The influence of geomorphological position and vegetation cover on the erosional and hydrological processes on a Mediterranean hillslope

Soil erosion and runoff rates are assumed to be highly dependent on slope position. However, little knowledge exists about the hydrogeomorphological processes at the pedon scale that support this idea. In order to assess the hydrological and erosional behaviour of soils at different slope positions, simulated rainfall experiments (55 mm was applied during one hour) were carried out on a south-facing slope with underlying limestone in south-east Spain. In the mean terms, the erosion rates (9 g m² hr⁻¹) and the runoff coefficients (12%) were very low at the scale of measurement (0·25 m²). The slope position does not affect erosion rates when the measurements are carried out under extreme dry conditions during summer. The low runoff rates found in summer under thunderstorms of high intensity (5 year return period) and the runon into surfaces with higher infiltration rates resulted in no detectable direct surface runoff (Hortonian) at the slope scale. This implies that erosion as a consequence of surface overland flow will only take place during events of high magnitude (55 mm hr⁻¹) and low frequency (>5 years). Vegetation is the most important factor determining the soil erosion and runoff rates within the slope. © 1998 John Wiley & Sons, Ltd.     

Role of a rheophyte in bench development on a sand‐bed river in southeast Australia

Casuarina cunninghamiana Miq. is an important rheophytic tree in New South Wales, Australia because it is fast growing and can tolerate flood disturbance. Widden Brook is an active sand‐bed stream that has widened substantially since initial European settlement in the early 1800s and is characterized by high flood variability and multi‐decadal periods of alternating high and low flood frequency, called flood‐ and drought‐dominated regimes. Channel contraction by bench formation is currently occurring. Conversion of coarse‐grained point bars to benches is an important process of channel contraction. When point bars grow to a height where suspended sediment is first deposited to thicknesses of at least 50 mm by sub‐bankfull floods, rapid establishment of C. cunninghamiana occurs. As the trees grow they partially block bankside flows, thereby locally reducing flow velocity and inducing further deposition on the benches. Such synergistic relationships between bar height and inundation, fine‐grained sediment deposition, tree establishment and the development of a bankside low current velocity zone are fundamental for bench development. Size‐class frequency data demonstrate that C. cunninghamiana on the benches consists of pure even‐aged stands with most trees clustering near the average diameter. Two benches have similar size class frequency distributions but a third has significantly smaller trees. Recruitment on benches is episodic, may occur in areas open to grazing and is dependent on favourable conditions that allow tree survival. These favourable conditions include high seed availability, low levels of competition, deposition of fine sediments and adequate moisture for tree growth. Although C. cunninghamiana germinates on bars, seedlings are eliminated by prolonged inundation or flood scour and do not reach maturity. Recurring catastrophic floods or a sequence of large floods in rapid succession episodically destroy benches by substantial channel widening and initiate a new phase of bar and bench development. A conceptual model of the conversion of point bars to benches by thick mud deposition and C. cunninghamiana recruitment has been developed for sand‐bed streams draining similar sandstone catchments. Copyright © 2009 John Wiley & Sons, Ltd.     

三江平原沼泽湿地植被净初级生产力空间变化特征分析

基于EOS/MODIS卫星2000～2005年的MOD17A3数据集,分析21世纪初三江平原沼泽湿地植被净初级生产力(NPP)时间变化和空间分异特征及其与气候因子(气温和降水)的关系,并采用空间分析方法,分析道路、河流、居民点等因子对沼泽湿地生产力的影响.结果表明,三江平原沼泽湿地生产力(C)的变化范围为92.2～675 g/(m2·a),平均值为374.2 g/(m2·a).沼泽湿地生产力主要受三江平原综合水热条件控制,其与气温和降水显著复相关,复相关系数为0.49(n=6,p<0.05).低生产力沼泽湿地主要分布在三江平原西、北部地区,高生产力沼泽湿地主要分布在东、南部地区.河流在0～8 km的范围内对三江平原沼泽湿地生产力有一定促进作用,但影响不显著.居民点扩建,道路修筑等人类活动影响沼泽湿地分布,并导致沼泽湿地生产力下降,其有效影响范围分别是0～6 km区域和0～8 km区域.     

Snow effects on alpine vegetation in the Qinghai-Tibetan Plateau

Understanding the relationships between snow and vegetation is important for interpretation of the responses of alpine ecosystems to climate changes. The Qinghai-Tibetan Plateau is regarded as an ideal area due to its undisturbed features with low population and relatively high snow cover. We used 500 m Moderate Resolution Imaging Spectroradiometer (MODIS) datasets during 2001–2010 to examine the snow–vegetation relationships, specifically, (1) the influence of snow melting date on vegetation green-up date and (2) the effects of snow cover duration on vegetation greenness. The results showed that the alpine vegetation responded strongly to snow phenology (i.e., snow melting date and snow cover duration) over large areas of the Qinghai-Tibetan Plateau. Snow melting date and vegetation green-up date were significantly correlated (p < 0.1) in 39.9% of meadow areas (accounting for 26.2% of vegetated areas) and 36.7% of steppe areas (28.1% of vegetated areas). Vegetation growth was influenced by different seasonal snow cover durations (SCDs) in different regions. Generally, the December–February and March–May SCDs played a significantly role in vegetation growth, both positively and negatively, depending on different water source regions. Snow's positive impact on vegetation was larger than the negative impact.     

