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1.
Amanda J. Holder Rebecca Rowe Niall P. McNamara Iain S. Donnison Jon P. McCalmont 《Global Change Biology Bioenergy》2019,11(11):1298-1317
When considering the large‐scale deployment of bioenergy crops, it is important to understand the implication for ecosystem hydrological processes and the influences of crop type and location. Based on the potential for future land use change (LUC), the 10,280 km2 West Wales Water Framework Directive River Basin District (UK) was selected as a typical grassland dominated district, and the Soil & Water Assessment Tool (SWAT) hydrology model with a geographic information systems interface was used to investigate implications for different bioenergy deployment scenarios. The study area was delineated into 855 sub‐basins and 7,108 hydrological response units based on rivers, soil type, land use, and slope. Changes in hydrological components for two bioenergy crops (Miscanthus and short rotation coppice, SRC) planted on 50% (2,192 km2) or 25% (1,096 km2) of existing improved pasture are quantified. Across the study area as a whole, only surface run‐off with SRC planted at the 50% level was significantly impacted, where it was reduced by up to 23% (during April). However, results varied spatially and a comparison of annual means for each sub‐basin and scenario revealed surface run‐off was significantly decreased and baseflow significantly increased (by a maximum of 40%) with both Miscanthus and SRC. Evapotranspiration was significantly increased with SRC (at both planting levels) and water yield was significantly reduced with SRC (at the 50% level) by up to 5%. Effects on streamflow were limited, varying between ?5% and +5% change (compared to baseline) in the majority of sub‐basins. The results suggest that for mesic temperate grasslands, adverse effects from the drying of soil and alterations to streamflow may not arise, and with surface run‐off reduced and baseflow increased, there could, depending on crop location, be potential benefits for flood and erosion mitigation. 相似文献
2.
蒸散(ET)是陆地生态系统水分收支的重要分量。为探究三江源区退化高寒草甸的蒸散特征,基于2016和2017年涡度相关和微气象系统的观测数据,定量研究了其生态系统的蒸散变化及其环境和生物因子的影响。为深入探讨不同时段的蒸散变化,根据土壤冻融状态和植被生长状况进一步将年蒸散划分为3个时段:冻结期、冻融交替期和消融期,其中在消融期中又划分出植物生长季(5—9月),并探讨了土壤冻融对年蒸散量的影响。结果表明:研究区2016和2017年的降水量分别为451.8 mm和442.3 mm,但2017年ET为485.6 mm,明显高于2016年的428.6 mm,两年ET的季节变化趋势相同,ET的最高值出现在生长旺季的7—8月,最低值出现在12月或1月,生长季ET分别占全年ET的73%和72%。2017年的冻结期和冻融交替期比2016年分别减少了8 d,2017年消融期的蒸散量比2016年增加了63.1 mm,其中生长季的蒸散量多36.3 mm。2016和2017年消融期的日蒸散速率分别为1.81 mm/d和1.97 mm/d,其中生长季为2.05 mm/d和2.29 mm/d,冻融交替期分别为0.9... 相似文献
3.
《Ecohydrology》2018,11(5)
Accurate quantification of terrestrial evapotranspiration and ecosystem productivity is of significant merit to better understand and predict the response of ecosystem energy, water, and carbon budgets under climate change. Existing diagnostic models have different focus on either water or carbon flux estimates with various model complexity and uncertainties induced by distinct representation of the coupling between water and carbon processes. Here, we propose a diagnostic model to estimate evapotranspiration and gross primary production that is based on biophysical mechanism yet simple for practical use. This is done by coupling the carbon and water fluxes via canopy conductance used in the Penman–Monteith–Leuning equation (named as PML_V2 model). The PML_V2 model takes Moderate Resolution Imaging Spectrometer leaf area index and meteorological variables as inputs. The model was tested against evapotranspiration and gross primary production observations at 9 eddy‐covariance sites in Australia, which are spread across wide climate conditions and ecosystems. Results indicate that the simulated evapotranspiration and gross primary production by the PML_V2 model are in good agreement with the measurements at 8‐day timescale, indicated by the cross site Nash–Sutcliffe efficiency being 0.70 and 0.66, R2 being 0.80 and 0.75, and root mean square error being 0.96 mm d−1 and 1.14 μmol m−2 s−1 for evapotranspiration and gross primary production, respectively. As the PML_V2 model only requires readily available climate and Moderate Resolution Imaging Spectrometer vegetation dynamics data and has few parameters, it can potentially be applied to estimate evapotranspiration and carbon assimilation simultaneously at long‐term and large spatial scales. 相似文献
4.
