Landsat Image-Based Spatiotemporal Variation Analysis of Erosion and Deposition off the Qingshuigou of the Yellow River Delta from 1984 to 2021

Owing to climate change and human activity,the Qingshuigou of the Yellow River Delta(YRD)has undergone dynamic changes in erosion and deposition.Therefore,studying these changes is important to ensure ecological protection and sustainable development.In this study,the trend of erosion-deposition evolution in the Qingshuigou was investigated based on 38 coastline phases extracted from Landsat series images of the YRD at one-year intervals from 1984 to 2021.The periodicity of the scouring and deposition evolution was also analyzed using wavelet analysis.Results showed that the total area of the Qingshuigou was affected by deposition and erosion and that the fluctuation first increased and then decreased.The total area reached a maximum in 1993.The depositional area first increased and then decreased,whereas the overall erosion area decreased.Deposition and erosion areas showed periodic changes to some extent;however,the periodic signal intensity decreased.Furthermore,factors including channel morphological evolution and variations in water and sediment discharge affect the spatiotemporal dynamics of erosion and deposition processes.The application of nonconsistency tests finally revealed that deposition area and flushing magnitude exhibited non-stationarities,which are potentially attributed to impacts from climatic change drivers.

Occurrence,Spatial Distribution,Sources and Risk Assessment of Per-and Polyfluoroalkyl Substances in Surface Sediments of the Yellow River Delta Wetland

Per-and polyfluoroalkyl substances(PFASs)are emerging persistent organic pollutants(POPs).In this study,47 surface sediment samples were collected from the Yellow River Delta wetland(YRDW)to investigate the occurrence,spatial distribution,potential sources,and ecological risks of PFASs.Twenty-three out of 26 targeted PFASs were detected in surface sediment samples from the YRDW,with totalΣ23PFASs concentrations ranging from 0.23 to 16.30 ng g^(-1) dw and a median value of 2.27 ng g^(-1) dw.Perfluorooctanoic acid(PFOA),perfluorobutanoic acid(PFBA)and perfluorooctanesulfonic acid(PFOS)were the main contaminants.The detection frequency and concentration of perfluoroalkyl carboxylic acids(PFCAs)were higher than those of perfluoroal-kanesulfonic acids(PFSAs),while those of long-chain PFASs were higher than those of short-chain PFASs.The emerging PFASs substitutes were dominated by 6:2 chlorinated polyfluoroalkyl ether sulfonic acid(6:2 Cl-PFESA).The distribution of PFASs is significantly influenced by the total organic carbon content in the sediments.The concentration of PFASs seems to be related to human activities,with high concentration levels of PFASs near locations such as beaches and villages.By using a positive matrix factorization model,the potential sources of PFASs in the region were identified as metal plating mist inhibitor and fluoropolymer manufacturing sources,metal plating industry and firefighting foam and textile treatment sources,and food packaging material sources.The risk assessment indicated that PFASs in YRDW sediments do not pose a significant ecological risk to benthic organisms in the region overall,but PFOA and PFOS exert a low to moderate risk at individual stations.

Activity Pattern and Habitat Use of Shorebirds in an Artificial Wetland Complex:A Case Study of Breeding Pied Avocet in the Yellow River Delta,China

With the loss of substantial natural wetlands in coastal zones,artificial wetlands provide alternative habitats for many shorebirds.Scientific management of artificial wetlands used by shorebirds plays an important role in maintaining the stability of shorebird population.Satellite tracking technique can obtain high-precision location information of individuals day and night,providing a good technical support for the study of quantitative relationship between waterfowls and their habitats.In this study,satellite tracking method,Remote Sensing(RS)and Geographic Information System(GIS)technology were used to analyze the activity pattern and habitat utilization characteristics of Pied Avocet during breeding period in an artificial wetland complex in the Yellow River Delta(YRD),China.The results showed that the breeding Pied Avocets had a small range of activity,with a total core and main home range of 33.10 km^(2) and 216.30 km^(2),respectively.This species tended to forage in the pond and salt pan during the day and night,respectively,with an unfixed staying time in the breeding ground.The distance between breeding ground and feeding ground was less than 6 km.It is emphasized that in addition to improving the conditions of the remaining natural habitats,effective managing artificial habitats is a priority for shorebird conservation.This research could provide reference for the management of artificial wetlands in coastal zones and supply technique support for the protection of shorebirds and their habitats,and alleviate human-bird conflicts and sustainable development of coastal zones.

