Energy Balance of Irrigated Intercropping Field in the Middle Reaches of Heihe River Basin

1 Introduction Most of the solar radiation that ecosystem seizes is con- sumed on latent, sensible and soil heat flux. Among them, latent heat flux shares the biggest part (Gutierrez and Meizer, 1994; Ham et al., 1991; Rachidi et al., 1993). The radiation budget and the energy balance are crucial to water conversion and effective water utilization. Also, they are important parts of research of water-saving ag- riculture (Mo et al., 1997). At present, the researches on radiation budget and e…     

半干旱夏季放牧草地能量收支和地表蒸散量变化特征

以半干旱区域典型夏季放牧草地为研究对象,采用涡动相关法,获取了2012年5月至2013年5月水汽和能量通量观测数据,分析夏季近地层能量收支特征、地表蒸散量变化及其气象控制因子。观测结果显示:生长季有效能量的分配以潜热通量为主,非生长季则以感热通量为主;地表蒸散日总量最大值为3.0mm,日蒸散量大小主要取决于土壤温度、气温和净辐射;降雨量的季节分布是地表蒸散量季节变化的一个重要的影响因子。     

Effects of Environmental Conditions and Aboveground Biomass on CO_2 Budget in Phragmites australis Wetland of Jiaozhou Bay,China

Estuarial saline wetlands have been recognized as a vital role in CO_2 cycling.However,insufficient attention has been paid to estimating CO_2 fluxes from estuarial saline wetlands.In this study,the static chamber-gas chromatography(GC) method was used to quantify CO_2 budget of an estuarial saline reed(Phragmites australis) wetland in Jiaozhou Bay in Qingdao City of Shandong Province,China during the reed growing season(May to October) in 2014.The CO_2 budget study involved net ecosystem CO_2 exchange(NEE),ecosystem respiration(Reco) and gross primary production(GPP).Temporal variation in CO_2 budget and the impact of air/soil temperature,illumination intensity and aboveground biomass exerted on CO_2 budget were analyzed.Results indicated that the wetland was acting as a net sink of 1129.16 g/m~2 during the entire growing season.Moreover,the values of Reco and GPP were 1744.89 g/m~2 and 2874.05 g/m~2,respectively;the ratio of Reco and GPP was 0.61.Diurnal and monthly patterns of CO_2 budget varied significantly during the study period.Reco showed exponential relationships with air temperature and soil temperature at 5 cm,10 cm,20 cm depths,and soil temperature at 5 cm depth was the most crucial influence factor among them.Meanwhile,temperature sensitivity(Q10) of Reco was negatively correlated with soil temperature.Light and temperature exerted strong controls over NEE and GPP.Aboveground biomass over the whole growing season showed non-linear relationships with CO_2 budget,while those during the early and peak growing season showed significant linear relationships with CO_2 budget.This research provides valuable reference for CO_2 exchange in estuarial saline wetland ecosystem.     

Energy Budget over Seasonal Snow Surface at an Open Site and Beneath Forest Canopy Openness during the Snowmelt Period in Western Tianshan Mountains,China

In this study, meteorological factors and snowmelt rate at an open site on sunny slope(OPS) and beneath forest canopy openness on shady slope(BFC) were measured using an automatic weather station and snow lysimeter during the snowmelt period in 2009, 2010 and 2013. The energy budget over snow surface was calculated according to these meteorological datasets. The analysis results indicated that the net shortwave radiation(K) and sensible heat flux(H) were energy sources, and the latent heat flux(LVE) was energy sinks of snow surfaces at all sites. The net longwave radiation(L) was energy sink at OPS and 80% BFC, but energy source at 20% BFC. The gain of K, H, and the loss of LVE at BFC were obviously lower than those at OPS. The L was the maximum difference of energy budget between snow surface at BFC and OPS. In warm and wet years, the most important factor of the energy budget variation at OPS was air humidity and the second mostimportant factor was air temperature. However, the ground surface temperature on the sunny slope was the most important factor for L and energy budget at BFC. With the increases in forest canopy openness and the slope of adjacent terrains, the influences of ground surface temperature on the sunny slope on L and the energy budget over snow surface at BFC increased, especially when the snow cover on the sunny slope melts completely.     