针对西北干旱区绿洲经济作物葡萄树冠层蒸腾及蒸散发特征的相关问题,在甘肃省敦煌市南湖绿洲开展无核白葡萄树液流速率及蒸散发观测试验,采用基于热平衡原理的包裹式茎流计,详细分析了典型生长季7—9月份葡萄树蒸腾耗水规律,使用\"单位叶面积上的平均液流速率SF×叶面积指数LAI\"的方法,实现了从单株到林分冠层蒸腾的尺度扩展,并通过与涡动相关技术所测蒸散发数据对比,详细研究了葡萄地冠层蒸腾及蒸散发规律。结果表明:典型生长季中葡萄树液流速率日变化为单峰型曲线,日均耗水量从2.76 kg到10 kg不等,胸径越大的葡萄树日均耗水量越大;冠层蒸腾及蒸散发日变化曲线亦为单峰型,白天8:00—12:00与17:00—20:00期间,葡萄冠层蒸腾与蒸散发曲线均比较吻合,该时间段葡萄地蒸散发绝大部分来源于葡萄冠层蒸腾,而12:00—17:00之间由于午后太阳辐射强烈土壤蒸发量增加,葡萄蒸散发大于冠层蒸腾;典型生长季3个月中,葡萄冠层蒸腾量的变化范围在1.88—8.12 mm/d之间,日均冠层蒸腾量为6.12 mm/d,蒸散发在1.74 mm/d至10.78 mm/d之间,日均蒸散发量为7.13 mm/d;日均土壤蒸发量约为1.01 mm/d,只占总蒸散发量的14.2%,日均冠层蒸腾占日均蒸散发的比重达到85.8%,说明该生长阶段冠层蒸散发以作物蒸腾为主。 相似文献
5.
J. Ben Keane Ross Morrison Niall P. McNamara Phil Ineson 《Global Change Biology Bioenergy》2019,11(12):1456-1470
Miscanthus x giganteus's efficacy as an energy crop relies on maintaining low greenhouse gas (GHG) emissions. As demand for Miscanthus is expected to rise to meet bioenergy targets, fertilizers and composts may be employed to increase yields, but will also increase GHG emissions. Manipulation experiments are vital to investigate the consequences of any fertilizer additions, but there is currently no way to measure whole‐plant GHG fluxes from crops taller than 2.5 m, such as Miscanthus, at the experimental plot scale. We employed a unique combination of eddy covariance (EC), soil chambers and an entirely new automated chamber system, SkyBeam, to measure high frequency (ca. hourly) fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from a Miscanthus crop amended with green compost. Untreated controls were also monitored in a fully replicated experimental design. Net ecosystem exchange (NEE) of CO2 was partitioned into soil respiration (Rs), gross primary productivity (GPP) and ecosystem respiration, and the crop was harvested to determine the effect of compost on crop productivity. Compost increased NEE emissions by 100% (p < .05), which was the result of a 20% increase of Rs (p < .06) and a 32% reduction in GPP (p < .05) and biomass of 37% (p < .06). Methane fluxes were small and unaffected by compost addition. N2O emissions increased 34% under compost during an emission event; otherwise, fluxes were low and often negative, even under dry conditions. Diurnal variation in N2O fluxes, with uptake during the day and emission at night was observed. These fluxes displayed a negative relationship with soil temperature and a hitherto undescribed diurnal temperature hysteresis. We conclude that compost addition negatively affected the productivity and environmental effects of Miscanthus cultivation during the first year following application. 相似文献
6.
