Decadal morphological evolution of the mouth zone of the Yangtze Estuary in response to human interventions

The morphology of the Yangtze Estuary has changed substantially at decadal time scales in response to natural processes, local human interference and reduced sediment supply. Due to its high sediment load, the morphodynamic response time of the estuary is short, providing a valuable semi-natural system to evaluate large-scale estuarine morphodynamic responses to interference. Previous studies primarily addressed local morphologic changes within the estuary, but since an overall sediment balance is missing, it remains unclear whether the estuary as a whole has shifted from sedimentation to erosion in response to reduced riverine sediment supply (e.g. resulting from construction of the Three Gorges Dam). In this paper we examine the morphological changes of two large shoals in the mouth zone (i.e. the Hengsha flat and the Jiuduan shoal) using bathymetric data collected between 1953 and 2016 and a series of satellite images. We observe that the two shoals accreted at different rates before 2010 but reverted to erosion thereafter. Human activities such as dredging and dumping contribute to erosion, masking the impacts of sediment source reduction. The effects of local human intervention (such as the construction of a navigation channel) are instantaneous and are likely to have already resulted in new dynamic equilibrium conditions. The morphodynamic response time of the mouth zone to riverine sediment decrease is further suggested to be >30 years (starting from the mid-1980s). Accounting for the different adaptation time scales of various human activities is essential when interpreting morphodynamic changes in large-scale estuaries and deltas. © 2019 John Wiley & Sons, Ltd.     

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.     

人与自然关系的修复——日本琵琶湖治理与生活环境主义的应用

湖泊的环境、生态问题与流域社会、经济密切相关.如何从社会学的角度认识和解决湖泊所遇到的问题,越来越受到各领域研究者的关注.环境社会学一种理论如何付诸于解决环境问题的实践？尚处于探索过程之中.通过了解日本环境社会学以及生活环境主义的起源和思想,总结日本琵琶湖将生活环境主义思想应用于湖泊治理中的各种方法和实例,分析环境社会学在湖泊治理中发挥的作用.通过环境社会学在琵琶湖的治理中的经验,探讨生活环境主义在湖泊治理中可能发挥的作用.认为在下一阶段的湖泊治理中修复“人与自然的关系”将会成为重要内容.     

Geomorphic evolution of the Qingshuigou channel of the Yellow River Delta in response to changing water and sediment regimes and human interventions

Delta channels are important landforms at the interface of sediment transfer from terrestrial to oceanic realms and affect large, and often vulnerable, human populations. Understanding these dynamics is pressing because delta processes are sensitive to climate change and human activity via adjustments in, for example, mean sea level and water/sediment regimes. Data collected over a 40-year period along a 110-km distributary channel of the Yellow River Delta offer an ideal opportunity to investigate morphological responses to changing water and sediment regimes and intensive human activity. Complementary data from the delta front provide an opportunity to explore the interaction between delta channel geomorphology and delta-front erosion–accretion patterns. Cross-section dimensions and shape, longitudinal gradation and a sediment budget are used to quantify spatial and temporal morphological change along the Qingshuigou channel. Distinctive periods of channel change are identified, and analysis provides a detailed understanding of the temporal and spatial adjustments of the channel to specific human interventions, including two artificial channel diversions and changes in water and sediment supply driven by river management, and downstream delta-front development. Adjustments to the diversions included a short-lived period of erosion upstream and significant erosion in the newly activated channel, which progressed downstream. Channel geomorphology widened and deepened during periods when management increased water yield and decreased sediment supply, and narrowed and shallowed during periods when management reduced water yield and the sediment load. Changes along the channel are driven by both upstream and downstream forcing. Finally, there is some evidence that changing delta-front erosion–accretion patterns played an important role in the geomorphic evolution of the deltaic channel; an area that requires further investigation. © 2020 John Wiley & Sons, Ltd.     

中国福建省亚热带山地4 000年来植被变化的孢粉记录

根据采自福建省中部戴云山脉亚高山水系源头地带(大致25°40'N,118°11'E)泥炭沉积洼地的孢粉纪录,对该地区亚热带山地植被近4 000年来的变化进行了研究.孢粉记录和其他沉积资料显示,3个取样点的泥炭沉积开始于4 000年前,很可能是全新世后期气候转冷的结果.在距今4 000～1 200年前期间,戴云山脉上部(海拔1 300～1 600 m)的植被为亚热带针阔叶混交类型,优势种属包括Cryptomeria(柳杉)、Castanopsis(栲)、Quercus(栎)和Tsuga(铁杉)等.距今1 200年前左右,该区域的植被发生了一次大的变化,表现在上述优势属种的孢粉在样品总孢粉数的比例突然下降,而Pinus(松),Gramineae(禾本科)以及Dicranopteris(芒萁)等属种的比例则提高了.这次剧烈的植被变化在其中的一个泥炭钻孔中留下了一层粘土记录,它代表了当时流域内植被受破坏后出现的严重土壤侵蚀.从泥炭沉积提取的孢粉记录还可以看出,研究区内广泛分布的松林是一种次生植被,它是人类不断干扰的结果.     

The changing world under the corona virus threat—from human needs to SDGs and what next?

