Herbaceous Versus Forested Riparian Vegetation: Narrow and Simple Versus Wide,Woody and Diverse Stream Habitat

We investigated interactions of riparian vegetative conditions upon a suite of channel morphological variables: active channel width, variability of width within a reach, large wood frequency, mesoscale habitat distributions, mesoscale habitat diversity, median particle size and per cent fines. We surveyed 49 wadeable streams, 45 with low levels of development, throughout the Upper Little Tennessee River Basin in the Southern Appalachians. Conversion of riparian forest to grass has reduced aquatic habitat area (quantified by active channel width), channel width variability, wood frequency, mesoscale habitat diversity and obstruction habitat (wood and rock jams), and such conversion has increased the fraction of run and glide habitat. Channels with grassy riparian zones were only one‐third to three‐fifths of the width of channels with forested riparian zones, and channels with grassy or narrow forested riparian zones were nearly devoid of wood. Particle size metrics were strongly affected by stream power and agricultural cover in the basin, but the data suggest that elimination of riparian forest reduces median bed particle size. Results indicate that even modest increases in the extent and width of forested riparian buffers would improve stream habitat conditions. Copyright © 2014 John Wiley & Sons, Ltd.     

Macroinvertebrate community structure and function associated with large wood in low gradient streams

Large woody debris (wood) plays a number of important roles in forested stream ecosystems. Wood in streams provides habitat and flow refugia for fish and invertebrates, and is a site of biofilm production that serves as food for grazing organisms. Logs added to streams are rapidly colonized by invertebrates, and this habitat alteration is accompanied by changes in community composition and functional processes. A multiple habitat, qualitative sampling approach was employed to evaluate macroinvertebrate communities associated with wood habitats in 71 stream reaches in central Michigan and southeastern Minnesota, two agricultural regions in the midwestern United States. Macroinvertebrate taxa were classified with respect to behaviour (e.g. sprawler, clinger, swimmer), as well as trophic/feeding characteristics. These traits were used to examine community structure as a function of wood abundance and distribution. Although wood is not abundant in these streams and logs are generally small in size, wood is a very important habitat in both Michigan and Minnesota: 86% and 95% of the total taxa encountered at Michigan and Minnesota study sites, respectively, were found in wood habitats. Differences in regional patterns in the distribution of taxa across habitats were observed between Michigan and Minnesota. These are believed to result from differences in the number of habitat types available, and the dominant substrate composition. Local invertebrate diversity increased in Michigan, but not Minnesota, with the presence of wood habitats in streams. The presence of wood at a site increased the average taxa richness by 15 and 10 taxa in Michigan and Minnesota, respectively. Macroinvertebrate behavioural attributes and functional traits associated with wood habitats suggest that community traits may vary due to both local difference in flow and the location of wood in the channel. Copyright © 2003 John Wiley & Sons, Ltd.     

Assessing the effectiveness of enhancement activities in urban streams: I. Habitat responses

Effects of stream enhancement on habitat conditions in five spring‐fed urban streams in Christchurch, New Zealand, were investigated. Stream enhancement consisted of riparian planting at three sites, and riparian planting and channel modifications at two sites, where a concrete dish channel and a timber‐lined channel were removed, and natural banks reinstated. Sites were surveyed prior to enhancement activities and 5 years after, and changes in riparian conditions (composition, horizontal and vertical cover), instream conditions (bank modifications, inorganic and organic material on the streambed), and hydraulic conditions (wetted perimeter, cross‐sectional area, depths and velocities) quantified. Enhanced sites generally had higher marginal vegetation cover, as well as increased overhanging riparian vegetation, reflecting planting of Carex sedges close to the water. Bed sediments changed at some sites, with the greatest change being replacement of a concrete channel with gravel and cobble substrate. Bryophyte cover declined at this site, reflecting loss of stable habitat where these plants grew. Bed sediments changed less at other sites, and cover of fine sediments increased in some enhanced sites, presumably from sediment runoff from nearby residential development. Filamentous algal cover decreased at one stream where shade increased, but increased in another stream where the removal of timber‐lined banks and creation of a large pond decreased shade. Stream enhancement increased variability in velocity at three of the five sites, but overall changes to stream hydraulics were small. Although enhancement activities altered the physical conditions of the streams, major changes occurred only to riparian vegetation and bank conditions. Lack of other major changes to instream physical conditions most likely reflected the limited range of channel morphology alterations undertaken. Moreover, the flat topography of Christchurch and naturally low stream discharge further constrained changes to instream physical conditions from enhancement activities. Sediment inputs from continuing urban development also negated the effects of adding coarse substrates. These over‐arching factors may constrain the success of future stream enhancement projects within Christchurch. Copyright © 2005 John Wiley & Sons, Ltd.     

