Analysis of surface and aerosol polarized reflectance for aerosol retrievals from polarized remote sensing in PRD urban region

A precise estimate of polarization induced by surface is crucial for polarized remote sensing dedicated to monitoring aerosol properties over urban area. The accurate knowledge of interaction between surface and aerosol polarized reflectance is essential for accurately achieving aerosol properties. In order to study surface and aerosol polarized reflectance for aerosol retrievals over urban area, a new airborne directional polarimetric camera (DPC) with high spatial resolution (4 m at 4000 m a.g.l) was developed. The surface polarized reflectance over distinct surface covers of urban area (forest, shrub, and soil) were studied using DPC measurements during a field campaign in the Pearl River Delta (PRD), China. The large variations were found in surface polarized reflectance of distinct urban covers due to surface type variability. For all surface types, the empirical BPDF model cannot describe accurately surface polarized reflectance at all possible illumination and observation geometries. From the quantitatively study of relationship between surface and aerosol polarized contribution to DPC measurements, we show that the polarized contributions of aerosol, which optical properties were defined by ground-based measurements, are much larger than the polarized contribution of surface, and found that the polarized contribution of surface covers increases with decreasing NDVI. The effect of polarization accuracy of measurements on aerosol retrieval was also investigated using DPC measurements, and found that 0.1% polarization accuracy of measurements can be neglected when AOD is retrieved using polarized measurements. Based on the information of effects of polarized reflectance differences between distinct surface covers and polarization accuracy of polarized measurements on retrieved aerosols over urban area, we found that the accuracy of aerosol retrieval over forest covers is higher than other surface types using polarized remote sensing.     

Impacts of afforestation on water quality trends in two catchments in mid-Wales

The impact of afforestation on stream-water chemistry for two catchments in central Wales is investigated. Trends in water chemistry are evaluated with forest age progressing at 8-15 years and 20-27 years. To assess the possible exacerbating effect of afforestation on surface-water acidification two moorland catchments are used as controls. Absolute differences in inter-catchment streamwater chemistry are evident. Differences in acidity between the moorland and the young forest site reflect site preparation and modifications to water pathways. Differences in the observed present day chemistry between the young and old forest result from past interactions between deposition changes during forest development. An estimate of the future impact of forest growth was attained from model predictions. The model was calibrated to present day stream-water chemistry and incorporates, cation uptake, evapotranspiration/ concentration effect and increased scavenging of occult and dry deposition. Predictions suggest the pH will decline to 5.3 when the young forest progresses to 20 years of age, which is still much higher than the pH recorded at the older forest site at the age of 20 years.     

Multiple regression models: a methodology for evaluating trihalomethane concentrations in drinking water from raw water characteristics

The presence of trihalomethanes (THMs) in drinking water has attracted the attention of both researchers and professionals, because of the harmful effects of these substances on human health. A multiple regression model was developed to estimate THM concentrations in finished drinking water, using data from the Menidi Treatment Plant of Athens. A number of routinely measured characteristics--including chlorine dose, chlorophyll a, temperature, pH and bromide--of raw water, were used to generate a reliable methodology for predicting both total THM and individual species concentrations. Seasonality effects were also considered during the analysis. In general, these models were found to give acceptable fits, estimating accurately lows and highs over the annual cycle.     

A coupled carbon-water-energy-vegetation model to assess responses of temperate forest ecosystems to changes in climate and atmospheric CO2. Part I. Model concept

Predictions of forest ecosystem response to changes in climate and atmospheric CO(2) concentration require hierarchically structured process models. Present forest simulation models have conceptual limitations that restrict their application to climate-change studies. A major drawback of forest succession models is that they often lack physiological details in the simulation of annual tree growth. On the other hand, aggregated ecosystem models assume spatially homogeneous forests, and do not account for successional changes in forest composition and canopy structure. The concept of a new coupled carbon-water-energy-forest vegetation model is presented which attempts to overcome the main limitations of existing models by implementing a modern view of ecological hierarchy and a robust approach for scaling ecological processes in space and time.     