Osvaldo M. R. Cabral Humberto R. Rocha John H. Gash Marcos A. V. Ligo Jonatan D. Tatsch Helber C. Freitas Emília Brasilio 《Global Change Biology Bioenergy》2012,4(5):555-565
The evapotranspiration (E) from a sugarcane plantation in the southeast Brazil was measured by the eddy‐covariance method during two consecutive cycles. These represented the second (393 days) and third year (374 days) re‐growth (ratoon). The total E in the first cycle was 829 mm, accounting for 69% of rainfall, whereas in the second cycle, it was 690 mm, despite the total rainfall (1353 mm) being 13% greater. The ratio of E to available energy, the evaporative fraction, exhibited a smaller variation between the first and second cycles: 0.58 and 0.51, respectively. The estimated interception losses were 88 and 90 mm, respectively, accounting for approximately 7% of the total rainfall. The sugarcane yield in the second cycle (61.5 ± 4.0 t ha?1) was 26% lower than the first cycle, as well as lower than the regional average for the third ratoon (76 t ha?1). The below average yield was associated with less available soil water at the beginning of the cycle, with the amount of rainfall recorded during the first 120 days of re‐growth in the second cycle being 16% of that recorded in the first (203 mm). 相似文献
7.
Peter G. Meehan Kevin P. McDonnell John M. Finnan 《Global Change Biology Bioenergy》2013,5(4):400-407
This study examines the amount of biomass loss occurring in Miscanthus × giganteus crop at harvest. The study assesses loss incurred as a direct result of the harvest systems employed to collect the material along with examining how the time of harvest effects the amount of loss occurring over the spring harvest window. Pre harvest losses of 4.8–5.1% were measured prior to harvest. There was no significant difference between pre harvest loss and post harvest loss when a self‐propelled forage harvester fitted with a maize harvesting header was used to harvest the crop. The use of a conditioner mower and baler significantly increased crop losses to 9.4–14.1%. This demonstrates that correct selection of the harvest system can significantly increase biomass recovery. Additional losses were measured at headlands when the mower/baler system was used, but headland losses will not occur when self‐propelled forage harvesters are utilized. Losses were significantly greater in the area beside the swath after the baler pass when compared to prior to baling. This study has shown that correct selection of harvest systems can significantly increase biomass recovery, with no significant difference in pre harvest loss or harvest loss occurring as a result of cutting the M. × giganteus crop at different dates during the harvest window (March 1st, March 25th, April 21st). 相似文献
8.
Jon P. McCalmont Niall P. McNamara Iain S. Donnison Kerrie Farrar John C. Clifton‐Brown 《Global Change Biology Bioenergy》2017,9(4):710-724
Conversion of large areas of agricultural grassland is inevitable if European and UK domestic production of biomass is to play a significant role in meeting demand. Understanding the impact of these land‐use changes on soil carbon cycling and stocks depends on accurate predictions from well‐parameterized models. Key considerations are cultivation disturbance and the effect of autotrophic root input stimulation on soil carbon decomposition under novel biomass crops. This study presents partitioned parameters from the conversion of semi‐improved grassland to Miscanthus bioenergy production and compares the contribution of autotrophic and heterotrophic respiration to overall ecosystem respiration of CO2 in the first and second years of establishment. Repeated measures of respiration from within and without root exclusion collars were used to produce time‐series model integrations separating live root inputs from decomposition of grass residues ploughed in with cultivation of the new crop. These parameters were then compared to total ecosystem respiration derived from eddy covariance sensors. Average soil surface respiration was 13.4% higher in the second growing season, increasing from 2.9 to 3.29 g CO2‐C m?2 day?1. Total ecosystem respiration followed a similar trend, increasing from 4.07 to 5.4 g CO2‐C m?2 day?1. Heterotrophic respiration from the root exclusion collars was 32.2% lower in the second growing season at 1.20 g CO2‐C m?2 day?1 compared to the previous year at 1.77 g CO2‐C m?2 day?1. Of the total respiration flux over the two‐year time period, aboveground autotrophic respiration plus litter decomposition contributed 38.46% to total ecosystem respiration while belowground autotrophic respiration and stimulation by live root inputs contributed 46.44% to soil surface respiration. This figure is notably higher than mean figures for nonforest soils derived from the literature and demonstrates the importance of crop‐specific parameterization of respiration models. 相似文献
9.
