Combined effect of climate change and human activities on the hydrological processes of an urban river: case study of the Xiaoqing River,China

ABSTRACT

The aim of this study is to reveal statistical characteristics and exceedance probability of discharge under the combined effect of climate change and human activities. The study is conducted in the Xiaoqing River in Jinan, China, based on data of discharge, land-use types and precipitation from the period 1970–2016. A multivariate joint probability distribution of the data is established to test the univariable, bivariable and trivariable change points. These are then used to calculate and analyse the risk probability of discharge exceeding the specific values under different conditions of precipitation and land-use type. The results show that the change point calculated by trivariate joint distribution can reduce the disturbance of the change point obtained with the univariable or bivariable approach and reflect the changes of various factors in the hydrological processes more objectively. When the land-use type is taken into consideration, the trivariate distribution can reflect the variation of hydrological processes more reasonably.     

Biomorphological scaling laws from convectively accelerated streams

Worldwide convectively accelerated streams flowing in downstream-narrowing river sections show that riverbed vegetation growing on alluvial sediment bars gradually disappears, forming a front beyond which vegetation is absent. We revise a recently proposed analytical model able to predict the expected longitudinal position of the vegetation front. The model was developed considering the steady state approximation of 1-D ecomorphodynamics equations. While the model was tested against flume experiments, its extension and application to the field is not trivial as it requires the definition of proper scaling laws governing the observed phenomenon. In this work, we present a procedure to calculate vegetation parameters and flow magnitude governing the equilibrium at the reach scale between hydromorphological and biological components in rivers with converging boundaries. We collected from worldwide rivers data of section topography, hydrogeomorphological and riparian vegetation characteristics to perform a statistical analysis aimed to validate the proposed procedure. Results are presented in the form of scaling laws correlating biological parameters of growth and decay from different vegetation species to flood return period and duration, respectively. Such relationships demonstrate the existence of underlying selective processes determining the riparian vegetation both in terms of species and cover. We interpret the selection of vegetation species from ecomorphodynamic processes occurring in convectively accelerated streams as the orchestrated dynamic action of flow, sediment and vegetation characteristics. © 2019 John Wiley & Sons, Ltd.     

Geomorphological evolution and sediment stratigraphy of numerically simulated alluvial fans

When a sediment laden river reaches a flat basin area the coarse fraction of their sediment load is deposited in a cone shaped structure called an alluvial fan. In this article we used the State Space Soil Production and Assessment Model (SSSPAM) coupled landform–soilscape evolution model to simulate the development of alluvial fans in two- and three-dimensional landforms. In SSSPAM the physical processes of erosion and armouring, soil weathering and sediment deposition were modelled using state-space matrices, in both two and three dimensions. The results of the two-dimensional fan showed that the fan grew vertically and laterally keeping a concave up long profile. It also showed a downstream fining of the sediments along the fan profile. Both of these observations are in agreement with available literature concerning natural and experimental fan formations. Simulations with the three-dimensional landform produced a fan with a semicircular shape with concave up long profiles and concave down cross profiles which is typical for fans found in nature and ones developed in laboratory conditions. During the simulation the main channel which brings sediment to the fan structure changed its position constantly leading to the semicircular shape of the fan. This behaviour is similar to the autogenic process of ‘fanhead trenching’ which is the major mechanism of sediment redistribution while the fan is developing. The three-dimensional fan simulation also exhibited the downstream fining of sediments from the fan apex to the peripheries. Further, the simulated fan also developed complex internal sediment stratification which is modelled by SSSPAM. Currently such complex sediment stratification is thought to be a result of allogenic processes. However, this simulation shows that, such complex internal sediment structures can develop through autogenic processes as well. © 2020 John Wiley & Sons, Ltd.     