Persistence of fertilization effects on soil organic carbon in degraded alpine wetlands in the Yellow River source region

In the restoration of degraded wetlands,fertilization can improve the vegetation-soil-microorganisms complex,thereby affecting the organic carbon content.However,it is currently unclear whether these effects are sustainable.This study employed Biolog-Eco surveys to investigate the changes in vegetation characteristics,soil physicochemical properties,and soil microbial functional diversity in degraded alpine wetlands of the source region of the Yellow River at 3 and 15 months after the application of nitrogen,phosphorus,and organic mixed fertilizer.The following results were obtained:The addition of nitrogen fertilizer and organic compost significantly affects the soil organic carbon content in degraded wetlands.Three months after fertilization,nitrogen addition increases soil organic carbon in both lightly and severely degraded wetlands,whereas after 15 months,organic compost enhanced the soil organic carbon level in severely degraded wetlands.Structural equation modeling indicates that fertilization decreases the soil pH and directly or indirectly influences the soil organic carbon levels through variations in the soil water content and the aboveground biomass of vegetation.Three months after fertilization,nitrogen fertilizer showed a direct positive effect on soil organic carbon.However,organic mixed fertilizer indirectly reduced soil organic carbon by increasing biomass and decreasing soil moisture.After 15 months,none of the fertilizers significantly affected the soil organic carbon level.In summary,it can be inferred that the addition of nitrogen fertilizer lacks sustainability in positively influencing the organic carbon content.

Impacts of multi-scenario land use change on ecosystem services and ecological security pattern: A case study of the Yellow River Delta

The Yellow River Delta(YRD), a critical economic zone along China's eastern coast, also functions as a vital ecological reserve in the lower Yellow River. Amidst rapid industrialization and urbanization, the region has witnessed significant land use/cover changes(LUCC), impacting ecosystem services(ES) and ecological security patterns(ESP). Investigating LUCC's effects on ES and ESP in the YRD is crucial for ecological security and sustainable development. This study utilized the PLUS model to simulate 2030 land use scenarios, including natural development(NDS), economic development(EDS), and ecological protection scenarios(EPS). Subsequently, the InVEST model and circuit theory were applied to assess ES and ESP under varying LUCC scenarios from 2010 to 2030. Findings indicate:(1) Notable LUCC from 2010 to 2030, marked by decreasing cropland and increasing construction land and water bodies.(2) From 2010 to 2020, improvements were observed in carbon storage,water yield, soil retention, and habitat quality, whereas 2020–2030 saw increases in water yield and soil retention but declines in habitat quality and carbon storage. Among the scenarios, EPS showed superior performance in all four ES.(3) Between 2010 and 2030, ecological sources, corridors, and pinchpoints expanded, displaying significant spatial heterogeneity. The EPS scenario yielded the most substantial increases in ecological sources,corridors, and pinchpoints, totaling 582.89 km^(2), 645.03 km^(2),and 64.43 km^(2), respectively. This study highlights the importance of EPS, offering insightful scientific guidance for the YRD's sustainable development.

Evaluation of Ecological Sustainable Development in the Yangtze River Delta Region Based on Ecological Footprint Theory

