Spatial distribution of interstitial assemblages in the floodplain of the rhǒne river

Interstitial invertebrate assemblages of the Rhǒne River were studied at the scale of the entire alluvial plain. Ten stations, located in five former channels, were sampled with a Bou-Rouch pump at 50 and 100 cm depth. The chemical characteristics of the interstitial water allowed the differentiation of stations without hydrological connections with the subterranean habitats, stations fed by surface water coming through the bank sediments and stations fed by true groundwater. The faunal assemblages reflect the difference between connected and isolated stations but did not demonstrate any differences related to the origin of the water. In fact the interstitial assemblages are distributed along a gradient from the margin of the floodplain (stations with a high physical stability associated with the absence of flood periods) to the area close to the main channel regularly influenced by floods. These results demonstrate that both groundwater characteristics and the position of the station in the floodplain influence the spatial distribution of interstitial fauna in the alluvial valley of the Rhǒne River.     

Stream regulation and nitrogen dynamics in sediment interstices: comparison of natural and straightened sectors of a third‐order stream

Nitrogen dynamics were studied in the interstitial environment (i.e. hyporheic zone) of a sandy‐bottom stream in a rural landscape. A third‐order stream in Brittany (France) was studied at 11 stations (riffles) to evaluate spatial patterns of water exchange between surface and interstitial habitats. More intensive sampling was conducted in three riffles selected according to their hydrological characteristics. Chemical characteristics (especially nitrogen) and microbial denitrification were studied at 12.5 and 25 cm depth upstream, and 25 cm depth downstream of each riffle. This study confirms that the interstitial habitat of a N‐rich stream acts as a sink for the nitrate‐nitrogen. Experimental manipulation of sediment cores indicates that denitrification is limited by carbon in surface (i.e. benthic) and by nitrate in hyporheic sediments. River regulation increases inputs of fine sediments, modifies river channel location, and generates changes in the spatial patterns of biogeochemical processes, water origins, and hydrologic exchanges. Copyright © 2004 John Wiley & Sons, Ltd.     

Spatio‐temporal variations in fish assemblages in a tropical regulated lower river course: an environmental guild

Fish assemblage patterns were studied in the lower river reach of the Uthokawiphatprasit anti‐salt dam, 6 km upstream from the Pak Panang River mouth, Southern Thailand, where the dam was opened occasionally depending on the upstream water level. Matrix data of the presence–absence of 71 fish species in 102 surveys was used in the analysis by applying a self‐organizing map (SOM) model. The trained SOM (lattice 8 × 7) showed that after 6 years of operation, five assemblage patterns were distinguished. These patterns described the probability of the occurrence of fish in each fish environmental guild, which according to changes in flow and water geomorphology. Clusters Ia and Ib were mostly the surveys in upstream stations and occupied by fish in potamonic guilds, whereas the fish in the estuarine guild and marine guilds showed a high probability of occurring in clusters IIa, IIb and IIc, which belonged to the surveys in downstream stations. The surveys of the stations near the dam (i.e. stations 5 and 6) during the opening phase were contained in cluster IIb. The Kruskal–Wallis test showed that there was no statistical difference in the probability of occurrence among assemblages of the diadromous, catadromous and semi‐anadromous fishes but not the amphidromous fishes, which had a low probability of occurrence in clusters Ia and Ib. The fish assemblages were arrayed along a longitudinal gradient, where salinity and pH were the most important controlling variables and explained 94.0% of the total inertia. Copyright © 2009 John Wiley & Sons, Ltd.     

Effects of bottom sediment restoration on interstitial habitat characteristics and benthic macroinvertebrate assemblages in a headwater stream

The restoration of in‐stream habitats by structural improvement of stream beds is more and more frequent, but the ecological consequences of such works are still little known. We have examined the influence of the deposit of a 15 cm gravel layer over the stream bottom on the chemical characteristics of the interstitial water, the sediment grain size and the composition of the benthic assemblages. We have compared a restored reach to an upstream control over three years and at three seasons each year. Dissolved oxygen, ammonium, nitrite and nitrate contents were measured in both surface and interstitial (?15 cm deep) waters, together with the depth of anoxia estimated using wooden stakes and fine sediment content at the surface. During the same period and seasons, benthic invertebrates were sampled at five points in each reach. The restoration induced an increase in vertical exchanges of water between surface and interstitial habitats, with an increase in the depth of hypoxia. Changes were observed in the composition of invertebrate communities, but not in the density or in the taxonomic richness of assemblages. These changes in assemblages were fragile: a local disturbance (such as a drying period) diminished the beneficial effect of the restoration with the disappearance of several organisms. The viability of such restoration works may be associated with catchment management designed to reduce fine sediment inputs to the river. Copyright © 2007 John Wiley & Sons, Ltd.     

