Pulses of seed release in riparian Salicaceae coincide with high atmospheric temperature

Riparian shrubs and trees in the Salicaceae family release their seeds when floods that create nursery sites for germination are more frequent, but little is known about the factors controlling temporal variations in seed release within the seed release period. The seed release of three riparian tree species dominating European floodplain forests (Populus alba L., Populus nigra L., and Salix alba L.) was monitored in spring 2007 and 2008 using seed traps placed along the Middle Ebro River, NE Spain. Correlations relating biweekly seed rain intensity (seeds trapped per square meter) to meteorological (atmospheric temperature, cumulative precipitation, relative humidity, solar radiation, mean wind speed) and hydrological (river discharge) variables were investigated. The best combination of environmental variables explaining seed rain intensity was identified using an Akaike information selection criterion‐based backward selection, after accounting for temporal autocorrelation both in seed rain intensity and environmental variables. Seed rain correlated positively with temperature for P. alba, P. nigra, and S. alba, though its effect decreased with relative humidity for P. nigra. Our results can help fine‐tune the design of environmental flows to promote sexual recruitment of Salicaceae trees: Planning water releases during the hottest days of the seed dispersal period, when seed rain peaks, should maximize seed germination density and thus increase the potential for successful seedling establishment.     

Simulated recruitment of riparian trees and shrubs under natural and regulated flow regimes on the Wisconsin River,USA

Models that link ecological responses to hydrologic changes are important for assessing the effects of flow regulation on aquatic and riparian ecosystems. Based on the Recruitment Box Model, a graphical model used to prescribe environmental flows for cottonwood (Populus spp.) recruitment, we designed a simulation model to represent the influence of river flow dynamics on seedling recruitment of riparian pioneer woody plants. The model simulates the influence of temporal patterns of river stage on dispersal, germination, initial recruitment and over‐winter survival of first‐year seedlings of riparian pioneer shrubs and trees. We used the model to simulate seedling recruitment patterns for five species (Acer saccharinum, Betula nigra, Populus deltoides, Salix nigra and Salix exigua) on the Wisconsin River (Wisconsin, USA) under three flow scenarios: historic (1935–2002), simulated natural (1915–1975) and simulated regulated flows (1915–1975). Simulation results agreed well with field‐observed relative differences among years (1997–2000) in seedling densities for the five focal species. Simulated successful recruitment years were highly synchronous among species, but species differed in their sensitivity to flows at different times during the growing season, consistent with among‐species differences in seed dispersal timing. Comparison of simulated natural and regulated flows for 1915–1975 showed that flow regulation decreased monthly flow variability, increased late summer to winter baseflow and reduced the magnitude of spring peaks. Simulated recruitment and over‐winter survival of tree seedlings of all species was enhanced under the regulated flow scenario, likely due to increased summer baseflow and reductions in peak flood magnitude. Our analyses show the utility of extending the Recruitment Box Model to include multiple species of riparian shrubs and trees, and the effects of post‐colonization flows on their recruitment success. However, some key functional relationships between flow patterns and woody seedling demography (e.g. shear stress thresholds for seedling mortality) have not been adequately quantified and merit further study. Copyright © 2006 John Wiley & Sons, Ltd.     

Hydrologic thresholds for riparian forest conservation in a regulated large Mediterranean river

Most riparian trees are phreatophytic, water table‐dependent plants which broadly differ in their tolerance to drought and permanent flooding. In semi‐arid settings, as water is limiting, inundations may be regarded as inputs rather than stresses for the survival of phreatophytes. In this study, the mortality rates and abundances of Populus alba, P. nigra, Salix alba and local Tamarix spp. were examined in 43 plots with different hydrologic conditions distributed across the floodplain of a large semi‐arid and Mediterranean river, the Ebro River (Spain). The objectives were to determine hydrologic thresholds for the maintenance of declining populations of those species, while providing novel information on their phreatophytic nature, and to examine shifts in the species composition along hydrologic gradients. All species exhibited significant relationships between mortality rates and hydrologic variables (deepest water table—WT, flood duration—FD and flood frequency—FF). S. alba was found to be the species with lowest tolerance to drier conditions (hydrologic thresholds for maintaining a mortality rate <50%: WT > ?1.22 m; FD: out of observation range; FF > 5.4 events y^?1), followed by P. nigra (WT > ?2.18 m; FD > 11.1%; FF > 3.8 events y^?1), Tamarix spp. (WT > ?2.96 m; FD > 3.7%; FF > 2.5 events y^?1) and P. alba (WT > ?3.45 m; FD > 1.7%; FF > 2.0 events y^?1). Only a significant reduction in S. alba relative abundance was observed as conditions got drier. The results provided quantitative information useful to guide management plans for the protection of Mediterranean phreatophytic tree species from further degradation and suggested that eventual natural or regulation‐induced droughts and groundwater declines would accelerate the loss of all phreatophytic species, especially S. alba. Copyright © 2010 John Wiley & Sons, Ltd.     