The ecological footprint was employed as a quantitative indicator of resource inputs,enabling a detailed account of the structure of biological resources and energy occupancy,as well as the variation of resource productivity in the Yangtze River Delta(YRD)Region.From 2004 to 2018,there were notable variations in the ecological productivity of different types of land on basis of China’s equilibrium factor across the three provinces and one city in the YRD region.Jiangsu Province exhibited the highest ecological productivity of arable land,while Anhui Province exhibited the highest ecological productivity of forest land.Shanghai City exhibited the highest ecological productivity of pasture land,while Zhejiang Province exhibited the highest ecological productivity of water area.In 2018,the proportion of arable land within the total ecological carrying capacity of the YRD region reached 74.35%.Furthermore,the contribution of Jiangsu and Anhui provinces to the YRD’s total ecological carrying capacity was 41.36%and 41.26%,respectively.In the construction of a new development pattern in the YRD region,which is dominated by the domestic cycle as the main body and mutually reinforced by domestic and international double-cycle,the YRD region should combine the utilization of natural forces with innovation in science,technology and cooperation mechanisms.Furthermore,the government should guide the concentration of social capital towards green industries.It is also recommended that the moderate reduction of ecological footprints should be encouraged,and that the security of biological resources and energy,the leadership in the field of cutting-edge science and technology should be ensured in YRD region.This will facilitate the formation of a new development pattern of higher-quality integration at the national level firstly.

Causes of Wetland Degradation and Ecological Restoration in the Yellow River Delta Region

Yellow River delta （YRD） is one of the biggest deltas that there is a large area of wetland in the world. Thanks to soil （sands） sediment carried by the Yellow River, there was averagely the newly formed land 21.3 km^2 in YRD. During the development of petroleum industry and urban expansion, wetlands were degraded due to population growth, irrational land use, in addition to adverse natural eco-environment such as lower precipitation, higher soil evaporation and soil salinazation. The major ecological measures to restore degraded wetland concerned with ensuring water supply, especially establishing perfect irrigation works; protecting virgin plant communities and assisting them to regenerate by the way of site preparation, improving living surroundings; introducing salt-tolerant plants to increase vegetation species and plant coverage, thereby enhancing the capability of wetland to combat contamination and pollution through plant remediation, uptake, absorption, etc. Finally making a comprehensive land use plan, accordingly removing deleterious facilities.

Remote Monitoring of Expansion of Aquaculture Ponds Along Coastal Region of the Yellow River Delta from 1983 to 2015

Aquaculture ponds are one of the fastest-growing land use types in valuable and fertile coastal areas and have caused serious environmental problems. Quantitative assessment of the extent, spatial distribution, and dynamics of aquaculture ponds is of utmost importance for sustainable economic development and scientific management of land and water resources in the coastal area. An object-oriented classification approach was applied to Landsat images acquired over three decades to investigate the long-term change of aquaculture ponds in the coastal region of the Yellow River Delta. The results indicated that the aquaculture ponds in the study area undergone a sharp expansion from 40.38 km^2 in 1983 to 1406.89 km^2 in 2015, and the fast expansion occurred during the period of 2010–2015 and 1990–2000. Natural wetlands, especially mudflat, and cropland were main land use types contributing to the increase of aquaculture ponds. The patches of aquaculture ponds were consequently prevalence in the north of the Yellow River Estuary and landscape metrics indicated an increase of the aquaculture ponds of the study area in the quantity and complexity. The expansion of aquaculture ponds inevitably had negative effects on the coastal environment, including loss of natural wetlands, water pollution and land subsidence, etc. The results from this study provide baseline data and valuable information for efficiently planning and managing aquaculture practices and for effectively implementing adequate regulations and protection measures.

Discussion on storm-induced liquefaction of the superficial stratum in the Yellow River subaqueous delta

Geological disasters on the superficial seafloor were revealed in geological investigation on the Yellow River subaqueous delta. Combined with dynamic triaxial tests and wave flume experiments, occurring conditions and forming patterns of liquefaction as well as motion of the liquefied soil were explained in this paper. Based on the viewpoint that the geological disasters were formed due to silty soil liquefaction under storm waves, re-stratification issue of the superficial stratum was analyzed. Movement of the liquefied soil agreed with the wave, leading to differentiation of the soil particles. Research issues in respect of geological, environment and engineering of storm-induced liquefaction were also discussed.

