基于GIS的雪崩对冰湖风险性评估——以喜马拉雅山科西河流域为例

雪崩是冰湖风险性评估的因子之一,借鉴欧美发展起来的雪崩模型,在冰湖溃决洪水频发的喜马拉雅山地区开展雪崩对冰湖风险性评估研究具有重要意义。基于ICIMOD IKONOS DEM和Landsat-TM数据,利用GIS方法提取了研究区雪崩形成的海拔、平面曲率、坡度和地表覆盖类型等估算因子,根据Av=(Al+Fy)×S×Rg模型估算了研究区潜在雪崩形成区域,并应用GIS方法和α-β模型估算了雪崩的传播路径。结果表明:潜在雪崩不易形成的"低"值多分布在谷底及地表覆盖类型为密林的山坡上,而"高"、"较高"值多分布在坡度为30°~50°、地表类型以裸岩或草地为主的山坡和冰川上,这些分布符合雪崩形成的客观实际;分析判断发现研究区内"高"值区域,也就是潜在雪崩形成区共有98处,其中有10处能够进入冰湖,对这些冰湖的稳定性造成风险,这意味着在分析研究区所有冰湖的溃决风险性时,只有受到潜在雪崩影响的9个冰湖需要考虑雪崩因素,其余冰湖在冰湖溃决诱因筛选中无需考虑雪崩因子。     

Groundwater contributions in water-salt balances of the lakes in the Badain Jaran Desert,China

Groundwater-fed lakes are essential for the ecology in arid and semiarid regions.As a typical arid region,the Badain Jaran Desert (BJD) is famous in the world for the presence of a large number of groundwater-fed saline lakes among the mega dunes.Based on the up to date geological surveys and observations,this study analyzed the groundwater contributions in water-salt balances of the lakes in the desert.We found different types of springs,including the sublacustrine springs that indicate an upward flow of groundwater under the lakebed.A simplified water balance model was developed to analyze the seasonal variations of water level in the Sumu Barun Jaran Lake,which revealed an approximately steady groundwater discharge in the lake and explained why the amplitude of seasonal changes in lake level is less than 0.5 m.In addition,a salt balance model was developed to evaluate the salt accumulations in the groundwater-fed lakes.The relative salt accumulation time is 800–7,000 years in typical saline lakes,which were estimated from the concentration of Cl-,indicating a long history evolution for the lakes in the BJD.Further researches are recommended to provide comprehensive investigations on the interactions between the lakes and groundwater in the BJD.     

Low disturbance seeding suppresses weeds in no‐tillage soyabean

Germination is a key process in the dynamics of weed populations. In no‐tillage systems, crop seeding is often found to induce seed germination in the seeding strip. In this research, experiments to investigate options for reducing weed seedling establishment were conducted in no‐till soyabean fields located in two sites in south Brazil. A first experiment revealed that a reduction in emergence of some important weed species can be achieved by lowering seeding speed. Further experiments showed the ability of a modified seeder to contribute to an additional reduction in weed establishment. On the modified seeder, coulter discs were equipped with lateral blades, to diminish soil disturbance and to maintain a uniform soil cover by properly cutting the mulch layer. In a field with a high level of residues, the modified seeder, in contrast to the standard seeder, prevented the increase of soil exposure when seeding at high speed. The predominant weeds were annual species. Averaged over all seeding rates, the new equipment led to a 56% reduction in within‐row weed density, compared with the standard seeder. Regardless of seeder type, overall weed density increased with seeding speed, but with the modified seeder, this increase was only half that of the standard seeder. The modified seeder reduced weed biomass by 30% and increased soyabean grain yield by 42%. The research demonstrated that relatively simple changes, like a minor modification to a seeder and a lower seeding speed, can contribute to more diverse and sustainable alternatives to predominantly chemical‐oriented weed management strategies.     

Effects of different soil management practices on total P and Olsen-P sediment loss: A field rainfall simulation study

Field rainfall simulations were conducted in 2002 and 2005 to study the effects of different soil management practices on the total phosphorous (TP) and Olsen-P losses by soil erosion and redistribution along a 15 m long slope in Luoyang, Henan province, China. Field plots were set up in 2001 and included the following soil management practices: subsoiling with mulch (SSM), no-till with mulch (NTM), reduced tillage (RT), and a conventional tillage control (CT). The results showed that there were no significant differences in TP and Olsen-P content in the sediment load between different plots after 6 years uniform tillage practices. The enrichment of TP and Olsen-P at the lower slope showed a clear redistribution along the slope. Effects of tillage practices on the temporal pattern of the enrichment ratio (ER) of TP and Olsen-P was not uniform. ER_TP values were initially high and diminished after a short period of time and leveled to the end of the rainfall test in CT and RT plots, but remained ≥ 1. The ER of Olsen-P at the end of rainfall simulation showed a significant difference when compared to the initial stage, 0.78 to 1.60, respectively. However, the temporal loss rate of TP and Olsen-P showed a similar pattern because it was more depending on the sediment loss rate than on the concentration in the sediment. SSM resulted in 96% less TP and Olsen-P erosion loss compared to CT in 2002. Also, SSM showed the highest reduction in TP and Olsen-P loss after 4 years consistent practice. RT reduced TP and Olsen-P loss by 30%, although the runoff reduction was not significant. NTM was the best alternative with respect to TP and Olsen-P conservation, when considering its lower operational costs.     