Effects of environmental conditions and aboveground biomass on CO<Subscript>2</Subscript> budget in <Emphasis Type="Italic">Phragmites australis</Emphasis> wetland of Jiaozhou Bay,China

Estuarial saline wetlands have been recognized as a vital role in CO₂ cycling. However, insufficient attention has been paid to estimating CO₂ fluxes from estuarial saline wetlands. In this study, the static chamber-gas chromatography (GC) method was used to quantify CO₂ budget of an estuarial saline reed (Phragmites australis) wetland in Jiaozhou Bay in Qingdao City of Shandong Province, China during the reed growing season (May to October) in 2014. The CO₂ budget study involved net ecosystem CO₂ exchange (NEE), ecosystem respiration (R_eco) and gross primary production (GPP). Temporal variation in CO₂ budget and the impact of air/soil temperature, illumination intensity and aboveground biomass exerted on CO₂ budget were analyzed. Results indicated that the wetland was acting as a net sink of 1129.16 g/m²during the entire growing season. Moreover, the values of R_eco and GPP were 1744.89 g/m² and 2874.05 g/m², respectively; the ratio of R_eco and GPP was 0.61. Diurnal and monthly patterns of CO₂ budget varied significantly during the study period. R_eco showed exponential relationships with air temperature and soil temperature at 5 cm, 10 cm, 20 cm depths, and soil temperature at 5 cm depth was the most crucial influence factor among them. Meanwhile, temperature sensitivity (Q₁₀) of R_eco was negatively correlated with soil temperature. Light and temperature exerted strong controls over NEE and GPP. Aboveground biomass over the whole growing season showed non-linear relationships with CO₂ budget, while those during the early and peak growing season showed significant linear relationships with CO₂ budget. This research provides valuable reference for CO₂ exchange in estuarial saline wetland ecosystem.     

Surface energy balance of Bayi Ice Cap in the middle of Qilian Mountains,China

Energy balance at the glacier surface is important for understanding the impacts of climate change on glaciers. Here, we analyzed the characteristics of the glacier surface energy fluxes along with their contributions to glacier melt on Bayi Ice Cap in Qilian Mountains by using a point-scale energy balance model. The half-hourly meteorological data from an automatic weather station (AWS) located on the glacier was used to drive the energy balance model. The model simulated results could accurately represent the mass-balance observations from the stake near the weather station during summer 2016. Our results showed the net radiation (86%) played an important role in the surface energy balance, and the contribution of the turbulent heat fluxes (14%) to the energy budget was relatively less important. A distinct behavior of energy balance, as compared to other continental glaciers in China (e.g., two adjacent glaciers Laohugou No. 12 Glacier and Qiyi Glacier), is the fact that a sustained period of positive turbulent latent flux exists on Bayi Ice Cap during August, causing faster melt rate in the month of August. Our study also presented the effect of frequent summer snowfall in slowing down surface melt by changing the surface albedo during the beginning of the melting season.     

Surface heat budget and solar radiation allocation at a melt pond during summer in the central Arctic Ocean

The heat budget of a melt pond surface and the solar radiation allocation at the melt pond are studied using the 2010 Chinese National Arctic Research Expedition data collected in the central Arctic. Temperature at a melt pond surface is proportional to the air temperature above it. However, the linear relationship between the two varies, depending on whether the air temperature is higher or lower than 0℃. The melt pond surface temperature is strongly influenced by the air temperature when the latter is lower than 0℃. Both net longwave radiation and turbulent heat flux can cause energy loss in a melt pond, but the loss by the latter is larger than that by the former. The turbulent heat flux is more than twice the net longwave radiation when the air temperature is lower than 0℃. More than 50% of the radiation energy entering the pond surface is absorbed by pond water. Very thin ice sheet on the pond surface(black ice) appears when the air temperature is lower than 0℃; on the other hand, only a small percentage(5.5%) of net longwave in the solar radiation is absorbed by such a thin ice sheet.     

