Natural Precipitation Research Articles

Further analysis of a snowfall enhancement project in the Snowy Mountains of Australia

The first phase of the Snowy Precipitation Enhancement Research Project (SPERP-1) was a confirmatory experiment on winter orographic cloud seeding (Manton et al., 2011). Analysis of the data (Manton and Warren, 2011) found that a statistically significant impact of seeding could be obtained by removing any 5-hour experimental units (EUs) for which the amount of released seeding material was below a specified minimum. Analysis of the SPERP-1 data is extended in the present work by first considering the uncertainties in the measurement of precipitation and in the methodology. It is found that the estimation of the natural precipitation in the target area, based solely on the precipitation in the designated control area, is a significant source of uncertainty. A systematic search for optimal predictors shows that both the Froude number of the low-level flow across the mountains and the control precipitation should be used to estimate the natural precipitation. Applying the optimal predictors for the natural precipitation, statistically significant impacts are found using all EUs. This approach also supports a novel analysis of the sensitivity of seeding impacts to environmental variables, such as wind speed and cloud top temperature. The spatial distribution of seeding impact across the target is investigated. Building on the results of SPERP-1, phase 2 of the experiment (SPERP-2) ran from 2010 to 2013 with the target area extended to the north along the mountain ridges. Using the revised methodology, the seeding impacts in SPERP-2 are found to be consistent with those in SPERP-1, provided that the natural precipitation is estimated accurately.

A savanna response to precipitation intensity.

As the atmosphere warms, precipitation events are becoming less frequent but more intense. A three-year experiment in Kruger National Park, South Africa, found that fewer, more intense precipitation events encouraged woody plant encroachment. To test whether or not these treatment responses persisted over time, here, we report results from all five years of that experiment. Grass growth, woody plant growth, total fine root number and area and hydrologic tracer uptake by grasses and woody plants were measured in six treated plots (8 m by 8 m) and six control plots. Treatment effects on soil moisture were measured continuously in one treated and one control plot. During the fourth year, increased precipitation intensity treatments continued to decrease water flux in surface soils (0–10 cm), increase water flux in deeper soils (20+ cm), decrease grass growth and increase woody plant growth. Greater root numbers at 20–40 cm and greater woody plant uptake of a hydrological tracer from 45–60 cm suggested that woody plants increased growth by increasing root number and activity (but not root area) in deeper soils. During the fifth year, natural precipitation events were large and intense so treatments had little effect on precipitation intensity or plant available water. Consistent with this effective treatment removal, there was no difference in grass or woody growth rates between control and treated plots, although woody plant biomass remained higher in treated than control plots due to treatment effects in the previous four years. Across the five years of this experiment, we found that 1) small increases in precipitation intensity can result in large increases in deep (20–130 cm) soil water availability, 2) plant growth responses to precipitation intensity are rapid and disappear quickly, and 3) because woody plants accumulate biomass, occasional increases in precipitation intensity can result in long-term increases in woody plant biomass (i.e., shrub encroachment). While results are likely to be site-specific, they provide experimental evidence of large ecohydrological responses to small changes in precipitation intensity.

Effect of organic ligands on Mg partitioning and Mg isotope fractionation during low-temperature precipitation of calcite in the absence of growth rate effects

Calcite growth rate has been previously shown to be the dominating parameter controlling both Mg partitioning and Mg isotope fractionation during calcite growth. In natural calcite precipitation environments - characterized by abundant organic material - the presence of dissolved organic molecules may affect these two parameters. In order to assess the role of organic molecules, steady state calcite growth experiments have been performed at 25°C, 1bar pCO2 and constant, within analytical uncertainty growth rate (rp=10−7.4molm−2s−1) in the presence of aqueous Mg and six organic ligands in the concentration range from 0.01 to 10mM. The organic ligands used in this study are: (i) acetic acid, (ii) citric acid, (iii) glutamic acid, (iv) salycilic acid, (v) glycine, and (vi) ethylenediaminetetraacetic acid (EDTA). These contain one or more carboxyl- and amino-groups that are commonly present in natural organic substances found in lacustrine, fluvial, soil, cave, as well as in marine and earliest diagenetic porewater environments. Results shown here indicate that the presence of these carboxyl- and amino-groups promotes an increase in the partition coefficient of Mg in calcite DMg=(Mg/Ca)calcite(Mg/Ca)fluid that can be attributed to their adsorption onto the calcite surfaces and the subsequent reduction of the active sites of growth. This increase of DMg values as a function of the supersaturation degree of calcite in the fluid phase can be described by the linear equation: LogDMg=0.3694(±0.0329)×SIcalcite-1.9066(±0.0147)R2=0.92 In contrast, data shown here suggest that the presence of organic ligands, with exception of citric acid, does not significantly affect the Mg isotope fractionation factor between calcite and reactive fluid. Citric acid likely exhibits larger fractionation between the Mg-ligand complexes and free aqueous Mg, compared to the other organic ligands studied in this work, as evidenced from the smaller Δ26Mgcalcite-fluid values. The main result shown here is that in Earth’s surface precipitation environments the presence of organic ligands is not a major factor affecting the Mg content or Mg-isotope composition of inorganic calcite. But in the presence of higher contents of organic macromolecules from byproducts of metabolic activities, humid, and fulvic acids and/or exopolymeric substances and matrices, an impact on Mg content or Mg isotope composition of calcite cannot be ruled out.

