甘肃河西走廊西大河中游湿地成因与保护对策研究

干旱的河西走廊永昌县境内分布有弥足珍贵的刘克庄、焦家庄、北海子、圣容寺等4块面积达20.38 km2的湿地,均分布于西大河中游的永昌盆地。湿地的形成是地貌-构造所控制的水文地质条件及地表水、地下水(泉水)相互转化共同作用的结果。受20世纪以来气候变暖趋势及人类过度开发利用水资源的影响,西大河中游湿地面积呈逐步减少的萎缩状态,目前较大的泉眼仅有879个,近30年来湿地面积减少40%以上。加强西大河上游祁连山径流形成区和水资源涵养区的生态环境保护,减少出山地表水的引用量,控制中游地下水开采量及地下水位,是保护有限湿地资源的主要对策措施。

西大河降水时间变化特征与规律分析

文章以石羊河流域西大河水库站为代表,以该站1956~2010年55年长系列实测降水量资料为依据,采用滑动平均和距平分析方法,系统分析了西大河降水的年际变化、年代际变化与季节变化特征,分析提出了年际、年代际与季节变化速率与变化规律,对科学、合理、准确地预测石羊河流域西大河未来时段降水过程、变化趋势及其年内季节分配具有重要指导作用。

西大河二级水电站2#隧洞光面爆破分析

西大河电站实际施工中由于岩体结构复杂多变,根据围岩分类,从而可以判别围岩的自稳能力和变形特性,提出支护、衬砌的方法。地下洞室围岩根据围岩的岩石强度、岩体完整程度、结构面状态、地下水和主要结构面产状及地应力等综合因素,并结合工程实际情况,采用水电围岩工程地质分类。结合西大河二级水电站工程施工实践,针对隧洞施工中影响质量和进度的主要问题(爆破)进行了探讨,提出了一些水工隧洞的爆破方法和爆破参数以及技术措施要求。

西大河地表水资源演变分析

通过对西大河水资源变化趋势进行分析,得出西大河流域57年间降水(1982-2012年间资料)、径流(1956-2012年间资料)呈小幅增加趋势且年降水量与径流量具有同步性。建议加大上游水文监测力度,做好洪水及中长期预测预报,为增强水库调蓄功能,提高水资源利用水平提供科学依据。

西大河森林资源与生态环境的关系探析

回顾了西大河天然林权属的演变过程,阐述了西大河森林对金昌地区环境和经济发展的地位和作用,分析了权属演变后西大河的生态环境问题,提出了西大河生态环境建设的对策。

骑着马儿望祁连——山丹军马场采风手记

昔读史书,对流行于匈奴的一段歌谣印象至深又有所不解:"失我焉支山,使我妇女无颜色;失我焉支山,使我六畜不蕃息".当年匈奴与汉王朝争锋,在西部进进退退,失地乃属常事,何以独对失去焉支山这样的优伤和失落呢?

Soil and Crop Damages as a Result of Levee Breaches on Ohio and Mississippi Rivers

Whenever levees on the Ohio or Mississippi rivers are breached, there are soil damages in the flooded areas that impact agricultural management capacities and crop productivity. Floodwaters coat the entire flooded land surface with sediments which include a variety of pollutants, nutrients and contaminants. The nature of the sediments in floodwaters varies with the topographical and land use characteristics of the watershed. The soil types, hydro-geologic features, volume of flow, time of year, agricultural use of fertilizers, pesticides, and other chemicals as well as upstream point sources such as sewage treatment plants, storm sewer drainage and other urban land uses will affect the extent of the contamination and fine scale remediation needed. Preliminary characterization and measurement of soils and sediment deposit at three locations that experienced recent natural and man induced levee breaches are analyzed to identify patterns of soil and crop damage. These findings provide guidance to the restoration of craters, gullies, land scoured areas and contaminated sediment depositional sites with a goal to improve decision-making, risk analysis and remedial effectiveness. Recommendations include： （1） improve characterization and measurement of eroded soils and distribution of sediment contaminants after levee breaching; （2） assess contamination effects on soil productivity and long term agricultural production in order to understand the impacts of flooding on agricultural soils; （3） evaluate reconstruction investments needed to repair levees based on return of the land to productivity and increased landscape resilience by reducing vulnerability to future flooding and levee breaching stress.