基于 ＲS 和 GIS 的土壤侵蚀强度快速分析: 以昌都市扎玉镇为例

以昌都市左贡县扎玉镇为例,选用中巴地球资源二号遥感数据、数字高程模型数据和土地利用类型数据,用遥感软件提取植被指数并进行密度分割,确定植被覆盖度,并对其进行分级; 用地理信息系统软件提取坡度信息,并对坡度进行分级; 在1∶ 5 万比例尺下修正已有的土地利用类型。结果统计扎玉镇 76. 26%的土壤处于轻度及以下侵蚀状态,强烈及以上的土壤侵蚀比例达 5. 48%,土壤侵蚀剧烈的地区主要分布在耕地部分,中度侵蚀的地区主要集中在林草地部分,因此土地利用合理化以及提高植被覆盖率可以有效减小土壤侵蚀强度。     

东北地区湿地的特点及形成与演替机制

东北地区湿地类型众多.通过分析解剖东北地区湿地的形成与演替机制,揭示了湿地的形成与演替过程中同时承受着自然与人为两种不同性质驱动力的影响,指出人类活动外在驱动力在较小的时空尺度下起着主导作用,如不加以正确引导而盲目开发,势必将导致湿地环境的恶化.     

间歇性河流湿地生态修复规划研究:以云南楚雄龙川江湿地为例

云南楚雄龙川江流域上游的水库建设和河道渠化等工程改变了河谷盆地、缓坡、农耕地、河道、间歇性河流湿地和季节性溪流的地形和水文条件,曾经支持健康河流生态系统的间歇性湿地大面积退化,导致河流自净能力下降、植被退化以及生物多样性降低。通过调查和评估龙川江湿地,分析间歇性河流湿地生态修复的轨迹,确定修复目标、参考模型和技术路线,并制定湿地管理计划,旨在恢复健康的河流湿地环境。在湿地修复措施方面,挖掘和重新连接关键生态属性的湿地斑块,通过间歇性湿地保留雨水和流域的径流水量,实施综合种植计划,在河岸两侧恢复具有重要生态意义的季节性湿地综合体等。     

近10 a来松嫩平原湿地研究的回顾与展望

松嫩平原是中国内陆湿地集中分布区之一。该区湿地类型有沼泽、湖泊、盐沼和稻田,此外还有水库和少量泥炭地。概述了该区湿地的研究现状,并指出目前研究热点。重点探讨了未来本区湿地的研究趋势,主要体现在湿地生态系统结构、功能和过程研究,湿地的区域生态功能评价,湿地污染及其治理,退化湿地恢复和重建,湿地多样性与湿地保护,湿地资源综合利用,湿地对全球变化响应和全球变化对湿地影响,湿地-草地-盐碱地转换机制和过程和驱动力等方面。     

Effect of vegetation with different evolution degree on soil organic matter in a semi-arid environment (Cabo de Gata-Níjar Natural Park, SE Spain)

The organic matter of the surface horizons of soils developed below scrub vegetation in a Mediterranean semi-arid area of great environmental interest (Cabo de Gata-Níjar Natural Park, SE Spain) has been studied. The study mainly concentrates on examining the influence of two vegetation types, one evolved (according to its successional stage), and the other clearly degraded as a result of prior removal of vegetation. In spite of the homogeneity in the results obtained from the analysis of the organic matter from the soils studied, a relationship may be established between vegetation biotype and characteristics and evolution of the soil organic matter. The evolved vegetation results in the presence in the soil of a somewhat more evolved and stable organic matter (demonstrated by certain chemical and microbiological aspects), resulting in a greater degree of humification, thus favouring the protection of the soil and the ecosystem as a whole. Hence, the presence of degraded vegetation might lead to soil degradation, something that is unsustainable in semi-arid areas that are particularly fragile in nature.     

翠湖湿地公园水域生物多样性保护与成效

探讨了北京市海淀区翠湖国家城市湿地公园的水域生物多样性及保护方法,论证了生物防治藻类、高等植被恢复等基于物质循环再生原理的方法对水域生物多样性恢复的效果。实践表明,人工湿地污水净水系统、以营养环节来控制水体富营养化的生物水体防治方法,对翠湖湿地的水质有明显的净化、保护和提升作用,对水域生物多样性的保护起到了积极的作用。