Variations in rare earth elements with environmental factors in lake surface sediments from 17 lakes in western China

Numerous lakes in western China are excellent sites for understanding environmental change.However,what dominates rare earth element(REE) variations are still under debate in the lake environmental research.In this study,we selected 28 surface sediment samples from 17 lakes(i.e.largescale lakes,small water bodies,etc.) in the QinghaiTibet Plateau and Xinjiang area.These samples were analyzed to reveal the behavior of the REEs and major elements.These REE patterns are characterized by light rare earth element(LREE) enrichment,weak Ce anomaly(0.84-0.98,0.94 on average) and negative Eu anomaly(0.53-1.00,0.67 on average).The homogeneous REE patterns may reflect similar REE of the source lithologys.However,the REE abundances showed some significant differences.In this study,water chemistry data analyses inferred that the highly REE values appear possibly in the saltwater lake,and also related to carbonate mineral,whereas p H played a minor role in REE concentrations.In large-scale lakes(e.g.Lake Bosten and Lake Ulungur),the results showed that the relatively larger REE values are in the margins of lakes.Moreover,lower REE contents are towards the central region.Comprehensive study suggested that five major factors control the REE contents:(1) The REE tends to increase with the increase of the weathering intensity.(2) Likewise,heavy mineral(i.e.rutile,anatase,zircon,etc.) are probably primary in these sediments because they are highly enriched in the REE.(3) The contribution of Fe-Mn oxides is significant in sediments because their concentrations highly correlate with the REE.(4) The carbonate mineral(mainly calcite) played a significant role on the REE values in the lakes because the REEs are incorporated into the carbonate minerals generating the low REE concentrations.(5) Major element analysis,mineral analysis,and grain-size data analysis showed that the REE distribution is chiefly influenced by finer grain-size component of lake sediments due to the decreasing proportion of quartz and feldspar than coarser one.Moreover,the clay minerals in finer grain-size sediments can highly absorb the REE.

Investigation of Adsorption Rates of Pb, Cd, Cu, Co and Ni to Fresh-water Surface Coatings Developed in Nanhu Lake

The adsorption kinetics of five heavy metals onto the natural surface coatings, which were collected in the Nanhu Lake in Changchun, Jilin Province, China, were investigated for the purpose of giving some explanations for the mechanisms of heavy metal adsorption onto the surface coatings with initial metal ions of 5 μmol/L. The results show that firstly, the adsorption of heavy metals onto the surface coatings follows the first order kinetics; secondly, the double-constant rate equation is suitable to describing the adsorption of heavy metals selected onto the natural aquatic surface coatings, following the order K_ Cu>K_ Pb>K_ Co>K_ Ni>K_ Cd; thirdly, there is a significant correlation between the adsorption rate and the physical and chemical characteristics of heavy metals, such as E 0, Δ_fH 0_m, and Δ_fG 0_m based on the linear regression analysis.

Influences of environmental factors on the modern 14C reservoir effects in Qinghai-Tibet Plateau lakes

The establishment of reliable age in the lake sediment profile mainly depends on the AMS 14C dating technique.However,the presence of the 14C lake reservoir effects(LREs)restricted for using radiocarbon dating in lake sediment,especially in dry and cold areas with a scarce plant cover in the Qinghai-Tibet Plateau.Hence,the discussion of influence factors of LREs is crucial.This paper selected 15 lakes(17 sediment and 3 plant samples)in the Qinghai-Tibet Plateau to examine the distribution characteristics of the modern LREs and their main influencing factors.In our study area,14 lakes were all affected by the LREs.The minimum 14C year is 5900 a BP towards the deep water area,whereas the maximum 14C year is up to 7185 a BP in the margins of Lake Heihai.The maximum 14C year is up to 7750 a BP,and the minimum 14C year is present-day carbon in the 15 lakes.One further study indicated that the LRE differences in individual lake are mostly owing to the contribution of exogenous carbonate.The results displayed that the LREs tended to increase with the increase of the salinity,moreover,the LREs of saltwater lakes or salt lakes were significantly larger than freshwater lakes due to the possible supply of old total dissolved inorganic carbon with a long residence time in the lakes.Moreover,the contribution of calcite played a significant role on the LREs.Additionally,the LREs differences are affected by the source of organic matter.The lake with groundwater supply shows large LRE due to likely being influenced by crustal and ancient CO_(2) uprising.