Interstitial fauna in newly‐created floodplain canals of a large regulated river

Artificial drainage canals are often dug in large river floodplains to prevent winter inundation when groundwater level increases. Nothing is known about the biodiversity of the interstitial fauna of these artificial aquatic systems. The water chemistry and interstitial fauna of four drainage canals along the River Rhône (dug 11–15 years ago) were sampled in July during 3 years (1995–1997). A total of 53 taxa were found, with both epigean and hypogean organisms, and some rare phreatobites previously considered as absent from this sector of the Rhône. The faunal assemblage is characterized by limited temporal variations between the 3 successive years. Differences in interstitial fauna composition between the four drainage canals were mostly linked to oxygen availability and to heterogeneity in water origin (true ground water or surface water infiltration through embankment). Low oxygen content results in poorly diversified assemblages, which are always dominated by the same small set of species. In contrast, heterogeneity in water origin resulted in elevated faunal diversity. Copyright © 2000 John Wiley & Sons, Ltd.     

Influence of regional factors on zooplankton structure in a saline lowland river: the Salado River (Buenos Aires province,Argentina)

Knowledge of regional factors influencing zooplankton structure in a semiarid river must include both the main channel and any tributaries in order to identify spatial and temporal patterns along with the main factor that affect the zooplankton community. Accordingly, seasonal samples were taken during 1997–1999 at 15 stations in the Salado River basin, where 172 species were identified (53 protozoans, 88 rotifers and 31 crustaceans). Conductivity and temperature optima and tolerances were calculated for the evident taxa. Different assemblages were recognized by cluster analysis, on the basis of their temperature and conductivity preferences. With respect to the zooplankton assemblages, three zones can be distinguished along the longitudinal axis of the basin: (1) the headwaters (the effluent from large saline shallow lakes), (2) the inter‐tributaries, and (3) the lower basin and associated shallow lakes. The spatial distribution of the assemblages was a result of the combined action of factors always promoting the dominance of rotifers. The influence of floodplain waters (backwater ponds, waterlogged depressions, flushing lakes) was attenuated progressively downstream, thus producing disadvantages for the crustaceans. The food availability and high nutrient concentrations related to land use in the headwaters favoured the co‐dominance of cladocerans and copepods along with the rotifers in that region. Copyright © 2008 John Wiley & Sons, Ltd.     

Hydrologic alterations in the Wabash River watershed,USA

Flow alteration of streams from anthropogenic impacts is ubiquitous worldwide. In this paper, we examine flow alteration in a single watershed, the Wabash River and suggest potential impacts on aquatic assemblages. The Indicators of Hydrologic Alteration (IHA) software was used to evaluate hydrological variables generated from daily discharge data of 80 USGS gauging stations, during the past several decades. We used the approach of regressions of hydrological variables against time to identify hydrologic change. An average of 6.9 hydrologic variables (of 33 variables) were significantly altered at each station, and stations with larger watersheds had an increased number of altered variables. A principal components (PC) analysis of altered hydrologic variables resulted in three of four PC axes that were correlated with watershed area. Significant results were: (1) larger streams were more likely to have hydrologic alteration than smaller streams; (2) streams with upstream dams had increased minimum flows for 1‐, 3‐, 7‐ and 30‐day intervals, decreased maximum flows for 1‐, 3‐, 7‐ and 30‐day intervals, increased fall rates, decreased summer monthly flows and decreased high pulse counts; (3) the presence of agriculture in upstream watersheds resulted in an increased number of zero flow days, increased low pulse counts and decreased high flows during October and April. No significant differences were detected in hydrologic alteration based on urban land‐use of upstream watersheds. Hydrologic alterations in the Wabash River watershed have undoubtedly resulted in ecological degradation. We suggest that changes in assemblages during the past century are linked to these hydrologic alterations. Copyright © 2008 John Wiley & Sons, Ltd.     

