The environmental DNA (eDNA) method is a novel technique for precise and efficient biological surveillance. Although eDNA has been widely used to monitor various freshwater organisms, eDNA dynamics ...in streams remain poorly understood. In this study, we investigated the eDNA dynamics of common carp (Cyprinus carpio) in a forested headwater stream affected by the effluent from a carp farm. We evaluated the longitudinal variation in carp eDNA along a river downstream from the farm and performed a temporal eDNA decay experiment using digital polymerase chain reaction. On the basis of the resulting decay constants, we built a model to simulate the advection and degradation of eDNA along the studied river. The observed eDNA flux (concentration multiplied by flow rate) decreased exponentially with distance downstream from the farm, and eDNA was detected 3 km downstream of the farm. Although the water temperatures were similar, the eDNA decay constant was lower in autumn than in summer. The simulated eDNA concentration was markedly larger (>10 times) than the observed concentration, suggesting that eDNA removal is accelerated in the stream environment compared to in conventional experimental settings.
Dam sedimentation is a crucial issue that interferes with flood control and electric power generation. To address this, sediment dredging, bypass tunnel, flushing, and sluicing have been applied. ...Despite the potential impacts of these operations on stream environments, few studies have explored the environmental/ecological consequences of such regime shifts in sediment dynamics. Specifically, impacts of sediment sluicing on stream fauna have never been reported. This study assessed primary impacts of sediment sluicing events operated with the two cascade dams (the Saigo and Ouchibaru Dams) on stream insects in the lower Mimi River, Japan. The sediment sluicing, accompanied by a major flooding event in the river, was first operated in September 2017. Stream insect data downstream of the four cascade dams, including the two sluicing dams and a reference river, were collected yearly or biyearly in winter and summer from 2010 to 2018. Following the initiation of retrofitting the Saigo Dam for optimizing sediment sluicing, a downstream reach of the dam experienced marked perturbations in terms of both individual density and species richness. The density and richness dramatically decreased and the community significantly differed in winter 2017 from pre-impact conditions. The density, richness, and community composition subsequently recovered in winter 2018, even after the sediment sluicing impact, suggesting that the anticipated negative ecological impacts of the sluicing are limited. Non-metric multidimensional scaling and permutational multivariate analysis of variance revealed distinct differences in communities between summer and winter samples at non-regulated sites or sites farther downstream of the dam that are characterized by fewer Simuliidae in summer and relatively abundant Heptageniidae. This could serve as a reference for assessments of ecological consequences of sediment sluicing in the region.
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•Ecological consequences of sediment sluicing are unknown•Effects of sluicing on stream insect communities are documented in a long-term study•Density and richness were negatively affected but recovered rapidly•Community composition was also recovered and approached non-regulated river•Impacts of the sediment sluicing on stream insects were limited
spp. are common bacteria present in the intestinal tracts of animals and are used as fecal indicators in aquatic environments. On the other hand, enterococci are also known as opportunistic ...pathogens. Elucidating their composition in the intestinal tracts of domestic animals can assist in estimating the sources of fecal contamination in aquatic environments. However, information on the species and composition of enterococci in animal hosts (except humans) is still lacking. In this study, enterococci were isolated from the feces of cattle, pigs, birds, and humans using selective media. Enterococcal species were identified using mass spectrometry technology, and each host was characterized by diversity and cluster analysis. The most dominant species were
in cattle,
in birds, and
in pigs and humans. Cattle had the highest alpha diversity, with high interindividual and livestock farm diversity. The dominant enterococcal species in pigs and humans were identical, and cluster analysis showed that the majority of the two hosts' species clustered together.
