Substrate Particle Size Research Articles

Process optimization of dry batch anaerobic digestion of municipal solid waste

Optimizing anaerobic digestion aims to maximize organic waste stabilization at shortdigestion period with higher biogas production. This paper presents different strategies tooptimize the anaerobic digestion of organic fraction of municipal solid waste in combinedprocess in which early flushing and microaeration were conducted during pre-stage, Also, theinfluence of substrate particle size reduction and the advantage of thermophilic system overmesophilic in the overall digestion process are presented, Additionally, an attempt was takento employ sequential staging concept by using a mature (old) reactor which underwent acombined digestion process. Importantly, process evaluation between an optimized combinedprocess and sequential staging concept were evaluated with the main objective of optimizingthe process, Process efficiency evaluation was based on biochemical methane potential(BMP) test The overall result suggest that the combined anaerobic digestion process can beoptimized by conducting shorter duration of pre-stage at reduced volume of flushing waterwith microearation, under thennophilic condition at reduced substrate particle size of 30 mm,Nevertheless, the sequential staging concept offers an improved operation over the combinedanaerobic digestion wherein the higher specific methane yield of 11.9 L CH4/kg VS.day wasachieved, Improved waste stabilization with 86% and 79% mass and volume reduction whichcorresponds to 84% process efficiency was obtained by sequential staging process,

Selection of a spawning aggregation site by Chromis hypsilepis (Pisces: Pomacentridae): habitat structure, transport potential, and food availability

Spawning aggregations form when fishes migrate to a site from their normal feeding grounds and form temporary groupings for breeding. Spawning aggregation sites are spatially rare, and demonstrating differences between a spawning aggregation site and unselected sites nearby is the first step towards understanding the benefits provided by the aggregation site. Chromis hyp- silepis (Pomacentridae) is a demersally spawning reef fish, one population of which reproduces in a large, single aggregation at a rocky reef off the central coast of New South Wales, Australia. This study compared the habitat structure (rugosity, reef slope, substratum particle size, and abundance of preferred spawning microhabitat) of the spawning aggregation site and several non-spawning sites, and tested the hypotheses that the spawning aggregation site provided greater off-reef larval transport and prey availability for brooding males. Substratum rugosity was significantly greater and the preferred spawning microhabitat was significantly more abundant at the spawning aggregation site. Reef relief and substratum particle size were not significantly different from non-spawning sites. Passively drifting surface current drogues released at the spawning aggregation site were more rapidly transported off the reef, but did not travel further or faster, than drogues released at a non- spawning site over a 12 h period. Biomass of the preferred prey (copepods of 0.441 to 1.49 mm equiv- alent spherical diameter) was not significantly greater, but was less variable, at the spawning aggre- gation site.

Sand as a medium for transmission of vibratory signals of prey in antlions Euroleon nostras (Neuroptera: Myrmeleontidae)

Abstract European pit‐building antlions (Euroleon nostras/ Geoffroy in Fourcroy/) detect their prey by sensing the vibrations that prey generate during locomotory activity. The behavioural reactions and some of the physical properties of substrate vibrations in sand are measured to observe signal transmission through the substrate. The frequency range of the signals of four arthropod species (Tenebrio molitor, Pyrrhocoris apterus, Formica sp. and Trachelipus rathkei) is 0.1–4.5 kHz and acceleration values are in the range 400 μm s−2 to 1.5 mm s−2. Substrate particle size and the frequency of prey signals both influence the propagation properties of vibratory signals. The damping coefficient at a frequency 300 Hz varies from 0.26 to 2.61 dB cm−1 and is inversely proportional to the size of the sand particle. The damping coefficient is positively correlated with the frequency of the pulses. Vibrations in finer sand are attenuated more strongly than in coarser sand and, consequently, an antlion detects its prey only at a short distance. The reaction distance is defined as the distance of the prey from the centre of the pit when the antlion begins tossing sand as a reaction to the presence of prey. The mean reaction distance is 3.3 cm in the finest sand (particle size ≤ 0.23 mm) and 12.3 cm in coarser sand (particle size 1–1.54 mm). The most convenient sands for prey detection are considered to be medium particle‐sized sands.

