Geochemical characteristics of heavy metals in the Xiangjiang River,China

The concentration of the heavy metals Cu, Cd, Pb and Zn in surface water and sediment samples taken from the length of the Xiangjiang River in China, revealed significant pollution in the vicinity of two industrial centres (Shuikoushan & Zhuzhou). Additional insight into the potential adverse effects of these elevated concentrations was obtained from studies of the physiochemical forms (speciation) of these metals in the water column and in sediments.     

Effects of floods on epilithon and benthic macroinvertebrate populations in an unstable New Zealand river

Temporal changes in epilithon biomass and benthic macroinvertebrate density were investigated in the Ashley River, a flood-prone river with an unpredictable discharge regime. Biomass, primary production and respiration of the epilithic community were highest in spring when filamentous algae were present and lowest following two large floods that occurred in close succession. Sixty invertebrate species were taken in benthic samples including 24 species of Trichoptera, 15 Diptera and 4 Ephemeroptera. Larvae of the mayfly Deleatidium (Leptophlebiidae) were numerically dominant and comprised up to 83 % of the fauna in any one month. Mean benthic invertebrate density was highest (9170–18 580 m^{–2) following long periods of low stable flow (< 30 m–3} s^–1) and lowest (230 m^–2) after a major flood (454 m^–3 s^–1). Reductions in benthic density occurred when flow exceeded about 30 m^–3 s^–1, the minimum discharge at which small cobbles are moved. Refuge seeking behaviours, flexible life histories and effective recolonization mechanisms enable the benthos of the Ashley River to persist and recover from frequent, temporally unpredictable disturbances.     

Bacterioplanktonic biomass and production in the river Meuse (Belgium)

This paper presents results of bacterial biomass determination by epifluorescence microscopy after acridine orange staining and ³H-thymidine incorporation measurements in the river Meuse. Bacterial production is calculated from thymidine incorporation using an experimental conversion factor (0.5 10¹⁸ bacterial cells produced per mole of thymidine incorporated into macromolecules). Seasonal variations of bacterial biomass and production at two stations are presented. Biomass ranges between 0.05 mgC · 1⁻¹ (in winter) and 0.8 mgC · 1⁻¹ (in summer). The variations of bacterial production seem to be closely linked to those of primary production; values lower than 1 μgC · 1⁻¹ · h⁻¹ are found in winter and high values (> 5 μgC 1⁻¹ · h ⁻¹) in summer. Longitudinal profiles in the Belgian course of the river show important increase of biomass and production from upstream to downstream. Bacterial growth yield (Y) has been determined (Y = 0.3) in order to calculate bacterial carbon uptake from bacterial production.     

Invertebrate drift in the Dan River,Israel

The Dan river, a principal source of the Jordan River, Israel, is unusually constant in discharge (8 m³·s^–1) and water temperature (15–16 °C). The Jordan headwaters constitute the southernmost oasis of a palearctic north temperate fauna, and presumably the very constancy of the Dan contributes to its important role as a regional refuge. However, little is known of river ecology from this region. We report a twelve month study of drift, undertaken to assess diel, seasonal, and spatial patterns of the abundance of drifting invertebrates.Diel periodicity in drift was detectable but minimal. Baetidae nymphs showed a pronounced nocturnal increase, gammarid amphipods a modest, twofold increase, while dipteran larvae showed no diel variation. Seasonal variation likewise was minimal and due principally to the Baetidae, while gammarid amphipods showed no significant seasonality. The notably small diel and seasonal variation in aquatic drift in the Dan may be attributable to the extremely constant physical regime.Spatial variation was substantial. Two stations located 30 and 200 m below the karstic exsurgence of the Dan provided drift densities among the lowest reported anywhere, whereas two stations located 1 and 4.5 km downstream had more typical drift densities. A water diversion project completed halfway through the study resulted in a 50% reduction in flow at the most downstream stations, but had no discernible effect on drift.     