Removal of the Invasive Shrub,Lonicera Maackii,from Riparian Forests Influences Headwater Stream Biota and Ecosystem Function

Riparian forests and streams are interlinked by cross‐system subsidies and alterations of the terrestrial environment can have substantial effects on aquatic biota and ecosystem function. In the Midwestern USA, the exotic shrub Lonicera maackii (Amur honeysuckle) has successfully invaded many riparian habitats, creating near‐monocultures in some locations. This terrestrial invasion has strong potential to modify cross‐system subsidies and impact stream ecosystems. We removed L. maackii from a riparian forest to assess impacts on the aquatic environment. In August 2010, removal occurred along a 150 m stream reach, 10 m downstream of a non‐removal reach, before natural leaf senescence. Over 74 days, in‐stream leaf litter [organic matter (OM)] was collected weekly from plots located in riffles (five/reach). Benthic algal biomass, above stream canopy cover, and macroinvertebrate density were measured for 18 months. L. maackii removal was associated with decreased canopy cover and a significant increase in total in‐stream leaf OM in early autumn (P < 0.05). Removal also differentially influenced the timing and abundance of specific leaf litter genera within the stream (P < 0.05). Macroinvertebrate density was significantly higher in the removal reach, especially during autumn 1 year after removal (P = 0.0294). In both reaches, macroinvertebrate density peaks lagged behind benthic algal biomass peaks. In summary, the removal of an invasive riparian shrub influenced the timing, deposition, quality and abundance of leaf litter habitat into a headwater stream, ostensibly driving bottom‐up effects on aquatic primary producer biomass and the macroinvertebrate community. Copyright © 2014 John Wiley & Sons, Ltd.     

Defining and Testing Targets for the Recovery of Tropical Streams Based on Macroinvertebrate Communities and Abiotic Conditions

Here, we set target values to measure the ecological improvement of streams, based on invertebrate communities, riparian vegetation, instream habitat conditions and water chemistry. The study area is a large tropical catchment (Rio das Velhas, Minas Gerais, Brazil) affected by pastures, mining areas and a large urbanized area but also includes natural protected areas. Two stream types were found in the catchment, based on stream size, elevation, climate and geology with significantly different macroinvertebrate communities. In spite of a marked wet/dry seasons' climatic pattern, that does not result in the segregation of communities. Four classes of global degradation (IV—bad to I—good condition) were defined based on the available abiotic information, corresponding to a gradient in structure and biotic metrics of macroinvertebrate communities, matching the current knowledge on taxa sensitivity to pollution and general disturbance. Class I corresponds to target conditions to be achieved under restoration programmes. Using this approach, we were able to detect an improvement of abiotic conditions in four urban streams that benefited from enhancement measures in 2007–2008. However, invertebrate communities improved clearly in only one site (biotic metrics and community structure). Our study highlighted that good water quality alone is not enough and that only the combined effect of water quality, riparian vegetation and instream habitat condition enhancement resulted in the improvement of invertebrate communities. An important limiting factor for macroinvertebrate communities' recovery may be the distance to source populations. We concluded that the combined use of biological and abiotic target values for measuring the recovery of streams is needed to fully achieve an ecological restoration. This approach can also be valuable in the regular monitoring of streams to assess stream degradation. Target values based on other biological elements, such as fishes and algae, and functional processes could also contribute to define more global and realistic goals. Copyright © 2013 John Wiley & Sons, Ltd.     

