Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Pensoft Publishers  

Urbanisation leads to the degradation of ecosystems through various factors, such as the deterioration of water quality, changes in water and material cycles and the degradation of biological habitats. Amongst these, aquatic organisms are particularly affected by the loss of habitats due to river canalisation and the impacts of invasive species. It has been widely reported that, in regions where invasive species have been introduced and native species have declined, homogenisation of fish populations occurs, resulting in a significant reduction in biodiversity. This loss of diversity disrupts the ecosystem’s stability and resilience, further compounding the negative effects of urbanisation on aquatic environments. However, the impact of urbanisation on fish populations varies depending on the local ecosystem and the degree of urbanisation, necessitating the examination of ecosystem changes induced by urbanisation in each specific region. The Peninsula Malaysia, which is the focus of this study, is a global hotspot for freshwater biodiversity. However, the effects of urbanisation on fish populations in this region have been scarcely studied. The Masai River Basin, which is the subject of this investigation, is located in the Iskandar Development Region, an area undergoing rapid urbanisation. Understanding the consequences of urbanisation on the fish populations and broader ecosystems in this region is critical for providing information for future conservation and management strategies.

A fish survey was conducted at 19 sites in the Masai River Basin, which is an urbanised watershed, focusing on river channels that have been straightened or converted into concrete-lined waterways. Additionally, fish surveys were conducted at eight sites in non-urbanised areas for comparison. The survey resulted in the collection of nine orders, 15 families, 28 genera, 32 species and a total of 3,007 individuals. In the urbanised sites, the proportion of native species in the total catch was extremely low, averaging only 10.4% across all sites, with invasive species making up the majority of the individuals captured. This indicates the significant shift in species composition due to urbanisation and the dominance of non-native species in these environments. On the other hand, in the non-urbanised areas, the proportion of native species was high at 88.7%, highlighting the significant impact of urbanisation on the invasion of non-native species. Particularly in the downstream areas of the urbanised watershed, species such as Poecilia sphenops, Mayaheros urophthalmus and Poecilia reticulata were frequently captured. In contrast, at sites in the upstream areas where forested habitats remained intact, native species listed on the IUCN Red List, such as Parambassis siamensis and Clarias batrachus, were captured. The study revealed that urbanisation and development in the targeted watershed are progressing rapidly, underscoring the urgent need for the conservation and restoration of habitats for these native species.

DOI： 10.3897/BDJ.13.e148173

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PubMed

Other Link： https://bdj.pensoft.net/article/148173/download/xml/

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

ABSTRACT

Riverine estuaries provide several ecosystem services to humankind. Notably, river estuaries are important habitats for both saltwater and freshwater organisms. However, the environment is experiencing degradation due to both direct and indirect anthropogenic impacts across various spatial scales (e.g., dredging, river channelization, land use change and dam construction). This study aims to reveal the relationship between the river estuarine fish fauna and the environmental factors including anthropogenic impacts as the basic knowledge necessary for the conservation and restoration. The Bōsō Peninsula (Japan) was selected as the study area. We identified the environmental factors that affected the fish species diversity and determined the factors that affected the habitat structure in the river, while focusing on anthropogenic impacts and topographical conditions. The fish species that occur in river estuaries are strongly influenced by habitat‐scale factors, such as flow velocity and water depth, along with watershed‐scale factors (such as wave exposure and direct fetch). In addition, the width–depth ratio, which indicates the degree of river channelization, was an important factor that controlled the habitat structure of the fish in the estuary. The results suggest the need for developing restoration plans based on the predictions of the potential physical environment, while considering the predictions for the occurrence of different fish species in the target area. Although this study is limited to the Bōsō Peninsula, our study can be used as a framework for improving future conservation and restoration plans for river estuaries in not just Japan but also other countries.

