Streams In South-eastern Australia Research Articles

Dumpster diving for diatom plastid 16S rRNA genes.

High throughput sequencing is improving the efficiency of monitoring diatoms, which inhabit and support aquatic ecosystems across the globe. In this study, we explored the potential of a standard V4 515F-806RB primer pair in recovering diatom plastid 16S rRNA sequences. We used PhytoREF to classify the 16S reads from our freshwater biofilm field sampling from three stream segments across two streams in south-eastern Australia and retrieved diatom community data from other, publicly deposited, Australian 16S amplicon datasets. When these diatom operational taxonomic units (OTUs) were traced using the default RDPII and NCBI databases, 68% were characterized as uncultured cyanobacteria. We analysed the 16S rRNA sequences from 72 stream biofilm samples, separated the chloroplast OTUs, and classified them using the PhytoREF database. After filtering the reads attributed to Bacillariophyta (relative abundance >1%), 71 diatom OTUs comprising more than 90% of the diatom reads in each stream biofilm sample were identified. Beta-diversity analyses demonstrated significantly different diatom assemblages and discrimination among river segments. To further test the approach, the diatom OTUs from our biofilm sampling were used as reference sequences to identify diatom reads from other Australian 16S rRNA datasets in the NCBI-SRA database. Across the three selected public datasets, 67 of our 71 diatom OTUs were detected in other Australian ecosystems. Our results show that diatom plastid 16S rRNA genes are readily amplified with existing 515F-806RB primer sets. Therefore, the volume of existing 16S rRNA amplicon datasets initially generated for microbial community profiling can also be used to detect, characterize, and map diatom distribution to inform phylogeny and ecological health assessments, and can be extended into a range of ecological and industrial applications. To our knowledge, this study represents the first attempt to classify freshwater samples using this approach and the first application of PhytoREF in Australia.

Dispersal decisions and personality in a freshwater fish

Historically, the differences in dispersal behaviour between individuals within a species has largely been ignored. Instead, we tend to assume all individuals within a population express similar phenotypes. However, evidence is growing for the importance of intraspecific variability in dispersal propensity and how this variability may influence population dynamics, as well as the role of environmental context in driving this behaviour. Individuals that are more likely to disperse can have other traits, such as being bolder or more aggressive, that collectively form behavioural syndromes. We tested for a behavioural syndrome in carp gudgeons (Hypseleotris spp.) species' complex, a type of small fish found in intermittent streams in southeastern Australia. Intermittent streams are an environment where selection may favour the evolution of different dispersal phenotypes, given the variable and unpredictable nature of flows. During dry periods, fish become isolated in refuge pools that vary in quality and persistence, and then can disperse when flow resumes. Dispersal can have costs (e.g. the risk of not finding another habitat) but also benefits (e.g. opportunity to find better habitat), meaning that different strategies (i.e. dispersing versus staying) may both be advantageous and thus evolve. Through a series of experiments that assessed these fish's latency to emergence into a novel environment and tendency to shoal, as well as movement behaviour in artificial streams, we found that (1) flow is not likely to be a movement cue, and (2) boldness, sociability and dispersal distance were repeatable, consistent with the notion that carp gudgeons exhibit personalities. To our knowledge, this is the first demonstration of a behavioural syndrome in a freshwater fish that inhabits intermittent streams. This finding contributes to our understanding of how carp gudgeons move through intermittent streams and the potential dynamics that allow these fish to persist in such harsh, hydrologically variable habitats.

