A preliminary macroinvertebrate Index of Biotic Integrity for bioassessment of the Kipkaren and Sosiani Rivers,Nzoia River basin,Kenya

Management efforts for the Lake Victoria Basin have been hampered by a lack of clear standards against which to judge the degree of environmental degradation, highlighting the need for a multi‐metric approach for this purpose. Indeed, management priorities for the Lake Victoria catchment must be based on reliable assessments of the biological integrity of the inflowing rivers that can potentially influence the ecological functioning of the lake. Accordingly, macroinvertebrate metrics were evaluated for their responsiveness to human impacts, utilizing Pearson’s correlations with physico‐chemical parameters. The resultant 9 metrics that provided the best discrimination between physico‐chemical samples, using the separation power of Mann–Whitney U and Kolmogorov–Smirnov tests (P < 0.05) from the 21 sampling sites utilized in this study were the: (i) abundances of Ephemeroptera, Plecoptera and Trichoptera; (ii) relative abundances of Diptera; (iii) Ephemeroptera, Plecoptera and Trichoptera:Diptera ratio; (iv) Oligochaeta, Mollusca, Hemiptera, Odonata and the proportions of tolerance taxa; (v) dominant taxa; and (vi) the relative proportions of invertebrates that fall into the gatherer and predator feeding groups, based on the variability they exhibited across the sampling sites. Using the inter‐quartile ranges to establish the scoring criteria, the index was able to delineate impacted from less‐impacted sites along the rivers, providing preliminary evidence of responses to changes in the ecosystem integrity exhibited by resident macroinvertebrate assemblages in both rivers.     

Effects of anthropogenic activities on macroinvertebrate assemblages in the littoral zone of Lake Hawassa,a tropical Rift Valley Lake in Ethiopia

In developing tropical countries, the littoral region of lakes is exposed to high human pressures, and the degradation effects are more evident on riparian vegetation and macrophytes. Human impacts on other biological entities, such as plankton and macroinvertebrates, are rarely investigated and reported. The present study focuses on assessing the effects of habitat disturbance on the littoral macroinvertebrate assemblages in Lake Hawassa, Ethiopia. Samples were taken from February to November 2015/16 from 12 sampling sites purposefully selected on the basis of percentage disturbance score (PDS) and categorized into minimally disturbed (four sites), moderately disturbed (five sites) and highly disturbed (three sites). Macroinvertebrate samples were collected from each site using a D‐frame net of 500 µm, with both in situ measurement and laboratory analysis of the environmental variables being conducted. A total of 23,051 macroinvertebrates belonging to 43 families were identified. Analysis of similarities (ANOSIM) and non‐metric multidimensional scaling (NMDS) analyses revealed significantly different macroinvertebrate assemblages among the disturbance levels (ANOSIM: p = .004, R = .55). Variables such as Biological Monitoring Working Party, Shannon diversity index, Ephemeroptera and Trichoptera (ET) family richness, and family richness exhibited a flawless pattern of decrease with increasing human disturbances and a negative correlation with nutrients. The reduction of these metrics for highly disturbed sites was attributable to the deterioration of vegetation and bottom substrate qualities, increasing stormwater inputs, lack of buffer zones and well‐planned land use induced by human interventions. It was evident anthropogenic activities in and around the littoral zone of the lake contributed to the degradation of habitat quality and decreased macroinvertebrate richness and abundance. Thus, effective lake management practices are recommended to rehabilitate the degraded littoral habitat quality in order to realize the sustainable use of this natural resource.     

