Effects of Poplar Plantations on the Physical and Chemical Properties of Soils: A Case Study in the North China Plain

In recent years, large areas of farmland in the North China Plain have been converted into short-rotation poplar plantations. To analyze the impacts of poplar plantations on soil, 22 soil samples were collected and assayed from the soil profiles of a corn field and a poplar plantation. The results showed that the average soil moisture content of the soil profile in the poplar field was 2.6 percent lower than that of the arable land. The maximum difference in soil moisture content was found in the upper 0-10 cm of topsoil. Soil organic matter and nitrogen, phosphorus and potassium in the cornfield were significantly higher than in the poplar field. Higher nutrient content in the corn field may result from higher fertilizer inputs and the practice of returning straw to the cropped field. The analysis also showed no significant increase in soil organic matter content in deeper soil layers of the poplar field, which means that the conditions are not favorable for the formation of soil organic matter, or that soil organic matter needs a longer time to develop. Elements such as magnesium, iron, manganese and copper in both the corn field and the poplar field had a tendency to accumulate with increasing soil depth. Magnesium, iron, manganese and copper in the 0-80 cm soil layer of the poplar field were higher than those of the cornfield, but the situation was reversed at depths greater than 80 cm. It is concluded that poplar trees consume a large amount of soil moisture and soil nutrients. Local governments should prevent the development of new plantations of fast-growing trees in farmland and help farmers to recover their farmland from forestry plantations.     

TM图像杨树林识别的MLC与LSU算法应用分析——以河北省文安县为例

以Landsat5 TM1、TM2、TM3、TM4、TM5和TM7等图像数据,经预处理后进行植被指数提取和主成分分析,生成13个波段数据集;并用最优指数法(OIF)选取目视解译波段,运用最大似然法(MLC)和线性光谱分解法(LSU)对华北平原农区河北省文安县2007年5月的杨树林地面积信息作了应用分析.结果表明:(1)...     

科尔沁沙地杨树苗木生长过程中蒸腾耗水规律研究

应用热平衡茎流测量技术,Li-6400光合作用测量系统和自动气象站,对科尔沁沙地杨树苗木生长过程中的蒸腾耗水规律及其与环境因子的关系进行研究。结果表明,杨树液流日变化曲线根据天气条件的不同呈现为多峰或宽峰状态,液流启动时间为04:30,并在21:00达到最低值。液流通量密度变化趋势与环境因子变化趋势相吻合,液流的变化是受各环境因子综合作用的结果。光合有效辐射(Q)和空气水蒸汽压亏缺(D)是杨树苗木蒸腾耗水的主要驱动因子,它们对于液流变化的影响快速而直接。杨树属于高耗水低水分利用型植物,适合在水分条件较好的立地条件下进行栽植。     

Populus nigra L. establishment and fluvial landform construction: biogeomorphic dynamics within a channelized river

Populations of the riparian pioneer species Populus nigra L. which establish on alluvial bars within river channels modulate sediment dynamics and fluvial landforms. Dense cohorts of P. nigra have colonized gravel point bars along the channelized River Garonne, France, during the last 20 years and have enhanced the vertical, lateral and longitudinal development of the bars. For this period, the geomorphic characteristics of two wooded point bars on this laterally stable river are closely linked to the spatial distribution and intensity of establishment and resistance of different cohorts of P. nigra. Furthermore, P. nigra colonization dynamics were controlled by engineer effects of this same species. This relationship is illustrated by a significant correlation between key geomorphic and biological variables measured in situ and characterized with a set of four aerial photographs taken between 2000 and 2010. The development of wooded point bars, which are discrete biogeomorphic units, over the studied period, appear to result from a specific biogeomorphic positive feedback of matter aggregation and vegetation establishment related to sediment trapping and stabilization by pioneer engineer plants. We propose a conceptual model of biogeomorphic unit construction for channelized, lateral stable rivers. We consider the resultant biogeomorphic units as functional from an ecological point of view because P. nigra enhances at the cohort scale (i) its own inherent capacity to resist hydrogeomorphic disturbances, and (ii) its resilience capacity as a result of successful colonization, especially downstream of mature poplar stands. Copyright © 2016 John Wiley & Sons, Ltd.     

Adaptive management of declining fisheries: When is it worth trying to rebuild stocks through fishery regulation?

Declining catches are typically taken to be a warning sign of overfishing. But in fact, many such declines have been driven by recruitment changes unrelated to stock size, as evidenced by the failure of stocks to recover after reduction in fishing or recovery despite the failure to reduce fishing. Given a declining pattern, supposedly precautionary decisions to reduce fishing should be treated as experimental management options with a high probability of not resulting in the desired recovery to more productive stock sizes. Simple decision tables can be used to compare such experimental options to “wait and see” options that do not involve fishing reductions. A case example with a grouper fishery in Kuwait demonstrates that experimental effort reduction may not be the best policy from a decision analysis perspective, at least when there are substantial reasons to expect recruitment changes unrelated to stock size. In this case, virtual population analysis and stock reduction analysis models indicate either unusually weak recruitment compensation (steepness h < 0.4) or progressive decline in recruitment carrying capacity, possibly caused by decreases in estuarine rearing habitat associated with declining flows of the Tigris and Euphrates Rivers.     