Assessing changes in structural vegetation and soil properties following riparian restoration

Efforts are underway in many areas to restore riparian zones to arrest and/or reverse their degradation and the subsequent loss of the ecosystem services they provide. Despite strong links between edaphic conditions and riparian zone function, limited research has tested how soil properties respond to restoration, especially in an experimental context. With this important knowledge gap in mind, we established a field experiment to asssess structural vegetation and soil responses in the eight years following livestock exclusion and replanting in lowland streams in south-eastern Australia. On three streams, paired restored and control sites were experimentally established and we monitored vegetation (stem density, cover of bare ground and tree canopy, and loadings of organic matter), once beforehand, and then biennually after restoration. Selected soil properties (total carbon, total nitrogen, plant-available phosphorus) were sampled once shortly after restoration, then after another five years. Significant changes in structural vegetation occurred (e.g. decreased bare ground, increased plant stem density, organic matter, and canopy cover). In contrast, those soil properties did not respond. A mega-drought occurred throughout much of the study which was immediately followed by severe flooding. The floods redistributed organic matter at our study sites, with this effect mediated by vegetation structure: the probability of organic matter retention was positively correlated with groundcover and stem density of plants. The timing of flooding was also correlated with increased soil carbon and nitrogen, which could be due to increased productivity in these systems (for the former), or potentially due to increased fertiliser inputs or increased fixation (for the latter). Our study is the first to comprehensively and experimentally test how vegetation, litter layer and surface soil properties respond following riparian restoration, and will help guide the development and implementation of other monitoring programmes.

Species-specific prevalence of mermithid parasites in populations of six congeneric host caddisflies of Ecnomus McLachlan, 1864 (Trichoptera: Ecnomidae)

ABSTRACTMermithid nematodes are entomophagous parasites and, despite being present in diverse aquatic insects, studies of caddisflies acting as definitive hosts are few and the ecological impacts on host populations are largely unknown. During a four-year study in a stream in southeastern Australia, parasitic mermithid worms were commonly found inside adult caddisflies, but only species of the genus Ecnomus McLachlan, 1864 (Ecnomidae). Ecnomus were the definitive host and parasite prevalence ranged from <1% to nearly 50% across six species. Species-specific prevalence varied little between years and was typically higher in males than in females. Parasite intensity ranged from 1 to 6 (median = 1), but did not vary between species or sexes. Infected hosts could fly, but were castrated and died when worms emerged. High prevalence and virulence (reproductive failure and death of the host) suggests that these parasites could potentially play a role in the population dynamics of some Ecnomus spp.

A landscape-scale field experiment reveals the importance of dispersal in a resource-limited metacommunity.

Dispersal may play a strong role in driving species diversity across landscapes. Theoretically, dispersal permits species to remain extant within a metacommunity, even if they are periodically excluded from some local communities. Field tests of dispersal effects are difficult, and most non-experimental data suggest that environmental conditions play the predominant role in setting species diversity. However, most such studies cannot differentiate between patterns caused primarily by dispersal constraints vs. abiotic factors vs. biotic constraints (e.g., priority effects). In 22km of a sand-bed stream in southeastern Australia, strong longitudinal gradients in the abiotic environment and detritus densities (resources) mean that downstream locations have abiotic conditions that may be physiologically stressful, low resource densities and low species diversities. We experimentally increased the retention of detritus over 40m stream lengths along the gradient, with other sites acting as controls. If dispersal is constrained, or abiotic or biotic factors primarily control community structure, then we predicted that increasing resources would result in no change in species composition. Alternatively, if dispersal is common, we predicted that species diversity would increase at treatment sites through colonization by species able to tolerate abiotic conditions downstream and able to invade established communities. Invertebrates were sampled prior to manipulation and then four times (1, 4, 9 and 12months) following manipulation. Detrital standing stocks increased by an order of magnitude at treatment sites. Over 1 yr, invertebrate densities and species richness also increased in treatment sites. Effect sizes were strong in middle and downstream areas, which were colonized by upstream species. Thus, faunal composition of the downstream treatment sites became more similar to upstream locales, and β-diversity across treatment sites declined as α-diversity increased. Out of 54 common taxa, roughly half responded to the experiment; responders and non-responders had similar proportions of upstream specialists and of different functional feeding groups. Contrary to many non-experimental studies, our results demonstrate that extensive dispersal can be very important and, for many species, potentially more important than the abiotic environment or biotic constraints in affecting community structure when adequate resources are available.

How sensitive are invertebrates to riparian-zone replanting in stream ecosystems?