DOI： 10.1002/aqc.70086

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

DOI： 10.2208/jscejj.24-16018

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Pensoft Publishers  

Alluvial fans, located near mountainous regions, are characterised by substantial sediment supply, large variations in flow and significant disturbances. The river channels on alluvial fans support a distinct biological community compared to those on alluvial plains. In Japan, gravel extraction and riverbed dredging to maintain flood discharge capacity were frequently carried out during the rapid economic growth period of the 1960s, leading to significant human impact on these rivers. As a result of frequent disturbances, the fish communities in these rivers tend to be less diverse. Furthermore, research on river channels in alluvial fans is limited compared to that on alluvial plains, resulting in a lack of detailed information on these ecosystems. Consequently, efforts for ecosystem conservation and restoration in these environments are insufficient.

A fish survey was conducted at a total of 26 sites across four river channels on alluvial fans, each with distinct geological characteristics. The results revealed the presence of 2,265 individuals belonging to 15 species and one genus (only the genus could be identified) within seven families. Amongst the confirmed species were Misgurnus anguillicaudatus (Cantor, 1842), Oncorhynchus masou ishikawae (Jordan and McGregor, 1925) and Cottus pollux Günther, 1873, all of which are listed in the local Red Data Book, highlighting the presence of rare species even in river channels on alluvial fans impacted by human activity. Furthermore, non-native species were found only at a single site in the upstream section, where four individuals of Oncorhynchus mykiss (Walbaum, 1792) were collected. The survey indicated that species diversity and fish species composition varied across the different rivers, suggesting that various factors, such as watershed geology, geomorphological processes and anthropogenic influences, contribute to differences in fish community structure.

DOI： 10.3897/BDJ.13.e159810

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PubMed

Other Link： https://bdj.pensoft.net/article/159810/download/xml/

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Proceedings of the IAHR World Congress  

In Japan, rivers in alluvial fans are undergoing large-scale channel excavation in response to climate change adaptation, but effective alternation techniques have yet to be proposed for nature-based solutions (NbS). Transverse ribs in this area are essential for ecosystem and riverbed protection. The ease of its formation is expected to vary depending on basin characteristics, especially geology, which controls sediment dynamics and flow regimes. This study aimed to clarify the effects of channel excavation and geology on the formation and renewal of transverse ribs within one year. Using orthogonal images generated from UAV photographs of the target reaches, a wide range of transverse ribs and gigantic rocks were monitored, and the results were compared statistically. The results show that transverse ribs are more likely to form in granite and andesite geology and less likely to form in accretionary geology. The renewal of the transverse ribs was mainly observed in the 1/60~1/20 gradient zone. The influence of river channel excavation was not statistically significant, and slight changes were found between a pair of datasets in 2023 and 2024 in the same areas.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Proceedings of the IAHR World Congress  

In Japan, large-scale sediment removal is undergone for climate change adaptation in the rivers of alluvial fans. The transverse ribs in such areas are important to the ecosystem and assist in riverbed protection, and no method has been proposed for channel-sediment removal that preserves this morphology. The ease of formation is expected to vary depending on the geology of a river basin. The objective of this study was to clarify the effects of channel-sediment removal and geology on the formation and renewal of transverse ribs within a period of one year. A wide range of transverse ribs and giant rocks were surveyed and compared using orthoimages generated from aerial photographs of rivers in the Fuji River system, Japan. The results showed that conglomerations are more likely to form in granite and andesite, and less likely to form in sedimentary rocks. Renewal of the transverse ribs was mainly observed in the 1/40–1/20 gradient zone. The influence of river-channel sediment removal was not as apparent, and the difference between those with and without sediment removal was indistinct compared to the results of other studies conducted in the same areas.

DOI： 10.64697/978-90-835589-7-4_41WC-P1796-cd

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Proceedings of the IAHR World Congress  

