River Delta Plain Research Articles

Aboveground biomass distributions and vegetation composition changes in Louisiana's Wax Lake Delta

The Wax Lake Delta (WLD) is an actively prograding delta in the Mississippi River Delta Plain that is otherwise experiencing widespread degradation and submergence of its coastal wetlands. The WLD is actively accumulating mineral and organic sediment that increases soil surface elevation, changing emergent wetland communities as the young delta develops. There is uncertainty in how the dynamics of community composition respond to net changes in soil elevation and determine aboveground biomass and carbon storage. This study utilizes high resolution imaging spectrometer data captured on October 17, 2016, to map the delta's dominant vegetation species and wetland types. We validated this vegetation map (overall accuracy = 77.62%, Kappa = 0.72) and compared it with a published species map that used WorldView-2 data collected five years earlier on October 16, 2011. This allowed us to map changes resulting from five years of delta development to determine changes in wetland forest species (Salix nigra), two dominant herbaceous wetland species (Colocasia esculenta and Polygonum punctatum), and various grass species. Results show an increase in C. esculenta and a marginal increase in forested wetlands (S. nigra). C. esculenta's expansion occurred largely from the delta island heads toward the fringes into wetland area previously occupied by P. punctatum, which saw a corresponding decline. Additionally, this study leveraged these species distributions with a published aboveground biomass (AGB) dataset to examine the dominant plant types' growth patterns across elevational gradients. We characterized variability in AGB by marsh platform elevation and across different elevational zones categorized by hydroperiod, or hydrogeomorphic zones. We found that the herbaceous plant species peak in AGB in the low intertidal zone and decrease with elevation before increasing slightly in the higher elevations, consistent with previous field-based mesocosm experiments for C. esculenta. With vegetation distributions, succession, and growth patterns in the WLD characterized, this study may inform future restoration efforts throughout the Mississippi River Delta Plain regarding the changing vegetation composition that may emerge following changes in surface elevation with sediment deposition.

Depositional sequences of the Mekong river delta and adjacent shelf over the past 140 kyr, southern Vietnam

Two 40 m-long sediment cores BL01 and SC02 were drilled in the lower Mekong River Delta plain and compared to high-resolution seismic profiles from the adjacent shelf documenting the presence of two depositional sequences (SQ1, SQ2) for the past 140 kyr. SQ2 is a fourth-order sequence and covers a complete sea-level cycle of 120 kyr. SQ1 is a fifth-order sequence comprising a sea-level half cycle in the past 20 kyr. These two sequences are bounded by the sequence boundaries (SB1, SB2) and the topographic surface. The transgressive systems tract (TST2) of SQ2 was probably formed during the sea-level rise from the Marine Isotope Stage (MIS) 6 lowstand to the MIS 5e highstand, indicated by riverine-estuarine and shallow-marine sediments. The regressive systems tract (RST2) of SQ2 corresponds to the sea-level lowering from MIS 5e to 3 with deltaic and alluvial plain sediments prevailing. These sediments were then gradually exposed to tropical subaerial processes to generate the formation of patchy reddish-orange stiff sandy silt and clay. The overlaying sequence SQ1 contains the lowstand systems tract (LST1), TST1, and RST1. LST1 consists of deltaic sediments at the shelf edge deposited during the MIS 2 sea-level lowstand. TST1 includes retrograding-fluvial, estuarine, and shallow-marine sediments deposited during the deglacial sea-level rise 19–8 cal kyr BP and the maximum flooding period 8–6 cal kyr BP before the advance of the modern Mekong River Delta. RST1 comprises the modern delta-facies association formed during the past 8 kyr and is restricted to the water depth of 25 m.

Contribution of Emissions from Cement to Air Quality in China

This study analyzed the concentrations of exhaust gas in the process (kiln head and kiln tail) of China's cement industry, based on data from continuous emission monitoring systems network in 2018. The cement emission inventory for China with high resolution (high resolution cement emission inventory for China, HCEC), using the bottom-up approach, was established. The results indicated that during 2018, the total emissions of PM, SO2, and NOx were 72893, 92568, and 878394 t, respectively. In terms of temporal evolution, the exhaust concentration of flue gas in the main process gradually decreased, with obvious emission reduction from the Blue Sky Protection Campaign. Regionally, the exhaust concentrations of flue gas of the kiln head and kiln tail in Beijing-Tianjin-Hebei and surrounding areas, and the Yangtze River Delta and Fenwei Plain, showed a considerable decline, with a high to average level in China. The flu concentrations of each city differed; the cement industry in Anhui Province generated the largest emission in the country, while Beijing and Tianjin showed the highest emission intensity per unit area.