Micro-benthic crustacean communities in tundra lakes of North-East European Russia

We studied micro-benthic copepods and cladocerans in the bottom substrates of 12 lakes in the Bol’shezemel’skaya tundra in North-East European Russia during the summer. About 30 species of Cladocera and 28 species and subspecies of Copepoda were found. The majority of the micro-crustaceans are palaearctic or northern palaearctic. But the harpacticoid fauna of the western part of the studied region had specific European features, and three species of the harpacticoid fauna in the eastern part of the region were Siberian. It is therefore a boundary territory for two zoogeographical regions, the arctic and subarctic zones. Acidophilic (Arcticocamptus arcticus (Lilljeborg 1902)) and halophilic (Microsetella norvegica (Boeck 1864)) harpacticoid species were found in the lakes of the eastern part of Bol’shezemel’skaya tundra. On basis of their way of locomotion we distinguished five ecological groups and on basis of their feeding habits four ecological groups of micro-crustaceans. Groups with a similar way of locomotion were likely distributed over the studied water bodies. Habitat (inshore versus offshore), substrate particle size and substrate hardness were of paramount importance for the species distribution.

Review of the effects of in-stream pipeline crossing construction on aquatic ecosystems and examination of Canadian methodologies for impact assessment

Pipeline crossing construction alters river and stream channels, hence may have detrimental effects on aquatic ecosystems. This review examines the effects of crossing construction on fish and fish habitat in rivers and streams, and recommends an approach to monitoring and assessment of impacts associated with these activities. Pipeline crossing construction is shown to not only compromise the integrity of the physical and chemical nature of fish habitat, but also to affect biological habitat (e.g., benthic invertebrates and invertebrate drift), and fish behavior and physiology. Indicators of effect include: water quality (total suspended solids TSS), physical habitat (substrate particle size, channel morphology), benthic invertebrate community structure and drift (abundance, species composition, diversity, standing crop), and fish behavior and physiology (hierarchy, feeding, respiration rate, loss of equilibrium, blood hematocrit and leukocrit levels, heart rate and stroke volume). The Before-After-Control-Impact (BACI) approach, which is often applied in Environmental Effects Monitoring (EEM), is recommended as a basis for impact assessment, as is consideration of site-specific sensitivities, assessment of significance, and cumulative effects.

Lake sturgeon spawning on artificial habitat in the St Lawrence River

Summary In 1996, lake sturgeon (Acipenser fulvescens) spawning was documented for the third consecutive year on an artificially placed gravel bed in the St Lawrence River. Two distinct spawning periods were observed in 1996. Spawning initially commenced on 17 June, when water temperature reached 15°C. A second spawning event was documented from 28 June to 1 July (16°C). Sturgeon egg densities were monitored in three transects on egg trays, on the gravel surface, and within interstitial spaces in the gravel. Counts of developing eggs in the gravel bed during both spawning periods were used to estimate a total of 275 000 eggs on the study area (0.075 ha). Average egg density was highest in the transect with the highest water velocities. Lake sturgeon fry were first observed in the gravel on 24 June (15.5°C), and first emergence from the gravel was documented on 28 June. Hatching following the second spawning event commenced on 3 July. Based on assessment of average embryo viability (61.6%) and egg-to-emergent fry survival (17.6%) an estimate of about 171 000 sturgeon eggs hatched, producing over 49 000 emergent fry. Current velocity, substrate particle size, depth of substrate, and maintenance of sediment-free interstitial spaces are important considerations in planning future spawning habitat enhancement projects.

Two lowland stream riffles – linkages between physical habitats and macroinvertebrates across multiple spatial scales