Improved daily precipitation nitrate and ammonium concentration models for the Chesapeake Bay Watershed

Daily precipitation nitrate and ammonium concentration models were developed for the Chesapeake Bay Watershed (USA) using a linear least-squares regression approach and precipitation chemistry data from 29 National Atmospheric Deposition Program/National Trends Network (NADP/NTN) sites. Only weekly samples that comprised a single precipitation event were used in model development. The most significant variables in both ammonium and nitrate models included: precipitation volume, the number of days since the last event, a measure of seasonality, latitude, and the proportion of land within 8km covered by forest or devoted to industry and transportation. Additional variables included in the nitrate model were the proportion of land within 0.8km covered by water and/or forest. Local and regional ammonia and nitrogen oxide emissions were not as well correlated as land cover. Modeled concentrations compared very well with event chemistry data collected at six NADP/AirMoN sites within the Chesapeake Bay Watershed. Wet deposition estimates were also consistent with observed deposition at selected sites. Accurately describing the spatial distribution of precipitation volume throughout the watershed is important in providing critical estimates of wet-fall deposition of ammonium and nitrate.     

Effects of cadmium on the photosynthetic activity in mature and young leaves of soybean plants

Cadmium (Cd) is a widely spread pollutant and can be easily taken up by crop from soil, resulting in a serious health issue for humans. The objective of this study was to comparatively investigate the photosynthetic activity, chlorophyll a fluorescence, chlorophyll contents, and spectral reflectance in mature and young leaves of soybean plants after being treated with different concentrations of Cd for 10 days. The photosynthetic rate, chlorophyll contents, actual photochemical efficiency of PSII, and photochemical quenching in the young leaves decreased more significantly with increasing concentrations of Cd in the nutrient solution, compared with those in the mature leaves, though the young leaves had less Cd concentrations. Thus, there was more excessive excited energy produced in the young leaves than that in the mature leaves. In the young leaves, due to more excessive excited energy, more reactive oxygen species may be generated, which further damaged the photosynthetic apparatus. It was supported by the fact that the decrease of reflectance in near-infrared wavelengths of the young leaves was more noticeable than that of the mature leaves. In addition, the chlorophyll a fluorescence transients of the young leaves was significantly different from that in the mature leaves, indicating that the electron transport of young leaves were inhibited much more severely than that of the mature leaves. These observations imply that the responses of photosynthetic activity of soybean leaves to Cd stress depend on their growth stage, and the Cd-induced inhibition of photosynthetic activity might be attributed to the decrease in chlorophyll contents and the decrease in mesophyll CO₂ assimilation ability cause by the Cd, which further decreased the consumption of ATP and NADPH, leading to accumulation of NADPH on the acceptor sides of the PSI, and then feedback inhibited electron transport in chloroplasts.     

Climatic sensitivity of temperate forests

Climatic change and associated global changes are of major interest to foresters, both in terms of forest ecology and of future forest production. Predicting the likely effects of global change on forests is extremely difficult due to the critical lack of information on regional changes in meteorological factors relevant to forests. However, existing models of forest production and forest distribution fail to take adequate account of what is already known. Climate and carbon dioxide concentrations have shown substantial changes over the last 100 years. Although the rate of change is likely to increase, recent proposed and implemented control strategies, together with better climatic models, are tending to suggest that the rate of change will be less than initially thought. This means that past changes may provide an increasingly useful source of information. In particular, information on the impact on forests of both long-term climate change and short-term climatic events is rapidly increasing. Such information should be built into future forest response models.     

