Role of the rhizosphere of a flooding-tolerant herb in promoting mercury methylation in water-level fluctuation zones

The water-level fluctuation zone(WLFZ) has been considered as a hotspot for mercury(Hg) methylation. Flooding-tolerant herbs are gradually acclimated to this water-land ecotone, tending to form substantial root systems for improving erosion resistance. Accompanying rhizosphere microzone plays crucial but unclear roles in methylmercury(Me Hg) formation in the WLFZ. Thus, we conducted this study in the WLFZ of the Three Gorges Reservoir, to explore effects of the rhizosphere of a dominant flooding-tolerant herb(bermudagrass) on Me Hg production. The elevated Hg and Me Hg in rhizosphere soils suggest that the rhizosphere environment provides favorable conditions for Hg accumulation and methylation. The increased bioavailable Hg and microbial activity in the rhizosphere probably serve as important factors driving Me Hg formation in the presence of bermudagrass. Simultaneously, the rhizosphere environments changed the richness, diversity, and distribution of hgc A-containing microorganisms. Here, a typical ironreducing bacterium( Geobacteraceae) has been screened, however, the majority of hgc A genes detected in rhizosphere, near-, and non-rhizosphere soils of the WLFZ were unclassified. Collectively, these results provide new insights into the elevated Me Hg production as related to microbial processes in the rhizosphere of perennial herbs in the WLFZ, with general implications for Hg cycling in other ecosystems with water-level fluctuations.

Fractal characterization of sediment particle-size distribution in the water-level fluctuation zone of the Three Gorges Reservoir, China

The combined effect of periodic water impoundment and seasonal natural flood events has created a 30 m high water-level fluctuation zone(WLFZ) around the Three Gorges Reservoir(TGR), China, forming a unique eco-landscape. Siltation, eutrophication, enrichment of heavy metals, and methane emissions in the WLFZ have been widely associated with sediment and soil particles generated from the upstream catchment or upland slopes. However, little attention has been paid to the complexity of sediment particle-size distributions in the WLFZ. In the present study, core samples(from a 345 cm thick sediment core from the base of the WLFZ), slope transect surface samples(across/up a WLFZ slope), and along-river/longitudinal surface samples(from the reservoir reaches) were collected. Laser granulometry and a volume-based fractal model were used to reveal the characteristics of sediment particle-size distributions. Results indicate that the alternation of coarse and fine particles in the sedimentary core profile is represented as a fluctuation of low and high values of fractal dimension(D), ranging from 2.59 to 2.77. On the WLFZ slope transect, surface sediment particles coarsen with increasing elevation, sand content increases from 3.3% to 78.5%, and D decreases from 2.76 to 2.53. Longitudinally, surface sediments demonstrate a downstream-fining trend, and D increases gradually downstream. D is significantly positively correlated with the fine particle content. We conclude that D is a useful measure for evaluating sediment particle-size distribution.

Influence of the Repeated Flooding on Growth and Development of Acorus calamus Vegetation in Water-level-fluctuation Zone of the Three Gorges Reservoir

[ Objective] The research aimed to study influence of the repeated flooding on growth and development of A. calamus in water-level-fluc- tuation zone of the Three Gorges Reservoir. [ Method] A. calamus plants were exposed to water under the dark conditions respectively in Septem- ber 2009 and September 2010. Then, they were taken away from the water, and grew in natural conditions in the following March and April respec- tively （ marked as S1, S2, S1 and S2）. The plant number was conducted statistics respectively. On May 7, the leaf number was made statistics. Length, width and rapid light responding curve of the leaf were determined. [ Result] Repeated flooding restrained significantly plant germination un- der the dark condition. Plant number in S1 and S2 groups decreased by 38.9% and 33.3% respectively compared with the control. It also reduced survival rate of the plant. Plant number in S2 group decreased by 16.7% （P 〈 0.05） compared with that of S2 group when they were taken away from the water. Both of flooding promoted elongation of the leaves, restrained leaves to grow wider, and also restrained leaf formation of the plants except for S1 and S1 groups. Total leaf length of a plant decreased markedly after the second flooding which in S1 and S2 groups were 50.6% and 36.9% respectively less than that after the first flooding. Total leaf number of the plant in S1and S2 groups reduced significantly, and they were only 63.1% and 38.5% respectively of the control. Compared with the first flooding, total leaf length of a plant in the control increased signifi- cantly and decreased remarkably in S2 group after the second flooding. Furthermore, light response ability of the relative electronic transfer rate （rETR） in S1 group wasn＇t significantly different from the control, and rETRmax, in S2 group was significantly less than the control. Moreover, non- photochemical quenching （NPQ） decreased remarkably in S1 and S2 groups. It indicated that A. calamus had good restore ability of the light re- sponse, but restoring of its heat dissipation capacity was slower. [ Conclusion] Repeated flooding inhibited plant growth and population recovery of A. calamus under the dark condition.

