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The regions near the Tropic of Cancer are a latitudinal geographical zone with typical climatic, topographic, and human landscape features. It is necessary to explore the region's net primary productivity (NPP) dynamics as it combines complex topography, various vegetation types, and intense human activities. The study sets the transect near the Tropic of Cancer (TCT) and uses the Carnegie–Ames–Stanford (CASA) model to estimate the NPP from 2000 to 2020. After using the RESTREND method, the paper calculates and compares the relative contributions of climate variability and anthropogenic activities to NPP changes. Finally, the geographical detector (Geodetector) model is applied to evaluate how anthropogenic and natural factors affect spatial distribution patterns and NPP changes. The results indicated that the average annual NPP is 820.39 gC·m−2·yr−1 during the 21 years. In addition, when the NPP varies, it increases over the entire study area, with a slope of 4.81 gC·m−2·yr−1, particularly in the western region. Across the entire research area, 63.39% and 77.44% of the total pixels positively contribute to climate variability and human activities in NPP, with a contribution of 0.90 and 3.91 gC·m−2·yr−1, respectively. Within the western, central, and eastern regions, anthropogenic activities have a stronger impact on NPP than climate variability, particularly pronounced in the eastern region. Furthermore, vegetation cover is the dominant factor in the spatial patterns and NPP trends across the TCT and the three regions. In contrast, climate factors are shown to be less influential in NPP distribution than in the western region. The results also demonstrated that the effect of population density and the GDP on NPP gradually rises. Two-factor interaction is much larger than any individual factor, with the dominant interaction factor being vegetation cover with climatic factors. Lastly, the findings revealed that anthropogenic activities positively promote NPP accumulation across the TCT, thus highlighting the importance of human activity-led ecological restoration and ecological protection measures that contribute to regional carbon sequestration and carbon balance. [ABSTRACT FROM AUTHOR]

The macro-tidal estuary with a mountain stream is a typical estuary on China′s southeast coast, characterized by intense dynamic forces, active sediment movements, and a robust response to human activities. It demands further investigation of its evolution mechanism under both natural conditions and anthropogenic stresses. This paper takes the Jiangxinyu reach of the Oujiang River estuary as a case example to explore the river′s evolution under the influence of human activities, including effects of longitudinal dam construction, sand mining, and shoreline adjustment since the 1970s. Measured data analysis and a two- dimensional flow and sediment mathematical model were used. The results confirm that anthropogenic stresses have altered the natural periodic alternation of the river′s main and side branches. Moreover, the undercutting of the riverbed caused by sand mining from the beginning of this century has increased tidal range by 0. 5 m and tidal prism by 47%, while weakening the discharge asymmetry and sediment transport asymmetry indices by 0. 08—0. 30 and 0. 28—0. 54, respectively. The undercutting of the riverbed has also weakened the ebb and flood asymmetry. These conditions have subsequently helped slow down the shrinkage of the side branch. The evolution mechanism is dominated by both natural and human activities. Overall, the research findings may be a reference for river evolution and protection under the influence of human activities. [ABSTRACT FROM AUTHOR]

• Groundwater hydrochemistry evolution interpretation from the viewpoint of water flow system. • Anthropogenic activities and natural processes are distinguished in different zones. • Practical implications for regional water resources exploitation strategy. Groundwater resources are increasingly exploited for industrial and agricultural purposes in many arid/semi-arid regions globally. In order to gain a harmonious development among groundwater resources and economic benefits, urgent investigation of the impacts of anthropogenic activities on the groundwater chemistry is required. Understanding hydrochemical mechanism of groundwater in Yinchuan Plain, arid and semi-arid area in Northwestern China, plays a significant role in water resources planning in this ecologically sensitive area. In this paper, a total of 460 phreatic water samples were collected, including 58 water samples containing isotopic data (D and 2H). Results demonstrate that water chemistry type and isotopic data of phreatic water presents a zonation characteristic from west to east and from south to north. In the eastern part of the Helan Mountain (A 1 zone), the type of hydrochemistry is mainly HCO 3 ·SO 4 -Ca·Mg, SO 4 ·HCO 3 -Ca·Mg, which is mainly recharged by the bedrock fissure water of Helan Mountain. However, in the southern Qingtongxia (A 2 zone) are HCO 3 -Na HCO 3 -Ca·Mg, which receives irrigation and spring water recharge. Phreatic aquifer in Multi-layered structure zone (A 3 zone) reflect multiple recharge sources to the aquifer, the water chemistry demonstrates diverse variations. The anion was dominated by the HCO 3 , while the cation is dominated by sodium. The predominant controlling factors of phreatic water hydrochemistry are divided into anthropogenic activities and natural conditions. Natural conditions mainly include the existence form and lithology of the aquifer, sources of groundwater recharge, soil salinity, and evaporation, mineral dissolution, ion exchange and adsorption and mixing effect. Meanwhile, among natural factors, minerals dissolution in groundwater is the main process dominating the hydrochemical evolution of the groundwater. The other is anthropogenic activities which can be classified as groundwater pollution, excessive exploitation or excretion of groundwater, and excessive groundwater recharge. [ABSTRACT FROM AUTHOR]

