Different roles of environmental variables and spatial factors in structuring stream benthic diatom and macroinvertebrate in Yangtze River Delta,China

Exploring the relative contribution of spatial factors and environmental variables in shaping communities is of widespread interest in biodiversity conservation and environmental management. Stream communities are hierarchically regulated by environmental variables over multiple spatial scales, and the reaction of different organisms to stressors are still equivocal. We sampled both macroinvertebrates and diatom at 80 sites and additional 10 sites for macroinvertebrates, field measured and laboratory analyzed environmental variables, from the tributaries of Qiantang River, Yangtze River Delta China in 2011. We used PCNM (principal coordinates of neighbor matrices) to generate spatial predictors. We applied redundancy analysis and variation partitioning procedures to identify key spatial and environmental factors, and to quantify their relative roles in shaping diatom and macroinvertebrate assemblages. Our results demonstrated the role of spatial and environmental variables differed in shaping benthic diatom and macroinvertebrate. Diatom assemblage variations were better explained by spatial factors, however macroinvertebrate assemblage variations were better explained by environmental variables. In terms of environmental variables, catchment scale variables (e.g., land use estimators, land use diversity) played the primary role in determining the patterns of both diatom and macroinvertebrate assemblages, whereas the influence of reach-scale variables (e.g., pH, substrates, and nutrients) appeared less. However, nutrients were the stronger factors influencing benthic diatom, whereas physical habitat (e.g., substrates) played more important role than water chemistry in structuring macroinvertebrates. Our results provided more evidence to the incorporation of spatial factors interpreting spatial patterns of stream organisms, and highlighted the useful of multiple organisms and environmental variables at different spatial scales in diagnosing mechanism of stream degradation and in building a sound stream conditions monitoring program for Yangtze River Delta.     

Environmental factors accounting for benthic macroinvertebrate assemblage structure at the sample scale in streams subjected to a gradient of cattle grazing

Macroinvertebrate assemblages were related to environmental factors that were quantified at the sample scale in streams subjected to a gradient of cattle grazing. Environmental factors and macroinvertebrates were concurrently collected so assemblage structure could be directly related to environmental factors and the relative importance of stressors associated with cattle grazing in structuring assemblages could be assessed. Based on multivariate and inferential statistics, measures of physical habitat (% fines and substrate homogeneity) had the strongest relationships with macroinvertebrate assemblage structure. Detrital food variables (coarse benthic and fine benthic organic matter) were also associated with assemblage structure, but the relationships were never as strong as those with physical habitat measures, while autochthonous food variables (chlorophyll a and epilithic biomass) appeared to have no association with assemblage structure. The amount of variation explained in taxa composition and macroinvertebrate metrics is within values reported from studies that have examined macroinvertebrate metric–sediment relationships. The % Coleoptera and % crawlers had consistent relationships with % fines during this study, which suggests they may be useful metrics when sediment is a suspected stressor to macroinvertebrate assemblages in Blue Ridge streams. Findings from this study also demonstrate the importance of quantitative sampling through time when research goals are to identify relationships between macroinvertebrates and environmental factors.     

Trophic structure of macrobenthos in the Tagus estuary and adjacent coastal shelf

The trophic structure of benthic communities in the Tagus estuary and adjacent coastal shelf was characterized according to a functional guild approach, based on sampling surveys conducted between 1987 and 2000. Macrobenthic organisms were assigned to seven distinct trophic groups (herbivorous, filter feeders, surface deposit feeders, subsurface deposit feeders, carnivores, filter feeders/detritivores, carnivores/detritivores) and the dominance of these groups was related to environmental variables using multivariate ordination techniques. Surface-deposit feeders were numerically dominant in the Tagus estuary, making up 52% of the benthic communities, while in the adjacent coastal shelf the assemblage was dominated by both surface-deposit feeders and filter feeders (37% and 33%, respectively). When biomass was considered, filter feeders and filter feeders/detritivores were the dominant groups in the estuary, while for the adjacent coastal shelf filter feeders represented 83% of the total biomass. Salinity, depth and sediment composition were the main factors structuring spatial distribution. Surface-deposit feeders were the most abundant macrobenthos of the upper estuary. Surface deposit feeders also dominated the middle and the lower estuary but the proportion of filter feeders as well as other trophic groups increased with salinity. Generally, a more even distribution of trophic structure was found at stations with high salinity. In the adjacent coastal shelf, the trophic diversity decreased with depth. The trophic structure revealed that filter feeders dominated in abundance and biomass in shallow sandy sediments (<25 m), while in deeper sandy mud and muddy habitats (>50 m to 260 m), deposit feeders and carnivores were the most important groups in abundance and biomass, respectively.     

