Benthic, Drifting and Marginal Macroinvertebrate Assemblages in a Lowland River: Temporal and Spatial Variations and Size Structure

Aquatic macroinvertebrates living in anastomosing lowland rivers use different habitats and respond differently to the hydrological regime. In this paper, the structure and composition of benthic, drifting and marginal macroinvertebrate assemblages are analyzed in the lowland river Ctalamochita (Córdoba, Argentina). The assemblages were studied in an annual cycle; a comparison among the composition of benthos, drift and marginal fauna was carried out; and size structure of the assemblages was characterized. Samples were obtained from two sites: a rural and an urban site. In total 73 taxa of aquatic macroinvertebrates were collected. Benthos was characterized by Chironomidae and Oligochaeta; marginal fauna was mainly constituted by Coleoptera, Heteroptera, Decapoda, the Trichoptera Nectopsyche sp., Ephemeroptera and Odonata. Drifting assemblage was composed by macroinvertebrates from local and remote upstream benthos, and from the marginal zone. Marginal fauna diversity was higher than benthos and drift. Total biomass of the assemblages pooled together was relatively equitably among size classes. Larger size classes consisted of organisms from the marginal zone whereas the smallest ones were composed by benthic and drifting organisms. In the study area there is habitat partitioning in the lateral dimension of the river. Marginal fauna was more diverse due to the asymmetry of transport and deposit processes, which generate a heterogeneous habitat in the bankside. The relation between fine substrate and high current velocity determines an unstable habitat in the central channel, which makes colonization by benthic macroinvertebrates difficult.     

黑河中游典型土地利用方式下土壤粒径分布及与有机碳的关系

土地利用方式是影响土壤粒径分布、土壤有机碳及其组成含量的重要因素。研究显示:黑河中游典型土地利用类型下,不同土壤粒径分布和土壤总有机碳(TOC)、活性有机碳(AOC)、非活性有机碳(NOC)的含量存在差异。剖面上TOC、AOC、NOC含量较高的旱地、水田、中覆盖度草地与含量较低的戈壁、裸土地、沙地、盐碱地相比,<1μm、1—5μm、5—10μm、10—50μm的粒径含量较高,而50—250μm、250—1000μm的含量较低,这种变化以50μm为分界,分析表明<50μm的粉粒和粘粒可起到固碳作用,而50—250μm、250—1000μm的砂粒起碳损失作用。统计结果表明,以50μm为分界,水田、戈壁、中覆盖度草地剖面上TOC、AOC、NOC与1—5μm、5—10μm、10—50μm呈正相关,与50—250μm、250—1000μm呈负相关。分析发现,粉粒和粘粒与土壤TOC、AOC、NOC的关系较显著,是影响和控制团聚体形成和稳定的重要因素。增加地表植被覆盖度、退化生态系统的植被恢复、农田耕种、防风固沙措施是提高土壤有机碳、粘粒和粉粒含量的方式,也为土壤团聚体的形成和稳定提供基础。     

Establishing the condition of lowland floodplain rivers: a palaeo-ecological approach

1. Current approaches for determining river ‘health’ rely on the establishment of a ‘reference’ condition. This is often difficult to achieve for lowland floodplain river systems because of the lack of pristine or pre-impacted sites and process models capable of predicting the effect of natural and human disturbances. 2. Using examples from the River Murray, Australia, this paper highlights the benefits of using palaeo-ecological studies in deciding on benchmark or pre-European settlement conditions for lowland floodplain river systems. 3. Physical, chemical and biological analyses of sediment obtained from shallow cores (< 2 m) extracted from a variety of floodplain sites on the River Murray and its tributaries reveal the extent and timing of catchment disturbances on this lowland river. Rates of sedimentation have increased by an order of magnitude since settlement; sediments now being deposited are finer, having implications for the nutrient status of the floodplain and the accumulation of heavy metals associated with these sediments. There has also been a sustained drop in the macrophyte cover of billabongs in the area, as inferred by chydorid cladoceran assemblages. The pre-European settlement diatom assemblages do not resemble those presently accumulating in billabongs in the region. 4. Whilst initially developed for lentic studies, palaeo-ecological studies are relevant to the establishment of benchmark conditions for lowland floodplain rivers. They are relatively straightforward, incorporate both historical and contemporary ecological information and can be applied to any lowland system.     

