Extremely distal fluvial sandstone within the playa system of Arnstadt Formation (Norian,Late Triassic), Central Germany

The Wachsenburg Sandstone of Thuringia (Central Germany) occurs within playa deposits of the Arnstadt Formation (Late Triassic, Norian) and furnishes an example of ephemeral river metamorphosis under dryland conditions. Characterized by high flow regime features, the sand-dominated lithofacies constitution exhibits sedimentation by channel processes under the influence of recurring flash floods. Bearing signatures of subaerial exposures, the fining-upward lithofacies cycles are bound by low-angle lateral accretion elements suggesting deposition in a meandering stream. Channel migration in response to point bar expansion and active bank erosion, led to the development of four laterally shifting point bar events. Unimodal palaeocurrent patterns with low variance and azimuthal dispersion support the point bar origin of the Wachsenburg Sandstone. With reduced water budget under largely semi-arid climate, the river progressively became smaller, highly sinuous and ultimately abandoned. The resulting point bar succession was finally covered with sheet flow deposits of over bank origin. The sandstone was deposited during a period of low base-level when the playa system temporarily fell dry.     

Self-Organizing Maps in Revealing Variation in Non-obligatory Riverine Fish in Long-term Data

Sensitiveness to the overall influence of the river channel regulation, impoundment and pollution was studied for 12 non-obligatory riverine (NOR) fish species in the Warta River, Poland, over the period of 1963–1998. Their total abundance has not considerably changed unlike the structure of their aggregation, which was revealed by a self-organizing map (SOM, Kohonen unsupervised artificial neural network) almost perfectly separating 1960s samples from 1990s ones. The greatest changes in proportion were recorded for the dominant roach Rutilus rutilus (from 28.6 to 60.0%), perch Perca fluviatilis (1.9 to 9.5%), pike Esox lucius (2.9 to 4.9%), and the former codominant bleak Alburbus alburnus (22.9 to 1.8%). They resulted from highly significant (p < 0.001), reaching even one order of magnitude, differences in the abundance of these species. Such remarkable alternations in dominant NOR ichthyofauna obviously influenced the whole fish assemblage structure, which was best illustrated by a clear vertical gradient over SOM in Simpson and Shannon indices. Thus, NOR species, both studied together and separately, can supply valuable information on the fish assemblage dynamics and should not be neglected in temporal analyses, often focused only on vulnerable obligatory riverine, migratory and/or endemic species.     

A Feasibility Study to Monitor the Macroinvertebrate Diversity of the River Nile Using Three Sampling Methods

The River Nile is one of the world’s major rivers. Its’ catchment in Egypt has a population of 75,000,000. River flow is highly regulated and there are known discharges of pollutants. 1035 km of the river downstream of the Aswan high dam was studied to test the hypothesis that representative qualitative samples can be used to estimate macroinvertebrate biodiversity. Benthic macroinvertebrates are difficult to sample in large rivers and a reliable sampling strategy is required to evaluate their ecological status. Three methods for sampling have been investigated. Ekman Grab, macrophyte sweep netting and Artificial Substrate Samplers (ASS) were used to sample 15 sites from Aswan to Cairo between September 2001 and June 2002. Organisms were identified to species level where possible. Taxon accretion curves indicated that the all taxa present at a site should be collected using either 15 grab samples, 10 macrophyte samples or 5 ASS. The best time to sample was May–June. The biodiversity of macroinvertebrates in the Nile was recorded as 50 taxa with values of 7–31 at individual bank-side sites. Mid-stream biodiversity was much lower (0–19). Lowest biodiversity occurred at sites with known pollution inputs whilst highest occurred at sites with high levels of sedimentation. A regular programme for biomonitoring is recommended which will allow current status to be confirmed and future changes detected.     

黑河流域水资源承载能力分析

黑河流域属资源性缺水地区,区域水资源难以满足当地社会经济发展和生态平衡的需要.随着西部大开发战略的逐步实施,西北干旱内陆河地区水资源的支撑作用将显得愈来愈重要.因此分析黑河流域水资源现状条件下对区域经济、社会发展的承载能力,显得极为重要.根据黑河流域具体情况,结合流域经济社会发展特点、生态环境状况,以遏制并逐步改善流域生态环境为基本前提,以流域水资源承载能力为约束.首先利用水资源承载压力指数计算了现状条件下黑河流域水资源承载压力度,得出目前黑河流域水资源承载能力属于超负荷承载.水资源将成为制约黑河流域社会经济发展和保证生态平衡的重要因素.当前必须立足于当地的水资源条件,按照以供定需的原则,合理安排生活、生产和生态用水,才能实现流域经济社会和生态环境的协调和可持续发展.然后针对超载现状,对黑河流域规划水平年（2010年）水资源承载能力作进一步的分析评价,根据相关预测资料设计了3种可能情景,利用流域评价的发展系数、协调系数、公平系数和可持续发展系数,从水资源开发利用方式、社会发展方式、经济发展模式、生态恢复程度等方面分析水资源承载能力,并计算其水资源承载压力度,同时结合水资源的可持续发展建立流域可持续发展评价指标体系,进行方案组合和各种发展模式的水资源优化配置.满足流域水资源支撑经济社会可持续发展判据的方案的承载能力指标即为该方案下的水资源可持续承载能力指标. 通过对黑河流域现状及规划水平年的水资源承载能力及可持续发展度分析评价,利用水资源可持续发展战略分析,选取出了最优发展模式,为流域的可持续发展提供了基本依据.通过寻求情景方案中水资源承载能力和可持续发展度的最佳组合,实现了经济、社会与生态的可持续发展目标.结果表明：通过努力,谋求经济和社会与水资源承载能力协调发展是有可能实现的.     

