Leaf‐Nets (LN): A New Quantitative Method for Sampling Macroinvertebrates in Non‐Wadeable Streams and Rivers

The ecological knowledge of large rivers is still scarce or highly fragmented mainly because of complex, laborious and expensive procedures to collect informative samples from the benthic biota. Standard sampling protocols for macroinvertebrates were mainly developed and calibrated for wadeable streams, while a number of heterogeneous non‐standard sampling procedures are available for large rivers. We propose the new, easy‐to‐build and cost‐effective leaf‐nets (LN) method to quantitatively sample benthic invertebrates in non‐wadeable waterways. The LN method uses Phragmites australis leaves as substrate and combines the characteristics of the leaf‐bags and the Hester–Dendy (HD) multiplates methods. We compared the effectiveness of the LN and HD methods in a near‐pristine and in an impacted stream‐reach (downstream an aquaculture plant) of a non‐wadeable second‐order stream of Central Apennines (Italy). Twenty‐five of the 34 cumulatively collected macroinvertebrate taxa were common to both methods, while seven taxa were found only on LN and two only on HD. Taxonomic richness and total macroinvertebrate abundance were higher for LN assemblages. Number of Ephemeroptera, Plecoptera and Trichoptera taxa (EPT) also tended to be higher on LN. Assemblage composition was different on LN and HD. Both methods documented a significant decrease in EPT taxa and a concomitant increase in the total abundance of more pollution‐tolerant taxa in the impacted stream‐reach, but the LN method was more sensitive to impact‐associated changes in macroinvertebrate assemblage structure. In contrast to the hardboard plates of HD, the assembled leaves of the LN may act as a direct or indirect food source and may better mimic the texture and composition of more heterogeneous natural substrates thus favouring the migration–colonization process from both bottom and littoral benthic invertebrates. The sampling efficiency, cost effectiveness and simplicity warrant the routine use of the new LN method in large‐river ecological assessment. Copyright © 2015 John Wiley & Sons, Ltd.     

Field and laboratory performance characteristics of a new protocol for sampling riverine macroinvertebrate assemblages

Measurement and estimation of performance characteristics (i.e. precision, bias, performance range, interferences and sensitivity) are often neglected in the development and use of biological sampling methods. However, knowledge of this information is critical in enabling potential users to assess data quality and make comparisons among different sampling methods. In this study, the performance characteristics were evaluated for both the field and laboratory components of a new large river macroinvertebrate bioassessment protocol (mLR‐BP) for non‐wadeable streams. We sampled 19 sites across two depth classes, collecting three replicate samples at each site and sorting three 300‐organism subsamples from each sample. The replicate samples provided data for estimates of precision in the laboratory and field, and abiotic variables allowed for measurements of overall sensitivity. Precision and performance range differed between shallow and deep sites, particularly for the field component. As compared with precision measured in other studies of bioassessment methods, the field component of the mLR‐BP performed similarly, particularly in shallow sites. Based on the measures of combined field and laboratory sensitivity, this protocol should be able to detect differences of approximately 20–25% in the metrics evaluated in this study, if used for bioassessment in similar types of rivers. With all sites and the field and laboratory components combined, metrics were most responsive to a gradient of urban land cover but also showed some relationship with agricultural land cover. However, metric responsiveness does not necessarily correlate with precision, and metric selection can influence the performance characteristics of the method. Overall, the sampling protocol shows great utility for bioassessment and monitoring of non‐wadeable rivers, as well as for measuring the success of restoration efforts. In addition, the design of this study provides a template for estimating performance characteristics in other non‐wadeable systems. Copyright © 2008 John Wiley & Sons, Ltd.     

