Freshwater ecosystems, despite their high species diversity, have been significantly degraded due to anthropogenic activities and climate change. An immediate accumulation of scientific knowledge is essential for effective conservation efforts; however, studies on mountain floodplain rivers remain limited. This study aims to identify the factors influencing the spatio-temporal variability of fish communities in a mountain floodplain river. We conducted surveys in August 2021, June 2022, September 2022, and June 2023 in the mid-river sections of the Butokamabetsu River in Hokkaido, Japan. Several 100-meter-long study sections were established, comprising four types: main channel and secondary channel in both upstream and downstream areas. Surveys were conducted on habitat environments, including velocity, depth, temperature, and fish community composition. Habitat environments varied significantly among section types, with the downstream secondary channel exhibiting notably smaller wetted width and water depth. Seasonally, water temperature and flow discharge decreased in late summer compared to early summer, with the summer of 2021 characterized by record high water temperatures and low flow discharge. In response to these habitat conditions, fish community structures differed. The downstream secondary channel hosted a high density of sand lamprey, Lethenteron reissneri, and small-sized Sakhalin taimen, Parahucho perryi. Seasonal changes in fish density, particularly in fluvial sculpin, Cottus nozawae, and stone loach, Noemacheilus barbatulus toni, were evident, possibly due to mortality over time. Additionally, data from the annual sampling periods (August 2021 and June 2022 vs. September 2022 and June 2023) indicated a trend of decreased small-sized Sakhalin taimen and fluvial sculpin during August 2021 and June 2022, attributed to the record hot summer. Overall, the study suggests that in mountain floodplain rivers like the Butokamabetsu River, the spatio-temporal variation of fish communities is determined by the presence of diverse river section types and changes in habitat environments at both seasonal and interannual temporal scales.

This study analyzed the relationship between the appearance pattern of benthic species and river floods over nine-years between 2012 and 2020, based on 94 fixed survey sites located in intertidal zones of the Kuma River estuary. The sediment condition showed that silt and clay contents increased from the middle to the end of the survey period, and were particularly high in 2020, indicating that the intertidal zones were fine grained. The α-diversity of benthic species was low in years with major river flood events, and γ-diversity showed a significant negative correlation with annual peak flow rate. The results suggest that species diversity responds to flooding events and tends to decrease, especially when major flood events occur. Moreover, variation in the appearance pattern of 55 benthic species was evaluated. The appearance patterns were classified into five types, and a type including 20 species, representing approximately 40% of the species, had a significant negative correlation with annual river flow rate. The 20 species consisted mainly of mud shrimps, a ghost shrimp, their symbionts, and species that inhabit gravelly and sandy sediments. In addition, one of the five types of patterns was a monotonous decrease in number of occurrences during the survey period, and most species belonging to the type mainly inhabit sandy sediment. Our findings suggest decreases in sandy intertidal habitats and the benthic species due to major river flood events and fine grained sediments over time. In future, when a major river flood event occurs in the Kuma River system, the benthic species inhabiting sandy sediment should be monitored, and improvements to the sediment conditions should be considered according to the results of monitoring.

Recruitment failure is a major process driving the global decline of freshwater mussels (Order Unionida), and the primary causes include habitat fragmentation and deterioration. Habitat fragmentation primarily disrupts the host-parasite relationship at the parasitic (larval) stage, whereas habitat deterioration leads to recruitment failure by affecting multiple life stages. However, the relationship between recruitment failure due to habitat deterioration and specific mussel life stages remains poorly understood. This review summarizes the relationship between recruitment failure caused by pollution (water and sediment) and life stages, with the aim of providing insights to support mussel conservation. Recruitment failure occurs when one or more of the critical life stages (adult, larval, or post-parasitic juvenile) are disrupted. Studies evaluating one or two consecutive stages—or comprehensive assessments of all three—have been conducted to identify bottlenecks and clarify how pollution limits recruitment. Previous studies have reported that the larval and post-parasitic juvenile stages may represent more significant bottlenecks than the adult stage under polluted conditions, with the post-parasitic juvenile stage being particularly vulnerable. A recent study by Miura et al. (2023) tested the effects of multiple stressors on mussel recruitment and identified bottleneck stages. This case demonstrated that recruitment failure in a lotic mussel species could occur if both the larval and post-parasitic juvenile stages were not fulfilled, as both represented critical bottlenecks. The study also indicated that nutrients and fine sediments synergistically reduced post-parasitic juvenile survival. This review highlights the importance of considering multiple mussel life stages and the interactive effects of multiple stressors on recruitment in polluted habitats for effective conservation. Future research should: 1) evaluate the effects of other interactive stressors on mussel recruitment by identifying critical bottleneck stages, and 2) determine population status. In addition, long-term populations and habitat monitoring should be implemented where such assessments are lacking.