采砂活动影响下鄱阳湖水陆交错带形态及景观格局变化

自长江干流限制无序采砂后,大量采砂船涌入鄱阳湖区作业导致水陆交错带形态与景观均发生明显的改变,人类活动深刻影响着鄱阳湖水陆交错带的稳定性。基于Landsat TM/OLI遥感影像数据,定量测算采砂活动对鄱阳湖水陆交错带形态和景观格局产生的影响,结果表明：(1)草滩与滩涂之间转化最为频繁,水域面积缩小,水陆交错带范围扩大;(2)东岸线和西岸线呈侵蚀状态,湖心岸线快速收缩;(3)鄱阳湖水陆交错带形状逐渐变得简单,而入江通道形状复杂化程度提高,其几何形态不规则化;(4)景观类型层次上,滩涂的破碎度最大,形状最为复杂,农田的破碎度和形状复杂程度最小,集聚性最强,草滩的连通性最好,沙地的景观指数幅度变化最大;(5)鄱阳湖水陆交错带破碎化程度逐渐降低,景观形状越来越复杂,景观多样性减少,整体连通性和集聚性增强;(6)采砂规模与鄱阳湖水陆交错带的形态指数呈负相关,与景观形状指数和入江通道的形态指数呈正相关,其均通过显著检验。     

河势特征分界下的黄河滩区周边城镇生境质量与景观格局演变

在黄河流域生态保护和高质量发展战略背景下,加强对黄河滩区生境质量及其驱动机制研究对区域生物多样性保护和生态韧性提升具有重要意义。以黄河滩区沿河城镇为研究区,依据河势特征将其划分为4个河段和14个子研究区,并基于InVEST模型与3类景观格局指数分析论证不同河势特征分界下生境质量与景观格局的时空演变规律。结果表明：（1）生境质量方面,2000-2020年研究区生境质量整体呈下降趋势,各河段生境质量平均值由大到小依次为河口段、弯曲段、游荡段、过渡段;（2）景观格局方面,各河段之间景观破碎度指数波动最小,并随城镇化发展破碎化程度逐渐减弱,连接度与复杂度波动明显,且因河势特征存在差异性变化;（3）生境质量与景观格局相关性方面,多数土地景观格局指数与生境质量显著相关,但关联程度有所下降。相同地类景观格局指数在不同河段内表现出不同甚至反向的互动关系。研究表明,河势特征是黄河滩区生境质量的全局性支撑或限制因素,其作用主要体现为对黄河滩区周边城镇土地空间发展的差异化影响,该影响直接作用于紧邻黄河地带的城镇组团,并间接影响其他区域,在一定程度上左右了城镇发展主向以及土地转化、空间格局的演变规律,最终影响区域生境质量的分布格局。研究结果对黄河滩区重要生态功能区的生境保护与生态系统功能调控具有一定的理论与实践价值。     

Ecology of the phytoplankton of the River Moselle: effects of disturbances on community structure and diversity

A data set on community composition of the phytoplankton of the River Moselle (France) has been used for testing the intermediate disturbance hypothesis (IDH). After a short presentation of the ecology of the river and of its phytoplankton, the main changes in composition and diversity of the suspended algal assemblage are described. It is emphasized that discharge fluctuations, related to weather changes, play a key role, but that biotic factors such as grazing and parasitism may also influence diversity in stable summer conditions.     

The rivers Rhine and Meuse in The Netherlands: present state and signs of ecological recovery

