The impact of physical disturbance on stream communities: lessons from road culverts

This study examined the impact of physical disturbance from long-established road culverts on stream macroinvertebrate communities. Three streams within a 6 km section of highway on the Avalon Peninsula, Newfoundland, Canada, were sampled. Streams had the entire upstream watershed and at least 100 m downstream of the road with natural boreal forest/barren vegetation and all had, within the sampled reaches, similar physical streambed characteristics. The fauna on stones from riffles was sampled at two upstream and three downstream sites, i.e., from 50 m above to about 100 m below the road in each stream. A total of 33 taxa were identified among the streams, with differences limited to a few rare taxa. The sample site communities did not significantly differ from each other with respect to the taxa present. Total macroinvertebrate abundance by site, for combined data of all streams, indicated the site at the exit of culvert plunge pool (site 3) had significantly elevated abundances. Analysis of individual taxa showed this was primarily due to very high numbers of Simulium spp. The other most notable changes were a decrease in numbers of Hydropsyche spp. and Elmidae below the road. The abundances of the remaining taxa were more variable among all sites. The study indicated that long-standing point source physical disturbance primarily impacted taxa abundance rather than community present/absent data, which will recolonize the disturbed zone by downstream drift. The differences in abundance are probably the result of the cleaning of substrate by abrasion, movement of substrate and reduction of detritus during each spate. Handling editor: D. Dudgeon     

山地河流浅滩生境潜流层大型无脊椎动物群落拓殖

通过包埋人工基质法研究大型无脊椎动物在山地河流潜流层中的拓殖过程。结果表明:群落个体密度在7—29 d呈"J"型增长,在29 d后骤然降低,55 d后呈波动趋势;物种丰富度在1—29 d呈增加趋势,29 d后呈波动状态;群落的生物量总体呈增加趋势。群落的物种丰富度、密度和生物量在第29、71和83天时没有显著性差异(P0.05),Shannon-Wiener多样性指数和Pielou均匀度指数在第55、71、83天没有显著性差异(P0.05),综合不同拓殖时间段物种的主成分分析,表明潜流层大型无脊椎动物群落在55 d后趋于稳定。群落优势种为摇蚊(Camptochironomus sp.)、河蚬(Corbicula fluminea)、四节蜉(Baetis sp.)、动蜉(Cinygmina sp.)、纹石蛾(Hydropsyche sp.)和扁泥甲科的一种(Psephenidae)。滤食者和收集者在整个拓殖过程中均是优势功能摄食群。群落拓殖过程是一个群落自身恢复能力和外部环境影响相互作用的过程,拓殖初期潜流层的结构是影响着无脊椎动物迁入的主要因素,中期动物的生活史特征起主要作用,稳定期之后群落可能受到各因素的综合影响。     

Colonization and production of macroinvertebrates on artificial substrata: upstream–downstream responses to a leaf litter exclusion manipulation

1. Macroinvertebrate colonization dynamics were examined on artificial substrata in a stream with terrestrial litter inputs excluded, downstream of the litter-exclusion treatment, and in a reference stream. 2. Short-term examination of the rates of organic matter accrual and invertebrate colonization demonstrated significantly lower accumulation of leaf detritus and invertebrates in the litter-excluded reach and a short distance downstream of that reach. 3. All major fractions of organic matter and invertebrates declined on artificial substrata during the 3-year litter exclusion. Further, secondary production on artificial substrata in the litter-excluded reach decreased from 6.2 to 1.5 g AFDM m⁻² year⁻¹ from pretreatment to the third year of litter exclusion, respectively. 4. Downstream, fine particulate organic matter on artificial substrata decreased during litter exclusion, and there was a significant reduction in colonization of collector-filterers. Total secondary production downstream of the litter exclusion declined >70%, demonstrating that downstream colonization dynamics are linked to upstream detritus inputs and processing by stream invertebrates.     