Quantitative simulation on soil moisture contents of two typical vegetation communities in Sanjiang Plain,China

Different types of vegetation occupy different geomorphology and water gradient environments in the San-jiang Plain,indicating that the soil moisture dynamics and water balance patterns of the different vegetation communi-ties might differ from each other.In this paper,a lowland system,perpendicular to the Nongjiang River in the Honghe National Nature Reserve(HNNR),was selected as the study area.The area was occupied by the non-wetland plant forest and the typical wetland plant meadow.The Microsoft Windows-based finite element analysis software package for simulating water,heat,and solute transport in variably saturated porous media(HYDRUS),which can quantita-tively simulate water,heat,and/or solute movement in variably-saturated porous media,was used to simulate soil moisture dynamics in the root zone(20-40 cm) of those two plant communities during the growing season in 2005.The simulation results for soil moisture were in a good agreement with measured data,with the coefficient of determi-nation(R2) of 0.44-0.69 and root mean square error(RMSE) ranging between 0.0291 cm3/cm3 and 0.0457 cm3/cm3,and index of agreement(d) being from 0.612 to 0.968.During the study period,the volumetric soil moisture content of meadow increased with the depth and its coefficient of variation decreased with the depth(from 20 cm to 40 cm),while under the forest the soil moisture content at different depths varied irregularly.The calculated result of water budget showed that the water budget deficit of the meadow was higher than that of the forest,suggesting that the meadow is more likely to suffer from water stress than the forest.The quantitative simulation by HYDRUS in this study did not take surface runoff and plant growth processes into account.Improved root water uptake and surface runoff models will be needed for higher accuracy in further researches.     

Seasonal variation of tidal prism and energy in the Changjiang River estuary:a numerical study

Tidal rivers are intrinsically complex because tidal propagation is influenced by river discharge. This study aims to examine the seasonal variation of tidal prism and energy variance in the tidal river of the Changjiang(Yangtze) River estuary in China. In order to quantify the behaviour of river and tide,we use numerical modelling that has been validated using measured data. We conduct our analysis by quantifying the discharge and energy variance in separate components for both the river and the tide,during wet and dry seasons. We note various definitions of tidal prism and explore the difference between tidal discharge on the flood and ebb and tidal storage volume. The results show that the river discharge attenuates the tidal motion and reduces the tidal flood discharge but the tidal storage volume is approximately constant with different riverine discharge since part of the fresh water discharge is intercepted and captured in the estuary due to the backwater effect. It appears that the tidal discharge adjusts according to the variation of river discharge to keep a constant tidal storage volume. An analysis of the hydraulics shows that the transition from tidal dominance(at the mouth) to river dominance(upstream) depends on the location of tidal current reversal which varies from wet season to dry season. Duringthe wet season,the Changjiang River estuary is totally dominated by energy from fresh water discharge.     

Thermal dynamics of the permafrost active layer under increased precipitation at the Qinghai-Tibet Plateau

Precipitation has a significant influence on the hydro-thermal state of the active layer in permafrost regions, which disturbs the surface energy balance, carbon flux, ecosystem, hydrological cycles and landscape processes. To better understand the hydro-thermal dynamics of active layer and the interactions between rainfall and permafrost, we applied the coupled heat and mass transfer model for soil-plant-atmosphere system into high-altitude permafrost regions in this study. Meteorological data, soil temperature, heat flux and moisture content from different depths within the active layer were used to calibrate and validate this model. Thereafter, the precipitation was increased to explore the effect of recent climatic wetting on the thermal state of the active layer. The primary results demonstrate that the variation of active layer thickness under the effect of short-term increased precipitation is not obvious, while soil surface heat flux can show the changing trends of thermal state in active layer, which should not be negligible. An increment in year-round precipitation leads to a cooling effect on active layers in the frozen season, i.e. verifying the insulating effect of "snow cover". However, in the thawed season, the increased precipitation created a heating effect on active layers, i.e. facilitating the degradation of permafrost. The soil thermal dynamic in single precipitation event reveals that the precipitation event seems to cool the active layer, while compared with the results under increased precipitation, climatic wetting trend has a different influence on the permafrost evolution.     

