Influence of below-cloud evaporation on stable isotopes of precipitation in the Yellow River source region

The study of below-cloud evaporation effects under clouds in the Yellow River source region is of great significance for regional water resource generation as well as for water resource security in the arid and semi-arid regions of northern China. In this study, we quantitatively assessed the evapotranspiration effect in the Yellow River source region from March to November based on the improved Stewart model. The study concluded that: (1) below-cloud evaporation was slightly higher in summer than in other seasons (residual fractions of raindrop evaporation were 80.57% in summer, 81.12% in spring, and 84.2% in autumn, respectively); and (2) sub-cloud evaporation diminishes with increasing altitude (residual fractions of raindrop evaporation were 83.09% in the western part of the area, 81.82% in the central part of the area, and 81.36% in the eastern part of the area, respectively). (3) The total linear index between study areas f and ∆d is 2.24, where f > 95%, it is 1.19; that is, the evaporation of raindrops increases by 1% and the reduction in the excess of mercury by about 2‰. (4) Local meteorological factors (temperature, precipitation, and relative humidity) and raindrop diameter have a cross-influence on below-cloud evaporation, with relative humidity having the most significant effect, with the highest correlation coefficient of 3.03 when relative humidity is less than 70%. The results of the study can provide a parameter basis for hydrological and climatic models in the Yellow River Basin.     

Mechanisms of isotopic control of precipitation in the Yellow River source region

The study of water vapour sources and water cycle patterns in the Yellow River source region is of great significance for ensuring water resource security in the arid and semi-arid regions of northern China. We established a precipitation stable isotope observation system in the Yellow River source region for three consecutive years (2020–2022), systematically analysed the spatial and temporal distribution characteristics of precipitation stable isotopes ²H and ¹⁸O in the Yellow River source region and their interrelationships with environmental factors and topography, and explored the regional water vapour transport pathways by using the HYSPLIT model and combining with the global reanalysis data. The results show that: (1) the δ¹⁸O and δ²H values of precipitation in the Yellow River source region follow the seasonal pattern, with the first half of the year being richer than the second half of the year; (2) the spatial variations of δ¹⁸O of precipitation in the Yellow River source region show a low in the southwest and a high in the northeast; (3) the water vapour source in the source area is basically stable, and the complex transport paths and the cross-effects of the local factors determine the stable isotope characteristics of the water, and the stable isotope characteristics of the water are determined by the cross-effects of the local factors, because the source of the water vapour and the local factors such as the height will not change significantly in the short term. Since the source of water vapour and local elevation factors will not change significantly in the short term, the precipitation pattern in the source area of the Yellow River can be considered to be basically stable.     

天目湖沙河水库水质对流域开发与保护的响应

利用长期水质监测资料,对苏南地区天目湖沙河水库十多年来的开发与保护工作的水库水质影响情况进行了分析.结果发现:大规模放养鳙鱼等不合理的渔业开发对水库硅藻、蓝藻等浮游植物异常增殖有较大的促进作用;在营养盐处于中富营养水平下,利用不同食性鱼类的组合调控,能够较快地抑制浮游植物的异常增殖,但当浮游植物生物量下降到一定程度以后,其控制能力下降,营养盐和气候因子的影响变得更为重要;流域的旅游开发和农业开发都对水库营养盐、透明度等水质指标产生较大影响,特别是坡地大规模茶叶种植等农业开发对水库氮的影响十分明显;春季少雨等气候变化因子对水库氮等营养盐浓度影响较大,但影响是短时段的.研究表明,合理调控水库渔业养殖,控制流域农业、旅游等开发活动强度,减少农业化肥施用量,恢复和扩大湿地等流域营养盐削减途径,是沙河水库水质保护的关键,也对同类水库水质保护具有示范价值.     

