Exploring hyperspectral bands and estimation indices for leaf nitrogen accumulation in wheat

Hyperspectral sensing can provide an effective means for fast and non-destructive estimation of leaf nitrogen (N) status in crop plants. The objectives of this study were to design a new method to extract hyperspectral spectrum information, to explore sensitive spectral bands, suitable bandwidth and best vegetation indices based on precise analysis of ground-based hyperspectral information, and to develop regression models for estimating leaf N accumulation per unit soil area (LNA, g N m⁻²) in winter wheat (Triticum aestivum L.). Three field experiments were conducted with different N rates and cultivar types in three consecutive growing seasons, and time-course measurements were taken on canopy hyperspectral reflectance and LNA under the various treatments. Then, normalized difference spectral indices (NDSI) and ratio spectral indices (RSI) based on the original spectrum and the first derivative spectrum were constructed within the range of 350–2500 nm, and their relationships with LNA were quantified. The results showed that both LNA and canopy hyperspectral reflectance in wheat changed with varied N rates, with consistent patterns across different cultivars and seasons. The sensitive spectral bands for LNA existed mainly within visible and near infrared regions. The best spectral indices for estimating LNA in wheat were found to be NDSI (R₈₆₀, R₇₂₀), RSI (R₉₉₀, R₇₂₀), NDSI (FD₇₃₆, FD₅₂₆) and RSI (FD₇₂₅, FD₅₁₆), and the regression models based on the above four spectral indices were formulated as Y = 26.34x^1.887, Y = 5.095x − 6.040, Y = 0.609 e^3.008x and Y = 0.388x^1.260, respectively, with R² greater than 0.81. Furthermore, expanding the bandwidth of NDSI (R₈₆₀, R₇₂₀) and RSI (R₉₉₀, R₇₂₀) from 1 nm to 100 nm at 1 nm interval produced the LNA monitoring models with similar performance within about 33 nm and 23 nm bandwidth, respectively, over which the statistical parameters of the models became less stable. From testing of the derived equations, the model for LNA estimation on NDSI (R₈₆₀, R₇₂₀), RSI (R₉₉₀, R₇₂₀), NDSI (FD₇₃₆, FD₅₂₆) and RSI (FD₇₂₅, FD₅₁₆) gave R² over 0.79 with more satisfactory performance than previously reported models and physical models in wheat. It can be concluded that the present hyperspectral parameters of NDSI (R₈₆₀, R₇₂₀), RSI (R₉₉₀, R₇₂₀), NDSI (FD₇₃₆, FD₅₂₆) and RSI (FD₇₂₅, FD₅₁₆) can be reliably used for estimating LNA in winter wheat.     

Thermo-hydro-mechanical modeling of unsaturated soils using isogeometric analysis: Model development and application to strain localization simulation

This study presents a thermo-hydro-mechanical (THM) model of unsaturated soils using isogeometric analysis (IGA). The framework employs Bézier extraction to connect IGA to the conventional finite element analysis (FEA), featuring the current study as one of the first attempts to develop an IGA-FEA framework for solving THM problems in unsaturated soils. IGA offers higher levels of interelement continuity making it an attractive method for solving highly nonlinear problems. The governing equations of linear momentum, mass, and energy balance are coupled based on the averaging procedure within the hybrid mixture theory. The Drucker-Prager yield surface is used to limit the modified effective stress where the model follows small strain, quasi-static loading conditions. Temperature dependency of the surface tension is implemented in the soil-water retention curve. Nonuniform rational B-splines (NURBS) basis functions are used in the standard Galerkin method and weak formulations of the balance equations. Displacement, capillary pressure, gas pressure, and temperature are four independent quantities that are approximated by NURBS in spatial discretization. The framework is used to simulate strain localization in an undrained dense sand subjected to plane strain biaxial compression under different temperatures and displacement velocities. Results show that an increase in the displacement rate leads to reduction in the equivalent plastic strain while an increase in the temperature leads to an increase in the equivalent plastic strain. The findings suggest that the proposed IGA-based framework offers a viable alternative for solving THM problems in unsaturated soils.     

Development of a coupled pile-to-pile interaction model for the dynamic analysis of pile groups subjected to vertical loads

Acta Geotechnica - This paper presents a new analytical model for calculating the dynamic performance of pile groups subjected to vertical loads. The derived solution allows considering the robust...     

Variation behavior of pore-water pressure in warm frozen soil under load and its relation to deformation

Acta Geotechnica - Containing a considerable amount of unfrozen water, frozen soil may produce excess pore-water pressure under external load, especially at temperatures near the thawing point. The...     