Quantitative reconstruction of Holocene sediment sources contributing to the central Jiangsu coast,China: New insights into source-to-sink processes

Coastal deltaic deposits are the primary locations for sediment storage on Earth, and quantifying their source contributions is a critical prerequisite for delineating S2S patterns in marginal seas. In most cases, quantification for the contribution by fine-grained sediments (i.e. particle size < 63 μm) is considered to be representative to constrain the overall sediment supply. However, this approach may be inappropriate because large differences exist between the two quantities. Here we propose an approach to solve the problem, which is based on the maximum number of tracers from multiple sediment size fractions incorporating the content of all size fractions of sediment. Using this approach, absolute source contributions during the Holocene are reconstructed that provide a first-order model for the S2S pattern of the central Jiangsu coast, China. The Huanghe River is the strongest driver for the Holocene sedimentation, with a mean contribution of ~72 ± 6% (1417 × 10⁸ t). The absolute contributions from the Changjiang and offshore areas were of secondary importance, (i.e. ~17 ± 1% (330 × 10⁸ t) and ~11 ± 5% (217 × 10⁸ t), respectively). The results show that a large difference between the relative and absolute source contributions and the assumption that the relative contribution represents the absolute contribution is invalid in a coastal setting. The impact of the Huanghe is mainly based on episodic events, such as the event of 1128–1855 AD . The model also reveals that the offshore sediments are as important as the Changjiang sediments for the central Jiangsu coast during the Holocene. Thus, the model provides both the time series and overall quantities of sediment supply during the formation and evolution of the Holocene tidal flats on the Jiangsu coast. Our findings shed new light on quantitative analysis of sediment sources applicable to future S2S studies of marginal seas. © 2020 John Wiley & Sons, Ltd.     

宁夏南部干旱-半干旱黄土梁峁区生态环境调查与生态建设模式——以西吉县城郊乡和马建乡生态环境调查为例

宁夏南部黄土高原区严重的水土流失、土地退化对当地的生产、生态、社会发展、人民生活带来极大的困难和危害,因此如何开展生态建设、促进社会经济发展,成为当地政府最为紧迫的任务之一。西吉县城郊乡和马建乡是干旱-半干旱黄土梁峁区典型代表地区,部分地区已经失去了依靠自身力量进行生态恢复和发展的可能性,因而需要在调查研究的基础上,制定合理的规划和生态建设模式,针对性的增加外部投入,进行生态重建。本文在对西吉县城郊乡和马建乡开展生态地质调查的基础上,分析研究了宁夏南部干旱-半干旱黄土梁峁区的主要生态环境问题,依据该区地质、地貌、气候、植被条件,初步总结了该地区适宜的生态建设模式,即高效生态农业建设模式,经济林园艺化管理的农果复合型生态农业建设模式,草灌（木）和畜牧业林木型生态农业模式,林草、林灌（木）和草灌（木）相互结合生态模式。     

Effects of aspect on weathering: anomalous behaviour of sandstone gravestones in southeast England

Rocks in the humid temperate zone tend to weather more severely on faces exposed to the prevailing winds than on their more sheltered leeward faces. In southeast England, however, gravestones composed of a non‐local, quartz‐rich sandstone exhibit a reverse weathering pattern. The east‐facing, lee sides exhibit a much greater depth and areal extent of weathering than the west sides which face the westerly wind and rain. Possible reasons for the asymmetric pattern of weathering are discussed. Copyright © 2000 John Wiley & Sons, Ltd.     

Hydrogeochemistry of shallow groundwater in an upland Scottish catchment

The hydrogeochemistry of shallow groundwater has been characterized in the Allt a'Mharcaidh catchment in the Scottish Cairngorms in order to: (i) assess the spatial and temporal variation in groundwater chemistry; (ii) identify the hydrogeochemical processes regulating its evolution; and (iii) examine the influence of groundwater on the quality and quantity of stream flow. Shallow groundwater in superficial drift deposits is circumneutral (pH∽7·1) and base cation concentrations are enriched compared with precipitation and drainage water from overlying podzolic soils. Modelling with NETPATH suggests that the dominant geochemical processes that account for this are the dissolution of plagioclase, K-feldspar and biotite. Groundwater emerging as springs from weathered granite underlying high altitude (>900 m) alpine soils shows similar characteristics, though weathering rates are lower, probably as a result of reduced residence times and lower temperatures. Chemical hydrograph separation techniques using acid neutralizing capacity (ANC) and Si as tracers show that groundwater is the dominant source of baseflow in the catchment and also buffers the chemistry of stream water at high flows: groundwater may account for as much as 50–60% of annual runoff in the catchment. Climate and land use in the Cairngorms are vulnerable to future changes, which may have major implications for hydrogeological processes in the area. © 1998 John Wiley & Sons, Ltd.     

