The response of epibenthic rotifers and microcrustacean communities to flow manipulations in lowland rivers

Non-flowing, slackwater habitats in lowland rivers support diverse and abundant benthic microfaunal communities; however, there is little information on how these communities respond to changes in hydrology. In this study, we tested two hypotheses: (1) microfaunal richness and density will be higher in slackwater habitats compared to flowing habitats; (2) altering the hydrology of a habitat will result in changes in the richness and density of microfauna over time so that communities will become similar to those found in a habitat with the same flow characteristics. Flowing and slackwater habitats were manipulated by constructing barriers to redirect flows, either away from flowing habitats and creating slackwater habitats, or towards a slackwater creating a flowing habitat. The resultant epibenthic microfaunal communities were compared to those in unmodified slackwaters and flowing habitats. Over a 4-month period, epibenthic microfaunal samples were collected from the four experimental treatments. Analysis of variance indicates that there was no difference in rotifer richness or abundance between habitat types, but significant differences in the richness and abundance of microcrustacean occurred with higher richness and densities occurring in the slackwater habitats compared to flowing habitats. Within four weeks of the treatments being applied, there was little difference in the microfaunal communities between the natural and created flowing habitats or between the natural and created slackwater habitats. As the hydrology of a river varies, slackwater habitats will be scoured and new habitats created. The microfauna populations associated with these habitats appear to have strategies that enable them to cope with the disturbance and to recolonise newly created slackwater areas.     

Description and evaluation of a sampling strategy for macroinvertebrate communities in Basque rivers (Spain)

This paper describes the results of a pilot study on the macroinvertebrate communities occurring in a fast-flowing river in Northern Spain. The objective was to devise a sampling strategy for use on a series of Basque rivers included in a site classification study. Two contrasted sites were chosen for the pilot-study on the River Lea (Bizkaia), at the headwaters and near the mouth. Taxon richness and distribution across the river was examined using two sampling techniques at each site. It was concluded that, ideally, timed sampling units should be collected at intervals across a river transect in order to acquire a representative list of taxa. In addition, adequate sampling in marginal areas was stressed because a number of taxa appeared to be exclusive to marginal areas. Sampling location and total sampling effort were also shown to be a major consideration when taxon lists were acquired for the application of routine biological surveillance techniques.     

Ecological research for the restoration and management of rivers and reservoirs in Japan

In Japan the River Law was amended in 1997 to expand the traditional roles of flood control and water supply in river management to include environmental conservation. Two major multidisciplinary research groups were also founded to address the environmental issues arising from the management of rivers and watershed areas in Japan. One called the River Ecology Research Group was formed in 1995 to search for an ideal dynamic state of rivers to be managed. Six case studies commenced involving measurements of natural and human impacts on representative rivers and their biota selected from different regions of the country. Restoration of natural rivers has also been attempted. The other, called the Watershed Ecology Research Group, was formed in 1998 to study the natural environment surrounding dams. It consists of four groups concerned with forest ecology in the headwaters, raptor management research, reservoir ecology, and flow regime research. The topics include modeling of regeneration dynamics of riparian forests, GIS mapping of endangered raptor habitats, developing measures to reduce eutrophication of reservoir water, and the use of biodiversity of benthic faunas as an indicator of environmental change in the downstream. In both groups, ecologists collaborate with engineers who are responsible for the river infrastructure, to predict future impacts and keep ecological perspectives for the maintenance of the healthy environment of rivers and reservoirs.     

Trends of macroinvertebrate community structure in glacier-fed rivers in relation to environmental conditions: a synthesis

1. Generalized additive models (GAMs) were used to predict macroinvertebrate taxonomic richness and individual taxon diversity at the reach level across seven European glacier-fed river sites from a set of 11 environmental variables. Maximum water temperature and channel stability were found to explain the most deviance in these models.
2. Using this information, and data from other recent studies of glacier-fed rivers, a modified conceptual model based on Milner & Petts (1994) is presented which predicts the occurrence of macroinvertebrate families and subfamilies as determined by maximum water temperature ( T _max) and channel stability. This deterministic model only applies to the summer meltwater period when abiotic variables drive community structure.
3. Where maximum water temperature is below 2 °C, Diamesinae chironomids are typically the sole inhabitants, but where T _max >2 °C but <4 °C Orthocladiinae are found and, where channels are more stable, Tipulidae and Oligochaeta also occur. Above 4 °C Perlodidae, Taeniopterygidae, Baetidae, Simuliidae and Empididae can be expected to be part of the glacier-fed river community, particularly in Europe.
4. At other times of the year when environmental conditions ameloriate, glacial rivers support higher macroinvertebrate abundance and diversity, with a number of taxa present that are not found during the summer melt period.
5. Dispersal constraints influence macroinvertebrate assemblages of many glacier-fed rivers located on islands and in some alpine areas.     