SPATIAL PATTERNS OF BENTHIC INVERTEBRATES IN REGULATED AND NATURAL RIVERS

Daily fluctuating flows in regulated rivers can lead to extensive areas of substrate that experience drying and wetting. I investigated the longitudinal and lateral patterns of benthic invertebrates in the regulated peaking Magpie River and neighbouring natural rivers. Nearly half of all invertebrates collected in the Magpie River originated from the upstream reservoir. Both lentic and lotic invertebrates, however, decreased in abundance to natural levels 5–8 km downstream. Closest to the dam, lotic invertebrates were twice as abundant as those found in natural rivers. In natural rivers Diptera, Ephemeroptera, Coleoptera and Trichoptera were more common in the shallow and slower areas along transects. The opposite was true in the regulated Magpie where densities increased with water depth and velocity, particularly for the dominant groups Diptera and Trichoptera. The abundance of worm‐like organisms (e.g. Enchytraeidae, Lumbricidae, Naididae) and snails (Basommatophora) increased considerably in the varial zone. There were 10 times more Odonata and Plecoptera in the natural rivers, but lateral trends were not evident in either type of river. The influence of sampling location along transects on the interpretation of the community composition can be clearly seen in a resampling of the data. This study illustrates the presence of longitudinal and lateral gradients, and this knowledge needs to be incorporated into the design of research or monitoring programmes. Failing to do so could jeopardize decisions with the management of our flowing waters. Copyright © 2011 John Wiley & Sons, Ltd.     

Invertebrate drift patterns in a regulated river: dams,periphyton biomass or longitudinal patterns?

Macroinvertebrate drift was sampled at 15 sites along the Tongariro River, New Zealand above and below two hydroelectric dams. Sixty‐seven invertebrate taxa were collected in the drift. Trichoptera (31) were the most diverse, followed by Diptera (13), Ephemeroptera (8) and Plecoptera (8). However, chironomidae were the numerically dominant taxa in the drift throughout the river and represented over 80% of all animals collected. Of these, Orthocladiinae and Diamesinae were the most abundant. Taxonomic richness declined with distance downstream and peaked at sites with intermediate levels of periphyton biomass. The per cent of Ephemeroptera, Plecoptera and Trichoptera (EPT) was 3–4 times higher in the unregulated section of the river and declined exponentially with both distance downstream and increase in periphyton biomass, but densities were similar along the river. Of the measured environmental variables periphyton biomass was most closely linked with drift community structure. Periphyton biomass was six times higher in the lower section of the river than the upper unregulated section. The autocorrelation between periphyton biomass and distance downstream complicates the interpretation of results. However, because of the distinct differences between above and below dam sections of river in periphyton biomass and the strong link between it and invertebrate drift we suggest that the alteration of flow patterns by the hydroelectric dams and the associated shift in periphyton biomass is the most likely explanation for invertebrate drift patterns in the river. Copyright © 2009 John Wiley & Sons, Ltd.     

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.     

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.     

Effects of human activities on benthic macroinvertebrate community composition and water quality in the upper catchment of the Mara River Basin,Kenya

Land‐use changes in the upper reaches of the Mara River Basin have modified their biophysical and hydrological processes, resulting in water quality degradation in streams. This study was conducted to investigate the effects of human activities on water quality and macroinvertebrates along the Nyangores River, one of the main tributaries of the Mara River, Kenya. Seven sampling sites were chosen to correspond to the loss of riparian cover, livestock watering and human activities (e.g. laundry washing, bathing, cultivation, wastewater inputs, dumping of solid wastes from urban areas and settlements along the river). Physical–chemical variables and water samples for nutrient analyses were collected monthly from February to July 2012. Benthic macroinvertebrates also were collected at the same sites as for the water quality samples. Two‐way analysis of variance tested the significant differences for each variable among the sites. Similarity percentages (SIMPER) analysis was used to identify the key taxa contributing to differences between minimally disturbed and most disturbed conditions in the study area. The results indicated increased nutrient concentrations in agricultural and settlement areas. Significant (P < 0.05) spatial–temporal variations in water quality variables were observed. A total of 42 macroinvertebrate genera were encountered, with Ephemeroptera, Plecoptera and Trichoptera orders dominating the minimally disturbed areas, and Diptera dominating the disturbed areas receiving point and no‐point solid and liquid wastes, including nutrients, from urban areas and settlements. Canonical correspondence analysis (CCA) revealed significant relationships between macroinvertebrate communities and measured physicochemical variables. The results of this study indicate the need for protection of riparian zones and treatment of sewerage wastes before their release into waterways. The dumping of solid wastes near streams and rivers also is discouraged, to maintain the quality of surface waters and aquatic organisms.     