Pyranometer offsets triggered by ambient meteorology: insights from laboratory and field experiments

Abstract. This study investigates the effects of ambient meteorology on the accuracy of radiation (R) measurements performed with pyranometers contained in various heating and ventilation systems (HV-systems). It focuses particularly on instrument offsets observed following precipitation events. To quantify pyranometer responses to precipitation, a series of controlled laboratory experiments as well as two targeted field campaigns were performed in 2016. The results indicate that precipitation (as simulated by spray tests or observed under ambient conditions) significantly affects the thermal environment of the instruments and thus their stability. Statistical analyses of laboratory experiments showed that precipitation triggers zero offsets of −4 W m−2 or more, independent of the HV-system. Similar offsets were observed in field experiments under ambient environmental conditions, indicating a clear exceedance of BSRN (Baseline Surface Radiation Network) targets following precipitation events. All pyranometers required substantial time to return to their initial signal states after the simulated precipitation events. Therefore, for BSRN-class measurements, the recommendation would be to flag the radiation measurements during a natural precipitation event and 90 min after it in nighttime conditions. Further daytime experiments show pyranometer offsets of 50 W m−2 or more in comparison to the reference system. As they show a substantially faster recovery, the recommendation would be to flag the radiation measurements within a natural precipitation event and 10 min after it in daytime conditions.

Experimental Manipulation of Precipitation Affects Soil Nitrogen Availability in Semiarid Mongolian Pine (Pinus sylvestris var. mongolica) Plantation

Expected changes in precipitation over large regions of the world under global climate change will have profound effects on terrestrial ecosystems in arid and semiarid regions. To explore how changes in the amount of precipitation in the growing season would affect soil nitrogen (N) availability in a semiarid ecosystem, we established rainout shelters and irrigation systems by simulating 30% reduced (DRY) and 30% increased precipitation (WET) relative to natural precipitation (Control) to measure some key soil process properties for two growing seasons in a nutrient-poor Mongolian pine (P. sylvestris var. mongolica) plantation. Both WET and DRY treatments significantly affected monthly soil inorganic nitrogen concentrations, which showed a higher inorganic N under DRY than Control in each month and lower in WET than Control. Monthly soil microbial biomass N content was reduced by DRY and raised by WET treatments. The results indicated the asynchrony of the availability of soil moisture and soil nutrients in Mongolian pine plantations at the Horqin Sandy Lands in Northeast China. Water limited plant growth in Mongolian pine plantations when precipitation decreased, and nitrogen limitation became increasingly important when precipitation increased. Accumulation of N in microbial biomass is an important mechanism for N cycling in this ecosystem. To effectively manage Mongolian pine plantations, it is advised that evapotranspiration is minimized when precipitation decreases and that there is an increase in soil N availability by protecting litterfall when precipitation increases.

Effects of resource addition on recovery of production and plant functional composition in degraded semiarid grasslands.

Degradation of semiarid ecosystems from overgrazing threatens a variety of ecosystem services. Rainfall and nitrogen commonly co-limit production in semiarid grassland ecosystems; however, few studies have reported how interactive effects of precipitation and nitrogen addition influence the recovery of grasslands degraded by overgrazing. We conducted a 6-year experiment manipulating precipitation (natural precipitation and simulated wet year precipitation) and nitrogen (0, 25 and 50kgNha-1) addition at two sites with different histories of livestock grazing (moderately and heavily grazed) in Inner Mongolian steppe. Our results suggest that recovery of plant community composition and recovery of production can be decoupled. Perennial grasses provide long-term stability of high-quality forage production in this system. Supplemental water combined with exclosures led, in the heavily grazed site, to the strongest recovery of perennial grasses, although widespread irrigation of rangeland is not a feasible management strategy in many semiarid and arid regions. N fertilization combined with exclosures, but without water addition, increased dominance of unpalatable annual species, which in turn retarded growth of perennial species and increased inter-annual variation in primary production at both sites. Alleviation of grazing pressure alone allowed recovery of desired perennial species via successional processes in the heavily grazed site. Our experiments suggest that recovery of primary production and desirable community composition are not necessarily correlated. The use of N fertilization for the management of overgrazed grassland needs careful and systematic evaluation, as it has potential to impede, rather than aid, recovery.