Phosphorus losses via surface runoff in rice-wheat cropping systems as impacted by rainfall regimes and fertilizer applications

Phosphorus（P） losses from agricultural soils contribute to eutrophication of surface waters. This field plot study investigated effects of rainfall regimes and P applications on P loss by surface runoff from rice（Oryza sativa L.） and wheat（Triticum aestivum L.） cropping systems in Lake Taihu region, China. The study was conducted on two types of paddy soils（Hydromorphic at Anzhen site, Wuxi City, and Degleyed at Xinzhuang site, Changshu City, Jiangsu Province） with different P status, and it covered 3 years with low, high and normal rainfall regimes. Four rates of mineral P fertilizer, i.e., no P（control）, 30 kg P ha^（–1） for rice and 20 kg P ha^（–1） for wheat（P_（30＋20））, 75 plus 40（P_（75＋40））, and 150 plus 80（P_（150＋80））, were applied as treatments. Runoff water from individual plots and runoff events was recorded and analyzed for total P and dissolved reactive P concentrations. Losses of total P and dissolved reactive P significantly increased with rainfall depth and P rates（P〈0.0001）. Annual total P losses ranged from 0.36–0.92 kg ha^–1 in control to 1.13–4.67 kg ha^–1 in P150＋80 at Anzhen, and correspondingly from 0.36–0.48 kg h^–1 to 1.26–1.88 kg ha^–1 at Xinzhuang, with 16–49% of total P as dissolved reactive P. In particular, large amounts of P were lost during heavy rainfall events that occurred shortly after P applications at Anzhen. On average of all P treatments, rice growing season constituted 37–86% of annual total P loss at Anzhen and 28–44% of that at Xinzhuang. In both crop seasons, P concentrations peaked in the first runoff events and decreased with time. During rice growing season, runoff P concentrations positively correlated（P〈0.0001） with P concentrations in field ponding water that was intentionally enclosed by construction of field bund. The relative high P loss during wheat growing season at Xinzhuang was due to high soil P status. In conclusion, P should be applied at rates balancing crop removal（20–30 kg P ha^–1 in this study） and at time excluding heavy rains. Moreover, irrigation and drainage water should be appropriately managed to reduce runoff P losses from rice-wheat cropping systems.

A general multi-objective programming model for minimum ecological flow or water level of inland water bodies

Assessment of ecological flow or water level for water bodies is important for the protection of de- graded or degrading ecosystems caused by water shortage in arid regions, and it has become a key issue in water resources planning. In the past several decades, many methods have been proposed to assess ecological flow for rivers and ecological water level for lakes or wetlands. To balance water uses by human and ecosystems, we proposed a general multi-objective programming model to determine minimum ecological flow or water level for inland water bodies, where two objectives are water index for human and habitat index for ecosystems, respectively Using the weighted sum method for multi-objective optimization, minimum ecological flow or water level can be determined from the breakpoint in the water index-habitat index curve, which is similar to the slope method to de- termine minimum ecological flow from wetted perimeter-discharge curve. However, the general multi-objective programming model is superior to the slope method in its physical meaning and calculation method. This model provides a general analysis method for ecological water uses of different inland water bodies, and can be used to define minimum ecological flow or water level by choosing appropriate water and habitat indices. Several com- monly used flow or water level assessment methods were found to be special cases of the general model, including the wetted perimeter method and the multi-objective physical habitat simulation method for ecological river flow, the inundated forest width method for regeneration flow of floodplain forest and the lake surface area method for eco- logical lake level. These methods were applied to determine minimum ecological flow or water level for two repre- sentative rivers and a lake in northern Xinjiang of China, including minimum ecological flow for the Ertix River, minimum regeneration flow for floodplain forest along the midstream of Kaxgar River, and minimum ecological lake level for the Ebinur Lake. The results illustrated the versatility of the general model, and can provide references for water resources planning and ecosystem protection for these rivers and lake.

Potential and limitations of satellite laser altimetry for monitoring water surface dynamics:ICESat for US lakes

Elevation measurements from the Ice,Cloud and Land Elevation Satellite(ICESat)have been applied to monitor dynamics of lakes and other surface water bodies.Despite such potential,the true utility of ICEsat--more generally,satellite laser altimetry--for continuously tracking surface water dynamics over time has not been adequately assessed,especially in the continental or global contexts.This study analyzed elevation derived from ICESat data for the conterminous United States and examined the potential and limitations of satellite laser altimetry in monitoring the water level dynamics.Owing to a lack of spatially-explicit ground-based water-level data,the high-fidelity land elevation data acquired by airborne lidar were firstly resorted to quantify ICESat’s ranging accuracy.Trend and frequency analyses were then performed to evaluate how reliably ICESat could capture water-level dynamics over a range of temporal scales,as compared to in-situ gauge measurements.The analytical results showed that ICESat had a vertical ranging error of 0.16 m at the footprint level-an lower limit on the detectable range of water-level dynamics.The sparsity of data over time was identified as a major factor limiting the use of ICESat for water dynamics studies.Of all the US lakes,only 361 had reliable ICESat measurements for more than two flight passes.Even for those lakes with sufficient temporal coverage,ICESat failed to capture the true interannual water-level dynamics in 32%of the cases.Our frequency analysis suggested that even with a repeat cycle of two months,ICESat could capture only 60%of the variations in water-level dynamics for at most 34%of the US lakes.To capture 60%of the water-level variation for most of the US lakes,a weekly repeated cycle(e.g.,less than 5 d)is needed-a requirement difficult to meet in current designs of spaceborne laser altimetry.Overall,the results highlight that current or near-future satellite laser missions,though with high ranging accuracies,are unlikely to fulfill the general needs in remotely monitoring water surface dynamics for lakes or reservoirs.