Responses of microbial activity in hyporheic pore water to biogeochemical changes in a drying headwater stream

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Distribution of solutes, microbes and invertebrates in river sediments along a riffle-pool-riffle sequence

• 1 Unlike riffles, research has focused rarely on the hyporheic zone of pools. To highlight the functioning of a pool, field investigations were performed in a riffle‐pool‐riffle sequence by integrating simultaneously physico‐chemistry, microbes and invertebrates. The study was conducted in a channel characterised by strong downwelling of surface water.
• 2 To include the downstream flux of water within the sediment, a longitudinal profile was studied along six stations situated: at the centre (Station 1) and at the lower end (Station 2) of the first riffle, at the upstream part (Station 3), at the centre (Station 4, at the inflection point) and at the lower end (Station 5) of the pool, and at the centre of the second riffle (Station 6). At each station, three replicate samples were taken and three sample depths were investigated (0.2, 0.5, and 1.0 m below the stream bed) on two dates.
• 3 Physico‐chemical parameters (vertical hydraulic gradient, oxygen concentration and specific conductance) differed between stations depending on infiltration rates. In contrast, organic matter and microbial parameters presented patchy distributions linked with factors other than the geomorphological pattern. Despite not very pronounced geomorphologic features, the slope variation at the centre of the pool (at the inflection point) affects the distribution of epigean and hypogean invertebrates.
• 4 Based upon faunal parameters, the pool could be divided into an upstream and a downstream part, the latter being more strongly influenced by surface water.
• 5 The pool should be considered as a heterogeneous area. In that respect, the inflection point of a pool may be as important as the top of a riffle in the functioning of river sediments.

     

Longitudinal patterns of invertebrates in the hyporheic zone of a glacial river

1. Longitudinal changes in physicochemical factors and the composition of the invertebrate community were examined in the hyporheic zone of a glacial river (Val Roseg, Switzerland) over a distance of 11 km from the glacier terminus. Multivariate analysis was used to determine the habitat preferences of taxa along an upstream‐downstream gradient of increasing temperature and groundwater contribution to river flow. 2. The hyporheos conformed to the longitudinal distribution model described for zoobenthic communities of glacial rivers in that taxonomic richness increased with distance from the glacier terminus. Spatial variation in taxonomic richness was best explained by temperature, the influence of groundwater, and the amount of organic matter. The overriding importance of these variables on the distribution of taxa was confirmed by the multivariate analysis. 3. The hyporheic zone contributed significantly to the overall biodiversity of the Roseg River. Whereas insect larvae were predominant in the benthos, hyporheic invertebrates were dominated by taxa belonging to the true groundwater fauna and the permanent hyporheos. Several permanently aquatic taxa (e.g. Nematoda, Ostracoda, Cyclopoida, Harpacticoida, Oligochaeta) appeared exclusively in the hyporheic zone or they extended farther upstream in the hyporheic layer than in the benthic layer. Leuctridae, Nemouridae, and Heptageniidae colonised hyporheic sediments where maximum water temperature was only 4 °C. 4. Despite strong seasonal changes in river discharge and physicochemistry in hyporheic water, the density and distribution of the hyporheos varied little over time. 5. Taxonomic richness increased markedly in the downstream part of a floodplain reach with an extensive upwelling zone. Upwelling groundwater not only maintained a permanent flow of water but also created several species‐rich habitats that added many species to the community of the main channel.     

Biological,chemical and physical characteristics of downwelling and upwelling zones in the hyporheic zone of a north-temperate stream

Along a single stream riffle, there is a typical flow pattern in which surface water enters the hyporheic zone in a downwelling zone at the head of the riffle and hyporheic water returns to the stream surface in an upwelling zone at the tail of the riffle. Distinct patterns of physical and chemical conditions in the hyporheic zone are likely to determine patterns of microbial activity and occurrence of hyporheic fauna. Interstitial water and core samples were taken at three depths in the downwelling and upwelling zones of a single riffle in the Speed River, Southern Ontario, Canada. Physical and chemical characteristics of the hyporheic water, bacterial density, protein content, detritus content and faunal composition of the hyporheic sediment were analysed. The downwelling and upwelling zones differed significantly in temperature, pH, redox potential, dissolved oxygen and nitrate with significant positive correlations occurring among the latter three. There were no differences in bacterial density or detritus content between the two zones nor between depths in either zone, but protein content, considered to be a measure of biofilm biomass, was significantly higher in the downwelling zone. Total density of hyporheic fauna and the number of taxa decreased with increasing depth in both upwelling and downwelling zones, and were positively correlated with surface water characteristics (oxygen, temperature and nitrate), sediment protein content and detritus; however, only a weak correlation was found with zone. The composition of taxa differed between the two zones, and faunal distribution was correlated with dissolved oxygen, detritus, protein content and depth.     