The behavioral and antioxidant response of the bivalve Gomphina veneriformis to sediment burial effect

A laboratory-based microcosm experiment was carried out to examine both the behavioral and antioxidant response of the clam Gomphina veneriformis under the conditions of 3 types of burial material(sand,silt,silt-sand mixture) with 3 burial depths(5 cm,15 cm,30 cm).The concentration of dissolved oxygen decreased significantly after 3 d of burial in all experimental groups.In silt and sand-silt mixture groups,the interstitial water quality became worsened with lower pH,and higher NH_4~+-N concentration,where clam mortality occurred simultaneously.However,clam samples in all sand groups and 5 cm,15 cm sand-silt mixture groups survived well for 8 d.Obviously fewer individuals left in the bottom sand in the 15 cm,30 cm silt groups and 30 cm sand-silt mixture groups than in the 5 cm groups.Therefore,it suggests that adding silt and increasing burial depth could stimulate the vertical movement of organisms and cause lethal effects.It was found that the burial depth was the key factor that influenced the activities of antioxidant enzymes,such as superoxide dismutase(SOD) and catalase(CAT).The SOD and CAT activities in the gills and hepatopancreases of organisms both showed significant upregulation in 30 cm burial depth after buried for 8 d.Higher enzyme activities were found in gills than in hepatopancreases,which indicated that the gills of the bivalve G.veneriformis were more susceptible to burial effects than hepatopancreases.Overall,this study shows that sediment burial could cause effects on the biological behavior and antioxidant enzyme activities.     

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Spatiotemporal evolution of C3/C4 vegetation and its controlling factors in southern China since the last glacial maximum

To date, few research have been reported on the evolution of C3/C4 vegetation in southern China, and the main mechanism influencing the evolution of C3/C4 vegetation is unclear. That makes it difficult for researchers to understand the competition mechanism of C3 and C4 plants under different climate environments and its relationship with the climate factors. It is also not conducive for researchers to assess the influence of future climate change on regional C3/C4 vegetation. Exactly, C3/C4 vegetation change in the regional-scale will have a significant impact on the global carbon cycle and agricultural production.Therefore, it is especially important to reconstruct the evolutionary history of C3/C4 vegetation in southern China and clarify the influencing mechanism of climate change. In this study, we systematically analyzed stable carbon isotope(δ13 C) of the longchain n-alkanes in sediment samples from eight lakes and four peat profiles in southern China, to reconstruct the spatiotemporal evolution of C3/C4 vegetation in these regions since the Last Glacial Maximum(LGM) and to investigate the climate factors that affect the C4 plant abundance change in the research area. The integrated long-chain n-alkane(C27–C33) stable carbon isotope results of samples from Zhanjiang Huguangyan Maar Lake, Xingyun Lake, Lugu Lake and Dingnan peat showed that, from the LGM to the Early Holocene, C4 plant relative abundance exhibited a gradually increasing trend from 21% to 34%. In the Middle Holocene, the C4 plant abundance significantly declined and reached a lowest value of 10%. In space, the C4 plant abundance generally exhibited a gradually declining trend from south to north in the LGM and the Early Holocene, while it showed an opposite trend in the Holocene Climate Optimum(6.0 cal ka BP). It reflected that the main influencing factor on C4 plants spatial distribution was changing from temperature to precipitation. This study indicated that temperature was the dominant factor affecting C4 plant distribution in southern China, however, when the temperature condition was appropriate, an increase in precipitation(especially more spring precipitation) would reduce the competitive advantages of C4 plants. Therefore, the combination of temperature and seasonal precipitation was the important factor that determines the C3/C4 vegetation proportion change in the southern China. Under the premise that the temperature will rise and precipitation will increase in the future, the reduction of a competitive advantage for the C4 plants could affect agricultural production in China.     

Settlement mechanism of piled-raft foundation due to cyclic train loads and its countermeasure

In this paper, numerical simulation with soil-water coupling finite element-finite difference (FE-FD) analysis is conducted to investigate the settlement and the excess pore water pressure (EPWP) of a piled-raft foundation due to cyclic high-speed (speed: 300km/h) train loading. To demonstrate the performance of this numerical simulation, the settlement and EPWP in the ground under the train loading within one month was calculated and confirmed by monitoring data, which shows that the change of the settlement and EPWP can be simulated well on the whole. In order to ensure the safety of train operation, countermeasure by the fracturing grouting is proposed. Two cases are analyzed, namely, grouting in No-4 softest layer and No-9 pile bearing layer respectively. It is found that fracturing grouting in the pile bearing layer (No-9 layer) has better effect on reducing the settlement.     

