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991.
Longer term effects of biological control on tamarisk evapotranspiration and carbon dioxide exchange
Biological control of Tamarix spp. (tamarisk) with Diorhabda spp. (tamarisk beetle) was initiated in several states in the Western United States in 2001. We analysed 12 years of evapotranspiration (ET), net ecosystem production (NEP), and beetle abundance data from a tamarisk-invaded site in Western Nevada along the Truckee River. Diorhabda carinulata (northern tamarisk beetle) appeared at the site in 2007. Large beetle outbreaks and associated defoliation of the tamarisk occurred in 2008 and 2009, then the beetle population was highly variable from year to year. Since 2016, the beetle population declined. Growing season ET noticeably declined from direct beetle herbivory in 2008, 2009, and 2010, but the decline in ET was seasonally transient as trees regrew leaves. In 2012 and 2013, total growing season ET was low, likely due to the combined effects of drought and beetle herbivory pressure. Total seasonal ET losses and NEP were primarily driven by annual precipitation with higher values in wetter years and reduced values when precipitation fell below 100 mm. In the last 2 years of the study, 2017–2018, there were few to no beetles observed at the site, and we measured increased tamarisk leaf area index, ET, and NEP. Since 2010 at the study site, no further releases of the beetles have occurred due to wildlife concerns, and subsequent declines in beetle populations where such that the “outbreak” conditions apparently required to impair tamarisk physiological function and significantly reduce ET have not occurred. ET and photosynthesis were highly correlated (r2 ≥ .91) to the Landsat-satellite normalized difference vegetation index (NDVI). Using a relationship between growing season ET and NDVI, we estimated ET for five additional tamarisk sites along several southwestern U.S. rivers. In the 2005 to 2018 analysis period, NDVI-estimated ET declined at all sites after beetle arrival with three sites showing a recovery in pre-beetle ET rates in subsequent years. At the other three sites, ET rates have not recovered to pre-beetle levels. 相似文献
992.
Guofeng Zhu Qiaozhuo Wan Leilei Yong Qiaoqiao Li Zhiyuan Zhang Huiwen Guo Yu Zhang Zhigang Sun Zhuanxia Zhang Huiying Ma 《水文研究》2020,34(25):4985-4995
The Dissolved Organic Carbon (DOC) content of rivers is the most significant part of the carbon cycle migration in the basin under consideration, and it is the basis for a comprehensive understanding of the regional carbon cycle. In this study, we periodically collected samples from four monitoring stations in the Xiying River Basin of the Qilian Mountains in the northern Qinghai-Tibet Plateau. We calculated the fluxes of organic carbon in the rivers within the study area and have discussed the influencing factors of DOC concentration in these rivers. The results showed that: (a) The DOC concentration and transport flux of the Xiying river showed significant seasonal changes. The DOC concentration during summer and autumn was higher than that in winter and spring, and the output flux in summer and autumn accounted for approximately 88.3% of the total annual output. (b) Precipitation runoff has a higher DOC concentration than meltwater runoff. Climate factors, river-water chemical characteristics, and seasonal frozen-soil changes in the river basin have significant effects on the river DOC concentration and transport flux. (c) Larger runoff causes higher DOC concentrations in rivers. Runoff is the primary means of carbon migration in the inland river basin. Carbon migration is significant from the upstream to the middle and downstream sections of the inland river basin. 相似文献
993.
Clay aquitards are semipermeable membranes that allow groundwater flow while retarding solute migration has been researched extensively but also subjected to much debate. At present, there is no evidence of whether the physical and chemical properties of clay soil and the isotopic composition of pore water affect the semipermeable membrane effect. In this study, we collected clay samples from drilling cores (30–90 m) in the Hengshui area located in the North China Plain (NCP), then extracted pore water using a high-pressure squeezing device. Vertical hydrochemical and isotopic profile variation trends for the pore water were revealed using hydrochemical (Cl−, Na+, Ca2+, K+, Mg2+, and SO42−) and stable isotopic measurements of H, O and Cl. The results showed that the hydrochemical clay interlayer pore water of the saline aquifer is Cl/SO4-Na/Mg type and the average total dissolved solids (TDS) are 10.17 g/L. However, the hydrochemical clay aquitard pore water is of the Cl/SO4-Na/Ca type with an average TDS of 1.90 g/L. The hydrochemical clay interlayer pore water of aquifer II is of Cl-Na/Ca type with an average TDS of 1.10 g/L. Our results showed that the water quality of the aquifer II is not affected by the upper part of the saline aquifer, thus the clay aquitard acts as a significant barrier to salt movement. A polarization layer concentrated in ions was formed between the upper part of the saline aquifer and the clay aquitard. The concentration polarization layer increases the salt-inhibition effect. H, O and Cl isotopic composition results showed significant fractionation. The pore water of aquifer II lacked heavy isotopes (2H, 18O, 37Cl), but had significant heavy isotope enrichment in the concentrated polarized layer (the δ2H value was −76‰, the δ18O value was −8.4‰, and the δ37Cl value was 1.59‰). Hyperfiltration thus played a significant role in isotope fractionation. 相似文献
994.
Major ions, nutrients, trace elements and pesticides distribution were studied in a coastal wetland heavily impacted by human development in Spain. Past land use has altered the local hydrodynamics leading to the partitioning of the ecosystem into a tideland subject to marine influence, and an artificial freshwater reservoir created by stream impoundment. The tideland stretch is flooded twice a day with a heavy metal plume that emerges from the mine-polluted estuary of Huelva and propagates landward depicting the same dispersal trend of major seawater ions. Additionally, the tidal channel receives acid discharges from industrial point sources that contribute to metal enhancement. The impounded area and stream tributaries are affected by agrochemicals runoff (nitrate, phosphate, pendimethalin, simazine, diuron and therbuthylazine) from surrounding agricultural lands. The tidal regime plays a crucial role in the transport and dispersion of pollutants, except in the artificial reservoir where freshwater exhibits a seasonal mineralization pattern. 相似文献
995.