Diel distribution patterns of fishes in a temperate large lowland river

During the day, juveniles and typical inshore species in the lower Oder River, Germany, inhabited the littoral (0·05–1·50 m deep) while potamal species inhabited the mid‐channel (40–100 m from the banks). During the night, two behavioural groups were distinguished: 1) potamal species and large individuals of other species, moved from offshore to the littoral, and 2) nocturnal foraging species, became active and increased in inshore and offshore habitats. Inshore, the most significant differences at night was the increasing density of silver bream Blicca bjoerkna increasing both total biomass and total length of fishes caught. Offshore, the increasing density of whitefin gudgeon Gobio albipinnatus at night was most significant. Additional night electrofishing improved the assessment of the abundance, age and size structure of typical potamal fish species. It should be incorporated in large river fish monitoring programmes.     

Using laser scattering to identify diatoms and conduct aggregation experiments

Laser in situ scattering and transmissometry (LISST) instruments are used to measure particle size distributions (PSDs) and volume concentrations in water. For populations of regularly shaped non-spherical particles, such as phytoplankton, the PSD produces a ‘scattering signature’ that corresponds to the shape of the particles. The objectives of this research were to describe the scattering signatures of six diatom species and to determine whether LISST instruments can be used as a tool to measure the aggregation of diatoms into larger particles. The scattering signatures of Chaetoceros muelleri var. subsalsum, Coscinodiscus wailesii, Thalassiosira weissflogii, Phaeodactylum tricornutum, Skeletonema costatum and S. marinoi were measured. The scattering signatures of individual species were consistent over time in batch culture and there were clear differences between species in terms of peak location, peak width, and relative peak height in the PSD. LISST was used to non-destructively follow the formation of diatom aggregates in the laboratory. Both rolling and warming cultures of S. costatum caused the cell chains to form aggregates, resulting in a change in the PSD, with a shift in peak position towards larger size bins. These experiments showed that the scattering signatures of unaggregated diatom species are conservative and that LISST instruments are useful tools to investigate the factors affecting diatom aggregation and disaggregation, with potential applications both in the laboratory and field.     

Ecological rehabilitation of the lowland basin of the river Rhine (NW Europe)

In this paper, the status of ecological rehabilitation of the Dutch lowland basin of the river Rhine has been reviewed. The historical perspective, mainly with regard to river regulation measures in the past, is given. The lower river Rhine comprises a man-dominated, strongly regulated catchment, polluted water and sediments, and annihilated and deteriorated ecosystems. During the past 25 years, the water quality and, to a lesser extent, the sediment quality, has improved considerably, hence leading to improvement of biotic diversity. The rehabilitation of lost and disturbed ecosystems started some 15 years ago. The non-refutable boundary conditions for restoration projects are protection against flooding and transport by cargo ships. Holistic ecological theories to promote river catchment management are available, but the rehabilitation projects dominantly rely on local and regional planning policies. The use and application of ecological criteria are increasingly playing a role in rehabilitation schemes. Ecological rehabilitation mainly focuses on nature conservation and restoration strategies, i.e. exploiting the hydrodynamic and morphodynamic potentials of the flowing river, and introducing a semi-natural grazing regime by large herbivores. Particularly the creation of new secondary channels contributes to the restoration of riverine habitat diversity and heterogeneity, and hence to the species diversity. The assessment of a number of rehabilitation projects has led to the conclusion that no general statement can be given concerning `success' or `failure' of specific restoration measures. The overall balance of 14 assessed projects out of approximately 30 running projects is positive. The highly dynamic river Waal offers the best possibilities for the restoration of natural sandy levees and back swamps. It will be very difficult to rehabilitate the hardwood floodplain forests under the present management conditions. Further recovery of the river biota depends on continued decrease of pollution, an increase of morphological dynamics, and the development of the original natural habitats.     

Composition and structure of phytoplankton in lowland rivers of the upper Ob basin

Taxonomic composition and structure of the phytoplankton were studied in the lowland rivers of the upper Ob basin: Barnaulka, Bol’shaya Losikha, and lower Inya. It has been shown that the phytoplankton of a large river system in Eurasia, exemplified by the Ob basin, is characterized by spatial heterogeneity in its taxonomic composition.     

Modelling the impact of benthic filter-feeders on the composition and biomass of river plankton