Clearing native vegetation has pervasive effects on stream and river ecosystems worldwide. The stated aims of replanting riparian vegetation often are to restore water quality and to re-establish biotic assemblages. However reach-scale restoration may do little to combat catchment-scale degradation, potentially inhibiting restoration success. Whether reinstating biodiversity is a realistic goal or appropriate indicator of restoration success over intermediate timeframes (&lt;30 years) is currently unclear. We measured the response of aquatic macroinvertebrate assemblages to riparian replanting in a chronosequence of replanted reaches on agricultural streams in south-eastern Australia. Sites had been replanted with native vegetation 8–22 years before the study. Indices of macroinvertebrate sensitivity did not respond to replanting over the time gradient, probably because replanting had little benefit for local water quality or in-stream habitat. The invertebrate assemblages were influenced mainly by catchment-scale effects and geomorphological characteristics, but were closer to reference condition at sites with lower total catchment agricultural land cover. Reach-scale replanting in heavily modified landscapes may not effectively return biodiversity to pre-clearance condition over decadal time-scales. Restoration goals, and the spatial and temporal scale of processes required to meet them, should be carefully considered, and monitoring methods explicitly matched to desired outcomes.

Bird responses to riparian management of degraded lowland streams in southeastern Australia

We assessed the degree to which fencing, livestock exclusion, and replanting of riparian zones affected avian assemblages in massively cleared landscapes. Measurements were made at three creeks in the southern Murray–Darling Basin in southeastern Australia, each of which had circa 1‐km long treated sections and paired “untreated” circa 1‐km sections, where no fencing, planting, or stock exclusion was done. We measured the change in vegetation characteristics and abundances of native birds for up to 8 years after works were completed. Prior to data collection, we developed expected responses of bird species based on the anticipated time‐courses of change in vegetation structure. We used hierarchical Bayesian models to explore the effects of the management actions, and to account for within‐site variation in vegetation characteristics. There were major changes in vegetation structure (reductions in bare ground and increases in shrubs and tree recruitment) but avian responses generally were small and not as expected. There are at least four possible reasons for the limited avian responses: (1) there has been a long‐term decline in woodland birds across the region; (2) the study was conducted during the longest drought in the instrumental record in the study region; (3) the total amount of replanted vegetation was small in a massively denuded region; and (4) monitoring may have been over too short a term to detect responses to longer‐term changes in structural vegetation.

Dispersal and recruitment of fish in an intermittent stream network

Animal movement is an important process connecting habitats in heterogeneous landscapes, and can play a key role in population persistence. Laboratory swim trials were conducted to determine and compare the dispersal capabilities of two native Australian fish, mountain galaxias (Galaxias olidus, Family Galaxiidae) and southern pygmy perch (Nannoperca australis, Family Nannopercidae) that maintain populations in hydrologically variable and intermittently flowing streams in south-eastern Australia. These experiments showed that G. olidus had significantly greater swimming endurance under a range of flow velocities. Concurrent field surveys were used to establish whether swimming abilities observed in laboratory studies were consistent with patterns of inferred movement from distribution and abundance patterns observed in the field. Data collected at multiple sites from headwater to lowland reaches along multiple streams revealed substantial temporal changes in the distribution of young-of-year (0+) G. olidus, with spawning occurring at upland sites in winter, followed by downstream larval migration and subsequent upstream movement in late spring. Observed spatial and temporal patterns in G. olidus abundances were consistent with a source-sink population structure, which may be disrupted by prolonged cease-to-flow periods during drought years. In contrast, results for N. australis suggested limited dispersal, with restricted local populations that persist at sites with permanent surface water. These field and laboratory findings complement our understanding of the spatial population structure of these two species in intermittent streams, and highlight the importance of understanding the role of dispersal in species conservation and habitat restoration.