Seasonal dynamics of macroinvertebrate assemblages in the benthos and associated with detritus packs in two low-order streams with different riparian vegetation

• 1 The seasonal dynamics of the benthic macroinvertebrate assemblage, and the subset of this assemblage colonising naturally formed detritus accumulations, was investigated in two streams in south‐west Ireland, one draining a conifer plantation (Streamhill West) and the other with deciduous riparian vegetation (Glenfinish). The streams differed in the quantity, quality and diversity of allochthonous detritus and in hydrochemistry, the conifer stream being more acid at high discharge. We expected the macroinvertebrate assemblage colonising detritus to differ in the two streams, due to differences in the diversity and quantity of detrital inputs.
• 2 Benthic density and taxon richness did not differ between the two streams, but the density of shredders was greater in the conifer stream, where there was a greater mass of benthic detritus. There was a significant positive correlation between shredder density and detritus biomass in both streams over the study period.
• 3 Detritus packs in the deciduous stream were colonised by a greater number of macroinvertebrates and taxa than in the conifer stream, but packs in both streams had a similar abundance of shredders. The relative abundance of taxa colonising detritus packs was almost always significantly different to that found in the source pool of the benthos.
• 4 Correspondence analysis illustrated that there were distinct faunal differences between the two streams overall and seasonally within each stream. Differences between the streams were related to species tolerances to acid episodes in the conifer stream. Canonical correspondence analysis demonstrated a distinct seasonal pattern in the detrital composition of the packs and a corresponding seasonal pattern in the structure of the detritus pack macroinvertebrate assemblage.
• 5 Within‐stream seasonal variation both in benthic and detritus pack assemblages and in detrital inputs was of similar magnitude to the between‐stream variation. The conifer stream received less and poorer quality detritus than the deciduous stream, yet it retained more detritus and had more shredders in the benthos. This apparent contradiction may be explained by the influence of hydrochemistry (during spate events) on the shredder assemblage, by differences in riparian vegetation between the two streams, and possibly by the ability of some taxa to exhibit more generalist feeding habits and thus supplement their diets in the absence of high quality detritus.

     

溪流潜流层大型无脊椎动物生态学研究进展

溪流潜流层是溪流表层水和地下水相互作用的群落交错区,生物多样性丰富,是溪流生态系统的重要组成部分.大型无脊椎动物位于潜流层食物网的顶层,直接影响着潜流层物质和能量动态,是河流健康潜在的指示生物,调节着潜流层的环境净化和生态缓冲功能,对溪流生态系统发挥着至关重要的作用.潜流层大型无脊椎动物类群按生活史划分为偶入动物、非典型潜流层动物和典型潜流层动物.潜流层孔隙大小、孔隙水流速、溶解氧、温度、可利用的食物源、渗透系数和水力停留时间是影响大型无脊椎动物在潜流层分布的主要因素.对于潜流层这样一个特殊的生态界面,针对不同的研究目的应该选择合适的取样和调查方法.潜流层大型无脊椎动物的生活史和生活史对策,在溪流生态系统物质循环和能量流动中作用的定量化分析,基于潜流层大型无脊椎动物的河流健康评价体系,以及潜流层作为“庇护地”对于大型无脊椎动物分布和进化的生态学意义,都值得进一步关注和深入研究.     

