Hydrogeomorphological processes and plant invasion. What interactions in the case of Asian knotweeds along the Herault River (France)?

Considered one of the five major threats to biodiversity worldwide, Invasive Alien Species (IAS) particularly threaten riparian ecosystems. Among the IAS found on riverbanks, Asian knotweeds (Reynoutria spp. including R. japonica Houtt.; R. sachalinensis [F.Schmidt] Nakai and the hybrid R. x bohemica Chrtek & Chrtkova) can barely be controlled as, once established, they disperse easily along stream banks via rhizome or stem fragments transported by water. However, the hydrogeomorphological processes underlying the establishment of Asian knotweeds are poorly understood. The objective of this study was to describe and model the hydrogeomorphological preferences of Asian knotweeds along a Mediterranean river. Based on exhaustive presence/absence surveys, we implemented two models related to the presence of Asian knotweeds: (1) at the river reach scale and (2) at the finer scale of the alluvial bar. Areas of low curvature identified as convex banks and the central parts of alluvial bars appear to be more susceptible to knotweed establishment. Highly disturbed areas were less favorable to maintaining plant species, including Asian knotweeds, while less disturbed areas with denser plant cover were more favorable to Asian knotweeds. The results seem to indicate a trade-off hypothesis in the knotweed establishment strategy between hydrogeomorphological constraints and strong interspecific competition. Analyzed in the light of the current literature, our final models are designed to integrate hydrogeomorphological processes in order to provide an operational tool to help river managers locate the areas most susceptible to knotweed invasion and with important implications for managing these species in riparian ecosystems.     

The impact of Japanese knotweed on river discharge at the watershed scale in New Jersey,USA

Recently, New Jersey has experienced several droughts and declared several critical water shortage areas, spurring interest in reducing freshwater resource depletion. Japanese knotweed (Reynoutria japonica Houtt.) is an invasive plant species that may have a significant effect on stream water loss. In order to assess the impact of this species on river-level water flow, we estimated total knotweed distribution along two tributaries of the Passaic River in New Jersey, USA using a combination of field measurements and GIS to calculate total daily water loss to the atmosphere from three stands of knotweed along these rivers. We measured total leaf area of each stand and transpiration rates across each stand from sun-up to sun-down. The average water loss was 8.5 L wate/day/m² of ground area covered in knotweed. Knowing the total distribution of knotweed along each river, the amount of river length covered by knotweed stands and the total water lost to the atmosphere per amount of knotweed along each river we were able to estimate the total amount of water transpired to the atmosphere by knotweed per river on a daily basis during its growing season. These results were compared to summer low flow rates to assess the impact on river flow during the growing season for Japanese knotweed. Our results suggest that knotweed along these rivers is reducing total flow by an average of 8% (approximately 800,000–1,400,000 L/day) during the summer months. This is important as the impact of invasive species on water resources in temperate areas is currently under-studied in ecohydrology.     

Giant hogweed at its northern distribution limit in North America: Experiments for a better understanding of its dispersal dynamics along rivers

We studied the reproduction and dispersal of giant hogweed (Heracleum mantegazzianum) at its northern distribution limit in North America (Québec, 2014–2016) to better understand the invasion dynamics of the species along rivers. Seeds were collected from a riparian population to conduct germination, floatation, and dispersal experiments. Data were analysed in comparison with a real invasion case that was initiated about 10 years ago along a river system. In Québec, giant hogweed individuals produce on average 14,000 to 16,000 seeds with a germination rate of 75–85%. Seeds with endosperm that fall in water likely sink within 5 hr. Along a small brook, most disperse over short distances (<40 m) in summer, although some can travel 100–300 m. These data suggest that late‐summer or early‐fall water dispersal of seeds would not explain the magnitude and rapidity of the invasion patterns observed along streams. We suggest that late‐fall and, especially, spring floods are the most efficient dispersal vectors for giant hogweed seeds and are likely responsible for the establishment of populations kilometres downstream from introduction points along river systems. The spread of giant hogweed would consequently be less influenced in the near future by a rise in temperature than by a change in the magnitude or timing of flood events.     