Chemical characterisation of rainwater at Stromboli Island (Italy): The effect of post-depositional processes

Volcanoes emit fluids and solid particles into the atmosphere that modify the chemical composition of natural precipitation. We have investigated the geochemistry of Stromboli's rainfall during the period from November 2014 to March 2016 using a network of a new type of sampler specifically designed for operations on volcanic islands. We found that most of the chemical modifications are due to processes occurring after the storage of rainwater in the sampling bottles. These processes include dissolution of volcanogenic soluble salts encrusting volcanic ash and a variable contribution of sea spray aerosol. Our data showed noticeably less scatter than has previously been achieved with a different sampling system that was more open to the atmosphere. This demonstrates the improved efficacy of the new sampler design. The data showed that post-depositional chemical alteration of rain samples dominates over processes occurring during droplet formation ad precipitation. This has important implications for the calculation of fluxes of chemicals from rainfall in volcanic regions.

Responses of non-structural carbohydrates of poplar seedlings to increased precipitation and nitrogen addition.

To understand the effects of precipitation increase and nitrogen addition on non-structural carbohydrates (NSC) of poplar seedlings, Populus × xiaozhuanica cv. Zhangwu seedlings were grown under a full factorial experimental design of two factors, i.e., three water treatments (W1,natural precipitation; W2, natural precipitation increased by 50%; W3, increased by 100%) and four N fertilization levels (N1,0 g N·m-2·a-1; N2,5 g N·m-2·a-1; N3,10 g N·m-2·a-1; N4,15 g N·m-2·a-1). The results showed that changes in NSC contents in each organ of P. Zhangwu seedlings reflected significant interactions between precipitation increase and nitrogen addition. With the increase of precipitation, under the N1 level, soluble sugar content was unchanged in leaves and branches, while the starch content decreased in leaves, branches, stems, coarse and fine roots. With the increase of precipitation, the soluble sugar content remained unchanged or declined, while the starch content decreased or firstly increased and then decreased in different organs under the N2 and N3 levels. The soluble sugar and starch contents increased or firstly decreased and then increased in different organs under the N4 level. With the increase of N addition, the soluble sugar content remained unchanged and the starch content increased in leaves, soluble sugar content increased and starch content was unchanged in fine roots in the W1 treatment. The soluble sugar content remained unchanged or firstly increased and then decreased, and the starch content decreased or firstly increased and then decreased in different organs in the W2 treatment. The soluble sugar, starch and NSC contents increased in the W3 treatment. In different precipitation and N addition treatments, the soluble sugar contents of P. Zhangwu seedlings ranged from 39.1 to 88.3 mg·g-1, with the highest value observed in leaves and the lowest value in fine roots, and the starch content ranged from 23.3 to 46.8 mg·g-1, with the highest in coarse roots and the lowest in fine roots.