SUMMARY 1. The POTAMON model [Everbecq E. et al . (2001) Water Research , 35 , 901] has been used to simulate the effect of benthic bivalves (mainly Dreissena polymorpha ) on the phytoplankton and zooplankton in a lowland Western European river (the Moselle). Here we use a modified version of the POTAMON model with five categories of phytoplankton ( Stephanodiscus , Cyclotella -like, large diatoms, Skeletonema and non-siliceous algae) to model filter-feeding effects of benthic bivalves in the Moselle. Zooplankton has been represented in the model by two categories, Brachionus -like and Keratella -like rotifers.
2. According to density estimates from field surveys (Bachmann V. et al . (1995) Hydroécologie Appliquée , 7 , 185, Bachmann V. & Usseglio-Polatera P. (1999) Hydrobiologia , 410 , 39), zebra mussel density varied among river stretches, and increased through the year to a maximum in summer. Dreissena filtration rates from the literature were used, and mussels have been assumed to feed on different phytoplankton categories (but less on large and filamentous diatoms) as well as on rotifers.
3. The simulations suggest a significant impact of benthic filter-feeders on potamoplankton and water quality in those stretches where the mussels are abundant, their impact being maximal in summer. Consequently, different plankton groups were not affected to the same extent, depending on their period of development and on indirect effects, such as predation by mussels on herbivorous zooplankton.
4. A daily carbon balance for a typical summer shows the effect of benthic filter-feeders on planktonic and benthic processes: the flux of organic matter to the bottom is greatly enhanced at high mussel density; conversely, production and breakdown of organic carbon in the water column are reduced. Mussel removal would drive the carbon balance of the river toward autotrophy only in the downstream stretches.     

The Abbreviated Impactor Measurement (AIM) Concept: Part II—Influence of Evaporation of a Volatile Component—Evaluation with a “Droplet-Producing” Pressurized Metered Dose Inhaler (pMDI)-Based Formulation Containing Ethanol as Cosolvent

The abbreviated impactor measurement (AIM) concept is a potential solution to the labor-intensive full-resolution cascade impactor (CI) methodology for inhaler aerosol aerodynamic particle size measurement. In this validation study, the effect of increasing the internal dead volume on determined mass fractions relating to aerodynamic particle size was explored with two abbreviated impactors both based on the Andersen nonviable cascade impactor (ACI) operating principle (Copley fast screening Andersen impactor [C-FSA] and Trudell fast screening Andersen impactor [T-FSA]). A pressurized metered dose inhaler-delivered aerosol producing liquid ethanol droplets after propellant evaporation was chosen to characterize these systems. Measures of extrafine, fine, and coarse particle mass fractions from the abbreviated systems were compared with corresponding data obtained by a full-resolution ACI. The use of liquid ethanol-sensitive filter paper provided insight by rendering locations visible where partly evaporated droplets were still present when the “droplet-producing” aerosol was sampled. Extrafine particle fractions based on impactor-sized mass were near equivalent in the range 48.6% to 54%, comparing either abbreviated system with the benchmark ACI-measured data. The fine particle fraction of the impactor-sized mass determined by the T-FSA (94.4 ± 1.7%) was greater than using the C-FSA (90.5 ± 1.4%) and almost identical with the ACI-measured value (95.3 ± 0.4%). The improved agreement between T-FSA and ACI is likely the result of increasing the dead space between the entry to the induction port and the uppermost impaction stage, compared with that for the C-FSA. This dead space is needed to provide comparable conditions for ethanol evaporation in the uppermost parts of these impactors.     

The Abbreviated Impactor Measurement (AIM) Concept: Part 1—Influence of Particle Bounce and Re-Entrainment—Evaluation with a “Dry” Pressurized Metered Dose Inhaler (pMDI)-Based Formulation

The abbreviated impactor measurement concept is a potential improvement to the labor-intensive full-resolution cascade impactor methodology for inhaler aerosol aerodynamic particle size distribution (APSD) measurement by virtue of being simpler and therefore quicker to execute. At the same time, improved measurement precision should be possible by eliminating stages upon which little or no drug mass is collected. Although several designs of abbreviated impactor systems have been developed in recent years, experimental work is lacking to validate the technique with aerosols produced by currently available inhalers. In part 1 of this two-part article that focuses on aerosols produced by pressurized metered dose inhalers (pMDIs), the evaluation of two abbreviated impactor systems (Copley fast screening Andersen impactor and Trudell fast screening Andersen impactor), based on the full-resolution eight-stage Andersen nonviable cascade impactor (ACI) operating principle, is reported with a formulation producing dry particles. The purpose was to investigate the potential for non-ideal collection behavior associated with particle bounce in relation to internal losses to surfaces from which particles containing active pharmaceutical ingredient are not normally recovered. Both abbreviated impactors were found to be substantially equivalent to the full-resolution ACI in terms of extra-fine and fine particle and coarse mass fractions used as metrics to characterize the APSD of these pMDI-produced aerosols when sampled at 28.3 L/min, provided that precautions are taken to coat collection plates to minimize bounce and entrainment.     