Spatial distribution and site selection adaptation mechanism of traditional villages along the Yellow River in Shanxi and Shaanxi

Site selection adaptability of traditional villages along rivers can be summarized as the local ecological wisdom accumulated and preserved by generations of villagers. The site selection and distribution pattern of traditional villages is closely related to the river. In this research, 97 traditional villages along the Yellow River in Shanxi and Shaanxi were selected as the research objects. Kernel density analysis, Area density analysis, River buffer zone and a self-designed river location function (RLF) were used to explore, calculate, and evaluate the spatial distribution and site selection adaptation mechanism of traditional villages along the Yellow River. Most traditional villages are located within 15 km buffer area. Villages are densely distributed in one high-density aggregation area and one middle-density aggregation area. The aggregation areas also represent a highest area density of river. The results of RLF show that there are six villages with a value between 1.8 and 2.2, which is consistent with the results of kernel density and river buffer zone analyses. It is concluded that site selection adaptation factors are composed of area density of river, distance from river, river width and bank form. At the same time, it is found that traditional villages are clustered on convex banks, which reflects the scientific value of ancient Chinese feng shuitheory. Our findings improve the understanding of the overall environment and pattern of traditional villages, provide a quantitative basis for the study of site selection adaptability, and offer operational technical guidance for current and future efforts for village renewal, planning, and construction.     

Tracking Change in the Illinois River using Stable Isotopes in Modern and Ancient Fishes

The Illinois River has been heavily modified by human activities. We examined the nitrogen and carbon stable isotope composition of collagen from fish bones in two Native American middens comparing them to modern fishes in the River today. We also compared ancient and modern fishes to three reference samples—(i) Illinois River phytoplankton; (ii) backwater lake sediment; and (iii) tissue from riverside trees. We found a large increase in δ¹⁵N values in modern fish bone collagen relative to ancient collagen. However, there is little change in δ¹³C between ancient and modern samples. Bone collagen from invasive carp species (Hypopthalmichthys and Cyprinus) are similar to modern phytoplankton. All fishes are different from riverside trees and backwater lake sediment. The large shift in δ¹⁵N values between ancient and modern fishes is probably caused by contamination of the river by Chicago treated wastewater and by denitrified fertilizer run‐off. Our results indicate a major change in nitrogen biogeochemistry in the modern river. Comparisons between ancient and modern δ¹³C values suggest little change in feeding behaviour of fishes between ancient and modern times. However, our data for invasive carp suggest strong competition with native planktivores. © 2016 The Authors. River Research and Applications Published by John Wiley & Sons Ltd.     

Beaver herbivory and its effect on cottonwood trees: influence of flooding along matched regulated and unregulated rivers

We compared beaver (Castor canadensis) foraging patterns on Fremont cottonwood (Populus deltoides subsp. wislizenii) saplings and the probability of saplings being cut on a 10 km reach of the flow‐regulated Green River and a 8.6 km reach of the free‐flowing Yampa River in northwestern Colorado. We measured the abundance and density of cottonwood on each reach and followed the fates of individually marked saplings in three patches of cottonwood on the Yampa River and two patches on the Green River. Two natural floods on the Yampa River and one controlled flood on the Green River between May 1998 and November 1999 allowed us to assess the effect of flooding on beaver herbivory. Independent of beaver herbivory, flow regulation on the Green River has caused a decrease in number of cottonwood patches per kilometre of river, area of patches per kilometre, and average stem density within cottonwood patches. The number of saplings cut per beaver colony was three times lower on the Green River than on the Yampa River but the probability of a sapling being cut by a beaver was still higher on the Green River because of lower sapling density there. Controlled flooding appeared to increase the rate of foraging on the Green River by inundating patches of cottonwood, which enhanced access by beaver. Our results suggest regulation can magnify the impact of beaver on cottonwood through interrelated effects on plant spatial distribution and cottonwood density, with the result that beaver herbivory will need to be considered in plans to enhance cottonwood populations along regulated rivers. Published in 2002 by John Wiley & Sons, Ltd.     