Comparison of littoral and deep water sampling methods for assessing macroinvertebrate assemblages along the longitudinal profile of a very large river (the Danube River,Europe)

We comparatively examined the role of littoral and deep water sampling methods in assessing macroinvertebrate assemblages and in characterizing longitudinal changes in assemblage structure along >2,500‐km–long course of the Danube River, Europe. The effectiveness of detecting taxa corresponded well with an inshore–offshore gradient in sampling (i.e., distance from shore). Nevertheless, each method (i.e., littoral multihabitat sampling, kick and sweep sampling, and deep water dredging) contributed to some degree to overall taxa richness and species composition. Sampling in different depth zones characterized different assemblages, and consequently, inshore–offshore position was at least as important determinant of assemblage structure as longitudinal position of sampling sites in the river. Although we found significant congruency in the spatial variability of assemblages among the sampling methods, the relationships were only moderate. Our study on the large Danube River confirms studies from smaller rivers in other geographic regions that littoral monitoring provides higher taxa richness and more responsive changes to longitudinal gradients than deep water samples. Nevertheless, it also shows that sampling in different depth zones provides supplementary information on assemblage structure. Understanding changes in macroinvertebrate assemblages related to differences in sampling method is crucial to improve the bioassessment and environmental management of large rivers.     

珠江重要河流底栖动物水质生物学评价

2011年和2012年调查了珠江流域66个样点的底栖动物和水化学指标,利用2011年北江11个样点和郁江17个样点的底栖动物群落和水化学指标,采用主成分分析法获得综合环境因子(主成分1和主成分2)。分析36个候选底栖动物参数与环境因子间的相关性,结合参数的分布范围,确定适于珠江流域开展河流生态系统生物学质量评价的3个底栖动物参数:双翅目百分比、刮食者百分比和BI指数,进而构建了珠江流域河流生物学质量评价的综合生物指数及评价等级(清洁、轻度污染、中度污染和重度污染)。66个样点的综合生物指数评价结果显示,珠江流域河流生物学质量以轻度至中度污染为主,占80.3%,清洁占13.6%,重度污染占有6%。研究表明,在珠江流域应用底栖动物开展中大型河流水质生物学评价具有良好的应用前景。     

Typology of a Great River Using Fish Assemblages: Implications for the Bioassessment of the Danube River

Matching habitat typology and ecological assemblages can be useful in environmental management. We examined whether a priori defined riverine sections correspond with distinct fish assemblage types along the >2000 km long course of the Danube River, Europe. We also tested whether different sampling methods (i.e. day and night inshore electric fishing and offshore benthic trawling) provide consistent typological results. Analysis of assemblage similarities, indicator species analysis, non‐metric multidimensional scaling (NMDS) and k‐means analyses indicated that fish assemblages of the a priori defined Upper‐, Middle and Lower‐Danubian sections differed slightly, but within class variability was high. Although indicator species analysis showed that the Upper‐Danube belongs to the barbel (Barbus barbus) zone and the Middle‐ and Lower Danube belong to the bream (Abramis spp) zone, indicator values of the character species were generally low. The NMDS analyses suggested a weak gradient in assemblage structure along the course of the river with relatively high variability between neighbouring sites. K‐means analyses revealed that many sampling sites were in a different class than the a priori defined sections, and classifications at other group numbers did not lead to better classification outcome. Overall, the results do not suggest clearly distinguishable assemblage types with distinct boundaries in the potamal section of a great river. Nevertheless, the division of the potamon to smaller sections may explain some variability in fish assemblage structure, and could be used for bioassessment purposes. The study also shows the importance of multihabitat and multigear surveys in the typological assessment of great rivers. Copyright © 2016 John Wiley & Sons, Ltd.     