Modern pollen assemblages of the surface lake sediments from the steppe and desert zones of the Tibetan Plateau

Modern pollen analysis is the basis for revealing the palaeovegetation and palaeoclimate changes from fossil pollen spectra.Many studies pertaining to the modern pollen assemblages on the Tibetan Plateau have been conducted,but little attention has been paid to pollen assemblages of surface lake sediments.In this study,modern pollen assemblages of surface lake sediments from 34 lakes in the steppe and desert zones of the Tibetan Plateau are investigated and results indicate that the two vegetation zones are dominated by non-arboreal pollen taxa and show distinctive characteristics.The pollen assemblages from the desert zone contain substantially high relative abundance of Chenopodiaceae while those from the steppe zone are dominated by Cyperaceae.Pollen ratios show great potential in terms of separating different vegetation zones and to indicate climate changes on the Tibetan Plateau.The Artemisia/Chenopodiaceae ratio and arboreal/non-arboreal pollen ratio could be used as proxies for winter precipitation.Artemisia/Cyperaceae ratio and the sum of relative abundance of xerophilous elements increase with enhanced warming and aridity.When considering the vegetation coverage around the lakes,hierarchical cluster analysis suggests that the studied sites can be divided into four clusters:meadow,steppe,desert-steppe,and desert.The pollen-based vegetation classification models are established using a random forest algorithm.The random forest model can effectively separate the modern pollen assemblages of the steppe zone from those of the desert zone on the Tibetan Plateau.The model for distinguishing the four vegetation clusters shows a weaker but still valid classifying power.It is expected that the random forest model can provide a powerful tool to reconstruct the palaeovegetation succession on the Tibetan Plateau when more pollen data from surface lake sediments are included.

西藏羊卓雍错湖面水热通量变化及其与气象因子的关联

Lake surface water-heat exchange and its climatic attribution critically influence alpine lakes’evaporation mechanism and water storage balance with climate change.Here,this paper first explored the hourly,daily,and monthly water-heat flux variations of the lake surface and their correlations with meteorological factors based on the eddy covariance turbulent flux observation over the Yamzhog Yumco,an alpine lake in south Tibet in the non-freezing period(April-December)in 2016 and 2017.We found that the average latent heat flux was much higher than the sensible heat flux on the lake surface from April to December.Meanwhile,the water-heat flux exhibited remarkable seasonal variation,with a prominent role of higher air temperature and humidity in summer jointly controlling the lake-air energy exchange.Moreover,the main controlling meteorological factors for the water-heat flux variation of the lake surface differed with diversified timescales.First,the lake-air temperature difference was the most significant meteorological factor related to sensible heat flux on the half-hourly,daily,and monthly timescales.Second,the latent heat flux was strongly positively correlated with wind speed and the synergies of wind speed and water vapor pressure deficit on the daily and half-hourly timescales.Third,the lake surface heat flux was significantly negatively correlated with net radiation flux on the daily and monthly scales.The negative correlation can be attributed to the seasonal variation of the water surface net radiation,and the phase difference in heat flux intensity caused by the lake-air temperature difference and heat capacity contrast.Our findings will hopefully improve the understanding of energy exchange and evaporation mechanisms for alpine lakes in a warming climate.

Variation of alpine lakes from 1986 to 2019 in the Headwater Area of the Yellow River,Tibetan Plateau using Google Earth Engine

To understand the variations in surface water associated with changes in air temperature,precipitation,and permafrost in the Headwater Area of the Yellow River(HAYR),we studied the dynamics of alpine lakes larger than 0.01 km^2 during 1986-2019 using Google Earth Engine(GEE)platform.The surface areas of water bodies in the HAYR were processed using mass remote sensing images consisting of Landsat TM/ETM-H/OLI,Sentinel-2A,and MODIS based on automatic extraction of water indices under GEE.Besides,the lake ice phenology of the Sister Lakes(the Gyaring Lake and the Ngoring Lake)was derived by threshold segmenting of water/ice area ratio.Results demonstrate that the change of surface areas experienced four stages:decreasing during 1986-2004,increasing during 2004-2012,decreasing again during 2012-2017,and increasing again during 2017-2019.Correspondingly,the number of small lakes decreased(-26.5 per year),increased(139.5 per year),again decreased(-109.0 per year),and again increased(433.0 per year).Eight lakes larger than 1 km^2 disappeared in 2004 but restored afterward.The overall trends in the area of small lakes(0.01-1 km^2),large lakes(>1 km^2),and all lakes during 1986-2019 were 0.4,3.1,and 3.4 km^2 per year,respectively.Although the onsets of freezing,freeze-up,breaking and the break-up of the Sister Lakes varied from year to year,there is no obvious trend regarding the lake ice phenology.Tendencies of lake variations in the HAYR are primarily related to the increased net precipitation and the declined aridity,followed by the construction of hydropower station around the outlet of the Ngoring Lake,as well as permafrost degradation.