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Ecological Engineering 53 (2013) 100– 105

Contents lists available at SciVerse ScienceDirect

Ecological Engineering

jo u r n al hom ep age: www.elsev ier .com/ locate /ec oleng

hort communication

acroinvertebrate response to environmental flows in headwater streams inestern Victoria, Australia

onathon K. Mackiea, Edwin T. Chesterb, Ty G. Matthewsa, Belinda J. Robsonb,∗

School of Life and Environmental Sciences, Deakin University, Warrnambool, Victoria, 3280, AustraliaSchool of Environmental Science, Murdoch University, 90 South St, Murdoch, 6150, Western Australia, Australia

r t i c l e i n f o

rticle history:eceived 23 August 2012eceived in revised form0 November 2012ccepted 3 December 2012vailable online 25 December 2012

eywords:limate changenvironmental flowntermittent streams

a b s t r a c t

Intermittent streams drain over half the Australian mainland and provide water for humans and habi-tat for aquatic biota. Increased water extraction for human use together with climate change will likelyreduce stream flow and extend dry periods across southern Australia, adversely affecting biota in bothperennial and intermittent streams. Environmental flows may be released to protect stream ecosystems,however there is limited knowledge of biotic responses to flow releases in headwater streams. The aimof this study was to examine post-drying recovery of macroinvertebrate assemblages in regulated head-water streams following small environmental flow releases (0.4ML/day). To determine how flow releasesaffected macroinvertebrate assemblages, two streams that received environmental flows were comparedwith other regulated and unregulated streams that were either perennial or intermittent (some withperennial pools). The two streams that received environmental flows showed progressive increases in

acroinvertebratesecolonisationecovery

taxa richness downstream of the release point over time, and taxa richness also increased over a fourweek period. The downstream reach of one of the streams receiving environmental flows had an assem-blage that resembled those of other perennial streams, while assemblages in the other stream were moresimilar to unregulated, intermittent streams. Relatively small environmental flow allocations can havepositive impacts on invertebrate assemblages in small regulated streams over short time periods (1–4weeks), indicating their potential benefit for ecological restoration of headwater streams.

© 2012 Elsevier B.V. All rights reserved.

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. Introduction

Climate change is increasing the frequency and duration ofroughts in many regions and together with escalating demands foruman consumption are reducing river flows worldwide (Stanleyt al., 1997; Chester and Robson, 2011; Deitch and Kondolf, 2012).ntermittent streams are an important component of the Australianandscape because they drain over half of the mainland and providen important water source for humans in semi-arid and mediter-anean climates (Gasith and Resh, 1999). Intermittent streams alsorovide habitat for a diverse range of aquatic flora (Robson et al.,008) and fauna, particularly invertebrates (Boulton, 1989; Robsont al., 2005; Bonada et al., 2008).

Impoundment, irrigation, diversion and groundwater extrac-

ion reduce stream flow in all regions of the world, but knowledgef the effects of water diversion and extraction on headwaternd intermittent streams is limited relative to larger, permanently

∗ Corresponding author. Tel.: +61 8 93602417.E-mail address: b.robson@murdoch.edu.au (B.J. Robson).

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925-8574/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.ecoleng.2012.12.018

owing streams (Robson et al., 2008; Deitch and Kondolf, 2012).nvironmental flows are usually provided as releases of water fromeservoirs and are designed to protect river ecosystems from theegative effects of flow regulation (Lind et al., 2007; Robson et al.,011). However, few studies have assessed the benefits of envi-onmental releases in small headwater streams, which may beerennial or intermittently-flowing.

This study aimed to examine post-drying recovery of macroin-ertebrate assemblages in headwater streams that received smallnvironmental flow releases. We hypothesised that environmen-al flow releases would lead to an increase in taxa richness in thetreams over a short time period (4 weeks) and that assemblagesould gradually come to resemble those in perennially-flowing

treams. The abundance of recruiting stoneflies (Plecoptera) andlackflies (Simuliidae) at flow release sites was of particular

nterest because they are known to differ between perennialnd intermittent streams elsewhere (Boulton and Lake, 1992).

wo headwater streams received environmental flows, both witherennial reaches directly upstream of off-take weirs. Prior to floweleases, both streams were intermittent directly downstream ofhe off-take weirs, owing to water extraction for human use.