Anaerobic microbial metabolism in hyporheic sediment of a gravel bar in a small lowland stream

Distribution of dissolved oxygen, nitrate, sulphate, carbon dioxide and dissolved organic carbon (DOC), acetate and lactate was studied in the stream and interstitial water along the subsurface flowpath in the hyporheic zone of a small lowland stream. Sediments were found to act as a source of nitrous oxide and methane. Interstitial methane concentrations were significantly much higher in comparison to those from surface water, and were significantly lower in the relatively well oxygenated downwelling zone than in the rather anoxic upwelling zone. The interstitial concentrations of O₂, NO₃^?1 and SO₄^?2 showed significant decline along the subsurface flowpath, while concentrations of CO₂, N₂O, DOC, acetate and lactate remained unchanged. In addition to field measurements, ex situ incubation of sediments was carried out in the laboratory. Maximal methane production was found in the incubation assay using acetate (mean value 380 µg CH₄ kg DW^?1 d^?1). Mean value of the denitrification potential was 1.1 mg N₂O kg DW^?1 d^?1. Nitrous oxide production potential reached 71–100% of denitrification potential. Our results demonstrate that respiration of oxygen, nitrate, sulphate and methanogenesis may coexist within the hyporheic zone and that anaerobic metabolism is an important pathway in organic carbon cycling in the Sitka stream sediments. Copyright © 2005 John Wiley & Sons, Ltd.     

Seasonality Characteristics and Spatio-temporal Trends of 7-day Low Flows in a Large, Semi-arid Watershed

Seasonality characteristics and spatio-temporal trends of 7-day low flows were investigated for the 41,470 km² semi-arid Karkheh watershed (western Iran), representing 12 stations with record length of 51 years (1958–2008). Hierarchical Cluster Analysis (HCA) was used to identify low-flow seasonality (clusters of low flow seasons). Monotonic trends were detected by the Mann-Kendall test. Breaks in low flow trends were detected by the Lombard’s change point test. Breaks in short-term trends were detected by the Lepage test. According to results seasonal clusters were different in most of the stations, indicating uniqueness in station low flow behaviour. Among the 12 stations studied, four stations showed seasonal monotonic trend and change points, some with abrupt change (change point in consecutive years). Two stations near watershed outlet with no monotonic trend showed abrupt change. Most seasonal change points (dates) compared well with documented droughts, highlighting drought impacts on low flow trends at affected stations. The Lepage test detected change point in seasonal low flow trends of most stations during 5- and 10-year periods. This research has shown that in semi-arid environments low flow seasonality characteristics may vary among stations, an indication that low flow trends should be evaluated individually for each station.     

Fish zonation and indicator species for the evaluation of the ecological status of rivers: example of the Loire basin (France)

In the context of river alteration, ecologists are asked to develop tools for the assessment of river integrity. Fish are known to be good bioindicators of the ecological condition of rivers. The Loire basin (France) is often considered as relatively little impacted compared to most other large European systems. But curiously, no study clearly addressed the question of fish assemblages patterns in this system in order to assess this status. Thus, we studied fish assemblages along the river network in the Loire basin using self‐organizing maps (SOMs) and we built a fish typology. Four basic assemblages were described and indicator species were identified. These assemblages varied in terms of individual species patterns as well as in terms of flow preference guilds and species richness. A discriminant analysis carried out on environmental variables revealed that they could be mainly determined by the slope, temperature and depth. Finally, fish assemblages were arrayed along a longitudinal gradient and roughly fitted the theoretical zonation expected in European rivers with the succession of brown trout (Salmo trutta fario), grayling (Thymallus thymallus), barbel (Barbus barbus) and bream (Abramis brama) zones in a downstream direction. Such patterns are still rarely observed in large European systems. However, the fish assemblage characteristic of the bream zone occurred more frequently than predicted on the basis of environmental variables. Such deviations between field data and theory suggest lotic‐to‐lentic shifts probably due to anthropogenic disturbances, especially in the grayling and barbel zones. In these river sectors, eurytopic and limnophilic species tend to replace rheophilic ones. Finally, the method used in this study to investigate fish patterns may be helpful to detect disturbances and may serve as a tool for the establishment of management plans. Copyright © 2007 John Wiley & Sons, Ltd.     