Invertebrate Metacommunity Structure and Dynamics in an Andean Glacial Stream Network Facing Climate Change

Under the ongoing climate change, understanding the mechanisms structuring the spatial distribution of aquatic species in glacial stream networks is of critical importance to predict the response of aquatic biodiversity in the face of glacier melting. In this study, we propose to use metacommunity theory as a conceptual framework to better understand how river network structure influences the spatial organization of aquatic communities in glacierized catchments. At 51 stream sites in an Andean glacierized catchment (Ecuador), we sampled benthic macroinvertebrates, measured physico-chemical and food resource conditions, and calculated geographical, altitudinal and glaciality distances among all sites. Using partial redundancy analysis, we partitioned community variation to evaluate the relative strength of environmental conditions (e.g., glaciality, food resource) vs. spatial processes (e.g., overland, watercourse, and downstream directional dispersal) in organizing the aquatic metacommunity. Results revealed that both environmental and spatial variables significantly explained community variation among sites. Among all environmental variables, the glacial influence component best explained community variation. Overland spatial variables based on geographical and altitudinal distances significantly affected community variation. Watercourse spatial variables based on glaciality distances had a unique significant effect on community variation. Within alpine catchment, glacial meltwater affects macroinvertebrate metacommunity structure in many ways. Indeed, the harsh environmental conditions characterizing glacial influence not only constitute the primary environmental filter but also, limit water-borne macroinvertebrate dispersal. Therefore, glacier runoff acts as an aquatic dispersal barrier, isolating species in headwater streams, and preventing non-adapted species to colonize throughout the entire stream network. Under a scenario of glacier runoff decrease, we expect a reduction in both environmental filtering and dispersal limitation, inducing a taxonomic homogenization of the aquatic fauna in glacierized catchments as well as the extinction of specialized species in headwater groundwater and glacier-fed streams, and consequently an irreversible reduction in regional diversity.     

Benthic macroinvertebrates in Swedish streams: community structure, taxon richness, and environmental relations

Spatial scale, e.g. from the stream channel, riparian zone, and catchment to the regional and global scale is currently an important topic in running water management and bioassessment. An increased knowledge of how the biota is affected by human alterations and management measures taken at different spatial scales is critical for improving the ecological quality of running waters. However, more knowledge is needed to better understand the relationship between environmental factors at different spatial scales, assemblage structure and taxon richness of running water organisms. In this study, benthic macroinvertebrate data from 628 randomly selected streams were analysed for geographical and environmental relationships. The dataset also included 100 environmental variables, from local measures such as in-stream substratum and vegetation type, catchment vegetation and land-use, and regional variables such as latitude and longitude. Cluster analysis of the macroinvertebrate data showed a continuous gradient in taxonomic composition among the cluster groups from north to south. Both locally measured variables (e.g. water chemistry, substratum composition) and regional factors (e.g. latitude, longitude, and an ecoregional delineation) were important for explaining the variation in assemblage structure and taxon richness for stream benthic macroinvertebrates. This result is of importance when planning conservation and management measurements, implementing large-scale biomonitoring programs, and predicting how human alterations (e.g. global warming) will affect running water ecosystems.     