l Engineering 53 (2013) 100– 105 101

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. Materials and methods

.1. Study sites

Flow regimes of seasonally-flowing streams in the Grampiansational Park exhibit strong inter-annual variability (Chester andobson, 2011). So, both regulated and unregulated streams as wells the two streams receiving flow releases were sampled to iden-ify whether flow releases influenced colonisation of assemblages.leven streams (seven unregulated and four regulated) were sam-led within the Glenelg and Wannon catchments in the Victoriaange in the Grampians National Park, Western Victoria, Australia.he seven unregulated streams included four intermittent streamshat were completely dry over summer 2008–2009 (i.e. with-ut perennial pools: Red Rock Creek, Hut Creek, Graham Creek,osquito Creek), one seasonally-flowing stream with a peren-

ial pool (Cultivation Creek) and the remaining two streams wereerennial (Honeysuckle Creek, Deep Creek).

There were two regulated streams that did not receive envi-onmental flows; Browns Creek and Number One Creek. Brownsreek is perennial upstream of the off-take weir. In contrast, Num-er One Creek is non-perennial, but does contain a perennial poolpstream of the weir. Reaches directly downstream of the weirs onoth of these two streams were completely dry during summer andutumn (December 2008–May 2009). The remaining two regulatedtreams (Gap Creek and Camp Creek) received environmental floweleases. Both these streams are perennial upstream of the off-takeeirs and intermittent directly downstream of the weirs, except

or the periods when they received environmental flows.Other than flow regulation via off-take weirs, all 11 streams are

argely unaffected by human impacts and share similar channelorphology and substratum of boulder-cobble (median particle

ize = 150 mm). Stream cross-sectional profiles were similar withidth ranging from 0.5–3 m and depths up to 0.5 m. All samp-

ing occurred in high gradient sections (≈ 250 m elevation). Furtherescriptions of these streams can be found in Robson et al. (2008)nd Chester and Robson (2011).

.2. Environmental flow releases

An environmental flow allocation of 0.4 ML per day was releasedy the local water authority into Camp Creek and Gap Creek duringpril 2009. This allocation was discontinued in Gap Creek in May009, and so flow below the weir did not resume until winter rainsaused overtopping of the weir in early June. Environmental flowsor Camp Creek were discontinued early in June. However, down-tream flow continued due to overtopping of the weir by winterains, permitting an extra sampling time. Gap Creek also receivednvironmental flows in a different manner to Camp Creek. Waterassed directly through the off-take weir in Camp Creek, whereaseleases in Gap Creek flowed into a pipe at the weir and was theneleased approximately 50 m downstream of the weir wall (Fig. 1).he pipe exit was covered with sand and gave the impression thatater was coming up from a spring.

.3. Study design

Before-after, control-impact designs are a standard of impactnd restoration assessment (e.g. Howson et al., 2012) but fre-uently need to be modified where there is limited temporal orpatial replication of the restoration. Therefore, we used reaches

pstream of weirs as the control locations and reaches down-tream of weirs as impact reaches in Camp and Gap Creeks. Theeaches upstream of weirs in two other perennial regulated streamsBrowns and Number One Creeks) where no flows were released

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amp Creek, but is extracted at the off-take weir and released via a pipe approxi-ately 50 m downstream in Gap Creek. Lines over the pipe in Gap Creek represent

he sediment layer through which water passes before flowing downstream.

lso served as controls. Unregulated streams served as referenceocations for comparison of assemblages that colonised the impacteaches following flow releases and included perennial streamsnd streams with varying degrees of intermittency. This design wasot ideal, it is unbalanced and the two impacts consisted of differ-nt environmental flow regimes, but this was largely beyond ourontrol and governed by the limited number of streams available.herefore, we acknowledge that caution be used in interpretationf these results. These results do provide a starting point for futurevaluations using better replicated studies and also contribute rarenformation regarding environmental flow effects in headwatertreams.

Within each stream we used fixed interval sampling (10 m inter-als) along 100 or 200 m stream lengths so that any longitudinalatterns in colonisation of the stream beds following environmen-al releases could be described. If colonists arrived in the releasetreams by passing through the weir, higher species richness woulde observed closer to the weir wall and the pattern would changecross sampling times as invertebrates dispersed gradually down-tream. If there was no longitudinal pattern, this would indicatehat colonists were arriving through other means such as flight oratching from desiccation resistant eggs in the sediment.