Numerical study on local scour characteristics around submarine pipelines in the Yellow River Delta silty sandy soil under waves and currents

Due to their high reliability and cost-efficiency,submarine pipelines are widely used in offshore oil and gas resource engineering.Due to the interaction of waves,currents,seabed,and pipeline structures,the soil around submarine pipelines is prone to local scour,severely affecting their operational safety.With the Yellow River Delta as the research area and based on the renormalized group(RNG)k-εturbulence model and Stokes fifth-order wave theory,this study solves the Navier-Stokes(N-S)equation using the finite difference method.The volume of fluid(VOF)method is used to describe the fluid-free surface,and a threedimensional numerical model of currents and waves-submarine pipeline-silty sandy seabed is established.The rationality of the numerical model is verified using a self-built waveflow flume.On this basis,in this study,the local scour development and characteristics of submarine pipelines in the Yellow River Delta silty sandy seabed in the prototype environment are explored and the influence of the presence of pipelines on hydrodynamic features such as surrounding flow field,shear stress,and turbulence intensity is analyzed.The results indicate that(1)local scour around submarine pipelines can be divided into three stages:rapid scour,slow scour,and stable scour.The maximum scour depth occurs directly below the pipeline,and the shape of the scour pits is asymmetric.(2)As the water depth decreases and the pipeline suspension height increases,the scour becomes more intense.(3)When currents go through a pipeline,a clear stagnation point is formed in front of the pipeline,and the flow velocity is positively correlated with the depth of scour.This study can provide a valuable reference for the protection of submarine pipelines in this area.

Examining the evolution of tidal creeks in the Huanghe River delta using multi-temporal Landsat images

Coastal tidal creeks are important channels for exchanges of material and energy between sea and land,and play an important role in the ecological protection of tidal flats.Although tidal creeks have evolved differently in various regions,the evolutionary process of tidal creeks in the Huanghe(Yellow)River delta of China,one of the most active deltas worldwide,is not entirely clear.Therefore,the evolution of tidal creeks in the delta from 1981 to 2021 was investigated by quantitatively analysing the tidal creeks and developing a standard for dividing their evolution periods.Visual interpretation and supervised classification methods were applied to the Landsat images to extract the tidal creek network,and 17 groups of tidal creek systems were selected.Results indicate that Creek S 1 was the most developed creek for having 113 tidal creeks totaling 65.8 km in length,while Creek E 3 had the fastest growth rate for having average annual increase of 1.9 km.Meanwhile,the level of tidal creeks increased,the average and median lengths of tidal creeks increased,and the number of tidal creeks decreased since 1981.The evolution of the tidal creek system could be divided into four stages,namely,rising,developing,stabilizing,and degrading.Analyses of a representative tidal creek show that there was no degenerated tidal creek during the rising period,with an increase in the number of 50 and a length increase of 57.9 km between 1981 and 1989.The proportion of new tidal creeks in the developing period was more than 50%and the new tidal creeks in the stabilizing period were equal to the degraded tidal creeks.Extinct tidal creeks were greater than 50%during the degrading period.There was no fixed order of tidal creek evolution in each period,and there may be a skip in evolution.Our findings provided a reference for studying the evolution of tidal creeks.

Effects of Vegetation Restoration Age on Soil C:N:P Stoichiometry in Yellow River Delta Coastal Wetland of China

Vegetation restoration can alter carbon(C),nitrogen(N),and phosphorus(P)cycles in coastal wetlands affecting C:N:P stoichiometry.However,the effects of restoration age on soil C:N:P stoichiometry are unclear.In this study,we examined the re-sponses of soil C,N,and P contents and their stoichiometric ratios to vegetation restoration age,focusing on below-ground processes and their relationships to aboveground vegetation community characteristics.We conducted an analysis of temporal gradients based on the'space for time'method to synthesize the effects of restoration age on soil C:N:P stoichiometry in the Yellow River Delta wetland of China.The findings suggest that the combined effects of restoration age and soil depth create complex patterns of shifting soil C:N:P stoichiometry.Specifically,restoration age significantly increased all topsoil C:N:P stoichiometries,except for soil total phosphorus(TP)and the C:N ratio,and slightly affected subsoil C:N:P stoichiometry.The effects of restoration age on the soil C:N ratio was well constrained owing to the coupled relationship between soil organic carbon(SOC)and total nitrogen(TN)contents,while soil TP con-tent was closely related to changes in plant species diversity.Importantly,we found that the topsoil C:N:P stoichiometry was signific-antly affected by plant species diversity,whereas the subsoil C:N:P stoichiometry was more easily regulated by pH and electric con-ductivity(EC).Overall,this study shows that vegetation restoration age elevated SOC and N contents and alleviated N limitation,which is useful for further assessing soil C:N:P stoichiometry in coastal restoration wetlands.

