Culvert replacements: improvement of stream biotic integrity?

Roads and associated stream crossings can modify and degrade natural hydrology of a system and alter organism movement. Culvert replacement and stream crossing improvements are extremely common and often done with the intent to improve biotic integrity of a system. We evaluated 3 sites where poor road‐stream crossings were improved by replacing improper culverts with full‐span natural bottom structures. We used a before‐after‐control‐impact paired series (BACIPS) design to determine if there was evidence of associated improvement in biotic integrity of the stream communities. Biotic integrity indices developed for coldwater fish and macroinvertebrates in the Northern Lakes and Forests Ecoregion were used to estimate responses of the biotic communities adjacent to culvert replacements. With poor to fair fish and macroinvertebrate communities prior to culvert replacement, we predicted communities would show improvement into the good range of the indices. With 2–4 years of pre‐data and 3–5 years of postdata, we were not able to detect improvements in overall biotic integrity utilizing fish or macroinvertebrate index scores. Road crossing improvements may synergistically restore stream ecosystems, restore natural sediment dynamics, and improve passage; however, in these cases local biotic integrity scores were not significantly improved. Culvert replacements are often developed based on the potential, or the perception, that they will restore ecological integrity and biological communities or fisheries; however, as restoration practitioners, researchers, and managers, assessing these claims and learning from prior restoration attempts is necessary.     

Productivity–diversity relationships for stream invertebrates differ geographically

More productive environments typically have more species, although the specific form of this relationship is unclear and can vary with spatial scale. This relationship has received little direct attention in lotic systems, and thus the nature of the relationship is unclear, as is any effect of spatial scale. We examined the link between stream primary productivity and macroinvertebrate diversity in Spain and New Zealand and hypothesized that macroinvertebrate diversity would increase log-linearly with increasing productivity in both regions. We sampled 24 streams in Cantabria, Spain, and 24 in the central North Island, New Zealand. Algal primary productivity was approximately three times higher in Spanish streams, but taxonomic richness of invertebrates did not differ between the regions. Richness and Shannon diversity only responded to productivity in the New Zealand streams, exhibiting the predicted log-linear increase. In the Spanish streams, only the total number of individuals increased with productivity. However, when plotted on the same axes, richness in the Spanish streams simply occurred on the linear portion of the graph to the right of the New Zealand streams. We speculate that productivity in the Spanish streams never became low enough to constrain diversity, but did in the New Zealand streams. Combining results from the two regions, there is no evidence of a decline in diversity with higher productivity.     

Do pools impede drift dispersal by stream insects?

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Can current velocity mediate trophic cascades in a mountain stream?

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Does carbon enrichment affect hyporheic invertebrates in a gravel stream?

For a period of one year we injected a solution of stream water enriched with glucose and inorganic nitrogen and phosphorus at two experimental sites into the hyporheic sediments of the Oberer Seebach, Austria. The biofilm reacted with a quantitative increase after two weeks. The hyporheic invertebrates were sampled with the Cage Pipe Trap method, where the number of trapped animals is determined by the spatial density and the activity of the invertebrates. Within two and six weeks, the hyporheic invertebrates exhibited a reaction indicating an utilization of the new food resources. Over a longer period of one year, three different reaction patterns appeared. The number of nematods and ostracods increased extensively, presumably caused by the modification of the spatial structure of the environment due to biofilm growth. The number of the small sized invertebrates decreased, reflecting the reduced feeding effort. And the number of the large insect larvae increased indicating that these group is mainly limited by space. The hyporheic zone is described as a ‘self-cleaning DOC filter’, an attribute that is particularly assigned to the ecotone between the riparian soil zone and the stream hyporheic zone.     

Is visual processing in the dorsal stream accessible to consciousness?