This study explored nature-based solutions (NbSs) for managing flood risks and supporting biodiversity in Japan's alluvial fan river floodplain, which is susceptible to sudden flooding. This study applied a 1D-2D flood simulation model to the Kamanashi River basin to evaluate three interventions in the floodplain area: widening of channel width, flood diversion to agricultural lands, and secondary levees. River widening has proven to be effective in reducing flood depth and damage by enhancing drainage in stagnant areas. Secondary levees also effectively dispersed the floodwater and reduced the depths in external flooding scenarios. Flood diversion to agricultural lands, however, increases urban flood risks, highlighting the need for careful placement of diversion sites and embankments to prevent unintended harm to urban areas. Ecologically, river widening facilitates biodiversity by creating sandbars that provide essential habitats for floodplain-dependent species with minimal species loss in sandbar-formed areas. However, in areas without sandbars, a slight decrease in species diversity was observed, suggesting that habitat conditions should be carefully managed. Overall, this study recommends river widening as a primary flood control measure because of its dual benefits for flood mitigation and biodiversity. Future research should examine the ecological effects of agricultural land diversion and the impact of double levees. A multistrategy approach may offer a balanced solution for optimizing flood control and ecological preservation.

DOI： 10.64697/978-90-835589-7-4_41WC-P2114-cd

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Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Understanding biota distribution patterns is essential for ecosystem conservation and restoration. In addition to biogeography, the distribution patterns of aquatic organisms that inhabit rivers vary longitudinally along river networks. Although longitudinal changes in distribution patterns in aquatic organisms along river networks have been studied in single river basins, it is crucial to understand these patterns at a regional ecological scale for broad-scale ecosystem conservation. This study aimed to elucidate the longitudinal distribution patterns of fish fauna and their correlation with environmental factors in several watersheds within the East Setouchi Ecological Region, renowned for its rich freshwater fish diversity in the Japanese archipelago. Data were obtained for 118 species across 10 watersheds and 85 sites, and the surveyed sites were classified into four longitudinal groups based on the similarity of the fish fauna. The lowest group comprised river estuaries, abundant in brackish-water fish, comprising primarily Gobiidae species. In lower watershed areas with low agricultural land and forest cover but high urbanization, all fish species selected as indicators were non-native. Upstream areas with a high percentage of agricultural land featured a mix of native Cyprinidae and non-native species such as Micropterus salmoides and Rhodeus ocellatus ocellatus. The most upstream groups, marked by significantly greater elevations and bed slopes, exclusively comprised native species as indicator species. Analyzing the longitudinal distribution patterns of fish fauna at multiple sites within the same ecological region enabled us to choose endemic fish species as indicators and identify important species for conservation. Additionally, the selection of sites characterized by significant urbanization and strong anthropogenic influences, along with the selection of non-native species as indicators, underscores the urgency of conserving native organisms in these areas, calling for continuous monitoring.

DOI： 10.1016/j.limno.2024.126187

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Vulnerability to flood damage is increasing due to the drastic increase in external forces caused by the climate change and high populations in urban areas. As there are limitations to structural flood control measures, measures that include land use optimization are essential for the resilience of humankind. This study investigated the relationship between water management, settlement, and land-use changes from the Paleolithic to the present day in the Kofu basin alluvial fan, Japan, which has a high flood frequency. The results of a chronological analysis of 191 archaeological sites showed that the highest elevation was 352 m in the Paleolithic period and the lowest elevation was 290 m in the Middle Ages, which later indicated the expansion of settlements into lowlands as time passed. Analysis of the relationship between land use and microtopography in the post-modern period also revealed that approximately until 1929, most of the settlement was located on natural levees. However, the construction of continuous levees since the modern era has led to settlements in areas with a high risk of flooding, which is known as the levee effect. While the importance of land use in flood control has been highlighted, here, by examining the relationship between the distribution of settlements, the change of river channels, and flood risk since the recorded history, we highlight the heterogeneity of the current practice of prioritizing development and the timeless universality of land use as a countermeasure for flood inundation.

