Changes in biota along a dry-land river in northwestern Zimbabwe: declines and improvements in river health related to land use

Macroinvertebrates were sampled from 15 sites along a dry-land river in northwestern Zimbabwe to assess biotic responses to land use changes along the course of the river. The headwater sites were protected by a riparian corridor of native forest, but this was replaced by intensive subsistence agriculture in the mid-reaches while the lower reaches were located within a protected wildlife area with diverse and wide riparian forests. Canonical correspondence analysis indicated that intensive agricultural activities within the mid-reaches caused severe degradation of the stream physical habitat through increased fine sediment deposition. This coincided with a significant decline in macroinvertebrate richness, diversity, and abundance at the agriculturally impacted mid-reach sites. The presence of wide riparian zones at the lower river sites resulted in significant improvements in stream physical habitat quality, and this was paralleled by significant recovery or reappearance of taxa that had disappeared from the mid-reaches. We suggest that restoration of the riparian vegetation within the mid-reaches of the Nyaodza River would lead to improved physical habitat and biotic health of this dry-land river.     

Effects of stream restorations on riparian mesohabitats,vegetation and carabid beetles

We investigated the effects of hydromorphological restoration measures (mainly the removal of bank fixations) on riparian mesohabitats, vegetation and carabid beetles by comparing 24 restored to nearby non-restored floodplain sections in Germany. Mesohabitats were recorded along ten equally-spaced transects, plant communities and riparian plant and carabid beetle species along three transects per section. Based on 18 indices including habitat and species diversity, taxonomic diversity and functional indices we compared the frequency and magnitude of changes following restoration, both for the overall dataset and for each site individually. Riparian habitat diversity doubled in restored sections compared to non-restored sections. The numbers of vegetation units and plant and carabid beetle species richness also doubled in restored sections, whereas changes in Shannon diversity were most pronounced for mesohabitats and riparian plants. Taxonomic diversity of carabid beetles decreased in restored sections reflecting post restoration dominance of riparian Bembidion species. Stress-tolerant pioneers of plant and especially carabid species benefit strongly from the re-establishment of open sand and gravel bars, while hygrophilous species, which also include non-riparian species, did not respond to restoration. We conclude that restoring river hydromorphology has almost generally positive effects on riparian habitats and riparian biodiversity. Riparian biota are thus well-suited indicators for the effects of hydromorphological restoration.     

Odonates as indicators of the ecological integrity of the river corridor: Development and application of the Odonate River Index (ORI) in northern Italy

The assessment of the ecological conditions of rivers is crucial for their appropriate management and restoration. Bioindicators commonly used to evaluate the river status (i.e. diatoms, aquatic macrophytes, benthic macroinvertebrates and fish) detect alterations of water quality, but are not particularly sensitive to hydromorphological degradation, which is another relevant pressure in river systems. Furthermore, those bioindicators are usually applied only to flowing channels. We developed a new multimetric index, the Odonate River Index (ORI), to assess the conditions of the whole corridor in alluvial rivers. The ORI is a development of an evaluation system proposed in Austria, and based on the Odonate Habitat Index (OHI). Odonates were chosen as bioindicators for the ecological integrity of the river corridor, since this taxon provides information on the conditions of their aquatic breeding sites, as well as on the surrounding terrestrial areas, due to its amphibiotic life cycle. We used a case study of 18 reaches from six Italian Alpine rivers, characterized by different morphological conditions and level of human impact. Within each study reach, we selected four sites, both lotic and lentic sites. Dragonfly surveys consisted in field observation of adults, and collection of larvae and exuviae. To define the best sampling strategy, we compared the results of the ORI metrics obtained varying the input data by combining different sampling methods: the best compromise between effort and exhaustiveness was obtained coupling the observation of adults with the collection of exuviae. We found the ORI to be a robust and reliable tool to assess the status of the river corridor in a wide range of environmental conditions and river morphology, being particularly suitable to detect hydromorphological degradation and alterations of the structure of aquatic and riparian vegetation. We identified two limiting factors for the applicability of this index: low water temperatures of the main channel (i.e. mean annual value below 10 °C) and river reaches with no or scarce aquatic and riparian vegetation. In addition to the assessment of river conditions, the ORI could also be applied for monitoring the effects of river restoration actions.     