Ichthyoplankton Assemblages of Coastal West-Central Lake Erie and Associated Habitat Characteristics

Early life stage survival often determines fish cohort strength and that survival is affected by habitat conditions. The structure and dynamics of ichthyoplankton assemblages can tell us much about biodiversity and fish population dynamics, but are poorly understood in nearshore areas of the Great Lakes, where most spawning and nursery habitats exist. Ichthyoplankton samples were collected with a neuston net in waters 2–13 m deep weekly or biweekly from mid-April through August, during 3 years (2000–2002) as part of a study of fish assemblages in west-central Lake Erie. A suite of abiotic variables was simultaneously measured to characterize habitat. Cluster and ordination analyses revealed several distinct ichthyoplankton assemblages that changed seasonally. A lake whitefish (Coregonus clupeaformis) dominated assemblage appeared first in April. In May, assemblages were dominated by several percid species. Summer assemblages were overwhelmingly dominated by emerald shiner (Notropis atherinoides), with large gizzard shad (Dorosoma cepedianum) and alewife (Alosa pseudoharengus) components. This seasonal trend in species assemblages was also associated with increasing temperature and water clarity. Water depth and drift processes may also play a role in structuring these assemblages. The most common and widely distributed assemblages were not associated with substratum type, which we characterized as either hard or soft. The timing of hatch and larval growth separated the major groups in time and may have adaptive significance for the members of each major assemblage. The quality and locations (with reference to lake circulation) of spawning and nursery grounds may determine larval success and affect year class strength.     

Inter‐habitat variation in the benthos of the Upper Missouri River (North Dakota,USA): implications for Great River bioassessment

We examined inter‐habitat variation in benthic macroinvertebrate assemblages in the 180‐km Garrison Reach of the Upper Missouri River, North Dakota (USA) in 2001–2003. The Garrison Reach is unchannelized with a mostly rural setting. Flows are regulated by Garrison Dam. We sampled benthos from three habitats defined a priori: channel, shoreline, and backwater. Benthic assemblages were different in each habitat. Average Bray‐Curtis dissimilarity in assemblage composition ranged from 89% for backwater versus channel habitat to 70% for backwater versus shoreline habitat. There were distinct intra‐habitat groups within a priori habitats: channel assemblages included moving‐sand assemblages and other‐substrate channel assemblages; backwater assemblages included connected (to the river channel) and unconnected backwater assemblages; shorelines assemblages varied between natural (unprotected) and riprap (rock revetment) shorelines. Abundance and taxa richness were lowest and spatial variability highest for moving‐sand channel assemblages. Abundance was highest in backwaters. Taxa richness in backwaters and along channel shorelines were similar. Assemblages in all three habitats were dominated by Nematoda, Oligochaeta and Chironomidae. Taxa in these groups comprised at least 80% of mean abundance in all three habitats. Taxa that discriminated among habitats included the psammophilic chironomid Chernovskiia for moving‐sand channel substrates versus all other habitats; Hydroptila (Trichoptera) for riprap vs natural shorelines, Aulodrilus (Oligochaeta) for connected versus unconnected backwaters; and Nematoda for backwater versus channel and shoreline versus channel. Based on overlap patterns in benthic assemblages among habitats, we concluded that sampling main channel shorelines should also capture much of the natural and stressor‐induced variation in connected backwater and channel habitat exclusive of moving‐sand channel habitat. Published in 2006 by John Wiley & Sons, Ltd.     