Hongxu Dong Steven V. Green Aya Nishiwaki Toshihiko Yamada J. Ryan Stewart Martin Deuter Erik J. Sacks 《Global Change Biology Bioenergy》2019,11(5):691-705
Miscanthus ×giganteus (M×g) is an important bioenergy feedstock crop. However, biomass production of Miscanthus has been largely limited to one sterile triploid cultivar, M×g ‘1993‐1780’, which we demonstrate can have insufficient overwintering ability in temperate regions with cold winters. Key objectives for Miscanthus breeding include greater biomass yield and better adaptation to different production environments than M×g ‘1993‐1780’. In this study, we evaluated 13 M×g genotypes, including ‘1993‐1780’, in replicated field trials conducted for three years at Urbana, IL; Dixon Springs, IL; and Jonesboro, AR. Entries were phenotyped for first‐winter overwintering ability and plant hardiness (ratio of new tillers to old), yield in years 2 and 3, and first heading date, plant height, and culm number in years 1 and 2. We observed substantial variation for overwintering ability and biomass yield among the M×g genotypes tested and identified ones with better overwintering ability and/or higher biomass yield than ‘1993‐1780’. Most entries at Urbana were damaged during the first winter, whereas few or no entries were damaged at Dixon Springs or Jonesboro. However, M×g ‘Nagara’ was entirely undamaged during the first winter and produced high biomass yields at Urbana (19.7 Mg/ha in year 2 and 20.9 Mg/ha in year 3), whereas M×g ‘1993‐1780’ exhibited an overwintering loss of 29%, had severely damaged survivors (hardiness score of 25%), and reduced biomass yield (8.1 Mg/ha in year 2 and 16.2 Mg/ha in year 3), indicating that M×g ‘Nagara’ could be a better choice in hardiness zone 5 (average annual minimum air temperature of ?23.3 to ?28.9°C) or lower. In Dixon Springs, where M×g ‘1993‐1780’ was undamaged by the first winter, it yielded highest among all the entries (21.6 Mg/ha in year 3), though not significantly higher than M×g ‘Nagara’ (18.2 Mg/ha in year 3). 相似文献
10.
The perennial energy crop Miscanthus × giganteus is recognized for its extraordinary nitrogen‐use efficiency. While the remobilization of nitrogen (N) to the rhizome after the growth phase contributes to this efficiency, the plant‐associated microbiome might also contribute, as N‐fixing bacterial species had been isolated from this grass. Here, we studied established Miscanthus × giganteus plots in southern Germany that either received 80 kg N ha?1 a?1 or that were not N‐fertilized for 14 years. The bacterial communities of the bulk soil, rhizosphere, roots and rhizomes were analysed. Major differences were encountered between plant‐associated fractions. Nitrogen had little effect on soil communities. The roots and rhizomes showed less microbial diversity than soil fractions. In these compartments, Actinobacteria and N‐fixing symbiosis‐associated Proteobacteria depended on N. Intriguingly, N2‐fixing‐related bacterial families were enriched in the rhizomes in long‐term zero N plots, while denitrifier‐related families were depleted. These findings point to the rhizome as a potentially interesting plant organ for N fixation and demonstrate long‐term differences in the organ‐specific bacterial communities associated with different N supply, which are mainly shaped by the plant. 相似文献
11.
