Impact of estuary barrage construction on fish assemblages in the lower part of a river and the role of fishways as a passage

The construction of an estuary barrage, an instream structure in the lower reaches of a river, causes significant physical changes in water flow patterns and river morphology, and results in altered environmental conditions. Here, we examined the impact of the Geum River estuary barrage, completed in 1990, on fish assemblages by using a literature search and fresh surveys of fishways in the barrage. We found that fish assemblages upstream and downstream of the barrage were altered following its completion. After construction, more species were found in the freshwater area, with a particularly great increase in freshwater species. Conversely, estuarine and marine species were only consistently caught in the downstream salt-water area, although the number of species increased. In total, 15,829 fish from 47 species and 20 families were identified at the three types (pool and weir, rubble type, and boat passage) of fishways in the barrage. The dominant species were Chelon haematocheilus, an estuarine species, Coilia nasus, a diadromous species, and Erythroculter erythropterus, a freshwater species. The mean total length of fish (101.9 ± 76.0 mm) in the boat passage fishway was approximately 100 mm lesser than those in the pool and weir (207.2 ± 112.8 mm) and rubble type (205.8 ± 112.7 mm) fishways. The boat passage fishway was the most efficient for fish movements. The current fishway system is not sufficient for fish migration, and thus additional ways are required to improve the system such as the boat passage. Few estuarine or diadromous species were found in both freshwater and salt-water areas, but freshwater fishes that accidently moved to salt-water area actively used fishways. Therefore, fishway management in the Geum River estuary barrage has to focus on freshwater fish; however, this may need to change to a focus on migratory fishes depending on ecological life cycles of migratory fish.     

Effect of different wavelengths of light on the antioxidant and immunity status of juvenile rock bream, <Emphasis Type="Italic">Oplegnathus fasciatus</Emphasis>, exposed to thermal stress

We investigated the effect of light wavelengths on antioxidant and immunity parameters in juvenile rock bream, Oplegnathus fasciatus, exposed to thermal stress (25 and 30°C). We exposed the fish to light emitting diodes (LEDs) emitting green (520 nm) and red light (630 nm) of 0.25 and 0.5 W/m² intensity, and measured the activity, and mRNA and protein expression levels of the antioxidant enzymes, superoxide dismutase, catalase, and glutathione peroxidase. We also determined the levels of plasma hydrogen peroxide (H₂O₂), melatonin, and lysozyme. Furthermore, the mRNA and protein levels of caspase-3 were measured and terminal transferase dUTP nick end labeling (TUNEL) assays were performed. We observed that mRNA expression and activities of antioxidant enzymes and plasma H₂O₂ levels were significantly higher after exposure to high temperatures. However, increases in these parameters were significantly lower after exposure to green LED light. The plasma melatonin and lysozyme levels were significantly lower in the different groups after exposure to high temperatures; however, in groups exposed to green LED light, their levels were significantly higher than those in the control group. The expression pattern of caspase-3 mRNA was similar to that of H₂O₂. The TUNEL assay showed that apoptosis was markedly higher at higher water temperatures than that at 20°C. These results indicate that high water temperatures induce oxidative stress and decrease the immunity in juvenile rock bream but green LED light inhibits the rise in oxidative stress and combats the decrease in immunity and should, thus, be useful in the culture of rock bream.     

Modeling of marine litter drift and beaching in the Japan Sea

Characteristics of drift and beaching of floating marine litter in the Japan Sea are examined numerically using the reanalysis data of the Japan Sea Forecasting System of Kyushu University. The residence time of model marine litter deployed uniformly over the surface of the Japan Sea strongly depends on the buoyancy ratio. However, almost all litter beaches or flows out through straits within 3 years. Experiments with inputs of litter imposed at large cities and the Tsushima Straits as well as river basins of the Japan Sea exhibit a good agreement with beach surveys with regard to country ratios of beached litter along the Japanese coast in cases of lighters. In a case of lighter, almost all lighters originating from Japan beach along the Japanese coast, while almost all lighters originating from a country surrounding the Japan Sea except Japan beach along the coast of that country and the Japanese coast.     