There are two highly interconnected clusters of visually responsive areas in the primate cortex. These two clusters have relatively few interconnections with each other, though those interconnections are undoubtedly important. One of the two main clusters (the dorsal stream) links the primary visual cortex (V1) to superior regions of the occipito-parietal cortex, while the other (the ventral stream) links V1 to inferior regions of the occipito-temporal cortex. According to our current understanding of the functional anatomy of these two systems, the dorsal stream's principal role is to provide real-time 'bottom-up' visual guidance of our movements online. In contrast, the ventral stream, in conjunction with top-down information from visual and semantic memory, provides perceptual representations that can serve recognition, visual thought, planning and memory offline. In recent years, this interpretation, initially based chiefly on studies of non-human primates and human neurological patients, has been well supported by functional MRI studies in humans. This perspective presents empirical evidence for the contention that the dorsal stream governs the visual control of movement without the intervention of visual awareness.     

Does stream flow structure woody riparian vegetation in subtropical catchments?

The primary objective of this study was to test the relevance of hydrological classification and class differences to the characteristics of woody riparian vegetation in a subtropical landscape in Queensland, Australia. We followed classification procedures of the environmental flow framework ELOHA – Ecological Limits of Hydrologic Alteration. Riparian surveys at 44 sites distributed across five flow classes recorded 191 woody riparian species and 15, 500 individuals. There were differences among flow classes for riparian species richness, total abundance, and abundance of regenerating native trees and shrubs. There were also significant class differences in the occurrence of three common tree species, and 21 indicator species (mostly native taxa) further distinguished the vegetation characteristics of each flow class. We investigated the influence of key drivers of riparian vegetation structure (climate, depth to water table, stream‐specific power, substrate type, degree of hydrologic alteration, and land use) on riparian vegetation. Patterns were explained largely by climate, particularly annual rainfall and temperature. Strong covarying drivers (hydrology and climate) prevented us from isolating the independent influences of these drivers on riparian assemblage structure. The prevalence of species considered typically rheophytic in some flow classes implies a more substantial role for flow in these classes but needs further testing. No relationships were found between land use and riparian vegetation composition and structure. This study demonstrates the relevance of flow classification to the structure of riparian vegetation in a subtropical landscape, and the influence of covarying drivers on riparian patterns. Management of environmental flows to influence riparian vegetation assemblages would likely have most potential in sites dominated by rheophytic species where hydrological influences override other controls. In contrast, where vegetation assemblages are dominated by a diverse array of typical rainforest species, and other factors including broad‐scale climatic gradients and topographic variables have greater influence than hydrology, riparian vegetation is likely to be less responsive to environmental flow management.     

Biotransformations in microstructured reactors: more than flowing with the stream?

The state of the art in the application of microstructured flow reactors for biocatalytic process research is reviewed. A microstructured reactor that is fully automated and analytically equipped presents a powerful screening tool with which to perform biocatalyst selection and optimization of process conditions at intermediary stages of process development. Enhanced mass transfer provided by the microstructured reactor can be exploited for process intensification, particularly during multiphase biocatalytic processing where mass transfer across phase boundaries is often limiting. Reversible immobilization of enzymes in microchannels remains a challenge for flexible realization of biotransformations in microstructured reactors. Compartmentalization in microstructured reactors could be useful in performing multistep chemoenzymatic conversions.     

Can natural selection maintain long-distance dispersal? Insight from a stream salamander system

Dispersal distributions are often characterized by many individuals that stay close to their origin and large variation in the distances moved by those that leave. This variation in dispersal distance can strongly influence demographic, ecological, and evolutionary processes. However, a lack of data on the fitness and phenotype of individual dispersers has impeded research on the role of natural selection in maintaining variation in dispersal distance. Six years of spatially explicit capture-mark-recapture data showed that survival increased with dispersal distance in the stream salamander Gyrinophilus porphyriticus. To understand the evolutionary implications of this fitness response, we tested whether variation in dispersal distance has a phenotypic basis. We used photographs of marked individuals to measure head, trunk, and leg morphology. We then tested whether dispersal distances over the six-year study period were predicted by these traits. Dispersal distance was significantly related to leg morphology: individuals with relatively long forelimbs and short hindlimbs dispersed the farthest. These results support the hypothesis that positive fitness consequences maintain phenotypes enabling long-distance dispersal. More broadly, they suggest that natural selection can promote variation in dispersal distance and associated phenotypes, offering an alternative to the view that dispersal distance is driven by stochastic or landscape-specific mechanisms.     