河北固城夏玉米比叶面积对水分梯度的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 河北固城夏玉米比叶面积对水分梯度的响应 DOI: 10.5846/stxb201701130104 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家行业专项（GYHY201306038） Response of specific leaf area of summer maize to water gradient in Hebei Gucheng Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:基于河北固城农试站2013-2015年夏玉米田间水分控制试验，研究了夏玉米比叶面积（SLA）随发育期的变化趋势，并分主要发育时段探讨了SLA与水分梯度的定量关系。结果表明，从七叶期开始夏玉米SLA随发育进程的推进总体呈下降趋势，七叶期至成熟期SLA变化范围平均为14.6-34.9m2/kg。尽管干旱胁迫会明显降低夏玉米地上绿叶面积和干重，但却使SLA表现出"补偿性"增大，用于弥补干旱胁迫导致光合产物不足引起的叶片扩张乏力。夏玉米出苗-拔节期、抽雄-成熟期土壤相对湿度（θ）每降低1%，SLA分别上升0.45m2/kg和0.07m2/kg，表明出苗-拔节期夏玉米对干旱的"适应"能力更强；而拔节-抽雄期SLA与θ的关系较为复杂，表现为先增大后减小的抛物线型。 Abstract:Specific leaf area (SLA), the ratio of green leaf area to its dry weight, is one of the most important parameters of leaf function evaluation, which could reflect resource utilization ability and adaptability to different environments of plants. Recently, many preliminary conclusions have been reported about the variation trend of maize SLA under drought stress, but most of them were qualitative descriptions and lacked quantitative analysis. In this study, based on water-control field experiments in Hebei Gucheng, China from 2013 to 2015, the variation trends of summer maize SLA on major developmental stages were investigated, and the quantitative relationships between SLA and soil moisture on different developmental stages were also established. As the experiment designed, 3 major developmental stages of summer maize (emergence to jointing, jointing to tasseling, tasseling to maturity), as well as[(emergence to jointing) + (jointing to tasseling)],[(emergence to jointing) + (tasseling to maturity)], and[(jointing to tasseling) + (tasseling to maturity)], were all water controlled in turn. The experiment was set with 4 water-control treatments and 1 contrast treatment, in which the soil relative moisture θ was ≤ 40% (T1), 40%-60% (T2), 60%-80% (T3), >80% (T4), and natural precipitation (T5), respectively. Results showed that the summer maize SLA presented a declining trend during the entire growing season, with an averaged variation range of 14.6-34.9m2/kg. Specifically, the SLA reached maximum value at seven-leaf stage (34.9m2/kg), declined rapidly at jointing stage (23.4m2/kg), decreased slightly at the tasseling stage (18.1-18.8m2/kg), and was the lowest at the maturity stage with an average of 14.6m2/kg. Experimental data showed that drought stress could significantly decrease the leaf area and dry weight of summer maize, but the SLA showed a "compensatory" larger value in order to compensate for the leaf expansion fatigue caused by insufficient photosynthates. The summer maize SLA had a significant linear negative correlation with soil moisture from the emergence to jointing and tasseling to maturity stages, with increase of 0.45m2/kg (emergence to jointing stage) and 0.07m2/kg (tasseling to maturity stage) when the soil relative moisture decreased by 1%, indicating that the summer maize had more adaptation to drought during emergence to jointing stage. However, the relationship between SLA and soil moisture on the jointing to tasseling stage was more complex; it first increased and then decreased with a parabola shape. 参考文献 相似文献 引证文献

降雨格局变化对白刺幼苗根系形态特征的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 降雨格局变化对白刺幼苗根系形态特征的影响 DOI: 10.5846/stxb201608161679 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（41361100，31560135，31360205，41461044）；甘肃省科技支撑项目（1604FKCA088）；中国博士后科学基金（2014M552514）；甘肃省高等学校科研项目（2015A-067，2015A-069） Response of the root morphology of Nitraria tangutorum seedlings to precipitation pattern changes Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为探讨荒漠植物白刺幼苗根系形态对降雨格局变化的响应特征，设置3个降雨量梯度（W-、W、W+）和2个降雨间隔时间梯度（T、T+）进行人工模拟试验，结果表明，1）降雨量和降雨间隔时间对白刺幼苗根系形态有不同程度的影响，且降雨量的作用效应更大。2）降雨量相同时，延长降雨间隔时间均使白刺幼苗主根长、根系平均直径、根体积和根表面积减小，但总根长和根系生物量和总生物量却增加，在高降雨量条件下（W+）延长降雨间隔时间白刺幼苗比根长和比表面积分别增加了45.09%和20.20%，但差异均不显著。3）降雨间隔时间相同时，降雨量减少30%仅使主根长平均增加12.06%，总根长、根平均直径、根体积和根表面积等根系形态指标均显著减少，比根长和比表面积变化不大；降雨量增加30%仅使比表面积显著增加，其余各形态指标差异均不显著，低降雨量条件下（W-）主根长与根冠比达到最大，其他指标均在高降雨量条件下（W+）达到最大。4）对8个根系形态参数进行主成分分析，根系生物量、总根长、总根表面积、比根长、比表面积和根体积6个根系生态参数受降雨格局影响显著。 Abstract:A global climate model has predicted changes in precipitation patterns, with extended periods of time between precipitation events; larger individual precipitation events are expected to increase. Furthermore, with global climate change, local area rainfall patterns have also changed. Over 80 years, the annual precipitation in arid areas of central Asia has generally shown an increasing trend. Such an altered precipitation regime will significantly alter the temporal supply of water to desert ecosystems, and thus have important effects on ecological processes, which could ultimately affect species composition and biological diversity. Root growth of seedlings is the most important stage in plant regeneration and the most sensitive in the plant life cycle to environmental conditions. The responses of root morphology to changes in precipitation and the ability of seedlings to adapt can directly affect the success of subsequent seedling establishment, and may affect regeneration dynamics. Nitraria tangutorum, a super-xerophytic shrub, exhibits a strong tolerance for drought, cold, and saline-alkali soil. The shrub vegetation type in which N. tangutorum is the dominant species is an important vegetation type in the deserts of northwestern China. As a result, N. tangutorum is the key species for the revegetation of these arid and semiarid areas. Most research has examined the impacts of the amount of precipitation on this species rather than the effects of both the amount and interval of precipitation. To understand how climate-driven changes in precipitation can affect desert plants, especially the response of the root morphology to precipitation patterns change, we conducted a controlled experiment with two factors: precipitation quantity (natural precipitation as a control, reduction of 30% and increase of 30%) and interval (time elapsed between two precipitation events; 5 or 10 days). The results showed that root morphological characteristics were influenced by total precipitation and precipitation interval, the former playing a more significant role than the latter. Under the same precipitation condition, the main root length, root diameter, root volume, and root surface area were decreased, total root length, root biomass, and total biomass were increased by extended precipitation intervals, and specific root length (SRL) and specific root area (SRA) were considerably increased by 45.09% and 20.20% in high precipitation, respectively, but the difference was not significant. For the same precipitation condition interval, the main root length was increased by 12.06%, total length, diameter, volume and surface area were significantly decreased, and SRL and SRA were basically unchanged in precipitation reduced by 30% conditions. The SRA increased significantly, but the other index differences were not significant. The main root length and root-shoot ratio were largest in low precipitation, but others (total root length, root surface area, average root diameter, root volume, root biomass, SRL and SRA) were larger in high precipitation conditions. Eight characteristics of root morphology were analyzed using principle component analysis. The characteristics of root biomass, total root length, total root surface area, SRL, SRA and root volume were significantly affected by precipitation pattern changes. We suggested that the root morphology of N. tangutorum seedlings was mainly affected by the amount of precipitation. However, the precipitation interval could be as important as the amount of precipitation for the root morphology of N. tangutorum seedlings. Increasing the precipitation amount and extending the precipitation interval (less frequent but higher volume precipitation events) enhanced root growth and population regeneration. 参考文献 相似文献 引证文献