An efficiency analysis of the low-head gate Dam Fishway for freshwater fish ascending Liuxi River in South China

The passing efficiency of the fishway for water plant dam in Liuxi River was evaluated by statistical analysis and comparison with other fishway based on the monitoring data from August in 2015 to July in 2016. The main contents of this paper includes that identifying the fish species, analyzing the influence factors of season and upper water level on passing efficiency, and comparing the result with other fishways in China and other countries. The results indicated that there are 1043 fishes, which belong to 39 species, 3 order, 10 families, and 37genera, were captured. The main passing season of the fishway is from April to October. When the water temperature in the fishway varies from 20 to 35 °C and the upper water level varies from 32.6 to 33 m, the fishway is more effective. There are 39 species fish can find the entrance and pass over the fishway. Compared with other fishways, the fishway works better, but the passing number is less than others. The study results play an important role in ecological operation for Liuxi Reservoir, fishway improvement and effective operation, and protection of fish resources. It also plays important role in demonstration and expansion fishway construction for low-head gate dam in Liuxi River and Pearl River Delta plains.

Human drivers accelerated the advance of Pearl River deltaic shoreline in the past 7500 years

In order to examine the role of human drivers in shoreline advance of the Pearl River delta plain over the past 7500 years, this study reconstructed several palaeo-shorelines based on sedimentary records, archaeological findings, historical archives, family ancestral books and modern survey data. With these shorelines, this study quantified the land growth rate for each of seven time periods spanning from the Neolithic-Bronze Ages, through the agricultural period, to the modern industrial era. The results show that, since c. 7500 cal. a BP as the sea level ceased to function as the primary driver, fluvial discharge and tide became the main natural drivers. Between 5500 BCE and 200 BCE, as fluvial discharge was progressively reduced, the amount of sediment drained out to the sea by tidal action was also progressively reduced due to the decrease of the estuarine space. As a result, the land growth rate was kept around 0.36–0.38 km2/a for this period. During the agricultural stage between 200 BCE and 1950 CE, human activity has led to a continuous increase of land growth rate, from 0.78 km2/a caused by land clearance (200 BCE to 960 CE) to 2.69 km2/a triggered by early land reclamation (960–1370 CE) and further to 4.50 km2/a as more advanced techniques were used (1370–1950 CE). Finally, a better organization of human power in land reclamation and the use of machinery since 1950 CE has accelerated the land growth to an average of 10.56 km2/a. The river damming and soil preservation projects in the past three decades have greatly reduced sediment supply and caused a significant slowdown in the shoreline advance.

Identifying the spatiotemporal dynamic of PM2.5 concentrations at multiple scales using geographically and temporally weighted regression model across China during 2015–2018

Fine particulate matter (PM2.5) is closely related to the air quality and public health. Numerous models have been introduced to simulate the PM2.5 concentrations at large scale based on remote sensing and auxiliary data. However, the data precision provided by these models are inadequate for epidemiology and pollutant exposure studies at medium or small scale. The present study aims to calibrate PM2.5 concentrations at 1 km resolution scale across China during 2015–2018 based on monitoring station data and auxiliary data using a novel geographically and temporally weighted regression model (GTWR). The cross-validation (CV) method and the geographically weighted regression (GWR) model are conducted for validation and cross-comparison. Additionally, the spatial autocorrelation and slope analysis methods are implemented to detect the spatiotemporal dynamic of PM2.5 concentrations. A sample-based CV of the GTWR model demonstrates an acceptable precision with a coefficient of determination equal to 0.67, a root-mean-square error of 10.32 μg/m3, and a mean prediction error of-6.56 μg/m3. This result proves that the GTWR model can simulate PM2.5 concentrations at a higher spatial resolution and accuracy across China than some previous models. Besides, the heterogeneity and spatiotemporal dynamic of PM2.5 concentrations are obvious, that is, the High-High (H-H) agglomeration areas with strong haze pollution were mainly concentrated in Beijing-Tianjin-Hebei (BTH), Yangtze River Delta (YRD), Chengdu-Chongqing (CY), and Guanzhong Plain (GZP). In addition, the PM2.5 concentrations are undergoing a decreasing trend in most of the study area, and the decrease in the BTH is dramatic. The results of the present study are helpful for calibrating and detecting the spatiotemporal dynamic of PM2.5 concentrations and useful for the government to make decisions about decreasing haze pollution in urban agglomeration scale.