Assessing macroinvertebrate community response to restoration of Big Spring Run: Expanded analysis of before‐after‐control‐impact sampling designs

Stream restoration projects utilize a variety of approaches to improve conditions for aquatic organisms or enhance ecosystem function. Alterations to abiotic conditions to enhance certain ecosystems services may not lead to concurrent changes in the benthic macroinvertebrate community indicative of improved stream health. Big Spring Run was the location of a novel restoration project to recreate an anabranching “wet meadow” habitat typical of precolonization conditions without the primary goal of restoring a macroinvertebrate community characteristic of single‐channel lotic systems. We examined the effect of the restoration on the macroinvertebrate community using a multivariate analysis of assemblage composition, a before‐after‐control‐impact (BACI) approach, and an assessment of potential aerial migrants. We also examined subsets of the data using a BACI approach that represented restricted sampling designs often employed in stream restoration projects. Benthic macroinvertebrates were collected in the Spring twice prior to restoration (2010 and 2011) and 3 years after restoration (2012–2014). Adult stream insects were collected in 2014. Analyses of benthic macroinvertebrates and adult insects using the full dataset suggested that restoration had no effect on the macroinvertebrate community due to poor in‐stream conditions likely from sediment deposition following restoration. Dispersal barriers are likely acting as a secondary constraint on recolonization. Analyses using subsets of the data demonstrated that reference site quality and sampling extent can alter conclusions from a BACI approach. We found that a holistic approach using multiple lines of evidence required a nuanced approach to interpreting the data but was also informative for assessing project success. Robust monitoring protocols are likely the best approach for producing convincing results through a single line of evidence. The additional BACI analyses performed for this study, however, allowed the modest sampling regime employed to generate a broad narrative demonstrating that the macroinvertebrate assemblage did not respond to this type of restoration. Thus, we believe the holistic approach we employed can strengthen assessments of stream restoration projects when resources for monitoring are limited.     

MACROINVERTEBRATE–PRESSURE RELATIONSHIPS IN BOATABLE NEW ZEALAND RIVERS: INFLUENCE OF UNDERLYING ENVIRONMENT AND SAMPLING SUBSTRATE

Responses of macroinvertebrate communities to human pressure are poorly known in large rivers compared with wadeable streams, in part because of variable substrate composition and the need to disentangle pressure responses from underlying natural environmental variation. To investigate the interaction between these factors, we sampled macroinvertebrates from the following: (i) submerged wood; (ii) littoral substrates < 0.8 m deep; and (iii) inorganic substrates in deep water (> 1.5 m) benthic habitats in eleven 6th‐ or 7th‐order New Zealand rivers spanning a catchment vegetation land cover gradient. Cluster analysis identified primary site groupings reflecting regional environmental characteristics and secondary groupings for moderate gradient rivers reflecting the extent of catchment native vegetation cover. Low pressure sites with high levels of native vegetation had higher habitat quality and higher percentages of several Ephemeroptera and Trichoptera taxa than sites in developed catchments, whereas developed sites were more typically dominated by Diptera, Mollusca and other Trichoptera. Partial regression analysis indicated that the combination of underlying environment and human pressure accounted for 77–89% of the variation in Ephemeroptera, Trichoptera and Plecoptera taxa richness, %Diptera and %Mollusca, with human pressure explaining more variance than underlying environment for %Mollusca. Analysis of replicate deepwater and littoral samples from moderate gradient sites at the upper and lower ends of the pressure gradient indicated that total Trichoptera and Diptera richness and %Diptera responded to land use differences in these boatable river catchments. Responses to human pressure were substrate specific with the combination of littoral and deepwater substrates providing the most consistent response and yielding the highest number of taxa. These results indicate that multiple substrate sampling is required to document the biodiversity and condition of boatable river macroinvertebrate communities and that spatial variation in the underlying natural environment needs to be accounted for when interpreting pressure–response relationships. Copyright © 2012 John Wiley & Sons, Ltd.     