The physical structure of two riffles in a lowland Danish stream was studied and its importance for the composition and density of the macroinvertebrate communities was evaluated. The two riffles were visually assessed to be very similar, but measurements revealed that they differed in overall hydraulic conditions, stability, substratum composition and consolidation. Differences affected abundance of both burrowing and surface dwelling macroinvertebrates. The unstable unconsolidated riffle had higher total macroinvertebrate abundance (4137 m−2 vs. 1698 m−2), diptera abundance (2329 m−2 vs. 386 m−2) and total estimated species richness (31.7 vs. 28.8) as well as lower evenness (0.77 vs. 0.83) than the compact riffle. Among samples within the unconsolidated riffle, variations in macroinvertebrate communities were related to differences in mean substratum particle size. Here a linear log–log relationship existed between macroinvertebrate abundance, the abundance of EPT taxa and the median particle size (r 2 total = 0.46, p = 0.002; r 2 EPT = 0.73, p < 0.001). No similar relationships were evident on the consolidated riffle. Moreover, macroinvertebrate communities on the unconsolidated riffle were dominated by species with a high colonising potential. Despite being assessed to the same morphological unit, physical variation between riffles was surprisingly high as the riffles differed substantially with respect to consolidation, substratum heterogeneity and overall hydraulic structure. Macroinvertebrate community structure and composition also differed between riffles despite being drawn from the same species pool. The findings address the question if we use the correct methods and parameters when assessing the macroinvertebrate communities at the scale of the morphological unit.

Effect of particle size based separation of milled corn stover on AFEX pretreatment and enzymatic digestibility

Particle size and compositional variance are found to have a substantial influence on ammonia fiber explosion (AFEX) pretreatment and enzymatic hydrolysis of lignocellulosic biomass. Corn stover was milled and fractionated into particle sizes of varying composition. The larger particle size fractions (rich in corn cob and stalk portions) were found to be more recalcitrant to hydrolysis compared to the smaller size fractions (rich in leaves and husk portion). Electron spectroscopy for chemical analysis (ESCA) and Fourier transform infrared spectroscopy (FTIR) were used for biomass surface and bulk compositional analysis, respectively. The ESCA results showed a 15-30% decrease in the O/C (oxygen to carbon) ratio after the pretreatment indicating an increase in the hydrophobic nature of biomass surface. FTIR results confirmed cleavage of the lignin-carbohydrate complex (LCC) for the AFEX-treated fractions. The spectroscopic results indicate the extraction of cleaved lignin phenolic fragments and other cell wall extractives to the biomass surface upon AFEX. Water washing of AFEX-treated fractions removed some of the hydrophobic extractives resulting in a 13% weight loss (dry weight basis). Phenolic content of wash stream was evaluated by the modified Prussian blue (MPB) method. Removal of ligno-phenolic extractives from the AFEX-treated biomass by water washing vastly improved the glucan conversion as compared to the unwashed samples. Reduction in substrate particle size was found to affect the AFEX process and rate of hydrolysis as well. Implications of the stover particle size, composition, and inhibitory role of the phenolic fragments on an integrated biorefinery are discussed.

Springs of the Alps – Sensitive Ecosystems to Environmental Change: From Biodiversity Assessments to Long-term Studies

The main aim of the present review is to synthesise the present level of knowledge on the hydrobiology of springs in the Alps. Springs are usually small, but complex and taxa rich. They have a mosaic structure, a high degree of individuality and an azonal character, due to the peculiar physicochemical stability. Springs are ecotones linking an aquifer to the uppermost section of a surface running water system. Due to adaptations, of which stenothermy is the most frequent, representatives of many groups of plants and animals have in springs their exclusive (crenobionts) or favourite (crenophiles) habitat. This leads to a peculiar longitudinal distribution of organisms. In spite of this complexity, springs (in particular high elevation springs of the Alps) have received much less attention than other types of inland waters. They are endangered habitats, being menaced by a series of direct impacts (primarily water abstractions) and indirect impacts. The classical Steinmann–Thienemann ecomorphological types are still used with differences in the physical and chemical characteristics and in the biota. In the Alps rheocrene springs (where current velocity is one of the most relevant factors and the importance of the fringing semi-aquatic habitats is reduced) are the most frequent. However, in nature, most springs are transition types among the three traditional ones and these can now be assessed thanks to procedures considering mainly the substrate particle size. The physicochemistry of springs is characterised by limited seasonal fluctuations and determined by the characteristics of the aquifer and by indirect (especially airborne contaminants) and direct impacts. Many groups of organisms are well represented and include indicators of the trophic and acid–base status, of hydrogeology, hydrological stability and biological integrity. The groups with the highest proportions of specialised taxa are mosses, water mites, dipterans, hydrobioid snails and caddisflies. Attempts are being made to add to the traditional spring types hydrochemistry and vegetation and to the regional faunistic types, diatom-based types, to combine different approaches and to consider also functional ones, such as the distinction between POM and mosses’ springs. Given the high proportion of spring-specific taxa, we propose to use the zoobenthos, especially water mites, for an evaluation of the biological integrity of springs, whilst autotrophs, and in particular diatoms, which are the most widespread and taxa-rich group, can provide excellent indicators of eutrophication, acidification and ionic strength. This would require the calibration of the most promising diatom-based procedures to the spring environment and improvement of the knowledge on the taxonomy and distribution of key zoobenthos groups in the Alps. Other areas where further research is required are the definition of integrated spring-types, the potential for recovery of autotrophs in restored springs, functional aspects, the applicability of paleolimnological techniques to springs and the link between impacts on the drainage basin and spring environmental quality. Only once the importance of springs can be understood and effective conservation measures are undertaken, will it be possible to use these peculiar environments characterised by stability and by integration in time and space of direct and indirect impacts as ideal study sites for long-term ecological research.