Abstract
It is well known that far-red light (FR; >700 nm) drives PSI photochemistry, but its effect on photosynthetic performance has received little attention. In this study, the effects of the ...addition of FR to red fluctuating light (FL) have on photosynthesis were examined in the leaves of Arabidopsis thaliana. Light-activated leaves were illuminated with FL alternating high light/low light (HL/LL) at 800/30 μmol m−2 s−1 for 10–15 min without or with FR at intensities that reflected natural conditions. The CO2 assimilation rates upon the transition from HL to LL were significantly greater with FR than without FR. The enhancement of photosynthesis by FR was small under the steady-state conditions and in the HL phases of FL. Proton conductivity through the thylakoid membrane (gH+) in the LL phases of FL, estimated from the dark relaxation kinetics of the electrochromic absorbance shift, was greater with FR than without FR. The relaxation of non-photochemical quenching (NPQ) in the PSII antenna system and the increase in PSII photochemistry in the LL phases accelerated in the presence of FR. Similar FR-effects in FL were confirmed in typical sun and shade plants. On the basis of these results, we concluded that FR exerted beneficial effects on photosynthesis in FL by exciting PSI and accelerating NPQ relaxation and PSII-yield increase. This was probably because of the increased gH+, which would reflect faster ΔpH dissipation and ATP synthesis.
This study demonstrates the inverse prediction of the discrete-element method (DEM) input friction coefficient from the DEM output powder properties such as the outflow rate, aerated bulk density, ...and repose angle. Support vector (SV) regression can reasonably reproduce the friction coefficient from the DEM output powder properties. Among the powder properties considered in this study, the outflow rate is found to be the most effective for predicting the friction coefficient. Other powder properties also contribute to improving the prediction accuracy. The accuracy of the SV model depends on the number of cases used for the inverse regression of the friction coefficient, and models with practical accuracy can be obtained for 100–200 cases. These results will lead to further use of machine learning in DEM simulations.
The green alga
often forms spherical aggregates called "marimo" in Lake Akan in Japan. In winter, marimo are exposed to low water temperatures at 1-4 °C but protected from strong sunlight by ice ...coverage, which may disappear due to global warming. In this study, photoinhibition in marimo was examined at 2 °C using chlorophyll fluorescence and 830 nm absorption. Filamentous cells of
dissected from marimo were exposed to strong light at 2 °C. Photosystem II (PSII) was markedly photoinhibited, while photosystem I was unaffected. When the cells with PSII damaged by the 4 h treatment were subsequently illuminated with moderate repair light at 2 °C, the maximal efficiency of PSII was recovered to the level before photoinhibition. However, after the longer photoinhibitory treatments, PSII efficiency did not recover by the repair light. When the cells were exposed to simulated diurnal light for 12 h per day, which was more ecological, the cells died within a few days. Our results showed new findings of the PSII repair at 2 °C and serious damage at the cellular level from prolonged high-light treatments. Further, we provided a clue to what may happen to marimo in Lake Akan in the near future.
The environmental DNA (eDNA) method is being increasingly applied in various environments. Although eDNA undergoes rapid degradation in aqueous environments, it has been detected in streams up to 10 ...km downstream from its source. As environmental bacteria can uptake free DNA, transfer their genetic traits, and amplify, there is a potential risk that they, rather than a target aquatic species, could become a source of measured eDNA. This study examined whether bacteria with incorporated fish DNA could be such a source by investigating the detectability of fish DNA generated by bacteria inhabiting river water and riverbed sediment. We attempted to detect common carp (Cyprinus carpio) eDNA in stream water and sediment samples and the DNA of common carp produced by bacterial colonies (Escherichia coli, total coliform, and heterotrophic bacteria) cultured from the samples. The eDNA was detected in the environmental samples but the carp DNA from the targeted bacteria was rarely detected in both water and riverbed sediment samples. Our results suggest that the risk of bacterium-induced false positive detection for fish eDNA is negligible.