Effects of grade control structures on the macroinvertebrate assemblage of an agriculturally impacted stream

Nearly 400 rock rip‐rap grade control structures (hereafter GCS) were recently placed in streams of western Iowa, USA to reduce streambank erosion and protect bridge infrastructure and farmland. In this region, streams are characterized by channelized reaches, highly incised banks and silt and sand substrates that normally support low macroinvertebrate abundance and diversity. Therefore, GCS composed of rip‐rap provide the majority of coarse substrate habitat for benthic macroinvertebrates in these streams. We sampled 20 sites on Walnut Creek, Montgomery County, Iowa to quantify macroinvertebrate assemblage characteristics (1) on GCS rip‐rap and at sites located (2) 5–50 m upstream of GCS, (3) 5–50 m downstream of GCS and (4) at least 1 km from any GCS (five sites each). Macroinvertebrate biomass, numerical densities and diversity were greatest at sites with coarse substrates, including GCS sites and one natural riffle site and relatively low at remaining sites with soft substrates. Densities of macroinvertebrates in the orders Ephemeroptera, Trichoptera, Diptera, Coleoptera and Acariformes were abundant on GCS rip‐rap. Increases in macroinvertebrate biomass, density and diversity at GCS may improve local efficiency of breakdown of organic matter and nutrient and energy flow, and provide enhanced food resources for aquatic vertebrates. However, lack of positive macroinvertebrate responses immediately upstream and downstream of GCS suggest that positive effects might be restricted to the small areas of streambed covered by GCS. Improved understanding of GCS effects at both local and ecosystem scales is essential for stream management when these structures are present. Copyright © 2007 John Wiley & Sons, Ltd.     

Sample size determination for soft‐bottom sampling in large rivers and comparison with the chironomid pupal exuvial technique (CPET)

Our objective in this study was to determine the adequate sample size for the use of grab sampling in the biomonitoring of large soft‐bottom rivers. We also compared two sampling methods, grab sampling and the Chironomid Pupal Exuvial Technique (CPET), in detecting anthropogenic impacts in a large boreal river and assessed the degree of concordance between the two data sets. Sample size determination showed that, at the lowest possible taxonomic level, a minimum of eight benthic samples was required to obtain a reliable picture of benthic communities. When using the CPET, the number of chironomid species was nearly twice that of all benthic macroinvertebrates in the grab samples. In addition, a majority of the chironomid species found in the grab samples was also detected using the CPET. Although both data sets indicated significant differences in benthic communities between the sampling sites in the river Kymi, a Mantel test showed that patterns in community composition were not concordant. This was mainly because benthic samples from the deep depositional areas of the river indicated poorer ecological status than did the CPET data, which integrate species from various depths and habitats. Thus, samples from a single macrohabitat may not adequately represent environmental conditions of large rivers. Overall, our results suggest that the CPET provides a reliable and cost‐effective alternative, or a supplementary assessment tool, to more traditional sampling methods when assessing anthropogenic stresses in large boreal rivers. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of sampling method on diatom composition for use in monitoring and assessing large river condition

Multiple diatom sampling methods exist for the assessment of lotic systems but few comparisons of their application efficacies in monitoring have been conducted. In this study 60 sites were sampled on four large, non‐wadeable rivers in Ohio and Kentucky, USA, which varied in depth, flow rate, surrounding land use and hydrologic modification. Four algae sampling methods were tested: three methods U.S. Environmental Protection Agency (U.S. EPA) Environmental Monitoring and Assessment Program (EMAP), U.S. Geological Survey (USGS QUAL and USGS QUAN) collected algae from rocks, debris and sediment in the littoral zone along a 1–2 km reach, while one method (USGS PHYTO) consisted of three cross‐river phytoplankton grab samples collected from a boat. Physical and chemical data were also collected. Little difference in diatom assemblage composition was found among the EMAP, QUAL and QUAN methods. Although compositionally similar, the PHYTO method collected a substantial proportion of relatively unique diatoms compared to the littoral zone methods. Two disturbance gradients were calculated, one based on 1 km upstream land use within a 500 m buffer, and the other based on principal component analysis dimension reduction of measured water parameters (PCAWQ). Metrics, generally indicators of eutrophication, were calculated for each sampling method and correlated with the disturbance gradients. After Bonferroni corrections, the EMAP method had six metrics correlated with the PCAWQ, while the PHYTO and QUAL methods each had four correlated metrics. Two QUAN metrics were correlated with the PCAWQ. Few metrics were correlated with the land use measure of disturbance. While the EMAP method had the most correlated metrics, this method, along with QUAL and QUAN methods are time and labour intensive (>1 h), relative to the phytoplankton method (<20 min). Resource managers may desire to weigh the benefits of two additional metrics with the EMAP method versus the costs associated with increased sampling time and effort. Published in 2007 by John Wiley & Sons, Ltd.     

