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781.
为分析蠡湖沉水植物恢复的光补偿深度和透明度条件,根据2012年4月和2013年4月蠡湖水下PAR(光合有效辐射)强度、ρ(SS)、透明度等监测数据以及沉水植物相关资料,探讨了沉水植物光补偿深度的空间分布特征及其影响因素. 结果表明:水下PAR强度随水深呈指数递减,α(光衰减系数)在0.97~6.04 m-1之间变化;光补偿深度空间分布格局均表现为西蠡湖大于东蠡湖、沿岸大于湖心的趋势,并且与水体透明度呈显著正相关;狐尾藻、金鱼藻、菹草、黑藻、苦草的光补偿深度及水体真光层深度分别是透明度的1.83、1.92、2.05、2.12、2.57和3.04倍. 回归分析表明,光补偿深度主要受ρ(SS)影响,其次为ρ(Chla). 以沉水植物群落光补偿深度(水体真光层深度)与水深的比值作为划分沉水植物群落恢复区域的参考依据,将蠡湖水域初步划分为“适宜区”“过渡区”和“暂不适宜区”,其中“适宜区”占蠡湖水域面积的29%. 相似文献
782.
Water plays an important role in the growth of plants. It is important to investigate the responses of different ecosystems to precipitation patterns, especially in terms of global changes involving extreme precipitation or drought. However, little is known about the rain-use efficiency (RUE) in China's forests and the correlation of the RUE with the precipitation and other environmental factors. Furthermore, it is unclear whether differences in the forest types or functional groups result in divergent RUE patterns. To investigate the RUE in China's forests, we analyzed the data from 1 266 sampling plots from 17 forest types. The results indicated that: (1) the mean RUE of China's forests is 1.21 g m-2 mm-1. The RUE and precipitation are negatively correlated in all the 17 forest types; (2) the average RUE of broadleaved forests (mainly angiosperms) is higher than that of coniferous forests (mainly gymnosperms), and the angiosperms are more adaptable to changes in the precipitation than gymnosperms; (3) the average RUE of deciduous forests is higher than that of the evergreen forests. The RUE of deciduous forests declines with increasing precipitation to a threshold value. However, the RUE of evergreen forests are unaffected by changes in the precipitation; and (4) the latitude and mean annual temperature are the major factors constraining the RUE under comprehensive environmental factors. We conclude that the mean RUE declines with increasing precipitation to a threshold value, and that the temperature is a crucial factor for RUE. © 2018 Science Press. All rights reserved. 相似文献
783.
大坝溃决将给人类社会带来巨大的灾难,因此国内外都很关注溃坝问题的研究。由于多数大坝均为土石坝,且土石坝是逐渐溃决的过程,而混凝土坝一般表现为瞬时溃决,因此土石坝溃决机理与溃决过程的研究对于溃坝过程数学模型的建立和致灾后果的评价具有重要的指导意义。自20世纪90年代以来,国内外学者围绕土石坝溃决机理开展了广泛深入的模型试验研究,取得了一系列重要的研究成果。分别从土石坝溃决原因、土石坝溃决机理研究进展、土石坝漫顶溃决模型试验、土石坝管涌溃决模型试验等方面介绍国内外的研究进展。重点针对土石坝坝型(均质坝、黏性心墙坝、面板堆石坝)和主要破坏模式(漫顶溃坝与管涌溃坝),介绍国内外开展的不同尺度的溃坝模型试验,分析研究了土石坝的溃决机理,并对今后的研究工作重点提出了相关建议。 相似文献
784.
Danyang Liu Johny Cabrera Lijuan Zhong Wenjing Wang Dingyuan Duan Xiaomao Wang Shuming Liu Yuefeng F. Xie 《Frontiers of Environmental Science & Engineering》2021,15(4):69
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787.
A series of novel mortars were developed from composite binder of uncalcined FGD gypsum, fly ash (FA) and ground granulated blast furnace slag (GGBFS) for the good utilization of flue gas desulphurization (FGD) gypsum. At a fixed ratio (20%) of GGBFS to the composite binder, keeping consistency of the mortar between 9.5 and 10.0 cm, the properties of the composite mortar were studied. The results show that higher water/binder (W/B) is required to keep the consistency when increasing the percentage of FGD gypsum. No obvious influences of the W/B and content of FGD gypsum on the bleeding of paste were observed which keeps lower than 2% under all experimental conditions tried. The highest compressive and flexural strengths (ratio is 20% FGD gypsum, 20% GGBFS and 60% FA) are 22.6 and 4.3 MPa at 28 days, respectively. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results indicate that massive ettringite crystals and C-S-H gels exist in the hydration products. At 90 days the mortars with FGD gypsum is dramatically smaller drying shrinkage (563-938 micro strain) than that without FGD gypsum (about 2250 micro strain). The release of the SO(4)(2-) from the mortar was analyzed, indicating that the dissolution of sulfate increases with FGD gypsum. The concentration of SO(4)(2-) releasing from the mortar with 10% FGD gypsum is almost equal to that obtained from the mortar without FGD gypsum. The release of SO(4)(2-) from the mortar with 20% FGD gypsum is 9200 mg·m(-2), which is lower than that from the mortar with 95% cement clinker and 5% FGD gypsum. 相似文献
788.
我国南方有1.58亿亩的红黄壤旱地,目前生产力水平很低。为了开发红黄壤旱地,挖掘其生产潜力,我们于1986~1989年在江西南昌进行了多熟制的定位试验。结果表明,红黄壤旱地发展多熟制可以大幅度提高土地生产力,培肥地力,达到生态效益、经济效益和社会效益同步增长。同时,为了全面、合理地评价耕作制度,文章采用了综合评判的方法,对本试验的6个多熟制的效益进行了系统分析,对其优劣作了较客观的评价,但这一分析方法还有待进一步完善。 相似文献
789.
In the semiarid Horqin sandy land of northern China, establishment of artificial sand-fixing shrubs on desertified sandy lands is an effective measure to control desertification and improve the regional environment. Caragana microphylla Lam. and Artemisia halodendron Turcz. ex Bess. are two of the dominant native shrub species, which are adapted well to windy and sandy environments, and thus, are widely used in revegetation programs to control desertification in Horqin region. To assess the effects of artificially planting these two shrub species on restoration of desertified sandy land, soil properties and plant colonization were measured 6 years after planting shrubs on shifting sand dunes. Soil samples were taken from two depths (0–5 cm and 5–20 cm) under the shrub canopy, in the mid-row location (alley) between shrub belts, and from nonvegetated shifting sand dune (as a control). Soil fine fractions, soil water holding capacity, soil organic C and total N have significantly increased, and pH and bulk density have declined at the 0–5-cm topsoil in both C. microphylla and A. halodendron. At the 5–20 cm subsurface soil, changes in soil properties are not significant, with exception of bulk density and organic C concentration under the canopy of A. halodendron and total N concentration under the canopy of C. microphylla. Soil amelioration processes are initiated under the shrub canopies, as higher C and N concentrations were found under the canopies compared with alleys. At the same time, the establishment of shrubs facilitates the colonization and development of herbaceous species. A. halodendron proved to have better effects in fixing the sand surface, improving soil properties, and restoring plant species in comparison to C. microphylla. 相似文献
790.