Land-use coverage as an indicator of riparian quality

Sustaining or restoring riparian quality is essential to achieve and maintain good stream health, as well as to guarantee the ecological functions that natural riparian areas provide. Therefore, quantifying riparian quality is a fundamental step to identify river reaches for conservation and/or restoration purposes. Most of the existing methods assessing riparian quality concentrate on field surveys of a few hundreds of metres, which become very laborious when trying to evaluate whole catchments or long river corridors. Riparian quality assessment obtains higher scores when riparian vegetation consists of forested areas, while land-uses lacking woody vegetation typically represent physical and functional discontinuities along river corridors that undermine riparian quality. Thus, this study aimed to analyse the ability of riparian land-cover data for modelling riparian quality over large areas. Multiple linear regression and Random Forest techniques were performed using land-use datasets at three different spatial scales: 1:5000 (Cantabrian Riparian Cover map), 1:25,000 (Spanish Land Cover Information System) and 1:100,000 (Corine Land Cover). Riparian quality field data was obtained using the Riparian Quality Index. Hydromorphological pressures affecting riparian vegetation were also included in the analysis to determine their relative weight in controlling riparian quality. Linear regression showed better predictive ability than Random Forest, although this may be due to our relatively small dataset (approx. 150 cases). Forest coverage highly determined riparian quality, while hydromorphological pressures and land-use coverage related to human activities played a smaller role in the models. While acceptable results were obtained when using high-resolution datasets, the use of Corine Land Cover led to a poor predictive ability.     

Spatial patterns in fish distributions and structure of the ichthyocenosis in the Água Nanci stream,upper Paraná River basin,Brazil

Samples of fishes were collected quarterly at three reaches in the Água Nanci stream, upper Paraná River basin, Brazil: near the spring, in the middle course, and near the mouth. Richness and evenness of the fish fauna increased between reaches towards the river mouth showing a correlation with stream width, pH and the presence of riparian vegetation. These variations in species richness and evenness, verified through Principal Component Analysis and Pearson correlation, suggest relations to habitat complexity, especially characterized by both the degree of preservation of dense riparian vegetation and high width at the lower reaches of the stream, providing a wide variety of hiding places for fish. Abundant species showed correlations with some environmental factors, suggesting habitat preferences.     

A tool to assess the ecological condition of tropical high Andean streams in Ecuador and Peru: The IMEERA index

The main objective of this study was to develop a highland Andean streams ecological assessment tool for managers to determine the biological quality in this broad area of South America. Sampling was conducted during the dry season at 123 sites in eight watersheds of high Andean streams from south of Peru to North of Ecuador. The sites were at elevations above 2000 m a.s.l., and ranged in anthropogenic disturbance from none or little (reference) to highly disturbed. Using the physicochemical, hydromorphological and aquatic macroinvertebrate assemblage attributes of the reference sites, two different elevation bioregions were identified (from 2000 to 3500 m a.s.l. and those sites at altitudes higher than 3500 m a.s.l.). Differences between these two bioregions were related to the change in altitude of the most relevant environmental factors, i.e., temperature, oxygen content of the water and the extent of forested vegetation in the basin and in the riparian zone. These features were paramount to having different macroinvertebrate assemblages as demonstrated by an MDS analysis of our data. Two versions of the multi-metric index IMEERA were developed (the acronym comes from the Spanish name ‘Índice Multimétrico del Estado Ecológico para Ríos Altoandinos’) that corresponded to the two bioregions. In the lower altitude bioregion (Bosque river type, IMEERA-B index), the pressure gradient was driven by the organic pollution and the hydromorphological degradation. While in the higher elevation bioregion (Páramo and Puna river types; IMEERA-P river type), the gradient was driven by the organic pollution and the habitat heterogeneity. The IMEERA B index includes six macroinvertebrate metrics using its richness, habit characteristics and tolerance/intolerance to disturbances (EPT taxa, % clingers, % climbers, intolerant taxa, ABI and % tolerant taxa). The IMEERA P index was calculated using four metrics corresponding to macroinvertebrate richness and its tolerance/intolerance to disturbances (total taxa, intolerant taxa, ABI and % tolerant taxa). The index was validated with a set of independent data from the headwaters of Guayllabamba River in Ecuador.     