Lowland stream restoration by sand addition: Impact,recovery, and beneficial effects on benthic invertebrates

Up to now, most lowland stream restoration projects were unsuccessful in terms of ecological recovery. Aiming to improve the success of stream restoration projects, a novel approach to restore sandy‐bottom lowland streams degraded by channel incision was launched, consisting of the addition of sand to the stream channel in combination with the introduction of coarse woody debris. Yet it remained unknown whether this novel measure of sand addition is actually effective in terms of biodiversity improvements. The aim of the present study was therefore to evaluate if sand addition can improve hydromorphological stream complexity on the short term leading to an increase in macroinvertebrate biodiversity. To this end, particle transport, water depth, current velocity, dissolved oxygen dynamics, and sediment composition were measured. The response of the macroinvertebrate community composition was determined at different stages during the disturbance and short‐term recovery process. Immediately downstream the sand addition site, transport and sedimentation of the sand were initially intense, until an equilibrium was reached and the physical conditions stabilized. The stream section matured fast as habitat formation took place within a short term. Macroinvertebrate diversity decreased initially but recovered rapidly following stabilization. Moreover, an increase in rheophilic taxa was observed in the newly formed habitats. Thus, although sand addition initially disturbed the stream, a relatively fast physical and biological recovery occurred, leading to improved instream conditions for a diverse macroinvertebrate community, including rheophilic taxa. Therefore, we concluded that sand addition is a promising restoration measure for incised lowland streams.     

Recent changes in riparian vegetation: possible consequences on dead wood processing along rivers

Little is known about changes in the composition of dead wood jams along rivers and the possible consequences of any such changes on the river ecosystem. Although tree zonation along the upstream‐to‐downstream continuum is weak and highly variable from a system to another, a clear transition appears in the piedmont zone, which is reflected by transitions in dead wood sources as well as for dead wood transport, storage and decomposition processes. In this paper, we focus on large lowland rivers of southwestern France, where riparian vegetation is increasingly fragmented, reduced in area and/or is entirely replaced by planted forests (poplar plantations). The amount and the potential role of dead wood is practically unknown in these rivers. One reason is that French legislation obliges landowners and public service managers to remove all material from the stream in order to maintain unobstructed river flows. The other reason is that unlike pristine streams in northern regions, these rivers have been regulated for several decades (Adour River) or even for several centuries (Garonne River). The vegetation component of the managed riparian landscape has changed in particular as a result of i) a decrease in stream dynamics, ii) the replacement of natural forests by planted ones, and iii) the invasion of natural communities by introduced woody species. The possible consequences of biological invasions on the role of dead wood jams are discussed in light of: i) a local study of wood jams along a moderately modified system; ii) changes observed in the composition of trees along the Adour River over the past 10 years; iii) a regional case study involving two chosen species. Whereas white willow populations are declining along streams in southwestern France, the box‐elder, introduced from the United States, has spread extensively in the last two decades. Statistical models would suggest that competitive pressures are limited between these two species, boxelder is expected to replace white willow in the near future as a consequence of an increase in river regulation and global warming. This can be expected to have important consequences on dead wood dynamics, and on the management of woody debris, especially since trends indicate a replacement of softwood species by hardwood species. Copyright © 2003 John Wiley & Sons, Ltd.     

Hydrogeomorphic and Biotic Drivers of Instream Wood Differ Across Sub‐basins of the Columbia River Basin,USA

Instream wood promotes habitat heterogeneity through its influence on flow hydraulics and channel geomorphology. Within the Columbia River Basin, USA, wood is vital for the creation and maintenance of habitat for threatened salmonids. However, our understanding of the relative roles of the climatic, geomorphic, and ecological processes that source wood to streams is limited, making it difficult to identify baseline predictions of instream wood and create targets for stream restoration. Here, we investigate how instream wood frequency and volume differ between seven sub‐basins of the interior Columbia River Basin and what processes shape these differences within these sub‐basins. We collected data on wood volume and frequency, discharge and stream power, and riparian and watershed forest structure for use in modelling wood volume and frequency. Using random forest models, we found that mean annual precipitation, riparian tree cover, and the individual watershed were the most important predictors of wood volume and frequency. Within sub‐basins, we used linear models, finding that some basins had unique predictors of wood. Discharge, watershed area, or precipitation often combined with forest cover, riparian conifer, and/or large tree cover in models of instream large wood volume and frequency. In many sub‐basins, models showed at least one hydrologic variable, indicative of transport competence and one ecological variable, indicative of the reach or upstream watershed's capability to grow measurable instream wood. We conclude that basin‐specific models yield important insights into the hydrologic and ecological processes that influence wood loads, creating tractable hypotheses for building predictive models of instream wood. Copyright © 2015 John Wiley & Sons, Ltd.     