Secondary seed dispersal in hydro‐fluctuation belts and its influence on the soil seed bank

The completion of the Three Gorges project altered the water level fluctuations from “summer submersion and winter exposure” to “summer exposure and winter submersion.” The reverse seasonal flooding has dramatically changed both the time and duration of exposure and submergence of reservoir banks. Secondary seed dispersal by water is the primary method of dispersal in hydro‐fluctuation belts. This study conducted field sampling and germination experiments to evaluate the effects of reverse seasonal flooding on species composition, diversity, and density of the secondary seed dispersal system and the soil seed bank, and their changes with elevation, in the Xiangzi River. The results indicate that that the secondary seed dispersal system and soil seed bank were associated with 42 and 50 plant species, respectively, and their average seed densities were 1,876.27 and 7,322.18 seeds/m², respectively. The quantity of seeds from secondary seed dispersal accounted for 20.40% of the soil seed bank. The species life‐form composition of both consisted mainly of annual and perennial grasses. Among these grasses, the dominant species in the secondary seed dispersal system were Cynodon dactylon and Paspalum distichum, whereas the dominant species in the soil seed bank were Solanum nigrum and Rumex dentatus. Due to the effects of reverse seasonal water level fluctuations, the species composition and quantity of the soil seed bank and secondary seed dispersal system largely exhibited similar spatial distribution characteristics, but some differences were observed. The species quantity, species diversity index, and seed density in the soil seed bank were the highest in the middle section of the hydro‐fluctuation belt, followed by the top section and then the bottom section. Conversely, the species quantity, species diversity index, and seed density in the secondary seed dispersal system were highest at the top section, followed by the middle section and then the bottom section.     

Physical engineering of an island‐braided river by two riparian tree species: Evidence from aerial images and airborne lidar

Following a review of the European distribution, habitat requirements and life history characteristics of two riparian tree species, Alnus incana (L.) Moench (grey alder, a member of the Betulaceae family) and Populus nigra L. (black poplar, a member of the Salicaceae family), we explore their changing spatial distribution and topographic position within a 7 km, island braided reach of the Tagliamento River, Italy, where Populus nigra dominates the woody vegetation cover. Combining field observations and information extracted from aerial images, airborne lidar data and river flow time series for the period 1986–2017, we investigate (a) the changing spatial distribution of all (P. nigra‐dominated) woody vegetation and of A. incana alone; (b) whether river bed topography can be associated with these changing spatial distributions and (c) we consider whether A. incana displays any particular characteristics in its spatial and topographic distribution that may indicate that it is complementing the physical engineering role of P. nigra. We show that A. incana predominantly grows in lines along channel, island and floodplain edges, bordering wooded areas dominated by P. nigra and that areas supporting A. incana are associated with the topographic development of the river bed. We conclude that A. incana appears to be acting as a complementary physical engineer to P. nigra, suggesting that similar complementary physical engineering of river beds may be achieved by species with different life history traits to influence landform development in other river environments.     

ECOLOGICAL RESTORATION UNDER PRESSURE FROM INVASIVE ANIMAL SPECIES: USE OF SALICACEAE CUTTINGS IN A RIVER BANK OVERRUN BY COYPU

