The Interplay between Canopy Structure and Topography and Its Impacts on Seasonal Variations in Surface Reflectance Patterns in the Boreal Region of Alaska—Implications for Surface Radiation Budget

Forests play an essential role in maintaining the Earth’s overall energy balance. The variability in forest canopy structure, topography, and underneath vegetation background conditions create uncertainty in modeling solar radiation at the Earth’s surface, particularly for boreal regions in high latitude. The purpose of this study is to analyze seasonal variation in visible, near-infrared, and shortwave infrared reflectance with respect to land cover classes, canopy structures, and topography in a boreal region of Alaska. We accomplished this investigation by fusing Landsat 8 images and LiDAR-derived canopy structural data and multivariate statistical analysis. Our study shows that canopy structure and topography interplay and influence reflectance spectra in a complex way, particularly during the snow season. We observed that deciduous trees, also tall with greater rugosity, are more dominant on the southern slope than on the northern slope. Taller trees are typically seen in higher elevations regardless of vegetation types. Surface reflectance in all studied wavelengths shows similar relationships with canopy cover, height, and rugosity, mainly due to close connections between these parameters. Visible and near-infrared reflectance decreases with canopy cover, tree height, and rugosity, especially for the evergreen forest. Deciduous forest shows more considerable variability of surface reflectance in all studied wavelengths, particularly in March, mainly due to the mixing effect of snow and vegetation. The multivariate statistical analysis demonstrates a significant tree shadow effect on surface reflectance for evergreen forests. However, the topographic shadow effect is prominent for deciduous forests during the winter season. These results provide great insight into understanding the role of vegetation structure and topography in surface radiation budget in the boreal region

Mobility of arsenic in the sub-surface environment: An integrated hydrogeochemical study and sorption model of the sandy aquifer materials

International audienceGroundwater and aquifer materials have been characterized geochemically at a field site located in the Chakdaha municipality of West Bengal, India. Sorption experiments were also carried out on a sandy aquifer material to understand the mobility of arsenic (As) in the sub-surface environments. The result shows that the areas associated with high groundwater As (mean: 1.8 μM) is typically associated with low Eh (mean: −129 mV), and high Fe (mean: 0.11 mM), where Fe2+/Fe(OH)3 couple is controlling groundwater redox potential. Analysis of the aquifer material total concentrations showed the dominance of As (range: 8.9–22 mg kg−1), Fe (range: 3.0–9.7% as Fe2O3) and Mn (range: 0.05–0.18% as MnO) in the silt-/clay-rich sediments; whereas fine-/medium-sand rich sediment contains considerably lower amount of As (<8.1 mg kg−1), Fe (range: 1.6–3.9% as Fe2O3) and Mn (range: 0.02–0.08% as MnO). The acid extractable As do not correlate with ascorbate extractable Fe-oxyhydroxide, however Fe-oxyhydroxide is generally high in the sediments from low groundwater As areas. Chemical speciation computations indicated Fe(II), Ca(II), Mg(II) and Mn(II) to be at equilibrium (with respect to calcite, dolomite and rhodochrosite) or slightly over-saturated (with respect to siderite). These carbonate minerals may therefore participate to the As immobilization. The measured total organic carbon (1%) and groundwater temperature (26–32 °C) coupled with sorption studies strongly favors microbially mediated Fe(III)-oxyhydroxide reduction as the dominant mechanism for the release of As in the groundwater. Oscillations of As, Mn and Fe concentrations with depth reflected pCO2 oscillations consecutive to microbial respiration intensity

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Growth, Nutrient Accumulation, and Drought Tolerance in Crop Plants with Silicon Application: A Review

Plants take up silicon (Si) from the soil which impacts their growth and nutrient accumulation. It increases plant resistance to abiotic and biotic stresses such as drought, salinity, and heavy metal, diseases, and pest infestation. However, until recently, research of Si application on the crop is limited. This article reviews the recent progress of research on Si application on crop growth and yield, nutrient availability in soil and accumulation, and drought tolerance of crop plants. The review’s findings show that Si improves crop development and output under stressful environmental conditions. Silicon increases the availability and accumulation of both macronutrients (nitrogen, potassium, calcium, and sulphur) and micronutrients (iron and manganese). It improves drought resistance by increasing plant water usage efficiency and reducing water loss during transportation. Silicon application is a crucial aspect of crop productivity because of all of these favorable attributes. The gaps in current understandings are identified. Based on the outcome of the present research, future scopes of research on this field are proposed