Geomorphic influence on intraspecific genetic differentiation and diversity along hyporheic corridors

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Invertebrate food webs along a stream resource gradient

1. The flow of energy through food webs with similar species can vary with both space and time. The river continuum concept (RCC) provides a useful framework for predicting variability in the biota and food availability along streams. We estimated the flow of organic matter (g m^?2 year^?1) through food webs, arrayed along a stream, that had different resource inputs. Four sites were sampled along the Little Tennessee River, North Carolina, U.S.A.: two fifth order sites, one sixth and one seventh order site. The dominant resource is leaf detritus in the upstream reach (the upstream fifth order site), algae in the mid‐reaches (the downstream fifth and sixth order sites), and suspended material downstream (seventh order site). 2. Eleven genera, contributing from 50 to 66% of the total macroinvertebrate secondary production of each site, were studied. We estimated organic matter flow from resource to consumer by combining previously measured rates of invertebrate secondary production with gut content analyses and assimilation efficiencies. 3. Organic matter flow through food webs increased in a downstream direction, while the structure of the food webs remained constant. The total food consumed by the taxa analysed increased from 34 g m^?2 year^?1 at the upstream site to 730 g m^?2 year^?1 at the most downstream site. We estimate that the organic matter consumed by the entire macroinvertebrate community ranged from 66 to 1164 g m^?2 year^?1. These results indicate that there is variation in the magnitude of organic matter flow through the food webs along this river continuum. 4. The dominant food resource consumed also changed along the gradient. Leaf detritus consumption decreased from 58% of the total consumption upstream to 6% downstream, whereas consumption of amorphous detritus increased from 18 to 64%. The proportion of animal material consumed also increased from 3 to 27%. The total consumption of autochthonous resources (diatoms and filamentous algae) increased along the continuum (from 6.41 to 34.05 g m^?2 year^?1). We conclude that these results are related to variation in resource availability, dietary shifts and invertebrate secondary production. These results link resource availability to energy flow, a relationship originally suggested by the RCC.     

Perspectives and predictions on the microbial ecology of the hyporheic zone

1. Studies of hyporheic microbial ecology have suggested an important role for hyporheic microbial processes in stream ecosystem functioning. Using evidence from microbial communities in other aquatic habitats, some predictions are made concerning the diversity of microbial types and microbial processes likely to occur in the hyporheic zone, and the relative importance of these various types to the hyporheic ecosystem. 2. It is predicted that the biofilm growth form of interstitial micro-organisms will create a variety of microniches, allowing coexistence of a great diversity of microbial types, and promoting the activity of some otherwise poor competitors. It is further predicted that the confluence of reduced groundwaters and aerobic surface waters will favour chemolithotrophic processes in the hyporheic zone, but that these will contribute significantly to hyporheic production only if surface water is very low in dissolved organic carbon, or the groundwater is extremely reduced, such as by the influence of riparian wetlands. A variety of anaerobic respiratory pathways, such as nitrate, ferric ion, sulphate and even methanogenic respiration will be employed in the hyporheic zone, with biofilm dynamics permitting these to occur even in aerobic sediments. Anaerobic pathways may account for a significant proportion of total hyporheic organic matter mineralization. 3. The role of fungi in hyporheic dynamics is, as yet, almost completely unstudied. However, it is expected that they will be important in breaking down buried particulate organic matter (POM), which may account for a large proportion of total stream POM. 4. Physicochemical conditions in hyporheic sediments appear to be highly heterogeneous, and this heterogeneity may be very important in the cycling of certain nutrients, especially nitrogen, which involves a series of steps requiring different conditions. 5. Various new techniques are now available by which biofilm dynamics and in situ microbial processes may be measured. Studies are recommended of intact microbial communities both at the microscale of the biofilm and at the scale of the heterogeneities occurring in hyporheic sediments. Studies are needed that measure actual rates of microbial processes under in situ conditions.     