Enhancing Subsurface Drainage to Control Salinity in Dryland Agriculture

Abstract. Controlling the physical processes of soil salinization involves lowering ground water levels, draining the vadose zones, and leaching excess salts from root zones. Plastic drain tubing strategically placed 1.5 to 1.8 m below the surface in semiarid lands can lower water tables and drain phreatic water, but irrigation is usually required to satisfactorily leach the offending salts. In non-irrigated drylands, the leaching process depends on natural precipitation, but the drier the climate, the greater the need for more leaching water. Possible practices which tap complementary water in conjunction with subsurface drainage include: (1) establishment of roughness barriers to trap wind-borne snow, and (2) pumping water from near-surface, ground water mounds. The mean electrical conductivity of saturated soil paste extracts sampled yearly from a semiarid site in Saskatchewan averaged 14.1 dS m-1 during the six years before the drainage was installed, 13.0 dS m-1 for two years just after drainage but before capturing blowing snow, and 9.6 dS m-1 for the six years following. The average barley grain harvested during the six years prior to drainage yielded 330 kg ha-1 and 2414 kg ha-1 after installation of the enhanced drainage system. In a follow-up sub-study, fall applications of 4.6 dS m-1 mounded ground water from a shallow well fitted with a solar-powered pump within a drainage system preceded spring seeding of alfalfa. Enhanced drainage improved mean seedling emergence from 20% to 79%. Every 28 mm of ground water applied, up to 2273 mm, increased alfalfa emergence by 1%. Keywords: Agricultural drainage, Plant emergence, Pre-seeding irrigation, Solar-powered pumping, Soil reclamation, Soil salinity, Windbreaks.