Patricia Y. Oikawa G. Darrel Jenerette David A. Grantz 《Global Change Biology Bioenergy》2015,7(5):974-983
High irradiance arid environments are promising, yet understudied, areas for biofuel production. We investigated the productivity and environmental trade‐offs of growing sorghum (Sorghum bicolor) as a biofuel feedstock in the low deserts of California (CA). Using a 5.3 ha experimental field in the Imperial Valley, CA, we measured aboveground biomass production and net ecosystem exchange of CO2 and H2O via eddy covariance over three growing periods between February and November 2012. Environmental conditions were extreme, with high irradiance, vapor pressure deficit (VPD), and air temperature throughout the growing season. Air temperature peaked in August with a maximum of 45.7 °C. Sorghum produced an annual aboveground biomass yield of 43.7 Mg per hectare. Net ecosystem exchange (NEE) was highest during the summer growth period and reached a maximum of ?68 μmol CO2 m?2 s?1. Water use efficiency, or biomass water ratio (BWR), was high (4.0 g dry biomass kg?1 H2O) despite high seasonal evapotranspiration (1094 kg H2O m?2). The BWR of sorghum surpassed that of many C4 biofuel candidate crops in the United States, as well as that of alfalfa which is currently widely grown in the Imperial Valley. Sorghum also outperformed many US biofuel crops in terms of radiation use efficiency (RUE), achieving 1.5 g dry biomass MJ?1. We found no evidence of saturation of NEE at high levels of photosynthetically active radiation (PAR) (up to 2250 μmol m?2 s?1). In addition, we found no evidence that NEE was inhibited by either high VPD or air temperature during peak photosynthetic phases. The combination of high productivity, high BWR, and high RUE suggests that sorghum is well adapted to this extreme environment. The biomass production rates and efficiency metrics spanning three growing periods provide fundamental data for future Life Cycle Assessments (LCA), which are needed to assess the sustainability of this sorghum biofuel feedstock system. 相似文献
12.
利用涡度相关系统、土壤水分TDR传感器,于2014年7月—2015年6月连续测定了民勤绿洲荒漠过渡带退化梭梭人工林蒸散量,研究不同天气条件下梭梭人工林的蒸散对外界环境因子的响应.结果表明: 梭梭人工林晴天蒸散量日变化具有明显的季节变化规律.梭梭人工林蒸散量日变化幅度在生长季初期逐渐增大,在生长旺盛期达到最大峰值(0.07 mm·h-1), 而后逐渐减小,至12月达到最低峰值(0.01 mm·h-1).不同天气条件下梭梭人工林蒸散日变化波动幅度差异较大,阴天蒸散日变化波动幅度最小,降水后蒸散波动明显增高,强降水(>9 mm·d-1)后日蒸散量显著增加至雨前的28倍,然后逐渐减少,并持续4个晴朗日后恢复至雨前蒸散量.在整个观测年,梭梭人工林蒸散总量为108 mm,占降水总量的98%,土壤水是梭梭人工林蒸散的水源,为主导因子.净辐射、光合有效辐射、空气温度、水汽压饱和差是决定植被用水和大气边界层水传输的气象动力,为显著影响梭梭人工林蒸散的主要因子.利用日蒸散量与环境因子数据建立了蒸散与土壤含水量和小气候因子的多元回归方程,拟合度(R2)高达0.80. 相似文献
13.
YANG Tian-wei ZHANG Ji Jerzy FALANDYSZ Graz·yna KRASI-SKA Martyna SABA WANG Yuan-zhong LIU Hong-gao 《生态学杂志》2015,34(12):3518
汞(Hg)是危害人类健康的主要重金属元素之一,多数食用菌对Hg有很强的富集能力,测定食用菌中Hg含量,并对其进行食用安全性评价具有重要意义。采用冷原子吸收直接测汞仪系统测定85份云南常见牛肝菌属真菌菌盖、菌柄中总Hg含量;以同一牛肝菌子实体菌盖与菌柄总Hg含量比(Q(C/S))分析牛肝菌属真菌对Hg的富集特征;根据联合国粮农组织和世界卫生组织(FAO/WHO)现行每周Hg允许摄入量(provisional tolerable weekly intake,PTWI)标准和中国GB 2762—2012规定的食用菌中Hg限量标准评价样品的食用安全性。结果表明,菌盖和菌柄中总Hg含量分别在0.13~22.00、0.20~8.40 mg·kg-1DW,不同产地、种类及不同采集年份的样品中总Hg含量存在明显差异;同一牛肝菌菌盖、菌柄总Hg含量比(Q(C/S))在0.28~4.08,92%的样品Q(C/S)1,表明多数样品中菌盖对Hg的富集能力强于菌柄。根据GB 2762—2012规定的食用菌及其制品中总Hg含量限量标准(≤0.1 mg·kg-1),发现所有测试样品的总Hg含量均超标;根据PTWI标准,假设成年人(60 kg)每周食用300 g新鲜牛肝菌,则多数样品Hg摄入量低于允许摄入量,无安全风险,而少数样品Hg摄入量高于允许摄入量,食用有一定的潜在风险。同时,牛肝菌总Hg含量与种类、产地、采集时间等因素密切相关,采食及安全评价需综合考虑这些因素。 相似文献
14.