Numerous studies have established the fundamental ecological role of riparian zones as well as the main threats they face, for example, by invasive species. Our study concerns a section of a gently sloping river in the western part of France where the coypu, an invasive aquatic rodent, damages streambanks and prevents the regeneration of natural vegetation. The aim was to assess the efficacy of different species used in bioengineering projects for streambank protection and for the restoration of woody habitats. A field experiment was established close to the river bank with cuttings of several woody species belonging to the Salicaceae family. The test consisted in comparing the following: (i) different species (six willows and one poplar); (ii) different cutting sizes; and (iii) the presence or absence of fencing (to protect against coypus). The experiment was conducted over three growing seasons (2009–2011). The measured response variables were the survivorship and the growth expressed firstly by the length and the number of shoots, and secondly by the height of plants. The results showed the following: (i) high growth and survivorship rates for all tested species, notwithstanding some significant differences between species; and (ii) positive effects of both the fencing and the planting of longer cuttings. After three growing seasons, Salix viminalis showed the highest growth in exclosures with a mean cumulative shoot length of 7.1 m, whereas outside exclosures S. purpurea had the highest growth with a mean cumulative shoot length of 3.9 m. Populus nigra and S. purpurea showed the lowest number of stems browsed by the coypu. The different methods were also compared for cost and time‐to‐establishment: the long cuttings of certain species afford a positive effect as significant as fencing (which is more expensive). Such analyses are useful when it is necessary to strike a balance between cost and efficiency, particularly in the context of invasiveness. Copyright © 2013 John Wiley & Sons, Ltd.     

Can the Regeneration of Vegetation from Riparian Seed Banks Support Biogeomorphic Succession and the Geomorphic Recovery of Degraded River Channels?

For rivers degraded by erosion and channel widening, the re‐establishment of riparian vegetation is essential. We assess the potential for riparian seed banks to facilitate natural channel contraction through the regeneration of plants involved in the biogeomorphic succession of three discrete geomorphic units of increasing age and height above the channel bed: bars, benches and floodplain. Standing vegetation upon each unit type was surveyed for four river reaches in the Hunter catchment of eastern Australia. Seed bank composition was determined using seedling emergence techniques on sediment sampled from the units. We compared species richness and composition, and longevity, growth form and seed dispersal mechanisms between the standing vegetation and seed bank species. The seed bank was similar across bars, benches and floodplain, containing mostly perennial pioneer herbs, sedges and rushes, dispersed by wind and hydrochory (water transport). While bar vegetation was similar to the seed bank, bench and floodplain vegetation included later successional species such as shrubs and trees, significantly more grasses and vines (benches: χ²_{5, N = 402} = 102.033, p < 0.001; floodplain: χ²_{5, N = 792} = 30.324, p < 0.001) and higher proportions of unassisted and animal‐dispersed seeds (benches: χ²_{5, N = 352} = 89.409, p < 0.001; floodplain: χ²_{5, N = 338} = 56.026, p < 0.001). The results suggest that seed banks may support early stages of biogeomorphic succession, via regeneration of pioneer plants. However, plants, such as shrubs and trees that are observed upon units of increasing age and height above the channel bed (i.e. benches and floodplain), are likely sourced from transient seeds produced by local vegetation, rather than seed banks. Copyright © 2014 John Wiley & Sons, Ltd.     

The potential role of tributaries as seed sources to an impoundment in Northern Sweden: a field experiment with seed mimics

Fragmentation and flow regulation of rivers by large dams are known to obstruct the longitudinal dispersal of waterborne plant propagules between impoundments, and to affect plant community composition. However, even several decades after a dam has been built, impoundments may still have a relatively species‐rich riparian flora. We hypothesized that free‐flowing tributaries act as the major gene pools for such impoundments, thus alleviating the fragmenting effect large dams have on the main channel. The importance of tributaries as seed sources was tested by releasing wooden seed mimics in three different‐sized (0.22–6.93 m³ s^?1) tributaries of an impoundment in the Ume River in Northern Sweden. In each tributary seed mimics were released, during the spring flood peak, from three points approximately 1, 2 and 3 km upstream the outlet in the impoundment. The importance of a tributary as a seed source increased with tributary size. Of the 9000 released seed mimics 1.5% reached the impoundment; 1.2% of the 9000 originated from the largest tributary and 0.3% from the middle‐sized one. The smallest tributary retained all its mimics. Copyright © 2007 John Wiley & Sons, Ltd.     