Nutrients,Conductivity and Plankton in a Landscape Approach to a Pampean Saline Lowland River (Salado River,Argentina)

Nutrients, conductivity and other physical and chemical parameters were measured seasonally in the main channel and in tributaries of the Salado River basin during the period March 1997–June 1999. The sampling began in a low water period and later included flood events. High water events were associated with high proportions of allochthonous compounds (polyphenols, suspended solids and organic matter). Nutrients and conductivity were related to hydrological conditions and different land uses in the catchment. A relationship was found between the land-use and nutrient concentrations due to the inflow of diffuse sources from agricultural lands. High nutrient concentrations and conductivity recorded in the headwaters were, respectively, related to the intensive agriculture in this area and the inflow of saline groundwater, drained by canals from endorheic basin to the main channel. Their effects on the middle and lower reaches were related to the discharge and inputs of other sub-catchments. Nutrients, sulphates, alkalinity and conductivity declined downstream towards the river mouth. The consequences for the plankton community of these spatio-temporal changes in the chemical characteristics are discussed. The heterogeneity of the Salado River is related to seasonality, land use and the geomorphological features of the basin.     

Effects of removal and regeneration of bankside vegetation on fish population dynamics in the Warta River,Poland

In March 1989 both banks of a 450 m section of the Warta River, 2 km above a reservoir, were cleared of their riparian vegetation (osiers, willows and alders). In October 1988 17 fish species had been recorded there, with a standing crop (SC) of 31.9 kg ha ^–1. In April 1989, the number of species decreased to 11, and their SC to 7.9 kg ha ^–1.Over the next three years new alder trees appeared and osiers regrew to 3.5 m. The SC in October 1990, October 1991 and May 1992 was recorded at 36.5, 66.2 and 40.9 kg ha ^–1, respectively. The primary effect was on phytophils, whose biomass was directly proportional to the height of the trees and osiers (r = 0.87, p = 0.05). The litho-phytophils appeared to occupy the habitat vacated by the phytophils soon after bank clearance (r = –0.87, p = 0.05), but then declined as the osiers grew.     

Size distribution analysis of recombinant adenovirus using disc centrifugation

Recombinant adenovirus is one of the primary vectors for human gene therapy. However, the aggregation of unstable virus has been a recurring problem during the production of purified virus for human therapeutics. To facilitate the development of a robust manufacturing process for recombinant adenovirus vectors, a convenient and reliable size distribution analytical assay is necessary and we demonstrate here that disc centrifuge sedimentation is applicable to this purpose. Using the disc centrifuge system and the line start method, the assay can provide particle size distribution of adenovirus samples within 30 min. The assay can detect virus concentrations down to 0.01% (w/v) or 3 × 10¹¹ particles per ml. The apparent hydrodynamic diameter of recombinant adenovirus was determined to be about 0.063 μm. Furthermore, the disc centrifuge analysis was able to detect adenovirus dimers, trimers, and tetramers, consistent with a rigid sphere approximation for adenovirus, as well as a large aggregate of 0.35 μm. The appearance of viral aggregates is confirmed by increased light scattering based on A₃₂₀/A₂₆₀ ratios. The technique could be useful for monitoring the kinetics of aggregation for adenovirus and other DNA and RNA viruses in the submicron region. Therefore, this novel assay provides a critical tool for purification development of viral vectors for meeting therapeutic and research needs. Received 18 September 1997/ Accepted in revised form 15 May 1998     

Evaluation of the TSI aerosol impactor 3306/3321 system using a redesigned impactor stage with solution and suspension metered-dose inhalers

The purpose of this research was to evaluate a redesigned impactor stage for the TSI Model 3306 Impactor Inlet with nozzles adjusted to obtain a target cut-point of 4.7 μm. It has been determined that the previous cut-point used in the Model 3306 was nominally closer to 4.14 μm, thus potentially impacting the characterization of aerosol mass. The reassessment of the Model 3306 was performed on 4 solution and 2 suspension metered-dose inhaler (MDI) formulations. The redesigned impactor stage resulted in a 5% to 6% increase in aerosol mass when compared with the previous impactor stage for the products Ventolin-HFA, Proventil-HFA, and 2 cyclosporin solution formulations with high ethanol concentrations (15% wt/wt). For the formulations with low ethanol concentrations (3% wt/wt), minimal differences were observed between the 2 cut-points. In addition, this study reevaluated the requirement of a vertical inlet extension length when using the TSI 3306/3321 system with the redesigned cut-point. It was shown that the use of a 20-cm extension provides mass and aerosol size distributions that are comparable to the Andersen 8-stage Cascade Impactor, for both solution and suspension MDIs. This work indicates that the TSI 3306/3321 system is suitable for preformulation studies of both suspension and solution MDI systems. Published: March 10, 2006