Sediment dynamics in a sand bed stream with riparian vegetation

The characteristic bed morphology of streams results from the action of various sediment fluxes. Sediment fluxes are difficult to quantify, and as a result, few studies have been able to characterize the relative importance of different transport mechanisms in shaping a river's bed at the reach scale. Even fewer studies have been able to address the impacts of introduced riparian vegetation on those fluxes. This study provides the first comprehensive set of flow and sediment measurements required to compute the fluxes in a sand bed stream with riparian vegetation. Data were collected in a reduced‐scale laboratory model of a reach of a sand bed stream in southeastern Australia that is undergoing rehabilitation using in‐stream riparian vegetation. The reach has a large‐radius meander and a variable width. Laboratory measurements included streamwise and transverse velocities, bed shear stresses, bed load transport, suspended sediment concentrations, and bed topography with and without riparian vegetation placed along the outer bank of the bend. The results unveiled the importance of secondary circulation as well as converging and diverging flow patterns in shaping the bed topography. Modifications due to the vegetation included a shift of the main flow away from the vegetated outer bank and an overall straightening of the flow in the reach, resulting in an increased deposition near the vegetated bank and a reduced deposition near the inner bank. This highlights the need for overall reach assessment of flow and sediment dynamics before revegetation, as its effects go beyond local bank protection.

Riparian vegetation removal alters consumer - resource stoichiometry in an Australian lowland stream

Anthropogenic impacts on stream ecosystems generate changes in nutrient and carbon availability which act as stoichiometric challenges to consumers. We tested the hypothesis that removal of Eucalyptus riparian vegetation alters in-stream resource stoichiometry with flow-on effects for a benthic consumer (the freshwater crayfish, Cherax destructor). Sites with high and low riparian canopy cover were selected on a lowland stream in south-eastern Australia. A reduction in riparian vegetation canopy cover was associated with decreased terrestrial detritus (low nutritional quality; high carbon to nitrogen (C : N) ratio) and increased cover of macrophytes and filamentous algae (high quality; low C : N ratio). This resource-quality shift was associated with a small but significant decrease in C. destructor C : N ratio (molar ratio of muscle tissue). This suggests that the animals are deviating from homeostasis and may be in better condition in the stream pools dominated by in-stream productivity. A significant negative relationship between C. destructor length and C : N ratio was observed, suggesting that resource-quality impacts may differ with age. The present study has shown that riparian loss alters stoichiometric interactions in stream benthic ecosystems, with potential consequences for stream processes such as nutrient cycling. Ecological stoichiometric theory should therefore be further utilised to make predictions of ecological impacts in freshwater systems.

Modelling aquatic exposure and effects of insecticides — Application to south-eastern Australia

Agricultural pesticides are widely used and can affect freshwater organisms. We applied a spatially explicit exposure model, validated for central Europe, to estimate exposure to insecticides through runoff for streams in south-eastern Australia. The model allows the identification of streams potentially affected by insecticide runoff located in 10 × 10 km grid cells. The computation of runoff relies on key environmental factors such as land use, soil texture, slope and precipitation. Additionally, the model predicted the ecological effect of insecticides on the macroinvertebrate community. We predicted insecticide surface runoff that results in a moderate to poor ecological quality for streams in half of the grid cells containing agricultural land. These results are in good accordance with the results obtained by estimating pesticide stress with a biotic index (SPEAR pesticides) based on macroinvertebrate monitoring data. We conclude that the exposure and effect model can act as an effective and cost-saving tool to identify high risk areas of insecticide exposure and to support stream management.

Response of two-spined blackfish Gadopsis bispinosus to short-term flow fluctuations in an upland Australian stream

Environmental flows are applied to regulated rivers, predominantly with the aim of benefiting native fauna. However, the outcomes for biodiversity and the mechanisms that underpin changes due to these manipulations are poorly understood. We examined the effects of elevated water release, of the magnitude used for riffle maintenance, on the movement and habitat use of the locally-threatened two-spined blackfish, Gadopsis bispinosus, in the Cotter River, a regulated upland stream in south-eastern Australia. We compared the behaviour of radio-tagged individuals during baseline flow conditions (0.12 m3 s−1) and during elevated flow releases (1.74 m3 s−1). Eight individuals (196 ± 8 mm TL) were radio-tracked at one site over 22 days, and six individuals (180 ± 5 mm TL) were monitored by fixed telemetry stations at a second site for 1 month. At both the sites, two-spined blackfish were nocturnal and occupied small linear ranges (23 ± 6 m). They preferentially used pools, but also used runs and riffles. Elevated discharge did not significantly affect movement, activity or dispersal of two-spined blackfish. Two individuals utilised inundated vegetation during high flow. Despite a small number of behavioural changes, there was no response to elevated flow at the population level. It is likely that the benthic nature of this species precludes its behaviour being affected by a 15-fold increase in-stream discharge. However, the indirect effects of flows of this magnitude on two-spined blackfish, and their responses to discharges of greater magnitude, remain to be investigated.