Bibliometric Analysis of Research Progress on Coastal Surface Water and Groundwater Interaction

The interactions among surface water, groundwater and seawater are closely related in the coastal area with complex hydrological conditions. A series of impacts from human activities and climate change are also more significant in this region. In order to understand the key knowledge and research status of surface water and groundwater interaction in coastal area, it is a useful method to analyze literatures in this research scope in the core database of Web of Science by using CiteSpace. The research achievements in this field were systematically sorted and potential research hotspots were explored, which may provide references for subsequent researches. The results show the following. \mathrm{①} The number of highly cited articles and highly burst articles in this research field has increased significantly since 2010. At present, this field is still in the development stage and has a broad research prospect. \mathrm{②} The United States, Australia, China and Germany have done plenty of researches on this issue and achieved a lot. At present, the number of research achievements supported by National Natural Science Foundation of China is in the lead over the world. \mathrm{③} Seawater intrusion, submarine groundwater discharge, the relationship between tide and hydrological conditions are the main research direction in this field. Hydrochemistry and isotopic analysis, and numerical simulation are the most important research methods in this field. \mathrm{④} The potential development directions and breakthroughs in this field include submarine groundwater discharge, the evolution of coastal mangrove wetlands, the migration and transformation of nutrients, the influences of different hydrological factors on coastal areas, and the impact of climate change on coastal areas. Overall, the future development of surface water and groundwater research in coastal areas is inseparable from the cross-integration of various disciplines, mutual verification of multiple methods and the introduction of new technical means.     

Cu–Mo Differential Mineralization Mechanism of the Dabate Polymetallic Deposit in Western Tianshan,NW China: Evidence from Geology,Fluid Inclusions,and Oxygen Isotope Systematics

Classic porphyry Cu–Mo deposits are mostly characterized by close temporal and spatial relationships between Cu and Mo mineralization. The northern Dabate Cu–Mo deposit is a newly discovered porphyry Cu–Mo polymetallic deposit in western Tianshan, northwest China. The Cu mineralization postdates the Mo mineralization and is located in shallower levels in the deposit, which is different from most classic porphyry Cu–Mo deposits. Detailed field investigations, together with microthermometry, laser Raman spectroscopy, and O‐isotope studies of fluid inclusions, were conducted to investigate the origin and evolution of ore‐forming fluids from the main Mo to main Cu stage of mineralization in the deposit. The results show that the ore‐forming fluids of the main Mo stage belonged to an NaCl + H₂O system of medium to high temperatures (280–310°C) and low salinities (2–4 wt% NaCl equivalent (eq.)), whereas that of the main Cu stage belonged to an F‐rich NaCl + CO₂ + H₂O system of medium to high temperatures (230–260°C) and medium to low salinities (4–10 wt% NaCl eq.). The δ¹⁸O values of the ore‐forming fluids decrease from 3.7–7.8‰ in the main Mo stage to ?7.5 to ?2.9‰ in the main Cu stage. These data indicate that the separation of Cu and Mo was closely related to a large‐scale vapor–brine separation of the early ore‐forming fluids, which produced the Mo‐bearing and Cu‐bearing fluids. Subsequently, the relatively reducing (CH₄‐rich) Mo‐bearing, ore‐forming fluids, dominantly of magmatic origin, caused mineralization in the rhyolite porphyry due to fluid boiling, whereas the relatively oxidizing (CO₂‐rich) Cu‐bearing, ore‐forming fluids mixed with meteoric water and precipitated chalcopyrite within the crushed zone at the contact between rhyolite porphyry and wall rock. We suggest that the separation of Cu and Mo in the deposit may be attributed to differences in the chemical properties of Cu and Mo, large‐scale vapor–brine separation of early ore‐forming fluids, and changes in oxygen fugacity.     

