Marine-Derived Fungi in Korea

Ocean Science Journal - Studies on marine fungi (termed as ‘marine-derived fungi’ in this paper) have been significantly increasing worldwide because of the critical role displayed by...     

Assessing distributed groundwater recharge rate using integrated surface water-groundwater modelling: application to Mihocheon watershed, South Korea

A method of estimating groundwater recharge, based on water-balance components using the SWAT-MODFLOW model (an integrated surface water-groundwater model), is described. A multi-reservoir storage routing module is suggested instead of a single storage routing module in SWAT; this represents a more realistic delay in the travel of water through the vadose zone. By using this module, the parameter related to the delay time can be optimized by checking the correlation between simulated recharge and observed groundwater levels. The final step of this procedure is to compare simulated groundwater levels as well as the simulated watershed stream flow with the observed groundwater levels and watershed stream flow. This method is applied to the Mihocheon watershed in South Korea to estimate spatio-temporal groundwater recharge distribution. The computed annual recharge rate is compared with the independently estimated recharge rate using BFLOW. The hydrologic modelling results show that the annual average recharge rate should be estimated by a long-term continuous simulation with a distributed hydrologic modelling technique.     

Molecular identification of anisakid nematodes third stage larvae isolated from common squid (Todarodes pacificus) in Korea

The occurrence of Genus Anisakis nematode larvae in marine fishes and cephalopods is epidemiologically important because Anisakis simplex larval stage can cause a clinical disease in humans when infected hosts are consumed raw. Common squid (Todarodes pacificus) from Korean waters were investigated for anisakid nematodes infection during 2009～2011. In total, 1,556 larvae were collected from 615 common squids and 732 of them were subsequently identified by PCR-RFLP analysis of ITS rDNA. Depending on the sampling locations, the nematode larvae from common squid showed different prevalence, intensity and species distribution. A high prevalence (P) and mean intensity (MI) of infection were observed in the Yellow Sea (n = 250, P = 86.0%, MI = 5.99 larvae/host) and the southern sea of Korea (n = 126, P = 57.1%, MI = 3.36 larvae/host). Anisakis pegreffii was dominantly found in common squid from the southern sea (127/ 140, 90.7%) and the Yellow Sea (561/565, 98.9%). In contrast, the P and MI of infection were relatively low in the East Sea (n = 239, P = 8.37%, MI = 1.25 larvae/host). A. pegreffii was not found from the East Sea and 52.0% (13/25) of the nematodes were identified as A. simplex. Most of them were found in the body cavity or digestive tract of common squid, which are rarely consumed raw by humans. Considering the differenences in anisakid nematode species distribution and their microhabitat in common squid, it remains unclear whether common squid plays an important role in the epidemiology of human anisakis infection in Korea. Further extensive identification of anisakid nematodes in common squid, with geographical and seasonal information will be necessary.     

Using urban effect corrected temperature data and a tree phenology model to project geographical shift of cherry flowering date in South Korea