Influence of dam removal on trichopteran assemblages in the lowland Drzewiczka River,Poland

The aim of this study is to assess the response of Trichoptera in a patchy tailwater stretch of the Drzewiczka River (Poland) to dam removal as compared to the previous pulse discharge disturbance. The study was carried out in the river at the end of a whitewater slalom canoeing track located downstream of the dam reservoir called Drzewieckie Lake (area 0.84 km²). Between February and April 2002, the dam reservoir was gradually emptied before its dredging, and the Drzewiczka River recovered its natural discharge (1.7–4.5 m³ s⁻¹) for several years (temporary renaturisation). Altogether, 120 monthly samples of macroinvertebrates and their environments were collected in two sampling cycles, S1 in 2000–2001 during high discharge fluctuations (2.1–12.0 m³ s⁻¹ daily) and S2 in 2002–2003 during renaturisation after emptying the reservoir, from the following five habitats: H_P—pool habitat, H_S—stagnant habitat, H_M—macrophyte habitat, H_B—bank habitat and H_R—riffle habitat. On the basis of trichopteran abundance, the patterns in their assemblages were recognised with use of a self-organising map that was a Kohonen artificial neural network. The obtained classification of trichopteran samples was found to be based in general on the spatial criterion, i.e. dependent on habitats, irrespective of which sampling cycle the samples originated from, which clearly showed that the habitat mosaic of the river bed was observed both in S1 and S2. In addition, a very important function was noted for riparian and land plants, which developed intensively at the bottom of the Drzewieckie Reservoir immediately after it was emptied. They restricted extensive transport of reservoir sediments to the downstream river reach, thus reducing differences between S1 and S2 in the tailwater. It is also worth noting that in S1, in comparison to S2, Cyrnus trimaculatus, Mystacides azurea and Lype reducta flowing downstream from the reservoir were observed more frequently in the river, which confirmed that impoundments can be conducive to the presence of certain species downstream of dams. Summing up, although artificial short-term flow fluctuations usually diminish the quality and quantity of benthos, the article presents a case in which they were small and short enough to allow the formation of a mosaic of bed patches and positively affected certain parameters of macrobenthic communities according to the intermediate disturbance hypothesis. Handling editor: David Dudgeon     

Long-term recovery from mine drainage disturbance of a macroinvertebrate community in the Ichi-kawa River,Japan

The effects of mine drainage on a benthic macroinvertebrate community and its recovery have been investigated for 25 years in the Ichi-kawa River in western Japan, focusing especially on change in community structure. Concentrations of arsenic, copper and zinc in the water were distinctly higher at sites just below the drainage than an upstream reference site before mine closure in 1973. Benthic communities there were severely damaged, as evidenced by reductions in the number of families and biomass. Chironomidae and a mayfly, Epeorus latifolium, predominated at the impacted sites, whereas stenopsychid caddisflies were dominant at the reference site. After mine closure, zinc concentrations significantly decreased downstream, although they remained higher than at the reference site. Following this, family richness and biomass of benthic communities clearly increased. In addition, the percentage of Trichoptera increased and, finally, Stenopsychidae became the dominant family in 1996 at all sites except just below the drainage. Therefore, the dominance of Stenopsychidae at the impacted sites is expected to be an indicator of complete recovery of the benthic community from the effect of mine drainage.     

Spatial and temporal trends in stream macroinvertebrate communities: the influence of catchment disturbance

Macroinvertebrate communities of five headwater streams in catchments disturbed by wildfire were compared with five similar streams with no catchment disturbance. Over the five years of observation, communities in disturbed streams were more similar to one another than they were to reference streams. Communities in disturbed streams exhibited more year-to-year variation than reference streams, although some indication of decreasing variation was evident through time, and species richness was greater in reference streams than disturbed streams. No increasing trend in richness over time was observed in disturbed streams. Stability of the relative abundance structure and persistence of dominant taxa through time may be characteristic of temperate streams over moderate time intervals. Local effects of catchment-wide disturbance have persistent effects that alter these trends.     