荒漠河岸胡杨林生态系统涡度相关通量数据处理与质量控制方法研究

涡度相关通量数据处理与质量控制是保证各观测台站数据质量、实现数据共享与综合集成的前提。然而,由于各个背景样地差异比较大,目前这一方面还没有统一、精确的方法可用。因此本文以黑河下游额济纳旗胡杨林生态系统8月份的涡度数据为例,介绍了各处理方法对通量结果的影响,结果表明:相比其它各校正方法而言,野点值剔除及密度效应校正(WPL)对CO2通量的影响最大,其值分别降低了11%和42%;WPL校正对潜热通量的影响最大,其值增加了6.5%;超声虚温校正对感热通量的影响最大,其值降低了9.3%。就数据质量控制与评价的方法研究,发现该样地能量平衡闭合率为71%,分别有65%和72%的数据通过了湍流的平稳性检验和湍流发展的充分性检验,数据质量较好。通过该研究,以期为荒漠河岸林生态系统涡度相关数据的处理提供参考。     

Grazing as a driver for Populus euphratica woodland degradation in the semi-arid Aibi Hu region, northwestern China

The endangered river plain woodlands of semi-arid Central Asia provide numerous ecosystem services. Previous studies have focused mainly on changes in water supply and salinity as the underlying mechanisms of Populus euphratica woodland’s decline. We tested whether vegetative regeneration of P. euphratica serves as an alternative pathway to propagation from seeds for reproduction in a degraded tree steppe in northwestern China and whether this method also works on grazed sites. We measured the effects of different grazing pressures on tree growth, survival, and vegetative regeneration. When subjected to high or moderate grazing pressure, P. euphratica populations failed to regenerate vegetatively, indicating recruitment limitation. A 25% increase of grazing pressure decreased the ramet density to 50% and the ramet height to 25%, as well as reducing the average age of ramets to one year. As overgrazing seriously limits the potential of natural recovery of P. euphratica a balance between livestock grazing and the regeneration of the Tugai forests is needed to sustain positive effects of increasing water tables and floods on tree vitality and regeneration. To restore population structure, and to support early vegetative regeneration long-term livestock management interventions to exclude livestock from degraded and recovered land need to be developed.     

An isotopic investigation of a near-surface groundwater system

ABSTRACT

The distribution of environmental tritium, deuterium and oxygen-18 in the unsaturated zone and the underlying sandy phreatic aquifer was studied throughout 1981 in an area of high pine forests in the Rhine valley near Heidelberg. The observed vertical distribution of isotopes in the unsaturated zone can be satisfactorily explained by the combined use of a multi-cell model for moisture transport and an evapotranspiration model. The distribution in the underlying aquifer of the tracer input at the water table obtained using this method is found by replacing the total vertical diffusion coefficient in the diffusion equation with the dispersion coefficient. In this way observed tritium profiles are satisfactorily simulated for the period 1966–1981. The stable isotope profile in the unsaturated zone however remains largely unexplained due to inadequate data on the stable isotope content of precipitation over the investigated area.     

THE WATER RESOURCES IN THE EUPHRATES RIVER AND THE TIGRIS RIVER VALLEYS AND POLITICAL RELATION BETWEEN COUNTRIES CONCERNED

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Crude oil families in the Euphrates Graben (Syria)

The most petroliferous province in Syria is the Euphrates Graben system in the eastern part of the country. The source of the produced light and heavy oils has been a matter of debate from a petroleum geochemistry perspective as there are several possible source rock and just one proven source rock (R'mah formation). Based on gross composition and oil-oil correlation of biomarker and non-biomarker characteristics, three oil families have here been identified in the study area. Crude oils of Family 1 have been found to be generated from a marine and clay-rich source rock that is older than Jurassic in age based on age-related biomarker parameters (steranes and nordiacholestane ratios). Maturity-related parameters (aliphatic biomarkers and diamondoids) signal that the source of this oil family had a high maturation level. These features fit very well to the Tanf Formation (Abba Group) which is equivalent to Lower Silurian Hot Shales found elsewhere in the Middle East and North Africa. However, the Upper Cretaceous R'mah Formation and Shiranish Formation were found to be responsible for generating the majority of the crude oils studied (Family 2). Compositional and molecular differences between Families 2A and 2B were attributed to facies and subtle maturation variations. Geochemical oil-source rock correlations indicate that Family 2A was most likely sourced from the Shiranish Formation, while Family 2B was sourced from the R'mah Formation. Secondary alteration processes influenced bulk petroleum composition, most notably the depletion of light ends and the lowering of API gravity, particularly in the northwestern part of the graben.