贝加尔针茅响应降水变化敏感指标及关键阈值

PDF HTML阅读 XML下载 导出引用 引用提醒 贝加尔针茅响应降水变化敏感指标及关键阈值 DOI: 10.5846/stxb201601270198 作者: 作者单位: 中国气象科学研究院,中国气象科学研究院,中国科学院植物研究所,中国科学院植物研究所,中国科学院植物研究所,中国气象科学研究院 作者简介: 通讯作者: 中图分类号: 基金项目: 公益性行业（气象）科研专项（重大专项）（GYHY201506001-3）；国家重点基础研究发展计划（973计划）（2010CB951301） Thresholds of Stipa baicalensis sensitive indicators response to precipitation change Author: Affiliation: Chinese Academy of Meteorological Sciences,Chinese Academy of Meteorological Sciences,,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:降水是影响中国北方草原群落结构和生产力的关键环境因子，弄清植物响应降水变化敏感指标，确定关键阈值，可为草原的科学管理与制定应对气候变化措施提供依据。以贝加尔针茅为材料，基于不同降水的模拟实验，采用正态总体统计容忍区间及容忍限的估算方法，对测定的叶面积、株高、叶绿素和叶N含量等14个植物生理生态指标响应降水变化的敏感性及其阈值进行了研究。结果表明，植株总叶面积、水势（或叶绿素含量）和地上生物量可分别从形态、生理和生物量积累三方面较好地指示贝加尔针茅对降水变化的敏感性，受到胁迫时的降水量（6、7和8月3个月份总降水量）阈值分别是283、276（276）mm和280 mm。研究结果可为客观辨识贝加尔针茅草原干旱的发生发展与监测预警提供参考。 Abstract:Precipitation is a crucial environmental factor that determines the community structure and productivity of temperate grasslands in northern China, located in the arid to semi-arid regions. As a result of the increase in greenhouse gases, precipitation patterns are projected to be changed, and the extreme weather events might become more common. Although many studies have focused on the effects of precipitation change on plant growth characteristics, none has quantified the relationship between precipitation and sensitive indicator (leaf area, plant height, chlorophyll content, etc.). Understanding this relationship is essential to a comprehensive appreciation and accurate prediction of the effects of climate change on plants. Stipa baicalensis, a high quality forage grass, is a dominant species in the meadow steppe in eastern Inner Mongolia, an area that has experienced severe degradation during recent decades and is therefore sensitive to climate change. Clarifying sensitive indicators and their thresholds in S. baicalensis as it responds to precipitation change could provide substantial evidence for both the scientific management of grassland and the drafting measures to address climate change. This experiment was conducted at the Institute of Botany, Chinese Academy of Sciences, from June to August (the main growing season) in 2011. S. baicalensis seeds and soils were gathered from the natural grassland in Inner Mongolia, China, in the autumn of the year before the experiment. Five precipitation levels (-30%, -15%, control, +15%, and +30%), based on the average monthly (June, July and August) natural precipitation of the seed provenances from 1978 to 2007, were used to simulate the effects of precipitation change on 14 eco-physiological indicators, including leaf area, plant height, chlorophyll and leaf N content, etc., in S. baicalensis. There were six replicates (i.e., six pots with four plants per pot) for each precipitation treatment. Each precipitation regime was converted to irrigation amounts for each month, which were then divided and applied every three days after 4:00 P.M. Each pot of plants was destructively harvested and separated into two parts (leaves and roots) at the end of the experiment. Plant height, tiller and leaf number, and leaf area were measured. Leaves and roots were dried and weighed to measure the aboveground biomass, belowground biomass, and leaf N concentration. The changes in precipitation strongly affected the biomass, leaf area, leaf number, plant height, chlorophyll, and leaf N content, etc., but did not influence leaf mass per area (LMA). The results indicated that total leaf area, leaf water potential (or chlorophyll content), and aboveground biomass can represent morphological, physiological, and biomass accumulation characteristics, respectively, and thereby help determine the sensitivity of S. baicalensis to precipitation change. By using the normal statistical tolerance limit, we found the critical points of these sensitive indicators, which were significantly affected by precipitation change, and their corresponding thresholds of precipitation. The threshold of precipitation (total precipitation of June, July, and August) was 283 mm for total leaf area, 276 mm for leaf water potential and chlorophyll content, and 280 mm for aboveground biomass. These results could contribute to objectively identifying the occurrence and development of drought events in S. baicalensis grasslands. 参考文献 相似文献 引证文献

Predictability of Seasonal Streamflow in a Changing Climate in the Sierra Nevada

The goal of this work is to assess climate change and its impact on the predictability of seasonal (i.e., April–July) streamflow in major water supply watersheds in the Sierra Nevada. The specific objective is threefold: (1) to examine the hydroclimatic impact of climate change on precipitation and temperature at the watershed scale, as well as the variability and trends in the predictand (i.e., April–July streamflow runoff) and its operational predictors (including 1 April snow water equivalent, October–March precipitation and runoff, and April–June precipitation) in a changing climate; (2) to detect potential changes in the predictability of April–July streamflow runoff in response to climate change; and (3) to assess the relationship between April–July streamflow runoff and potential new predictors and the corresponding trend. Historical records (water year 1930–2015) of annual peak snow water equivalent, monthly full natural flow, monthly temperature and precipitation data from 12 major watersheds in the west side of the Sierra Nevada in California (which are of great water supply interest) are analyzed. The Mann-Kendall Trend-Free Pre-Whitening procedure is applied in trend analysis. The results indicate that no significant changes in both the predictand and predictors are detected. However, their variabilities tend to be increasing in general. Additionally, the predictability of the April–July runoff contributed from each predictor is generally increasing. The study further shows that standardized precipitation, runoff, and snow indices have higher predictability than their raw data counterparts. These findings are meaningful from both theoretical and practical perspectives, in terms of guiding the development of new forecasting models and enhancing the current operational forecasting model, respectively, for improved seasonal streamflow forecasting.