Persistence and stability of macroinvertebrate communities in streams of Denali National Park, Alaska: implications for biological monitoring

1. Macroinvertebrate communities were studied from 1994 to 2001/2002 (except 1997) in six streams in Denali National Park, interior Alaska. All six streams were potential reference streams with no known impairment. 2. Abundance of individual taxa varied markedly from year to year. Overall, abundance decreased over the study period, particularly with respect to mayflies. Stonefly taxa showed lower persistence and were sometimes absent from a stream in any particular year. 3. Mean community persistence for the six streams, as measured by Jaccard's similarity coefficients between years, varied from 0.48 in the year pair 1999–2000 to 0.78 in 1998–99. Tattler Creek (a small stable stream) supported the most persistent macroinvertebrate community and Highway Pass Creek (a small, unstable creek) the least. Mean community persistence showed a significant relationship with mean winter snowfall (November to March) for the six streams. 4. The highest community compositional stability was found in Tattler Creek and the lowest in Highway Pass Creek, but stability varied markedly over time for the six streams, peaking in 1994–95 and reaching a minimum in 2000–01. Compositional stability was significantly related to the Pfankuch Index of channel stability. 5. The composition metrics % Chironomidae, % dominant taxa, %EPT, % Ephemeroptera and % Plecoptera, employed as part of the Alaska Stream Condition Index, varied over almost their entire range in these pristine streams across the 9 years of the study. 6. This study demonstrates the wide range of natural variation that occurs in benthic macroinvertebrate communities in these pristine central Alaskan streams, potentially limiting the applicability of composition metrics for the biological monitoring of water quality in these systems.     

Phases in the development of riverine plankton: Examples from the rivers Rhine and Meuse

Observations on phyto and zooplankton in two hydrographically different rivers were compared in order to discriminate phases in plankton development. Along the longitudinal axis of the River Rhine a gradual increase in the development of phytoplankton was observed, which reached its maximumca. 100 km before the river flows into its artificial sedimentation area. The development of rotifer populations was slightly retarded as compared with that of phytoplankton and highest population densities were only reached in the sedimentation area. Crustaceans developed in significant numbers, not until the river water had entered the sedimentation area. Development of zooplankton coincided here with a strong decrease in the density of phytoplankton. A similar trend in plankton development was observed in the River Meuse, although in this river the highest densities of phyto and zooplankton already occurred in its middle reaches. The differences in the timing of plankton growth in the two rivers are probably caused by differences in flow regime between both rivers. The River Rhine, which is fed by rainwater and melting of glaciers in the Alps, has a relatively constant discharge. On the other hand, the low discharge of the rain-fed River Meuse combined with an increased residence time of the water as a consequence of large numbers of weirs, allows a full cycle of plankton development long before its discharge into the sea. This phenomenon was also reflected in the silicate cycle in the Meuse, where the consumption by planktonic diatoms and the regeneration of silicate of deposits seem to be important. In contrast, in the main branches of the River Rhine only the effects of silicate consumption were detectable.     

Ecology of leaf pack macroinvertebrate communities in streams of the Fraser River Basin, British Columbia

1. To characterise geographic and small scale variation in the structure of macroinvertebrate communities in stream leaf packs, we collected one to three natural leaf pack communities from 119 reference streams in the Fraser River Basin and quantified their variability and correlation with aspects of the stream environment at several scales. We also sampled leaf packs in 19 test streams in the same geographic area exposed to stressors (nine logged, seven farmed, three mined catchments) to evaluate the leaf pack community as a tool for bioassessment. 2. There was substantial variation in the composition of invertebrate communities in leaf packs among reference streams of the Fraser River Basin. Capnia and Zapada (stoneflies), Baetis and Ephemerella (mayflies) and Tvetnia (midge) were the most common taxa found in the leaf packs. There were three types of assemblages identified by non‐metric multidimensional scaling; Capnia, Baetis and Ephemerella communities. 3. Leaf pack communities from the 19 test streams were plotted on a non‐metric multidimensional scaling ordination of the reference communities, and 14 of 19 sites fell outside the 80% confidence ellipse of the reference sites, including eight of nine logged, four of seven farmed and one of three mined catchments. Most of these streams plotted on the ordination near the Ephemerella reference communities. Reference stream communities had a similar number of genera per leaf pack (12.0) and genera per site (18.7) as the test streams (12.6 genera per leaf pack and 18.7 genera per site). Among the test sites, the farmed catchments had higher genera per leaf pack (17.8) and genera per site (21.9) than either the logged (11.5 genera per leaf pack; 19.9 genera per site) or mined (3.4 genera per leaf pack; 7.7 genera per site) catchments. 4. Heterogeneity of leaf pack communities within a site decreased as the number of genera found at the site increased. This was determined by allometric regression of the number of genera found at a site on the maximum number of genera possible, given the average number found per leaf pack. 5. There was a significant relationship between the composition of the leaf pack invertebrate community and stream geography (latitude, longitude, altitude, stream order). Canonical correspondence analysis showed differences among ‘big river’, ‘mountain stream’ and ‘southern’ communities. 6. There was no relationship between the composition of the leaf pack invertebrate community and stream channel and flow characteristics (bank dimensions, flow, slope). There was a significant relationship between the composition of the leaf pack invertebrate community and water quality of the stream (oxygen, nitrogen, phosphorus, conductivity, pH, temperature). ‘Cold, oxygen rich water’ communities were distinguishable from communities in streams with warmer, lower oxygen concentration. ‘High nutrient water’ communities were also distinct from communities in low nutrient streams. There was no relationship between the composition of the leaf pack invertebrate community and the nature of the leaf pack itself (i.e. morphology, decomposition, coniferous needle content). 7. Invertebrate communities in leaf packs show substantial, interpretable variation among reference streams. They are sensitive to human stressors at a landscape scale such as forestry and agriculture. Their diversity and composition varies at different spatial scales in a way that is at least partially explained by the environment of the stream and its catchment area.     