Phytoplankton Distribution in Saginaw Bay

Phytoplankton cell counts were made on samples taken in Saginaw Bay during each of 11 cruises from April 1980 through November 1980. A spring assemblage numerically dominated by diatoms was followed by a brief period of dominance by green algae. Blue-green algae were numerically dominant from July through October when diatoms again became the dominant taxonomic group. Two regions of the bay were recognized based on the results of cluster analysis and principal component analysis of the average phytoplankton assemblage. The inner bay was typified by algal species with a Saginaw River origin and/or species typical of eutrophic waters in the Great Lakes. The outer region was typified in part by species of open Lake Huron. Wild Fowl Bay and the area to the southwest of Oak Point each have unique phytoplankton assemblages and are apparently not well integrated with the rest of the bay. On occasion, stations at or near the eastern side of the Saginaw Bay-Lake Huron interface have phytoplankton assemblages similar to inner bay and/or Wild Fowl Bay or Oak Point waters. Taken together, these findings indicate a possible strong nearshore effect on transport of Saginaw Bay populations to Lake Huron. The nearshore effect modifies the effect of Saginaw River on the phytoplankton of the Saginaw Bay-Lake Huron system.     

梯级水电站群优化调度算法研究

根据梯级水电站群远程集控调度的特点,研究了适用于梯级水电站群的优化调度算法。讨论了梯级水电站群优化调度准则,对几种典型优化算法的适应性和局限性进行了分析比较。结果表明,在流域梯级电站数量较少时可采用动态规划算法,在流域梯级电站规模较大时可采用基于遗传算法的改进型优化算法。按照流域梯级水电站的实际情况采用适应的优化算法,才能发挥梯级水电站远程集控优化调度系统的优势。     

Responses of Chironomid larvae (insecta,Diptera) to ecological quality in Mediterranean river mesohabitats (South Italy)

Chironomid larvae and pupae were studied in selected Mediterranean rivers with the aim of identifying pool and riffle taxa assemblages and of analysing their response to ecological quality gradients. Macroinvertebrate samples were collected in six Italian rivers along a pool‐riffle sequence in three seasons following a multihabitat sampling technique. Chironomids were identified as genus/species, other macroinvertebrates as family/genus. The main physico‐chemical, hydromorphological and geographical data were collected. Samples were ascribed to five quality classes according to the STAR_ICM index. Based on Chironomid taxa, principal component analysis (PCA) axis 1 represented an organic pollution gradient, axis 2 represented seasonality. Pool and riffle samples were significantly different according to taxa assemblages. Similar results were obtained with PCA based on the whole macrobenthic community. Indicator value (IndVal) analysis facilitated the detection of the Chironomid indicators of high/good quality pools (e.g. Conchapelopia pallidula, Rheopelopia ornata, Epoicocladius ephemerae) and riffles (Tvetenia calvescens, Eukiefferiella gracei). The Berger–Parker dominance index based on Chironomid assemblages in pools was correlated to PCA axis 1 and performed well in discriminating between quality classes. In riffles, no correlations to PCA axes were detected and a wide overlap between quality classes was present. Thus, assessment in the analysed river type may focus on pool mesohabitat as this seems to represent best the ecological gradient of sites. Copyright © 2009 John Wiley & Sons, Ltd.     

Temporal changes in the periphytic algal communities in a drowned tropical forest reservoir in Malaysia: Lake Kenyir

Periphytic algal assemblages, comprising bacillariophytes, cyanophytes and chlorophytes of standing dead trees in Lake Kenyir, a tropical drowned forest reservoir, were studied during 1995. A total of 317 algal taxa were identified in this study. The monthly floral mean species richness and cell count data demonstrated significant temporal differences between the months, in one-way anova (P < 0.05). Both redundancy analysis and cluster analysis on monthly blue-green abundance and diatom assemblages exhibited conspicuous groupings among the months, with underpinning seasonal differences. The responses were not similar, however, between the upstream and downstream ends of the lake. The grouping or clustering of months can be generalized as: (i) November, December and January as the monsoonal months; (ii) February, March, April and May as the transitional months; and (iii) June to October as the dry months. Based on stepwise multiple regression with forward selection, alkalinity and dissolved oxygen concentration were significant environmental predictors at the downstream dam sampling site, and reactive silica, electrical conductivity, Secchi depth transparency and sunshine hours were significant predicators at the upstream riverine sampling site, based on Monte Carlo tests. Being a ploymictic, mesotrophic lake, the limnology and temporal changes for Lake Kenyir appears to be complex and driven by monsoons, as evidenced from the temporal changes in its periphytic algae communities, particularly the diatom assemblages. The downstream sampling site (site 1) at the dam, in the main basin and deeper zone of the lake, the seasonal amplitude was likely complex because of thermocline formation and stratification processes. In contrast, the upstream sampling site in the Petang River (site 2) exhibited a clearer distinction between the dry and monsoon months, based on its cyanophyte and diatom floral assemblages. These study results are pertinent for lake management, especially for developing biomonitoring programmes or lake productivity studies, as well as for climate change studies, within the context of tropical lake ecology.     