Benthic fluxes of dissolved oxygen and nutrients across hydrogeomorphic zones in a coastal deltaic floodplain within the Mississippi River delta plain

We tested the hypothesis that benthic fluxes will increase spatially in a coastal deltaic floodplain as sediment organic matter increases in response to developing hydrogeomorphic zones along a chronosequence of the active Mississippi River Delta. A continuous flow-through core system was used to incubate intact sediment cores from three hydrogeomorphic zones along a chronosequence in the emerging Wax Lake Delta (WLD). Organic matter content increased from younger to older deltaic sediments from subtidal to supratidal hydrogeomorphic zones, which were coupled with increasing benthic oxygen and nitrogen fluxes. Mean net denitrification rate in spring was 100 µmol N2–N m−2 h−1 with significantly lower rates occurring in the younger intertidal zones (T4 transect, − 22 µmol N2–N m−2 h−1) and higher rates occurring in the older supratidal zones (T2 and T1 transects, 330 and 262 µmol N2–N m−2 h−1, respectively). Mean net denitrification rate in summer was 397 µmol N2–N m−2 h−1 without significant site-to-site variability except for the supratidal-T2 site (911 µmol N2–N m−2 h−1) showing higher denitrification rate than the other sites. Based on seasonal temperature and inundation time, annual rates of benthic NO3− removal varied from − 0.5 to − 3.4 mol m−2 y−1 and N2–N production rates varied from 1.0 to 3.2 mol N m−2 y−1 across WLD. The subtidal zone had the lowest fluxes associated with lower organic matter content, but was the hydrogeomorphic zone with the largest area and longest flood duration, and therefore contributed over half of N removal in WLD. The estimated annual NO3− removal of 896 Mg N y−1 in WLD accounts for 10 to 27% of total NO3− load to WLD, most of which is converted to N2 through denitrification. As a small prograding coastal deltaic floodplain under early stages of delta development, WLD is a continuously emerging ecosystem where the capacity of N removal increases by 0.2 to 2% per year prior to riverine NO3− is export to coastal ocean. These results highlight the contribution of the coastal deltaic floodplain in an active coastal basin in processing elevated riverine NO3− at continental margins with coastal ocean. The potential loss of this ecosystem service in N removal may increase in global significance as delta areas decline as result of accelerated relative sea level rise and decreased sediment loading in major river basins around the world.

Estuarine submerged aquatic vegetation habitat provides organic carbon storage across a shifting landscape

Submerged aquatic vegetation (SAV) thrives across the estuarine salinity gradient providing valuable ecosystem services. Within the saline portion of estuaries, seagrass areas are frequently cited as hotspots for their role in capturing and retaining organic carbon (Corg). Non-seagrass SAV, located in the fresh to brackish estuarine areas, may also retain significant soil Corg, yet their role remains unquantified. Given rapidly occurring landscape and salinity changes due to human and natural disturbances, landscape level carbon pool estimates from estuarine SAV habitat blue carbon estimates are needed. We assessed Corg stocks in SAV habitat soils from estuarine freshwater to saline habitats (interior deltaic) to saline barrier islands (Chandeleur Island) within the Mississippi River Delta Plain (MRDP), Louisiana, USA. SAV habitats contain Corg stocks equivalent to those reported for other estuarine vegetation types (seagrass, salt marsh, mangrove). Interior deltaic SAV Corg stocks (231.6 ± 19.5 Mg Corg ha−1) were similar across the salinity gradient, and significantly higher than at barrier island sites (56.6 ± 10.4 Mg Corg ha−1). Within the MRDP, shallow water SAV habitat covers up to an estimated 28,000 ha, indicating that soil Corg storage is potentially 6.4 ± 0.1 Tg representing an unaccounted Corg pool. Extrapolated across Louisiana, and the Gulf of Mexico, this represents a major unaccounted pool of soil Corg. As marshes continue to erode, the ability of coastal SAV habitat to offset some of the lost carbon sequestration may be valuable. Our estimates of Corg sequestration rates indicated that conversion of eroding marsh to potential SAV habitat may help to offset the reduction of Corg sequestration rates. Across Louisiana, we estimated SAV to offset this loss by as much as 79,000 Mg C yr−1 between the 1960s and 2000s.

Evolution Characteristics and Stratigraphic Division of Quaternary Sedimentary in the South Wing of Yangtze River Delta, East China

This paper discusses the sporo pollen assemblage, evolution of sedimentary environment, sedimentary facies and the lithotope characteristics revealed by boreholes since pliocene epoch by carrying out 14C dating, sporo pollen and micro-paleontological analysis of sediments in borehole BK01 (depth 237.80 m) in the southern flank of the Yangtze River Delta Plain. According to the results of this study, there are 17 species of foraminifera that have been identified as 11 genera, including 16 benthic foraminifera and 1 planktonic foraminifera；8 species of Ostracoda that have been identified as 8 genera; sporo pollen analysis shows that there are 37 types, including 18 species of woody plant pollen, 11 species of herbaceous plant pollen, 8 species of fern spores, of which, in the sporo pollen assemblage, woody plants have the highest content (about 85.1%), ferns spores have about 8.7%, and herbaceous plants have only 6.3%. Sedimentary environment records can be divided into 18 sporo pollen assemblage zones according to borehole lithology, sporo pollen assemblage and micropaleontology analysis. The results show that the BK01 bore strata from bottom to top can be divided into carbonaceous mudstone (Ech), Jiaxing Formation (N-Qp1j), Qiangang Formation (Qp2q) Dongpu Formation (Qp3d), Ningbo Formation (Qp3n) and Zhenhai Formation (Qhzh).