As an important part of the global ecosystem, wetlands and their dynamics greatly influence regional eco-environment systems. To understand the distributions, change processes and temporal-spatial characteristics of the wetlands of the inland river basin in an arid region (Heihe River Basin, HRB), this paper employed multi-source remote sensing data to facilitate multi-temporal monitoring of the HRB wetland using a wetland information extraction method. First, we performed monitoring of these wetlands for the years 2000, 2007, 2011 and 2014; then, we analyzed the variation characteristics of the spatial-temporal dynamics of the wetlands in the HRB over the last 15 years via the landscape dynamic change model and the transformation matrix. In addition, we studied the possible driving mechanisms of these changes. The research results showed that the total area of the HRB wetlands had decreased by 2959.13 hectares in the last 15 years (Since 2000), and the annual average loss was 1.09%. The dynamics characterizing the HRB wetlands generally presented a trend of slow increase after an initial decrease, which can be classified into three stages. From 2000 to 2007, the total wetland area rapidly decreased; from 2007 to 2011, the area slowly decreased; and from 2011 to 2014, the area gradually increased. The dynamic changing processes characterizing the wetland resources were ascribed to a combination of natural processes and human activities. The main driving mechanisms of wetland dynamic changes include climatic conditions, upper reach water inflows, population, water resources, cultivated area, and policy. The findings of this study can served as reference and support for the conservation and management of wetland resources in the HRB. [ABSTRACT FROM AUTHOR]

On 20 August 2005, a landslide with a volume of about 400 m occurred at Fu Yung Shan Tsuen, Tsuen Wan in Hong Kong during a severe rainstorm with a return period of about 100 years on a hillside that has been disturbed locally by past human activities. The incident resulted in one fatality and permanent evacuation of residents of four squatter structures in the vicinity. A forensic investigation into the landslide was carried out to review the mechanism and probable causes of the landslide. The key contributory factors in the landslide were diagnosed. The investigation concluded that the landslide was probably caused by the loss of soil suction and transient build-up of groundwater pressure in the near-surface soil materials following prolonged and intense rainfall. The paper presents the methodology adopted for the landslide study, findings of the investigation and the lessons learnt from this fatal landslide. [ABSTRACT FROM AUTHOR]

Coastal morphodynamics and environmental changes have been obviously altered by global warming, sea-level fluctuations, and human activities. Palynological analysis is one of the most important tools for providing information on vegetation, climate, and environmental change, which can be relatively sensitive indicators of human activity during the Holocene. However, Holocene coastal morphodynamics and palynological evidence from the Pearl River Delta and coastal areas has not been sufficiently studied. In this paper, we carry out analyses using detailed grain-size and palynological records of pollen, spores, freshwater algae, and marine dinoflagellate cysts from Borehole QZK13 in the Pearl River Estuary (PRE), southern China. The results show information relating coastal morphodynamics, vegetation evolution, climate changes, and anthropogenic activities during the Holocene based on radiocarbon chronology. In general, the PRE experienced marine transgressive processes; sea-level and the coastline tended to migrate landward between 10,700 and 4250 cal yr BP. Meanwhile, abundant arboreal pollen (mainly Castanopsis , Quercus -evergreen, Oleaceae, and Castanea) and small amounts of non-arboreal pollen (mainly Poaceae, Cyperaceae, and Artemisia) were observed in Borehole QZK13, which suggests that subtropical evergreen broadleaved forests were distributed throughout the PRE and adjacent areas, and relatively warm and moist climatic conditions were present during the early-middle Holocene. After that, there were relatively cool and wet climatic conditions, and marine regressive processes occurred in the PRE during the Late Holocene (ca. 4250–960 cal yr BP) indicated by an abrupt increase in aquatic herbs and Dicranopteris. Moreover, we hypothesize that the Neolithic "cultural fault" in the PRE is likely related to frequent storm surges induced by extreme typhoon events that occurred ca. 3000–2700 yr BP. • Grain size, pollen, spores, freshwater algae and dinoflagellate cysts from the Pearl River Estuary were investigated. • Three major phases shown by palynological results were corresponding to the changes in vegetation and climate. • We hypothesized that the Neolithic "cultural fault" is probably related to the storm surges induced by extreme typhoon events. • Natural vegetation cover has suffered large-scale destruction by ancient humans during the Late Holocene. [ABSTRACT FROM AUTHOR]