Modeling plant response to tropospheric ozone: a critical review

The advantages and disadvantages, benefits and limitations, of a number of published mathematical models representing the effects of ozone on crops and native vegetation are described. Several levels of modeling are addressed: word models, graphic models, mathematical models, and computer simulation implementation. Special attention is given to evaluating: (1) how the interaction between ozone exposure and vegetation effects is quantified, (2) the status of field testing of the model, and (3) the adequacy of information for enabling other investigators to replicate the model for further testing. Original contributions, not previously published, are made in this evaluation in the form of: (1) graphic model flow charts for published models, (2) clarification of mathematical equations for existing models, (3) graphic forms of functional relations comprising portions of models, and (4) graphic displays of model output performance versus observed data. The models that are evaluated cover acute exposure-response models, statistical and mechanistic-process models, including a partial model of ambient exposure versus ozone flux, and uptake. They also cover chronic exposure statistical approaches, including time-series modeling, mechanistic-process models, 'disintegrated' models of forest system simulations, chronic flux density-uptake-response, and models for regional effects assessment in forests and agricultural lands.     

可视化黄浦江水环境数学模型系统设计与开发

随着信息技术的高速发展,传统的水环境数学模型与数据库技术、GIS技术、可视化编程工具紧密结合,水环境数学模型的可视化是其发展的一个重要趋势,也是开发水环境决策支持系统和水环境数学模型商业软件的重要基础。对可视化水环境数学模型的设计框架进行了初步探讨,并结合自主开发的可视化黄浦江二维水环境数学模型系统,介绍可视化水环境数学模型的设计与开发。     

Water and sectoral policies in agriculture–forest frontiers: An expanded interdisciplinary research approach

Major land use changes such as deforestation and restoration influence water resources in agriculture–forest landscapes. Changes are observed in water flows, groundwater infiltration, water quality and rainfall. Interdisciplinary water–forest research has unravelled biophysical parts of the interplay that influences forest and water resources. In this Perspective paper, we propose an expanded interdisciplinary research approach to study water and policies in agriculture–forest frontiers. The approach differs in four important aspects from previous ones: (i) a conceptual ‘frontier’ understanding; an analytical focus on (ii) agriculture and (iii) policy–water linkages; (iv) empirical attention to northern and southern countries. The approach is put into practice with the “Pendulum” framework, with interventions and the agriculture–forest frontier oscillating over time between exploitation and restoration. Through the approach, a better understanding will be provided on the dynamic interplay of water and policies in oscillating agriculture–forest frontiers, with changing outcomes for people and environment.     

Modeling habitat suitability for moose in coastal northern Sweden: empirical vs process-oriented approaches

Habitat models may provide viable tools for co-management of large ungulates and forest resources, yet their applicability has not been comprehensively evaluated in managed forest. We examined 2 inherently different approaches to model the relative winter habitat suitability for moose (Alces alces) in the coastal area of northern Sweden. An empirical approach based on GPS positions of 15 female moose was used to scrutinize the assumptions and functional mechanisms of a process-oriented, conceptual approach, based on published material on the species' preferences for habitat components related to food and cover. For both model approaches habitat was described using estimates of forest-stand characteristics based on satellite imagery. The empirical model also included variables relating to topographic properties of the landscape as well as distances to landscape features. The output from both models was a habitat suitability index (HSI) score, enabling the models to be compared with each other. The models showed different results, highlighting the need to include the spatially explicit distribution of environmental variables in future conceptual, process-oriented models.     

Assessing the risk of N leaching from forest soils across a steep N deposition gradient in Sweden

Nitrogen leaching from boreal and temporal forests, where normally most of the nitrogen is retained, has the potential to increase acidification of soil and water and eutrophication of the Baltic Sea. In parts of Sweden, where the nitrogen deposition has been intermediate to high during recent decades, there are indications that the soils are close to nitrogen saturation. In this study, four different approaches were used to assess the risk of nitrogen leaching from forest soils in different parts of Sweden. Nitrate concentrations in soil water and C:N ratios in the humus layer where interpreted, together with model results from mass balance calculations and detailed dynamic modelling. All four approaches pointed at a risk of nitrogen leaching from forest soils in southern Sweden. However, there was a substantial variation on a local scale. Basing the assessment on four different approaches makes the assessment robust.     