DOI： 10.1016/j.ijdrr.2024.104578

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.11532/river.30.0_281

DOI： https://doi.org/10.11532/river.30.0_281

Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

Abstract

River estuaries are influenced by terrestrial and marine areas, and have a unique environment that is constantly fluctuating. They are also important habitats for biodiversity conservation. Tanegashima Island is significantly influenced by the Kuroshio Current. Although nearby Yakushima Island has been recognized as a World Natural Heritage site and information on many species has been collected, there is little information on species inhabiting the river estuaries of Tanegashima Island. In this study, the river estuarine ichthyofauna of 26 small and medium‐sized rivers on Tanegashima Island was surveyed and a total of 2758 individuals of 29 species and one genus belonging to 15 families were collected. The fish fauna of the river estuaries of Tanegashima Island were classified into three groups, namely the river estuaries where coastal terraces are underdeveloped and drowned valleys are formed, the river group where the riverbed gradient at the mouth is high, and other river groups. Environmental factors selected as being important for ordination of fish fauna were the altitude of the headstreams at the watershed scale, the gradient of the river estuarine area, and the presence or absence of rapids in the estuary. The importance of the geohistorical factor of drowned valley formation, in addition to habitat and watershed scale environmental factors, as a factor on river estuarine fish fauna is an important finding for future conservation of local biota diversity.

DOI： 10.1111/jfb.15649

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

Abstract

River estuaries are habitats for a variety of organisms, including many temperature‐sensitive species; water temperatures in estuaries are affected by several factors as they are influenced by both terrestrial and marine environments. Therefore, understanding the factors that influence river estuaries are essential for environmental management. However, no information exists on temperature change at high temporal resolution and over a wide area; moreover, the relationship with environmental factors has not yet been clarified. Here, we have described the actual status of water temperature change in riverine estuaries and its relationship with environmental factors for a wide area of the Japanese archipelago. Our results indicated that 217 of 294 rivers showed a significant monthly increase in water temperature. The average annual change in rates of water temperature increase was the highest in October at 0.090°C yr⁻¹ and lowest in February at 0.068°C yr⁻¹. Furthermore, snowfall, air temperature increase, sea water temperature, and land use were identified as factors increasing the rate of water temperature increase. Factors influencing the increase in river estuarine water temperature varied from month to month—with meteorological factors being the strongest influencers from spring to fall, and anthropogenic factors in winter. Our findings emphasize the importance of considering not only meteorological and oceanographic phenomena, but also anthropogenic influences and topographic features to understand the pattern of water temperature changes in river estuaries.

DOI： 10.1002/lno.12507

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Water Switzerland  

Japan’s rivers are shaped by distinctive topography and abundant rainfall, and they face flooding and sediment supply escalation concerns under climate change. Small- and medium-sized rivers tend to catch unprecedented forces that exceed planned levels, leading to substantial widening and excavation. Thus, there is a demand for a method that is capable of managing significant flood flows over an extended period. The spur dike can maintain channel clearance by promoting erosion as well as providing bank protection. However, the effectiveness of this spur dike function has not been well studied in small- and medium-sized rivers and curved reaches. In this study, we evaluate the function of spur dikes in improving channel sustainability based on examples of small- and medium-sized rivers that have maintained their channel for more than ten years after spur dike installation. First, the applicability of the empirical rule was evaluated by comparing it with actual cases of erosion depths in curved sections in Japan. Next, one-dimensional simulations were performed to evaluate the sustainability of the section over a long period. Finally, a depth-averaged morphodynamic simulation, including the secondary flow effect, was applied to evaluate the location of the flow core and elevation changes due to the spur dike. The results showed that a slight difference in the ratio of river curvature radius to river width (r/B) caused the river channel to be erosive and sedimentary. The reasons for the difference were the cross-sectional expansion caused by the excavation of the bend and the difference in the plane flow regime caused by the shift of the flow core to the inside of the bend. Although it is structurally challenging to reproduce localized scour around a spur dike in a depth-averaged simulation, it is essential for designing to apply the simulation model and combine empirical knowledge.