The cooling fluctuation events during Holocene in the tropical zone of China

Forty-eight samples are chosen to discuss the distribution in space and time of the cooling fluctuation events during Holocene in the tropical zone of China in this paper. The authors consider that the Neoglaciations II and III (or Cooling Event) have a widespread impact on the drop in temperature of 1–2 °C or less than 2 °C. The YD Event was dated at 11,300-10,200 a BP in the tropical mainland and its dating is 11,400-10,500 a BP in the sea area with a drop in temperature of 4–6 °C. The distribution of Event B and Neoglaciation I is taking a position of north, with a drop in temperature of 2.5–3.0 °C. The Cooling Event shows the temporality in time. The Cooling Event shows the limitation of regional distribution with a drop in temperature of less than 1.5°C. The more recent the cooling event is, the smaller the drop amplitude in temperature will be. In the eastern part of tropical zone seven events are complete in all varieties but the cooling fluctuation is weaker in the western part. In Hainan Island and South China Sea the appearance of cooling fluctuations is synchronous with each other.

Effects of seasonal water-level fluctuation on soil pore structure in the Three Gorges Reservoir,China

Inundation of the Three Gorges Reservoir has created a 30-m water-level fluctuation zone with seasonal hydrological alternations of submergence and exposure, which may greatly affect soil properties and bank stability. The aim of this study was to investigate the response of soil pore structure to seasonal water-level fluctuation in the reservoir, and particularly, the hydrological change of wetting and drying cycles. Soil pore structure was visualized with industrial X-ray computed tomography and digital image analysis techniques. The results showed that soil total porosity(? 100 ?m), total pore number, total throat number, and mean throat surface area increased significantly under wetting and drying cycles. Soil porosity, pore number and throat numberwithin each size class increased in the course of wetting and drying cycles. The coordination number, degree of anisotropy and fractal dimension were indicating an increase. In contrast, the mean shape factor, pore-throat ratio, and Euler-Poincaré number decreased due to wetting and drying cycles. These illustrated that the wetting and drying cycles made soil pore structure become more porous, continuous, heterogeneous and complex. It can thus be deduced that the water-level fluctuation would modify soil porosity, pore size distribution, and pore morphology in the Three Gorges Reservoir, which may have profound implications for soil processes, soil functions, and bank stability.

THE RELATIONSHIP BETWEEN INLAND LAKES EVOLUTION AND CLIMATIC FLUCTUATION IN ARID ZONE

The evolution of the inland lakes in arid and semi-arid zones is accorded with the climatic fluctuation. The humid climate is in harmony with the higher water level and greater lake water quantity budget while arid climate is in correspondence with the lower water level and little water budget. Based on the analysis of the lake fluctuation and lake budget change, with the aid of the data of geom’orphology, palynology, sedimentology and chronology, It is found that the climate experienced a warm and humid period during 7000-3500 yr. B. P. and showed a drying and warming trend in the last century in the Central Asia.