Does an increase in irradiance influence periphyton in a heavily-grazed woodland stream?

Summary Irradiance level and grazer density were manipulated in a factorial design to examine the relative effects of biotic and abiotic factors on periphyton biomass, productivity, and taxonomic structure in a heavily grazed, woodland stream. Irradiance levels were increased from 0.26 to 12.42 mol quanta/m²/d by placing metal halide lamps over the stream. The major grazer in this system was the prosobranch snail Elimia clavaeformis. Its densities were reduced from ca. 750 individuals/m² to near zero by raising platforms off the stream bottom. Experimental treatments were maintained for 48 days. Biomass-specific carbon fixation rates increased significantly in response to higher light levels, indicating that periphyton communities were light-limited at this time of year. However, positive effects of irradiance on areal-specific carbon fixation and biomass were detected only when grazer density was reduced. Basal cells of the chlorophyte Stigeoclonium dominated communities exposed either to low light or high grazing pressure. When light was increased and grazer density reduced, large or upright diatoms became more abundant. Results from this study indicated that limitation of periphyton photosynthesis could be mitigated by increasing the levels of an abiotic resource (light) to this system, but that periphyton biomass was controlled by biotic interactions.     

Temporally stable abundance–occupancy relationships and occupancy frequency patterns in stream insects

The interspecific relationship between local abundance and regional distribution, as well as the occupancy frequency distribution, are widely studied topics in macroecology. A positive abundance-occupancy relationship has been found in a majority of studies, and satellite species modes are typically dominant in occupancy frequency distributions. However, there are a number of exceptions to these "general" findings, and only a few studies have examined these patterns and their temporal variability in stream organisms. I examined both abundance-occupancy relationships and occupancy frequency distributions in stream insects in a boreal drainage system over six consecutive years. I found that the positive interspecific abundance-occupancy relationship was highly stable temporally, with coefficients of determination ranging from 0.25 to 0.47 over the years. There were no strong differences in the strength and slope of the abundance-occupancy relationship between non-predatory and predatory insect species in each year. Temporally stable abundance-occupancy relationships were paralleled by among-year patterns in both abundance and occupancy, with locally abundant and widely distributed species remaining locally abundant and widely distributed over the years, while locally uncommon and regionally rare species showed the opposite. Occupancy frequency distributions were strongly right-skewed, mirroring the dominance of the left-most satellite mode of regionally rare species. That the abundance-occupancy relationship, species' abundances and distributions, as well as the dominance of satellite species in occupancy frequency distribution were temporally stable suggest that niche-based models are strong candidates for explaining these patterns in stream insects. By contrast, metapopulation-based models that predict clear temporal variability in species' abundance and occupancy, as well as bimodal occupancy frequency distributions, are less plausible candidates for explaining the observed patterns. The present findings are the opposite to those in some terrestrial studies, but they are in agreement with other terrestrial studies and with a few previous studies on stream organisms.     

Mechanisms structuring stream fish assemblages: Are there lessons from introduced species?