Assessing the influence of highway and high-speed railway construction on local climate using Landsat images in karst areas

Large-scale transportation infrastructure construction in ecologically vulnerable areas such as the karst region of Southwest China requires estimation method for better project design. This research was carried out on a four-lane highway(the Guilin-Guiyang highway, G76) and a two-lane highspeed railway(the Guilin-Guiyang high-speed railway,GGHSR) in karst areas in Guizhou and Guangxi provinces. The highway and high-speed railway were constructed in the 2010 s and covered by Landsat images whose multispectral information could be used for research purposes. In this study, the severity of the impact and the CO_2 emissions from the G76 and GGHSR construction were evaluated. Landsat images and field meteorological measurements were applied to calculate the surface functional parameters(surface temperature and surface wetness) and heat fluxes(latent, sensible and ground heat flux) before and during the highway and high-speed railway construction; the amount of CO_2 emissions during the G76 and GGHSR construction were determined by using budget sheets, which record the detail consumptions of materials and energy. The results showed that the decrease of water evaporation from the highway and high-speed railway construction can reach up to 26.4 m~3 and 20.1 m~3 per kilometer, which corresponds to an average decrease in the vegetation cooling effect of 18.0 MWh per day per highway kilometer and 13.7 MWh per day per high-speed railway kilometer, respectively. At the meantime, the average CO_2 emission densities from the G76 and GGHSR construction can reach up to 24813.7 and 36921.1 t/km, respectively. This study implied that extensive line constructions have a significant impact on the local climate and the energy balance, and it is evident that selecting and planting appropriate plant species can compensate for the adverse effects of line constructions in karst mountain regions.     

喀斯特地区不同岩土组构对岩溶碳通量的影响

我国南方喀斯特地区岩石裸露率高、土层浅薄且分布不均,这种特殊的岩土组构如何影响水文过程对于准确估算岩溶碳通量具有重要意义。水化学径流法是计算流域尺度岩溶碳通量的常用方法,其中流域面积和流量作为2个重要参数在喀斯特地区往往难以准确获取。在普定喀斯特生态系统观测研究站设计了一组岩土比(1:1和4:1)和一组土层厚度(5,20,100 cm)共计5种岩土组构的模拟试验场。通过一个完整水文年的流量和水化学监测,定量研究了岩石裸露率和土层厚度对水文过程以及岩溶碳通量的影响。研究结果表明,5个模拟试验场岩溶碳通量平均值为(17±3) gC/m2/a,受渗漏量控制,雨季(5-10月)约占95%;岩石裸露率(2组岩土组构之间)对渗漏量的影响可达14%,且随着岩石裸露率增加,入渗系数也相应增加;土层厚度对渗漏量的影响仅在1%~2%之间。此外,对8个野外流域观测数据的分析发现,入渗系数与岩溶碳通量的相关性最为显著,说明入渗系数是喀斯特地区不同岩土组构地质背景影响和控制岩溶碳通量的主要因素,同时这种影响可能随降雨量变化而变化,即入渗系数并非常数。      

Role of sea ice in air-sea exchange and its relation to sea fog

Synchronous or quasi-synchronous stereoscopic sea-ice-air comprehensive observation was conducted during the First China Arctic Expedition in summer of 1999. Based on these data, the role of sea ice in sea-air exchange was studied. The study shows that the kinds, distribution and thickness of sea ice and their variation significantly influence the air-sea heat exchange. In floating ice area, the heat momentum transferred from ocean to atmosphere is in form of latent heat; latent heat flux is closely related to floating ice concentration; if floating ice is less, the heat flux would be larger. Latent heat flux is about 21 23.6 W*m-2, which is greater than sensible heat flux. On ice field or giant floating ice, heat momentum transferred from atmosphere to sea ice or snow surface is in form of sensible heat. In the floating ice area or polynya, sea-air exchange is the most active, and also the most sensible for climate. Also this area is the most important condition for the creation of Arctic vapor fog. The heat exchange of a large-scale vapor fog process of about 500000 km2 on Aug. 21 22,1999 was calculated; the heat momentum transferred from ocean to air was about 14.8×109 kW. There are various kinds of sea fog, radiation fog, vapor fog and advection fog, forming in the Arctic Ocean in summer. One important cause is the existence of sea ice and its resultant complexity of both underlying surface and sea-air exchange.     