LARGE‐WOOD LOADING FROM NATURAL AND ENGINEERED PROCESSES AT THE WATERSHED SCALE

Large wood, both live and dead, is essential for producing complex habitat in many streams, especially in forested watersheds that support salmonid populations. The addition of engineered wood structures is a common approach taken in many streams where past watershed management practices have resulted in reduced wood loading. We examined six 300‐m stream reaches in the Lagunitas Creek watershed, Northern California, to determine (i) the distribution of large wood in the bankfull channel and 10‐year floodplain, (ii) the influence of large wood on the size and distribution of pools and (iii) whether streams with engineered wood structures had greater diversity of pool habitat to support salmonid populations. We found that the amount of large wood in the bankfull channel and the amount available for recruitment from the 10‐year floodplain were highly variable among and within reaches examined and largely dependent on the local geomorphic setting. Stream reaches with engineered wood structures had elevated pool frequencies relative to reaches without these structures, suggesting a higher capacity to support salmonids during critical life stages. Among large wood pieces that had a strong influence on pool formation, 23% had an attached root wad and 66% were part of a cluster. All of the study reaches we examined had lower volumes of large wood in their bankfull channels than similar stream types with natural wood‐loading levels, suggesting that increased additions of large wood could provide ecosystem benefits over time. These principles can be understood and transferred effectively to other watersheds using a framework of wood‐loading process domains. Copyright © 2012 John Wiley & Sons, Ltd.     

Macroinvertebrate assemblages in streams of interior Alaska following alluvial gold mining

Alluvial gold mining, or placer mining, represents a major disturbance to stream ecosystems in interior Alaska. This process typically involves re‐routing the stream to one side of the valley while the gravels are removed across the floodplain for processing. The stream is then re‐directed back into a reclaimed new channel after mining has ceased in that section of stream. Macroinvertebrate colonization of reclaimed stream reaches is necessary for benthic community recovery following mining. Macroinvertebrate community assemblages at 36 sites on six streams in interior Alaska were examined. Sites with different mining histories were compared to control sites. TWINSPAN classification and ordination of sites using macroinvertebrate abundance indicated a greater similarity of sites within watersheds than between watersheds even though each watershed had a history of mining including recently mined sites. Significant differences were found for total invertebrate abundance, percentage dominant taxon and mean total biomass of macroinvertebrates between control sites and sites that were recently mined (≤10 years) and sites mined 12–50 years ago. Total macroinvertebrate abundance and biomass was lower and taxon dominance higher in both groups of sites with a history of mining. No significant difference in these or other measures was found for sites where mining occurred upstream. There was also no significant relationship between time since mining and the biotic measures used to summarize macroinvertebrate community structure. Although taxon richness recovered rapidly, no individual taxon was found to be a specific indicator of macroinvertebrate recovery since mining. Copyright © 2004 John Wiley & Sons, Ltd.     

The development of hydraulic and geomorphic complexity in recently formed streams in Glacier Bay National Park,Alaska

Geomorphic and hydraulic complexity within five streams representing 200 years of stream development were examined in Glacier Bay National Park, Alaska. Channel geomorphic units (CGUs) were mapped using a hierarchical approach, which defined stream habitat according to morphological and hydraulic characteristics. Detailed hydraulic assessment within the geomorphic units allowed differences in hydraulic characteristics across the 200‐year chronosequence to be documented. Channel geomorphology and hydrology changed as stream age increased. Younger streams were dominated by fast flowing geomorphic units such as rapids and riffles with little hydraulic or landscape diversity. As stream age increased, slower flowing habitat units such as glides and pools became more dominant, resulting in increased geomorphic, hydraulic and landscape diversity. These results suggest that geomorphic and hydraulic complexity develop over time, creating habitat features likely to be favoured by instream biota, enhancing biodiversity and abundance. Copyright © 2009 John Wiley & Sons, Ltd.     