Guangjia Jiang Dianwei Liu Kaishan Song Zongming Wang Bai Zhang Yuandong Wang 《中国地理科学(英文版)》2010,20(4):337-344
This study applied a multivariate model based on three simulated sensors to estimating water quality variables in Shitoukoumen
Reservoir, Changchun City, Jilin Province, China, including concentration of total suspended matter, concentration of chlorophyll-a and non-pigment matter absorption. Two field campaigns for spectra measurements with a total of 40 samples were carried out
on June 13 and September 23, 2008. The in-situ spectra were recalculated to the spectral bands and sensitivities of the instruments
applied in this paper, i.e. Landsat TM, Alos and P6, by using the average method. And the recalculated spectra were used for
estimating water quality variables by the single model and multivariate model. The results show that the multivariate model
is superior to the single model as the multivariate model takes the combined effects of water components into consideration
and can estimate water quality variables simultaneously. According to R
2 and RMSE, Alos is superior to other sensors for water quality variables estimation although the precision of non-pigment matter absorption
inversion performed the second. 相似文献
996.
997.
珠江口东岸地区海水入侵三维溶质数值模拟研究 总被引:1,自引:0,他引:1
在建立水文地质概念模型的基础上,运用FEFLOW软件建立珠江口东岸地区海水入侵三维溶质模型,并利用研究区水位和水质的动态观测资料对模型进行识别和校正。运用模型进行情景模拟,预测现状开采条件下地下水的水质演化趋势。预测2010年,第四系含水层海水入侵面积为115.98km2,基岩裂隙含水层海水入侵面积为89.36km2,2020年,第四系含水层海水入侵面积为106.83km2,基岩裂隙含水层海水入侵面积为82.76km2。预测结果表明:在现状开采条件下,第四系和基岩裂隙含水层海水入侵程度有所缓解,海水入侵面积逐渐减少,Cl-高浓度区域逐渐变小。 相似文献
998.
毛苔草、漂筏苔草沼泽地与大豆地近地层晴夜气温和相对湿度分布及对比研究 总被引:1,自引:0,他引:1
采用野外定位观测方法,在2008年6~9月期间选取16个晴夜,在三江平原典型毛苔草、漂筏苔草(Ass.Carex pseudocuraica-Carex lasiocarpa)沼泽地及其邻近大豆地中,在距地表0.5m、1.5m、3m和5m四个高度上进行了气温和相对湿度观测;根据实测数据,分析了沼泽地和大豆地各高度夜间气温和相对湿度的分布规律及其差异。研究结果显示,晴夜,沼泽地和大豆地近地层气温的垂直分布都为逆温分布,与之相对应,二者的相对湿度垂直分布都为湿型分布;以四个高度的16夜平均气温和相对湿度为基础数据,计算得到的沼泽地近地层气温(相对湿度)的垂直递增(减)率为0.53℃/m(1.76%/m),大豆地则为0.34℃/m(1.35%/m),沼泽地近地层气温(相对湿度)的垂直递增(减)率略大(小);对比两种下垫面晴夜各观测高度的气温和相对湿度,发现只在0.5m高度上二者有明显差异,沼泽地16夜平均的气温比大豆地低0.85℃,其相对湿度比大豆地高4.39%,这是因为沼泽地植被冠层的平均高度接近0.5m,夜间植被冠层的长波辐射最强,所以其气温相对较低,相对湿度相对偏高,而大豆地的最低气温出现在地面;沼泽地和大豆... 相似文献
999.
层状盐岩蠕变变形相互作用研究 总被引:2,自引:1,他引:1
考虑泥岩夹层和盐岩的弹性性质和稳态蠕变性质,通过数值试验方法计算层状复合盐岩体在单轴和低围压三轴荷载作用下蠕变变形过程中力学相互作用和变形时效规律,分析泥岩夹层和盐岩层因蠕变率不匹配对层状盐岩蠕变的影响,初步讨论了层状复合岩体的复合材料研究方法。结果表明,层状盐岩中泥岩夹层与盐岩因弹性参数不匹配产生的初始应力集中在蠕变过程中发生松弛,因泥岩夹层与盐岩层蠕变率不匹配导致两者之间应力重分布,泥岩夹层对盐岩层的蠕变有明显抑制作用。这些分析体现了层状盐岩蠕变过程的非线性性质,为建立层状盐岩体合理本构模型奠定了基础。 相似文献
1000.
通过对化学成分相关性的研究认为,晶间卤水中的NaCl是饱和的,MgCl2是不饱和的,KCl饱和与不饱和两种卤水共存。随着晶间卤水密度的降低,NaCl含量升高,MgCl2含量降低,KCl含量先升后降。且存在高钾晶卤带和高钾固相带。晶间卤水浓度变化的原因是阶段性淡化。固相钾主要以光卤石形式存在,晶卤钾与固相钾存在单向平衡。目前,S3盐层大部分部位的光卤石处于溶解状态,溶解的KCl进入晶间卤水,MgCl2仍留存于固相中;可溶性镁在盐层中可能存在另一种形式—被粘土吸附。在S3盐层沉积和盐湖干涸过程,曾出现盐滩和湖水并存的局面。 相似文献