Relating macroinvertebrate community structure to environmental characteristics and sediment contamination at the scale of the St. Lawrence River

There is still no assessment of the impact of sediment chemicals and environmental conditions on macroinvertebrates at the scale of the St. Lawrence River. In order to assess these impacts in the fluvial section of the St. Lawrence River including the Montreal harbour, the community structure of macroinvertebrates using different taxonomic aggregations (genus and family) and taxa attributes (abundance, presence–absence, indicator taxa) was assessed. The goal of the study was to determine the indicator taxa of macroinvertebrates along the fluvial continuum and relate changes in macroinvertebrate community to sediment chemical conditions and environmental characteristics of habitats using variance partitioning. This study also evaluated which taxonomic level and taxa attributes of macroinvertebrates were the most suitable for bioassessment of quality of sediments and habitat environment in the St. Lawrence River. Four different macroinvertebrate assemblages were found distributed along the fluvial continuum using either abundance or presence–absence data and genus or family levels. Indicator taxa characteristic of the different macroinvertebrate communities were associated with the sediment contamination gradient. However, habitat environmental characteristics (water masses, sulphur and DOC in sediments) had more influence on macroinvertebrate assemblages than sediment contamination. Our study confirms that family level analysis can give information comparable to the genus level analysis using presence–absence or abundance of macroinvertebrates, yet a higher number of indicator taxa were detected at the genus level.     

Structure of Macroinvertebrate Communities in Relation to Environmental Variables in a Subtropical Asian River System

Subtropical Asian rivers support a highly diverse array of benthic macroinvertebrates. Yet, their biodiversity and functionality has been poorly investigated. We choose the Chishui River system, one of the largest un‐dammed, first level branches upstream of the Yangtze River, China, to: 1) determine the spatial pattern of macroinvertebrate diversity and community structure, and 2) examine the influence of variables at local habitat and basin scales on the distribution of macroinvertebrate communities. Samples were collected from 43 sites in spring of 2007. After Canonical Correspondence Analysis, two basin and five habitat variables were found to be significant predictors of the macroinvertebrate community structure. Variance partitioning analysis showed that habitat physical variables had a greater influence than other environmental variables in macroinvertebrate community, which suggested that preserving habitat, especially upstream, should be strongly considered in biological conservation. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Analysis of macrobenthic communities in Flanders,Belgium, using a stepwise input variable selection procedure with artificial neural networks

The effect of environmental conditions on river macrobenthic communities was studied using a dataset consisting of 343 sediment samples from unnavigable watercourses in Flanders, Belgium. Artificial neural network models were used to analyse the relation among river characteristics and macrobenthic communities. The dataset included presence or absence of macroinvertebrate taxa and 12 physicochemical and hydromorphological variables for each sampling site. The abiotic variables served as input for the artificial neural networks to predict the macrobenthic community. The effects of the input variables on model performance were assessed in order to identify the most diagnostic river characteristics for macrobenthic community composition. This was done by consecutively eliminating the least important variables and, when beneficial for model performance, adding previously removed ones again. This stepwise input variable selection procedure was tested not only on a model predicting the entire macrobenthic community, but also on three models, each predicting an individual taxon. Additionally, during each step of the stepwise leave-one-out procedure, a sensitivity analysis was performed to determine the response of the predicted macroinvertebrate taxa to the input variables applied. This research illustrated that a combination of input variable selection with sensitivity analyses can contribute to the development of reliable and ecologically relevant ANN models. The river characteristics predicting presence or absence of the benthic macroinvertebrates best were the Julian day, conductivity, and dissolved oxygen content. These conditions reflect the importance of discharges of untreated wastewater that occurred during the period of investigation in nearly all Flemish rivers.     

Short-term responses of macroinvertebrate drift following experimental sediment flushing in a Japanese headwater channel

We examined short-term responses of macroinvertebrate drift associated with experimental sediment flushing in a headwater. Increases in the drifting abundances of Ephemeroptera and Plecoptera coincided with increases in bed load yield rather than peaks in discharge or suspended sediment concentrations. The approach and arrival of a sediment wave may provide a physical cue that initiates the escape of benthic macroinvertebrates. Because fine bed load sediments, with diameters <4 mm, tended to accumulate on and in the substrate matrix, such sedimentation affected the benthic macroinvertebrates residing on and in the substrate, increasing the number of macroinvertebrates in the drift. Therefore, the decreases observed in the densities of most macroinvertebrate taxa following sediment flushing were probably associated with sediment deposition and the resulting escape of macroinvertebrates from benthic habitats. The magnitudes of the decreases in macroinvertebrate density were lower at sites located 200 m downstream from the sediment sources than at sites located 20 m downstream. The results from this experimental flushing study suggest that bed load movement and resulting sediment accumulation alter macroinvertebrate drift patterns and cause decreases in the abundances of benthic macroinvertebrates in headwater streams.     