Soil anti-scourability enhanced by herbaceous species roots in a reservoir water level fluctuation zone

Revegetation is one of the successful approaches to soil consolidation and streambank protection in reservoir water level fluctuation zones(WLFZs).However,little research has been conducted to explore the impact of herbaceous species roots on soil anti-scourability during different growth stages and under different degrees of inundation in this zone.This study sampled two typical grasslands(Hemarthria compressa grassland and Xanthium sibiricum grassland)at two elevations(172 and 165 m a.s.l.)in the water level fluctuation zone(WLFZ)in the Three Gorges Reservoir(TGR)of China to quantify the changes in soil and root properties and their effects on soil anti-scourability.A simulated scouring experiment was conducted to test the soil anti-scourability in April and August of 2018.The results showed that the discrepancy in inundation duration and predominant herbaceous species was associated with a difference in root biomass between the two grasslands.The root weight density(RWD)values in the topsoil(0-10 cm)ranged from 7.31 to 13 mg cm^(-3) for the Hemarthria compressa grassland,while smaller values ranging from 0.48 to 8.61 mg cm^(-3) were observed for the Xanthium sibiricum grassland.In addition,the root biomass of the two herbs was significantly greater at 172 m a.s.l.than that at 165 m a.s.l.in the early recovery growth period(April).Both herbs can effectively improve the soil properties;the organic matter contents of the grasslands were 128.06%to 191.99%higher than that in the bare land(CK),while the increase in the water-stable aggregate ranged from 8.21%to 18.56%.Similarly,the topsoil antiscourability indices in both the herbaceous grasslands were larger than those in the CK.The correlation coefficients between the root length density(RLD),root surface area density(RSAD)and root volume density(RVD)of fine roots and the soil antiscourability index were 0.501,0.776 and 0.936,respectively.Moreover,the change in the soil antiscourability index was more sensitive to alternations in the RLD with diameters less than 0.5 mm.Overall,the present study showed that the perennial herbaceous(H.compressa)has great potential as a countermeasure to reduce or mitigate the impact of erosion in the WLFZ of the Three Gorges Reservoir.

Protection and Ecological Restoration of Water Level Fluctuation Zone in the Three Gorges Reservoir

Water level fluctuation zone(hereinafter referred to as "WLFZ") is a transitional ecosystem between terrestrial ecosystem and aquatic ecosystem,and also a key area to control its neighboring terrestrial and aquatic ecosystem. After the Three Gorges Reservoir was put into use,ecological environment of its WLFZ has aroused wide concern from domestic and foreign experts. On the basis of introducing characteristics of WLFZ of the Three Gorges Reservoir,current ecological environment and main problems of this area were analyzed,plant selection and configuration was elaborated as well as the implementation effect of many WLFZ protection and ecological restoration modes. In view of the actual conditions,pertinent suggestions were proposed for WLFZ of the Three Gorges Reservoir,namely classified protection and ecological restoration,enhancing monitoring and assessment of current situation and change tendency,carrying out technical researches and demonstration of WLFZ wetland ecological restoration.

Evolution Mechanism of Slip Zone Under Fluctuation of Ground Water Table of Landslide

The fluctuation of ground water table of landslide caused by the changing of rain fall and reservoir water level leads the slip zone to possess the complicated deformation features of stepped and vibration.Actual role of the ground water fluctuation to landslide is the synthesis of pore pressure,chemical intenerating

Water-Level Fluctuations of Urmia Lake: Relationship with the Long-Term Changes of Meteorological Variables (Solutions for Water-Crisis Management in Urmia Lake Basin)

Urmia Lake in northwest of Iran, through the recent years has been extremely faced with the water crisis. Climate variations and anthropogenic impacts could be two main affiliated factors in this regard. We considered the long term data series of precipitation, temperature and evaporation in monthly and yearly scales in order to compare to water-level values of Urmia Lake. The statistics approaches such as: standard deviation, trend analysis, T test, Pearson and Spearman correlations, liner regression are used to analyze all variables. The results released that the water-level of Urmia Lake along with the precipitation and temperature of the lake’s basin have experienced the periodic changes through 1961 to 2010, as there are some gradual dryness trends on the study area according to precipitation and temperature variations. Urmia Lake periodic water-level fluctuations show more significant correlation to temperature than the precipitation. Whiles, the water-level’s decreasing behavior especially through 1998 to 2010 is more harsh and different than the rate that is considered for precipitation’s decrease and temperature’s increase. Thus, there could be some anthropogenic factors in the basin which produced some supplementary causes to shrink Urmia Lake. Extracting the double precipitation over the basin through introducing and categorizing of atmospheric synoptic systems in order to cloud seeding operation could be one of urgent and innovative solutions to mitigate water crisis in the basin.