Dynamics Characteristics and Topographic Profile Shaping Process of Feiyan Shoal at the Yellow River Delta

Feiyan Shoal is a sub Yellow River Delta, which was formed from Jan. 1964 to May 1976, when the Yellow River entered sea via Diaokou Channel. Since the terminal reach shifted to Qingshuigou channel in 1976, Feiyan Shoal has been experiencing severe erosion and retreat. This paper explains the evolutionary characteristics of the typical profile of Feiyan Shoal from the perspective of dynamical force and sediments＇ characteristics. All this is on the basis of the data of topographic profiles observed since the 1970s and the samples of hydrology and sediments collected in situ in Apr. 2004, the analysis of the retreating distance, and the tidal and wave friction velocity distribution. Feiyan Shoal topographical profile has experienced a course of ＂fast erosion and retrogression - slow eroding modulation - fluctuate triggering change＂ in recent 30 years, which is also the gradual disappearing process of the delta front. The different intensity of sediment erosion resistance is the main reason for the erosion speed changes. Due to the hydrodynamic force changes, the water depth range of maximum retreating distance and between erosion and progradation became shallow. It indicates that the storm tide will still be the triggering force of seashore topographic profile evolutions in the future.

Dynamic Changes in the Wetland Landscape Pattern of the Yellow River Delta from 1976 to 2016 Based on Satellite Data

The Yellow River Delta wetland is the youngest wetland ecosystem in China's warm temperate zone. To better understand how its landscape pattern has changed over time and the underlying factors responsible, this study analyzed the dynamic changes of wetlands using five Landsat series of images, namely MSS(Mulri Spectral Scanner), TM(Thematic Mapper), and OLI(Operational Land Imager) sensors in 1976, 1986, 1996, 2006, and 2016. Object-oriented classification and the combination of spatial and spectral features and both the Normalized Difference Vegetation Index(NDVI) and Normalized Difference Water Index(NDWI), as well as brightness characteristic indices, were used to classify the images in eCognition software. Landscape pattern changes in the Yellow River Delta over the past 40 years were then delineated using transition matrix and landscape index methods. Results show that: 1) from1976 to 2016, the total area of wetlands in the study area decreased from 2594.76 to 2491.79 km^2, while that of natural wetlands decreased by 954.03 km^2 whereas human-made wetlands increased by 851.06 km^2. 2) The transformation of natural wetlands was extensive: 31.34% of those covered by Suaeda heteropteras were transformed into reservoirs and ponds, and 24.71% with Phragmites australis coverage were transformed into dry farmland. Some human-made wetlands were transformed into non-wetlands types: 1.55% of reservoirs and ponds became construction land, and likewise 21.27% were transformed into dry farmland. 3) From 1976 to 2016, as the intensity of human activities increased, the number of landscape types in the study area continuously increased. Patches were scattered and more fragmented. The whole landscape became more complex. In short, over the past 40 years, the wetlands of the Yellow River Delta have been degraded, with the area of natural wetlands substantially reduced. Human activities were the dominant forces driving these changes in the Yellow River Delta.

Characteristics of grassland degradation and driving forces in the source region of the Yellow River from 1985 to 2000