Study of the grain size, particle size and roughness of substrate in relation to the magnetic properties of electroplated permalloy

In this work, the substrate grain size effect on the deposition of Ni 79Fe 21 film by electroplating has been studied. The morphology, surface roughness, particle size and magnetic properties of the deposited films are investigated in detail. The investigation shows that the grain size of the deposited films scales with the increase of the substrate grain size. It has shown that the surface roughness of the substrate is of importance. The smoother the substrate surface, the smaller the surface roughness and material coercivity of the deposited Ni 79Fe 21 film. This study indicates that the smoothness and uniformity of the substrate surface are important parameters to be taken into account during electroplating. Under such consideration, Ni 81Fe 19/Cu composite wire has been deposited by sputtering a layer of Cu on the Cu substrate surface to improve Cu wire surface smoothness and uniformity. It is found that with the sputtered Cu layer, the GMI effect of the deposited Ni 81Fe 19/Cu composite wire has been significantly increased.

HABITAT USE BY NATIVE AND STOCKED TROUT (SALMO TRUTTA L.) IN TWO NORTHEAST STREAMS, PORTUGAL

Habitat use by stocked and native brown trout (Salmo trutta L.) was assessed in two headwater streams of North-eastern Portugal. Underwater observations were made during the summer season in three successive years to evaluate the effect of supplemental trout stocking. Multivariate analysis techniques applied to data sets on microhabitat use were exploited to identify the focal elevation (distance of fish from the bottom), total depth and cover as the variables that contribute most to the discrimination between stocked and native trout. Preference curves computed for native and stocked trout of the same age (1+), showed a distinct pattern in their ability to explore the available microhabitat resources. Stocked trout tended to occupy deeper pools (total depth > 100 cm vs. 60-100 cm for native trout), holding higher focal elevations (140-160 cm vs. < 20 cm for native) with lower water column velocities (< 10 cm.s-1 vs. 10-20 cm.s-1 for native) and no specific preference for cover. In contrast, native trout displayed a clear preference for microhabitats with coarse substrate (particle size > 22.5 cm) and cover (combination of boulders and overhanging vegetation or undercut banks). Furthermore, a high poststocking movement of 80% hatchery-reared fish was verified just one month after their release, suggesting that stocking did not contribute to the sustainable populations in either stream, and is far from being an adequate management technique.

Functional biodiversity of macroinvertebrate assemblages along major ecological gradients of boreal headwater streams