Synopsis Stream fish faunas are being increasingly subjected to non-native fishes. Successful establishment of non-native forms varies widely between geographic regions (38–77%), but is generally greater in areas that are either altered by man or initially depauperate in fish species. While such introductions have generally had undesirable effects on native fish species, they show no signs of decreasing. Thus, this essay is an attempt to determine if the introduction of non-native fishes may provide insights into processes structuring stream fish assemblages. There are, unfortunately, few detailed ecological studies documenting the response of stream fish assemblages to introduced fishes. Of the 31 studies included in my analysis, the majority (77%) documents a decline in native fishes following the introduction of exotic or transplanted forms. Only 10 studies examined shifts in resource use, of which 5 documented or suggested shifts in habitat. Overall, the responses of native stream fish assemblages to non-native fishes suggest that biotic interactions are important in structuring the impacted assemblages, being implicated in 62% of the studies. Proposed or demonstrated mechanisms are divided equally between competition and predation. Unfortunately, pre-disturbance data are generally lacking so that processes important in structuring native fish assemblages cannot be determined.     

Do stream fish track climate change? Assessing distribution shifts in recent decades

Understanding the ability of species to shift their distribution ranges in response to climate change is crucial for conservation biologists and resources managers. Although freshwater ecosystems include some of the most imperilled fauna worldwide, such range shifts have been poorly documented in streams and rivers and have never been compared to the current velocity of climate change. Based on national monitoring data, we examined the distributional changes of 32 stream fish species in France and quantified potential time lags in species responses, providing a unique opportunity to analyze range shifts over recent decades of warming in freshwater environments. A multi‐facetted approach, based on several range measures along spatial gradients, allowed us to quantify range shifts of numerous species across the whole hydrographic network between an initial period (1980–1992) and a contemporary one (2003–2009), and to contrast them to the rates of isotherm shift in elevation and stream distance. Our results highlight systematic species shifts towards higher elevation and upstream, with mean shifts in range centre of 13.7 m decade^?1 and 0.6 km decade^?1, respectively. Fish species displayed dispersal‐driven expansions along the altitudinal gradient at their upper range limit (61.5 m decade^?1), while substantial range contractions at the lower limit (6.3 km decade^?1) were documented for most species along the upstream–downstream gradient. Despite being consistent with the geographic variation in climate change velocities, these patterns reveal that the majority of stream fish have not shifted at a pace sufficient to track changing climate, in particular at their range centre where range shifts lag far behind expectation. Our study provides evidence that stream fish are currently responding to recent climate warming at a greater rate than many terrestrial organisms, although not as much as needed to cope with future climate modifications.     

Relationships between bacterial productivity and organic carbon at a soil—stream interface

Microbial communities at soil-stream interfaces may be particularly important in regulating amounts and forms of nutrients that leave upland soils and enter stream ecosystems. While microbial communities are thought to be responsible for key nutrient transformations within near-stream sediments, there is relatively little mechanistic information on factors that control microbial activities in these areas. In this study, we examine the roles of dissolved organic carbon (DOC) vs. particulate organic carbon (POC) as potential controls on rates of bacterial productivity (measured as incorporation of [3H]thymidine into bacterial DNA) and amounts of bacterial biomass (measured as fatty acid yield) in sediments along a transect perpendicular to a soil–stream interface. We hypothesized that spatial patterns in bacterial productivity would vary in response to strong and persistent patterns in pore-water concentrations of DOC that were observed along a soil-stream transect throughout a 2-year period. Our results did not support the existence of such a link between pore-water DOC and bacterial productivity. In contrast, we found bacterial productivity and biomass were related to small-scale spatial variations in sediment POC on 3 of 4 sample dates. While our results indicate that total bacterial productivity in near-stream sediments is not consistently linked to spatial variations in pore-water DOC, it is likely that DOC and POC are not mutually exclusive and the relative contribution of DOC and POC to sedimentary microbes varies temporally and spatially in different riparian habitats. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nutrient retention function of a stream wetland complex—A high-frequency monitoring approach