The Sustainable Development of Choronymic Cultural Landscapes in China Based on Geo-Informatic Tupu

As a part of cultural landscapes, toponyms with abundant cultural connotations and a long history are valuable cultural heritage assets. Choronyms not only reflect natural and social phenomena but also help with relevant management and naming work. In order to explore the historical development sequence of choronymic cultural landscape evolution, we analyze the spatial–temporal pattern evolution, spatial–temporal variation, spatial association, and semantic evolution of choronymic cultural landscapes since the Qin dynasty. We adopt the sequent snapshot model and an event-based state amendment model to establish a spatio-temporal database. That can provide decision supports and theoretical reference for the sustainable development of toponymic landscapes. Results indicate the following: (1) Spatial distribution of toponym density has been different since the Qin dynasty. The cores of toponym density spread from the middle-lower reaches of the Yellow River to Yangtze Plain, Chengdu Plain, Pearl River Delta Plain. (2) Spatial distribution of choronyms is agglomerative since the Qin dynasty and uneven at national and provincial scales since the Yuan dynasty. Temporal distribution of toponyms at different levels is centralized. (3) Spatial agglomeration phenomena of toponyms are positively clustered in nine periods. The Ming dynasty presents the largest degree of spatial aggregation. (4) Words relevant to blessings, orientation, and hydrological features have high proportions in the top 20 words. (5) Spatial distribution of county-level choronyms named over the last 1000 years and “Millennium Ancient Counties” are unbalanced at national and provincial scales.

Biogeochemical and reactive transport modeling of arsenic in groundwaters from the Mississippi River delta plain: An analog for the As-affected aquifers of South and Southeast Asia

Abstract Arsenic (As) concentrations and speciation were measured in groundwaters from the upper Chicot aquifer in southern Louisiana to: (1) ascertain the geochemical processes responsible for its mobilization into the groundwater; and (2) investigate the fate and transport of As in the aquifer following its mobilization into solution. Ancillary geochemical parameters, including dissolved iron (Fe) concentrations and speciation, major solutes, pH, and alkalinity were also quantified in the groundwaters, along with the mineralogy and geochemistry of the aquifer sediments. Arsenic concentrations as high as 644 nmol kg−1 (48.2 μg kg−1) were measured in the groundwaters, with the arsenite oxyanion (H3AsIIIO30) accounting for ca. 60%, on average, of the total dissolved As, and the remaining ca. 40% consisting of the arsenate oxyanion (i.e., H2AsVO42−). The groundwaters are Na – HCO3 type waters of slightly alkaline pH (8.09 ≤ pH ≤ 8.34), moderately high mineralization (7.3 mmol kg−1 ≤ I ≤ 13.7 mmol kg−1), and high Fe(II) concentrations (18 μmol kg−1 ≤ Fe(II) ≤ 47 μmol kg−1), and thus are compositionally similar to As-affected groundwaters from South and Southeast Asia (e.g., Bangladesh, West Bengal, India, and Vietnam). Groundwaters with the highest As concentrations also have the highest Fe(II) concentrations, which is consistent with reductive dissolution of Fe(III) oxides/oxyhydroxides releasing sorbed or co-precipitated As into the groundwaters. Biogeochemical reactive transport modeling that employs rates laws for microbial respiration indicates that dissimilatory reduction of Fe(III) oxides/oxyhydroxides coupled to organic matter oxidation can explain the high As concentrations along the mid-reaches of the studied flow path. Geochemical analysis of the aquifer sediments further demonstrates that the bulk of the environmentally mobile As in the aquifer is associated with Fe(III) oxides/oxyhydroxides and/or chemisorbed (i.e., inner-sphere surface complexed) onto aquifer mineral surfaces. Model calculations confirm that mobilization of 2–8% of this labile As could support the high As concentrations measured in these groundwaters. Reactive transport modeling coupled to the generalized double-layer surface complexation model predicts that As(III) could be transported ca. 10 km down gradient from the current location of the As “hot-spot” after 150 years, whereas As(V) is predicted to move between 2.4 km and 8.5 km depending on the composition of Fe(III) oxides/oxyhydroxides in the aquifer. Reactive transport modeling also illustrates how retardation and attenuation of As(III) and As(V) along flow paths in aquifer systems is strongly dependent on the type and content of Fe(III) oxides/oxyhydroxides present in the aquifer with higher contents of amorphous to poorly crystalline forms leading to greater retardation and attenuation of both As species. The data and modeling indicate that although As is readily mobilized by microbial reduction of Fe(III) oxides/oxyhydroxides, its tendency to form strong, inner sphere surface complexes on Fe(III) oxides/oxyhydroxides remaining in the aquifer will control the fate and transport of As once released into solution. We suggest that these observations may help explain the “patchy” spatial distributions of As concentrations commonly observed in As-affected aquifers, such as those of South and Southeast Asia.