River flow indexing using British benthic macroinvertebrates: a framework for setting hydroecological objectives

A method linking qualitative and semi‐quantitative change in riverine benthic macroinvertebrate communities to prevailing flow regimes is proposed. The Lotic‐invertebrate Index for Flow Evaluation (LIFE) technique is based on data derived from established survey methods, that incorporate sampling strategies considered highly appropriate for assessing the impact of variable flows on benthic populations. Hydroecological links have been investigated in a number of English rivers, after correlating LIFE scores obtained over a number of years with several hundred different flow variables. This process identifies the most significant relationships between flow and LIFE which, in turn, enables those features of flow that are of critical importance in influencing community structure in different rivers to be defined. Summer flow variables are thus highlighted as being most influential in predicting community structure in most chalk and limestone streams, whereas invertebrate communities colonizing rivers draining impermeable catchments are much more influenced by short‐term hydrological events. Biota present in rivers with regulated or augmented flows tend to be most strongly affected by non‐seasonal, interannual flow variation. These responses provide opportunities for analysing and elucidating hydroecological relationships in some detail, and it should ultimately be possible to use these data to set highly relevant, cost‐effective hydroecological objectives. An example is presented to show how this might be accomplished. Key areas of further work include the need to provide robust procedures for setting hydroecological objectives, investigation of habitat quality and LIFE score relationships in natural and degraded river reaches and evaluation of potential links with other biological modelling methods such as RIVPACS. Copyright © 1999 John Wiley & Sons, Ltd.     

The Interplay between Environmental Conditions and Filamentous Algae Mat Formation in Two Agricultural Influenced South African Rivers

The regulation of nutrient inputs into rivers dominated by agriculture land use activities is an important aspect of ecological resilience of aquatic systems and the management of river eutrophication. The overabundance of benthic filamentous algae mats in river systems due to nutrient enrichment can modify the habitats of macroinvertebrate and fish communities as well as clogging irrigation crop sprayers of downstream water users. The current study examined over a period of 2 years (2013–2014) the interplay between physical and chemical river characteristics and epilithic filamentous algae biomass in two South African agricultural influenced rivers. The study area consisted of the Touw and Duiwe Rivers, which run into a proclaimed Ramsar site, namely, the Wilderness Lake System. A strong positive correlation was observed between the maximum filamentous algae biomass (97 chl‐a mg m^?2) observed during the dry season and the average water column alkalinity >30 mg l^?1. The benthic trophic status of the nine sampling sites during the dry seasons indicated the highest benthic algae biomass with mesotrophic (1.7–21 chl‐a mg m^?2) to hypertrophic (>84 chl‐a mg m^?2) conditions. During the dry season, only three sampling sites were below the suggested guideline value (35 µg l^?1) for total phosphorus (TP), while four sampling sites were below the total nitrogen guideline of 252 µg l^?1. In the wet season, two sites were below TP values with five sites below total nitrogen guideline values. From the data gathered, it was evident that water column alkalinity and hardness were the main drivers for the formation or absence of benthic filamentous algae mats in the two river systems and that nitrogen and/or phosphorus concentrations was overshadowed by the physical and chemical characteristics of the river systems at certain sites. Nutrient results for the river bottom sediments revealed that the sediment qualities were variable at the different sampling sites, but more specifically along the longitudinal paths of flow. It was apparent that the high TP concentrations in the water column and bottom sediment, which were lowest during the dry season, were associated with the highest epilithic filamentous algae mat formation. The outcome of the current study shows that a more holistic approach must be followed for the development of future eutrophication guidelines and nutrient thresholds in South African rivers influenced by agriculture land use activities. Copyright © 2016 John Wiley & Sons, Ltd.     