江苏省沿江开发区水环境容量核算研究

在分析江苏省沿江开发区水文条件和污染状况的基础上,对规划年(2015年、2020年)沿江规划区域15个县(市)内的水环境容量、污染物入河量及限制排污总量进行计算核定,以分析规划实施的区域污染物总量控制是否满足区域水环境承载力要求,可以为区域资源优化分配和污染物总量控制方案提供科学依据。     

巴音河下游河床渗透系数空间变异性研究

河床垂向渗透系数是研究河流与地下水转化关系和转化强度的重要水文地质参数。选取柴达木盆地巴音河为研究对象,采用水头下降竖管试验法测定了巴音河下游细土平原带38组河床垂向渗透系数,利用传统统计学方法检验分析了其分布规律和空间变异性。结果表明,河床沉积物垂向渗透系数(Kv)在1. 77～15. 56 m/d之间变化,总体呈现正态分布,且沿流程逐渐变小。河中心沉积物的Kv值明显大于河两岸,但其变异系数小于两岸。沉积物的颗粒大小与分布是导致河床沉积物垂向渗透系数变异的关键因素,河流形态与交互带水文过程对河床沉积物Kv的影响也不容忽视。     

Statistical Distribution of Streambed Vertical Hydraulic Conductivity along the Platte River,Nebraska

Streambed vertical hydraulic conductivity (K _v ) plays an important role in understanding and quantifying the stream–aquifer interactions. While several researchers have discussed the spatial variability of streambed horizontal hydraulic conductivity or K _v at one or several close-located sites in a river, they did not develop any statistical distribution analysis of streambed K _v at distant sites along a large river. In this paper, the statistical distribution and spatial variation of streambed K _v at 18 test sites in a 300-km reach of the Platte River in Nebraska are presented. In-situ permeameter tests using the falling-head method were carried out to calculate the streambed K _v values. Fine-grained sediments transported by two tributaries, the Loup River and the Elkhorn River, to the Platte River appear to result in lower streambed K _v values downstream of the confluences between the Platte River and the tributaries. The streambed K _v values were found to be normally distributed at nearly each test site. When the correlated K _v values were eliminated from the grid sampling plots, the remaining independent sub-datasets of streambed K _v values were still in normal distribution at each test site. Furthermore, the combined streambed K _v values upstream of the first confluence between the Platte River and the Loup River was normally distributed, which may be due to the lack of tributaries in-between and thus streambed sediments were well distributed in this reach and belonged to a single population of hydraulic conductivity values. In contrast, the combined dataset of all measurements conducted downstream of this confluence was no longer in normal distribution, presumably as a result of the mixing of different sediment sources.     

Physical engineering of an island‐braided river by two riparian tree species: Evidence from aerial images and airborne lidar

Following a review of the European distribution, habitat requirements and life history characteristics of two riparian tree species, Alnus incana (L.) Moench (grey alder, a member of the Betulaceae family) and Populus nigra L. (black poplar, a member of the Salicaceae family), we explore their changing spatial distribution and topographic position within a 7 km, island braided reach of the Tagliamento River, Italy, where Populus nigra dominates the woody vegetation cover. Combining field observations and information extracted from aerial images, airborne lidar data and river flow time series for the period 1986–2017, we investigate (a) the changing spatial distribution of all (P. nigra‐dominated) woody vegetation and of A. incana alone; (b) whether river bed topography can be associated with these changing spatial distributions and (c) we consider whether A. incana displays any particular characteristics in its spatial and topographic distribution that may indicate that it is complementing the physical engineering role of P. nigra. We show that A. incana predominantly grows in lines along channel, island and floodplain edges, bordering wooded areas dominated by P. nigra and that areas supporting A. incana are associated with the topographic development of the river bed. We conclude that A. incana appears to be acting as a complementary physical engineer to P. nigra, suggesting that similar complementary physical engineering of river beds may be achieved by species with different life history traits to influence landform development in other river environments.     