Importance of low-flow and high-flow characteristics to restoration of riparian vegetation along rivers in arid south-western United States

1. Riparian vegetation in dry regions is influenced by low‐flow and high‐flow components of the surface and groundwater flow regimes. The duration of no‐flow periods in the surface stream controls vegetation structure along the low‐flow channel, while depth, magnitude and rate of groundwater decline influence phreatophytic vegetation in the floodplain. Flood flows influence vegetation along channels and floodplains by increasing water availability and by creating ecosystem disturbance. 2. On reference rivers in Arizona's Sonoran Desert region, the combination of perennial stream flows, shallow groundwater in the riparian (stream) aquifer, and frequent flooding results in high plant species diversity and landscape heterogeneity and an abundance of pioneer wetland plant species in the floodplain. Vegetation changes on hydrologically altered river reaches are varied, given the great extent of flow regime changes ranging from stream and aquifer dewatering on reaches affected by stream diversion and groundwater pumping to altered timing, frequency, and magnitude of flood flows on reaches downstream of flow‐regulating dams. 3. As stream flows become more intermittent, diversity and cover of herbaceous species along the low‐flow channel decline. As groundwater deepens, diversity of riparian plant species (particularly perennial species) and landscape patches are reduced and species composition in the floodplain shifts from wetland pioneer trees (Populus, Salix) to more drought‐tolerant shrub species including Tamarix (introduced) and Bebbia. 4. On impounded rivers, changes in flood timing can simplify landscape patch structure and shift species composition from mixed forests composed of Populus and Salix, which have narrow regeneration windows, to the more reproductively opportunistic Tamarix. If flows are not diverted, suppression of flooding can result in increased density of riparian vegetation, leading in some cases to very high abundance of Tamarix patches. Coarsening of sediments in river reaches below dams, associated with sediment retention in reservoirs, contributes to reduced cover and richness of herbaceous vegetation by reducing water and nutrient‐holding capacity of soils. 5. These changes have implications for river restoration. They suggest that patch diversity, riparian plant species diversity, and abundance of flood‐dependent wetland tree species such as Populus and Salix can be increased by restoring fluvial dynamics on flood‐suppressed rivers and by increasing water availability in rivers subject to water diversion or withdrawal. On impounded rivers, restoration of plant species diversity also may hinge on restoration of sediment transport. 6. Determining the causes of vegetation change is critical for determining riparian restoration strategies. Of the many riparian restoration efforts underway in south‐western United States, some focus on re‐establishing hydrogeomorphic processes by restoring appropriate flows of surface water, groundwater and sediment, while many others focus on manipulating vegetation structure by planting trees (e.g. Populus) or removing trees (e.g. Tamarix). The latter approaches, in and of themselves, may not yield desired restoration outcomes if the tree species are indicators, rather than prime causes, of underlying changes in the physical environment.     