Summary1. Biodiversity–environment relationships are increasingly well‐understood in the context of species richness and species composition, whereas other aspects of biodiversity, including variability in functional diversity (FD), have received rather little rigorous attention. For streams, most studies to date have examined either taxonomic assemblage patterns or have experimentally addressed the importance of species richness for ecosystem functioning.2. I examined the relationships of the functional biodiversity of stream macroinvertebrates to major environmental and spatial gradients across 111 boreal headwater streams in Finland. Functional biodiversity encompassed functional richness (FR – the number of functional groups derived from a combination of functional feeding groups and habit trait groups), FD – the number of functional groups and division of individuals among these groups, and functional evenness (FE – the division of individuals among functional groups). Furthermore, functional structure (FS) comprised the composition and abundance of functional groups at each site.3. FR increased with increasing pH, with additional variation related to moss cover, total nitrogen, water colour and substratum particle size. FD similarly increased with increasing pH and decreased with increasing canopy cover. FE decreased with increasing canopy cover and water colour. Significant variation in FS was attributable to pH, stream width, moss cover, substratum particle size, nitrogen, water colour with the dominant pattern in FS being related to the increase of shredder‐sprawlers and the decrease of scraper‐swimmers in acidic conditions.4. In regression analysis and redundancy analysis, variation in functional biodiversity was not only related to local environmental factors, but a considerable proportion of variability was also attributable to spatial patterning of environmental variables and pure spatial gradients. For FR, 23.4% was related to pure environmental effects, 15.0% to shared environmental and spatial effects and 8.0% to spatial trends. For FD, 13.8% was attributable to environmental effects, 15.2% to shared environmental and spatial effects and 5% to spatial trends. For FE, 9.0% was related to environmental variables, 12.7% to shared effects of environmental and spatial variables and 4.5% to spatial variables. For FS, 13.5% was related to environmental effects, 16.9% to shared environmental and spatial effects and 15.4% to spatial trends.5. Given that functional biodiversity should portray variability in ecosystem functioning, one might expect to find functionally rather differing ecosystems at the opposite ends of major environmental gradients (e.g. acidity, stream size). However, the degree to which variation in the functional biodiversity of stream macroinvertebrates truly portrays variability in ecosystem functioning is difficult to judge because species traits, such as feeding roles and habit traits, are themselves strongly affected by the habitat template.6. If functional characteristics show strong responses to natural environmental gradients, they also are likely to do so to anthropogenic environmental changes, including changes in habitat structure, organic inputs and acidifying elements. However, given the considerable degree of spatial structure in functional biodiversity, one should not expect that only the local environment and anthropogenic changes therein are responsible for this variability. Rather, the spatial context, as well as natural variability along environmental gradients, should also be explicitly considered in applied research.

Substrate particle size affects pit building decision and pit size in the antlion larvae Euroleon nostras (Neuroptera: Myrmeleontidae)

Abstract. The larvae of the antlion Euroleon nostras are pit‐builders, constructing pitfall traps in loose sand. The number of pits and the pit diameter are recorded when larvae are kept in substrates with different particle sizes. The most convenient pit‐building sand fractions are two fractions with fine sand (≤ 0.23 mm; 0.23–0.54 mm). The largest pits are constructed in sand with a particle size of 0.23–0.54 mm. In this sand fraction, larvae of all three instars most readily build pits. No pits are constructed in sand with a particle size greater than 1.54 mm. First‐ and second‐instar larvae avoid building pits in substrates of particle size 1–1.54 mm, but third‐instar larvae construct pits in this sand fraction. It is assumed that the antlion is capable of distinguishing between substrate types and this hypothesis is tested by giving larvae the choice of building a pit in one of four particle‐size fractions. Larvae of all three instars prefer to build pits in the fraction with a particle size of 0.23–0.54 mm. Only third‐instar larvae build pits in all four fractions, but only occasionally in the coarser fraction.

Predicting microhabitat selection in juvenile Atlantic salmon Salmo salar by the use of logistic regression and classification trees

Summary1. We compared the capacity of logistic regression (LR) and classification tree (CT) models to predict microhabitat use and the summer distribution of juvenile Atlantic salmon, Salmo salar, in two reaches of a small stream in eastern Quebec.2. The models predicted the presence or absence of salmon at a location on the basis of habitat features (depth, current velocity, presence of instream and overhead cover, substratum particle size, and distance to stream bank) measured at that location. Models were validated by means of crossover field tests evaluating the performance of models developed for one reach (calibration trials) when applied to the other reach (validation trials). Model performance was evaluated with regard to accuracy, generality and ease of use and interpretation. Prediction maps based on habitat features were also built to compare the observed position of fish with those predicted by LR and CT models.3. The spatial distribution of active fish differed markedly from that of resting fish, apparently as a result of the selection for water greater than about 30 cm depth by active fish and for the presence of rocky cover by resting fish.4. All models made accurate predictions, validated by crossover trials. For both LR and CT models, the prediction maps reflected well the actual fish distributions. However, CT models were easier to build and interpret than LR models. CT models also had less variable performance and a smaller decline in predictive capability in crossover trials (for fish at rest), suggesting that they may be more transferable than LR models.