Comparison of macroinvertebrate assemblages across a gradient of flow permanence in an agricultural watershed

In the south‐eastern United States and globally, increasing human water demand coupled with climate change is diminishing stream flows and increasing stream intermittency in many watersheds. We characterized benthic invertebrate assemblages across a stream flow gradient ranging from intermittent to perennial following a multiyear drought by examining the functional traits that can influence assemblage response to drying. We sampled 13 reaches within the Lower Flint River Basin in south‐western Georgia, from September to December 2013. Reaches included perennial, near‐perennial (ceased flowing but maintained a wetted channel during drought), intermittent‐dry (seasonally dry), and intermittent‐frequent (frequently dry). Distinct assemblages were documented across this gradient. Reaches that dried during the drought had a lower richness of aquatic insects, especially Ephemeroptera, Plecoptera, and Trichoptera taxa, partly due to inadequate time for life cycle completion and lack of adaptations to avoid drying. Intermittent reaches also included abundant and unique noninsect taxa such as Gammarus spp. and Isopoda. Projected trends towards increased water demand and drought severity and frequency in the south‐eastern United States will magnify shifts towards dominance by drought‐tolerant taxa as greater portions of stream networks become intermittent.     

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.     

Response of macroinvertebrate and diatom communities to human‐induced physical alteration in mountain streams

It is generally argued that epilithic diatoms and macroinvertebrates are highly sensitive to changes in water quality, while only a few studies have been conducted on their response to physical disturbance. The main purpose of this research is to investigate whether these two communities respond to physical river disturbance like banks, substrate and flux alteration induced by human action. We sampled 12 high‐altitude streams in the Gran Paradiso National Park, a protected area where the main human activities are limited to hiking and high‐altitude pasture. The sampled stretches of the rivers were characterized with respect to their geomorphological features and possible human modifications. Water uptake for power supply, riverbed and bank modifications represented the main human activities which could determinate alterations in community structure and composition. Habitat structure was evaluated using the Southern European River Habitat (RHS–SE), while the biological status of the river has been estimated by means of the following biotic and diatomic indices: IBE, BMWP, ASPT, Ephemeroptera, Plecoptera and Trichoptera families (EPT) for macroinvertebrates, EPI‐D, IBD and IPS for diatoms. A general concordance between chemical parameters and structure of biological communities was observed. On the other hand, the RHS–SE highlighted the main geomorphological features and detected some slight physical alterations, as quantified by the indices Habitat Modification Score (HMS) and Habitat Quality Assessment (HQA). In short, our findings demonstrate that morphological alterations, even if slight, affect biological diversity and the presence of some specific taxa, while biological indices are independent of the level of physical modifications. Copyright © 2008 John Wiley & Sons, Ltd.     

Macroinvertebrate assemblages in floodplain habitats of the lower river murray,South Australia

Macroinvertebrates were sampled in seven microhabitats (submerged woody debris, reeds, sedges, inundated grass, floating aquatic vegetation, lignum, and the unvegetated littoral) at thirteen sites representing six macrohabitats (single temporary and permanent ox-bow lakes (billabongs), fast and slow-flowing anabranches, backwaters, and the main channel) of the River Murray, and Australian lowland river. Sites were sampled in spring 1988, shortly after floodwaters had receded. Most of the 95 taxa collected were aquatic insects. Detritivores were most abundant in all macrohabitats except the temporary billabong where predators predominated. Scrapers were only abundant in the permanent billabong. The temporary billabong harboured the most species and individuals whereas slowly-flowing anabranches contained the fewest species and individuals. At the microhabitat level, most taxa and individuals occurred in stands of aquatic vegetation. The unvegetated littoral zone was the most depauperate microhabitat. Multivariate analyses illustrated the distinctiveness of the faunal assemblage found in the temporary billabong. Subsequent analyses of the permanently inundated macrohabitats indicated gradients related to current velocity and the extent to which the sites were continuous with the main river. Current velocity apparently determined assemblage composition at the macrohabitat scale whereas the structural complexity of submerged vegetation operated at the microhabitat scale. The relatively large number of taxa collected from this area emphasizes the importance of a range of macrohabitats and microhabitats to faunal diversity in a floodplain ecosystem. Although there was little faunal overlap between billabongs and the main river, billabongs probably serve as refuges for many lentic taxa that rely upon regular inundation to survive. Surveys of floodplain rivers for management purposes must include samples from aquatic habitats adjacent to the main channel because the fauna of the floodplain is potentially most threatened by regulation and alteration of the flooding regime.     