DOI： 10.3390/w16040575

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.2208/jscejj.23-16101

DOI： https://doi.org/10.2208/jscejj.23-16101

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Estuaries and Coasts  

This study was conducted to clarify the relationship between fish species composition and environmental factors at various scales in river estuaries in the Japanese archipelago. The estuaries harbor diverse fish species composition due to their complex topography, varied climatic zones, and ocean currents. Non-hierarchical cluster analysis classified the fish species composition of 100 river estuaries (58 families, 152 species, and 486,356 individuals) into five groups. The highest number of species was confirmed in the group of river estuaries located in southwestern Japan and flowing into the inner bay (55.1 ± 9.6 species), characterized by an abundance of the number of Gobiidae species. In contrast, the species number was the lowest in the groups consisting of river estuaries that primarily belong to the northern Japanese archipelago (15.3 ± 3.3 species) that were characterized by an abundance of the number of cold-water fishes such as Salmonidae, Pleuronectidae, and Osmeridae. The highest fish species diversity was confirmed in the groups consisting of river estuaries flowing into the inner bays of southwestern Japan, which had a large tidal range (344 ± 132 cm), suggesting that the large tidal differences create a diverse tidal flat environment that supports fish species diversity. These results indicate that regional species diversity and geographical factors influence the classification of fish fauna. In northeastern Japan, the classification was influenced by geographic area and associated water temperature changes, whereas in southwestern Japan, tidal differences and wave effects could be more important. Understanding the factors that influence the fish species composition of a target river is fundamental to estuarine conservation, and the findings of this study provide basic knowledge for conservation.

DOI： 10.1007/s12237-023-01248-0

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Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Intense anthropogenic impacts in tidal rivers can cause habitat loss and ecosystem degradation. In addition, changes in water temperature associated with climate change are significantly impacting the distribution area of fish fauna within tidal rivers. In the present study, we used long-term fish fauna data to determine the relationship between climate change-induced increases in water temperature and changes in the distribution of fish species in tidal rivers in the Japanese archipelago. The distribution ranges of many subtropical and tropical fish species were found to move northward in areas affected by warm currents, suggesting further possible distributional dispersal in future. This study is the first to examine the nationwide distributional changes and future projections of fish fauna in tidal rivers. The results suggest that many subtropical and tropical fishes are expanding their distribution areas in tidal rivers and in coastal and estuarine areas.

DOI： 10.1007/s10113-023-02098-z

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Other Link： https://link.springer.com/article/10.1007/s10113-023-02098-z/fulltext.html

Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

Dams have contributed to population growth and technological innovation by reducing the risk of flooding and allowing humans to cultivate productive alluvial soils on river floodplains. However, in countries where many dams have already been constructed, many problems have been observed, such as river environment degradation, aging of the embankments, and inadequate dam performance. As the social and natural environment surrounding dams is becoming more complex and diverse, it is necessary to understand the current overall status of dams and the history of their construction such that we may consider how social capital and dams are related to human society and the natural environment. In this study, the relationship of basic information of dams and the social background in which the dams exist was examined for Japan, where dam construction began in earnest in the late 1800s and became a driving force for economic development. The situations surrounding dams are drastically changing, as maintenance and management costs increase due to the aging of dams and water demand varies due to changes in the industrial structure of a region. Simultaneously, there are instances where dams are expected to reduce damage, such as in the presence of more severe and frequent droughts and floods caused by climate change. It is therefore necessary to remove or restructure dams while considering numerous complex and diverse factors, such as the local social conditions, potential future changes, and environmental impact of rivers.

DOI： 10.1002/rra.4129

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media {LLC}  

This study investigated the fish fauna diversity of the Shimokita and Tsugaru peninsulas in the northernmost part of the main island of Japan. Since ocean currents influence brackish and saltwater fish distribution and dispersion, it is assumed that in the target area where ocean currents are complex, the ichthyofaunal diversity of river estuaries may vary significantly between rivers. In addition, the target area is located on a peninsula with complex topography, and topographical factors are also considered major factors influencing the fish fauna. During the field survey, 6879 individuals of fish from 34 species were collected from 25 river estuarine areas. Furthermore, the cluster analysis results indicated that the Tsugaru Warm Current, which flows from the warm current (Tsushima Current) on the Sea of Japan side to the Pacific Ocean side, strongly influences the presence of fish fauna in the regional river estuarine areas. Moreover, the wave exposure was marginal in rivers flowing into the Tsugaru Strait (7.4 ± 5.8), and saltwater fishes were absent, whereas fishes that depend on the gravel bed were observed. The bed slope of the estuarine river area of this group was large (1.65 ± 0.99%). The riverbed comprised stone and gravel, suggesting that in addition to biogeography, environmental factors strongly influence the presence of fish fauna. Furthermore, compared with previous studies conducted in the Shimokita Peninsula, the distribution area of the southern Gymnogobius species expanded, possibly due to the increase in seawater temperature caused by climate change. In the target area, where currents and topography are complex, it became clear that the area into which the river flows and topographical factors determine the fish fauna of river estuaries, suggesting that elucidating the relationship between complex environmental factors and biota is important for riverine environmental management and conservation ecology.