Annual cycle and inter-annual variability of gross primary production and ecosystem respiration in a floodprone river during a 15-year period

1. Temporal variation in ecosystem metabolism over a 15‐year period (1986–2000) was evaluated in a seventh order channelised gravel bed river (mean annual discharge 48.7 m³ s^?1) of the Swiss Plateau. The river is subject to frequent disturbance by bed‐moving spates. Daily integrals of gross primary production (GPP) and ecosystem respiration (ER) were calculated based on single‐station diel oxygen curves. 2. Seasonal decomposition of the time series of monthly metabolism rates showed that approximately 50% of the variation of GPP and ER can be attributed to season. Annual GPP averaged 5.0 ± 0.6 g O₂ m^?2 day^?1 and showed no long‐term trend. 3. Ecosystem respiration, averaging 6.2 ± 1.4 g O₂ m^?2 day^?1, declined from 8.8 to 4.1 g O₂ m^?2 day^?1 during the 15‐year period. This significant trend paralleled a decline in nitrate and soluble reactive phosphorus concentrations, and the biochemical oxygen demand discharged by sewage treatment facilities upstream of the study reach. The ratio of GPP to ER (P/R) increased from 0.53 to about 1 as consequence of ER reduction. 4. Bed moving spates reduced GPP by 49% and ER by 19%. Postspate recovery of GPP was rapid between spring and autumn and slow during winter. Recovery of ER lacked any seasonal pattern. Annual patterns of daily GPP and to a minor extent of daily ER can be described as a sequence of recovery periods frequently truncated by spates. 5. The study showed that disturbance by frequent bed‐moving spates resulted in major stochastic variation in GPP and ER but annual patterns were still characterised by a distinct seasonal cycle. It also became evident that stream metabolism is a suitable method to assess effects of gradual changes in water quality.     

The thermal regime of rivers: a review

1. The thermal regime of rivers plays an important role in the overall health of aquatic ecosystems, including water quality issues and the distribution of aquatic species within the river environment. Consequently, for conducting environmental impact assessments as well as for effective fisheries management, it is important to understand the thermal behaviour of rivers and related heat exchange processes. 2. This study reviews the different river thermal processes responsible for water temperature variability on both the temporal (e.g. diel, daily, seasonal) and spatial scales, as well as providing information related to different water temperature models currently found in the literature. 3. Water temperature models are generally classified into three groups: regression, stochastic and deterministic models. Deterministic models employ an energy budget approach to predict river water temperature, whereas regression and stochastic models generally rely on air to water temperature relationships. 4. Water temperature variability can occur naturally or as a result of anthropogenic perturbations, such as thermal pollution, deforestation, flow modification and climate change. Literature information is provided on the thermal regime of rivers in relation to anthropogenic impacts and such information will contribute to the better protection of fish habitat and more efficient fisheries management.     

THE INFLUENCE OF P-RETENTION BY SOILS AND SEDIMENTS ON THE WATER QUALITY OF THE LIONS RIVER

SUMMARY

The soils of Midmar dam catchment and the sediments of the Lions river are shown to have high P-retention properties. Present conditions result in little leaching of PO₄ ^?4 from the soils and favour a net transport of P from overlying water to the sediments. P levels in the water are likely to remain low even if the loading rate of P were increased substantially. It is postulated however that other factors may induce a release of P from the sediments and adversely affect the load carried by the water.     

A PRELIMINARY EVALUATION OF ASPECTS OF SASS (SOUTH AFRICAN SCORING SYSTEM) FOR THE RAPID BIOASSESSMENT OF WATER QUALITY IN RIVERS,WITH PARTICULAR REFERENCE TO THE INCORPORATION OF SASS IN A NATIONAL BIOMONITORING PROGRAMME

Summary

The rapid bioassessment method, SASS (South African Scoring System) has been developed to assess water quality in riverine ecosystems. It is a scoring system based on the presence or absence of macroinvertebrate groups, and yields three values, namely SASS4 Score, Number of Taxa and Average Score Per Taxon (ASPT). The current and future use of SASS, including incorporation into the National Biomonitoring Programme for Riverine Ecosystems, necessitates evaluation of this bioassessment method. This study focuses on three aspects. namely spatial variation in SASS scores, including regional and longitudinal (sub-regional) variation; temporal variation in SASS scores, and the effect of biotope availability on SASS scores.