Growth, Nutrient Accumulation, and Drought Tolerance in Crop Plants with Silicon Application: A Review

Plants take up silicon (Si) from the soil which impacts their growth and nutrient accumulation. It increases plant resistance to abiotic and biotic stresses such as drought, salinity, and heavy metal, diseases, and pest infestation. However, until recently, research of Si application on the crop is limited. This article reviews the recent progress of research on Si application on crop growth and yield, nutrient availability in soil and accumulation, and drought tolerance of crop plants. The review&rsquo;s findings show that Si improves crop development and output under stressful environmental conditions. Silicon increases the availability and accumulation of both macronutrients (nitrogen, potassium, calcium, and sulphur) and micronutrients (iron and manganese). It improves drought resistance by increasing plant water usage efficiency and reducing water loss during transportation. Silicon application is a crucial aspect of crop productivity because of all of these favorable attributes. The gaps in current understandings are identified. Based on the outcome of the present research, future scopes of research on this field are proposed

Application of natural citric acid sources and their role on arsenic removal from drinking water: a green chemistry approach

Solar Oxidation and Removal of Arsenic (SORAS) is a low-cost non-hazardous technique for the removal of arsenic (As) from groundwater. In this study, we tested the efficiency of natural citric acid sources extracted from tomato, lemon and lime to promote SORAS for As removal at the household level. The experiment was conducted in the laboratory using both synthetic solutions and natural groundwater samples collected from As-polluted areas in West Bengal. The role of As/Fe molar ratios and citrate doses on As removal efficiency were checked in synthetic samples. The results demonstrate that tomato juice (as citric acid) was more efficient to remove As from both synthetic (percentage of removal: 78–98%) and natural groundwater (90–97%) samples compared to lemon (61–83% and 79–85%, respectively) and lime (39–69% and 63–70%, respectively) juices. The As/Fe molar ratio and the citrate dose showed an 'optimized central tendency' on As removal. Anti-oxidants, e.g. 'hydroxycinnamates', found in tomato, were shown to have a higher capacity to catalyze SORAS photochemical reactions compared to 'flavanones' found in lemon or lime. The application of this method has several advantages, such as eco- and user- friendliness and affordability at the household level compared to other low-cost techniques

Biogeochemical characteristics of Kuan-Tzu-Ling, Chung-Lun and Bao-Lai hot springs in southern Taiwan

Hot springs are the important natural sources of geothermally heated groundwater from the Earth's crust. Kuan-Tzu-Ling (KTL), Chung-Lun (CL) and Bao-Lai (BL) are well-known hot springs in southern Taiwan. Fluid and mud (sediments) samples were collected from the eruption points of three hot springs for detailed biogeochemical characterization. The fluid sample displays relatively high concentrations of Na+ and Cl− compared with K+, Mg2+, Ca2+, NO2 −, and SO4 2−, suggesting a possible marine origin. The concentrations of Fe, Cr, Mn, Ni, V and Zn were significantly higher in the mud sediments compared with fluids, whereas high concentrations of As, Ba, Cu, Se, Sr and Rb were observed in the fluids. This suggests that electronegative elements were released during sediment-water interactions. High As concentration in the fluids was observed to be associated with low redox (Eh) conditions. The FTIR spectra of the humic acid fractions of the sediments showed the presence of possible functional groups of secondary amines, ureas, urethanesm (amide), and silicon. The sulfate-reducing deltaproteobacterium 99% similar to Desulfovibrio psychrotolerans (GU329907) were rich in the CL hot spring while mesophilic, proteolytic, thiosulfate- and sulfur-reducing bacterium that 99% similar to Clostridium sulfidigenes (GU329908) were rich in the BL hot spring