DOI： 10.1007/s12237-022-01097-3

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Other Link： https://link.springer.com/article/10.1007/s12237-022-01097-3/fulltext.html

Language：English   Publishing type：Research paper (scientific journal)   Publisher：{MDPI} {AG}  

<jats:p>An open levee system is a traditional flood mitigation system for reducing the expansion of inland flooding and decreasing the peak flow. However, there have been few quantitative studies on its feasibility. Furthermore, the differences in applicability depending on the topography and the construction of continuous levees have not been fully examined. We studied its feasibility based on simulations in the Kuji River area, where the vast Typhoon Hagibis occurred. Morphological models representing the past (the 1940s) and the present (2019), obtained by modifying the highly accurate digital elevation models (DEM) via the tracing of aerial photos, were applied to a 2D unsteady flow simulation model to reveal the effects of the levee system on river hydrography and overland flood behavior. The results indicated that inundation flow through an open area decreased both inundation duration and depth, while the reduction of peak discharge is relatively insignificant at approximately 10%. The sub levees are not adequate under the current conditions and floodwater volume, and their effectiveness depends on the surrounding conditions, such as the development of continuous levees.</jats:p>

DOI： 10.3390/w14091343

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Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media {LLC}  

Headstream areas, which are located in the uppermost reaches of mountain streams, are important sections for investigating the geomorphology of stream channels and their generative mechanisms, because they are close to sediment supply sources and generally suffer little anthropogenic impacts. In this study, the occurrences and characteristics of bed morphologies in a sandstone-dominated headstream area are explored at two scales—reach and unit—which are often overlooked. As a result of field investigations, cascades and step–pools were found to occupy the majority of the stream channel laterally at the reach scale. However, most of the elevation differences were accounted for by fall–pools, cascades, and step–pools, suggesting the importance of bed morphologies with large elevation losses in the headstream area. In addition, the characteristics of the bed morphologies at the reach scale were closely related to the longitudinal profiles of each stream. The mean gradients of the reach-scale bed morphologies were 46.9% for fall–pools, 23.9% for cascades, 16.8% for step–pools, and 5.9% for pool–riffles. At the unit scale, pools occupied the majority of the stream laterally, and > 80% of the elevation differences in all the studied rivers were occupied by falls, bedrock cascades, cascades, and steps. Although there have been no studies on the elevation loss functions and characteristics of falls, this study revealed the importance of fall–pool reaches and fall units in a sandstone-dominated headwater area in the Kantō Range of Japan.

DOI： 10.1007/s10201-021-00690-y

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Other Link： https://link.springer.com/article/10.1007/s10201-021-00690-y/fulltext.html

Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier {BV}  

Pools play an important role among stream bed morphologies in mountain streams. They provide habitat and contribute to energy dissipation. However, they have received only marginal attention compared with step structures, and their forms and driving factors, such as stream-channel characteristics and structural characteristics of upstream morphologies, remain unclear. Therefore, the purpose of this study was to determine the structural characteristics of pools, including morphology, size, and deposit conditions, and the factors controlling them. Based on the results of a field survey for a channel length of 9524 m, with 428 reaches and 1302 pools, the correlations between the pool spacing, morphology, size, and deposit conditions of the pool, and controlling factors were investigated for three rock types (granite, rhyolite, and sandstone). The average pool spacing calculated by dividing the interval length of the pool by the channel width was 8.80, 12.87, 4.56, and 16.14 for fall-pool, cascade, step-pool and pool-riffle respectively. This is due to the fact that the target streams are first-order streams with small widths as well as their regional characteristics, that is, few log jams and forced pools. In addition, the depositional depth of the pools varies depending on the geology. The maximum percentage of sediment deposition in the pool was 78%, 33%, and 34% for granite, rhyolite, and sandstone, respectively. Thus, the sedimentation in granite is significantly greater than in the rhyolite and sandstone headstream areas. This is probably due to the discontinuous weathering of granite during which it is broken down into large-sized core stones and fine grains. The difference in the depositional environment of the pools depending on the geology indicates that the biota that use those pools as a habitat may also differ. However, research on the microhabitats of pools is lacked, and research regarding the future perspectives of ecosystems is required.