Mid–late Holocene event registered in organo-siliciclastic sediments of Lagoa Salgada carbonate system, southeast Brazil

Abstract. The formation of the Paraíba do Sul river delta plain on the coast of Rio de Janeiro state, Brazil, gave rise to diverse lagoons formed under different sea level regimes and climate variations. Sedimentary core lithology, organic matter geochemistry, and isotopic composition (δ13C and δ15N) were analyzed to interpret the sedimentation of the paleoenvironment of the Lagoa Salgada carbonate system. Different lithofacies reflect variations in the depositional environment. The abundance of silt and clay between 5.8 and 3.7 kyr enhances the interpretation of a transgressive system, which promoted the stagnation of coarse sediment deposition due to coast drowning. Geochemistry data from this period (5.8–3.7 kyr) suggest the dominance of a wet climate with an increase of C3 plants and a marked dry event between 4.2 and 3.8 kyr. This dryer event also matches with previously published records from around the world, indicating a global event at 4.2 ka. Between 3.8 and 1.5 kyr, Lagoa Salgada was isolated; sand and silt arrived at the system by erosion with the retreat of the ocean and less fluvial drainage. Geochemistry from this moment marks the changes to favorable conditions for microorganisms active in the precipitation of carbonates, forming microbial mats and stromatolites in the drier phase.

Modeling sediment texture of river-deltaic wetlands in the Lower Barataria Bay and Lower Breton Sound, Louisiana, USA

Wetlands in the Mississippi River Delta Plain (MRDP) have been suffering from a high rate of land loss. Sediment cores have been drilled into the wetlands to understand their growth and degradation and to provide subsurface information for the coastal protection and restoration projects. However, few three-dimensional (3D) stratigraphy models have been developed for the wetlands on a regional scale, due to difficulties in correlating large amount of spatial scattered subsurface data and integrated visualization of stratigraphic features and topobathymetric features. In this study, a 3D model was constructed in the Lower Barataria Bay (LBB) and the Lower Breton Sound (LBS), covering an area of 190 km2 and extending from 0.5 to − 4 m in elevation. Sediment composition (sand%, silt%, and clay%) was spatially interpolated, using a compositional kriging method, extended from ordinary kriging by a log-ratio transformation. Instead of visualizing three composition components independently, sediment composition was translated into sediment texture to be visualized as sediment types. Modeling results intuitively show spatial distribution of stratigraphic features and their spatial relationships with topobathymetric features such as marsh surface, river channel, and dredging channels. Results show a silty depositional package, which consists of crevasse splays and periodic overbank flooding deposits, made up the largest portion of the wetlands. A clayey blanket is observed to cover most part of the LBB and landward side of the LBS. A large area of clayey blanket in the seaward part of the LBS has apparently been eroded away, which is likely caused by coastal reworking processes.

Spatio-temporal evolution and the influencing factors of PM2.5 in China between 2000 and 2015

High concentrations of PM2.5 are universally considered as a main cause for haze formation. Therefore, it is important to identify the spatial heterogeneity and influencing factors of PM2.5 concentrations for regional air quality control and management. In this study, PM2.5 data from 2000 to 2015 was determined from an inversion of NASA atmospheric remote sensing images. Using geo-statistics, geographic detectors, and geo-spatial analysis methods, the spatio-temporal evolution patterns and driving factors of PM2.5 concentration in China were evaluated. The main results are as follows. (1) In general, the average concentration of PM2.5 in China increased quickly and reached its peak value in 2006; subsequently, concentrations remained between 21.84 and 35.08 μg/m3. (2) PM2.5 is strikingly heterogeneous in China, with higher concentrations in the north and east than in the south and west. In particular, areas with relatively high PM2.5 concentrations are primarily in four regions, the Huang-Huai-Hai Plain, Lower Yangtze River Delta Plain, Sichuan Basin, and Taklimakan Desert. Among them, Beijing-Tianjin-Hebei Region has the highest concentration of PM2.5. (3) The center of gravity of PM2.5 has generally moved northeastward, which indicates an increasingly serious haze in eastern China. High-value PM2.5 concentrations have moved eastward, while low-value PM2.5 has moved westward. (4) Spatial autocorrelation analysis indicates a significantly positive spatial correlation. The “High-High” PM2.5 agglomeration areas are distributed in the Huang-Huai-Hai Plain, Fenhe-Weihe River Basin, Sichuan Basin, and Jianghan Plain regions. The “Low-Low” PM2.5 agglomeration areas include Inner Mongolia and Heilongjiang, north of the Great Wall, Qinghai-Tibet Plateau, and Taiwan, Hainan, and Fujian and other southeast coastal cities and islands. (5) Geographic detection analysis indicates that both natural and anthropogenic factors account for spatial variations in PM2.5 concentration. Geographical location, population density, automobile quantity, industrial discharge, and straw burning are the main driving forces of PM2.5 concentration in China.