The ability of riverine ecosystems to retain nutrients depends on different hydrological, chemical and biological conditions including exchange processes between streams and wetlands. We investigated nutrient retention in a stream wetland complex on the time scale of daily hydrological exchange between both systems. Daily mass balances of NO₃-N, NH₄-N, TP and SRP were calculated with data obtained by two automated measurement stations in a stream reach upstream and downstream of a wetland. The pattern of hydrological exchange between stream and wetland was used to classify characteristic hydrological periods like floods, base and low flows. The nutrient retention function of the stream wetland complex varied considerably during phases of similar hydrologic conditions. Despite re-wetting measures in the wetland, an overall net export of all nutrients except for NH₄-N characterised the whole growing season. Nitrate retention occurred during summer flood (retention in the wetland, 23 kg NO₃-N d^?1, 17% of the input load) and low flow (retention in the stream, 1 kg NO₃-N d^?1, 2% of the input load). TP retention during summer could be assigned to sedimentation (0.7 kg TP d^?1, 7% during flooding in the wetland, 0.2 kg TP d^?1, 4% during low flow in the stream). SRP retention was only intermittent. We concluded that the nutrient retention of streams and wetlands can only be optimised by restoration measures that regard both systems as one functional unit in terms of nutrient retention.     

Flight activity of insects along a mountain stream: is directional flight adaptive?

1. Flight activity of Trichoptera, Plecoptera and Ephemeroptera was studied by sticky trapping for 12 months at five sites along a New Zealand mountain stream. Over 19 000 insects were captured by the traps, which were located in forest and grassland reaches, including a reach with intermittent flow.
2. Most species occurred predominantly in forest or grassland, although some were trapped throughout the stream. Longitudinal distributions of adults and their larvae were strongly correlated.
3. Flight periods of 24 caddisflies, three mayflies and four stoneflies ranged from 2 to 12 months. Six species were trapped in all months and 17 (55%) in more than 5 months.
4. The most abundant forest-dwelling caddisfly species were over-represented on the downstream sides of sticky traps located in, and immediately below, forest indicating a majority was flying upstream. Upstream flight compensates for downstream drift of larvae and should maximize the likelihood that forest-dwelling species will locate preferred habitat for egg, larval and/or adult development. Unlike the caddisflies, the stonefly Spaniocerca zelandica was over-represented on the upstream sides of traps, suggesting that some adults may float or fly downstream following emergence.
5. In contrast to forest-dwelling species, only one common caddisfly ( Oxyethira albiceps ) was over-represented on the downstream sides of traps at grassland sites. Unlike the forest-dwelling species, most species taken at the downstream sites probably came from a variety of sources, including a nearby stream.     

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.     

Plant–microbe interactions and nitrogen dynamics during wetland establishment in a desert stream

In late-successional steady state ecosystems, plants and microbes compete for nutrients and nutrient retention efficiency is expected to decline when inputs exceed biotic demand. In carbon (C)-poor environments typical of early primary succession, nitrogen (N) uptake by C-limited microbes may be limited by inputs of detritus and exudates derived from contemporaneous plant production. If plants are N-limited in these environments, then this differential limitation may lead to positive relationships between N inputs and N retention efficiency. Further, the mechanisms of N removal may vary as a function of inputs if plant-derived C promotes denitrification. These hypotheses were tested using field surveys and greenhouse microcosms simulating the colonization of desert stream channel sediments by herbaceous vegetation. In field surveys of wetland (ciénega) and gravelbed habitat, plant biomass was positively correlated with nitrate (NO₃ ^?) concentration. Manipulation of NO₃ ^? in flow-through microcosms produced positive relationships among NO₃ ^? supply, plant production, and tissue N content, and a negative relationship with root:shoot ratio. These results are consistent with N limitation of herbaceous vegetation in Sycamore Creek and suggest that N availability may influence transitions between and resilience of wetland and gravelbed stable states in desert streams. Increased biomass in high N treatments resulted in elevated rates of denitrification and shifts from co-limitation by C and NO₃ ^? to limitation by NO₃ ^? alone. Overall NO₃ ^? retention efficiency and the relative importance of denitrification increased with increasing N inputs. Thus the coupling of plant growth and microbial processes in low C environments alters the relationship between N inputs and exports due to increased N removal under high input regimes that exceed assimilative demand.