.4. Field sampling

In the streams that received environmental flows (Camp andap Creeks), invertebrates were sampled by searching 100 mirectly upstream, and 200 m directly downstream of the off-takeeir. The 100 m section upstream of the weir was considered suf-cient to provide adequate representation of the diversity andelative abundance for that stream. However, because the capac-ty of benthic invertebrates to colonise downstream of the off-take

eirs was unknown, it was decided that 200 m should be sampledhere. In all other streams a 100 m reach was sampled.

Streams were sampled at each time irrespective of whether theyere flowing or dry, so we needed a method of sampling that wouldork in both dry and inundated conditions. Invertebrates at all

nundated sites were sampled using 15 min timed searches at each

0 m interval within the reach. Dry streams were sampled using aimed search (1 h) for aestivating invertebrates. Some of the inter-

ittent streams had small refuge pools (approximately 5 m × 3 m).e were concerned that removing invertebrates may have reduced

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he population size of some species and disturbed refuge wateruality (e.g. by disturbing anoxic sediments). Therefore, individualocks, leaves and other benthic material were carefully searchedor invertebrates to minimise disturbance. At the two intermit-ent streams containing a single perennial pool both the pool and

100 m reach downstream of the pool were sampled as describedbove. When flow resumed, data from the pool and the 100 m sam-les were combined to estimate the abundance and diversity of thattream.

For consistency, invertebrates were identified in situ in alltreams, regardless of flow regime. A hand lens (10×) facilitatedeld identifications, but not all specimens could be identifiedo species level. A few individuals of each taxon were collectedor laboratory identification. Rank relative abundance was alsoecorded: <5 = present but rare, 5–10 = present, 10–20 = common,0–50 = abundant, 50–100 = very abundant.

.5. Data analysis

The use of fixed interval sampling imposes some limitations onnalyses because the same assumptions cannot be made about theata as if random sampling is used. Therefore, for analysis of taxaichness and assemblage composition, invertebrate data at each0 m interval was pooled to represent total taxon diversity of eachtream at each sampling time. The Bray-Curtis similarity measureas calculated using presence/absence data and was represented

sing non-metric multi-dimensional scaling (nMDS) plots usingRIMER, version 6 (Clarke and Gorley, 2006). When comparing thenvertebrate assemblage that developed following the release ofnvironmental flow to other stream types, the 100 m closest to the

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ig. 2. Invertebrate taxa richness for intermittent and perennial streams from April to Noowing in June). Data for perennial, regulated streams (Camp Creek, Gap Creek, Browns

id-grey bars = intermittent reaches with a perennial pool and pale shaded bars = interm

eering 53 (2013) 100– 105

ownstream side of the weir was used. Temporal trajectories thatepresented variation in invertebrate assemblage over time werearked with arrows on the ordination plots.Multiple linear regression was used to test for relationships

etween taxa richness and increasing distance upstream (100 m)nd downstream (200 m) of the weir (taxa richness was not pooledcross the 10 m intervals within sites for this analysis) using SPSSersion 17.0. Assumptions of normality and homogeneity of vari-nce were met using untransformed data. T-tests were used toetermine whether the slopes of the lines (from the regression) dif-ered, that is, whether the pattern of species richness downstreamf the weirs in Camp and Gap Creeks and upstream of the weir inap Creek, differed between sampling times.

. Results

.1. Comparison of macroinvertebrates among streamsexcluding reaches receiving environmental flow)

Thirty-five taxa were found among 11 streams, of which 21ere common to both perennial and intermittent streams, and

4 were unique to perennial streams. Intermittent streams didot contain taxa that were not also present within perennialtreams. Therefore, perennial streams had greater taxa richnessegardless of the time sampled (Fig. 2). The lowest taxa rich-ess occurred in intermittent streams that were completely dry

n summer (Fig. 2). Number One and Cultivation Creeks, whichontained perennial pools, had higher taxa richness than thether intermittent streams that were completely dry in summerFig. 2); 8 taxa were found across the pools. Trichoptera were

vember, 2009. Missing bars = streams not sampled at that time (e.g. Gap Creek notCreek) are from reaches upstream of weirs. Dark shaded bars = perennial reaches,ittent reaches that dried completely during summer-autumn.