Partitioning of macroinvertebrate communities in a large New Zealand river highlights the role of multiple shore‐zone habitat types

Bank stabilization is increasing along large rivers as urban areas expand, and the need to protect infrastructure increases in the face of changing climate and flow patterns, but the cumulative effects of different stabilization approaches on reach‐scale biodiversity are not well understood. We investigated physical habitat characteristics and macroinvertebrate community composition and diversity for four shore‐zone habitat types across nested spatial scales over two sampling occasions. Distinct physical conditions were evident for riprap, beach and willow (mixed trees dominated by Salix spp.) habitats, reflecting variations in the combinations of shade, water velocity and substrate size/type, but there was wide variation in habitat conditions for mixed willow‐riprap sites. Additive biodiversity partitioning decomposed reach (γ) diversity into within (α) and among (β₁) sample, among habitat (β₂), and among site (β₃) components, and highlighted significant effects of all spatial scales on macroinvertebrate diversity. Low autumn water levels led to truncated species accumulation curves at beach sites where macrophyte beds that supported macroinvertebrates became stranded, or elevated species accumulation curves for exposed willow‐riprap sites where the river benthos was sampled during hydrological disconnection of bank habitats. Spring and autumn differences in macroinvertebrate community composition were stronger than differences between habitat types. Our findings (a) highlight the interacting effect of river level with shore‐zone habitat function, and (b) underscore the importance of maintaining a diversity of bank habitat types at multiple sites along river shore‐zones to maximize macroinvertebrate diversity.     

Seasonal effects of a hydropeaking dam on a downstream benthic macroinvertebrate community

As more hydroelectric dams regulate rivers to meet growing energy demands, there is ongoing concern about downstream effects, including impacts on downstream benthic macroinvertebrate (BMI) communities. Hydropeaking is a common hydroelectric practice where short‐term variation in power production leads to large and often rapid fluctuations in discharge and water level. There are key knowledge gaps on the ecosystem impacts of hydropeaking in large rivers, the seasonality of these impacts, and whether dams can be managed to lessen impacts. We assessed how patterns of hydropeaking affect abundance, taxonomic richness, and relative tolerance of BMIs in the Saskatchewan River (Saskatchewan, Canada). Reaches immediately (<2 km) downstream of the dam generally had high densities of BMIs and comparable taxonomic diversity relative to upstream locations but were characterized by lower ratios of sensitive (e.g., Ephemeroptera, Plecoptera, and Trichoptera) to tolerant (e.g., Chironomidae) taxa. The magnitude of effect varied with seasonal changes in discharge. Understanding the effects of river regulation on BMI biodiversity and river health has implications for mitigating the impacts of hydropeaking dams on downstream ecosystems. Although we demonstrated that a hydropeaking dam may contribute to a significantly different downstream BMI assemblage, we emphasize that seasonality is a key consideration. The greatest differences between upstream and downstream locations occurred in spring, suggesting standard methods of late summer and fall sampling may underestimate ecosystem‐scale impacts.     

An eutrophication index for lowland sandy rivers in Mediterranean coastal climatic regions of Southern Africa