Plant dispersal along rivers fragmented by dams

To understand the influence of dams on connectivity of riparian plant communities along rivers, we examined plant dispersal by water (hydrochory) and riparian plant community attributes upstream and downstream from dams on two rivers in the southern Rocky Mountains, Colorado, USA. Drifting plant propagules were collected from the water column along reaches upstream and downstream from dams to examine the longitudinal and temporal variation in seed‐pool species composition and concentration of water‐transported seeds. Similarities between species composition of the hydrochoric seed pool and local standing riparian vegetation were used to evaluate the degree of longitudinal connectivity along river corridors and to isolate the relative contributions of local versus regional species pools to hydrochoric species composition. Furthermore, several synthetic attributes (longevity, origin, life‐form and dispersal mode) and species composition of riparian plant communities were examined to explore the effects of interrupted propagule dispersal on standing vegetation. We estimated that as many as 120 million seeds were transported via hydrochory along free‐flowing reaches of the Rocky Mountain streams in a single growing season. Seed concentration (seeds/m³) in the water column was reduced by 70–94% along reaches downstream from dams compared to free‐flowing reaches. The similarity in species composition of hydrochoric seeds and local standing vegetation was nearly two times greater downstream from reservoirs compared to upstream. This suggests that hydrochory complements local species pools by importing seeds from throughout the upstream catchment area along free‐flowing river reaches, but that hydrochoric seeds are derived primarily from local sources along regulated river reaches. Species richness recovers as a function of downstream distance from contributions of standing vegetation and seeds from tributary streams. Hydrochory may extend the period over which viable seeds of a parent population are dispersed. Even after dispersal of parent populations has terminated, seeds may continue to be available due to residence time in water transport. This extension of the ‘effective dispersal window’ of some species may exceed two weeks or more and may influence the likelihood of successful establishment. In this study, synthetic attributes of riparian vegetation did not differ significantly between free‐flowing and regulated reaches, whereas formal statistical comparisons of community composition upstream and downstream from reservoirs indicate that there are differences in community composition upstream and downstream from dams. These findings suggest that the consequences of 50 to 100 years of fragmentation result in community‐wide effects along Rocky Mountain streams and that these effects may be partially explained by dam‐caused disruption in connectivity of plant populations. Copyright © 2005 John Wiley & Sons, Ltd.     

Evidence for hydrochory and the deposition of viable seeds within winter flow‐deposited sediments: the River Dove,Derbyshire, UK

Previous studies of the influence of hydrochory on plant dispersal have focused on relationships with existing vegetation patterns or litter deposits. River sediment deposition studies have assessed sediment accretion rates, particle size and quality. The link between seed and sediment transport and deposition has been overlooked and never quantified. This paper presents observations of over‐winter viable seed and sediment deposition on three river margin sites along the River Dove, England. At these sites, 105 paired artificial turf mats were installed on the river bank top, face and toe from October 1999 to March 2000 to collect river‐deposited material. From each pair, one mat was used to determine the dry weight; median particle size; percentage sand, silt, clay and organic content of deposited sediment. The other was used in germination trials to determine the number and species of deposited viable seeds. Topographic surveys and water level measurements supported the estimation of the hydrological characteristics of each mat location. Few seeds and little sediment were found on mats not inundated by river water. For these inundated, sediment characteristics varied primarily with elevation (relative to local mean river water level during the study period), with less marked between‐site contrasts. The species composition of viable seeds also varied with elevation. Detrended correspondence analysis (DCA) revealed associations between river/wetland‐related seed species and the bank toe samples. Regression analysis revealed significant relationships between seed number, sediment properties and mat elevation. Redundancy analysis (RDA) revealed associations between the species and abundance of viable seeds and elevation, sediment weight and organic matter content. These analyses suggest that sediment and seed deposition by rivers are closely related processes. The implications of these results for seed remobilization and dispersal and hydrochory within riparian zones are discussed, as are the implications of changes in sediment/seed delivery mechanisms, river flow regimes, and the hydraulic properties of river margins for seeds, sediments and riparian vegetation patterns. Copyright © 2003 John Wiley & Sons, Ltd.     