周期性水位波动对三峡水库消落带土壤有机碳含量和密度的影响

为探究水位波动对三峡水库消落带土壤有机碳的影响,在三峡水库消落带采集和测定了受不同水淹强度影响的石灰土、紫色土、黄壤及其植物样品,并运用Kruskal-Wallis非参数检验和基于冗余分析的典范分析等方法进行了研究。结果表明:周期性水淹增加了石灰土和紫色土的有机碳含量和密度,但降低了黄壤的有机碳含量和密度。此外,石灰土的有机碳分布还受地上生物量、土壤pH和土层深度的影响,紫色土的有机碳分布还受土层深度和地上生物量的影响,而黄壤的有机碳含量和密度则与地上生物量、土层深度和地下生物量有关。总之,周期性水位波动对消落带土壤有机碳影响深刻,但土壤类型分异了有机碳对水位波动的响应。

考虑消落带岩体劣化影响的典型危岩岸坡稳定性研究

三峡库区周期性水位升降引起的消落带岩体劣化对典型危岩岸坡稳定性具有重大影响。基于野外调研及地勘资料,采用通用离散单元法程序(universal distinct element code,简称UDEC)研究了消落带劣化区形态对近水平层状高陡危岩岸坡的稳定性影响。研究表明:目前三峡库区巫山段的近水平层状危岩岸坡消落带岩体劣化严重,在不同消落带劣化区存在紧密层状、松散碎裂状、溶蚀凹腔状、含挤压碎裂带等典型消落带劣化区形态;含有第1种消落带劣化区形态的危岩岸坡稳定性较好,危岩体位移较小,失稳模式为滑移破坏;含有第2种消落带劣化区形态的危岩岸坡危岩体先向坡内偏移,其后随着消落带岩体支撑强度弱化向坡外倾倒破坏;含有第3种消落带劣化区形态的危岩岸坡危岩体向坡外位移较大,失稳模式为倾倒破坏;含有第4种消落带劣化区形态的危岩岸坡稳定性主要受挤压破碎带的力学性质控制,易产生沿破碎带切割面的旋转滑移破坏;通过对以上4种劣化区形态的危岩岸坡增加防治加固措施,危岩体的变形位移得到了不同程度的有效控制。

南四湖消落带底泥中磷及微生物群落结构研究

研究不同频率干湿交替条件下,南四湖消落带底泥磷形态变化及其与生物群落结构的关联性,可为维持南四湖消落带水生态系统健康及保障南四湖水质提供技术支持。文章模拟了南四湖消落带底泥不同频率干湿交替过程,通过高通量测序技术分析了底泥生物群落的变化特征。结果表明:在干湿交替过程中,底泥总磷、无机磷呈降低趋势,而有机磷基本保持不变;不同干湿交替过程中消落带底泥微生物群落结构比较稳定,但群落丰度变化显著;频繁干湿交替不利于消落带底泥保持微生物多样性;消落带底泥中蓝藻门(Cyanobacteria)和疣微菌门(Verrucomicrobiota)与底泥中NaOH-P呈显著负相关,变形菌门(Proteobacteria)与总磷则呈正相关。

城市湿地公园消落带景观生态重建模式探讨——以南昌市马兰圩湿地公园为例

消落带区域因季节性淹没与裸露,水流反复冲刷,加之人类活动频繁,是城市生态系统的生态敏感区和脆弱区。前人相关研究多聚焦于三峡库区或大江大河的消落带土壤、植被、生境与污染物等方面,较少关注城市湿地公园的消落带,尤其是其生态重建与生态恢复方面。以南昌市马兰圩湿地公园消落带为例,系统分析了其消落带的现状及存在的问题,并基于此提出了湿地公园消落带的生态重建原则与模式,以最大限度地恢复这一区域的生态、环境和经济功能,从而为城市湿地公园的消落带生态恢复与重建提供参考。