Livelihood Strategy Change and Land Use Change——Case of Danzam Village in Upper Dadu River Watershed,Tibetan Plateau of China

Land use change in rural China since the 1980s, induced by institution reforms, urbanization, industrialization and population increase, has received more attention. However, case studies on how institution reforms affect farmers＇ livelihood strategies and drive land use change are scarce. By means of cropland plots investigations and interviews with farmers, this study examines livelihood strategy change and land use change in Danzam Village of Jinchuan County in the upper Dadu River watershed, eastern Tibetan Plateau, China. The results show that, during the collective system period, as surplus labor forces could not be transferred to the secondary and tertiary industries, they had to choose agricultural involution as their livelihood strategy, then the farmers had to produce more grains by land reclamation, increasing multiple cropping index, improving input of labor, fertilizer, pesticide and adopting advanced agricultural techniques. During the household responsibility system period, as labors being transferred to the secondary and tertiary industries, farmers chose livelihood diversification strategy. Therefore, labor input to grain planting was greatly reduced, which drove the transformation of grain to horticulture, vegetable or wasteland and decrease of multiple cropping index. This study provides a new insight into understanding linkages among institution reforms, livelihood strategy of smallholders and land use change in rural China.

Variation of Extreme Precipitation over Large River Basins in China

A new available dataset of daily observational precipitation is used to study the temporal and spatial variability of extreme precipitation events for 1956-2008 in the ten large river basins of China. The maximum daily rainfall and heavy precipitation days （≥50 mm d^-1） are analyzed for the basins of the Songhua River, Liaohe River, Haihe River, Yellow River, Northwest China Rivers, Huaihe River, Yangtze River, Pearl River, Southeast China Rivers, and Southwest China Rivers. The results indicate that the maximum daily rainfall was increasing in southern river basins, while it was decreasing in northern river basins, which leads to no discernible increasing or decreasing trend in the maximum daily rainfall of whole China,especially 2001. The national averaged heavy precipitation days shows an insignificant increase. However, a rise in heavy precipitation days of southern river basins and a decline of northern river basins are observed.

Permeability and Sedimentation Characteristics of Pleistocene Fluvio-glacial Deposits in the Dadu River Valley,Southwest China

There exist many fluvio-glacial deposits in the valley of Dadu River, Southwest China, which dates back to the Pleistocene. As some of the deposits are located within the seasonal water fluctuation zone of reservoirs, the seepage of groundwater acts as one of the key factors influencing their stability. Investigation into the sediment properties and permeability is, therefore, crucial for evaluating the sediment stability. In this study, in-situ permeability and sieving tests have been carried out to determine grain size distribution, correlations of permeability and hydraulic gradients, and relations between permeability and sedimentation properties. Test results indicate that the deposits are composed mostly of sands, gravels, cobbles and boulders, and the percentage of fines is less than 5%. The sediments have high densities, low porosities and natural moisture contents. At low hydraulic gradients, the seepage velocity obeys the Darcy＇s law, while a non- Darcy permeability is observed with hydraulic gradient exceeding a certain value （about 0.5 - 0.7）. The linear permeability coefficient ranges from 0.003 to 0.009 cm/s. Seepage failure occurs above a threshold between 1.1 and 1.5. The test data fit well with the non-linear permeability equations suggested by Forchheimer and Izbash. The non-Darcy permeability proves to be in accordance with the seepage equation suggested by Izbash with the power ＇m＇ of about 0.6 - 0.7. The characteristic grain sizes of the studied deposits are found in a narrow range between 0.024 and o.o31 mm, which is much lowerthan the effective grain size （dlo）.

The Impact of Pollution on the Bouregreg Estuary （Morocco, Atlantic Ocean）： The Molluscs as an Indicator of Metal Contamination

On the Morrocan Atlantic coast, the estuary of the Bouregreg was submitted to many anthropic effects. After the dam Sidi Mohammed ben Abdellah was built in 1974, the flow became almost null. The waters of the estuary are meant for recreational activities, fishing, but at the same time they receive water collecting domestic and industrial wastewater. The waste in old landfills was not treated and leaked into the river water. The matter gets worse with the action of tides which make it difficult to escape the pollution load （physicochemical, bacteriological, heavy metals, etc.）. The concentrations of heavy metals （Pb, Fe, Cu and Cr） recorded in the sediments are higher than those found in the two molluscs. However, we have found out that Mytilus has accumulated more heavy metals （Cr, Pb and Zn） than Solen marginatus. The Zn makes an exception： It presents a greater concentration in the molluscs （63.015 mg/kg dry weight for Mytilus and 232.736 mg/kg dry weigh for Solen） than in the sediments （57.639 mg/kg）. The amount of these metals exceeds the standard values. The impact of the marine pollution on human health derives from the consumption by humans of heavy-metal polluted molluscs. The detected concentrations of these pollutants are superior to the permissible maximum amounts.