Design and performance evaluation of a 1000-year evapotranspiration-capillary surface barrier

Surface barrier technology is used to isolate radioactive waste and to reduce or eliminate recharge water to the waste zone for 1000 years or longer. However, the design and evaluation of such a barrier is challenging because of the extremely long design life. After establishing a set of design and performance objectives, a package of design solutions was developed for 1000-year surface barriers over nuclear waste sites. The Prototype Hanford Barrier (PHB) was then constructed in 1994 in the field over an existing waste site as a demonstration. The barrier was tested to evaluate surface-barrier design and performance at the field scale under conditions of enhanced and natural precipitation and of no vegetation. The monitoring data demonstrate that the barrier satisfied nearly all objectives in the past two decades. The PHB far exceeded the Resource Conservation and Recovery Act criteria, functioned in Hanford's semiarid climate, limited drainage to well below the 0.5 mm yr−1 performance criterion, limited runoff, and minimized erosion and bio-intrusion. Given the two-decade record of successful performance and consideration of the processes and mechanisms that could affect barrier stability and hydrology in the future, the results suggest the PHB is very likely to perform for its 1000-year design life. This conclusion is based on two assumptions: (1) the exposed subgrade receives protection against erosion and (2) institutional controls prevent inadvertent human activity at the barrier. The PHB design can serve as the basis for site-specific barriers over waste sites containing underground nuclear waste, uranium mine tailings, and hazardous mine waste.

Effect of Ag and Cu additions on natural aging and precipitation hardening behavior in Al-Mg-Si alloys

The effects of Ag and/or Cu additions on the natural aging and precipitation hardening behavior of Al-Mg-Si alloys were investigated by using hardness test, differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). Both Ag and Cu additions enhanced the hardening kinetics of Al-Mg-Si alloys during natural aging (NA) and artificial aging (AA) treatments. The strong interaction of Cu, Ag and Mg atoms is responsible for the improved precipitation kinetics of these alloys, resulting in a refinement of clusters and precipitates. The stronger interaction between Ag and Mg results in lower T4 hardness and higher AA hardness, compared to Cu. This is potentially beneficial for automobile applications where rapid hardening during paint baking is required. Both Ag and Cu additions reduce the detrimental effect of NA on subsequent AA, due to the formation of Ag or Cu-containing clusters. The clear advantage of Ag addition, compared to Cu, is the improvement of precipitation hardening response of Al-Mg-Si alloys.

Filling the interspace-restoring arid land mosses: source populations, organic matter, and overwintering govern success.

Biological soil crusts contribute to ecosystem functions and occupy space that could be available to invasive annual grasses. Given disturbances in the semiarid shrub steppe communities, we embarked on a set of studies to investigate restoration potential of mosses in sagebrush steppe ecosystems. We examined establishment and growth of two moss species common to the Great Basin, USA: Bryum argenteum and Syntrichia ruralis from two environmental settings (warm dry vs. cool moist). Moss fragments were inoculated into a third warm dry setting, on bare soil in spring and fall, both with and without a jute net and with and without spring irrigation. Moss cover was monitored in spring seasons of three consecutive years. Both moss species increased in cover over the winter. When Bryum received spring irrigation that was out of sync with natural precipitation patterns, moss cover increased and then crashed, taking two seasons to recover. Syntrichia did not respond to the irrigation treatment. The addition of jute net increased moss cover under all conditions, except Syntrichia following fall inoculation, which required a second winter to increase in cover. The warm dry population of Bryum combined with jute achieved on average 60% cover compared to the cool moist population that achieved only 28% cover by the end of the study. Differences were less pronounced for Syntrichia where moss from the warm dry population with jute achieved on average 51% cover compared to the cool moist population that achieved 43% cover by the end of the study. Restoration of arid land mosses may quickly protect soils from erosion while occupying sites before invasive plants. We show that higher moss cover will be achieved quickly with the addition of organic matter and when moss fragments originate from sites with a climate that is similar to that of the restoration site.