Resolving the Holocene alluvial record in southeastern Australia using luminescence and radiocarbon techniques

AbstractA previous assessment of radiocarbon (14C) dates from alluvial units in southeastern Australia revealed a gap in the geochronological record that coincides with the Holocene climatic optimum. This gap in the alluvial record can be further refined using optically stimulated luminescence (OSL). The chronology of Holocene river terraces on Widden Brook, a sandy alluvial stream in southeastern Australia, was established using 14C and OSL techniques. Combined use of these independent techniques allows for a more rigorous assessment of the alluvial record. The robust chronology, consisting of 38 14C and 11 OSL samples, permitted identification of significant depositional variation within the catchment, resulting from localised geomorphic processes. The three terrace sequences identified yielded distinct chronologies, suggesting alluvial deposition at different times. The sequences exhibited a continuous chronology, which indicated continuous deposition throughout the Holocene. The chronology of terrace sequences within this catchment suggests that terrace formation can be attributed to localised geomorphic processes rather than climatic forcing. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Large versus small wood in streams: the effect of wood dimension on macroinvertebrate communities

Conventionally, most research and restoration involving in-stream wood focuses on large wood (> 0.1 m diameter), excluding any smaller pieces. However, this may neglect a major component of in-stream habitat, as small wood can constitute the majority of pieces, particularly in small streams. The ecological benefi t of large wood is well established, but corresponding benefi ts associated with small wood (0.05-0.1 m diameter) have not been demonstrated. To test the effect of wood dimension on macroinvertebrate community composition, we compared the fauna occupying large wood habitats with that occupying small wood at eight streams in south-eastern Australia. The relationships between wood dimensions and its macroinvertebrate fauna were complex. Community composi- tion did not vary with wood dimension, and no signifi cant correlations were found between other macroinvertebrate attributes (including family richness and evenness) and wood dimension, including diameter. However, analysis of covariance suggested that large wood supported a greater diversity and abundance of macroinvertebrates, indicat- ing that the method of analysis could infl uence the result. Adjustment for differences in sample dimension using rarefaction determined that these fi ndings were likely to be a result of the surface area and volumes sampled varying with the dimension of the wood. Per unit surface area, and per unit volume, small wood supported a similar number of families to large wood. Thus we conclude that, relative to the available surface area, small and large wood can be equivalent in their contribution to the available habitat in a stream. Therefore, the potential value of small wood as a habitat resource warrants its explicit consideration for inclusion in ecological and rehabilitation studies.

Spatially explicit modeling of habitat dynamics and fish population persistence in an intermittent lowland stream

In temperate and arid climate zones many streams and rivers flow intermittently, seasonally contracting to a sequence of isolated pools or waterholes over the dry period, before reconnecting in the wetter parts of the year. This seasonal drying process is central to our understanding of the population dynamics of aquatic organisms such as fish and invertebrates in these systems. However, there is a dearth of empirical data on the temporal dynamics of such populations. We describe a spatially explicit individual-based model (SEIBM) of fish population dynamics in such systems, which we use to explore the long-term population viability of the carp gudgeon Hypseleotris spp. in a lowland stream in southeastern Australia. We explicitly consider the impacts of interannual variability in stream flow, for example, due to drought, on habitat availability and hence population persistence. Our results support observations that these populations are naturally highly variable, with simulated fish population sizes typically varying over four orders of magnitude within a 50-year simulation run. The most sensitive parameters in the model relate to the amount of water (habitat) in the system: annual rainfall, seepage loss from the pools, and the carrying capacity (number of individuals per cubic meter) of the pools as they dry down. It seems likely that temporal source sink dynamics allow the fish populations to persist in these systems, with good years (high rainfall and brief cease-to-flow [CTF] periods) buffering against periods of drought. In dry years during which the stream may contract to very low numbers of pools, each of these persistent pools becomes crucial for the persistence of the population in the system. Climate change projections for this area suggest decreases in rainfall and increased incidence of drought; under these environmental conditions the long-term persistence of these fish populations is uncertain.