Physical habitat structure in Danish lowland streams

Dredging or channelization has physically modified the majority (90%) of the 64 000 km of Danish stream network with substantial habitat degradation as a result. Analyses of physical habitat structure in streams, biota, catchment features and regional differences in hydrology, topography and geology have never been carried out in Denmark. Therefore, there is little knowledge of processes, interactions and patterns across the different scales. Physical habitats, catchment parameters and macroinvertebrates were sampled at 39 sites in three major river systems during summer and winter 1993. In‐stream physical conditions and catchment attributes affect the physical habitat structure in Danish lowland streams. Local differences in hydrology, land use, catchment topography and soil types correlated to the in‐stream physical habitat parameters. Local differences in hydrology and topography resulted in a separation of the Suså streams with respect to physical habitats. Mud deposition was pronounced at sites with low discharge and low near‐bed current velocity. Low mud cover was primarily associated with streams with high discharge located in pristine catchments. Stability in the streams was therefore closely linked to in‐stream deposition of fine sediment. Generally, macroinvertebrate community diversity increased as discharge increased. Mud cover negatively affected macroinvertebrate diversity and EPT taxon richness. Regional physical habitat structure and macroinvertebrate community structure were primarily associated with local variations in hydrology, geology and topography. Low‐energy streams were primarily located in the Suså river system and the high‐energy streams in the Gudenå and Storå river systems, leading to extensive deposition of mud during summer. Streams in the Suså river system generally had lower diversity and species richness compared to the streams in the Gudenå and Storå river systems. Hydraulic conditions and substratum dynamics in streams are important when managing lowland streams. This study therefore analysed interactions and parameter correlations between physical habitats, stream stability and catchment attributes as well as macroinvertebrate community structure across multiple scales. Copyright © 2004 John Wiley & Sons, Ltd.     

Mitigation of impacts of cattle access on stream ecosystems: Efficacy of fencing

Headwater streams can constitute up to 80% of river channel length and are vulnerable to anthropogenic pressures due to their high connectivity to adjacent land, large relative catchment size and low dilution capacity. In these environments, unrestricted cattle access is a potentially significant cause of water quality deterioration, resulting from increases in stream bank erosion, riparian damage and sediment deposition among others. Several studies have reported improvements in the physico-chemical and hydromorphological conditions of streams following the elimination of cattle access; few, however, have focussed on the ecological impacts of such management practices. Here, such impacts are assessed. The study explores the short-term effects of cattle exclusion by comparing habitat conditions, sediment deposition and instream macroinvertebrate communities upstream and downstream of cattle access points prior to, and 1 year following exclusion via fencing. The long-term effects are also measured by reassessing a small stream catchment entirely fenced off from cattle access in 2008 under a dedicated management plan. In the short term, cattle exclusion led to a reduction in deposited sediment downstream of cattle access points and a related homogenisation of macroinvertebrate community structure between upstream and downstream of cattle access points. Increased abundances of specific indicator taxa (Ancylus fluviatilis, Glossosomatidae and Elmidae) in the fenced catchment following 9 years of exclusion highlight the long-term ecological benefits of such mitigation practices. These findings highlight the importance of incentivised agri-environment measures in reducing the negative impacts of cattle access to vulnerable aquatic ecosystems.     

Cascade macroinvertebrate assemblages for in‐stream flow criteria and biomonitoring of tropical mountain streams

Few comprehensive studies on stream assessment and biomonitoring have been conducted in tropical, freshwater watersheds. Currently under threat from climate change, urbanization and increasing freshwater demands, there is a need for innovative approaches to tropical watershed assessment and management. This study investigated cascade habitat macroinvertebrate communities among four tropical mountain streams with the goal of enhancing future efforts to identify flow biocriteria for watersheds of Polynesia. Cascade macroinvertebrate communities were compared between streams of differing size and magnitude of flow removal to evaluate the biological effects of water withdrawal on benthic communities. Two cascade microhabitats, identified as torrenticolous and amphibious, were evaluated for macroinvertebrate community differences and presence of native taxa among watersheds. Cascade habitat in general was reduced, by as much as 98%, in downstream reaches, having a significant impact on the stream ecosystem physical template important for native stream communities. In addition, two‐way ANOVA results revealed no main effects, but significant interactions of watershed size and flow removal on mean macroinvertebrate density for torrenticolous microhabitats; however, the opposite was true for the amphibious microhabitat. Diversity was significantly higher under undiverted flow conditions (t = 4.21, df = 272, p = 0.0004) and in torrenticolous microhabitats (t = 3.86, df = 272, p < 0.0001) over the entire study period. The amphibious microhabitat was composed of 39% native taxa, while the torrenticolous microhabitat contained <7%. This study provides new options for biomonitoring of native populations in Polynesian watersheds. Further studies that support the development of in‐stream flow criteria to preserve cascades are important to understanding the role of this habitat in tropical stream ecosystem function. Copyright © 2010 John Wiley & Sons, Ltd.     