Co-occurrence of arsenic and fluoride in groundwater of semi-arid regions in Latin America: genesis, mobility and remediation

Several million people around the world are currently exposed to excessive amounts of arsenic (As) and fluoride (F) in their drinking water. Although the individual toxic effects of As and F have been analyzed, there are few studies addressing their co-occurrences and water treatment options. Several studies conducted in arid and semi-arid regions of Latin America show that the co-occurrences of As and F in drinking water are linked to the volcaniclastic particles in the loess or alluvium, alkaline pH, and limited recharge. The As and F contamination results from water–rock interactions and may be accelerated by geothermal and mining activities, as well as by aquifer over-exploitation. These types of contamination are particularly pronounced in arid and semi-arid regions, where high As concentrations often show a direct relationship with high F concentrations. Enrichment of F is generally related to fluorite dissolution and it is also associated with high Cl, Br, and V concentrations. The methods of As and F removal, such as chemical precipitation followed by filtration and reverse osmosis, are currently being used at different scales and scenarios in Latin America. Although such technologies are available in Latin America, it is still urgent to develop technologies and methods capable of monitoring and removing both of these contaminants simultaneously from drinking water, with a particular focus towards small-scale rural operations

Assessment of arsenic exposure from groundwater and rice in Bengal Delta Region, West Bengal, India

(As) induced identifiable health outcomes are now spreading across Indian subcontinent with continuous discovery of high As concentrations in groundwater. This study deals with groundwater hydrochemistry vis-à-vis As exposure assessment among rural population in Chakdaha block, West Bengal, India. The water quality survey reveals that 96% of the tubewells exceed WHO guideline value (10 μg/L of As). The groundwaters are generally anoxic (−283 to −22 mV) with circum-neutral pH (6.3 to 7.8). The hydrochemistry is dominated by HCO3− (208 to 440 mg/L), Ca2+ (79 to 178 mg/L) and Mg2+ (17 to 45 mg/L) ions along with high concentrations of AsT (As total, below detection limit to 0.29 mg/L), FeT (Fe total, 1.2 to 16 mg/L), and Fe(II) (0.74 to 16 mg/L). The result demonstrates that Fe(II)–Fe(III) cycling is the dominant process for the release of As from aquifer sediments to groundwater (and vice versa), which is mainly controlled by the local biogeochemical conditions. The exposure scenario reveals that the consumption of groundwater and rice are the major pathways of As accumulation in human body, which is explained by the dietary habit of the surveyed population. Finally, regular awareness campaign is essential as part of the management and prevention of health outcomes

Arsenic mobilization in the aquifers of three physiographic settings of West Bengal, India: understanding geogenic and anthropogenic influences

A comparative hydrogeochemical study was carried out in West Bengal, India covering three physiographic regions, Debagram and Chakdaha located in the Bhagirathi-Hooghly alluvial plain and Baruipur in the delta front, to demonstrate the control of geogenic and anthropogenic influences on groundwater arsenic (As) mobilization. Groundwater samples (n = 90) from tube wells were analyzed for different physico-chemical parameters. The low redox potential (Eh = -185 to -86 mV) and dominant As(III) and Fe(II) concentrations are indicative of anoxic nature of the aquifer. The shallow (100 m) aquifers of Bhagirathi-Hooghly alluvial plains as well as shallow aquifers of delta front are characterized by Ca 2+ {single bond}HCO 3 - type water, whereas Na + and Cl - enrichment is found in the deeper aquifer of delta front. The equilibrium of groundwater with respect to carbonate minerals and their precipitation/dissolution seems to be controlling the overall groundwater chemistry. The low SO 4 2- and high DOC, PO 4 3- and HCO 3 concentrations in groundwater signify ongoing microbial mediated redox processes favoring As mobilization in the aquifer. The As release is influenced by both geogenic (i.e. geomorphology) and anthropogenic (i.e. unsewered sanitation) processes. Multiple geochemical processes, e.g., Fe-oxyhydroxides reduction and carbonate dissolution, are responsible for high As occurrence in groundwaters