泾河长系列水沙变化规律与归因研究

近些年泾河径流量及来沙量大幅减少,在一定程度上影响到流域的水资源开发利用,为了厘清水沙减少程度及变化特征,探寻其变化背后的驱动因素,采用联合滑动t检验、距平累积曲线法和Copula等方法,从不同层面对泾河长系列水沙规律进行了研究。同时,建立分布式水文模型,分情景对泾河流域径流泥沙对气候和土地利用变化的响应进行了模拟。结果表明:气候变化对径流和泥沙减少的贡献率约为21. 20%和6. 08%;土地利用变化对径流泥沙减少的贡献率约为4. 04%和11. 08%;泾河流域径流泥沙变化除受气候变化影响外,还与土地利用(覆被)类型、面积比重等有关。研究结论表明:人为拦蓄和引水是河川径流减少的主要原因,而泥沙减少的主因除了退耕还林还草之外,通过淤地坝等水保措施直接拦沙也起到了重要作用。     

An overview of non‐native species invasions in urban river corridors

Recent studies have highlighted cities as prime locations for the introduction, establishment, and spread of non‐native and invasive species. As the hydrological arteries of cities, urban river corridors have an important role to play in influencing species invasions. This overview examines existing literature to consider (a) how the landscape functions of urban river corridors (habitat, conduit, barrier/filter, sink, and source) relate to species invasions; (b) the organismal and geographical foci of research into non‐native species invasions along urban rivers; and (c) the need to more fully consider the roles that non‐native species may play in the recombinant communities of novel urban river ecosystems. The review ends with an identification of research priorities at the intersection of urban river corridor function and invasion biology.     

Assessing the effects of hydrological and chemical stressors on macroinvertebrate community in an Alpine river: The Adige River as a case study

In this study, the combined effects of hydrological and chemical stressors on benthic macroinvertebrates were evaluated in order to explore the response of the biological community to multiple stressors. The Adige River, located in the south‐eastern Alps, was selected as a case study because representative of the situation of a large river in which the variety of stressors present in the Alpine region act simultaneously. As expected, streamflow showed a seasonal pattern, with high flows in the spring–summer period; however, locally, the natural hydrological regime was altered by the presence of hydropower systems, which chiefly affected low flows. Multivariate analysis showed seasonal and spatial patterns in both chemical and hydrological parameters with a clear gradient in the concentration of nitrate, personal care, and pharmaceutical products moving from headwaters to the main stem of the river. The macroinvertebrate community composition was significantly different in summer and winter and between up and downstream sites. Streamflow alteration chiefly due to water use by hydropower affected community composition but not richness or diversity. Gammarus sp., Hirudinea, and Psychomyia sp., were positively correlated with flow variability, increasing their densities in the sites with higher streamflow variability because of hydropeaking. The results obtained in this study show that the composition of the macroinvertebrate community responded to seasonality and to changes in the main stressors along the river and highlights the importance of the spatial and temporal variability of stressors in this Alpine river. Taking into account, this variability will help the decision‐making process for improving basin management.     

基于长序列的黄河下游游荡型河道河势演变

分析黄河下游游荡型河道河势的时空演变规律,为进一步认识黄河下游河道演变特征、开展河道整治提供理论支撑和实践价值。在系统收集、整理1960-2015年黄河下游游荡型河段典型断面的河势观测资料基础上,利用Mann-Kendall趋势检验和Fisher断点检验方法分析1960-2015年黄河下游游荡型河道典型断面多年平均河宽及主流线迁移速率变化情况。结果表明:近60年黄河下游游荡型河道在平面形态上呈藕节状分布,而其主流线调整速率的时空分布规律并不显著;黄河下游于店断面、禅房断面是平面藕节状分布的关键节点,将全河段划分为3段(第一段铁谢至于店断面,河宽均值为1 627m;第二段于店至禅房断面,河宽均值为1 477m;第三段禅房至高村断面,河宽均值为1 074m)。     