Recovery of benthic macroinvertebrate and adult dragonfly assemblages in response to large scale removal of riparian invasive alien trees

Invasive alien organisms can impact adversely on indigenous biodiversity, while riparian invasive alien trees (IATs), through shading of the habitat, can be a key threat to stream invertebrates. We ask here whether stream fauna can recover when the key threat of riparian IATs is removed. Specifically, we address whether IAT invasion, and subsequent IAT removal, changes benthic macroinvertebrate and adult dragonfly assemblages, for the worse or for the better respectively. Natural riparian zones were controls. There were statistically significant differences between stream reaches with natural, IAT-infested and IAT-cleared riparian vegetation types, based on several metrics: immature macroinvertebrate taxon richness, average score per macroinvertebrate taxon (ASPT), a macroinvertebrate subset (Ephemeroptera, Plecoptera, Trichoptera and Odonata larvae; EPTO), and adult dragonfly species richness. Reaches with natural vegetation, or cleared of IATs, supported greater relative diversity of macroinvertebrates than reaches shaded by dense IATs. Greatest macroinvertebrate ASPT and EPTO were in reaches bordered by natural vegetation and those bordered by vegetation cleared of IATs, and the lowest where the riparian corridor was IATs. Highest number of adult dragonflies species was along streams cleared of dense IATs. Overall, results showed that removal of a highly invasive, dense canopy of alien trees enables recovery of aquatic biodiversity. As benthic macroinvertebrate scores and adult dragonfly species richness are correlated and additive, their combined use is recommended for river condition assessments.     

伊洛河流域草本植物群落物种多样性

生物多样性沿环境梯度的变化是生物多样性研究的重要内容,环境梯度包含了多种环境因子(海拔高度、水热条件、人类扰动等)的综合。以伊洛河流域草本植物群落为对象,沿河从入黄河口到河源地选取典型样地调查研究伊洛河流域草本植物群落物种多样性及其分布格局。结果表明:物种丰富度和Shannon-Wiener多样性指数沿河均稍呈"S"型曲线变化,不同群落类型中分布格局差别不大,各群落类型中的物种丰富度和多样性均呈现出中游丘陵山地交界区最高,上游河源区次之,下游平原地区最低的趋势;β多样性指数的变化趋势与α多样性较一致,总体上呈现出中游丘陵山地区物种更替速率较快,平原区更替较慢;在流域内上游河源地属于自然植被区,人为干扰较轻,具有较高的物种多样性,物种替代主要受物种的竞争扩散能力和生境条件的制约;在下游平原农业区,人类活动强烈,区域内以人工生态系统为主,物种组成简单,物种替代具有跳跃性的特征,主要受人类活动的制约;在中游从自然生态系统向农业生态系统的过渡区域,人类活动的扰动有一定的强度,导致该区域内自然分布种和伴人种混合生长,具有较高的物种多样性和较快的物种替代速率。总体上伊洛河流域草本植物群落物种多样性分布格局强烈的受到人类活动的影响,物种替代速率较高。     

塔里木河中游洪水漫溢区荒漠河岸林实生苗更新

以塔里木河中游荒漠河岸林为研究对象,2008年6月至2009年8月,对洪水漫溢区河漫滩裸地、林下及林隙三种生境植物一年生实生苗进行了调查。结果表明：实生苗更新主要依赖洪水漫溢,在非漫溢区没有发现实生苗存在;洪水降低了漫溢区的土壤盐度,更重要的是其提供了宝贵的水分条件,在时间和水量上都有效地满足了胡杨等植物种子萌发和幼株生长的水分需求;河漫滩是河岸林种子实生苗产生的基地,洪水漫溢后的河漫滩种子实生苗密度显著大于其余两生境内实生苗密度,同时该生境内物种多样性也显著高于林下和林隙生境;光照决定着漫溢区实生苗能否成林,光照不同的空间样点上,实生苗发生数量和个体生长均存在显著差异,光照强的河漫滩,实生苗发生数量较多且幼苗能保持较高的生长活力和较多的生物量积累。     