The significance of meandering channel to habitat diversity and fish assemblage: a case study in the Shibetsu River,northern Japan

This study examined the structure and function of habitats for fish, the contribution to fish populations, and the effects of channel modification on habitats and fish populations in the lowland meandering Shibetsu River, northern Japan. Electrofishing and environmental measurements were conducted in bank areas of habitats constituting natural meandering and modified reaches. All types of habitats in a meandering reach highly contributed to the fish population(s). In particular, the contributions of lateral and wood habitats to fish populations were generally high, despite the low spatial extent of these habitats. The modified reach was simplified and had fewer types of habitats with uniform currents, and there was a low abundance of most fish within these habitats. Abundance of each fish group (taxa) was negatively affected by the changes in the habitats and/or channel shortening (i.e., decrease in the absolute abundance of habitat) due to river modification, which was implemented during 1950–1978. This study suggests that the recovery of all the habitat types is important in meander restoration and that the changes in habitat types and abundance should be examined in monitoring meander restoration and channel shortening.     

Longitudinal and temporal changes in functional organization of macroinvertebrate communities in the Lam Tsuen River,Hong Kong

The functional organization of macroinvertebrate communities along the Lam Tsuen River, New Territories, Hong Kong, was investigated in 1976 and 1978–79. Longitudinal changes in functional group representation in 1976 generally matched those predicted by the River Continuum hypothesis, although shredders were poorly represented in the headwaters. This could be attributed to a lack of shading and limited allochthonous inputs from the scrubland watershed. In 1978–79 community organization was modified by nutrients and organic matter inputs from domestic and agricultural sources. An increase in generalists and the establishment of deposit-feeder populations in the middle and lower course was accompanied by relative declines in collector, filter-feeder and predator diversity. Shredders and scrapers were also adversely affected. Seasonal influences were mediated through the effects of rainfall on river discharge. The river was ‘flushed-out’ during the wet season and community organization tended toward that seen in 1976. Effects of cultural eutrophication were pronounced during the dry season and marked alterations in middle and lower course functional group representation were noted. Apparently, differing environmental tolerances of individual taxa cause marked changes in functional group representation and community structure in rivers affected by cultural eutrophication. Department of Zoology, The University of Hong Kong     

Seasonal variation in diet and trophic relationships within the fish communities of the lower Slave River, Northwest Territories, Canada

Increased industrial activities on the Peace and Athabasca River systems have raised concerns about cumulative impacts on fish and water resources downstream, in the Slave River of Alberta and the Northwest Territories, Canada. Because very little information was available on the fish communities in this system, we examined spatial and temporal patterns of diet for nine species (four piscivores and five invertebrate feeders) from three different types of habitat along the lower Slave River system and assessed trophic relationships within the communities. All actively feeding species exhibited seasonal variations in diet within and among the study areas. Dietary overlap was generally low throughout all seasons and locations. In the lower Slave River and its major tributary, the Salt River, substantial dietary overlap between piscivores (particularly walleye, Stizostedion vitreum), and invertebrate feeders occurred in the spring. In the summer no overlap occurred as walleye shifted to a more piscivorous diet, attaining a moderate degree of overlap with northern pike, Esox lucius. Compared with the Slave River, which is a large but homogeneous system upstream of its delta at Great Slave Lake, there was a greater diversity of actively feeding invertebrate feeders in the Salt River. Three of the latter were benthic feeders exhibiting moderate degrees of diet overlap during spring and summer. During the fall, few fish were feeding. Most fishes in the lower Slave River system are generalist, opportunistic feeders, consuming a number of different prey, the importance of which varies spatially and seasonally, as the abundance of these prey varies in the environment.     