An Assessment of Fish Assemblage Structure in a Large River

The Penobscot River drains the largest watershed in Maine and once provided spawning and rearing habitats to 11 species of diadromous fishes. The construction of dams blocked migrations of these fishes and likely changed the structure and function of fish assemblages throughout the river. The proposed removal of two main‐stem dams, improved upstream fish passage at a third dam, and construction of a fish bypass on a dam obstructing a major tributary is anticipated to increase passage of and improve habitat connectivity for both diadromous and resident fishes. We captured 61 837 fish of 35 species in the Penobscot River and major tributaries, through 114 km of boat electrofishing. Patterns of fish assemblage structure did not change considerably during our sampling; relatively few species contributed to seasonal and annual variability within the main‐stem river, including smallmouth bass Micropterus dolomieu, white sucker Catostomus commersonii, pumpkinseed Lepomis gibbosus, and golden shiner Notemigonus crysoleucas. However, distinct fish assemblages were present among river sections bounded by dams. Many diadromous species were restricted to tidal waters downriver of the Veazie Dam; Fundulus species were also abundant within the tidal river section. Smallmouth bass and pumpkinseed were most prevalent within the Veazie Dam impoundment and the free‐flowing river section immediately upriver, suggesting the importance of both types of habitat that supports multiple life stages of these species. Further upriver, brown bullhead Ameiurus nebulosus, yellow perch Perca flavescens, chain pickerel Esox niger, and cyprinid species were more prevalent than within any other river section. Our findings describe baseline spatial patterns of fish assemblages in the Penobscot River in relation to dams with which to compare assessments after dam removal occurs. Copyright © 2014 John Wiley & Sons, Ltd.     

Temporal distribution and taxonomic composition differences of larval fish in a large navigable river: A comparison of artificial dike structures and natural habitat

Distributions of larval fish in a regulated river were determined by sampling 15 sites in 2003 using larval fish light traps. Typical of large river systems in the Mississippi River drainage, collections in the Kanawha River were dominated (>93%) by Cyprinidae and Percidae species. Catch per unit effort (CPUE) along artificial dike structures were higher than CPUE along other shoreline sites, indicating the importance of these structures as nurseries. Taxonomic richness within artificial dike structures was greater than or equal to normal shoreline reference sites. Cyprinidae (Pimphales type and Notropis type) were collected significantly more on artificial structures than reference sites (p < 0.01). We collected higher numbers and observed greater CPUE of some sport fishes (Percidae) at the artificial dike structures. Percidae CPUE was significantly higher (p < 0.01) on artificial dike structures than reference sites. Percidae distribution appears to be positively influenced by the introduction of artificial dike structures in comparison to other abundant fish groups. Artificial dike structures encouraged taxonomic and larval fish diversity, and positively influenced some game fish species. The results of this study suggest that artificial dike structures are habitats that increase larval fish diversity in large, navigable rivers. Copyright © 2010 John Wiley & Sons, Ltd.     

Spatial and Temporal Relationships Between the Invasive Snail Bithynia tentaculata and Submersed Aquatic Vegetation in Pool 8 of the Upper Mississippi River

Bithynia tentaculata is an invasive snail that was first reported in Lake Michigan in 1871 and has since spread throughout a number of freshwater systems of the USA. This invasion has been extremely problematic in the Upper Mississippi River as the snails serve as intermediate hosts for several trematode parasites that have been associated with waterfowl mortality in the region. This study was designed to assess the abundance and distribution of B. tentaculata relative to submersed aquatic vegetation as macrophytes provide important nesting and food resources for migrating waterfowl. Temporal changes in both vegetation and snail densities were compared between 2007 and 2015. Between these years, B. tentaculata densities have nearly quadrupled despite minor changes in vegetation abundance, distribution and composition. Understanding the spatial distribution of B. tentaculata in relation to other habitat features, including submersed vegetation, and quantifying any further changes in the abundance and distribution of B. tentaculata over time will be important for better identifying areas of risk for disease transmission to waterfowl. Copyright © 2017 John Wiley & Sons, Ltd.     