Variation in the timing of river entry of Atlantic salmon (Salmo salar L.) in the Baltic

The timing of river entry in the Atlantic salmon is known to depend on genetic, demographic and environmental factors, but little is known about the relative magnitude of among population and among year variation and covariation in this respect in natural state Atlantic salmon rives. To investigate this, variability in the timing of river entry in three historical Finnish Atlantic salmon populations were analyzed using salmon trap data collected during 1870- 1902. The analyses reveled that 1 ） the timing of river entry differed substantially and consistently among the rivers, and that 2） variation among the rivers was much larger than variation among years. Annual variations were not explained by regional environmental conditions, whereas in one river the timing of the local flood peak was a significant predictor of the timing of river entry. Differences in the timing of salmon entry to geographically closely situated rivers suggests that a regionally fixed opening date for coastal fisheries might not be the best management strategy as it may lead to uneven exploitation of salmon populations from different rivers [ Current Zoology 55 （5） ： 342 - 349, 2009] .

Temporal and Spatial Distribution Patterns of Grain Crops in the West Liaohe River Basin

Here,we quantitatively determine temporal and spatial distribution characteristics of main grain crops in the West Liaohe River basin,Inner Mongolia,China,from 2000 to 2010 based on MODIS remote sensing data and NDVI time series information for the years 2000,2005 and 2010.Phenological calendars and a decisionmaking tree extraction model were also used to obtain spatial distribution information of spring maize,spring wheat and soybean.We found that in 2010,the sown area of the main grain crops in the West Liaohe River basin was 11 965.08km2,of which,the sown area for spring maize accounted for 92.28%and was concentrated in the lower reaches of the region.Spring wheat accounted for 3.14% and was mainly in the middle reaches.Soybean accounted for 4.58% and was predominantly in the upper reaches.From 2000 to 2005,the sown area of these grain crops in the West Liaohe River basin grew by 29.77%,mainly in the lower reaches： spring maize grew by 38.99%,spring wheat by 39.04% and soybean by 21.27%.From 2005 to 2010,growth in the sown area of these crops was slow（5.18% growth） and mainly in the lower reaches of the basin.The sown area of spring maize increased,but decreased for both spring wheat and soybean.

The 5400 a BP extreme weakening event of the Asian summer monsoon and cultural evolution

We explored a time series of the Asian summer monsoon(ASM) variability during the transition period from the middle to the late Holocene in the marginal Asian monsoon region. We used an absolutely dated ^(230)Th record with only a ~20-year dating error, and oxygen isotope data with an 8-year average temporal resolution from the top 22-mm segment of stalagmite WXB07-4 from Wanxiang Cave, western Loess Plateau. The ASM intensity weakened gradually from 6420 to 4920 a BP, which was mainly characterized by three phases:(1) a strengthening phase with a higher precipitation amount between 6420 and 6170 a BP;(2) a smooth fluctuating interval during 6170–5700 a BP; and(3) a sudden extreme weakening period from 5700 to 4920 a BP. Interestingly, the extreme weakening interval of the ASM occurred during the period between 5700 and 4920 a BP, an abrupt change dated at 5430 a BP, which is known as the 5400 a BP, or 5.4 ka BP, event. The period included 290 years of gradual weakening, and 350 years of slow strengthening. This was synchronous with some cave records from the Asian monsoon region within dating errors. Comparing with Chinese archaeological archives over the past 7000 years, the early decline of the Yangshao Culture in the Yellow River Basin and the Hongshan Culture in the West Liao River Basin occurred during the period of gradual decrease of ASM precipitation. The dramatic decline in precipitation, caused by the extreme weakening of the ASM at 5400 a BP,may have been partly related to the decline of the Miaodigou Culture at the Yangguanzhai site in the Weihe River valley; the middle Yangshao Culture in western Henan in the Yellow River Basin; the early Dawenkou Culture on the lower reaches of the Yellow River; and the middle Hongshan Culture in the west of the Liaohe River valley. During the later period of the 5400 a BP event(5430–4920 a BP), a small amplitude increase and a subsequent sharp decrease of ASM precipitation may have also been linked to the contemporaneous prosperity and disappearance of the late Yangshao and Hongshan cultures; the disappearance of the late Yangshao Culture represented by the Yangguanzhai site in the Guanzhong basin on the Weihe River; the fourth phase of the late Yangshao Culture on the upstream Dadiwan site; the beginning of the middle Dawenkou Culture, the formation of its late stage,and the rise of the Longshan culture; and the rise of the Qujialing and Liangzhu cultures on the lower Yangtze River. Compared with the stalagmite precipitation records on the Qinghai-Tibetan Plateau, the rise and expansion of the Majiayao Culture in the upper Yellow River valley at 5300 a BP may have also been connected to the more dramatic increase of the summer monsoon precipitation at higher, rather than lower, altitudes during the late 5400 a BP event.