Runoff and sediment response to tree control and seeding on a high soil erosion potential site in Utah: evidence for reversal of an abiotic threshold

AbstractExpansion of piñon (Pinus spp.) and juniper (Juniperus spp.) trees into semi‐arid sagebrush steppe may cause these systems to pass a biotic threshold into weed dominance and recurrent fire, as well as pass an abiotic threshold of accelerated soil erosion. To determine effects of chaining to reduce trees and seeding to increase vegetation cover, we measured runoff and sediment after natural precipitation on 10 m2 intercanopy runoff plots on untreated and treated areas over a 5‐year period. The former sagebrush steppe study site was in an advanced phase of tree infilling before treatment and is underlain by lacustrine sediments with clay loam soils on moderate steep slopes. These characteristics, and the potential for high‐intensity thundershowers, make this site one of high soil erosion potential. Chaining‐seeding greatly increased vegetation cover from 4.5% on untreated plots to 23.5% on chained‐seeded plots by the first year after treatment. These cover increases were associated with runoff that was reduced from 44.2 to 9.4 L and sediment from 557.9 to 53.9 g from runoff plots, averaged over the 5 years. Piecewise regression indicated significant threshold decreases in runoff and sediment when vegetation cover exceeded 12 and 11%. High annual precipitation (53 cm) supported successful revegetation on this site in association with chaining and produced sufficient intercanopy cover to reverse an abiotic threshold of soil loss that is associated with advanced tree infilling. Tree reduction and restoration of intercanopy vegetation may have significant hydrologic benefits on sites with high erosion potential where piñon–juniper has expanded into sagebrush steppe.

Physical, Chemical, and Engineering Properties of Landfill Stabilized Waste

AbstractIn order to utilize landfill stabilized waste (LSW) as growing substrate for plants during restoration projects, LSW were sampled from five landfills; the properties of unconsolidated samples and those after 3 years of settlement were determined in comparison with farm soil. Results showed that (i) unconsolidated LSW was a soil‐like material with high porosity and infiltration rate, which also had low bulk density and shear strength. After 3 years of settlement, its physical properties were similar to those of farm soil. (ii) The contents of available K, available N, available P, and organic matter of LSW were 5·0–21·6 times higher than the values of surrounding farm soil. (iii) The waste samples from 3/5 landfills were suitable for cultivation based on their heavy metal contents, but two samples contained over‐limit Hg and/or Zn. (iv) LSW had higher water content, and generally, less surface runoff was generated on LSW slope under natural precipitation compared with the farm soil slope. (v) Water extract of LSW had no significant effect on seed germination, and the effect of LSW on seedling growth depended on plant species. On the basis of the results, LSW can be used in ecological restoration as plant‐growing substrate, but measures should be taken to prevent heavy metal contamination and soil erosion. Copyright © 2016 John Wiley & Sons, Ltd.

Determination of Infiltration Rate and Soil Indices using Double Ring Infiltrometer and Implementing it by GIS and RS for Selected Areas in Zaheerabad, India

Background/Objectives: Infiltration is important process due to which rainwater percolates into the soil and moves down to join the groundwater. Methods/Statistical Analysis: There are two methods used for measuring infiltration like indirect method and direct method. In indirect method, infiltrometer, rain simulators are used. Direct method is done by the analysis of runoff hydrograph resulting from natural precipitation. For small watersheds, like milli and micro infiltrometer values and storm hydrograph analysis gives best results. Findings: The infiltration process is affected by surface runoff, ground water recharge and erosion of soil. At a certain moment the infiltration capacity of soil is indicated by maximum infiltration rate. By adopting Ф index, which gives average rate throughout the rainfall, it is well suited for calculating maximum run off from a major storm on wet soils. In this study constant infiltration rates of the soils under different soil conditions were studied, compared with the infiltration rates and were verified with IS code 15792-2008. Because of highest infiltration rate in Malchalma village surface water is available even in summer. It has been proved that maximum infiltration results in excess of ground water. Application/Improvements: It is a strenuous task to measure infiltration in the field. The infiltration rates can be estimated from the proposed model by using ArcGIS 10.2.2 different images have been developed.

Opposing effects of nitrogen and water addition on soil bacterial and fungal communities in the Inner Mongolia steppe: A field experiment

Grasslands are important ecosystems and make up 40% of the terrestrial ecosystems worldwide. The Inner Mongolia steppe is the main grassland region of China, and nitrogen (N) and water availability are two important factors that limit the productivity of these grasslands. We tested how N and water addition influence the composition of the microbial community in the soil using PLFA, and soil physical and chemical properties in two semiarid grassland sites in Inner Mongolia during two consecutive years. In both sites, a split-plot design was employed with two water treatments (natural precipitation, stimulated wet year precipitation) and three N treatments (0kgNha−1, 25kgNha−1, 50kgNha−1). Water addition greatly increased soil fungi and decreased bacteria while N had opposite effects. Water addition resulted in a significant increase in soil pH and electric conductivity. N addition did not lead to consistent changes in soil characteristics. Multivariate analysis showed that PLFA composition varied between all treatments but was mainly influenced by water addition. This study provides insight into how climatic changes such as alternations in rainfall and N deposition shape the soil microbial communities in Inner Mongolia steppes.