Assessing the effectiveness of enhancement activities in urban streams: II. Responses of invertebrate communities

The effects of habitat enhancement on the invertebrate communities in five urban streams in Christchurch, New Zealand, were investigated. All streams underwent riparian planting, while extensive channel modifications were made at two streams, where a concrete dish channel and a wooden timber‐lined stream were removed and natural banks reinstated. Benthic invertebrates were collected before enhancement and 5 years after from the same locations. Invertebrates were also collected from control sites in each stream in 2001. Desired goals of enhancement activities included increasing the densities of mayflies and caddisflies, and decreasing densities of oligochaetes, snails and midges. Enhancement activities changed riparian vegetation and bank conditions, as well as substrate composition, instream organic matter and variability of instream velocities. Invertebrate communities prior to enhancement were typical of those in urban environments, and dominated by snails (Potamopyrgus, Physa), the amphipod Paracalliope, the hydroptilid caddisfly Oxyethira, oligochaetes and chironomids. Stream enhancement caused only small changes to the invertebrate community, with subtle shifts in overall abundance, species evenness, diversity, and ordination scores. Lack of a consistent strong response by invertebrates to enhancement activities, and continued absence of caddisflies and mayflies from enhanced sites may reflect lack of sufficient change to instream conditions as a result of stream enhancement, colonization bottlenecks for aerial stages of these animals, and the inability of individuals outside the urban watershed to perceive these enhanced ‘islands’ of good habitat. Alternatively, contamination of streambed sediments, excess sedimentation and reduced base flows may be limiting factors precluding successful invertebrate colonization in enhanced sites. These results highlight the importance of setting clear goals and objectives necessary to meet these goals. Enhancement of riparian zones in urban streams may not be adequate to improve benthic invertebrate communities. Identifying over‐arching factors that potentially limit invertebrate communities will enable the enhancement potential of streams to be better assessed, and allow managers to identify sites where recovery of biological communities is possible, and where such recovery is not. Copyright © 2005 John Wiley & Sons, Ltd.     

Soil seed banks of degraded riparian zones in southeastern Australia and their potential contribution to the restoration of understorey vegetation

Although soil seed banks are understood to be integral to the vegetation dynamics and restoration of many ecosystems, little is known of their role in riparian zones. In this study, we investigated soil seed banks of riparian zones of contrasting condition in an agricultural landscape and evaluated their potential to influence riparian restoration. We examined the composition and structure of germinable soil seed banks along lateral gradients from stream channels in both cleared and wooded riparian zones of three lowland creeks within the Goulburn Broken catchment in temperate southeastern Australia. Environmental correlates of soil seed bank characteristics and similarity to extant vegetation were also examined. We found an abundant and species‐rich soil seed bank mostly comprising propagules of perennial rushes and sedges and annual and perennial grasses with many species of annual forbs. While the majority of identifiable germinants and species were native, exotic species were common at all locations. Soil seed bank composition was relatively homogeneous among streams and along lateral gradients from the channel. Riparian condition (i.e. cleared or wooded), however, had a strong influence on soil seed bank composition and structure with cleared reaches containing more species, more germinable annual grasses and higher total numbers of germinable seeds. Soil seed bank composition was correlated with site openness suggesting that extant vegetation structure plays an important role in soil seed bank dynamics. Recruitment from the in situ soil seed bank will help restore only some components of the riparian plant community and may hinder restoration by introducing undesirable species. Copyright © 2008 John Wiley & Sons, Ltd.     

Invertebrate communities in Compensation Creek,a man‐made stream in boreal Newfoundland: The influence of large woody debris

Benthic invertebrate communities were examined in Compensation Creek, a man‐made stream in south‐central Newfoundland, Canada. Samples taken in September 2006 and September 2007 from large woody debris (LWD) were compared with samples from benthic environments to determine whether LWD supported a more diverse and abundant invertebrate community. Benthic habitats in a nearby natural stream were also sampled. Taxa composition was similar between the man‐made and the natural stream, highlighting successful colonization for the majority of taxa. Within Compensation Creek, taxa richness was higher in benthic habitats than on LWD, likely influenced by the successional age of the stream and surrounding habitat. The more complex benthic substrate provided refugia and allowed for the accumulation of fine detritus as a food source. Scrapers were almost completely absent from LWD and collector‐gatherer abundance was greater in the benthos. Collector‐filterer abundance was more than six times greater near the pond outflow than farther downstream when discharge was high, but abundances were almost equal when discharge was reduced. Riparian vegetation has not fully established around the man‐made stream, whereas it is overhanging and extensive at the natural stream, leading to more leaf‐litter input for shredders. As the morphology of Compensation Creek changes, the invertebrate community will continue to develop and likely increase utilization of accumulated detritus at LWD. Copyright © 2009 John Wiley & Sons, Ltd.     