松嫩平原不同土壤基质条件下羊草种群年龄结构的研究

通过对不同土壤基质条件下羊草Leymus chinensis种群年龄结构进行研究,结果表明:5月中旬在松嫩平原羊草种群营养生长期,分蘖株均由1龄、2龄、3龄3个龄级组成,呈增长型年龄结构,其中均以1龄和2龄级分蘖株占绝对优势,为89.4%～99.7%,3龄株仅占0.3%～10.6%;根茎均由2龄、3龄、4龄3个龄级组成,根茎长度及其质量均以2龄级最高,3龄次之,4龄最小;根茎物质的储量均随着龄级的升高而降低,羊草种群对低龄植株、根茎的大比例投资是羊草种群扩大其空间的一种十分有效的生态对策.     

免耕与常规耕作潮棕壤交换性阳离子的剖面分布特征

通过田间定位试验.研究了不同耕作方式对潮棕壤0-100 cm深度6个土层土壤交换性阳离子的影响.结果表明,与常规耕作相比,免耕使土壤表层pH显著增,.而电导率下降;同时,免耕增加了表层土壤可交换性K~+含量,降低了可交换性Na~+含量,但对可交换性Ca~(2+),Mg~(2+)和阳离子交换量没有产生显著影响.相关分析结果表明,可交换性K~+与土壤养分含量没有显著相关性,而可交换性Na~+,Ca~(2+),Mg~(2+)和阳离子交换量与有机质和全氮含量均呈负相关关系.     

搁田始期对水稻成穗率、产量形成和群体质量的影响

 1992年至1994年在江苏省扬州、宜兴、金湖、盐城郊区进行试验，结果表明：1)适当提早搁田有利于稳定穗数提高成穗率，改善群体质量，增加有效叶面积率，增加每穗总粒数，提高抽穗期的单茎茎鞘重和抽穗至成熟期的干物质重量。2)在基蘖肥用量占总施氮量60%时，总茎蘖苗数达预期穗数80%时搁田，能显著提高成穗率和群体质量。在N叶期搁田，并持续1个叶龄期，对N叶内的分蘖芽长度有抑制作用，茎蘖生长呈迟缓状态     

长期保护性耕作对黄土高原旱地土壤养分和作物产量的影响

通过长期定位试验,研究了黄土高原西部旱农区传统耕作措施(T)和5种保护性耕作措施免耕+秸秆覆盖(NTS)、免耕(NT)、传统耕作+秸秆还田(TS)、传统耕作+地膜覆盖(TP)和免耕+地膜覆盖(NTP)对土壤有机质、速效养分以及作物产量的影响。结果表明,经过6 a不同耕作措施后,各处理土壤有机C、NO3-N以及速效P含量均有所提高,其中有机C含量比试验初期提高了4.92%~18.05%,NO3-N含量提高了17.98%~31.08%,速效P含量提高143.04%~212.87%。各处理土壤速效钾含量均有所下降,其中以NTS和TS降幅较小,仅为2.75%和6.26%。6 a间小麦和豌豆平均产量均以NTS最高(分别为2 030 kg·hm-2和1 381 kg·hm-2),而NT最低(1 608 kg·hm-2和1 060 kg·hm-2)。传统耕作秸秆还田能促进土壤耕层肥力的提高,但产量效应不明显;地膜覆盖有些年份增产效应明显,但不利于土壤肥力的持续提高。因此,在黄土高原西部旱农区实施免耕秸秆覆盖既有利于作物产量的提高,也可以改善耕层土壤肥力。     

1980-2007年喜马拉雅东段洛扎地区冰川和冰湖变化研究

利用1980年地形图、1988/1990年Landsat TM、2000年Landsat ETM＋、2007年ALOS AVNIR-2遥感资料和近41年（1967-2007年）的气温、降水量资料对喜马拉雅东段洛扎地区的冰川、冰湖变化特征及变化原因进行了研究。结果表明：1）1980-2007年,本区冰川面积从491.64...