Spatial Variation and Risk Assessment of Arsenic and Heavy Metals in Surface Water and Suspended Particulate Matter in Tail Reaches of the Yellow River,China

To determine the pollution levels and potential toxic risks of arsenic(As) and heavy metals(Cr, Ni, Cu, Zn, Pb and Cd) in water and suspended particulate matter(SPM) in tail reaches(including freshwater reach and low-salinity reach) of the Yellow River as the Flow-Sediment Regulation Project(FSRP) has been carried out for approximately 15 yr, the surface water and SPM were sampled at pre-flood(April) and post-flood seasons(October). Results showed that similar changes of As and metal levels in water and SPM were observed along the tail reaches at pre-flood or post-flood season. Compared to pre-flood season, the levels of As, Cu, Cr and Ni in freshwater reach and the concentrations of Cr and Ni in low-salinity reach rose greatly at post-flood season. The levels of As and metals in SPM of freshwater reach or low-salinity reach at pre-flood season were significantly higher than those at post-flood season(P < 0.01).The pollutions of As and metals in surface water of tail reaches at pre-flood or post-flood season were not serious. The SPM in freshwater reach at pre-flood season were polluted by Cd, As, Cr, Cu and Ni while those in low-salinity reach were polluted by Cd and Cr. The SPM in freshwater reach at post-flood season were polluted by Cd and Pb while those in low-salinity reach were polluted by Cd and Cr.Cd was identified as heavy metal of primary concern at both pre-flood and post-flood seasons. Combined with the existed data reported in present research, this study found that the toxic risk of As and metals in SPM of tail reaches at pre-flood season was higher than that at post-flood season, implying that the implementation of FSRP during flooding season, to a great extent, reduced the toxic risk of these elements. With the long-term implementation of FSRP, the pollution levels of As and metals(particularly for Cd) in SPM of tail reaches might be elevated and the potential toxic risk primarily produced by Cr, Ni and As might be increased if effective measures were not taken in future.     

太阳能腔式吸热器光热转换特性及其在油田上的应用

以油田规模化利用太阳能为背景,建立基于蒙特卡洛射线踪迹法的腔式吸热器光热转换物理模型和数学模型,通过数值模拟计算腔式吸热器的热流密度分布特性,设计一种新型太阳能腔式吸热器,结合油田应用对太阳能腔式吸热器出口水温进行计算.结果表明,新型太阳能腔式吸热器的热流密度分布基本呈正态分布,在太阳辐射强度为1100W/m2,最大辐射热流为0.22MW/m2时,系统实际聚光比为200,吸热器出口水温为50.2e,能够满足油田应用需求.     

Numerical study of the seasonal salinity budget of the upper ocean in the Bay of Bengal in 2014

Impact factors on the salinity budget,especially the eddy salt fluxes and smaller-scale diffusive salt fluxes for the upper 50 m of the Bay of Bengal(BoB) in 2014 are investigated using a box model based on the Regional Ocean Modeling System(ROMS) daily outputs.The model results reproduce that the precipitation and river runoffs are the dominant factors modulating the sharp salinity decrease during the summer monsoon season.The analysis shows that the salinity increase after the summer monsoon is mostly due to the meridional advective and diffusive salt fluxes.The vertical advective salt flux,which is sensitive to the different signals of the wind stress curl,plays an important role in balancing the salinity change induced by the meridional advective salt flux during both the summer and winter monsoon seasons.Distinctive spatial mesosc ale structures are presented in the eddy salt flux throughout the year,and their contributions are sizeable(over 30% in the meridional direction and about 10%-30% in the vertical direction).The meridional eddy salt flux is larger in the monsoon seasons than that in the inter-monsoon seasons,and in a positive pattern near the western boundary during the winter monsoon and autumn inter-monsoon.The vertical eddy salt flux makes an important contribution to the salinity budget,especially along the coastal area and around the Andaman and Nicobar Islands.The vertical eddy salt flux becomes large when a tropical cyclone passes the area.     