Practically Applicable Central Limit Theorem for Spatial Statistics

Let {Z(s):s∈D⊆ℝ ^d } be a zero mean stationary random field observed at a finite number of locations. Lahiri (Sankhya Ser. A 65:356–388, 2003) proved spatial central limit theorems (CLT) for ∑ _i=1 ⁿ Z(s _i ) assuming a ‘nearly infill domain sampling’. Applications of his results depended on the underlying spatial sampling region and the design in a complicated fashion. The main objective of this paper is to provide CLTs that could be applied easily in practice. We present two main results assuming a ‘nearly infill domain sampling’ defined mainly in terms of dependence. Theorem 1 establishes a CLT for ∑ _i=1 ⁿ Z(s _i ) and Theorem 2 is obtained mainly for applications to density estimates. We report on a simulation study for illustrating a way of applying our results in practice.     

Numerical study on the interaction among a nonlinear wave,composite breakwater and sandy seabed

Most previous investigations related to composite breakwaters have focused on the wave forces acting on the structure itself from a hydrodynamic aspect. The foundational aspects of a composite breakwater under wave-induced cyclic loading are also important in studying the stability of a composite breakwater. In this study, numerical simulations were performed to investigate the wave-induced pore water pressure and flow changes inside the rubble mound of the composite breakwater and seabed foundation. The validity and applicability of the numerical model were demonstrated by comparing numerical results with existing experimental data. Moreover, the present model clearly has shown that the instantaneous directions of pore water flow motion inside the seabed induced by surface waves are in good agreement with the general wave-induced pore water flow inside the seabed. The model is further used to discuss the stability of a composite breakwater, i.e., the interaction among nonlinear waves, composite breakwater and seabed. Numerical results suggest that the stability of a composite breakwater is affected by not only downward shear flow generating on the seaward slope face of the rubble mound but, also, a high and dense pore water pressure gradient inside the rubble mound and seabed foundation.     

Analytical and statistical approach for evaluating the effects of a river barrage on river–aquifer interactions

The construction of a river barrage can increase groundwater levels upstream of the barrage during the rainy season. Analytical and statistical approaches were applied to evaluate the relationship between groundwater and river water at the Changnyeong–Haman river barrage in Korea using time series data of water level and electrical conductivity from June 2011 to September 2014. An artificial neural network based time series model was designed to filter out the effect of rainfall from the groundwater level data in the study area. Aquifer diffusivity and river resistance were estimated from the analytical solution of a one‐dimensional unit step response function by using the filtered groundwater level data. River resistance increased in response to groundwater level fluctuations. Cross‐correlation analyses between the groundwater and the river water showed that the lag time increased during the observation period for both the water level and the electrical conductivity while the cross‐correlation function declined for the same period. The results indicated that a constant river stage maintained at the river barrage can weaken the hydrologic stress and reduce the exchange of material between the river and the adjacent aquifer because of the deposition of fine sediment on the river bottom and walls. Copyright © 2016 John Wiley & Sons, Ltd.     

A note on linear dispersion and shoaling properties in extended Boussinesq equations

A set of optimum parameter α is obtained to evaluate the linear dispersion and shoaling properties in the extended Boussinesq equations of [Madsen and Sorensen, 1992 and Nwogu, 1993], and [Chen and Liu, 1995]. Optimum α values are determined to produce minimal errors in each wave property of phase velocity, group velocity, or shoaling coefficient relative to the analytical one given by the Stokes wave theory. Comparisons are made of the percent errors in phase velocity, group velocity, and shoaling coefficient produced by the Boussinesq equations with a different set of optimum α values. The case with a fixed value of α = −0.4 is also presented in the comparison. The comparisons reveal that the optimum α value tuned for a particular wave property gives in general poor results for other properties. Considering all the properties simultaneously, the fixed value of α = −0.4 may give overall accuracies in phase velocity and shoaling coefficient for all the types of Boussinesq equations selected in this study.     

Assessment of acoustic iterative inverse method for bubble sizing to experimental data

Comparative study was carried out for an acoustic iterative inverse method to estimate bubble size distributions in water. Conventional bubble sizing methods consider only sound attenuation for sizing. Choi and Yoon [IEEE, 26(1), 125–130 (2001)] reported an acoustic iterative inverse method, which extracts the sound speed component from the measured sound attenuation. It can more accurately estimate the bubble size distributions in water than do the conventional methods. The estimation results of acoustic iterative inverse method were compared with other experimental data. The experimental data show good agreement with the estimation from the acoustic iterative inverse method. This iterative technique can be utilized for bubble sizing in the ocean.