Reintroducing wood to streams in agricultural landscapes: changes in velocity profile,stage and erosion rates

Historically, perceived increases in erosion and flooding levels have been attributed to in‐stream wood and used to justify its removal from streams and rivers around the world. More recently, recognition of the adverse morphological and biological impacts caused by this removal has led to rehabilitation projects that actively reintroduce wood to streams. However, a perception remains amongst some members of the general community that wood additions increase the likelihood of flooding and erosion in the target streams. To test whether there was a basis for this perception, we experimentally added wood to eight streams across southwest Victoria and Gippsland, Australia. The velocity, stage and bed and bank erosion rates were compared with those of unaltered reaches. We detected localized changes in the velocity and stage parameters but that these were unlikely to operate at the reach‐scale. Bed erosion rates, where maximum erosion was assumed if pins were not recovered, showed increased erosion due to wood additions but this was not supported by channel shape analyses, which identified short‐term increases in the variability of the channel shape, followed by longer‐term stability at treatment sites. We found no clear evidence of increased longer‐term rates of erosion or flooding associated with the introduction of wood to streams over the 18‐month study period. It remains important to carefully design rehabilitation works, but the lack of adverse effects on stream morphology and increased variability of the in‐stream environment suggests improved habitat diversity, supporting the use of wood addition as a stream rehabilitation technique. Copyright © 2008 John Wiley & Sons, Ltd.     

DYNAMICS OF IN‐STREAM WOOD AND ITS IMPORTANCE AS FISH HABITAT IN A LARGE TROPICAL FLOODPLAIN RIVER

The recruitment of wood from the riparian zone to rivers and streams provides a complex habitat for aquatic organisms and can influence both aquatic biodiversity and ecosystem function. The Daly River in the wet–dry tropics of northern Australia is a highly seasonal, perennially flowing sand‐bed river where surveys of river wood aggregations at the reach scale (~2 km) in 2008 and 2009 recorded densities of 37–78 km^?1 and identified distinct types of river wood aggregations: key pieces, standing trees, fallen trees, wrack and single pieces. After larger than average flows in the 2008/2009 wet season, between 46% and 51% of the surveyed river wood had moved. The distribution of wood age classes indicated continual recruitment and slow turnover of wood within the river. Surveys of fish and habitat characteristics at the mesohabitat scale (~100 m) showed fish species richness; diversity and fish abundance were not correlated to the proportion of wood present. Fish assemblage structure was associated with wood cover as well as other environmental variables such as stream width and depth. The importance of in‐stream wood also varied for different species and age classes of fish. This study documents the dynamic nature of river wood aggregations and their complex and variable distribution and suggests their importance as fish habitat in this tropical river. Copyright © 2012 John Wiley & Sons, Ltd.     

Ecological effects of flow regulation on macroinvertebrate and periphytic diatom assemblages in the Hawkesbury–Nepean River,Australia

The effects of flow regulation on macroinvertebrates and periphytic diatoms were examined in the Hawkesbury–Nepean River system in Australia. Regulated sites below eight dams or weirs were compared with unregulated sites above the impoundments and sites on two nearby unregulated streams. The management of the water supply during the study created two types of flow regulation, sites with water supply releases and sites with comparatively small or no releases. The macroinvertebrate communities in three habitats and periphytic diatoms below the storages and weirs differed from the biota at unregulated sites above the weirs and on unregulated systems. The number of macroinvertebrate taxa in riffle and pool‐rock assemblages was significantly lower at regulated sites when compared with unregulated sites and the number of stream edge macroinvertebrate and diatom taxa was unaffected by regulation. Riffle and pool‐rock macroinvertebrate assemblages differed between the two types of regulation. However, periphytic diatom and edge habitat macroinvertebrate assemblages did not differ between the two types of flow regulation. Examination of environmental variables associated with the change in the biota suggested that the principal effect of the management of the water supply system in the Hawkesbury–Nepean River was changed hydrology rather than altered water quality. Copyright © 2001 John Wiley & Sons, Ltd.