钱塘江中游流域不同空间尺度环境因子对底栖动物群落的影响

溪流底栖动物群落结构受不同空间尺度环境因子的共同作用。基于2010年钱塘江中游流域60个样点的大型底栖无脊椎动物和环境变量数据,寻找与研究流域底栖动物群落结构变化密切相关的关键环境变量,解析流域尺度和河段尺度的环境因子对底栖动物群落的相对影响。PCA分析表明该区域的主要环境梯度是流域内的土地利用类型及其引起的溪流物理生境退化程度和水体营养状态。CCA分析发现影响底栖动物群落的流域尺度的关键环境变量是纬度、海拔、样点所在流域大小、森林用地百分比,河段尺度是总氮、总磷、钙浓度、二氧化硅浓度和平均底质得分。偏CCA分析得到两种尺度环境因子对底栖动物变异的总解释量为26.4%,流域尺度和河段尺度变量分别为总解释量的50%和31%;方差分解结果表明研究区域大型底栖无脊椎动物受到两种尺度环境因子的综合影响,且流域尺度环境因子较河段尺度环境因子更为重要,体现了其在溪流生态系统保护、恢复、监测和评价中的重要参考价值。     

Macroinvertebrate community traits and nitrate removal in stream sediments

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Community structure or function: effects of environmental stress on benthic macroinvertebrates at different spatial scales

1. This study investigated the relation of benthic macroinvertebrates to environmental gradients in Central European lowland rivers. Taxonomic structure (taxa) and functional composition (metrics) were related to gradients at four different spatial scales (ecoregion, catchment, reach and site). The environmental variables at the catchment‐, reach‐ and site scales reflected the intensity of human impact: catchment and floodplain land use, riparian and floodplain degradation, flow regulation and river bank and bed modification. 2. Field surveys and GIS yielded 130 parameters characterising the hydromorphology and land use of 75 river sections in Sweden, the Netherlands, Germany and Poland. Two hundred and forty‐four macroinvertebrate taxa and 84 derived community metrics and biotic indices such as functional guilds, diversity and composition measures were included in the analysis. 3. Canonical Correspondence Analysis (CCA) and Redundancy Analysis (RDA) showed that hydromorphological and land use variables explained 11.4%, 22.1% and 15.8% of the taxa variance at the catchment (‘macro’), reach (‘meso’) and site (‘micro’) scales, respectively, compared with 14.9%, 33.2% and 21.5% of the variance associated with the derived metrics. Ecoregion and season accounted for 10.9% and 20.5% of the variance of the taxonomic structure and functional composition, respectively. 4. Partial CCA (pCCA) and RDA (pRDA) showed that the unique variance explained was slightly higher for taxa than for metrics. By contrast, the joint variance explained for metrics was much higher at all spatial scales and largest at the reach scale. Environmental variables explained 46.8% of metric variance and 32.4% of taxonomic structure. 5. Canonical Correspondence Analysis and RDA identified clear environmental gradients along the two main ordination axes, namely, land use and hydromorphological degradation. The impact of catchment land use on benthic macroinvertebrates was mainly revealed by the proportion of urban areas. At the reach scale, riparian and floodplain attributes (bank fixation, riparian wooded vegetation, shading) and the proportion of large woody debris were strong predictors of the taxonomic structure and functional composition of benthic macroinvertebrates. At the site scale, artificial substrata indicated human impact, particularly the proportion of macro‐ and mesolithal used for bank enforcement (rip–rap). 6. Our study revealed the importance of benthic macroinvertebrate functional measures (functional guilds, composition and abundance measures, sensitivity and tolerance measures, diversity measures) for detecting the impact of hydromorphological stress at different spatial scales.     