Comparative analysis of glacial and nival streamflow regimes with implications for lotic habitat quantity and fish species richness

Growing interest in the differential responses of glacial and nival rivers to climatic forcing, and in ecological distinctions between the two streamflow regimes, suggests the need for a better comparative understanding of how the annual hydrologic cycle differs with presence or absence of catchment glacial cover. In this study, timing and magnitude characteristics of the average annual hydrographs of five glacierized and four nival catchments in the southwestern Canadian subarctic are empirically identified and compared. Likely effects upon fish habitat are qualitatively assessed, and net fisheries potential is tentatively investigated using taxa richness data. The chief hydrological conclusions at P < 0.05 using Kolmogorov–Smirnov and empirical orthogonal function analyses are: (1) catchment glacial cover results in freshets that are longer, larger, and peak later than those experienced by the nival regime; (2) the winter baseflows of glacial rivers are also much higher on a unit‐catchment‐area basis; and (3) basin scale and degree of catchment glacial cover are of comparable importance in determining the magnitude of the annual hydrologic cycle. These differences arise from the greater availability, both in volume and over time, of meltwater in glacial catchments, which in part reflects the consistently negative alpine glacial mass balances observed both in the present study area and globally under historical climatic warming. Such regime distinctions result in increased spawning season and winter aquatic habitat availability, which may in turn offset negative habitat characteristics previously identified for glacial river ecosystems. While previous studies have suggested that glacial influences tend to decrease macroinvertebrate diversity and increase salmon populations, preliminary analysis of available fish species presence/absence data from the current study area tentatively appears to suggest similar or, perhaps, slightly higher fish taxa richness relative to nival streams; in all three cases, however, catchment lake cover may play a key hydroecological modifying role. The results strongly confirm and extend existing understanding of glacial–nival regime differences with respect to both streamflow and fisheries ecology, and raise new questions for future research. Copyright © 2005 John Wiley & Sons, Ltd.     

Structural and functional changes of tropical riffle macroinvertebrate communities associated with stream flow withdrawal

Tropical island streams worldwide are threatened by existing or proposed dams and diversions that remove freshwater for human use; yet, there have been few studies that address the effects on aquatic communities. The objective of this study was to quantify changes in tropical macroinvertebrate communities associated with stream flow withdrawal. Benthic macroinvertebrates were collected from riffle habitats located above and below a stream diversion on Maui, Hawaii, from June to August 2000. Native and introduced taxa were identified from both locations. The most dominant taxon was midges (Diptera: Chironomidae) followed by two introduced caddisflies, Cheumatopsyche analis (Banks) (Trichoptera: Hydropsychidae) and Hydroptila potosina (Buenoa‐Soria) (Trichoptera: Hydroptilidae). A native shrimp, Atyoida bisulcata, and beach fly, Procanace sp. (Diptera: Canacidae), were either eliminated from or significantly reduced below the diversion. Mean total macroinvertebrate densities were greater above (13 357 individuals/m²) the diversion compared to below (10 360 individuals/m²). Mean total macroinvertebrate biomass was significantly reduced by 60 per cent below the diversion, but specific taxa did not show this effect. These results suggest that diverted stream flow limited macroinvertebrate colonization and growth, expressed as reduced community density and biomass, which may alter the structure and function of other trophic levels within tropical stream food webs. Copyright © 2008 John Wiley & Sons, Ltd.     

Disturbance by aquatic plant management in streams: Effects on benthic invertebrates