长三角平原区县域土壤磷素流失风险及其空间不确定性的快速评估

PDF HTML阅读 XML下载 导出引用 引用提醒 长三角平原区县域土壤磷素流失风险及其空间不确定性的快速评估 DOI: 10.5846/stxb201810072156 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41771249）；国家科技支撑计划课题（2015BAD06B02-2）；南京土壤研究所"一三五"计划和领域前沿项目（ISSASIP1623）；中国科学院青年创新促进会（2018348） Rapid assessment of soil phosphorus loss risk and its spatial uncertainty in county areas of the Yangtze River Delta Plain Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:磷素是水体富营养化的关键限制因子，其中从农田土壤中流失的磷往往是水体磷素的主要来源。然而，土壤磷素的流失风险不仅与土壤磷素水平直接相关，其他环境因子，如距受纳水体距离、磷肥施用量、地表径流潜力等也强烈影响其流失风险。同时，基于有限样本预测得到的流失风险必然具有一定的空间不确定性。以长三角典型县域金坛区为研究案例，首先结合多个环境因子构建快速磷指数（RPI）评估模型，再利用稳健地统计学方法识别土壤全磷的空间离群值，并利用序贯高斯模型（SGS）模拟土壤全磷可能的空间分布格局，最后将其多个可能的模拟结果及上述主要因子输入到RPI模型，用以快速评估土壤磷素流失风险及其空间不确定性。结果显示，金坛区土壤磷素流失的高风险区和土壤全磷高值区分布格局在研究区北部、中部具有一定的相似性，而在中西部的旱地区两者出现差异性。高风险区主要沿着河流呈现条带状及斑块状分布，较高及以上风险区（快速磷指数值大于0.93）的面积占金坛区面积的65.88%。概率阈值分别设定为0.50、0.75、0.85、0.95时，其超标面积占金坛区总面积分别达到16.71%、5.74%、2.84%、1.04%。引入多个相关环境因子并结合经稳健处理的SGS进行流失风险指数的空间模拟和不确定性评估，可以快速评估区域农田土壤磷素流失风险及不确定性，进而为区域土壤磷素调控提供必要的空间决策支持。 Abstract:Phosphorus is a key limiting factor for the eutrophication of water bodies. The phosphorus migrating from farmland soils is commonly recognized as the main source of phosphorus in water bodies. Therefore, a better understanding of the loss risk and its spatial uncertainty of soil phosphorus are important for the decision maker to regulate the loss of soil phosphorus at the local and regional scale. In this study, a total of 259 farmland topsoil samples (0-20 cm) was collected from the Jintan District, Changzhou City, Jiangsu Province, for the analysis of soil total phosphorus contents. Apart from soil total phosphorus, we introduced other environmental factors, such as the distance from receiving water body, phosphate fertilizer application rate, and surface runoff potential, into the assessment of the loss risk of soil phosphorus. Furthermore, the prediction of risk indices based on limited samples inevitably has certain spatial uncertainty. Here, a rapid phosphorus index (RPI) assessment model was firstly constructed based on the multiple environmental factors introduced above. And then, the robust geostatistical methods were applied for identifying possible spatial outliers of soil phosphorus data, and the sequential Gaussian simulation (SGS) model with the dataset being removed the spatial outliers was used to simulate the possible spatial distribution pattern of soil total phosphorus. Finally, multiple equiprobable realizations of soil total phosphorus and related environmental factors were input into the RPI model to evaluate the risk of soil phosphorus loss and represent associated spatial uncertainty. The results showed that the high-risk areas of soil phosphorus loss were mainly located in the eastern and middle parts of the Jintan District, which were similar with the high-value areas of soil total phosphorus. The dryland soil total phosphorus located in the mid-west of the study area was relatively low, while the loss risk of soil phosphorus was still at a high level. Such spatial distribution patterns of soil phosphorus loss risk were mainly caused by agricultural inputs. Moreover, the environment factors (i.e., the distance from receiving water body, surface runoff potential, etc.) in these areas were also favorable for soil phosphorus loss. The areas with high level risk of soil phosphorus loss represented zonal distribution along the rivers in the study area. The highest risk area with RPI value exceeding 1.06 made up 24.94% of the study area, whereas the high-risk area (RPI value from 0.93 to 1.05) was relatively larger, accounting for an area percentage of 40.94%. Overall, the risk of soil phosphorus loss was high across the study area. In the process of the uncertainty assessment, the critical threshold value was set to be 1.06 for identifying the highest risk area. When the critical probabilities were set to be 0.50, 0.75, 0.85, and 0.95, respectively, the area exceeding the critical threshold value accounted for 16.71%, 5.74%, 2.84%, and 1.04% of the total area of Jintan District. The critical probability of rapid phosphorus index value exceeding the threshold value was greater than 85% in the north area, and around the Taohu Lake. We introduced environmental factors (the distance from receiving water body, phosphate fertilizer application rate, surface runoff potential) to assess the soil phosphorus loss, which can assess the spatial uncertainty of soil phosphorus loss at a county scale quickly. The knowledge of spatial uncertainty is helpful for the decision maker to delimit the critical source areas and regulate the regional soil phosphorus loss. 参考文献 相似文献 引证文献