Summer habitat relationships of barbels in south‐west Spain

An analysis was made of the associations with local habitat features of barbels ( Barbus sp.) of a Mediterranean river basin. The analysis was based on the presence data from sampling the upper, middle, and lower reaches of 31 rivers in the middle Guadiana River basin (south‐west Spain). Numerous local habitat variables were determined, including the river's size and substratum, physicochemical variables of water, and the aquatic and riparian vegetation. For each species, a univariate analysis was performed using preference indices, and logistic regression was used to construct a parsimonious multivariate model and Gaussian response models with the most influential variables, quantifying the species' limits of tolerance. Distinct habitat associations for every species were obtained, mainly relating Barbus comiza to the larger habitats and higher water levels, Barbus microcephalus to the maintenance of lotic conditions and Barbus sclateri to more fluctuating rivers. Barbus steindachneri showed a different habitat relationship from that of the genetically almost identical B. comiza . Cover played a significant role in all but B. comiza .     

伊洛河流域外来草本植物分布格局

外来生物入侵及其防治已经成为生态学关注的重点和热点问题.目前的研究主要集中在外来入侵种上,然而入侵种仅占外来种中很少一部分,因此,研究外来种现有分布格局对研究生物入侵及其防治有重要意义.以伊洛河流域草本植物群落中的外来种为对象,沿河从河源地到入黄河口选取典型样地,在调查流域内草本植物群落中物种组成的基础上选取外来种,并对外来种种类组成及其分布格局进行研究.结果表明:流域内有外来草本植物27种,分属于15科,种类较多的科为菊科、苋科和豆科;引入方式以有意引种为主.流域横向不同生境间,河滩地在水流的养分富集、季节性洪水物理干扰及人为活动扰动作用下,呈现出受外来种分布较多,而受人类活动扰动最强且营养丰富的农田分布较小的分布格局;纵向环境梯度下,上游河源山地属于自然植被区,人为干扰较轻,且受外来种影响较小;中游丘陵区从自然生态系统向农业生态系统的过渡区域,人类活动的扰动有所加强;下游平原农业区,人类活动强烈,区域内以人工生态系统为主,群落物种组成简单但受外来种影响最大,受自然环境和人类活动的双重影响.不同物种在不同生境间差异明显,其中,小蓬草、钻叶紫菀和反枝苋广泛分布于3种生境中.总体上,伊洛河外来草本植物分布格局在自然因素的基础上强烈受人为因素的影响,呈现出从上游到下游逐渐增多的趋势.     

黄河干流河岸带植物群落特征及其影响因子分析

作为河岸带生态系统的关键组成部分,河岸带植被为许多动植物提供了栖息地以及迁徙或扩散的廊道,并对非点源污染物有着缓冲和过滤作用。黄河是我国湿地的重要组成部分,也是生物多样性分布的关键地带。但是,目前黄河水资源的过度利用如农业灌溉和干流拦河水利工程的兴建在很大程度上改变了原有的水文情势,对河岸带植被发育带来了不利影响。另外,黄河两岸的加固硬化进一步破坏了河岸带植物的生存环境。然而,过去对于黄河河岸带植被仅有对个别河段的调查。为了解目前黄河河岸带植被现状,于2008年4-6月及2008年9-10月对黄河干流河岸带植被进行了两次系统调查,以期为黄河河岸带植被多样性的保护、河岸带的开发管理提供理论支持。对群落的物种组成、多样性进行了分析,并采用双向指示种分析法对黄河干流河岸带植被进行了数量分类。共采集到木本和草本植物169种,隶属于37科124属。区系分析表明黄河干流河岸带植被区系地理成分多样。空间分布方面,中游河段草本植物无论在种类数、密度、生物量上都较上游和下游河段丰富。TWINSPAN将植被划分为17个群落,论述了各群落的特征。环境分析表明,影响黄河干流河岸带植被空间分布的主要生态因子是海拔、年均气温、年均降雨量、年均径流量和平均最大流速。       