The eutrophication of waterways has become an endemic global problem. Nutrient enrichment from agriculture activities and waste water treatment plants are major drivers, but it remains unclear how lowland sandy rivers respond to eutrophication. The objective of this study was the development and verification of eutrophication index for sandy rivers (EISR) to prioritize nutrient enrichment river stretches caused by different land use activities that include point and nonpoint sources of nutrient enrich water. The Berg River drainage system in South Africa served as a case study area for this purpose during the dry seasons (December and January) of 2015 and 2016. In the initial EISR development phase, periphyton, benthic biomass (chl‐a mg m^?2), and macroinvertebrate families were employed as benthic bioindicators of river bedforms, whereas in the second phase, physicochemical and abiotic variables were used as target indicator. Using a weight of support approach, the site receiving sewage effluent was categorize as heavily polluted whereas sites impacted by agriculture land use activities were polluted. The EISR that focuses strongly on benthic bioindicators, which are close to the transfer of nutrients and energy in the food web, showed a distinct difference between river bedform impacted by sewage effluent and agriculture none point source. A maximum benthic algae biomass of 110 mg m^?2 chl‐a was recorded with higher sediment orthophosphate concentration at sewage‐impacted sites. The outcome of the proposed EISR showed that it can be employed as a decision support tool for eutrophication management of sandy rivers.     

LONG‐TERM TAXON‐SPECIFIC RESPONSES OF MACROINVERTEBRATES TO DAM REMOVAL IN A MID‐SIZED SWEDISH STREAM

Dam removal to restore ecologically impaired rivers is becoming increasingly common. Although the target often is to facilitate fish migration, dam removal has also been assumed to benefit other types of organisms. Because few studies thus far deal with effects of dam removal on stream macroinvertebrates and because results have been equivocal, we investigated both short‐ and longer‐term dam‐removal effects on downstream macroinvertebrate communities. We did this in a before‐and‐after study of the removal of a dam located in a south Swedish stream. We sampled the benthic fauna 6 months before dam removal and both 6 months and 3.5 years after the dam was removed. We compared species composition, taxonomic richness, total densities and densities of macroinvertebrate groups before and after dam removal and between downstream and reference sites. We found that dam removal reduced some macroinvertebrate taxa at the downstream site, but we found no effect on community composition. Although this corroborates results from previous short‐term studies, we also found a reduction of taxonomic richness and that some dam‐removal effects persisted or even increased over time. The most likely explanation for the suppression of benthic macroinvertebrate richness following dam removal is a significantly increased sediment transport from the former reservoir and a subsequent loss of preferred substrates. Our results indicate that adverse dam‐removal effects may be long lasting but taxon specific. We therefore call for longer‐term studies on a variety of organisms to better understand how dam removal may influence downstream macroinvertebrate communities. Copyright © 2012 John Wiley & Sons, Ltd.     

Small hydropower dam alters the taxonomic composition of benthic macroinvertebrate assemblages in a neotropical river

Hydropower dams substantially modify lotic ecosystems. Most studies regarding their ecological impacts are based on large dams and provide little information about the far more abundant effects of small hydropower dams. Our aim was to characterize the ecological effects of a small hydropower dam and run‐of‐the‐river reservoir on the structure of benthic macroinvertebrate assemblages in the Pandeiros River located in the neotropical savanna of Brazil. We tested the hypothesis that benthic macroinvertebrate assemblages in sites directly affected by the dam and reservoir would show a different taxonomic structure compared with those in free‐flowing sites. We expected to find sensitive native species associated with the free‐flowing sites, whereas resistant and non‐native invasive taxa were expected in impounded sites. We also explored associations between the presence of native and non‐native invasive taxa to each habitat type. We found that the structure of benthic macroinvertebrate assemblages was significantly different between free‐flowing and impounded sites. Also, we found that the dam and reservoir facilitated colonization of non‐native invasive species (Corbicula fluminea and Melanoides tuberculata) because only in those sites they were found in high abundance, in contrast to the free‐flowing sites. Although the environmental conditions imposed by the impoundment altered the structure of benthic macroinvertebrate assemblages, the effects were limited to sites closest to the dam. Our results highlight the necessity of understanding physical habitat changes caused by the presence and management of run‐of‐the‐river dams and reservoirs.     