Do instream habitat variables and the abundance of brown troutSalmo trutta(L.) affect the distribution and growth of stone loach,Barbatula barbatula(L.)?

Abstract – Along a stream, we investigated whether the abundance of stone loach (Barbatula barbatula, L.) was related to the presence of brown trout (Salmo trutta, L.) and instream habitat variables. First, a field survey was carried out where different habitat variables and the densities of both species were quantified and subjected to principal components analysis. Then the abundance of stone loach was related to the scores of the retained axes (eigenvalues &gt;1). The abundance of stone loach was positively correlated to substrate particle size, amount of shade, temperature, discharge and current velocity, but negatively correlated to brown trout abundance. Secondly, a month‐long field enclosure experiment in a stream was performed to test for any negative effects of brown trout on stone loach growth. Four treatments were used: intraspecific competition (stone loach at double density), interspecific competition (stone loach + small trout), predation (stone loach + large trout) and a control (stone loach alone). The results showed that large trout tended to have negative effects on final stone loach biomass. The absence of a negative effect of large trout on resource density suggests that nonlethal effects rather than resource competition caused this trend.

Microdistribution of chironomids (Diptera: Chironomidae) in Alpine streams: an autoecological perspective

Chironomid communities from three glacial and three non-glacial high mountain streams in three Alpine river basins were analyzed (Conca, Niscli, Cornisello, NE Italy, 46° N, 10° E). Eighteen sampling reaches belonging to five stream types (kryal, subkryal, glacio-rhithral, kreno-rhithral, outlet) were investigated. At each reach, geomorphological, physical, chemical and biological data were collected. Field surveys were carried out during three periods per year from 1996 to 1998: immediately after spring snowmelt, in mid-summer and in early autumn. In all, 439 zoobenthos samples were collected from 5 to 10 microhabitats of 0.1 m2 in each reach and date using a standard pond net (mesh size of 250 μm). About 50% of individuals collected were chironomids (26 673 specimens, 53 taxa), with densities ranging from 4 to 2652 ind m−2. With few exceptions, they dominated as number of taxa and individuals in all reaches. Chironomid subfamilies Diamesinae and Orthocladiinae were most abundant, especially in glacial reaches, where Diamesa spp. constituted up to 100% of the total fauna. Chironomid distribution was analyzed in relation to 37 abiotic variables, referring to stream origin, hydrology, geomorphology, physics and chemistry. Diamesa steinboecki, D. latitarsis gr. A and Pseudokiefferiella parva were the taxa best associated with ‘glacial’ conditions (i.e. high channel instability or presence of bedrock, high suspended solids and total phosphorous content, low conductivity and silica content, highly variable diel discharge and low mean temperature), while Pseudodiamesa branickii, Corynoneura spp., Eukiefferiella spp., Parorthocladius nudipennis, Tvetenia calvescens/bavarica, Thienemaniella spp. and Micropsectra atrofasciata were mostly associated with ‘non-glacial’ conditions. Substratum particle size, water depth, current velocity, the presence of riffles/pools and of mosses/algae (Hydrurus foetidus) were the major factors affecting microdistribution of chironomids in the investigated streams.

Effects of stream flow intermittency on riparian vegetation of a semiarid region river (San Pedro River, Arizona)