Modeling the long-term transport and accumulation of radionuclides in the landscape for derivation of dose conversion factors

To evaluate the radiological impact of potential releases to the biosphere from a geological repository for spent nuclear fuel, it is necessary to assess the long-term dynamics of the distribution of radionuclides in the environment. In this paper, we propose an approach for making prognoses of the distribution and fluxes of radionuclides released from the geosphere, in discharges of contaminated groundwater, to an evolving landscape. The biosphere changes during the temperate part (spanning approximately 20,000 years) of an interglacial period are handled by building biosphere models for the projected succession of situations. Radionuclide transport in the landscape is modeled dynamically with a series of interconnected radioecological models of those ecosystem types (sea, lake, running water, mire, agricultural land and forest) that occur at present, and are projected to occur in the future, in a candidate area for a geological repository in Sweden. The transformation between ecosystems is modeled as discrete events occurring every thousand years by substituting one model by another. Examples of predictions of the radionuclide distribution in the landscape are presented for several scenarios with discharge locations varying in time and space. The article also outlines an approach for estimating the exposure of man resulting from all possible reasonable uses of a potentially contaminated landscape, which was used for derivation of Landscape Dose Factors.     

Sensitivity of a forest ecosystem model to climate parametrization schemes

An analysis of the climate parametrization scheme adopted by conventional forest gap models revealed that most models assume a constant climate and are difficult to calibrate consistently. Tree growth showed unrealistically sensitive threshold effects along ecological gradients of temperature and precipitation. A new parametrization was compared with its predecessors in terms of the model's capability to predict realistic steady state species compositions at three test sites in the Alps. Applying the new model variant ForClim to some climate-change scenarios suggests that forest gap models are highly sensitive to climate pametrizations, regardless of the realism with which they simulate forests for the current climate. Moreover, the precision of climate scenarios based on General Circulation Models (GCM), for example, falls short of ForClim's sensitivity. Climate-dependent processes in forest gap models should be rehearsed before these models are used in impact studies of climatic change.     

Use of satellite imagery to assess the trophic state of Miyun Reservoir, Beijing, China

The objective of this research is to explore an appropriate way of monitoring and assessing water quality by satellite remote sensing techniques in the Miyun reservoir of Beijing, China. Two scene Thematic Mapper images in May and October of 2003 were acquired and simultaneous in situ measurements, sampling and analysis were conducted. Statistical analysis indicates that satellite-based normalized ratio vegetation index (NRVI) and in situ measured water chlorophyll a (Chl-a) concentration have very high correlation. Two linear regression models with high determination coefficients were constructed for NRVI and Chl-a of sample points. According to the modified trophic state index map, water quality in the western section of Miyun reservoir was consistently higher than in the eastern section during the two months tested. The trophic grade of the eastern reservoir remained mesotrophic with a tendency for eutrophication.     

Using optical remote sensing techniques to track the development of ozone-induced stress

In this paper, a literature review about optical remote sensing (RS) of O₃ stress is presented. Studies on O₃-induced effects on vegetation reflectance have been conducted since late ‘70s based on the analysis of optical RS data. Literature review reveals that traditional RS techniques were able to detect changes in leaf and canopy reflectance related to O₃-induced stress when visible symptoms already occurred. Only recently, advanced RS techniques using hyperspectral sensors, demonstrated the feasibility of detecting the stress in its early phase by monitoring excess energy dissipation pathways such as chlorophyll fluorescence and non-photochemical quenching (NPQ). Steady-state fluorescence (Fs), measured by exploiting the Fraunhofer line depth principle and NPQ related xanthophyll-cycle, estimated through the photochemical reflectance index (PRI) responded to O₃ fumigation before visible symptoms occurred. This opens up new possibilities for the early detection of vegetation O₃ stress by means of hyperspectral RS.     