J.K. Mackie et al. / Ecological Engineering 53 (2013) 100– 105 103

Fig. 3. Non-metric dimensional scaling (NMDS) ordination comparing inverte-brate assemblage among stream flow regimes. Arrows represent seasonal changein assemblages at single reaches from the dry period (April) to flowing (August)2009. All 11 streams are included, but numbers of replicate samples for individualstreams differ due to variability in flow regimes. (a) Arrows show temporal change inassemblage composition in intermittent streams between summer-autumn, whenstreams were dry, and when flows resumed in winter; (b) arrows indicate tempo-ral change in assemblage composition in reaches of the two streams that receivede

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Ciirichness closest to the weir, but as time progressed, taxa spread

nvironmental flows (Gap Creek and Camp Creek).

he most diverse order (11 species from the families Calocidae,onoesucidae, Glossosomatidae, Helicopsychidae, Hydrobiosidae,ydropsychidae, Leptoceridae), followed by Plecoptera (8 speciesf Gripopterygidae and 1 Austroperlidae). Molluscs were absentnd crustaceans were rare, so assemblages were dominated bynsects (90%). The most common taxa shared between streamypes were plecopterans and dipterans which were also the

ost common taxa found in intermittent streams. The graz-rs Sclerocyphon spp. (Coleoptera, Psephenidae), Agapetus sp.Glossosomatidae), and the detritivore Acruroperla atra (Sámal)Austroperlidae) were only found in perennial streams. Two taxaere recorded within intermittent streams during April despite

hese streams being dry (Fig. 2). Both were aestivating isopodpecies: Heterias sp. (Janiridae) and Paraphreatoicus relictus NichollsPhreatoicidae).

Variation in invertebrate assemblages over time was clearlyower in perennial streams than intermittent streams (Fig. 3a).nce flow recommenced within intermittent streams, their inver-

ebrate assemblages became more similar (Fig. 3a). Taxa that firstppeared in intermittent steams following resumption of flow were

toneflies (Plecoptera) and blackflies (Simuliidae: Austrosimuliumpp.).

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ig. 4. Parallel lines fitted using multiple linear regression for taxa richness withncreased distance downstream of off-take weir (a) Gap Creek; (b) Camp Creek,uring the sampling period April to August 2009. Note different scales on y-axes.

.2. Comparison of macroinvertebrate assemblages in streameaches receiving environmental flow with other streams.

The development of invertebrate assemblages downstreamf off-take weirs following environmental flow releases differedetween Camp Creek and Gap Creek. For Gap Creek, assemblagesampled in May and November resembled those of intermittenttreams (Fig. 3b). In contrast, assemblages downstream of the weirn Camp Creek resembled those characteristic of perennial streamsnd varied less over time (Fig. 3b).

.3. In-stream patterns in assemblage composition and taxaichness in the streams receiving environmental flow releases.

Although invertebrate assemblages differed between Gap andamp Creeks, the pattern of increasing taxa richness with increas-

ng distance downstream from the weir was similar over time. Thats, upon environmental flow release, both streams had greater taxa

urther downstream (Fig. 4 a, b).For reaches upstream of the weir in Gap Creek, the number

f species decreased with increasing distance upstream, at all

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ampling times (t = -3.76, P = 0.001). There were significant differ-nces in the mean number of taxa upstream of the weir whenomparing April (x = 2.1) to both August (x = 4.6) and Novemberx = 3.7), (t = −2.17, P = 0.039, t = −3.390, P = 0.002 respectively).owever, the mean number of taxa did not differ between Augustnd November. Taxa richness was relatively high and compara-le to other perennial streams despite these significant changesver time (Fig. 2). During November, the upstream section hadve more taxa than downstream of the weir, with stoneflies (Ple-optera) being most common. Other species such as KoorrnongaV2 (Ephemeroptera: Leptophlebiidae) and dipterans (Simuliidae)ere recorded downstream, but only in low abundances.

Below the off-take weir in Gap Creek, the relationship betweenecreasing taxa richness and increasing distance downstream dif-ered between April and August (t = −2.15, P = 0.038). During April,axa richness was highest closest to the off-take weir with taxa rich-ess decreasing with increasing distance. August sampling showedhat this relationship had changed and that taxa richness was sim-lar regardless of distance downstream (Fig. 4a)

In Camp Creek, taxa richness upstream of the weir did nothange regardless of distance from the weir or time sampled. Taxaichness was always higher upstream of the weir than downstream.

total of 13 taxa were recorded upstream of the weir and 10ere found downstream following the commencement of the flow

elease. Lectrides varians Mosely (Trichoptera: Leptoceridae) andelicopsyche tillyardi Mosely (Trichoptera: Helicopsychidae) wereery abundant, nearly 10 times greater than the majority of otheraxa found. Sclerocyphon spp. were also common.