Habitat Restoration in the Context of Watershed Prioritization: The Ecological Performance of Urban Stream Restoration Projects in Portland,Oregon

In Portland (Oregon, USA), restoration actions have been undertaken at the watershed scale (e.g. revegetation and stormwater management) to improve water quality and, where water quality and quantity are adequate at the reach scale, to increase habitat heterogeneity. Habitat enhancement in urban streams can be important for threatened species, but challenging, because of altered catchment hydrology and urban encroachment on floodplains and channel banks. To evaluate reach‐scale restoration projects in the Tryon Creek watershed, we sampled benthic macroinvertebrates and conducted habitat quality surveys pre‐project and over 4 years post‐project. Species sensitive to pollution and diversity of trophic groups increased after restoration. Taxonomic diversity increased after restoration but was still low compared with reference streams. We found no significant changes in trait proportions and functional diversity. Functional diversity, proportion of shredders and semivoltine invertebrates were significantly higher in reference streams than in the restored stream reaches. We hypothesized that inputs of coarse particulate organic matter and land use at watershed scale may explain the differences in biodiversity between restored and reference stream reaches. Habitat variables did not change from pre‐project to post‐project, so they could not explain community changes. This may have been partly attributable to insensitivity of the visual estimate methods used but likely also reflects the importance of watershed variables on aquatic biota—suggesting watershed actions may be more effective for the ecological recovery of streams. For future projects, we recommend multihabitat benthic sampling supported by studies of channel geomorphology to better understand stream response to restoration actions. Copyright © 2014 John Wiley & Sons, Ltd.     

Evaluating stream restoration: A case study from two partially developed 4th order Connecticut,U.S.A. streams and evaluation monitoring strategies

Stream rehabilitation and enhancement projects in the Norwalk River (urban‐forest watershed) and Merrick Brook (agriculture‐forest watershed) were evaluated. Instream structure installation, streambank stabilization and meander re‐creation were performed 2–5 years before monitoring. Physical, chemical and biological variables were monitored at control, enhanced (treatment sites originally controls), impaired and rehabilitated (treatment sites originally impaired) sites for three field seasons to evaluate the projects and formulate monitoring strategies. Small improvements in local habitat and macroinvertebrate assemblages were observed at rehabilitated sites on the Norwalk River however control conditions were not attained. Changes to stream health were less evident at the reach scale suggesting that watershed processes that form and maintain habitat were too altered for more widespread recovery. A localized sediment source from a failing streambank was eliminated from Merrick Brook protecting the abundant nearby quality habitat, yet fining occurred at the rehabilitation site due to hydraulic changes leading to localized shifts in macroinvertebrate assemblages. Single‐season sampling created a useful snapshot to compare enhanced and rehabilitated sites to control and impaired sites. We recommend a tiered sampling strategy where effectiveness monitoring may include a detailed effort at many sites over a short time (as performed here), a relatively low level of detail (e.g. a rapid assessment) at an intermediate number of sites over a short time, and a detailed long‐term monitoring at few sites (e.g. before‐after‐control‐impact, BACI). More research is needed to continue the trend of increased project evaluation to advance the science and application of stream restoration. Copyright © 2010 John Wiley & Sons, Ltd.     

Benthic macroinvertebrate assemblages in large river secondary channels: Contemporaneous and legacy effects of flow connectivity

In large rivers, secondary channels occur where the main channel is divided by an instream island, forming one or multiple smaller channels outside the main channel. Secondary channels are highly variable in morphometry, flow characteristics, and degree of connectivity to the main channel. Engineered closing structures at the upstream end of most secondary channels restrict inflow from the main channel, resulting in gradients of flow connectivity among secondary channels that vary with river stage. We investigated the relationship of flow connectivity to benthic macroinvertebrate assemblage richness and structure among a series of secondary channels of the Lower Mississippi River. Samples were collected over 2 years at times of high and low river stages. We discovered (1) macroinvertebrate assemblage structure and taxonomic richness varied along the flow connectivity gradient, and (2) there was a legacy effect of prior connection on assemblage structure that lasted up to a year. We contend that for management and restoration planning aimed at conservation of large river biological diversity, an important consideration are the life history requirements of animals utilizing secondary channel habitats.