Internal generation of waves: Delta source function method and source term addition method

In this study, we investigate two internal wave generation methods in numerical modeling of time-dependent equations for water wave propagation, i.e., delta source function method and source term addition method, the latter of which has been called the line source method in literatures. We derive delta source functions for the Boussinesq-type equations and extended mild-slope equations. By applying the fractional step splitting method, we show that the delta source function method is equivalent to the source term addition method employing the energy velocity. This suggests that the energy velocity should be used rather than the phase velocity for the transport of incident wave energy in the source term addition method. Finally, the performance of the delta source function method is verified by accurately generating nonlinear cnoidal waves as well as linear waves for horizontally one-dimensional cases.     

Vertical distribution of giant jellyfish, <Emphasis Type="Italic">Nemopilema nomurai</Emphasis> using acoustics and optics

Nemopilema nomurai jellyfish, which are believed to complete their development in the East China Sea, have started migrating into the Yellow Sea in recent years. We obtained biomass estimates of this species in the Yellow Sea using bottom trawl fishing gear and sighting surveys over a 5-year period. These methods are effective for obtaining N. nomurai jellyfish density estimates and information about the community distribution near the bottom or surface of the sea. To verify the vertical distributions of giant jellyfish between, we used hydroacoustic equipment, including an optical stereo camera system attached to a towed sledge and an echo counting method with scientific echosounder system. Acoustic and optical data were collected while the vessel moved at 3 knots, from which the distribution and density of N. nomurai jellyfish were analyzed. Subsequently, the camera system was towed from a 7 m mean depth to sea level, with the detection range of the acoustic system extending from an 8 m depth to the bottom surface. The optical and acoustic methods indicated the presence of vertical distribution of 0.11³ (inds/m³) and 0.064 (inds/m3), respectively. However, the vertical distribution indicated that around 93% of individuals occurred at a depth range of 10–40 m; thus, a 2.4-fold greater density was estimated by acoustic echo counting compared to the optical method.     

Effect of agricultural land use on the chemistry of groundwater from basaltic aquifers, Jeju Island, South Korea

Geochemical processes were identified as controlling factors of groundwater chemistry, including chemical weathering, salinization from seawater and dry sea-salt deposition, nitrate contamination, and rainfall recharge. These geochemical processes were identified using principal component analysis of major element chemistry of groundwater from basaltic aquifers in Jeju Island, South Korea, a volcanic island with intense agricultural activities. The contribution of the geochemical processes to groundwater chemistry was quantified by a simple mass-balance approach. The geochemical effects due to seawater were considered based on Cl contributions, whereas the effects due to natural chemical weathering were based on alkalinity. Nitrogenous fertilizers, and especially the associated nitrification processes, appear to significantly affect groundwater chemistry. A strong correlation was observed between Na, Mg, Ca, SO₄ and Cl, and nitrate concentrations in groundwater. Correspondingly, the total major cations, Cl, and SO₄ in groundwater were assessed to estimate relative effect of N-fertilizer use on groundwater chemistry. Cl originates more from nitrate sources than from seawater, whereas SO₄ originates mostly from rainwater. N-fertilizer use has shown the greatest effect on groundwater chemistry, particularly when nitrate concentrations exceed 6–7 mg/L NO₃–N. Nitrate contamination significantly affects groundwater quality and 18% of groundwater samples have contamination-dominated chemistry.     

Molecular expression of opsin gene in growing juvenile mackerel (<Emphasis Type="Italic">Scomber japonicus</Emphasis> Houttuyn)

Fish have developed color vision that is closely adapted to their photic environments, where both spectral sensitivity and the number of visual opsins are influenced. The mackerel used in this study is one of the most important fishery stocks in Korea. The opsin gene of the mackerel juveniles after 20 days in hatching was isolated and characterized based on the molecular study of visual photoreceptor. The full-length mackerel opsin gene was obtained by PCR amplification of genomic DNA, as well as cDNA synthesis. Sequence analysis of the opsin gene showed that it contained a 1,080 bp open reading frame encoding 360 amino acids. Based on Schiff’s base formation (S114, K119), glycosylation (E3, F37) and palmitoylation (S281, 282), the deduced amino acid sequence had a typical rod opsin. The mackerel and Gempylus serpens showed 73.7% DNA homology on opsin gene, which was higher than any other of investigated species. In the analysis of phylogenetic relationship, the genetic placement of the mackerel is closer to that of Scombroidei than Labroidei, with supporting somewhat strong bootstrap value. In the analysis of Northern and RT-PCR, the probed products were observed only in rapidly growing juveniles. These findings indicate that in mackerel opsin mRNA expression can be detected in day-20 hatching larvae. It may play an important role in stimulating growth hormone.     