The San Pedro River in the southwestern United States retains a natural flood regime and has several reaches with perennial stream flow and shallow ground water. However, much of the river flows intermittently. Urbanization-linked declines in regional ground-water levels have raised concerns over the future status of the riverine ecosystem in some parts of the river, while restoration-linked decreases in agricultural ground-water pumping are expected to increase stream flows in other parts. This study describes the response of the streamside herbaceous vegetation to changes in stream flow permanence. During the early summer dry season, streamside herbaceous cover and species richness declined continuously across spatial gradients of flow permanence, and composition shifted from hydric to mesic species at sites with more intermittent flow. Hydrologic threshold values were evident for one plant functional group: Schoenoplectus acutus, Juncus torreyi, and other hydric riparian plants declined sharply in cover with loss of perennial stream flow. In contrast, cover of mesic riparian perennials (including Cynodon dactylon, an introduced species) increased at sites with intermittent flow. Patterns of hydric and mesic riparian annuals varied by season: in the early summer dry season their cover declined continuously as flow became more intermittent, while in the late summer wet season their cover increased as the flow became more intermittent. Periodic drought at the intermittent sites may increase opportunities for establishment of these annuals during the monsoonal flood season. During the late summer flood season, stream flow was present at most sites, and fewer vegetation traits were correlated with flow permanence; cover and richness were correlated with other environmental factors including site elevation and substrate nitrate level and particle size. Although perennial-flow and intermittent-flow sites support different streamside plant communities, all of the plant functional groups are abundant at perennial-flow sites when viewing the ecosystem at broader spatial and temporal scales: mesic riparian perennials are common in the floodplain zone adjacent to the river channel and late-summer hydric and mesic annuals are periodically abundant after large floods. Copyright © 2005 John Wiley & Sons, Ltd.

Effect of a saponin-based surfactant on water absorption, processing characteristics and in vitro ruminal fermentation of barley grain

The effects of a saponin-based surfactant on tempered barley grain were studied in three in vitro experiments. In Experiment 1, barley kernels were tempered at 220 or 246 g/kg moisture with surfactant included at 0, 60 or 120 μl/kg dry matter (DM). Surfactant increased ( P < 0.05) the rate of water uptake during the initial 2 h of tempering, but not if tempering was extended beyond 4 h. Experiment 2 evaluated effects of surfactant on barley grain processing characteristics. Surfactant was included at 0, 60, 120, or 240 μl/kg DM during tempering of barley (190 g/kg moisture; 2 or 4 h), then the barley was processed with rollers set 2.032, 2.223 or 2.413 mm apart. Surfactant did not affect ( P > 0.05) the processing index (PI) of the barley or the particle size distribution. Increasing the roller distance from 2.032 to 2.413 mm increased ( P < 0.05) the PI and the proportion of particles with 3.35–4.75 mm diameter, and reduced ( P < 0.05) the proportions of particles larger than 4.75 mm or smaller than 2.36 mm. No surfactant × roller distance interactive effects on processing characteristics were observed. In Experiment 3, barley was tempered (190 g/kg moisture; 2 h) with surfactant at 0 or 120 μl/kg DM and processed with rollers at 2.032 or 2.413 mm, then incubated in batch culture with surfactant supplemented at 0 or 360 μl/kg DM. Apparent in vitro dry matter digestibility (IVDMD) and gas production were higher ( P < 0.01) with rollers at 2.032 mm than at 2.413 mm. Irrespective of substrate particle size, applying surfactant during tempering and/or prior to incubation reduced ( P < 0.05) the 4 h IVDMD, accumulation of volatile fatty acids (VFA) and reducing sugars, and molar percentage of acetic acid in the VFA, but it increased ( P < 0.05) the molar percentage of butyric acid. The acetate:propionate ratio at 4 h was reduced ( P < 0.05) by surfactant applied during (120 μl/kg DM) and/or after (360 μl/kg DM) tempering if the barley had been rolled at 2.032 mm, but at 2.413 mm roller spacing this effect on acetate:propionate was observed only with the maximum application of surfactant (120 + 360 μl/kg DM). Despite enhancing the initial rate of water absorption by barley kernels, surfactant applied during tempering did not affect the processing characteristics of barley. Added during or after tempering, surfactant reduced the extent of IVDMD measured at 4 h, but not at 24 h.