南昌市象湖湿地公园消落带植物景观生态修复策略

为减轻城市湿地公园的消落带生态退化问题(环境污染、水土流失、土壤侵蚀、功能退化等),探求高效的生态修复策略。以南昌市象湖湿地公园为研究对象,在系统分析消落带的共性生态环境问题及现状基础上,提出了相应的景观生态修复策略:1)在广泛调查地域性消落带植物种类及其群落组成的基础上,筛选出适合公园环境的湿生植物种类;2)适度调整消落带的护坡和护岸结构,以自然式护岸为主;3)以乡土的湿生植物为主,建议配植适生植物群落,修复受损的消落带生境,形成特色护岸景观。研究城市湿地公园消落带的植物景观生态修复,有利于实现消落带生境修复、景观游憩、水体净化、减污增汇等生态效益,以构建生态环境友好型的消落带景观。

潮汐波动带偏载超深基坑变形控制数值模拟分析及工程实践

随着我国地下空间的持续开发,穿江越河及邻江邻河的地下工程项目越来越多,这类项目往往伴随邻山且邻水的工程特定环境,其深基坑工程变形机制和影响效力尚不明确,相关控制手段亦少有研究。依托杭州市某紧邻钱塘江的市政隧道工程,考虑潮汐波动影响对36.4m超深大偏载基坑变形进行了三维数值模拟分析,提出相应变形控制方法并进行工程实践。研究表明:通过依托工程基坑内外水位监测数据的理论分析和数值求解,建立基坑渗流场时空演化模型,得知潮汐水流进入土层边界时的水头衰减较大,在渗流路径中,水头变化较稳定,基坑附近地下水对潮汐循环荷载的响应有明显滞后性,基坑周围产生较高孔隙水压力。运用有限元软件采用修正Mohr-Coulomb弹塑性本构模型,建立偏载深基坑开挖及周围环境影响的数值模拟三维模型,为模拟潮汐波动带的影响,简化在基坑河流底部分别施加25kPa和65kPa均布荷载,得出相较于普通环境,潮汐动力影响下的基坑变形控制更应引起重视,通过三维数值模拟及工程实践,验证了超深基坑采用“1 200mm地下连续墙+5道混凝土支撑+2道钢支撑”的联合支护形式是一种有效的临近钱塘江超深基坑的支护对策。

农业耕作和外来植物入侵对金沙江下游库区新生消落带土壤养分和酶活性的影响

金沙江下游梯级水电站新生消落带上农业耕作较为普遍,同时广泛存在外来植物入侵,这可能会对其土壤养分状况产生潜在影响。基于此,以乌东德电站库区新生消落带为研究区域,以淹水后自然形成的狗牙根(Cynodon dactylon)群落为对照,选择典型农作物玉米(Zea mays)与入侵植物银胶菊(Parthenium hysterophorus)为研究对象,通过比较不同群落下0~10 cm和10~20 cm深度土壤养分含量及酶活性差异,探讨农业耕作和外来植物入侵对消落带土壤养分状况的影响。结果表明:①玉米和银胶菊群落下0~10 cm土层有机质、全氮、全磷、速效钾含量显著高于狗牙根群落(P<0.05),增幅为24.58%~136.98%;10~20 cm土层的有机质、氮磷钾养分全量和速效养分含量也较狗牙根群落显著高出16.67%~141.68%(P<0.05)。②相较狗牙根群落,玉米和银胶菊群落下0~10 cm和10~20 cm土层的脲酶、蔗糖酶、碱性磷酸酶、硝酸还原酶活性均显著增加(P<0.05),增幅为5.60%~378.65%。3个群落中,银胶菊群落土壤酶指数最高,较狗牙根群落显著高出23.49%(P<0.05)。③消落带土壤有机质、全氮、全磷、碱解氮、有效磷、速效钾含量均与脲酶、蔗糖酶、硝酸还原酶、碱性磷酸酶活性之间呈显著正相关(P<0.05),表明上述酶活性可作为消落带土壤养分状况变化的有效表征。总的来看,农耕活动和银胶菊入侵促进了落干期金沙江下游新生消落带土壤养分的积累和有效性的增加。因此,应加强消落带农业耕作的管控并尽快开展入侵植物防治,以减少淹水期消落带土壤养分流失风险。