15.
Biofuel made from conventional (e.g., maize (Zea mays L.)) and cellulosic crops (e.g., switchgrass (Panicum virgatum L.) and Miscanthus (Miscanthus × giganteus)) provides alternative energy to fossil fuels and has been considered to mitigate greenhouse gas emissions. To estimate the large‐scale carbon and nitrogen dynamics of these biofuel ecosystems, process‐based models are needed. Here, we developed an agroecosystem model (AgTEM) based on the Terrestrial Ecosystem Model for these ecosystems. The model was incorporated with biogeochemical and ecophysiological processes including crop phenology, biomass allocation, nitrification, and denitrification, as well as agronomic management of irrigation and fertilization. It was used to estimate crop yield, biomass, net carbon exchange, and nitrous oxide emissions at an ecosystem level. The model was first parameterized for maize, switchgrass, and Miscanthus ecosystems and then validated with field observation data. We found that AgTEM well reproduces the annual net primary production and nitrous oxide fluxes of most sites, with over 85% of total variation explained by the model. Local sensitivity analysis indicated that the model sensitivity varies among different ecosystems. Net primary production of maize is sensitive to temperature, precipitation, cloudiness, fertilizer, and irrigation and less sensitive to atmospheric CO2 concentrations. In contrast, the net primary production of switchgrass and Miscanthus is most sensitive to temperature among all factors. Nitrous oxide fluxes are sensitive to management in maize ecosystems, and sensitive to climate factors in cellulosic ecosystems. The developed model should help advance our understanding of carbon and nitrogen dynamics of these biofuel ecosystems at both site and regional levels. 相似文献
16.
基于Penman-Monteith模型的两个蒸散模型在夏玉米农田的参数修正及性能评价 总被引：3，自引：0，他引：3
利用涡度相关系统和小气象系统对2013—2015年夏玉米生长季的蒸散量和气象数据进行实时观测,基于观测数据对以Penman-Monteith模型为基础的FAO-PM模型和KP-PM模型进行分析:首先利用2013和2014年数据对两个模型中的关键参数进行校正,其次利用两个模型对2015年夏玉米农田的日蒸散量进行计算,并与测量值对比,说明两个模型在夏玉米农田的适用性;最后采用分阶段法对KP-PM模型中的经验系数进行修正.结果表明: FAO-PM模型对2015年夏玉米农田日蒸散量的计算值更加接近测量值;利用分阶段法对KP-PM模型进行修正后,模型对日蒸散量的计算效果有了很大提高,且计算值比FAO-PM模型更接近测量值.模型中关键系数与气象条件之间有很大关系,因此利用模型进行蒸散预测时,必须先对模型进行参数校正.该研究可为其他研究人员利用模型估算蒸散量提供方法上的参考. 相似文献
17.
Water-vapor flux over a planted coniferous forest ecosystem near Qianyanzhou, Jiangxi Province, China, was continuously measured with the eddy covariance technique for 2004. How environmental variables, including net radiation, air temperature, and soil moisture, affected water-vapor flux variation was studied in detail. Results showed that winter had the lowest monthly water-vapor flux value, whereas summer had the highest. The diurnal variation of water-vapor flux showed different patterns for clear and cloudy days. The annual total evapotranspiration was 736.1 mm. Regression analysis showed that daily water-vapor flux was significantly correlated with net radiation, air temperature, soil temperature, and soil heat flux on both clear and cloudy days, all in quadratic relationships. Stepwise regression analysis demonstrated that a different set of environmental factors controlled water-vapor flux on days with different weather conditions. From this study, it was clear that these environmental variables, especially net radiation and soil temperature, regulated water-vapor flux over the planted coniferous ecosystem. 相似文献
18.