Benthic invertebrates community of the River Euphrates upstream and downstream sectors of Al-Qadisia dam,Iraq

The benthic fauna of the river Euphrates upstream and downstream sectors of Al-Qadisia dam, mid Iraq, was studied for a period of two years (1993 and 1994). Five sampling stations were selected. One station was located upstream the dam, while the other four stations were downstream. A total of 65 taxa were identified. It was clear that the station located immediately downstream (station 2) showed the highest total mean annual density (individuals/m²) represented by higher number of taxa. The benthic community was dominated by oligochaetes especially of families Naididae and Tubificidae as well as chironomid larvae of which the genus Polypedilum was the most dominant one. Seasonal fluctuation of the community showed that the peak of the total number of individuals had appeared during autumn and winter months. Community index of similarity (ISE) was computed for faunal comparison between station 1 and the other stations. © 1998 John Wiley & Sons, Ltd.     

Identification of Priority Areas for the Conservation of Stream Fish Assemblages: Implications for River Management in France

Financial and human resources allocated to biodiversity conservation are often limited, making it impossible to protect all natural places, and priority areas for protection must be identified. In this study, we applied ecological niche models to predict fish assemblages in the stream network of France. Four non‐correlated conservation objectives were derived from these species assemblages: taxonomic diversity, functional diversity, natural heritage importance and socio‐economic value. We proposed a multi‐objective prioritization method based on the Pareto optimality principle to rank the planning units (i.e. 6097 subcatchments) according to their inherent trade‐offs between the four conservation objectives. Four types of hydrosystems of great conservation importance presenting specific fish assemblages were identified: (i) the most upstream areas of large catchments; (ii) the most downstream areas of large catchments; (iii) the small coastal catchments of the English Channel and the Atlantic Ocean; and (iv) the Mediterranean streams of medium altitude. The fish assemblages characterizing these hydrosystems were complementary and representative of the entire fish fauna of France. Most of these priority subcatchments were found to be practically suitable for the implementation of conservation actions, which is very promising for the protection of river biodiversity. Copyright © 2016 John Wiley & Sons, Ltd.     

Phytoplankton Composition,Abundance, and Distribution: Nearshore Lake Ontario and Oswego River and Harbor

Phytoplankton samples were collected during July, August, and October of 1981 from 16 stations located in the nearshore of Lake Ontario and in the Oswego Harbor and river. Phytoplankton assemblages observed represented many species widely recognized as associated with eutrophic environments and environments possessing high chloride levels. Picoplankton and diatoms were the dominant groups on a numerical and bioyolume basis, respectively. The eutrophic species Stephanodicus tenuis, Fragilaria capucina, and Scenedesmus spp. were present in the Oswego Harbor and river with substantially higher abundances than in the nearshore region of Lake Ontario. A decrease in abundance of the historically prevalent Asterionella and Tabellaria and an increase in cryptomonads is suggested for the Oswego area. Halophilic species dominated the diatom assemblage of the Oswego Harbor and mouth of the Oswego River. The abundance of halophilic species was correlated with high conductivity and chloride levels. Cyclotella atomus, Cyclotella cryptica, and Cyclotella meneghiniana, the dominant halophilic species at the harbor and river stations, accounted for 36.6% of the total diatom abundance.     

国内梯级泵站调水工程运行调度综述

简析调水工程梯级泵站运行时的安全可靠性与经济性问题,综述国内梯级泵站调水工程运行调度研究的进展,并提出了需要进一步研究的问题:①加强梯级泵站调水工程运行调度的计算机仿真研究;②开展提高梯级泵站实时调度自动化水平的研究。