基于因子分析法优选河流水体中氮浓度预测方法的研究

定量的河流水体中氮浓度预测方法有很多种,如何优选出预测精度较高的方法一直是学术界多年来致力于研究的重点。本研究采用因子分析法对预测方法的精度评价指标进行分析,并建立了预测方法精度的评价模型,对回归分析法、神经网络法、灰色系统法和增长率统计法4种水体氮浓度预测方法进行综合评估,优选出精度较高的河流水体氮浓度预测模型——BP神经网络预测模型。结果表明,此评估模型对类似研究具有一定的参考价值,能为选择出合适的河流水体氮浓度预测方法提供依据。     

Representative boreal forest habitats in northern Europe,and a revised model for ecosystem management and biodiversity conservation

The natural range of variation of ecosystems provides reference conditions for sustainable management and biodiversity conservation. We review how the understanding of natural reference conditions of boreal forests in northern Europe has changed from earlier perceptions of even-aged dynamics driven by stand-replacing disturbances towards current understanding highlighting the role of non-stand-replacing disturbances and the resultant complex forest dynamics and structures. We show how earlier views and conceptual models of forest disturbance dynamics, including the influential ASIO model, provide estimates of reference conditions that are outside the natural range of variation. Based on a research synthesis, we present a revised forest reference model incorporating the observed complexity of ecosystem dynamics and the prevalence of old forests. Finally, we outline a management model and demonstrate its use in forest ecosystem management and show how regional conservation area needs can be estimated. We conclude that attaining favourable conservation status in northern Europe’s boreal forests requires increasing emphasis on ecosystem management and conservation for old forest characteristics.Electronic supplementary materialThe online version of this article (10.1007/s13280-020-01444-3) contains supplementary material, which is available to authorized users.     

Regional estimation of current and future forest biomass

The 90,674 wildland fires that burned 2.9 million ha at an estimated suppression cost of $1.6 billion in the United States during the 2000 fire season demonstrated that forest fuel loading has become a hazard to life, property, and ecosystem health as a result of past fire exclusion policies and practices. The fire regime at any given location in these regions is a result of complex interactions between forest biomass, topography, ignitions, and weather. Forest structure and biomass are important aspects in determining current and future fire regimes. Efforts to quantify live and dead forest biomass at the local to regional scale has been hindered by the uncertainty surrounding the measurement and modeling of forest ecosystem processes and fluxes. The interaction of elevated CO2 with climate, soil nutrients, and other forest management factors that affect forest growth and fuel loading will play a major role in determining future forest stand growth and the distribution of species across the southern United States. The use of satellite image analysis has been tested for timely and accurate measurement of spatially explicit land use change and is well suited for use in inventory and monitoring of forest carbon. The incorporation of Landsat Thematic Mapper data coupled with a physiologically based productivity model (PnET), soil water holding capacity, and historic and projected climatic data provides an opportunity to enhance field plot based forest inventory and monitoring methodologies. We use periodic forest inventory data from the USDA Forest Service's Forest Inventory and Analysis (FIA) project to obtain estimates of forest area and type to generate estimates of carbon storage for evergreen, deciduous, and mixed forest classes for use in an assessment of remotely sensed forest cover at the regional scale for the southern United States. The displays of net primary productivity (NPP) generated from the PnET model show areas of high and low forest carbon storage potential and their spatial relationship to other landscape features for the southern United States. At the regional scale, predicted annual NPP in 1992 ranged from 836 to 2181 g/m2/year for evergreen forests and 769-2634 g/m2/year for deciduous forests with a regional mean for all forest land of 1448 g/m2/year. Prediction of annual NPP in 2050 ranged from 913 to 2076 g/m2/year for evergreen forest types to 1214-2376 g/m2/year for deciduous forest types with a regional mean for all forest land of 1659 g/m2/year. The changes in forest productivity from 1992 to 2050 are shown to display potential areas of increased or decreased forest biomass. This methodology addresses the need for spatially quantifying forest carbon in the terrestrial biosphere to assess forest productivity and wildland fire fuels.     

水环境数学模型的研究进展

在作者多年研究工作和查阅大量文献资料的基础上,本文综述了环境数学模型国内外的研究现状、发展历史及未来趋势。重点介绍了这方面研究的最新进展。该文还介绍了本领域所涉及的理论和实际应用问题,提出了今后值得进行研究的若干前沿课题,给出了60余篇关于水环境数学模型研究的主要参考文献目录。