The effect of aquatic plant removal on benthic invertebrates and their habitat was studied in two macrophyte-rich streams of the Swiss Plateau. In each stream, habitat conditions (macrophyte biomass, current velocity, water depth) and invertebrate densities were monitored in a control reach and in a reach where plants were removed by cutting. Biological samples were taken and physical parameters measured on three dates before and six dates after plant removal in both reaches. Responses to plant removal were similar in both streams; macrophyte cutting initially decreased mean plant biomass (ca. 85%) and total number of invertebrates (ca. 65%). Variation between replicates was, however, higher in one of the streams, causing fewer effects on plants and invertebrates to be statistically significant. Plant cutting affected mainly taxa that used macrophytes as habitat (e.g. Simuliidae, Chironomidae), whereas highly mobile taxa (e.g. Ephemeroptera) and taxa living on or within the bed sediments (e.g. Trichoptera, Bivalvia) were less affected. Taxa that decreased after plant removal recovered within 4–6 months, although recovery of macrophytes was quite different in both streams. Invertebrate recovery also seemed to be seasonally dependent, with cutting having a less severe impact during summer than spring. Our results suggest that macrophytes in streams should be removed only in summer, preferably leaving some plant beds to act as refugia for phytophilous invertebrates. © 1998 John Wiley & Sons, Ltd.     

Discontinuities in the distribution of invertebrates in impounded south island rivers,New Zealand

The invertebrate fauna of 10 river systems, five with impoundments and five without, were sampled. No significant difference was found either in taxonomic richness or invertebrate densities between impounded and unimpounded sites at similar positions along river continua. However, plecopteran species richness was significantly lower and plecopteran density reduced in post-impoundment sites. Densities of Deleatidium spp. (Ephemeroptera: Leptephlebiidae) were significantly lower at lake outlets compared with other sites. Two species of Zelandobius (Plecoptera: Gripopterygidae) and Eriopterini (Diptera: Tipulidae) snowed distributions apparently curtailed by impoundments, whereas Potamopyrgus antipodarum (Mollusca: Hydrobiidae) had an extended distribution. Margalef's, Menhinick's, Berger-Parker and Shannon indices, total taxa present and plecopteran taxa were plotted against stream order, stream width and distance from the source. Menhinick's and Shannon-Weaver indices produced statistically significant but weak regressions, and discontinuity distances and intensity could not be accurately calculated. The usefulness of diversity indices as a measure of the magnitude of impoundment effects in the South Island seems to be limited.     

Influence of Flow on Community Structure and Production of Snag‐Dwelling Macroinvertebrates in an Impaired Low‐Gradient River

The natural flow regime of rivers has been altered throughout the world in a variety of ways, with many alterations resulting in reduced flows. While restoring impaired systems remains a societal imperative, a fundamental understanding of the effects of reduced flows on river ecosystem structure and function is needed to refine restoration goals and guide implementation. We quantified the effects of chronic low flows on snag‐dwelling macroinvertebrate community structure and production in a low‐gradient river. Macroinvertebrates commonly associated with flowing water (e.g. passive filter‐feeders (PFF)) and higher quality habitats (e.g. Ephemeroptera, Plecoptera and Trichoptera (EPT)) had significantly higher abundance and biomass, and showed trends of higher production, in faster flowing reaches upstream of a hydrologic disconnection created by a drainage ditch. The presence of EPT and PFF groups resulted in a significantly more diverse community composed of larger‐sized individuals compared with downstream, low‐flow reaches, where smaller‐bodied taxa (e.g. small crustaceans), and groups reflective of degraded conditions (e.g. Oligochaeta, Isopoda and Chironomidae) dominated production. Multivariate analyses suggested that differences between these two disparate communities were driven by water velocity and organic matter resources. Mean estimates of total community production did not differ significantly between the two reaches, however, there were areas in low‐flow reaches that attained high secondary production because of patchily distributed and highly productive chironomids. Results demonstrate that long‐term reductions in flows, even in a low‐gradient river, can lead to significant shifts in macroinvertebrate communities, ultimately influencing energy flow pathways in stream food webs. Copyright © 2015 John Wiley & Sons, Ltd.     