Temperate zone deciduous tree phenology may be vulnerable to projected temperature change, and associated geographical impact is of concern to ecologists. Although many phenology models have been introduced to evaluate climate change impact, there has been little attempt to show the spatial variation across a geographical region due to contamination by the urban heat island (UHI) effect as well as the insufficient spatial resolution of temperature data. We present a practical method for assessing climate change impact on tree phenology at spatial scales sufficient to accommodate the UHI effect. A thermal time-based two-step phenological model was adapted to simulate and project flowering dates of Japanese cherry (Prunus serrulata var. spontanea) in South Korea under the changing climates. The model consists of two sequential periods: the rest period described by chilling requirements and the forcing period described by heating requirements. Daily maximum and minimum temperature are used to calculate daily chill units until a pre-determined chilling requirement for rest release is met. After the projected rest release date, daily heat units (growing degree days) are accumulated until a pre-determined heating requirement for flowering is achieved. Model parameters were derived from the observed bud-burst and flowering dates of cherry tree at the Seoul station of the Korea Meteorological Administration (KMA), along with daily temperature data for 1923–1948. The model was validated using the observed data at 18 locations across South Korea during 1955–2004 with a root mean square error of 5.1 days. This model was used to project flowering dates of Japanese cherry in South Korea from 1941 to 2100. Gridded data sets of daily maximum and minimum temperature with a 270 m grid spacing were prepared for the climatological normal years 1941–1970 and 1971–2000 based on observations at 56 KMA stations and a geospatial interpolation scheme for correcting urban heat island effect as well as elevation effect. We obtained a 25 km-resolution, 2011–2100 temperature projection data set covering peninsular Korea under the auspices of the Inter-governmental Panel on Climate Change—Special Report on Emission Scenarios A2 from the Meteorological Research Institute of KMA. The data set was converted to 270 m gridded data for the climatological years 2011–2040, 2041–2070 and 2071–2100. The phenology model was run by the gridded daily maximum and minimum temperature data sets, each representing climatological normal years for 1941–1970, 1971–2000, 2011–2040, 2041–2070, and 2071–2100. According to the model calculation, the spatially averaged flowering date for the 1971–2000 normal is earlier than that for 1941–1970 by 5.2 days. Compared with the current normal (1971–2000), flowering of Japanese cherry is expected to be earlier by 9, 21, and 29 days in the future normal years 2011–2040, 2041–2070, and 2071–2100, respectively. Southern coastal areas might experience springs with incomplete or even no flowering caused by insufficient chilling required for breaking bud dormancy.     

Hydrogeological studies on the mechanical behavior of landfill gases and leachate of the Nanjido Landfill in Seoul, Korea

 The Nanjido Landfill is the largest uncontrolled landfill in Korea and it causes various kinds of environmental problems. Landfill gases and leachate are recognized as the most serious environmental problems associated with the landfill. This study employs a series of numerical models and uses test data to interpret the distribution and flow of landfill gases and leachate. Leachate seepage appears about 40–60 m higher than the estimated basal groundwater table. Thus, seepage data indicate that perched or floating leachate layers are formed in the unsaturated zone of the landfill. The leachate production rate is estimated using infiltration test data and a model for unsaturated groundwater flow. Geochemical data indicate that the landfill leachate degrades the basal groundwater quality along the downgradient zone. The environmental impact of the leachate on river water is estimated. Received: 17 June 1996 · Accepted: 2 October 1996     

Three-dimensional imaging of subsurface structures using resistivity data

We have developed a three-dimensional inverse scheme for carrying out DC resistivity surveys, incorporating complicated topography as well as arbitrary electrode arrays. The algorithm is based on the finite-element approximation to the forward problem, so that the effect of topographic variation on the resistivity data is effectively evaluated and incorporated in the inversion. Furthermore, we have enhanced the resolving power of the inversion using the active constraint balancing method. Numerical verifications show that a correct earth image can be derived even when complicated topographic variation exists. By inverting the real field data acquired at a site for an underground sewage disposal plant, we obtained a reasonable image of the subsurface structures, which correlates well with the surface geology and drill log data.     

Particle dynamics as controlled by the flow field of the eastern equatorial Pacific