长江中下游成矿带铁-铜成矿系统结构的地球物理探测: 综合分析

成矿系统是在深部过程驱动下形成的、具有自组织的能量及物质迁移-汇聚系统。系统在形成和演化过程中,在岩石圈不同尺度上留下“痕迹”,这种“痕迹”可以通过地球物理、地球化学和遥感等方法进行探测或观测。文章尝试在成矿系统理论框架下,对近10多年来在长江中下游成矿带进行的多尺度地球物理、地球化学探测结果进行分析,识别典型陆内成矿系统“源区”“通道”“场所”的地球物理、地球化学“痕迹”,尝试构建陆内成矿系统的空间结构模型。主要结论有:(1)长江中下游晚中生代的大规模铁、铜多金属成矿作用是一个完整的成矿系统。该系统包括3个子系统,分别为与高钾钙碱性岩浆岩有关的夕卡岩-斑岩成矿子系统、与橄榄安粗岩有关的陆相火山岩铁(硫)成矿子系统和与碱性岩有关的铜-金(铀)成矿子系统。(2)成矿系统的“源区”来自富集地幔的熔融、底侵,并在壳/幔边界与下地壳物质的混合,具有多级分布特点。幔源岩浆与地壳物质混合的比例决定了成矿金属的类型。(3)成矿带发育的“鳄鱼嘴”构造是铁铜成矿系统的主干“通道”。成矿系统“末端”矿质沉淀的“场所”主要受近地表褶皱、断裂、层间滑脱断层,以及由它们形成的断裂(裂隙)网络控制。(4)区域磁异常、放射性和地球化学异常是成矿系统残留“痕迹”的响应和“标识”。通过分析不同尺度的“标识”特征,可以深入认识成矿系统的空间结构,并可用于深部成矿预测。     

南海北部深水区东西构造差异性及其动力学机制

This paper overviews research progress in observation, theoretical analysis and numerical modeling of submesoscale dynamic processes in the South China Sea(SCS) particularly during recent five years. The submesoscale processes are defined according to both spatial and dynamic scales, and divided into four subcategories as submesoscale waves, submesoscale vortexes, submesoscale shelf processes, and submesoscale turbulence. The major new findings are as follows.(1) Systematic mooring observations provide new insights into the solitary waves(ISWs) and the typhoon-forced near-inertial waves(NIWs), of which a new type of ISWs with period of 23 h was observed in the northern SCS(NSCS), and the influences of background vorticity, summer monsoon onset, and deep meridional overturning circulation on the NIWs, as well as nonlinear wave-wave interaction between the NIWs and internal tides, are better understood. On the other hand, satellite altimeter sea surface height data are used to reveal the internal tide radiation patterns and provide solid evidence for that the ISWs in the northeastern SCS originate from the Luzon Strait.(2) Submesoscale offshore jets and associated vortex trains off the Vietnam coast in the western boundary of the SCS were observed from satellite chlorophyll concentration images. Spiral trains with the horizontal scale of 15–30 km and the spacing of 50–80 km were identified.(3) 3-D vertical circulation in the upwelling region east of Hainan Island was theoretically analyzed. The results show that distribution patterns of all the dynamic terms are featured by wave-like structures with horizontal wavelength scale of 20–40 km.(4) Numerical models have been used for the research of submesoscale turbulence. Submesoscale vertical pump of an anticyclonic eddy and the spatiotemporal features of submesoscale processes in the northeastern SCS are well modeled.     

Modelling eruption cycles and decay of mud volcanoes

Recent debates about the eruptive behavior of mud volcanoes and their activation mechanisms have been driven particularly by the LUSI eruption in Indonesia that resulted in huge commercial and cultural damages. Numerical modeling of mud volcanoes, of which few exist, can provide insight into eruptive behavior and contribute to hazard evaluation. In this paper, we present a simple model to describe fluid escape from an underground reservoir through a conduit, extruded as a mud volcano at the surface. The governing equations result in oscillatory behavior, and we study the influence of changes in rheological properties of surrounding rock and fluid characteristics of the mud on extrusion dynamics. We focus on understanding long-term eruption behavior, flow cycles, and decay factors. Model results can be used to estimate the discharge rates and extruded volume from assumptions on the mud reservoir and conduit, or conversely, the reservoir or conduit properties from discharge rates.