Experimental reductions in stream flow alter litter processing and consumer subsidies in headwater streams

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Flow regulation by dams affects ecosystem metabolism in Mediterranean rivers

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Influence of hyporheic zone characteristics on the structure and activity of microbial assemblages

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Visiting the hyporheic zone: young Atlantic salmon move through the substratum

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The upstream/downstream movement paradox of lotic invertebrates: quantitative evidence from a Welsh mountain stream

• 1 This study attempts to determine the mechanisms by which the downstream displacement of lotic invertebrates is compensated by the upstream movements of immatures and adults. To this end, submerged and aerial traps were set up at three sites, each 100 m apart on a small mountain stream (Yr Ogof) in North Wales and operated for 12 months.
• 2 At Site 1 (the source), 19.3% of the benthic invertebrates lost as drift were replaced by the upstream movement of aquatic stages. At Site 2, the average upstream compensation was 51.1% (although there was a marked difference between the two traps at the site). At downstream Site 3 the average compensation was 55.4%. The net loss of benthos downstream over 1 year was estimated to be 261920 individuals from Site 1, 41891 from Site 2, and 40470 from Site 3.
• 3 At Sites 1 and 2, the numbers of invertebrates drifting were positively correlated with both current speed and water depth. At Sites 2 and 3, the numbers moving upstream were positively correlated with water temperature. At all three sites, the numbers of animals drifting were positively correlated with the numbers moving upstream, under water.
• 4 In none of the eight common species of stoneffy did females show a strong overall upstream flight preference—however, two species, Leuctra nigra and Nemoura erratica, showed a significant downstream preference.
• 5 As with the stonefly nymphs, most of the caddisfly larvae showed a longitudinal distribution. Agapetus fuscipes larvae were most abundant at Site 1, yet females showed no preferred flight direction—this would seem to be inappropriate for maintaining this larval distribution pattern. However, females caught moving upstream at Site 2 were bigger and contained twice as many eggs, which were also larger, than females moving upstream at Site 1. The flight patterns of the other Trichoptera also seemed inappropriate for maintaining their respective larval distributions. Immature insects moved upstream at certain sites and times, but trends were not consistent. There was no correlation between female flight direction and local wind speed and direction.
• 6 Downstream displacement of the most abundant non-insect species, Gammarus pulex, was quite considerable at all three sites. However, at several times during the year the numbers moving upstream approached or exceeded those drifting. Maintenance of benthic population densities in this species is thought to be through a combination of upstream movement (which was highly correlated with benthic density at Sites 1 and 3) and production of young over a long (10 month) reproductive period. Maintenance of the benthic populations of the immature stages of the majority of insect species in Yr Ogof is thought to be through oviposition by females in the vicinity of their emergence sites.

     

Sources and seasonal patterns of dissolved organic matter (DOM) in the hyporheic zone

The hyporheic zone is a region underneath streambeds that integrates surface and groundwater. Although its location is central to biogeochemical linkages between the riparian zone, dissolved nutrients, and benthic biota, the seasonal quality and likely sources of dissolved organic matter (DOM) in the hyporheic zone are not well understood. To investigate DOM characteristics in the hyporheic zone, water from the surface and subsurface (at depths 20, 60, and 100 cm below the streambed) was sampled every 4 weeks from 2007 to 2008 in a third-order stream in southern Ontario. Using UV spectroscopy, measures of spectral slopes, aromaticity, and A ₂₅₄/A ₃₆₅ ratios (molecular weight) were obtained. Temporal changes in these measures were consistent with watershed processes such as shedding of leaf litter in the fall, and photochemical and biofilm influence in the spring and summer. The fluorescence index (a measure of relative DOM source) suggested that at the surface and in the downwelling zone, DOM microbial sources increased with depth in the sediment, regardless of the season. Excitation–emission matrices (EEMs) showed seasonally distinct, protein-like DOM components of bacterial origin that were stronger in the fall. Leachates from specific allochthonous DOM sources—leaf litter from Betula papyrifera (white birch) and Thuja occidentalis (white cedar)—and an autochthonous source, biofilm, were isolated and incubated with unfiltered surface water. EEMs from these leachates indicated that these sources could indeed help explain observed patterns of DOM in surface and subsurface waters. These results suggest that although DOM sources were relatively constant, biogeochemical processing within the hyporheic zone resulted a DOM pool that was temporally dynamic and altered the nature of organic matter transported downstream into lakes and rivers.     

