Understanding the seasonality of Cs concentrations in aquatic animals is crucial for reviving local inland fisheries. The seasonality of Cs concentrations in animals is expected to vary, even if focal species consume similarly contaminated foods because the Cs excretion rate is species-specific, and Cs uptake by foraging autochthonous food resources also vary among seasons. Here, we conducted a seasonal monitoring survey of dissolved Cs concentrations as an indicator of the contamination level of food resources and measured Cs concentrations in two carnivorous aquatic animals (Palaemon paucidens and Rhinogobius sp.
View Article and Find Full Text PDFUnderstanding biodiversity resilience after a major disturbance is a key issue in basic and applied science. Plant diversity in gravel-bed rivers is affected by flood events, which are one of the most effective disturbance agents in the flow regime, affecting species distribution, and ecosystem dynamics. Although disturbance plays a critical role in community assembly mechanisms, how plant diversity recovers after a severe disturbance, such as a 100-year flood event remains unknown.
View Article and Find Full Text PDFHyporheic zone (HZ) locates below the riverbed providing habitat for macroinvertebrates from where the winged adult insects (i.e., hyporheic insects, HIs) emerge and bring out aquatic resources to the riparian zone.
View Article and Find Full Text PDFRiverbeds downstream of dams are starved of sediment, impacting habitat structure and ecological function. Despite the implementation of sediment management techniques, there has been no evaluation of their conservational effectiveness; the impacts on high trophic level organisms remain unknown. This study examined the effects of sediment replenishment on riverbeds and macroinvertebrates in a dammed river before and after sediment replenishment.
View Article and Find Full Text PDFRunning waters contribute substantially to global carbon fluxes through decomposition of terrestrial plant litter by aquatic microorganisms and detritivores. Diversity of this litter may influence instream decomposition globally in ways that are not yet understood. We investigated latitudinal differences in decomposition of litter mixtures of low and high functional diversity in 40 streams on 6 continents and spanning 113° of latitude.
View Article and Find Full Text PDFWe developed a food web-based transfer factor (TF) to study contaminant movements from multiple prey items to a predator based on the dietary contributions of prey items with their respective contamination levels. TF was used to evaluate the transfer of Cs into whitespotted char (Salvelinus leucomaenis) from the trophic structure of a stream-riparian ecosystem in headwater streams draining a Japanese cedar forest. We also examined the applicability of this method by comparing sites with different contamination levels but similar surrounding environments in Fukushima and Gunma.
View Article and Find Full Text PDFIt is important to understand the changes in the Cs concentration in litter through leaching when considering that Cs is transferred from basal food resources to animals in forested streams. We found that the difference of Cs activity concentration in litter between forest and stream was associated with both litter type and Cs fallout volume around Fukushima, Japan. The Cs activity concentrations in the litter of evergreen conifers tended to be greater than those in the litter of broad-leaved deciduous trees because of the absence of deciduous leaves during the fallout period in March 2011.
View Article and Find Full Text PDFUnderstanding the mechanisms of (137)Cs movement across different ecosystems is crucial for projecting the environmental impact and management of nuclear contamination events. Here, we report differential movement of (137)Cs in adjacent forest and stream ecosystems. The food webs of the forest and stream ecosystems in our study were similar, in that they were both dominated by detrital-based food webs and the basal energy source was terrestrial litter.
View Article and Find Full Text PDFIn Japanese forests suffering from the Fukushima Daiichi Nuclear Power Plant accident, litter fall provides a large amount of radiocesium from forests to streams. Submerged litter is processed to become a vital food resource for various stream organisms through initial leaching and subsequent decomposition. Although leaching from litter can detach radiocesium similarly to potassium, radiocesium leaching and its migration are poorly understood.
View Article and Find Full Text PDF1. The passive or active movement of organisms between habitat patches plays important roles in achieving ecosystem resilience to disturbance and long-term control of population levels. However, causal mechanisms of disturbance-induced movements of mobile biota across heterogeneous habitat patches at a relatively short time-scale are little understood.
View Article and Find Full Text PDFWe determined the extent that a riparian buffer reduces stream suspended sediment concentrations by filtering road runoff during 18 rain events in a 2.5-ha, multi-use watershed in northern Thailand. The dominant buffer species was the perennial sedge Fimbristylis aphylla Zoll.
View Article and Find Full Text PDFEnergy and nutrient subsidies transported across ecosystem boundaries are increasingly appreciated as key drivers of consumer-resource dynamics. As purveyors of pulsed marine-derived nutrients (MDN), spawning salmon are one such cross-ecosystem subsidy to freshwaters connected to the north Pacific. We examined how salmon carcasses influenced detrital processing in an oligotrophic stream.
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