Water-vapor flux over a planted coniferous forest ecosystem near Qianyanzhou, Jiangxi Province, China, was continuously measured with the eddy covariance technique for 2004. How environmental variables, including net radiation, air temperature, and soil moisture, affected water-vapor flux variation was studied in detail. Results showed that winter had the lowest monthly water-vapor flux value, whereas summer had the highest. The diurnal variation of water-vapor flux showed different patterns for clear and cloudy days. The annual total evapotranspiration was 736.1 mm. Regression analysis showed that daily water-vapor flux was significantly correlated with net radiation, air temperature, soil temperature, and soil heat flux on both clear and cloudy days, all in quadratic relationships. Stepwise regression analysis demonstrated that a different set of environmental factors controlled water-vapor flux on days with different weather conditions. From this study, it was clear that these environmental variables, especially net radiation and soil temperature, regulated water-vapor flux over the planted coniferous ecosystem. 相似文献
19.
利用涡度相关技术研究了2004年千烟洲人工针叶林生态系统的水汽通量变化特征,结合气象要素的观测,进一步分析了净辐射、温度、水分、热量等环境因子对水汽通量的影响。结果表明:全年各月各时刻的水汽通量大多为正值,夏季大于春秋两季,冬季最小。其中7月份为全年最高,日最大值达到0·149gm-2·s-1;1月份最低,日最高值仅为0·021gm-2·s-1。不同天气条件下(晴天和多云)水汽通量的日变化有明显区别。全年蒸散量为736·1mm,占总降水量(1323·6mm)的55·6%。除7月份和10月份外,各月的蒸散量都要小于降水,尤以3、4月份差别最大,2004年10月出现典型的秋旱,但蒸散量和常年相差不大。水汽通量对净辐射、气温、地温、以及土壤热通量的变化都有很好的响应,两种天气条件下都能达到显著水平,可以用一元二次方程表达其间的关系。逐步回归分析显示晴天和多云时入选的变量不完全相同,晴天主要是净辐射、温度(气温、地温)、水分(饱和水汽压差),多云时包括净辐射、地温、土壤热通量和水分(空气相对湿度、土壤含水量)。可见气象条件在很大程度上制约着水汽通量的变化,而以辐射和地温的影响最大。 相似文献
20.
Revegetation is a common method to combat desertification in arid and semi‐arid areas worldwide. The objective of this study was to characterize the evapotranspiration (ET) of a 20‐year‐old revegetated area of the Tengger Desert. During the measurement period from 2009 to 2012, ET was measured by the eddy covariance technique. The result showed that the values for mean daily ET were 0.43, 0.39, 0.43 and 0.59 mm d−1 in 2009–2012, respectively. In the non‐growing season, the diurnal ET variation showed a normal distribution with a maximum value occurring at noon, while it showed multimodal distribution trend occurred in a dry day and a unimodal trend in a wet day with a maximum value occurring at noon in the growing season. During the 4‐year measurements, despite the large inter‐annual variation of precipitation (annual mean precipitation of 164.4 ± 33.5 mm), the water loss through ET (667.5 mm) was almost equal to rainfall (657.8 mm), and the mean of ET/P was 1.01.The annual ET amounts were 153.6, 143.3, 156.2 and 214.4 mm y−1 in 2009–2012, respectively, with corresponding ratio between accumulated ET and precipitation (ET/P) of 1.03, 1.14, 0.82 and 1.12. This indicated that the annual ET amounts can be modified by the soil water storage, which led to water loss through ET exceeding the water input by precipitation in a drier year, and soil water can be replenished in a wetter year. Thus, the vegetation protection system using plantations of xerophyte shrubs in the present study area is a success with a trade‐off of acceptable hydrological consequences that deserve to be popularized. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献