DOI： 10.1016/j.catena.2021.105760

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

To mitigate urban flooding, conserving pervious areas and securing the infiltration capacity are important. The infiltration capacity of an area can be significantly reduced by compaction; thus, we attempted to build a runoff reduction technology that can ensure the infiltration capacity even after compaction to mitigate urban flooding. Herein, we revealed the relationship between the degree of compaction and infiltration capacity of amended soils using humus and bamboo chips. We performed a watering infiltration experiment, which initially demonstrated the nonoccurrence of surface runoff in all experimental materials for rainfall intensities of 60 and 120 mm hr⁻¹, without compaction. However, as the degree of compaction increased, humus mixed with soil exhibited behaviour similar to that of unimproved soil and the surface runoff exceeded seepage drainage. In contrast, in the case of bamboo chips mixed with soil, the surface runoff remained small even at high degrees of compaction. Consequently, when the rainfall intensity was 120 mm hr⁻¹ and compaction was 3 kg cm⁻², the surface runoff per unit time for bamboo chips mixed with soil was 2.4 times less than that for humus mixed with soil and 2.2 times less than that for unimproved soil. Moreover, such differences were observed in the infiltration capacity with respect to compaction because of the void structure owing to soil improvement. Thus, we conclude that soil improvement using bamboo chips can be considered an effective technology to mitigate urban flooding.

DOI： 10.1111/sum.12705

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1111/sum.12705

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Pensoft Publishers  

<jats:p>Urbanisation has facilitated changes in the hydrological cycle, sediment dynamics and habitat loss and it has had a tremendous impact on river ecosystems. Moreover, the invasion of non-native species reduces the number of native species with the progress of urbanisation, thereby resulting in the homogenisation of fish fauna and significant decrease in diversity. However, the effects of urbanisation on fish fauna vary depending on the region, degree of urbanisation and number of years since the construction of the city. Hence, it is necessary to collect information on how fish fauna changes due to urbanisation in different regions. The target site of the present study is the Tsurumi River, of which approximately 85% of the basin is urbanised and many of the river channels have been affected by straightening and concrete channelling. Monitoring of biota has been conducted mainly in downstream areas; however, data on fish fauna in upstream areas and tributaries of the river, which have been substantially affected by urbanisation, are lacking.</jats:p>
<jats:p>Surveys were conducted at 71 sites in the Tsurumi River Basin during summers and winters, focusing on river channels that have been straightened or converted to concrete channels due to urbanisation. As a result of this investigation, 10 families, 28 species and 9,335 individuals were collected. Some of the fish collected included rare species, such as <jats:italic>Tanakia lanceolata</jats:italic>, <jats:italic>Lefua echigonia</jats:italic> and <jats:italic>Pseudobagrus tokiensis</jats:italic>, indicating that, even in rivers that have been severely impacted by human activities, there are still rare indigenous species living there, albeit in limited numbers. In addition, <jats:italic>Misgurnus</jats:italic> sp. (clade B2), <jats:italic>Micropterus salmoides</jats:italic>, <jats:italic>Lepomis macrochirus</jats:italic> and <jats:italic>Poecilia reticulata</jats:italic> were confirmed to be non-native species. Misgurnus sp. (clade B2) was widespread; however, populations of carnivorous non-native alien species were small. The data are all accessible from the document “database_fish_urban_tsurumi” (https://ipt.pensoft.net/manage/resource?r=database_fish_urban_tsurumi).</jats:p>

DOI： 10.3897/BDJ.10.e83527

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