Seed banks and seed survival of submersion for an emerging plant invader in the Colorado River system,USA

Soil seed banks along shorelines and the ability of seeds to survive submersion in water are among potential factors that can influence seed supply, a frequent driver of riparian plant invasions. We investigated germinable soil seed banks and the ability of seeds to germinate after different durations of submersion in water for non-native ravennagrass (Saccharum ravennae), an emerging but poorly understood invader of riparian habitats in the American Southwest, including along the Lake Powell section of the Colorado River where we performed the study. We assessed soil seed bank composition in 27 ravennagrass-invaded plots using the emergence technique and evaluated effects on ravennagrass germination of submersion in river water for up to 15 months in a laboratory experiment. Ravennagrass was sparse in soil seed banks, detected in samples from only one of the 27 plots. Instead, soil seed banks were dominated by the non-native annual cheatgrass (Bromus tectorum) and a mixture of native early colonizers (e.g., Pseudognaphalium stramineum) and shrubs (e.g., Baccharis emoryi). Although ravennagrass seed germination was low (<9%) in the submersion experiment, some seeds retained germinability after 15 months of continuous submersion in water. Results suggest that while ravennagrass may have limited on-site, readily germinable soil seed banks, potential implications of its protracted seed viability in water for dispersal along waterways warrants further attention.     

Dams select individual morphology but do not modify upstream migration speed of tropical amphidromous gobies

Fish locomotor performance depends on inter‐individual morphological differences and influences the response of populations to anthropogenic impacts. Amphidromous gobies, Sicyopterus lagocephalus and Cotylopus acutipinnis can climb up obstacles several metres high, after their arrival in rivers from the ocean. A previous study demonstrated that juveniles of S. lagocephalus performed better than C. acutipinnis when challenged with an artificial climbing ramp, and that individual morphology explained climbing performance for both species. This present study was focused on the effects of two 10‐m high dams on the individual morphological selection of these species. We hypothesized that, compared with C. acutipinnis, (a) S. lagocephalus juveniles will reach the dams faster after they arrive in freshwater and (b) their morphology will play a lesser role in their capacity to climb up the dams. Anatomical traits were measured for 186 and 201 S. lagocephalus and 179 and 221 C. acutipinnis captured downstream and upstream of the dams, respectively. The time they spent in freshwater was estimated by examining the microstructures of their otoliths. As expected, S. lagocephalus individuals reached the dams 10–20 days faster than C. acutipinnis, and their morphology upstream and downstream of the dams did not differ, in contrast to C. acutipinnis. Upstream of the dam, C. acutipinnis had a larger pelvic sucker than downstream, confirming experimental observations. It suggests that juveniles of the cosmopolitan S. lagocephalus have more efficient upstream migration capacities than the endemic C. acutipinnis. Moreover, differences in individual morphologies above and below barriers appear efficient for quantifying their impact on upstream migration of amphidromous species.     

Composition of the seed bank in drawdown areas of Navigation Pool 8 of the Upper Mississippi River

In an effort to enhance aquatic plant production and habitat diversity on the Upper Mississippi River (UMR), resource managers considered water level reduction as a management tool to increase the area of emergent and submersed aquatic vegetation by natural seed germination. To quantify the availability of seed, we assessed the potential seed bank of selected areas of Navigation Pool 8 of the UMR from substrate samples collected in spring 2000. We tested these samples for viable seed content under four hydrologic conditions: dry, moist, shallow flooded and submerged. Forty‐seven species were identified in the seed bank, including 27 obligate wetland, 10 facultative wetland and 7 upland species. Dominant taxa within the seed bank included Sagittaria spp., Lindernia dubia, Zosterella dubia, Cyperus spp., Eragrostis spp. and Leersia oryzoides. Of the four hydrologic treatments, moist substrates had the greatest species diversity and were the most productive, yielding an average density of 1420 seedlings m^?2. Emergent and submersed aquatic species were widely distributed, each type occurring in more than 90% of the samples. Timing of seedling germination varied among species and has implications for scheduling drawdowns to promote establishment of desired species. Seed bank results were correlated with the vegetation response on substrates exposed during a reduction of water levels of Pool 8 during summer 2001. Experimentally determining the composition and viability of seed banks from drawdown areas provides information useful in predicting the types of vegetation that may develop on exposed substrates. Further, these findings provide resource managers a better understanding of the potential for achieving desired vegetation response through water level reductions. Published in 2008 by John Wiley & Sons, Ltd.     