The COVID-19(coronavirus)disease has affected over 100 countries in a matter of weeks.The way humans live and work on planet Earth has changed profoundly over the last months.Many lives and livelihoods have been lost.Ways of working,shopping,and social interactions are all vastly different for most of us.We do not know when the current crisis will end,or how far we will"return"to the way things were before the pandemic.The world is experiencing one of the most transformative moments of the last 100 years.The social,economic,and political influences of the COVID-19 crisis have already been hugely momentous,we do not utterly understand it.Looking ahead,we have inevitably had to make important public health,economic,governance,and ecological decisions with less information than usual and to reverse recently adopted policies,which can lead to an era of disruptive transformations to sustainability.During these historic times,we must understand the hidden reality of the earth system and attempt to transform our needs so that we all have a sustained future on our planet.     

夏季两种类型高温特征对比和舒适度评价

对上海金山1981—2010年湿热型高温和干热型高温的基本特征以及背景场特征进行分析,并结合人体舒适度讨论两类高温对人们生活工作影响的特点和规律。结果表明:1干热型高温由强大副高控制,地面处于高压顶后或顶前的晴空区;湿热型高温由较强副高控制,地面多处于低压底部,易受水汽影响。2干热年较湿热年,西太平洋副高偏西、偏强,南亚高压偏东、偏北、偏强,夏季风较强,尤其是南风分量偏强显著,下沉运动偏强。3湿热年纬圈方向900hPa以下为上升运动,利于对流活动的发生。4两类高温皆有全天持续热不舒适特点,白天湿度作用明显,湿热型高温持续极热特征突出,严重不舒适感强烈;夜间主要受温度影响,干热型高温造成不舒适感较大。     

Holocene Amazon rainforest–savanna dynamics and climatic implications: high‐resolution pollen record from Laguna Loma Linda in eastern Colombia

We present a high‐resolution pollen record of a 695‐cm‐long sediment core from Laguna Loma Linda, located at an altitude of 310 m in the transitional zone between the savannas of the Llanos Orientales and the Amazonian rainforest, about 100 km from the Eastern Cordillera. Based on eight AMS ¹⁴C ages, the record represents the last 8700 ¹⁴C yr BP. During the period from 8700 to 6000 ¹⁴C yr BP the vegetation was dominated by grass savanna with only a few woody taxa, such as Curatella and Byrsonima, present in low abundance. Gallery forest along the drainage system apparently was poorly developed. Compared with today, precipitation must have been significantly lower and seasonality stronger. During the period from 6000 to 3600 ¹⁴C yr BP, rainforest taxa increased markedly, reflecting an increase in precipitation. Rainforest and gallery forest taxa such as Moraceae/Urticaceae, Melastomataceae, Alchornea, Cecropia and Acalypha, were abundant, whereas Poaceae were reduced in frequency. From 3600 to 2300 ¹⁴C yr BP rainforest taxa continued to increase; Moraceae/Urticaceae became very frequent, and Myrtaceae and Myrsine became common. Savanna vegetation decreased continuously. We infer that precipitation was still increasing, and that the length of the annual dry period possibly shortened. From 2300 ¹⁴C yr BP onwards, grass savanna (mainly represented by Poaceae) expanded and Mauritia palms became frequent. This reflects increased human impact on the vegetation. Copyright © 2000 John Wiley & Sons, Ltd.     

我国海岸带环境蠕变问题的若干事实及其适应性研究

综述了我国海岸带环境蠕变问题的若干事实,如海平面上升、海水入侵、海岸侵蚀及风暴潮等灾害加剧,海洋污染,赤潮频发,渔业资源衰退,红树林遭受破坏,珊瑚礁生态环境退化,海草床生态环境退化以及滨海湿地锐减等。探讨了我国海岸带环境蠕变问题适应性研究体系的建立及未来亟待开展的研究工作。     

Fish assemblages in Tanzanian mangrove creek systems influenced by solar salt farm constructions

Deforestation of mangrove forests is common occurrence worldwide. We examined fish assemblage composition in three mangrove creek systems in Tanzania (East Africa), including two creeks where the upper parts were partly clear-cut of mangrove forest due to the construction of solar salt farms, and one creek with undisturbed mangrove forest. Fish were caught monthly for one year using a seine net (each haul covering 170 m²) within three locations in each creek, i.e. at the upper, intermediate and lower reaches. Density, biomass and species number of fish were lower in the upper deforested sites compared to the mangrove-fringed sites at the intermediate and lower parts in the two creeks affected by deforestation, whereas there were no differences among the three sites in the undisturbed mangrove creek system. In addition, multivariate analyses showed that the structure of fish assemblages varied between forested and clear-cut sites within the two disturbed creeks, but not within the undisturbed creek. Across the season, we found no significant differences except for a tendency of a minor increase in fish densities during the rainy season. At least 75% of the fishes were juveniles and of commercial interest for coastal fisheries and/or aquaculture. Mugil cephalus, Gerres oyena and Chanos chanos were the most abundant species in the forested sites. The dominant species in the clear-cut areas were M. cephalus and Elops machnata, which were both found in relatively low abundances compared to the undisturbed areas. The conversion of mangrove forests into solar salt farms not only altered fish assemblage composition, but also water and sediment conditions. In comparison with undisturbed areas, the clear-cut sites showed higher salinity, water temperature as well as organic matter and chlorophyll a in the sediments. Our results suggest that mangrove habitat loss and changes in environmental conditions caused by salt farm developments will decrease fish densities, biomass and species numbers as well as alter the overall fish assemblage composition in the salt farm area but not downstream in the creek.