CRITICAL PROCESSES AND MAJOR FACTORS THAT DRIVE NITROGEN TRANSPORT FROM FARMLAND TO SURFACE WATER BODIES

Agricultural non-point source pollution is increasingly an important issue affecting surface water quality.Currently,the majority of the studies on nitrogen loss have focused on the agricultural field scale,however,the response of surface water quality at the watershed scale into the nitrogen loss at the field scale is poorly understood.The present study systematically reviewed the critical processes and major factors that nitrogen transport from farm fields to surface water bodies.The critical processes of farmland nitrogen entering surface water bodies involve the processes of nitrogen transport from farmland to ditches and the transformation processes of nitrogen during migration in ditches/rivers.Nitrogen transport from farmland to ditches is one of the prerequisites and critical processes for farmland nitrogen transport to surface water bodies.The transformation of nitrogen forms in ditches/rivers is an intermediate process in the migration of nitrogen from farmland to surface water bodies.Nitrogen loss from farmland is related to soil storage and exogenous inputs.Therefore,nitrogen input management should not only consider the current input,but also the contribution of soil storage due to the historical surpluses.Ditches/rivers have a strong retention capacity for nitrogen,which will significantly affect the process of farmland nitrogen entering surface water bodies.The factors affecting nitrogen transformation in river/ditches can be placed in four categories:(1)factors affecting hydraulic retention time,(2)factors affecting contact area,(3)factors affecting biological activity,and(4)forms and amount of nitrogen loading to river/ditches.Ditch systems are more biologically(including plants and microbes)active than rivers with biological factors having a greater influence on nitrogen transformation.When developing pollution prevention and control strategies,ecological ditches can be constructed to increase biological activity and reduce the amount of surplus nitrogen entering the water body.The present research should be valuable for the evaluation of environment impacts of nitrogen loss and the non-point source pollution control.

A Novel Inversion Approach for the Kernel-Driven BRDF Model for Heterogeneous Pixels

The bidirectional reflectance distribution function(BRDF)of the land surface contains information relating to its physical structure and composition.Accurate BRDF modeling for heterogeneous pixels is important for global ecosystem monitoring and radiation balance studies.However,the original kerneldriven models,which many operational BRDF/Albedo algorithms have adopted,do not explicitly consider the heterogeneity within heterogeneous pixels,which may result in large fitting residuals.In this paper,we attempted to improve the fitting ability of the kernel-driven models over heterogeneous pixels by changing the inversion approach and proposed a dynamic weighted least squares(DWLS)inversion approach.The performance of DWLS and the traditional ordinary least squares(OLS)inversion approach were compared using simulated data.We also evaluated its ability to reconstruct multiangle satellite observations and provide accurate BRDF using unmanned aerial vehicle observations.The results show that the developed DWLS approach improves the accuracy of modeled BRDF of heterogeneous pixels.The DWLS approach applied to satellite observations shows better performance than the OLS method in study regions and exhibits smaller mean fitting residuals both in the red and near-infrared bands.The DWLS approach also shows higher BRDF modeling accuracy than the OLS approach with unmanned aerial vehicle observations.These results indicate that the DWLS inversion approach can be a better choice when kernel-driven models are used for heterogeneous pixels.

基于站点的生物多样性星空地一体化遥感监测

科学制定生物多样性保护和恢复政策,需要空间上连续、时间上高频的物种和生境分布以及物种迁移信息支持,遥感是目前能满足该要求的有效技术手段。近年来,遥感平台和载荷技术高速发展,综合多平台、多尺度、多模式遥感技术,开展基于站点的星空地一体化遥感观测试验,可以对地表进行时空多维度、立体连续观测,为生物多样性遥感监测提供了新的契机。本文总结了使用遥感技术监测生物多样性的主要方法,回顾了典型的星空地一体化遥感观测试验。综述以往研究发现,一方面,现有遥感试验还缺少对生物多样性直接监测指标的观测,另一方面,生物多样性遥感监测方法也缺少星空地多维立体观测平台的支撑,亟需加强两者的融合,开展基于站点的生物多样性星空地一体化遥感监测研究。以设于我国四川王朗大熊猫国家级自然保护区内的王朗山地生态遥感综合观测试验站为例,展示了星空地一体化遥感综合观测试验平台在生物多样性监测中的应用潜力。星空地一体化遥感观测可以提供物种和生境的综合定量信息,与生态模型有机结合,可以刻画生物多样性的时空格局与动态过程,有助于挖掘过程机理,提高生物多样性监测的信息化水平。

Performance testing of a heat pump system with auxiliary hot water under different ambient temperatures

In recent decades,solar collector and heat pump combinations have been widely applied to supply heat and hot water,such as in heat supply and power generation for domestic and commercial buildings and relevant applications in the manufacturing and agricultural industries.However,the solar-assisted heat pumps already in extensive use may undergo system performance deterioration in a cold environment.To solve this problem,we designed a heat pump system assisted with hot water where a water medium was used to store energy to assist the operation of the heat pump at low temperatures.Three factors were comprehensively considered:the opening degree of the electronic expansion valve,the temperature of the low-temperature heat source,and the auxiliary hot water temperature.Crossover experiments were designed with three levels for each factor,and 36 groups of experiments were carried out.The results showed that as the auxiliary hot water temperature increased,the heating capacity and the coefficient of performance also increased.Thus,the overall working efficiency of the system improved.According to the orthogonal test,the most important influencing factor of system performance was the auxiliary hot water temperature,followed by the ambient temperature and opening degree of the electronic expansion valve.These results fully demonstrated that the addition of auxiliary hot water could dramatically improve system performance.In addition,optimization of the opening degree of the electronic expansion valve produced different results,indicating that the optimal value ranged from 50%−75%.

A Broadband Green-Red Vegetation Index for Monitoring Gross Primary Production Phenology

The chlorophyll/carotenoid index(CCI)is increasingly used for remotely tracking the phenology of photosynthesis.However,CCI is restricted to few satellites incorporating the 531nm band.This study reveals that the Moderate Resolution Imaging Spectroradiometer(MODIS)broadband green reflectance(band 4)is significantly correlated with this xanthophyll-sensitive narrowband(band 11)(R^(2)=0:98,p<0:001),and consequently,the broadband green-red vegetation index GRVI—computed with MODIS band 1 and band 4—is significantly correlated with CCI—computed with MODIS band 1 and band 11(R^(2)=0:97,p<0:001).GRVI and CCI performed similarly in extracting phenological metrics of the dates of the start and end of the season(EOS)when evaluated with gross primary production(GPP)measurements from eddy covariance towers.For EOS extraction of evergreen needleleaf forest,GRVI even overperformed solar-induced chlorophyll fluorescence which is seen as a direct proxy of plant photosynthesis.This study opens the door for GPP and photosynthetic phenology monitoring from a wide set of sensors with broadbands in the green and red spectral regions.