Three-dimensional topography corrections of magnetotelluric data

Topographic effects due to irregular surface terrain may prevent accurate interpretation of magnetotelluric (MT) data. Three-dimensional (3-D) topographic effects have been investigated for a trapezoidal hill model using an edge finite-element method. The 3-D topography generates significant MT anomalies, and has both galvanic and inductive effects in any polarization. This paper presents two different correction algorithms, which are applied to the impedance tensor and to both electric and magnetic fields, respectively, to reduce topographic effects on MT data. The correction procedures using a homogeneous background resistivity derived from a simple averaging method effectively decrease distortions caused by surface topography, and improve the quality of subsurface interpretation. Nonlinear least-squares inversion of topography-corrected data successfully recovers most of structures including a conductive or resistive dyke.     

Household and community responses to impacts of climate change in the rural hills of Nepal

The research was designed to answer how households and local communities in rural Nepal are responding to the impacts of climate change. Using four villages as case study units, a mixed method approach was adopted in a multi-scaled process carried out at community, district and national levels. The research found that adaptation practices being adopted differ according to household well-being and are largely governed by access to education, information and resources within the community. Responses such as livelihood and income diversification, internal migration, share cropping, taking consumption loans, use of alternative energy and use of bio-pesticides were found to mostly vary according to well-being status of the interviewees. Development of adaptation plans, strategies and support mechanisms should take account of the different adaptation practices and needs of households. If such individual situations are not considered, adaptation responses may be ineffective or even be maladaptive and increase vulnerability. The research also found that the autonomous, unplanned and reactive nature of adaptation practices chosen by rural communities can contribute to further inequity and unequal power relations. The knowledge generated from this research contributes to understanding of how climate change contributes to vulnerability, but also how local practices and lack of an effective climate policy or response measures may magnify the effects of many existing drivers of vulnerability in terms of maladaptation and increasing social inequalities.     

A seismic hazard assessment and the results of detailed seismic zoning for urban territories of Sakhalin Island

This work briefly discusses the main features of probabilistic seismic hazard analysis (PSHA). Special attention is paid to the identification and quantification of uncertainties related to seismic source characteristics and seismic engineering models for prediction of strong ground motions. The principal seismic models and the results of PSHA application for detailed seismic zoning of urban territories in Sakhalin Island are presented.     

Assessment of ecological flow rate by flow duration and environmental management class in the Geum River, Korea

This study attempted to analyze flow duration in a basin using a method to estimate environmental flow developed by the International Water Management Institute, and simulate the effects of runoff characteristics unique to a river and flow variability due to basin developments on aquatic ecosystems. To do so, KModSim, a simulation model for basin-wide water distribution, was used to assess flow duration in the Geum River basin, one of the four major river basins in Korea, by environmental management class (EMC). Flow duration curves by EMC at Sutong and Gongju sites were derived on the basis of natural flow in the Geum River basin. As a result, they were found to be consistent with the results of previous studies. Time series of mean monthly flow data by EMC were plotted together with those of simulated flow data by reservoir operation scenario; Sutong and Gongju points both showed flow behaviors corresponding almost to “A” in EMC. In addition, the characteristics of habitats by species of fish were identified through monitoring fish habitat at the Sutong site, so that optimal ecological flow rate was estimated. For this purpose, relations between flow discharge and weighted usable area for Coreoleuciscus splendidus and Pseudopungtungia nigra were projected using physical habitat simulation system, and EMCs consistent with flow duration curves (estimated taking in-stream flow) were assessed. The results or findings reported in this study are expected to serve as basic data for making a plan to efficiently monitor and manage aquatic ecosystems in the Geum River basin.     

Recent increase in surface fCO<Subscript>2</Subscript> in the western subtropical North Pacific

We observed unusually high levels (> 440 μatm) of carbon dioxide fugacity (fCO₂) in surface seawater in the western subtropical North Pacific, the area where Subtropical Mode Water is formed, during summer 2015. The NOAA Kuroshio Extension Observatory moored buoy located in this region also measured high CO₂ values, up to 500 μatm during this period. These high sea surface fCO₂ (fCO_2SW) values are explained by much higher normalized total dissolved inorganic carbon and slightly higher normalized total alkalinity concentrations in this region compared to the equatorial Pacific. Moreover, these values are much higher than the climatological CO₂ values, even considering increasing atmospheric CO₂, indicating a recent large increase in sea surface CO₂ concentrations. A large seasonal change in sea surface temperature contributed to higher surface fCO_2SW in the summer of 2015.