Energetics and temporal variability of internal tides in Luzon Strait: a nonhydrostatic numerical simulation

A fully nonlinear,three-dimensional nonhydrostatic model driven by four principal tidal constituents(M2,S2,K1,and O1) is used to investigate the spatial-temporal characteristics and energetics of internal tides in Luzon Strait(LS).The model results show that,during spring(neap) tides,about 64(47) GW(1 GW=109 W) of barotropic tidal energy is consumed in LS,of which 59.0%(50.5%) is converted to baroclinic tides.About 22(11) GW of the derived baroclinic energy flux subsequently passes from LS,among which 50.9%(54.3%) flows westward into the South China Sea(SCS) and 45.0%(39.7%) eastward into the Pacific Ocean,and the remaining 16(13) GW is lost locally owing to dissipation and convection.It is revealed that generation areas of internal tides vary with the spring and neap tide,indicating different source areas for internal solitary waves in the northern SCS.The region around the Batan Islands is the most important generation region of internal tides during both spring and neap tides.In addition,the baroclinic tidal energy has pronounced seasonal variability.Both the total energy transferred from barotropic tides to baroclinic tides and the baroclinic energy flux flowing out of LS are the highest in summer and lowest in winter.     

EFFECT OF ELECTRIC FERTILIZER ON SOIL PROPERTIES

Electric fertilizer, i. e. exerting electric field on plants during growing season instead of chemical fertilizer, is a kind of physical fertilizer, and the third kind of fertilizer with developmental prospect after inorganic fertilizer and organic fertilizer. For the purpose of studying the changes of physical and chemical properties of soil after exerting electric field, five treatments with different applications of chemical fertilizer were arranged on the black soil in Yushu City of Jilin Province by randomized block method, and electric field was exerted on plants every ten days during the growing season. Through sample analysis the paper arrives at following conclusions: 1) Exerting electric field can make soil‘s granular structure increase, bulk density decrease, moisture capacity increase,thus improving the perviousness of soil. 2) Exerting electric field can make microorganism‘s number increase and activity strengthen, thus activating nutrient and increasing organic matter content. 3) Exerting electric field with 0.1A medium has the best effect. So the chemical fertilizer can be saved. Therefore, we can say that the application of electric fertilizer is favorable for decreasing chemical poison, improving soil, relaxing the contradiction between the supply and demand of chemical fertilizer, and decreasing production cost of agriculture and forestry.     

青藏高原土壤热交换的计算方案及初步分析

从地温满足的热传导方程出发，导出了计算土壤平均和瞬时热通量的计算方案。该计算方案可同时计算出土壤热通量随时间和随深度的变化。它利用整层的地温信息来计算任一层的热通量，这种方案克服了用差分方案进行直接计算的局限性。然后使用中日亚洲季风观测实验期间的地温自动观测站资料和相应的常规观测资料，计算了青藏高原上土壤热通量及其变化，结果表明，不论是常规观测站还是自动观测站，其结果与青藏高原第一次观测实验所用热流板的直接观测结果是相近的，因而这种计算方案是实用而有效的。     

黄河三角洲蒸散的遥感研究

蒸散是水资源管理的一个重要参数。与传统的蒸散计算方法相比 ,利用遥感进行蒸散研究具有快速、准确、大区域尺度及地图可视化显示等特点。 SEBAL模型是一个应用遥感影像收集到的可见光波段、近红外和热红外波段信息对大区域范围进行蒸散计算的模型 ,它是基于地表能量平衡方程 ,通过计算地表净辐射通量 ,土壤热通量和显热通量 ,最后计算出用于蒸散的潜热通量 ,进而计算出遥感影像拍摄时的瞬时蒸散及当天的总蒸散量。本文利用 SEBAL模型采用 ETM+影像对黄河三角洲进行了遥感蒸散研究 ,并对黄河三角洲的蒸散特点进行了分析。蒸散研究对黄河三角洲水资源的合理利用有潜在的指导意义。