The source region of the Yellow River is located in the middle east of the Tibetan Plateau in northwest China. The total area is about 51,700 km^2, mainly covered by grassland （79%）, unused land （16%） and water （4%）. The increasing land utilization in this area has increased the risk of environmental degradation. The land use/cover data （1985 and 2000） provided by the Data Center of Resources and Environment in the Chinese Academy of Sciences were used to analyze the land cover change in the source region of the Yellow River. DEM （1：250,000） data, roads and settlement data were used to analyze the spatial characteristics of grasslands degradation. The ArcGIS 9 software was used to convert data types and do the overlay, reclassification and zonal statistic analysis. Results show that grassland degradation is the most important land cover change in the study area, which occupied 8.24% of the region＇s total area. Human activities are the main causes of the grassland degradation in the source region of the Yellow River： 1） the degradation rate is higher on the sunny slope than on the shady slope; 2） the grassland degradation rate decreases with an increase in the elevation, and it has a correlation coefficient of -0.93; 3） the nearer to the settlements the grassland is, the higher the degradation rate. Especially within a distance range of 12 km to the settlements, the grassland degradation rate is highly related with the distance, with a coefficient of -0.99; and 4） in the range of 4 km, the degradation rate decreases with the increase of distance to the roads, with a correlation coefficient of -0.98. Besides some physical factors, human activities have been the most important driving forces of the grassland degradation in the source region of the Yellow River since 1985. To resolve the degradation problems, population control is essential, and therefore, it can reduce the social demand of livestock products from the grassland. To achieve sustainable development, it needs to improve the management of grassland ecosystem.

Changes in freezing and thawing indices over the source region of the Yellow River from 1980 to 2014

Freezing and thawing indices are not only of great significance for permafrost research but also are important indicators of the effects of climate change.However,to date,research on ground-surface freezing and thawing indices and their relationship with air indices is limited.Based on daily air and ground-surface temperatures collected from 11 meteorological stations in the source region of the Yellow River,the freezing and thawing indices were calculated,and their spatial distribution and trends were analyzed.The air-freezing index(AFI),air-thawing index(ATI),ground surface-freezing index(GFI),ground surface-thawing index(GTI),air thawing-freezing index ratio(Na)and surface ground thawing-freezing index ratio(Ng)were 1554.64,1153.93,1.55,2484.85,850.57℃-days and 3.44,respectively.Altitude affected the spatial distribution of the freezing and thawing indices.As the altitude increased,the freezing indices gradually increased,and the thawing indices and thawing-freezing index ratio decreased.From 1980 to 2014,the AFI and GFI decreased at rates of 8.61 and 11.06℃-days a^(-1),the ATI and GTI increased at 9.65 and 14.53℃-days a^(-1),and Na and Ng significantly increased at 0.21 and 0.79 decade^(-1).Changes in the freezing and thawing indices were associated with increases in the air and ground-surface temperatures.The rates of change of the ground surface freezing and thawing indices were faster than the air ones because the rate of increase of the groundsurface temperature was faster than that of the air and the difference between the ground surface and air increased.The change point of the time series of freezing and thawing indices occurred in 2000–2001.After 2000–2001,the AFI and GFI were lower than before the change point,and the changing trend was lower.The ATI,GTI,Na and Ng during 2001–2014 were higher,with faster rates than before.In addition,the annual thawing indices composed a greater proportion of the mean annual air temperature and mean annual ground surface temperature than the annual freezing indices.This study provides the necessary basis for research on and prediction of permafrost changes,especially changes in the depth of the active permafrost layer,climate change,and possible evolution of the ecological environment over the source region of the Yellow River on the Qinghai-Tibet Plateau.

Response of delta sedimentary system to variation of water and sediment in the Yellow River over past six decades

In order to find out the variation process of water-sediment and its effect on the Yellow River Delta, the water discharge and sediment load at Lijin from 1950 to 2007 and the decrease of water discharge and sediment load in the Yellow River Basin caused by human disturbances were analyzed by means of statistics. It was shown that the water discharge and sediment load into the sea were decreasing from 1950 to 2007 with serious fluctuation. The human activities were the main cause for decrease of water discharge and sediment load into the sea. From 1950 to 2005, the average annual reduction of water discharge and sediment load by means of water-soil conservation practices were 2.02×10^9 m^3 and 3.41×10^8 t respectively, and the average annual volume by water abstraction for industry and agriculture were 2.52×10^10 m^3 and 2.42×10^8 t respectively. The average sediment trapped by Sanmenxia Reservoir was 1.45×10^8 t from 1960 to 2007, and the average sediment retention of Xiaolangdi Reservoir was 2.398×10^8t from 1997 to 2007. Compared to the data records at Huanyuankou, the water discharge and sediment load into the sea decreased with siltation in the lower reaches and increased with scouring in the lower reaches. The coastline near river mouth extended and the delta area increased when the ratio of accumulative sediment load and accumulative water discharge into the sea （SSCT） is 25.4-26.0 kg/m^3 in different time periods. However, the sharp decrease of water discharge and sediment load into the sea in recent years, especially the Yellow River into the sea at Qing 8, the entire Yellow River Delta has turned into erosion from siltation, and the time for a reversal of the state was about 1997.