河流岸带湿地沉积物重金属分布对植被物种多样性和底栖动物群落特征的影响

河流岸带湿地栖息地完整性对河流水环境、水生态和水文的安全与健康具有重要意义,为探究河流岸带湿地表层沉积物重金属分布特征及其对植被和底栖动物的影响,对滦河干流上中下游河段表层沉积物、植物群落和底栖动物调查分析,采用生物毒性效应系数法和综合潜在生态风险指数法评价沉积物重金属污染特征,采用植被物种多样性指数和底栖动物完整性指数评价滦河植物和底栖动物群落特征,探究岸带湿地沉积物重金属空间分布与植被及底栖动物群落特征之间关系。结果表明,滦河表层沉积物总体呈清洁水平,但不同河段重金属空间分布差异较大,下游重金属生态危害系数和潜在生态风险指数高于上中游。湿地物种调查共识别维管束植物219种,大型无脊椎底栖动物105种,综合评价结果表明下游植物群落物种多样性和底栖动物群落完整性低于上中游。滦河下游岸带湿地沉积物重金属对生物群落具有生物毒性和潜在的生态风险,降低了植被物种多样性和底栖动物群落完整性。大型底栖动物完整性指数能够综合反映底栖动物群落结构特征变化,对河岸带湿地生态健康评价和监测具有重要意义。     

河水漫溢对塔里木河下游荒漠河岸林地表植被与土壤种子库的影响

采用种子萌发法,研究了河水漫溢对塔里木河下游荒漠河岸林地表植被与土壤种子库的影响.结果表明：塔里木河下游漫溢区地表植被分属8科13属14种,非漫溢区为10科21属26种植物;与非漫溢区相比,漫溢区地表植被中出现了一些浅根系和喜湿的草本植物;漫溢区单位面积物种数、植被盖度、植株密度、物种多样性指数和丰富度指数均比非漫溢区有明显增加.漫溢区土壤种子库中有物种19种,比非漫溢区增加了5种;漫溢区土壤种子库总密度比非漫溢区增加了3.94倍;与非漫溢区相比,漫溢区1年生草本植物种子的比例增加了23.07%,而灌木植物种子比例减少了20.99%;多年生草本的变化则不明显;河水漫溢提高了土壤种子库的生物多样性.漫溢区和非漫溢区土壤种子库与地表植被的共有物种分别为18和9种,土壤种子库与地表植被的相似性系数分别为0.842和 0.667.     

Effects of pasture development on the ecological functions of riparian forests in Hokkaido in northern Japan

In the summer, the forest canopy lowers the water temperature, which is very important for anadromous fish, and its population density is significantly lower in grassland streams. Leaf litter and terrestrial invertebrates are the critical food resources for stream organisms. In a basin where the riparian forest is preserved, but other areas have been cut, the amount of leaf litter is almost equivalent to that in an intact natural basin. The annual input of terrestrial invertebrates falling into the forested reaches was 1.7 times greater than that in the grassland reaches, and fish biomass was significantly less in the grassland reaches. In-stream large woody debris creates storage sites for organic and inorganic matter and enhances habitat diversity for aquatic biota. However, the volume and number of large wood pieces decreased significantly with pasture development, because it clears the riparian forests and covers the riverbanks with grass. Fine sediment is a prominent by-product of agricultural development and adversely impacts periphyton productivity, the density and diversity of aquatic invertebrates, fish feeding, fish spawning and egg survival. We also examine the adequate width of a riparian buffer if it is to be able to satisfy its ecological functions.     