NORTH BRETON ISLAND RESTORATION, DESIGNING TO INCREASE A BARRIER ISLAND’S HABITAT AND LONGEVITY

The product and purpose of a well-planned program of investigation and design will be realized later this year when restoration construction begins on North Breton Island. North Breton Island is the southern-most of a chain of barrier islands forming the Chandeleur Islands. The barrier island formation lies within the Mississippi River delta plain system approximately 62 miles southeast from the metropolitan city of New Orleans, LA. Under the authority of the Natural Resource Damage Assessment (NRDA) process, NRDA Trustees selected enhancement of North Breton Island as part of the 2014 Deepwater Horizon NRDA Phase III Early Restoration Plan to help restore injuries to natural resources (Trustees, 2014). The U.S. Fish and Wildlife Service (USFWS) is the lead implementing agency for this Project. The Project includes restoring the barrier shoreline along the entire length of North Breton Island through beach, dune, and marsh fill placement utilizing an offshore sand source in the Borrow Area located approximately 3.3 nautical miles (NM) east of the Restoration Area in the Gulf of Mexico.

Groundwater flow modelling of main groundwater reservoirs in the Gdańsk region, Poland

Abstract During the last nine years, the 133 main groundwater reservoirs in Poland (MGR) have been documented; these were published last year. Some of these are situated in the coastal zone of the southern Baltic Sea. MGR numbers 111 and 112 are in the Gdańsk area and are discussed in the present paper. The study area is situated on the border region of the moraine plateau of the Cashubian Lakeland, the western part of the Vistula River delta plain and the Bay of Gdańsk. The area of the main groundwater reservoir in no. 112 is developed in Quaternary strata and referred to as Żuławy Gdańskie; it comprises predominantly the city of Gdańsk and slightly exceeds 100 km2. There is also a Cretaceous aquifer, rich in groundwater resources, which is named MGR no. 111, beneath the Quaternary reservoir mentioned above. The area studied and modelled totalled 364 km2, on account of the hydraulic connection between these aquifers. Methods of hydrogeological research, groundwater flow simulations, resources calculation are outlined in the present paper.

Hydro-geochemical characteristics of the groundwater resources in the southern part of the Red River’s Delta plain, Vietnam

In this study, the origin and recharge areas as well as the chemistry of the groundwater in the southern part of the Red River Delta plain, in Thai Binh, Nam Dinh and Ninh Binh provinces (North Vietnam) was investigated by using isotopic techniques combined with geochemical analysis. Groundwaters under the study were those that are available in the Holocene, Pleistocene, Neogene and Triassic aquifers. Groundwater in the Holocene aquifer is brackish of Na–Cl type with an electric conductivity as high as up to 6000 µS cm−1. The water in the shallow aquifer comprises three end-members: the local precipitation, Red River’s water and intruded seawater. Groundwater in the Pleistocene, Neogene and Triassic aquifers in the Southwest of the study region is fresh containing less than 1 g L−1 of total dissolved solids and is characterized by the Ca–Na–HCO3 type. However, groundwater in the deep aquifers in the Northeast area is brackish of Na–Ca–Cl–HCO3 ion type containing more than 1 g L−1 TDS. The chemistry of groundwater in the study region is controlled by three processes, namely the incongruent dissolution of the biogenic high Mg-calcite, the reduction of sulphate and iron oxyhydroxide with organic matters present in the aquifers. The salinity in deep aquifers in the NE was attributed to the diffusion of saline pore water from aquifer or/and aquitard deposits to the recharge water. Groundwater in the Pleistocene, Neogene and Triassic aquifers in the study region seem to have meteoric origin with long traveling time and it mixed with the saline pore water that migrated from the aquifers sediments, as it was evident from the water isotopic compositions. The isotopic compositions of water (δ2H and δ18O) in the Neogene and Triassic aquifers are similar to that found in the Pleistocene aquifer suggesting the aquifers are hydraulically connected to each other due to the over-extraction rate of fresh water from the latter aquifer. Recharge area of groundwater in the Pleistocene and Neogene aquifers is suggested to be from the NW extension of the region and out crops at a highland at an altitude of 140–160-m above sea level (masl). The recharge water flows from northwesterly towards southeasterly to the sea coast. The results of the 14C-dating for groundwater combined with the hydraulic heads distribution in the deep aquifers revealed that the saline groundwater is flowing from the NE and backwards from the sea side to the production well field in the center of the region due to the high rate of groundwater mining. In order to mitigate the saltwater intrusion and avoid deterioration of the quality of the groundwater that is currently being mined and supplied to the local population, it needs to develop and implement an appropriate strategy for the groundwater resource management in the region.