Rheoreaction impacts dispersal of fish larvae in restored rivers

Connectivity of nurseries and spawning habitats for young of the year life stage is essential for successful recruitment of fish populations and therefore provides a key indicator for river restoration measures. Models for dispersal offer the potential to draw conclusions regarding restoration scenarios and to fill knowledge gaps about possible implications for fish populations. A newly developed rheoreaction‐based correlated random walk model (RCRW), in combination with a three‐dimensional numerical model and a non‐steady‐state particle tracing model, was applied for nase carp larvae (Chondrostoma nasus) before and after a restoration project on the river Danube, Austria. Spatio‐temporal patterns of dispersal of virtual larvae, attached with rheoreactive behaviour, were analysed within both scenarios. In comparison to the heavily modified river reach, the restored reach enabled a greater amount of upstream movement from the release site and showed a generally higher variability of spatio‐temporal distribution patterns. In contrast, estimated total settlement of rheoreactive larvae was substantially higher for the situation prior to the restoration measure. By comparing model results with a previously field experiment it was found that model simulations including rheoreaction as a single behaviour for navigation could not explain the whole pattern of larval dispersal. Therefore it is highly recommended for future studies to develop larval dispersal models by considering other factors (i.e., behaviour, bio‐energetics and environmental factors) of existing and future individual‐based models, which could serve as a tool to analyse the effect of restoration measures for recruitment of riverine fish populations.     

Giant hogweed at its northern distribution limit in North America: Experiments for a better understanding of its dispersal dynamics along rivers

We studied the reproduction and dispersal of giant hogweed (Heracleum mantegazzianum) at its northern distribution limit in North America (Québec, 2014–2016) to better understand the invasion dynamics of the species along rivers. Seeds were collected from a riparian population to conduct germination, floatation, and dispersal experiments. Data were analysed in comparison with a real invasion case that was initiated about 10 years ago along a river system. In Québec, giant hogweed individuals produce on average 14,000 to 16,000 seeds with a germination rate of 75–85%. Seeds with endosperm that fall in water likely sink within 5 hr. Along a small brook, most disperse over short distances (<40 m) in summer, although some can travel 100–300 m. These data suggest that late‐summer or early‐fall water dispersal of seeds would not explain the magnitude and rapidity of the invasion patterns observed along streams. We suggest that late‐fall and, especially, spring floods are the most efficient dispersal vectors for giant hogweed seeds and are likely responsible for the establishment of populations kilometres downstream from introduction points along river systems. The spread of giant hogweed would consequently be less influenced in the near future by a rise in temperature than by a change in the magnitude or timing of flood events.     

The occurrence of vulnerable seagrass species Halophila beccarii Ascherson, 1871 from restored mangrove of Koduvally Estuary,south‐west coast of India

The ocean turf grass, Halophila beccarii Ascherson, 1871 was recorded for the first time in the intertidal region of the restored mangrove ecosystem of the Koduvally Estuary on the south‐west coast of India. It was found co‐existing in the shallow muddy area of the mangroves, dominated by mangrove trees of Rhizophora mucronata and Sonneratia alba, and macroalgae, Ulva sp., Enteromorpha sp. and Chaetomorpha sp. The meadow is sparsely scattered with shoots near the mangroves, with a mean density of 720 shoots/m². Details regarding the morphology and hydrographic conditions are described. The occurrence of H. beccarii in the Koduvally estuary is an encouraging sign of improved ecosystem health through mangrove restoration. The development of seagrass meadow in the estuary will improve the sediment stability and water quality. A further comprehensive study on the spatiotemporal variation of this species in the estuary is also recommended for conservation and management of this vulnerable seagrass species.     

Effects of an enhanced flood on riparian plants of the River Murray,South Australia

In October 2000, the flow of the River Murray entering South Australia was increased from 32 000 to 42 050 ML day^?1 by release of water from an offstream reservoir, and a downstream weir was raised by 500 mm to impound the flood and enhance local floodplain inundation. The flood was maintained for about two weeks, although the duration of inundation was longer at low elevations on the floodplain. Vegetation at three sites was surveyed before and after the flood to examine the impact of inundation on the growth and germination of flood‐tolerant, flood‐dependent and flood‐intolerant species. Among 32 recorded species, Atriplex vesicaria (bladder saltbush, Chenopodiaceae), Sporobolus mitchellii (rats tail couch, Graminae) and Sarcocornia quinqueflora (samphire, Chenopodiaceae) accounted for nearly 82% of the total cover/abundance. Flood‐tolerant and flood‐dependent species (e.g. S. mitchellii) grew and germinated and flood‐intolerant species (e.g. A. vesicaria) senesced. No aquatic plants germinated or established, despite favourable conditions, suggesting an impoverished seed bank or grazing. Based on the growth but lack of germination of flood‐tolerant and flood‐dependent species, the value of small, occasional interventions in environmental flow management may be to maintain existing communities rather than restore degraded ones. Copyright © 2004 John Wiley & Sons, Ltd.     