崇明东滩盐沼湿地大型底栖动物功能群分布特征及其影响因子

以长江口崇明东滩典型盐沼分布区为研究区域,在不同站位固定样地月际取样调查基础上,分析了大型底栖动物食性功能群沿高程梯度的分布特征及其主要影响因子,特别是外来入侵植物的影响。结果表明,不同高程区域,大型底栖动物优势种不同,除中潮带分布区以杂食性和植食性功能群为主外,其余各区域均以杂食性功能群为主。沿高程梯度,大型底栖动物各功能群的多度和生物量均发生极显著的变化(P<0.01),而不同功能群在不同植被带间的差异情况有所不同。其中,高程最低的光滩区域,肉食性功能群多度和生物量均显著高于高程相对较高的植被带(P<0.05);中潮带海三棱藨草分布区植食性功能群多度和生物量均显著高于其他高程区域(P<0.05)。主要生境因子,包括沉积物总磷、总氮、有机质、速效磷、硝态氮、铵态氮、中值粒径,以及植物的植株高度和地上部分生物量干重等指标,均随高程梯度变化显著(P<0.05),但不同因子变化特征有所不同。外来种互花米草的入侵并未造成相应区域大型底栖动物优势功能群的改变,但区域内杂食性功能群的多度和生物量均显著增加(P<0.05);环境因子中的部分因子,包括沉积物速效磷、硝态氮、铵态氮和有机质含量,表现出与同高程的本地种芦苇分布区间的显著差异(P<0.05)。导致大型底栖动物食性功能群组成及分布发生变化是多种生境因子综合作用的结果,而对不同食性功能群起作用的主要影响因子存在差异。沉积物营养盐含量差异是造成大型底栖动物食性功能群多度变化的最主要因素;沉积物盐度是影响大型底栖动物食性功能群生物量的最主要因素。要完整揭示底栖动物功能群分布特征及其影响因子的作用机理,需要综合考虑水文、植被、沉积物等多种生境因子。     

Using geophysical information to define benthic habitats in a large river

1. Most attempts to describe the distribution of benthic macroinvertebrates in large rivers have used local (grab‐scale) assessments of environmental conditions, and have had limited ability to account for spatial variation in macroinvertebrate populations. 2. We tested the ability of a habitat classification system based on multibeam bathymetry, side‐scan sonar, and chirp sub‐bottom seismics to identify large‐scale habitat units (‘facies’) and account for macroinvertebrate distribution in the Hudson River, a large tidal river in eastern New York. 3. Partial linear regression analysis showed that sediment facies were generally more effective than local or positional variables in explaining various aspects of the macroinvertebrate community (community structure, density of all invertebrates, density of fish forage, density of a pest species –Dreissena polymorpha). 4. Large‐scale habitats may be effective at explaining macroinvertebrate distributions in large rivers because they are integrative and describe habitat at the spatial scales of dominant controlling processes.     

Do isolation and local habitat jointly limit the structure of stream invertebrate assemblages?

1. Both local and regional processes simultaneously control species assemblages depending on spatial habitat configuration. In dendritic networks like streams, the unique spatial arrangement of habitats produces various combinations of local habitat size and isolation. Stream invertebrate assemblages could therefore be controlled by different combinations of local and regional processes, depending on their location in the network. 2. Using quantile regression, we investigated how local habitat size, local environmental conditions and spatial isolation influenced variation in assemblage composition. Adult Trichoptera and benthic macroinvertebrate assemblages were represented by non‐metric multidimensional scaling (NMDS) ordination scores, as were local environmental conditions, in four headwater stream networks in New Zealand. 3. With increasing local habitat size, there was a decrease in variation in assemblage composition (NMDS scores) of both adult Trichoptera and benthic macroinvertebrates. This relationship between habitat size and assemblage variation was related to local habitat conditions at the upper limit of assemblage variability and spatial isolation at the lower limit of assemblage variability, for both adult Trichoptera and benthic assemblages, indicating joint local and regional controls on stream invertebrate assemblages. 4. The relationships between local assemblages and their neighbours, based on community similarity scores, differed between benthic macroinvertebrates and adult Trichoptera. For benthic assemblages, the larger the stream, the more similar assemblages were to neighbouring assemblages, whereas there was no consistent relationship between assemblage similarity and stream size for adult Trichoptera. This difference in structuring could be attributed to contrasting spatial influences linked to the different dispersal modes of adults and larvae. However, because adult and benthic assemblages are not independent, the influence of life stage on spatial distribution is difficult to determine (i.e. it is essentially a ‘chicken and egg’ argument). 5. Overall, our approach using quantile regression to evaluate limit responses, rather than regressions on means, has highlighted the joint importance of local habitat and spatial processes in structuring stream invertebrate assemblages. Furthermore, we have provided evidence for the importance of the spatial network arrangement and interactions between life stages and dispersal processes, in structuring stream assemblages.     