Regional accessibility of land traffic network in the Yangtze River Delta

In a given district, the accessibility of any point should be the synthetically evaluation of the internal and external accessibilities. Using MapX component and Delphi, the author presents an information system to calculate and analyze regional accessibility according to the shortest travel time, generating thus a mark diffusing figure. Based on land traffic network, this paper assesses the present and the future regional accessibilities of sixteen major cities in the Yangtze River Delta. The result shows that the regional accessibility of the Yangtze River Delta presents a fan with Shanghai as its core. The top two most accessible cities are Shanghai and Jiaxing, and the bottom two ones are Taizhou （Zhejiang province） and Nantong With the construction of Sutong Bridge, Hangzhouwan Bridge and Zhoushan Bridge, the regional internal accessibility of all cities will be improved. Especially for Shaoxing, Ningbo and Taizhou （Jiangsu province）, the regional internal accessibility will be decreased by one hour, and other cities will be shortened by about 25 minutes averagely. As the construction of Yangkou Harbor in Nantong, the regional external accessibility of the harbor cities in Jiangsu province will be speeded up by about one hour.

Spatiotemporal Variation of Plant Diversity Under a Unique Estuarine Wetland Gradient System in the Yellow River Delta, China

Multiple natural and human factors in estuarine wetlands result in complicated land surface characteristics with distinct spatial and temporal heterogeneities,thereby contributing to the difficulty in identifying spatiotemporal variations and influencing factors of plant diversity.A unique estuarine wetland gradient system(UEWGS)consisting of soil,vegetation,heat,distance,landscape,and anthropogenic gradients was established based on the ecological features of estuarine wetland through remote sensing and field investigation methods.It resolved the complicated land surface characteristics,covered all aspects of factors influencing plant diversity,and possessed distinct spatiotemporal heterogeneities.The Yellow River Delta,the largest estuarine wetland in the northern China,was selected as the study area to demonstrate UEWGS in four seasons in 2017.A total of 123 species were recorded with considerable seasonal difference.Phragmites australis,Suaeda salsa,and Tamarix chinensis were the dominant species,and crop species also played important roles.In single effect,all aspects of gradients exerted significant influences,yet only vegetation gradient possessed significant influences in all seasons.In comprehensive effect,soil,vegetation,heat,and distance gradients showed significant gross influences.Moisture content in soil gradient and net primary productivity in vegetation gradient possessed significant net influences in all seasons and can be considered as the main driving factor and indicator,respectively,of plant diversity.The results validated the significance of UEWGS in revealing the plant diversity spatiotemporal characteristics and influencing factors,and UEWGS possessed universal applicability in the spatiotemporal analysis of plant diversity in estuarine areas.

Influencing factors of water resources in the source region of the Yellow River

Taking the source region of the Yellow River as a study area and based on the data from Madoi Meteorological Station and Huangheyan Hydrological Station covering the period 1955-2005, this paper analyses the changing trends of surface water resources, climate and frozen ground and reveals their causes. Results show that there exist frequent fluctuations from high to low water flow in the 51-year period. In general, the discharge has shown a de- clining trend in the 51 years especially since the 1990s. The annual distribution shows one peak which, year on year is getting smaller. （1） Precipitation has a significant and sustained influence on discharge. （2） A sharp rise of temperature resulted in the increase of evaporation and the decrease of discharge, which has a greater effect than on ice-snow melting. （3） Frozen ground tends to be degraded markedly. There is a significant positive correlation be- tween the permafrost thickness and the discharge. （4） Evaporation rates are significantly increasing, leading to the decrease of discharge. 70% of the discharge reduction resulted from climate change, and the remaining 30% may have been caused by human activities.