Decreasing taxa richness with increasing distance downstreamf the weir was also found in Camp Creek (Fig. 4b). This patternas most pronounced during April and differed significantly from

hose in June and August (t = −3.75, P = 0.015, t = −2.51 P < 0.001,espectively). Similar trends were found during June and Augustt = −1.25, P = 0.215) as more species began to occur further down-tream (Fig. 4b). The average number of taxa for a given distanceownstream nearly doubled from April (2.3) to August (4) (Fig. 4b).

n November, there was no relationship between taxa richness andistance downstream of the weir, with similar numbers of taxaccurring directly below the weir and at 100 m downstream (dataot shown).

. Discussion

.1. Macroinvertebrate assemblages (excluding streams receivingnvironmental flows)

Invertebrate assemblages found within intermittent streamsere a subset of those found in perennial reaches and the peren-ial reaches were also less variable over time, which is consistentith other studies at the same location (Chester and Robson, 2011).ne reason for these observed differences was the synchronous

ecruitment of stoneflies and blackflies, which was observed inntermittent streams, but not perennial streams. These taxa haveeen described elsewhere as early colonists that hatch from des-

ccation resistant eggs, and can increase in large numbers duringhe onset of winter (Boulton and Lake, 1992). The small size andarge abundances of stoneflies observed immediately after floweturn within intermittent streams in the Victoria Range suggestsatching from desiccation resistant eggs. Blackflies probably alsoatched from desiccation-resistant eggs, as they appeared shortly

fter flow resumed and have also been documented to have this lifeycle trait (Williams and Hynes, 1977; Boulton and Lake, 1992). Ifoth of these taxa have ability to lay desiccation-resistant eggs,he high abundances found in intermittent streams after flow

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eering 53 (2013) 100– 105

esumption could be a result of accumulation of eggs from the pre-ious season. In contrast, eggs from these two taxa that hatch in theerennial streams may not be delayed, leading to more consistentbundances with fewer seasonal peaks.

Two aestivating species of isopod were found in intermit-ent streams during the dry period: Heterias sp. (Janiridae) andaraphreatoicus relictus (Phreatoicidea). Both were found on theamp streambed directly under large boulders. Isopods are usu-lly absent from temporary waters because they are sedentary andack desiccation-resistant stages (Williams, 1985) although Chesternd Robson (2011) have also reported P.relictus in damp sedimenteneath stones in other Victoria Range streams. This demonstratesn important behavioural trait that isopods use to avoid drying.oulton (1989) mentions that the use of crayfish burrows by janirid

sopods is important for their survival in another Australian river.urther studies are required to identify if this type of refuge is oftensed by isopods within intermittent streams because most Aus-ralian janirid and phreatoicid isopods are short-range endemicsnd some have become extinct due to water extraction (Wilson,008).

.2. Invertebrate assemblage following the release ofnvironmental flows

The invertebrate assemblage that developed downstream fromhe off-take weir in Camp Creek resembled that of perennialtreams and therefore showed a positive response to the releasef environment flows. Over time, taxa richness increased furtherownstream to the extent that there was no difference between theeir wall and a further 100 m downstream by November. To our

nowledge, this is the only study that has documented invertebrateesponses to environmental releases in small headwater streamsr in streams where the environmental release has changed theegulated flow regime from intermittent to perennial.

Of the taxa that colonised the wetted downstream reach inamp Creek, most have the potential to have done so via driftr aerial pathways, some could have colonised via desiccationesistant eggs (stoneflies, blackflies), while only a few (isopods,ater pennies) could have come from aestivation. None of these

pecies use hyporheic refuges (Chester and Robson, 2011) and theongitudinal pattern strongly suggests initial colonisation imme-iately downstream of the weir. Therefore, the high taxa richnessecorded shortly after the commencement of environmental floweleases in Camp Creek is likely to be a result of drift/crawlingigration through the weir. Late in-star trichopterans Lectrides

arians (Leptoceridae), Triplectides truncatus Neboiss (Leptoceri-ae) and Helicopsyche tillyardi (Helicopsychidae) pupae were found

short distance downstream from the off-take weir, two weeksfter the release commenced. Given their size and advanced stagef development, it is unlikely that these individuals would haveolonised from sources other than by drift given that perennialeaches upstream provided a reliable source of colonists, especiallys taxa richness did not change regardless of distance upstream.uring one occasion, a fine-meshed net was placed over the weirutlet on Camp Creek for approximate two hours. It collected L. var-

ans, T. truncatus and stoneflies, further supporting drift/crawlingigration as the dominant source for downstream colonisation.Aestivating taxa are also believed to contribute to early recoloni-

ation. For example, early instar Sclerocyphon spp. are virtuallympossible to see in the field (Smith, 1981), and can become activefter being in a dry stream bed for 13 weeks (Boulton, 1989).