Hydropower Development,Riverine Connectivity,and Non‐sport Fish Species: criteria for Hydraulic Design of Fishways

Hydropower barriers are among the most conspicuous anthropogenic alterations to natural riverine connectivity, resulting in species‐specific effects linked to dispersal abilities, especially swimming performance. They may present a particular problem for small‐bodied ‘non‐sport fish’, such as those that characterize the freshwater communities of temperate regions in the Southern Hemisphere. Recent studies have suggested that nature‐like fishways could ensure passage of diverse fish assemblages through hydropower barriers. Through experiments performed in a swim tunnel, we present, for the first time, fishway design criteria for two non‐sport species endemic to Chile, a country experiencing rapid hydropower development. In`cremental velocity tests showed that Cheirodon galusdae and juveniles of Basilichthys microlepidotus were capable of very similar standardized critical swimming speeds of 69.7 and 69.6 cm s^?1, respectively. When expressed in units of body lengths, C. galusdae was capable of very high critical speeds of 16.2 bl s^?1, whereas for B. microlepidotus, this was 7.6 bl s^?1. However, fixed velocity tests revealed that the swimming endurance of the latter species was slightly higher. Dimensionless analysis showed a clear relationship between fatigue time and fish Froude number, similar to that already described for subcarangiforms. Based on these results, we present fishway design curves indicating a transition from sustained to prolonged swimming at a fishway length of 15 m. Our results show that the swimming capacity of these species is well‐suited to the mean flow velocity field described for nature‐like fishways. However, more work is required to understand the effects of turbulence on the passage of non‐sport species. Copyright © 2016 John Wiley & Sons, Ltd.     

Using United States Geological Survey stream gages to predict flow and temperature conditions to maintain freshwater mussel habitat

Habitat conditions necessary to support freshwater mussels can be difficult to characterize and predict, particularly for rare or endangered species such as the federally endangered dwarf wedgemussel, Alasmidonta heterodon. In this study, we evaluate flow and temperature conditions in three areas of the mainstem Delaware River known to consistently support A. heterodon, and we develop predictive models using the U.S. Geological Survey (USGS) stream gages and thermal stations in order to identify conditions under which habitat alteration could threaten the species. Flow and temperature prediction models based on nearby existing USGS gage and thermal stations were predictive for all three sites. Both discharge prediction and water depth profile models indicate one location (Site 3) was the most vulnerable to low‐flow conditions as it requires the highest discharge rate (26.3 cms) at the USGS Callicoon gage to maintain both the full wetted perimeter (P_full) and minimal wetted perimeter (P_min) and prevent occlusion of areas that contain A. heterodon. Flow management targets aimed at protecting Site 3 should also protect Sites 1 and 2. Although analyses indicated significant benthic habitat available in all three sites even under low discharge rates, specific mussel locations could be vulnerable to dewatering and thermal stress if only P_min values were maintained. Results indicate the magnitude of site temperature deviations from thermal stations varied by site and river temperature. In general, our results suggest that existing temperature and stream gage infrastructure may be used predictively to evaluate the effects of different flow targets on mainstem Delaware River A. heterodon habitat.     

Effects of reservoir management on abundance,condition, parasitism and reproductive traits of downstream mussels

The large‐scale impoundment of rivers has led to global declines in freshwater mussel populations. It is important to understand the mechanisms underlying these declines to initiate an effective recovery strategy. We examined population traits of three Quadrula species (Quadrula pustulosa, Q. cylindrica and Q. quadrula) at three locations that were exposed to two different reservoir management regimes: releases that mimicked natural flow patterns and releases that were higher and colder in summer months than the natural system. We found lower mussel density, higher hermaphroditism and parasitism rates, and reduced body condition downstream of the dam with unnatural flow regimes. Sex ratios varied on a species and site basis. We found more Quadrula cylindrica females than males averaged across all three sampling sites while Q. pustulosa was male biased across all sites and at site 1. We observed approximately equal sex ratios in Quadrula quadrula. Population disturbances downstream of the more naturally‐regulated dam were not as severe. Our data indicate that dam operation can have effects on a variety of mussel life history characteristics that may ultimately reduce population viability. Copyright © 2010 John Wiley & Sons, Ltd.