Early stages of leaf decomposition are mediated by aquatic fungi in the hyporheic zone of woodland streams

1. Leaf litter constitutes the major source of organic matter and energy in woodland stream ecosystems. A substantial part of leaf litter entering running waters may be buried in the streambed as a consequence of flooding and sediment movement. While decomposition of leaf litter in surface waters is relatively well understood, its fate when incorporated into river sediments, as well as the involvement of invertebrate and fungal decomposers in such conditions, remain poorly documented. 2. We tested experimentally the hypotheses that the small interstices of the sediment restrict the access of the largest shredders to buried organic matter without compromising that of aquatic hyphomycetes and that fungal decomposers in the hyporheic zone, at least partly, compensate for the role of invertebrate detritivores in the benthic zone. 3. Alder leaves were introduced in a stream either buried in the sediment (hyporheic), buried after 2 weeks of exposure at the sediment surface (benthic‐hyporheic), or exposed at the sediment surface for the entire experiment (benthic). Leaf decomposition was markedly faster on the streambed surface than in the two other treatments (2.1‐ and 2.8‐fold faster than in the benthic‐hyporheic and hyporheic treatments, respectively). 4. Fungal assemblages were generally less diverse in the hyporheic habitat with a few species tending to be relatively favoured by such conditions. Both fungal biomass and sporulation rates were reduced in the hyporheic treatment, with the leaves subject to the benthic‐hyporheic treatment exhibiting an intermediate pattern. The initial 2‐week stage in the benthic habitat shaped the fungal assemblages, even for leaves later subjected to the hyporheic conditions. 5. The abundance and biomass of shredders drastically decreased with burial, except for Leuctra spp., which increased and was by far the most common leaf‐associated taxon in the hyporheic zone. Leuctra spp. was one of the rare shredder taxa displaying morphological characteristics that increased performance within the limited space of sediment interstices. 6. The carbon budgets indicated that the relative contributions of the two main decomposers, shredders and fungi, varied considerably depending on the location within the streambed. While the shredder biomass represented almost 50% of the initial carbon transformed after 80 days in the benthic treatment, its contribution was <0.3% in the hyporheic one and 2.0% in the combined benthic‐hyporheic treatment. In contrast, mycelial and conidial production in the permanently hyporheic environment accounted for 12% of leaf mass loss, i.e. 2–3 times more than in the two other conditions. These results suggest that the role of fungi is particularly important in the hyporheic zone. 7. Our findings indicate that burial within the substratum reduces the litter breakdown rate by limiting the access of both invertebrate and fungal decomposers to leaves. As a consequence, the hyporheic zone may be an important region of organic matter storage in woodland streams and serve as a fungal inoculum reservoir contributing to further dispersal. Through the temporary retention of litter by burial, the hyporheic zone must play a significant role in the carbon metabolism and overall functioning of headwater stream ecosystems.     

Variation in material transport and water chemistry along a large ephemeral river in the Namib Desert

• 1 The chemical characteristics of floodwaters in ephemeral rivers are little known, particularly with regard to their organic loads. These rivers typically exhibit a pronounced downstream hydrological decay but few studies have documented its effect on chemical characteristics and material transport. To develop a better understanding of the dynamics of floods and associated material transport in large ephemeral rivers, floods of the ephemeral Kuiseb River in south‐western Africa were tracked and repeatedly sampled at multiple points along the river's lower 220 km.
• 2 We quantified the composition and transport of solute and sediment loads in relation to longitudinal hydrological patterns associated with downstream hydrological decay. Source and sink areas for transported materials were identified, and the composition and transport dynamics of the organic matter load were compared to those described from more mesic systems.
• 3 Concentrations of sediments and solutes transported by floods in the Kuiseb River tended to increase downstream in association with pronounced hydrological decay. The contribution of particulate organic matter to total organic load is among the highest recorded, despite our observation of unusually high levels of dissolved organic matter. Hydrological decay resulted in deposition of all transported material within the lower Kuiseb River, with no discharge of water or materials to the Atlantic Ocean.
• 4 Our results suggest that longitudinal variation in surface flow and associated patterns of material transport renders the lower Kuiseb River a sink for materials transported from upstream. The downstream transport and deposition of large amounts of labile organic matter provides an important carbon supplement to heterotrophic communities within the river's lower reaches.