准噶尔盆地西北部P-T转换期不整合的发育演化特征及意义*

二叠纪晚期—三叠纪早期是准噶尔盆地演化的重要转换期,发育了具有特色性的不整合面。本研究以该盆地的西北部为例,综合利用地震和钻井资料,探讨该时期不整合的发育演化特征及其地质意义。研究表明,转换期发育P₃/P₂期主要不整合与T₁/P₃期次要不整合,它们在研究区北部叠加复合,构成了三叠系底界叠合不整合面,在南部被上二叠统所分隔而独立存在;转换期经历了主要不整合的形成、主要不整合被上二叠统超覆、次要不整合与叠合不整合的形成及其被三叠系最终超覆4个演化阶段。不整合的发育演化特征揭示了晚海西期和早印支期构造运动对准噶尔盆地影响的强弱程度、地层记录的“楔形体”内涵以及上二叠统与下三叠统的层序归属。P-T转换期不整合面及其相邻地层形成了有效的油气运移通道、良好的储盖组合和类型众多的圈闭,因此具有重要的油气勘探意义。     

涉县盆地控盆构造晚第四纪活动特征

涉县断裂为太行山隆起区内涉县盆地的控盆构造,走向由NE转为近EW向,倾向NW/N,中部在井店东被EW向断裂错断,是控制涉县盆地的一组断裂。本文采用地质地貌调查、河流阶地分析和地质测年等方法,研究了涉县断裂晚第四纪活动特征。研究发现,涉县断裂带由多组断裂构成,带宽约200m,在清漳河两侧表现为山前的陡崖地貌、基岩破碎变形带,具有正断兼走滑特征,在基岩变形带上部发育走向NNE向和NWW向次级滑动面,次级滑动面错断第四系黄土,最新活动到晚更新世;断裂在盆地区通过,地表形成低缓陡坎,断裂错断Q2-3地层,表现为上陡下缓的正断层。通过对涉县断裂两侧清漳河河流阶地、夷平面和地层年龄综合分析,估算涉县断裂晚更新世以来平均垂直滑动速率为0.06～0.08mm/a,中更新世以来平均垂直滑动速率为0.22～0.34mm/a,垂直差异活动主要发生于中更新世期间。     

太湖水体和沉积物细菌群落分布格局及其驱动因素

水体和沉积物是湖泊生态系统中迥异但又紧密相连的两类生境,栖息在这两类生境中的细菌在维持生态系统平衡和驱动元素循环中起着关键性作用。为了探究湖泊水体和沉积物细菌群落的分布格局,本文对太湖四个湖区水体和沉积物中细菌群落进行调查,基于高通量测序技术和统计分析手段,分析这两类生境中的细菌群落组成和多样性水平、分布特征及其驱动因素。结果表明:放线菌门(Actinobacteria)、变形菌门(Proteobacteria)和蓝细菌门(Cyanobacteria)是水体细菌群落中最主要的细菌门,而沉积物中Proteobacteria占据优势地位。在两类生境中,太湖西部区域细菌群落丰富度和独特性(LCBD)相对较高,各区域群落结构表现出显著性差异。对水体而言,电导率、pH值、PC1(重金属组成)和沉积物孔隙度是驱动细菌丰富度的重要因子,PC1、水温及pH值是影响细菌群落LCBD的重要因子,而细菌网络复杂性随pH值的增加而增加,且在高pH环境中占主导地位;对沉积物而言,其丰富度和LCBD的重要影响因子均是沉积物中总磷和锂,细菌网络复杂性随金属元素施加的环境压力增大而降低,但随总磷、磷酸盐和铵态氮浓度的...     

长江中下游湖泊群不同生活型水生植物分布的时空变化(1986—2020年)

不同生活型水生植物对水环境的影响和碳固持能力不同,开展大尺度范围内不同生活型水生植物的时空分布和动态变化研究,是全面掌握湖泊水生态环境变化趋势、准确核算水生生态系统碳源/碳汇的前提。以长江中下游10 km²以上(共131个)的湖泊为研究对象,基于野外调查和先验知识,通过光谱分析,研发了不同生活型水生植物遥感高精度机器学习识别算法,解析了长江中下游湖泊群不同生活型水生植物的时空变化规律。研究表明,长江中下游湖泊群不同生活型水生植物遥感监测精度为0.81,Kappa系数为0.74;1986—2020年长江中下游湖泊群水生植物面积为2541.58~4571.42 km²,占湖泊总面积的15.99%~28.77%,沉水植物是优势类型(Max_1995年=2649.21 km²,Min_2005年=921.38 km²),其次是挺水植物(Max_2005年=1779.44 km²,Min_2020年=569.05 km²)和浮叶植物(Max_2015年=685.68 km²,Min_2000年=293.04 km²);水生植物主要分布在长江干流流域湖泊群,其次是鄱阳湖流域、洞庭湖流域、太湖流域和汉江流域;变化趋势上,1986—2020年长江中下游湖泊群水生植物面积呈现先增长(1986—1995年)、后下降(1995—2010年)、再增加(2010年后)的趋势。本研究可为长江中下游湖泊群生态环境调查及水环境管理提供重要参考。