NON‐UNIFORM CHANGES TO WHITEWATER RECREATION IN CALIFORNIA'S SIERRA NEVADA FROM REGIONAL CLIMATE WARMING

Whitewater recreation is an aesthetic ecosystem service potentially affected by climate warming alterations to runoff. In California's Sierra Nevada, climate change is likely to reduce water availability with warmer air temperatures and stationary or decreasing precipitation, which will likely alter whitewater recreation opportunities. In this study, we identified 128 whitewater runs on the west slope of the Sierra Nevada within a 13‐basin study area that ranged from serene float trips to remote, difficult, kayak expeditions. We used a spatially explicit, one‐dimensional rainfall‐runoff model to estimate the unregulated hydrology at specific locations within flow thresholds amenable to whitewater recreation. Climate warming scenarios were simulated by increasing air temperature by 2 °C, 4 °C and 6 °C and assuming no change in precipitation. With mild warming, the average number of boatable weeks per year increases, but more extreme warming decreases the average boatable weeks per year across the Sierra Nevada. Runs in low‐elevation drainages, such as the Cosumnes and the Tule River Basins, are most vulnerable to changes in boatable weeks. Yet, high‐elevation watersheds, such as the Kern River, also have a large reduction in boatable weeks. Watersheds in the central Sierra Nevada show an increase in boatable weeks. Overall, we found elevation and run type to be the best predictors of resiliency for Sierra Nevada whitewater runs. Recreation is important for management of rivers, yet it is difficult to quantify and to plan for. This research provides a sensitivity analysis approach to climate warming for the Sierra Nevada and presents a method that can be applied to other regions and whitewater rivers. The observed reduction in whitewater recreation opportunities in unregulated rivers because of climate warming and continued increases in population will likely increase the importance of whitewater boating on regulated rivers and thus the reliance on operations for meeting multiple demands. Copyright © 2011 John Wiley & Sons, Ltd.     

Response of the aquatic macroinvertebrate communities to dam construction on the Thomson river,Southeastern Australia

Aquatic macroinvertebrates were sampled above and below the site of the Thomson Dam, Victoria, Australia, over a two-year period during dam construction. Total number of species and the number of species and individuals per sample were all lower for 33 km below the dam site, compared with sites upstream. Ordination analysis showed that the major differences between the study sites were related to longitudinal position in the river. The second ordination axis could be related to seasonal changes in the fauna. Variations in the pattern of axis 2 scores at sites downstream of the damsite suggested continuing changes in the community at these sites during the study, possibly due to increases in the density of species favoured by sediment deposition (e.g. Cheumatopsyche sp. 2: Trichoptera, Hydropsychidae). Classification analysis separated the faunal communities at sites above and below the construction zone. Inverse classifications indicated species with disjunct distributions on either side of the dam site. By comparison with preconstruction data and surrounding undisturbed rivers, species likely to have been disadvantaged by increased sedimentation were identified. These included Atalophlebioides sp. 1 (Ephemeroptera, Leptophlebiidae), Stenoperla australis (Plecoptera, Eustheniidae) and Scirtidae (Coleoptera).     

Effects of land‐cover transitions on emerging aquatic insects and environmental characteristics of headwater streams in an agricultural catchment

Streams and their adjacent riparian zones are increasingly viewed as interdependent systems linked by reciprocal exchanges of energy, organisms, and materials. We assessed potential associations between the emerging aquatic insect flux and transitions between agricultural land and forest fragments to better understand these stream‐riparian linkages in managed landscapes. We sampled stream environmental conditions and emerging insects at 28 sites distributed along three streams flowing through agriculture‐forest‐agriculture transitions in central Ohio, USA, in the summer of 2012. Ephemeroptera and Trichoptera (ET) taxa had higher flux densities in forests (mean and 95% CI: 0.3 insects m^?2 d^?1 [0.1, 0.8]) compared to agriculture (mean and 95% CI: 0 insect m^?2 d^?1 [0, 0.1]; p = .004), and ET taxa were found in 67% of forested sites compared to only 15% of agricultural sites. In contrast, Dolichopodidae were more strongly associated with agricultural land (mean and 95% CI: 0.6 insect m^?2 d^?1 [0.3 to 1.2]) than forests (mean and 95% CI: 0.1 insects m^?2 d^?1 [0.1, 0.2]; p = .002). Although Chironomidae were the most numerically abundant, ET taxa were among the larger bodied insects and comprised >30% of the total biomass flux, illustrating the importance of taxonomic traits in mediating flux dynamics. Mechanisms driving emerging insect flux were related to substrate grain‐size distribution, channel width, and nutrient concentrations. Overall, our results demonstrate that small forest fragments are strongly related to the aquatic‐to‐terrestrial insect flux and thus have important implications for terrestrial biodiversity and food webs in agricultural landscapes.     

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.