Relationships between ecosystem metabolism, benthic macroinvertebrate densities, and environmental variables in a sub-arctic Alaskan river

Relationships between environmental variables, ecosystem metabolism, and benthos are not well understood in sub-arctic ecosystems. The goal of this study was to investigate environmental drivers of river ecosystem metabolism and macroinvertebrate density in a sub-arctic river. We estimated primary production and respiration rates, sampled benthic macroinvertebrates, and monitored light intensity, discharge rate, and nutrient concentrations in the Chena River, interior Alaska, over two summers. We employed Random Forests models to identify predictor variables for metabolism rates and benthic macroinvertebrate density and biomass, and calculated Spearman correlations between in-stream nutrient levels and metabolism rates. Models indicated that discharge and length of time between high water events were the most important factors measured for predicting metabolism rates. Discharge was the most important variable for predicting benthic macroinvertebrate density and biomass. Primary production rate peaked at intermediate discharge, respiration rate was lowest at the greatest time since last high water event, and benthic macroinvertebrate density was lowest at high discharge rates. The ratio of dissolved inorganic nitrogen to soluble reactive phosphorus ranged from 27:1 to 172:1. We found that discharge plays a key role in regulating stream ecosystem metabolism, but that low phosphorous levels also likely limit primary production in this sub-arctic stream.     

Relative influence of variables at multiple spatial scales on stream macroinvertebrates in the Northern Lakes and Forest ecoregion, U.S.A.

• 1 We used 94 sites within the Northern Lakes and Forests ecoregion spanning Minnesota, Wisconsin and Michigan to identify environmental variables at the catchment, reach and riparian scales that influence stream macroinvertebrates. Redundancy analyses (RDA) found significantly influential variables within each scale and compared their relative importance in structuring macroinvertebrate assemblages.
• 2 Environmental variables included landcover, geology and groundwater delivery estimates at the catchment scale, water chemistry, channel morphology and stream habitat at the reach scale, and landcover influences at three distances perpendicular to the stream at the riparian scale. Macroinvertebrate responses were characterised with 22 assemblage attributes, and the relative abundance and presence/absence of 66 taxa.
• 3 Each scale defined macroinvertebrates along an erosional to depositional gradient. Wisconsin's macroinvertebrate index of biotic integrity, Ephemeroptera–Plecoptera–Trichoptera taxa and erosional taxa corresponded with forest streams, whereas organic pollution tolerant, Chironomidae and depositional taxa corresponded with wetland streams. Reach scale analyses defined the gradient similarly as dissolved oxygen and wide, shallow channels (erosional) opposed instream macrophytes and pool habitats (depositional). Riparian forests within 30 m of the stream coincided with an erosional assemblage and biotic integrity.
• 4 Next, we combined all significant environmental variables across scales to compare the relative influence of each spatial scale on macroinvertebrates. Partial RDA procedures described how much of the explained variance was attributable to each spatial scale and each interrelated scale combination.
• 5 Our results appeared consistent with the concept of hierarchical functioning of scale in which large‐scale variables restrict the potential for macroinvertebrate traits or taxa at smaller spatial scales. Catchment and reach variables were equally influential in defining assemblage attributes, whereas the reach scale was more influential in determining relative abundance and presence/absence.
• 6 Ultimately, comprehending the relative influence of catchment and reach scale properties in structuring stream biota will assist prioritising the scale at which to rehabilitate, manage and derive policies for stream ecosystem integrity.

     

Concordance among stream assemblages and spatial autocorrelation along a fragmented gradient