Profiles made during the JGOFS EgPac October 1992 time series cruise to the equator with a Large Aggregate Profiling System (LAPS) recorded the concentration and size distribution of particles in the marine snow size range ( > 0.5 mm diameter). Profiles were made routinely at local midnight during the twenty day occupation of the time series station on the equator. The LAPS data set, when combined with the CTD/transmissometer data set from the EgPac program's intensive profiling operation, reveals a complex dynamic of particle production and aggregation driven by the equatorial flow field.During the cruise, the influence of the passage of a Tropical Instability Wave (TIW) was observed in the transmissometer/aggregate and temperature/salinity data sets. A peak in particle production rate occurred in conjunction with the maximum shoaling of the thermocline and a minimum in the aggregate volume concentration. Subsequently, the particle load in the surface water increased followed by an increase in the aggregate abundance. Quasi -oligotrophic conditions on the equator (subsurface particle and aggregate maxima and decreased particle production rates) toward the end of the time series corresponded to the appearance of stratified low salinity water characteristic of more northerly conditions.The variations in temperature and salinity fields are ascribed to the passage of a TIW; in sequence: the trailing edge, the northwestward-flowing cool cusp water and the convergent front. Current meters at the equator recorded a rotational flow at 80 m, with a shift from southeastward to northeastward flow during this sequence. A simple conceptual model of meridional flow field is presented in which poleward transport of the upwelled water from the equator returns at shallow depths to mix with the EUC. The signature of this return flow is reflected in the decrease in the vertical gradients of nutrients and oxygen at the equator with respect to the poleward gradients, and a subsurface particle maximum below the EUC. The flow field's effect on the distribution of particles is reflected in the meridional pattern of the sediment accumulation rate (Murray and Leinen, 1996). The return flow of particles to the equator is reflected in the maximum in accumulation rate near the equator. The longterm influence of TIW's is reflected in the asymmetry of the accumulation rates across the equator as described by Murray and Leinen (1996), with the maximum accumulation rate found south of the equator, a local minimum in accumulation rate at approximately 2°N, and a local maximum near 4°N.     

Variations of amplitude, wavelength and phase velocity of plane progressing waves over uniformly sloping beaches

The mysterious variation of the amplitude of waves progressing towards the shore over sloping beaches has been clarified explicitly by linear theory. The phase velocity of the waves increases rapidly as the waves travel across the surf zone towards the shore, as does the wavelength. The phase of the waves near shore is nearly stationary if the beach slope is small. Hence the waves are not sinusoidal near shore but surge towards the shore if the slope is small.     

Nutrient Fluxes through the Taiwan Strait in Spring and Summer 1999

Transports of water and nutrients (N and P) through the Taiwan Strait were calculated using chemical hydrography and currents observed in May and August 1999. The surveys were conducted along a transect across the strait in the middle section. The velocity fields were determined by phase-averaging currents measured using shipboard Acoustic Doppler Current Profiler (ADCP) on two repeats, which were separated by 1.5 cycles of the dominant M₂ tide. Nutrient distributions were also derived from phase-averaged data. The volume transports determined from the two surveys were similar (2.0 Sv and 2.2 Sv, respectively). By contrast, the nutrient fluxes obtained in August (1.82 kmol N/s and 0.34 kmol P/s) were significantly higher than those in May (0.96 kmol N/s and 0.16 kmol P/s), apparently due to coastal upwelling under southwest monsoon in summer. The rather low N/P ratios (6.0 and 5.4 by atoms) of the nutrient fluxes were attributed to the widespread N-deficiency in the upper water column of the North Pacific. The nutrient fluxes were fed mainly through a meridional deep channel off southwest Taiwan. The nutrient contributions from the Taiwan Strait to the East China Sea in spring and summer are comparable to the total riverine contributions from the Changjiang (also know as the Yangtze River) and other smaller rivers for nitrogen, but 8–17 times larger than the latter for phosphate. Therefore, the Taiwan Strait inflow may serve as an important supplement for the P-limiting condition in the huge coastal plume in the East China Sea.     

Probabilistic approach for active control based on structural energy

This paper presents an active control algorithm using the probability density function of structural energy. It is assumed that structural energy under excitation has a Rayleigh probability distribution. This assumption is based on the fact that the Rayleigh distribution satisfies the condition that the structural energy is always positive and the occurrence probability of minimum energy is zero. The magnitude of the control force is determined by the probability that the structural energy exceeds the specified target critical energy, and the sign of the control force is determined by the Lyapunov controller design method. The proposed control algorithm shows much reduction of peak responses under seismic excitation compared with the LQR controller, and it can consider the control force limit in the controller design. Also, the chattering problem which sometimes occurs in the Lyapunov controller can be avoided. Copyright © 2003 John Wiley & Sons, Ltd.