Alterations in natural flow regimes caused by dams can significantly alter the aquatic habitats of stream organisms. However, few studies have characterized flow regulation to assess its impacts on ...stream fauna in the context of interannually variable extreme floods. This study aims to understand the variation in stream animals along flow regulation gradients due to hydropower dams in a catchment experiencing typhoons. We observed freshwater fishes and stream insects at fully regulated sites (receiving residual flow), moderately regulated sites (receiving hydropower outflow), and nonregulated site (tributary) in the Mimi River catchment in southern Japan, in summer and winter from 2010 to 2018. We computed indicators of hydrologic alteration (IHA) in each calendar/water (July to June) year from 2007 to 2017 and selected subsets of IHA based on principal component analysis (PCA) and variance inflation factor. The largest variance was mainly explained by minimum discharge levels (e.g., 30-day annual minimum) and flow variability among IHAs, distinguishing the moderately regulated and nonregulated sites from fully regulated sites because of residual flow and suppressed high pulses in the fully regulated sites. Generalized additive models revealed that annual maxima of specific discharge were most significant predictors of fish and insect metrics while its effects were generally inconsistent between summer and winter. Non-metric multidimensional scaling revealed that insect communities were clustered into the regulation extents in both seasons. The differences in winter fauna between the regulated and nonregulated sites, characterized by Ephemeroptera-Plecoptera-Trichoptera abundance, were associated with maximum discharge and high pulse numbers. Fish community variation did not correspond to flow regime gradients. Our findings on mechanistic ecohydrological consequences of various flow regulations, supported by long-term observations, will be useful for river managers attempting to compensate for alterations in flow regime and ecological integrity.
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•Little is known about impacts of flow regulation with typhoons on stream animals.•Long-term flow and organism data at a catchment subject to typhoons were used.•Flow regimes were characterized to assess relevant impacts on insects and fish.•Insect community was sensitive to flow regimes and typhoons.•Eco-hydrological consequences of flow regulation will be useful to river managers.
Abstract
Efficient desalination through a reverse osmosis (RO) membrane requires the prior removal of blockade-causing substances from raw seawater. To achieve ultrahigh-speed processing of a ...pretreatment process for seawater RO desalination, we combine traditional softening with ballasted flocculation (SBF) for Ca
2+
and Mg
2+
removal. An alkaline mixture of Ca(OH)
2
and Na
2
CO
3
was the most suitable softening agent for Ca
2+
and Mg
2+
removal with a reduced amount of generated sludge. This softening treatment simultaneously removed the suspended solids and bacteria from actual seawater. The settling velocity of the suspended solids generated via seawater softening was extremely low. Under the optimum conditions for desalinating actual seawater using an anionic polymer flocculant and microsand, the settling velocity exceeded 3.5 cm/s, 833 times higher than that of softening without ballasted flocculation. The amount of sludge after standing for 3 min was 76.5% lower in SBF than in conventional softening. The silt density index of the treated seawater met the water-supply standard of RO membranes (i.e., <3.0). Furthermore, the SBF-generated sludge exhibited considerably improved dewatering property than the sludge obtained via conventional softening. SBF can efficiently and quickly remove the causative substances of RO membrane fouling from seawater, thereby improving the treatability of generated sludge. SBF provides a new pretreatment process for seawater desalination using RO membranes.
In the ballasted flocculation, high-speed sedimentation of suspensions is achieved using a microsand as a ballast material and a polymer flocculant combined with microflocs made of polyaluminum ...chloride (PAC) as an inorganic coagulant. In this study, three turbid water samples containing kaolin clay (kaolin concentration: 20, 200, and 500 mg/L) were treated by coagulation-sedimentation and ballasted flocculation. The effects of pH and PAC dosage, which are the controlling parameters for coagulation, and the microsand (silica sand) and polymer dosages, which are the controlling parameters for ballasted treatment, on the treatment efficiency and floc settling velocity were examined. The floc settling velocity under the optimum conditions was 17 times higher than that of the conventional coagulation-sedimentation process using PAC. The turbidity was 0.54 turbidity unit (TU) (TU as the kaolin standard), and its removal efficiency was 99.7%. Furthermore, turbid water samples with different kaolin concentrations (20 and 500 mg/L) were treated via the ballasted flocculation. In this study, fundamental information on the optimization of each dosage condition of coagulant, ballast, and polymer and pH condition in ballasted flocculation was obtained, and the removal mechanisms under optimal, underoptimistic and overoptimistic conditions were proposed.
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