Spatial pattern of riparian vegetation in desert of the lower Tarim River basin

AimsRevealing the spatial pattern of riparian vegetation in hyper-arid regions can improve our understanding on the water relations of riparian vegetation in the desert watershed ecosystem, and also can provide valuable scientific guidance for desertification control and water resources management of watershed of the arid region in northwestern China. This research objective is to show the spatial distribution and structures of typical riparian vegetation in hyper-arid desert watershed from regional and overall perspective.Methods Based on Landsat-8 OLI remote sensing images and a large number of field vegetation surveys, the supervised classification method was used to distinguish three main vegetation categories in the lower Tarim River basin: Tamarix thicket, Populus euphratica woodland, and Phragmites australis grassland. The leaf area index (LAI) of Tamarix thickets and Populus euphratica woodlands were inverted by using the remote-sensed LAI inversion empirical model that we developed.Important findings Supervised classification supporting abundant information of ground objects by remote sensing was an effective method to determine desert riparian vegetation categories in arid desert regions. The area was 336.4 km² for the Populus euphratica woodlands and 405.3 km² for the Tamarix thickets, respectively. The Tamarix thickets had a wider distribution range while the Populus euphratica woodlands grew near the river channel. The overall LAI of the riparian vegetation was low. The average LAI value was 0.253 for the Tamarix thickets and 0.252 for the Populus euphratica woodlands. The areas of vegetation with the LAI value of less than 0.5 accounted for 92.4% and 90.1% of the total area of the Tamarix thickets and the Populus euphratica woodlands, respectively. The statistic results showed that large spatial variability of the riparian vegetation LAI existed. The spatial variability of the Populus euphratica woodlands was larger than that of the Tamarix thickets. The LAI values of the riparian vegetation had a significant negative exponential relationship with the distances away from the river channel. The LAI values declined rapidly within the distance of 1 km from the river channel and they were generally lower than 0.1 when the distances beyond 1 km, which indicated that the riparian vegetation was mainly distributed within 1 km from both side of the river. This research indicated three basic characteristics of the spatial pattern in riparian vegetation from hyper-arid desert regions, including overall sparse spatial distribution, high spatial variability and negative exponential relationship between LAI and distance away from the river channel.     

塔里木河下游河岸带植被的空间结构特征

揭示我国内陆河流域下游河岸带植被的空间结构特征, 对于了解我国西北干旱区荒漠河岸带植被的空间分布规律、指导荒漠化治理和内陆河水资源管理具有重要意义。该研究基于野外大范围植被调查数据支持下的遥感监督分类方法, 利用Landsat-8 OLI遥感数字图像, 辨识了塔里木河下游柽柳(Tamarix spp.)灌丛、胡杨(Populus euphratica)疏林和芦苇(Phragmites australis)草地3类主要的河岸带植被, 并利用建立的叶面积指数(LAI)遥感反演经验模型反演了研究区柽柳灌丛和胡杨疏林的叶面积指数, 旨在从区域尺度和总体趋势上分析荒漠河岸带植被的空间结构和分布特征。结果表明: 在有详细地物资料的基础上, 遥感监督分类可以作为一种干旱区荒漠河岸带植被分类的有效方法; 遥感分类结果显示塔里木河下游胡杨疏林分布面积约336.4 km², 柽柳灌丛约为405.3 km², 胡杨疏林总体更靠近河道, 柽柳灌丛分布范围更广; 河岸带植被LAI整体很低, 柽柳灌丛和胡杨疏林平均LAI值分别为0.253和0.252, LAI小于0.5的植被对应面积分别占柽柳灌丛和胡杨疏林总面积的92.4%和90.1%, 表明了塔里木河下游荒漠河岸植被空间上稀疏分布的特征; 统计结果显示, 河岸带植被结构存在巨大的空间变异性, 其中胡杨疏林比柽柳灌丛的空间变异性更大; 河岸带植被LAI随距河道距离呈现显著负指数分布规律, 在离河道1 km范围内LAI随离河道距离快速下降, 而1 km外区域叶面积指数普遍低于0.1, 表明植被主要分布在河道两侧1 km范围内。整体稀疏的空间分布、显著的空间变异性, 以及由LAI体现的植被盖度随距河道距离的负指数下降规律是荒漠河岸带植被空间结构的3个基本特征。     