We examined species diversity of wintering waterbirds in the Seta River, which flows out of Lake Biwa, by comparing modified riffle and pool habitats. Observations were conducted on 21 days between December 6, 2020, and February 19, 2021, excluding rainy days, for 1.5 hours around noon each day. Censuses were carried out while walking along the right downstream bank, and individual birds were located on Google Earth satellite images divided into 11 districts defined by artificial and natural features. For each individual, we recorded behavior: diving, dabbling, surface feeding, resting, moving, or others, based on several seconds of observation. Shannon's diversity index (Hʼ) was calculated for each habitat type. A total of 11 species were recorded in the riffle and 9 in the pool, with the common coot being the dominant species. The average Hʼ differed significantly between the riffle and the pool. In the uppermost reach of the Seta River, which has been modified into an artificial channel, a navigation route dredged to a depth of 7.5 m was maintained to ensure vessel passage. This created deep areas that supported diving waterbirds. On the shallow bar opposite the erosional bank of the pool, a large submerged macrophyte bed was present, where common coot was abundant, feeding surface, resting, but not dabbling. Dabbling behavior in other species occurred only in a few individuals within two riffle districts, where mid-channel bars appeared to create a complex depth structure that constrained the development of extensive submerged vegetation. This likely prevented particular waterbird species that feed it from an extreme increase. Incorporating the diversity index (Hʼ) with analyses of water depth structure and shoreline features provided deeper insights into the habitats that support waterfowl communities following river channelization and shoreline hardening.

To achieve flood control and biodiversity conservation in Japan, attention has been given to storing floodwater in abandoned rice paddies and converting them into wetlands under non-flood conditions. However, it is not clear how terrestrial animals in abandoned rice paddies respond to flooding. We have temporarily inundated an abandoned rice paddy in Tomisato City, Chiba Prefecture, Japan, and observed animal behavior after the inundation with environmental citizen science. A total of 325 records from 20 orders and 88 taxa were collected. Arthropods represented 93% of the total taxa. The number of records was significantly higher immediately after the inundation than three hours after. It was possibly due to the completion of each taxon's migration. Coleoptera had the largest number of records for both vertical and horizontal migration. Araneae, Orthoptera, Hemiptera, Lepidoptera, and Hymenoptera also had relatively large numbers of records for vertical and horizontal migration. Odonata, especially Sympetrum spp., visited the water body and some individuals showed egg-laying behavior. Behavior sometimes showed both horizontal and vertical migration, even within the same species. This result may be partly due to differences in passive or active flood avoidance behavior depending on the microenvironment where the target species was at the time of the temporal inundation or where it reached. Our survey program provided a large amount of monitoring data in a short period, and the questionnaire survey indicated that the program provided a high satisfaction level for participants and an opportunity to reflect on biodiversity.

At the free session FC1 in 2024 meeting of ECES, the applicability and innovation of digital twin technology in the environmental field were discussed from technical and social perspectives. Digital twins were recognized as a key tool for promoting information sharing and reducing environmental impact. Game engine-based river modeling was highlighted to support consensus building, while generative design was seen as enhancing rational river form optimization. Challenges such as simplifying field observations, utilizing open data, and improving designers' environmental literacy were identified, along with the importance of data structuring for rapid post-disaster recovery.

Managing deer and mitigating their impact on vegetation is an urgent issue that requires a simple, low-cost monitoring method for rapid assessment of deer behavior and its negative effects. In this study, I used an uncrewed aerial vehicle (UAV) platform, which allowed us to evaluate the impact of deer on wetland vegetation. The study was conducted at Mizorogaike Marsh (Kita-ku, Kyoto City, Kyoto Prefecture), using Menyanthes trifoliata and Zizania latifolia as indicator species. UAV-based aerial imagery was captured in October 2015 and 2023, as these species are easily distinguishable from other plants during this period. This study provides essential baseline data for long-term wetland monitoring.