Patterns of spatial autocorrelation of biota and distributional similarity (concordance) between assemblages of different organism groups have important implications in both theoretical ecology and biodiversity conservation. Here we report environmental gradients and spatial distribution patterns of taxonomic composition among stream fish, benthic macroinvertebrate, and diatom assemblages along a fragmented stream in south‐western France. We quantified spatial patterns of lotic assemblage structure along this stream, and we tested for concordance in distribution patterns among the three taxonomic groups. Our results showed that both environmental characteristics and stream assemblages were spatially autocorrelated. For stream fish and diatom assemblages, these patterns reflected assemblage changes along the longitudinal stream gradient, whereas environmental variables and benthic macroinvertebrates exhibited a more patchy spatial pattern. Cross‐taxa concordance was significant between stream fish and diatoms, and between stream fish and benthic macroinvertebrates. The assemblage concordance between stream fish and diatoms could be attributed to similar responses along the longitudinal gradient, whereas those between stream fish and benthic macroinvertebrates may result from biotic interactions. Based on potential dispersal capacities of taxa, our results validated the hypotheses that weakly dispersing taxa exhibit greater concordance than highly dispersing ones and that dispersal capacities affect how taxonomic groups respond to their local environment. Both diatoms and highly dispersing stream fish were affected by stream fragmentation (i.e. the number of dams between sites), while the effect of fragmentation was not significant for invertebrates that fly well in their adult stage, thus emphasizing the importance of the way of dispersal. These results suggest that addressing the effects of dispersal capacity on stream assemblage patterns is crucial to identifying mechanisms behind patterns and to better understanding the determinants of stream biodiversity.     

Biological quality metrics: their variability and appropriate scale for assessing streams

The concept of spatial scale is at the research frontier in ecology, and although focus has been placed on trying to determine the role of spatial scale in structuring communities, there still is a further need to standardize which organism groups are to be used at which scale and under which circumstances in environmental assessment. This paper contributes to the understanding of the variability at different spatial scales (reach, stream, river basin) of metrics characterizing communities of different biological quality elements (macrophytes, fishes, macroinvertebrates and benthic diatoms) as defined by the Water Framework Directive. For this purpose, high-quality reaches from medium-sized lowland streams of Latvia, Ecoregion 15 (Baltic) were sampled using a nested hierarchical sampling design: (river basin → stream → reach). The variability of metrics within the different groups of biological quality elements confirmed that large-bodied organisms (macrophytes and fish) were less variable than small-bodied organisms (macroinvertebrates and benthic diatoms) at reach, stream and river basin scales. Single metrics of biological quality elements had the largest variation at the reach scale compared with stream and basin scales. There were no significant correlations between biodiversity indices of the different organism groups. The correlation between diversity indices (Shannon’s and Simpson’s) of the biological quality elements (macrophytes, fish, benthic macroinvertebrates and benthic diatoms) and a number of measured environmental variables varied among the different organism groups. Relationships between diversity indices and environmental factors were established for all groups of biological quality elements. Our results showed that metrics of macrophytes and fish could be used for assessing ecological quality at the river basin scale, whereas metrics of macroinvertebrates and benthic diatoms were most appropriate at a smaller scale.     

Dams and Flow in the Cotter River, Australia: Effects on Instream Trophic Structure and Benthic Metabolism

This study assessed benthic macroinvertebrates and periphyton and its responses to managed river-flows, in riffles downstream of three dams on the Cotter River, Australian Capital Territory. Benthic macroinvertebrates and periphyton were also assessed in adjacent tributaries of the river, as well as in a nearby unregulated river and its tributaries. Food sources of four macroinvertebrate taxa (Leptophlebiidae, Elmidae, Glossosomatidae and Orthocladiinae) were determined by stable isotope analysis of the invertebrates and their potential food, in conjunction with examination of the gut contents of individual invertebrates. Components of benthic periphyton were the main food source for the selected taxa. Orthocladiinae consumed primarily amorphous detritus, while Elmidae, Glossosomatidae and Leptophlebiidae consumed diatoms. Enclosed benthic chambers were used to measure the response of benthic metabolism to monthly flow spikes released from one of the dams. The balance of benthic metabolism as measured by the Production/Respiration ratio (P/R) showed a shift towards production after the release of flow spikes. At sites downstream of the dams, there was more periphyton chlorophyll-a in the form of filamentous green algae than at sites in the unregulated river and the tributaries, and macroinvertebrate taxa using periphyton as a food resource were missing or reduced in abundance relative to sites without dams. However, the site downstream of the dam with environmental flow releases had more macroinvertebrate taxa and less periphyton cholorophyll-a content than sites downstream of dams without managed environmental flows, suggesting that a more suitable food supply resulting from environmental flow releases shifted macroinvertebrate communities towards those of unregulated streams.