Integrating and extending ecological river assessment: Concept and test with two restoration projects

While the number of river restoration projects is increasing, studies on their success or failure relative to expectations are still rare. Only a few decision support methodologies and integrative methods for evaluating the ecological status of rivers are used in river restoration projects, thereby limiting informed management decisions in restoration planning as well as success control. Moreover, studies quantifying river restoration effects are often based on the assessment of a single organism group, and the effects on terrestrial communities are often neglected. In addition, potential effects of water quality or hydrological degradation are often not considered for the evaluation of restoration projects.We used multi-attribute value theory to re-formulate an existing river assessment protocol and extend it to a more comprehensive, integrated ecological assessment program. We considered habitat conditions, water quality regarding nutrients, micropollutants and heavy metals, and five instream and terrestrial organism groups (fish, benthic invertebrates, aquatic vegetation, ground beetles and riparian vegetation). The physical, chemical and biological states of the rivers were assessed separately and combined to value the overall ecological state.The assessment procedure was then applied to restored and unrestored sites at two Swiss rivers to test its feasibility in quantifying the effect of river restoration. Uncertainty in observations was taken into account and propagated through the assessment framework to evaluate the significance of differences between the ecological states of restored and unrestored reaches. In the restored sites, we measured a higher width variability of the river, as well as a higher width of the riparian zone and a higher richness of organism groups. According to the ecological assessment, the river morphology and the biological states were significantly better at the restored sites, with the largest differences detected for ground beetles and fish communities, followed by benthic invertebrates and riparian vegetation. The state of the aquatic vegetation was slightly lower at the restored sites. According to our assessment, the presence of invasive plant species counteracted the potential ecological gain. Water quality could be a causal factor contributing to the absence of larger improvements.Overall, we found significantly better biological and physical states, and integrated ecological states at the restored sites. Even in the absence of comprehensive before-after data, based on the similarity of the reaches before restoration and mechanistic biological knowledge, this can be safely interpreted as a causal consequence of restoration. An integrative perspective across aquatic and riparian organism groups was important to assess the biological effects, because organism groups responded differently to restoration. In addition, the potential deteriorating effect of water quality demonstrates the importance of integrated planning for the reduction of morphological, water quality and hydrological degradation.     

Plant species richness in ephemeral and perennial reaches of a dryland river

Ephemeral reaches are common along desert rivers but are less well studied than those with perennial stream flow. This study contrasted riparian plant species richness and composition (extant vegetation and soil seed bank) between stream reaches with different low-flow conditions (perennial vs. ephemeral flow) but similar flood patterns and similar watershed-derived species pools. Data were collected at Cienega Creek (Arizona, USA) over a 2 year period spanning drought conditions and wetter conditions. Consistent with expectations relating to water limitation effects on diversity, species richness in the riparian zone was lower at ephemeral-flow sites during a season with minimal precipitation and no overbank flooding; under these conditions, the more permanent water sources of the perennial-flow sites sustain the larger number of species. During seasons with greater precipitation and elevated stream flows, in contrast, species richness at ephemeral-flow sites increased to levels at or slightly above those of perennial-flow sites. For values pooled across two wet seasons of a calendar year, year-round richness was greater at the two ephemeral-flow sites (total of 92 vascular plant species) than at the two perennial-flow sites (68 species). This greater year-round richness was a combination of multiple factors: greater light, space, and bare ground, a diverse soil seed bank (with the seed banks equally species-rich among hydrologic types), and moderately abundant precipitation and flooding sufficient to stimulate establishment of opportunistic species (mainly annuals) during the bimodal wet seasons. These results indicate that long-term patterns of site water availability, by influencing woody plant cover, mediate the diversity response to episodic water pulses in dryland rivers. The results also have implications for riparian conservation efforts, which to date have focused primarily on perennial stream reaches: ephemeral reaches of spatially intermittent rivers harbor many riparian plant species, and warrant conservation efforts, as well.