The effect of instream rehabilitation structures on macroinvertebrates in lowland rivers

Summary Many lowland rivers in Western Europe have been substantially modified to aid land drainage and support the intensification of agriculture. Although there have been many attempts at rehabilitation, few have been systematically evaluated on ecological criteria. Macroinvertebrates were assessed in 13 UK lowland rivers containing instream rehabilitation structures, seven with artificial riffles (intended to mimic natural gravel riffles) and six with flow deflectors (intended to increase flow, depth and substrate heterogeneity within the channel). In each river, invertebrates were compared between stretches of river with and without rehabilitation structures. Rehabilitated and reference stretches were subdivided into different benthic and macrophyte habitats. Three macroinvertebrate samples were taken once in July/August 1999 from each habitat across all schemes and rivers. Current velocity, depth and substratum particle size were recorded at the same time from each habitat. Artificial riffle benthos had faster current, a coarser substratum and was shallower than reference benthos. Depth and substratum particle size differed little between flow deflector and reference benthos, although velocity downstream of the deflector tip was greater, and velocity in the lee of the deflector lower, than reference benthos. At a habitat scale, the benthos of artificial riffles, but not flow deflectors, had higher abundance, taxon richness and diversity than reference benthos. The impact of artificial riffles was most marked for benthic rheophilic taxa. In all rivers, macroinvertebrate diversity was highest in marginal macrophytes and abundance highest in instream macrophytes. Although invertebrate communities were distinct between artificial riffle (but not flow deflector) and reference benthos, these differences were negligible in comparison to those between benthic and macrophyte habitats. Neither artificial riffles nor flow deflectors had any significant impact on the taxon richness of the benthos or of the rehabilitated stretch of the river as a whole. Invertebrate diversity of rehabilitated stretches related closely to that of reference stretches, indicating that larger scale factors constrained any impact of rehabilitation. Synthesis and applications. Local rehabilitation structures appeared to have minor biological effects in lowland rivers. We suggest that post‐project appraisal should be more rigorously applied to rehabilitation schemes, measuring success against more clearly defined goals. We also advocate a greater emphasis on large‐scale riparian, floodplain and catchment rehabilitation, rather than small‐scale channel rehabilitation. Such a change in approach needs more effective cooperation and collaboration between all catchment users.

GRIT-SITE SELECTION OF BLACK BRANT: PARTICLE SIZE OR CALCIUM CONTENT?

We examined selection of grit-ingestion sites by Black Brant ( Branta bernicla nigricans )o n South Humboldt Bay, California in relation to particle size and calcium content. We hypothesized that Brant site selection was dependent primarily upon calcium content and secondarily upon distribution of substrate particle size. We (1) mapped grit-ingestion sites, (2) ranked their importance by Brant abundance and individual movement probabilities between sites, (3) characterized Brant gizzard grit and compared it with grit available at ingestion sites, and (4) compared calcium content and particle-size distribution between ingestion sites and unused sites, and between primary and secondary ingestion sites. Brant repeatedly congregated at specific, discrete sites during the 2 years of observation. The distribution of gizzard-grit particle size was right-skewed toward larger particles ( .0.5 mm) relative to the proportional availability of particle sizes in the substrate. We found no significant differences in calcium content or particle size between sites where grit was ingested and unused sites. Within used sites, the calcium content of substrates at the primary ingestion site was significantly higher than at the secondary ingestion sites, as ranked by Brant abundance and between-site movement proba- bilities. Our findings from the field corroborate previous laboratory results, and confirm that calcium is a sig- nificant ecological factor for this species. Received 14 May 2004, accepted 19 October 2004. Preferred sites for gizzard-grit ingestion may be used faithfully by wild bird popula- tions for many decades (McIlhenny 1932), but site selection of this resource is understudied. It has long been accepted that gizzard grit (hereafter grit) is an essential aid for grinding food (Leopold 1931), and captive birds de- prived of grit experience elevated mortality (McCann 1939). In some waterfowl, amount of grit in the gizzard and size of grit particles are related to diet, with more grit and smaller particles in the gizzards of herbivores com- pared to omnivores and carnivores (Thomas et al. 1977, Skead and Mitchell 1983). Leo- pold (1933) proposed that grit could be a source of mineral calcium for birds. This is well-documented only for Ring-necked Pheas- ant (Phasianus colchicus), a species whose grit consumption is driven primarily by the need for calcium and only secondarily as a grinding material (McCann 1939)—and whose distribution and abundance is influ- enced by the availability of calciferous grit (Leopold 1931; McCann 1939, 1961; Dale