The ecosystems of the rivers Rhine and Meuse have suffered drastic environmental changes, for example because of the regulation of the stream bed and the construction of weirs and dams. Furthermore, discharges of industrial and municipal waste water have caused the water quality of these rivers to deteriorate; this problem became acute in the sixties and seventies. Recently some chemical parameters of water quality have improved in the Rhine, and as a consequence some aquatic communities are showing signs of recovery after decades of severe degradation. This paper describes the present state of the aquatic communities in the Dutch part of the rivers Rhine and Meuse, using published observations on plankton, macrophytes, invertebrates, and fish. The sparse information on the food chain in these rivers is summarized. The main channels of the Rhine and Meuse are characterized by a dense plankton that develops rapidly in the nutrient-rich river waters. The stream beds, now dominated by wave-exposed sand and gravel, have a sparse fauna and flora. The river banks, mostly consolidated by blocks of stone, offer a substratum for numerous benthic organisms, particularly now that the water quality has improved. The floodplain waters and old river channels harbour a flora and fauna rich in species. The degree of water exchange with the river is crucial for the ecological development of the river and its backwaters. Today the freshwater tidal reaches of the rivers occupy a very restricted area, and only remnants of the previously abundant vegetation of rushes are found. Losses in the numbers of animal and plant species, notably those specific to rivers, are evident, but over the last 15 years several species have returned. Allochthonous species (exotics), including crustaceans and molluscs, have also settled in the Rhine and Meuse. Fish species characteristic of these rivers, such as river lamprey, sea trout, barbel, and flounder, have recently been observed in appreciable numbers. The Rhine Action Programme provides a framework for the large-scale rehabilitation of the Rhine. Experiments on re-stocking the Rhine with Atlantic salmon and on the ecological rehabilitation of floodplains are being carried out on the assumption that there will be a further reduction of the pollution load. A similar programme is required for the Meuse.     

Distribution and seasonal dynamics of Rhodophyta in the Preto River basin,southeastern Brazil

Distribution and seasonal dynamics of freshwater Rhodophyta were investigated in the Preto River basin, located in northwestern São Paulo State, southeastern Brazil. Twenty-two sites were sampled, six monthly during one year, four bimonthly during two years, and 12 twice (hot-rainy and cool-dry seasons) during the study period (May 1989 through March 1991). Red algal representatives were found in 19 sites (86.4%). Four species occurred in the basin with varying frequencies:Batrachospermum delicatulum (54.5%),Compsopogon coeruleus (36.4%),B. bicudoi (13.6%) andB. virgatum (4.5%). In addition, Chantransia stage of the batrachospermalean species was found in 17 sites (77.3%).B. bicudoi, B. virgatum andC. coeruleus occurred only in large stream segments ( 3-order), generally in the main river, whereasB. delicatulum was more frequent in small streams ( 3-order). The stream variables most closely related to the species distribution in the basin were specific conductance, pH and oxygen.B. bicudoi andB. delicatulum showed a marked seasonality: gametophytes were observed from late fall to early spring, while the Chantransia stage generally occurred throughout the year.C. coeruleus was observed throughout the year in most sites, but the populations were generally more abundant from late fall to early spring. The combination of lower temperature and reduced turbidity resulting in increased illumination to the benthic algae during the dry winter months promotes the gametophytic growth of the batrachospermalean species, whereas current velocity was found to be the most influential stream variable forC. coeruleus. The persistance of the Chantransia stage throughout the year as well as its tolerance to wider environmental conditions are key factors in the efficiency of the batrachospermalean life history strategy in lotic ecosystems.     

Provenance,genotype, and flooding influence growth and resource acquisition characteristics in a clonal,riparian shrub

Premise

Riparian plants can exhibit intraspecific phenotypic variability across the landscape related to temperature and flooding gradients. Phenotypes that vary across a climate gradient are often partly genetically determined and may differ in their response to inundation. Changes to inundation patterns across a climate gradient could thus result in site-specific inundation responses. Phenotypic variability is more often studied in riparian trees, yet riparian shrubs are key elements of riparian systems and may differ from trees in phenotypic variability and environmental responses.

Methods

We tested whether individuals of a clonal, riparian shrub, Pluchea sericea, collected from provenances spanning a temperature gradient differed in their phenotypes and responses to inundation and to what degree any differences were related to genotype. Plants were subjected to different inundation depths and a subset genotyped. Variables related to growth and resource acquisition were measured and analyzed using hierarchical, multivariate Bayesian linear regressions.

Results

Individuals from different provenances differed in their phenotypes, but not in their response to inundation. Phenotypes were not related to provenance temperature but were partially governed by genotype. Growth was more strongly influenced by inundation, while resource acquisition was more strongly controlled by genotype.

Conclusions

Growth and resource acquisition responses in a clonal, riparian shrub are affected by changes to inundation and plant demographics in unique ways. Shrubs appear to differ from trees in their responses to environmental change. Understanding environmental effects on shrubs separately from those of trees will be a key part of evaluating impacts of environmental change on riparian ecosystems.