Organic matter distribution in floodplains can be predicted using spatial and vegetation structure data

Riparian forest ecosystems play a significant role in the storage of organic carbon. However, the knowledge on the spatial patterns of organic matter distribution which is crucial to the assessment of the C sequestration potential of riparian ecosystems is still lacking. The aim of our study was to identify predictors of organic matter distribution in floodplain soils and vegetation. We analysed the depth distribution of soil horizons to 1 m below the surface, calculated the organic C content and quantified living biomass and woody debris at 67 sampling plots in the Donau–Auen National Park (Austria) along principle spatial gradients (longitudinal, lateral and vertical to river direction). Multiple regression models were fitted using hierarchical partitioning of spatial information, which was supplemented by forest stand parameters as possible predictors of soil C. The concentration of organic C in the subsoil horizons increased significantly with distance to the main channel. In addition, the thickness of soil horizons enriched with organic matter increased downstream which probably indicates the effect of riverbed changes over the last two centuries. Model prediction of soil parameters was improved with the inclusion of vegetation structure variables which are a consequence of local river dynamics. Highly dynamic locations indicated by higher stem numbers, greater understory vegetation cover, lower mean stem diameter and lower canopy cover showed significantly lower concentrations of soil organic C and lower total organic C stocks. We conclude that spatial information and vegetation structure can indicate gradients of geomorphic floodplain dynamic, which is the main driver of organic matter storage. Copyright © 2010 John Wiley & Sons, Ltd.     

The invasion of a large lake by the Eurasian genotype of common reed: The influence of roads and residential construction

The Eurasian genotype of common reed (Phragmites australis) is one of the most aggressive plant invading North American wetlands. There is, however, little published evidence on establishment patterns of populations along lakes of the St. Lawrence River–Great Lakes watershed. We tested the hypothesis that the recent invasion of Great Lake Saint-François (Québec, Canada) by common reed was facilitated by a dense road system and by an intense residence construction activity along lakeshores. A total of 345 and 2914 reed stands were mapped along lakeshores, and along the road system of the study area, respectively. The probability of finding a reed stand on a lakeshore increases with the proximity of the lake's outlet, and of a paved road, but decreases with the proximity of a residence built since 1990. It is likely that common reed first spread along the road system, and that wind dispersal of seeds then favored the establishment of populations on lakeshores. Our model does not support the hypothesis that residential construction facilitated the establishment of reed stands, probably because the recent residential construction boom occurred essentially in the southern part of the lake, where the number of roadside reed populations is much lower than in the northern part (lower seed rain). The invasion of Great Lake Saint-François shows that the spread of the plant is not restricted to major river or road systems. Large or small lakes, if submitted to intense diaspore pressure, can also be at risk.     

Aquatic macroinvertebrate assemblages of two contrasting floodplains: The rhǒne and ain rivers,France

The study examines the relationship between floodplain aquatic macroinvertebrates and sector-scale parameters such as geomorphology and history of regulation. The assemblages of six groups of invertebrates (Molluscs, Crustaceans, Ephemeroptera, Odonata, Trichoptera, and Coleoptera) were compared in various types of former channels from two contrasting but adjacent floodplain sectors: (1) the Jons sector of the Rhǒne River where successive meandering and braiding phases has left diversified fluvial forms in the landscape but where the main river is now embanked, and (2) the unregulated Ain River sector where the river is still actively meandering, although this process is being slowed by incision. The results demonstrate little difference in faunal composition between the two sectors but a significant difference in faunal structure. In the Rhǒne floodplain, there was a clear distinction between the faunal assemblages together with a high taxa richness at the scale of the sector (dominance of the beta diversity). In the Ain floodplain, the faunal assemblages were overlapping and the taxa richness was high at the sample scale (alpha diversity). Sector-scale spatial patterns of the faunal assemblages along former channels were also distinct: between-channel heterogeneity dominated in the Rhǒne, whereas within-channel heterogeneity dominated on the Ain. These results stress the influence of geomorphological and historical determinants on the floodplain communities and, conversely, the relevance of macroinvertebrate assemblages for the assessment, at the landscape scale, of aquatic systems within the floodplains.