Resilience-based retrofitting of existing urban RC-frame buildings using seismic isolation

The improvement of the seismic resilience of existing reinforced-concrete (RC) frame buildings, which is essential for the seismic resilience of a city, has become a critical issue. Although seismic isolation is an effective method for improving the resilient performance of such buildings, target-oriented quantitative improvements of the resilient performance of these buildings have been reported rarely. To address this gap, the seismic resilience of two existing RC frame buildings located in a high seismic intensity region of China were assessed based on the Chinese Standard for Seismic Resilience Assessment of Buildings. The critical engineering demand parameters (EDPs) affecting the seismic resilience of such buildings were identified. Subsequently, the seismic resilience of buildings retrofitted with different isolation schemes (i.e., yield ratios) were evaluated and compared, with emphasis on the relationships among yield ratios, EDPs, and levels of seismic resilience. Accordingly, to achieve the highest level of seismic resilience with respect to the Chinese standard, a yield ratio of 3% was recommended and successfully applied to the target-oriented design for the seismic-resilience improvement of an existing RC frame building. The research outcome can provide an important reference for the resilience-based retrofitting of existing RC frame buildings using seismic isolation in urban cities.

     

太湖西北湖区浮游植物和无机、有机氮的时空分布特征

以太湖重度蓝藻水华发生的西北湖区为研究对象,从河口至湖心区设置5个采样点,于2012年10月至2013年10月逐月采集表层水体样品,测定了水温、溶解氧和浮游细菌丰度,并分析了浮游植物群落结构的组成、溶解性无机氮(DIN)和有机氮(DON)浓度以及氮磷比.研究结果表明,太湖西北湖区浮游植物主要由蓝藻、硅藻、绿藻和隐藻组成.可能由于风、浪等混合作用使太湖西北湖区不同采样点之间蓝藻细胞密度没有显著差异.蓝藻生物量在浮游植物中所占比例最高为34%±15%,春季部分点位隐藻生物量高于50%,表明隐藻与蓝藻的相互竞争趋势显著.CCA排序图结果表明,DIN、DON浓度以及总氮∶总磷比(TN∶TP比)是影响西北湖区浮游植物优势属分布的重要环境因子.5个采样点铵态氮(NH_4~+-N)与DIN浓度具有显著差异,与DON浓度没有显著差异.夏季蓝藻水华暴发期间,可能由于蓝藻的吸收利用引起NH_4~+-N和硝态氮(NO_3~--N)浓度迅速降低.此外,由于NH_4~+-N浓度还可能受到沉积物NH_4~+-N释放的影响,因此,蓝藻细胞密度与NO_3~--N的相关系数和显著水平均高于NH_4~+-N.夏季TN∶TP比和DIN∶TP比降至最低,表明该湖区浮游植物,尤其是蓝藻的生长可能受到氮限制.蓝藻细胞密度与DON浓度呈显著负相关,表明在氮限制条件下,DON可能是蓝藻氮素利用的重要补充.     

2008—2022年上海大莲湖湿地营养盐时空分布特征、水质评价及来源解析

为了解大莲湖湿地区域水体营养盐的时空分布特征及污染来源,本文系统汇整了2008—2022年大莲湖湿地的水质数据,于2021—2022年丰水期和枯水期针对6种不同土地利用类型进行水样采集分析,也于2021年平水期进行各指标的24 h昼夜监测分析。年际研究结果表明,2008—2022年期间大莲湖湖区总氮(TN)浓度基本处于《地表水环境质量标准》(GB3838—2002)Ⅳ～Ⅴ类水质标准,在2009年枯水期达到最大值(2.97 mg/L);湖区氨氮浓度近年来满足Ⅲ类水质标准;总磷浓度在2021年的丰水期达到最大值0.79 mg/L,超过Ⅴ类水标准限值0.4 mg/L。湖区水质较生态修复之前有所好转,但营养盐浓度依旧处于较高水平。整体趋势与淀山湖的营养盐浓度基本一致,说明上游淀山湖入湖来水可能是造成大莲湖营养盐增高的原因之一。季节性研究结果显示,水体各类指标存在一定季节性差异,枯水期略劣于丰水期。不排除入湖河流带来的污染对大莲湖湿地区域产生影响,丰枯水期鱼塘和荷花塘水体营养盐和有机物质超标现象突出,尤其是鱼塘点位TN浓度是Ⅴ类水标准限值2.0 mg/L的2～4倍。24 h昼夜监测结果发现,大部...