he abundance of Sclerocyphon spp. increased from April to June,uggesting that initial recolonisation was probably the result ofestivation, but with increased environmental flow duration, driftigration contributed to their relative abundance. Ephemeroptera

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nd Trichoptera larvae were the most common taxa found furthestownstream of the weir in Camp Creek. These insects have ofteneen shown to have strong dispersal capabilities as adults (Graynd Fisher, 1981), so hatching of eggs laid by aerial colonists possi-ly contributed to the recolonisation process of these two speciesnce downstream habitat had been inundated for some weeks.

Although the pattern of greater taxa richness with increasedistance downstream of the off-take weir over time in Gap Creekas similar to that in Camp Creek, the invertebrate assemblagesid not respond as well to environmental flows, with taxa richnessnd assemblage composition more closely resembling that of inter-ittent streams. Taxa richness upstream from the weir was not as

onsistent as in Camp Creek, because taxa richness increased overistance from the weir and over time. This may have contributedo the low taxa richness found downstream of the weir.

The lower taxa richness found downstream of the weir in Gapreek is thought to be a result of two main factors. Firstly, the way

n which environmental flow was released is likely to disconnectownstream reaches from faunal assemblages directly above theeir. This occurs because drifting invertebrates must go through a

ayer of sediment upon exiting the extraction pipe. This is likely toct as a filter and probably reduces survival rates and therefore con-ributions to recolonisation via drift. The effect of sediment loadsn invertebrate communities is well documented (Newcombe andacdonald, 1991; Waters, 1995). Filter-feeding apparatus becomes

logged by sediment, grazing invertebrates may be affected due tomothering of algal habitat (Vuori and Joensuu, 1996) and physicalbrasion by sediment particulates may damage vital organs, suchs the external gills of many invertebrates (Newcome and MacDon-ld, 1991). Therefore, it is probable that passing through a layer ofne sediment would greatly reduce invertebrate survival.

Secondly, the duration of the environmental flow release inap Creek during autumn was not sufficient to ensure continualow downstream of the weir, resulting in the streambed drying ineaches downstream of the weir before the onset of winter flows.uration of environmental flow plays a crucial role in achievingesired ecological outcomes (Robson et al., 2011). The short dura-ion of environmental flows in Gap Creek could have contributedo the lower taxa richness and fewer aestivating taxa found down-tream of the weir. Invertebrates capable of aestivation may only beble to complete this process once in their life time (Wickson et al.,012). Therefore, irregular stopping and starting of flow caused byhe short duration of environmental flows could have negativelyffected aestivating invertebrates, which may be waiting for theeturn of water to activate them from a dry resistant stage (Wicksont al., 2012). Mechanisms have been documented that prevent pre-ature emergence (Williams, 2006; Wickson et al., 2012) however,

he influence of short-term drying and inundation (resulting fromegulation) and whether it will exhaust these protective mecha-isms and create physiological challenges for aestivating speciesemains largely unknown.

. Conclusion

The effectiveness of environmental flow releases dependsainly on how they are managed; important factors such as

tream connectivity, duration and timing of flow strongly influ-nce outcomes (Gippel and Stewardson, 1998, King et al., 2008;obson et al., 2011). The present study showed that sustained floweleases can enhance invertebrate taxa richness to the point wheressemblages resembled those in unregulated perennial streams.

owever, in the stream where flows were interrupted by dryingnd where colonisation from upstream was impeded, recovery ofnvertebrate assemblages did not occur to the same extent. There-ore, this study shows the importance of connectivity and duration

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f flow releases and that relatively small environmental flowllocations (0.4ML/day) can have positive impacts on stream inver-ebrate assemblages in small, regulated perennial streams over ahort period of time (weeks). Further studies with greater spatiali.e. more headwater streams receiving environmental flows) andemporal replication (i.e. multiple years of releases) are required toetermine the generality of these conclusions.

cknowledgments

This work was funded by Wannon Water, Deakin University,urdoch University and the Glenelg-Hopkins Catchment Manage-ent Authority using permit No. 10004699 from the Department

f Sustainability and Environment/Parks Victoria.

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