TEQ g(-1) dw) in 0-20 cm of sediment and from ND to 45.61 pg g(-1) dw (from ND to 0.67 WHO-TEQ g(-1) dw) in 20-40 cm of sediment for 17 PCDD/Fs (WHO-TEQ: WHO-endorsed toxic equivalents). Major PCDD/Fs identified and confirmed were high-chlorinated congeners including OCDD/Fs and HpCDD/Fs in the two depths. For high-chlorinated PCDD/Fs such as O, Hp-CDD/Fs across the depth of sediment, sediment had a higher proportion in 0-20 cm than that in 20-40 cm. On the contrary, for low-chlorinated PCDD/Fs such as T, Pe, Hx-CDD/Fs, the lower proportion was found in 0-20 cm. The results demonstrated that PCDD/Fs loads in the sediment of Xingyun Lake were very low compared to loads in the other regions about 8 years after closedown of a majority of pulp production with chlorine, which indicated that pulp production was an important emission source of dioxins.