Can macroinvertebrate rapid bioassessment methods be used to assess river health during drought in south eastern Australian streams?

Summary Despite significant concern about drought impacts in Australia, there have been no broad‐scale studies of drought effects on river health. A severe and prolonged drought has been acting on many streams in south eastern Australia over the past decade. EPA Victoria has undertaken rapid bioassessment (RBA) of over 250 stream reference sites since 1990, providing an opportunity for a before‐after‐control‐impact investigation of drought related changes to macroinvertebrate indices and water quality. This study uses data from 1990 to 2004 to critically evaluate the effectiveness of using RBA methods and indices, which were designed for assessment of human impacts, for monitoring streams during drought. Reference stream sites across Victoria (those with minimal anthropogenic disturbances and repeatedly sampled) were classified as being ‘in drought’ or ‘not in drought’ using the Bureau of Meteorology’s rainfall deficiency definition. Four biological indices (SIGNAL, EPT, Family Richness and AUSRIVAS) were calculated for combined autumn and spring samples for edge and riffle habitats for the selected sites. General linear models and paired t‐tests were used to detect drought related changes to index and water quality values at state‐wide and bioregional scales. Changes in taxa constancy were examined to determine which taxa were sensitive to or benefited from drought conditions. Frequency of site failure against biological objectives specified in the State Environment Protection Policy (Waters of Victoria) (herein termed ‘SEPP WoV’) before and during drought was also examined to detect changes in a management context. Few significant changes in index values were detected for riffle habitat samples. Rates of failure against biological objectives were similar before and during drought for riffle samples. In contrast, edge habitat AUSRIVAS and SIGNAL scores were significantly reduced at the state‐wide scale and most indices showed significant declines in the lower altitude forests, and foothills and coastal plains bioregions. Generally, more pollution tolerant, lentic taxa replaced sensitive and flow‐requiring taxa in edge samples during drought. In contrast, there were few reductions in the taxa of riffle samples during drought. However, many pool preferring, but pollution sensitive taxa occurred more frequently in riffle areas. Hence, the riffle community began to resemble that of pools and edges. This was attributed to decreased flow and increased ‘lentic’ habitat opportunities in riffles. Detection of a drought effect was confined to the edge habitat and site failure could be assigned to drought and anthropogenic impacts, in conjunction or alone. The riffle sampling protocol was resistant to detection of drought effects as samples were only taken when sufficient water was present within this habitat. Therefore, biological changes at sites not meeting policy objectives for riffle habitats can be attributed to anthropogenic rather than drought impacts.

Sediment instability affects the rate and location of primary production and respiration in a sand-bed stream

Creightons Creek, a rural stream in southeastern Australia, has been severely degraded by large-scale sedimentation of sand in the streambed. Our paper highlights the use of whole-stream metabolism measurements, fluorescein diacetate hydrolysis studies, and in situ enzyme mapping to examine the effect of sediment instability on benthic and hyporheic metabolism across seasonal and flow variations in Creightons Creek. Median gross primary production (GPP) and ecosystem respiration (ER24) rates, determined over a 20-mo period with the whole-stream single-station diurnal O2 change method, ranged between 0 and 0.5 g O2 m−2 d−1 and 0.6 and 3.7 g O2 m−2 d−1, respectively. These values gave photosynthesis/respiration (P/R) ratios between 0.00 and 0.41, indicative of a heterotrophic system. Creightons Creek was expected to support higher GPP because it has an open canopy, clear water, warm temperatures, and sufficient nutrients. However, this once-clay-bottomed stream now has an abrasive benthic layer of sand that moves continuously, even at low flows, and this layer has inhibited the growth of benthic primary producers (0–2 mg/m2 of chlorophyll a). During high flows, when scour and abrasion from the bed movement were at a maximum, the highest relative enzyme activity was located in the hyporheic zone at a depth of 7 to 12 cm, where the sediment was more stable. During low flows, the highest enzyme activity occurred in the upper 4 cm of the sediment profile. Our study shows that the instability of the sediment bed is a major factor determining the rates and locations of metabolism.