The sedimentary evolution of Yangtze River delta since MIS3: A new chronology evidence revealed by OSL dating

Abstract The Yangtze River delta, one of the largest tide-dominated deltas in the world, is a valuable archive for studying the land-sea interaction. Previous investigations have mainly focused on the Holocene Yangtze River delta initiation and the coastal dynamics in response to sea level changes based on analysis of the stratigraphic and sedimentologic evidences. However, the detailed depositional history of the Yangtze River delta prior to Holocene is still poorly understood owing to a deficiency of accurate absolute chronologies. In this study, a 60-m-long core (EGQD14) was drilled in the front edge of modern Yangtze River deltaic plain. The sedimentary features were analyzed based on the data of sediment particle size composition, colors, textures and intra-structure description; a total of 20 sediment samples were collected from this core for optically stimulated luminescence (OSL) dating. The single aliquot regenerative dose (SAR) protocol was applied to fine (4–11 μm in diameter) and coarse (63–100 μm or 100–200 μm) grained quartz extracts to determine their equivalent dose (De). The bleaching levels of different grain-sized fractions were investigated. We found that 63–100 μm grains and fine grains are generally well-bleached, and are appropriate for establishing the chronology of the studying core. However, ages of 100–200 μm grains appear to be problematic as potential feldspar contamination, revealed by remarkable infrared (IR) depletion ratios as low as to 0.3. Thus, ages derived only from 4–11 μm and 63–100 μm fractions were used for the reconstruction of chronological framework. The sedimentary history of the Yangtze River delta since the Marine Isotope Stage 3 (MIS3) was inferred by combination of a 50-ka spanning stratigraphic sequence of the EGQD14 core with previously investigated sedimentary stratigraphy in the study area. This study provided a new chronological evidence of the Yangtze River delta sedimentary evolution over the last ∼50 ka, which generally underwent the terrestrial fluvial, floodplain, tidal flat, estuary-neritic, deltaic and modern Yangtze River delta plain sedimentary environments.

Late-Quaternary glacial to postglacial sedimentation in three adjacent fjord-lakes of the Québec North Shore (eastern Canadian Shield)

High-resolution swath bathymetry imagery allowed mapping in great detail the sublacustrine geomorphology of lakes Pentecôte, Walker and Pasteur, three deep adjacent fjord-lakes of the Québec North Shore (eastern Canada). These sedimentary basins have been glacio-isostatically uplifted to form deep steep-sided elongated lakes. Their key geographical position and limnogeological characteristics typical of fjords suggest exceptional potential for long-term high-resolution paleoenvironmental reconstitutions. Acoustic subbottom profiles acquired using a bi-frequency Chirp echosounder (3.5 & 12 kHz), together with cm- and m-long sediment core data, reveal the presence of four acoustic stratigraphic units. The acoustic basement (Unit 1) represents the structural bedrock and/or the ice-contact sediments of the Laurentide Ice Sheet and reveals V-shaped bedrock valleys at the bottom of the lakes occupied by ice-loaded sediments in a basin-fill geometry (Unit 2). Moraines observed at the bottom of lakes and in their structural valleys indicate a deglaciation punctuated by short-term ice margin stabilizations. Following ice retreat and their isolation, the fjord-lakes were filled by a thick draping sequence of rhythmically laminated silts and clays (Unit 3) deposited during glaciomarine and/or glaciolacustrine settings. These sediments were episodically disturbed by mass-movements during deglaciation due to glacial-isostatic rebound. AMS 14C dating reveal that the transition between deglaciation of the lakes Pentecôte and Walker watersheds and the development of para- and post-glacial conditions occurred around 8000 cal BP. The development of the lake-head river delta plain during the Holocene provided a constant source of fluvial sediment supply to the lakes and the formation of turbidity current bedforms on the sublacustrine delta slopes. The upper sediment succession (i.e., ∼4–∼6.5 m) consists of a continuous para-to post-glacial sediment drape (Unit 4) that contains laminated and massive sediment and series of Rapidly Deposited Layers. These results allow establishing a conceptual model of how a glaciated coastal fjord evolves during and after deglaciation in a context of rapid glacio-isostatically induced forced regression.