三峡水库消落带土壤反硝化及DOM的影响

在重庆主城与涪陵选取了3个典型点位采集土壤样品,并对土壤的理化性质、原位反硝化速率、溶解性有机质(DOM)驱动的反硝化以及库区土壤的微生物进行了考察与分析.结果显示在海拔145~155m区间,淹水期镇安镇、涪陵区和鱼嘴镇最高氨氮(NH_(4)^(+)-N)平均浓度分别为31.32,28.63和19.23mg/kg,均高于落干期.在淹水期,与高海拔区域土壤中硝酸盐氮(NO_(3)^(-)-N)平均浓度相比,低海拔土壤中NO_(3)^(-)-N平均浓度分别增大了46.91%(镇安镇)、37.89%(涪陵区)和29.69%(鱼嘴镇).在淹水期,土壤有机质(SOM)平均浓度随着海拔高程的降低而降低,镇安镇、涪陵区和鱼嘴镇分别从109.16,80.93和82.61mg/kg降至65.63,64.53,53.41mg/kg.土壤中NH_(4)^(+)-N和NO_(3)^(-)-N的含量与现场反硝化速率呈显著正相关(P<0.05),在提供充足的碳(C)和氮(N)营养元素后,土壤潜在反硝化速率表现出较大的时间和空间差异性.在由DOM驱动的反硝化实验中,DOM降解符合一级动力学模型(R^(2)>0.93),N2O累积量符合Logistic模型(R^(2)>0.97).在三峡水库消落带土壤中,反硝化功能微生物主要是Bacillus和Comamonadaceae,其丰度变化与土壤潜在反硝化速率呈现显著的正相关性(P<0.05).

水位变动区硫酸根侵蚀对混凝土氯离子传输影响试验研究

海洋环境水位变动区是氯离子和硫酸根离子侵蚀最严重的区域,氯离子主要破坏钢筋钝化膜引起钢筋锈蚀,硫酸根离子侵蚀除导致混凝土物理力学性能劣化外,还对氯离子在混凝土中的传输产生影响。目前针对硫酸根离子对氯离子传输影响的研究主要采用将试件浸泡在侵蚀溶液中的方式,不能反应耐久性问题更为严重的海洋水位变动区混凝土内离子传输规律。文章采用自主研制的潮汐循环模拟系统,开展了海洋环境水位变动区单一氯离子和氯离子-硫酸根离子耦合环境下氯离子传输特性物理试验,研究了硫酸根离子侵蚀对混凝土中氯离子传输规律的影响,给出了混凝土表面氯离子浓度和表观氯离子扩散系数的时变公式,建立了海洋环境水位变动区考虑硫酸根离子侵蚀效应的氯离子扩散模型。结果表明,早期由于硫酸根离子侵蚀在混凝土中生成石膏和钙矾石的填充作用,阻碍了氯离子在混凝土中的传输,使混凝土中氯离子浓度降低。

分区参数对超声速湍流燃烧动态分区火焰面模拟的影响

文章基于动态分区火焰面模型(DZFM)和改进延迟分离涡(IDDES)湍流模型对DLR中心支板稳焰的超声速燃烧室进行数值模拟.对无反应状态燃烧室的模拟准备复现了燃烧室内复杂的波系结构以及中心射流失稳发展过程,燃烧状态下的模拟结果较好地捕捉了火焰推举、OH基团以及平均温度等火焰结构特征,由此验证了所采用数值模拟方法的适用性.此外,由反应状态标量(OH基)在混合分数空间中的分布可知,反应标量与混合分数在全场内不满足强相关性.通过增加流向坐标、马赫数以及燃烧热释放速率作分区参数可显著抑制反应状态标量在混合分数空间内的条件脉动,其中热释放速率的作用最显著.进一步对比采用不同多参数分区的DZFM模型所得火焰结构,发现对于处于预混燃烧状态的支板尾迹区以及高雷诺数剪切层区域火焰,采用包含燃烧热释放速率、流向坐标以及混合分数作为分区指标的三参数分区DZFM模型可显著提高模型的准确性.