Association of reduced riparian vegetation cover in agricultural landscapes with coarse detritus dynamics in lowland streams

Studies were conducted on streams flowing through agricultural floodplains in south-eastern Australia to quantify whether reductions in riparian canopy cover were associated with alterations to the input and benthic standing stocks of coarse allochthonous detritus. Comparisons were made among three farmland reaches and three reaches within reserves with intact cover of remnant overstorey trees. Detritus inputs to these reaches were measured monthly over 2 years using litter traps. Direct inputs to streams within the reserves were relatively high (550–617 g ash free dry weight (AFDW) m–2 year–1), but were lower at farmland reaches with the lowest canopy covers (83–117 gAFDW m–2 year–1). Only a minor fraction of the total allochthonous input (&lt;10%) entered any of the study reaches laterally. The mean amounts of benthic detritus were lowest in the most open farmland reaches. Standing stocks of benthic detritus were found to be highly patchy across a large number of agricultural streams, but were consistently very low where the streamside canopy cover was below ~35%. Canopy cover should be restored along cleared agricultural streams because allochthonous detritus is a major source of food and habitat for aquatic ecosystems. Given the absence of pristine lowland streams in south-eastern Australia, those reaches with the most intact remnant overstorey canopies should be used to guide restoration.

Do scrapers increase downstream? Patterns in southeastern Australian streams

We measured scraper biomass and relative abundance and epilithic chlorophyll and organic matter on a single occasion at 17 sites ranging from order 1 to order 4 on five streams in southeastern Australia. Biomass of invertebrate scrapers was not related to chlorophyll concentration and was negatively related to epilithic organic matter. Neither scraper biomass nor relative proportion of scrapers increased downstream as predicted by the river continuum concept, and a power analysis indicated a greater than 90% probability that there was no relationship between either parameter and either stream order and upstream catchment area. We conclude that scraper biomass does not depend on algal standing crop as predicted by the RCC but is more likely to be influenced by total epilithon. Keywords : stream, invertebrate scraper, epilithon, functional feeding group Journal of Aquatic Sciences Vol. 21(1) 2006: 33-41

Ecological Effects of Serial Impoundment on the Cotter River, Australia

This study examines the ecological effects of serial impoundments (three dams) on a rocky upland stream in southeastern Australia. Physical, chemical and biological changes were quantified and interpreted within a three-level hierarchy of effects model developed previously by Petts [1984, Impounded Rivers. John Wiley and Sons, New York] and the Australian Rivers Assessment System (AUSRIVAS) to predict pre-dam biota. First-order effects were decreased median monthly discharges and floods of lesser magnitude following construction of the dams. No effect on water characteristics (pH, electrical conductivity and major ions) was evident. The second-order effect on channel morphology was a decrease in bank-full cross-sectional area by up to 75% because of reduced flows. At all sites, the predominantly cobble streambed was armoured and generally highly stable. The discharge required to initiate movement of the streambed surface sediments (38.9 m3 s−1) was 40% less frequent since construction of the dams, implying alteration to the natural disturbance regime for benthic biota. Benthic algal growth appeared more prolific at sites directly below dams. Fewer macroinvertebrate taxa than expected and modified assemblages within 1 km of all three dams were third-order effects. Compared to reference conditions, macroinvertebrate samples from the sites directly below the dams had relatively more Chironomidae larvae, Oligochaeta and Acarina, and fewer of the more sensitive taxa, Plecoptera, Ephemeroptera, Trichoptera and Coleoptera. Biological recovery to the macroinvertebrate assemblage was evident within 4 km downstream of the second dam.