Taxonomic and size structures of phytophilous macroinvertebrate communities in Vallisneria and Trapa beds of the Hudson River, New York

Phytophilous macroinvertebrates (PMI) were sampled from the surfaces and surrounding water of two aquatic plant species, Vallisneria americana and Trapa natans, which have substantially different morphologies. It was expected that the plants would harbor invertebrate communities of different structure. Total density of PMI was consistently greater in Vallisneria than inTrapa, e.g. 6× greater per m³ water and 21× greater per m² leaf surface in August. Each macrophyte harbored taxa that were either significantly more abundant or present only with that macrophyte; the herbivore Galerucella nymphaceae (Coleptera: Chrysomelidae) was abundant on Trapa. Vallisneria harbored 34 taxa vs. 40 taxa in Trapa, but similarity was low (Morisita's C=0.55–0.66). Predaceous invertebrates were more prevalent in Trapa than in Vallisneria, as were larger individuals. Both PMI communities exhibited shifts in size distribution between July and August. Standing crop of Trapa was 3× greater than forVallisneria. These two macrophyte beds clearly support PMI communities of different taxonomic and size structure, which is believed to be related to the differences in macrophyte morphology.     

An application of different bioindicators for assessing water quality: a case study in the rivers Alfeios and Pineios (Peloponnisos, Greece)

A number of bioindicators and biotic indices and scores based on benthic macroinvertebrates, diatoms, fishes, aquatic and riparian vegetation in relation to physicochemical parameters have been applied in assessing the water quality of the rivers Alfeios and Pineios (Peloponnisos, Greece). According to the findings, the water quality in both rivers varied from very poor to very good. Among the bioindicators used, the benthic macroinvertebrates seem to be the most reliable. The BBI and IBE were the most applicable indexes while the applicability of the IBMWP and IASPT in the Greek region can be enforced with the inclusion of the Diptreran family Rhagionidae and the Coleopteran family Elminthidae.     

Spatial patterning of benthic macroinvertebrate communities using Geo-self-organizing map (Geo-SOM): A case study in the Nakdong River,South Korea

Characterizing community responses to environmental disturbances is difficult because of the complexity of heterogeneous ecosystems. A geographical self-organizing map (Geo-SOM) was applied to present the spatial distribution patterns of benthic communities in a river. The benthic macroinvertebrate communities were collected in the mainstream of the Nakdong River in South Korea. Geo-SOM is a machine learning technique that extracts spatial patterns of given data across spatial weight k values (0–5), which control the vicinity of the map, to extract geographical information effectively. In the results, clusters were formed mainly according to the topography on a large scale and anthropogenic impacts on a small-scale showing consistency in spatial patterning for benthic communities in the gradient across different degrees of spatial weight. Geo-SOM provided both comprehensive and detailed views for presenting species-space relationships. Corresponding to the decrease in k value (more weight in geographical information), we accumulated data variations to present a comprehensive view of spatial species distributions. Overall, correlations between species were more associated with latitude rather than longitude. The feasibility of spatial clustering was also demonstrated with the effective differentiation of community indices. Community indices were effectively differentiated into clusters in the Geo-SOM. Finally, Geo-SOM is a useful tool for extracting the spatial distribution patterns of communities in a comprehensible manner for the monitoring and management of communities in aquatic ecosystems.     

The long,the short and the stalled: on the attributes of phytoplankton selected by physical mixing in lakes and rivers

Paradoxically, although turbulence characterises the open water environments of planktonic organisms in lakes, rivers and seas, most species of phytoplankton are smaller than the size of the smallest eddies dissipating the energy and, so, must function in an immediate medium which is inherently viscous. Intensively mixed systems, such as wind-stirred shallow lakes, rivers and estuaries, however, constantly readjust the vertical position of suspended algae and, often, other non-living, light-absorbing particles with the effect that the light field to which the algae are subject is erratic and the received day-time light dose is aggregately depressed: cells need to photoadapt accordingly. In fluvial environments the additional constraint of rapid, horizontal, supposedly unidirectional, transport is applied, requiring the attribute of rapid processing of primary products and cell replication. Significant downstream recruitment, however, is benefitted by the presence of so-called dead-zones which retain water (and suspended plankton) sufficiently to accommodate additional cell divisions.