Release characteristics of molasses from a well-type barrier system in groundwater: a large test tank study for nitrate removal

A pilot-scale study was conducted to characterize the performance of molasses' release from a well-type barrier system harboring solidifying molasses named slowly released molasses (SRM) as a reactive medium to promote indigenous denitrifying activity. A SRM rod was made by mixing molasses with paraffin wax, cellulose, and silica sands in a cylindrical mold. Two SRM systems harboring 30 and 60 SRM rods, referred to as Systems A and B, respectively, were constructed in a large flow tank (L × W × D = 8 m × 4 m × 2 m) filled with natural sands. These two systems continuously delivered molasses with groundwater flow over 96 days, with decreasing molasses' concentrations ranging from 763 to 95 and 1,150 to 183 mg L^?1 as chemical oxygen demand values (COD) for Systems A and B, respectively. From simulation results with an aid of the upscaled mass transfer function (MTF) model, the molasses' mass flux was slowly decreased with time, exhibiting 57, 11, and 3 mg COD day^?1 in 10, 100, and 365 days in System A, and 138, 25, and 6 mg COD day^?1 in System B, respectively; 90, 70, and 50 % of total molasses' mass remained after 12, 63, and 267 days in System A and 12, 65, and 291 days in System B, respectively. This study demonstrates that SRM system can provide a remedial alternative for long-term in situ treatment of nitrate-contaminated groundwater.     

Seasonal variation of the neustonic zooplankton community in southern waters of Korea

We investigated the seasonal variation of the neustonic zooplankton community in the surface layer (above 30 cm in depth) of 16 stations in southern waters of Korea from April 2002 to April 2003. In the neustonic community, copepods accounted for 59% of total organisms, as the most predominant group, while other dominant groups were invertebrate larvae, cladocerans, tunicates and fish eggs. Pontellid copepods, a major group of neustonic zooplankton, showed a marked seasonal variation and displayed a significant positive correlation with temperature (P < 0.05). Fish eggs appeared from spring to early summer in the inshore waters while tunicates and oceanic copepods (Eucalanus spp. and Euchaeta spp.) were dominant in the offshore waters during high temperature periods. This suggests that the distribution pattern of the neustonic zooplankton is seasonally affected by the hydrological conditions of in- and offshore waters. The abundance of zooplankton was higher in the surface layer (< 15 cm) than in the subsurface layer (15–30 cm), and was also higher at night than during the daytime. Of the dominant copepod families, the density of acartiid and pontellid copepods was higher in the surface layer than the subsurface layer. The density of acartiid and corycaeid copepods was significantly higher during daytime than nighttime. This indicates that the surface layer in temperate regions may provide a favorable habitat for neustonic copepods despite the dynamic environmental fluctuations.     

The effect of grain size on the viscosity and yield stress of fine-grained sediments

In debris flow modelling,the viscosity and yield stress of fine-grained sediments should be determined in order to better characterize sediment flow.In particular,it is important to understand the effect of grain size on the rheology of fine-grained sediments associated with yielding.When looking at the relationship between shear stress and shear rate before yielding,a high-viscosity zone（called pseudoNewtonian viscosity） towards the apparent yield stress exists.After yielding,plastic viscosity（called Bingham viscosity） governs the flow.To examine the effect of grain size on the rheological characteristics of fine-grained sediments,clay-rich materials（from the Adriatic Sea,Italy; Cambridge Fjord,Canada; and the Mediterranean Sea,Spain）,silt-rich debris flow materials（from La Valette,France） and silt-rich materials（iron tailings from Canada） were compared.Rheological characteristics were examined using a modified Bingham model.The materials examined,including the Canadian inorganic and sensitive clays,exhibit typical shear thinning behavior and strong thixotropy.In the relationships between the liquidity index and rheological values（viscosity and apparent yield stress）,the effect of grain size on viscosity and yield stress is significant at a given liquidity index.The viscosity and yield stress of debris flow materials are higher than those of low-activity clays at the same liquid state.However the viscosity and yield stress of the tailings,which are mainly composed of silt-sized particles,are slightly lower than those of low-activity clays.     

Transposon mutagenesis of Psychrobacter cryohalolentis PAMC 21807 by tri-parental conjugation

Random mutagenesis is commonly used to study gene function. The screening of mutants exhibiting specific pheno- types assists in the identification of phenotype-related genes. In the current study, we isolated Antarctic bacteria, and developed a transposon Tn5 mutagenesis system. A total of 26 strains were isolated from seawater and freshwater near Antarctic King Sejong Research Station, King George Island. Six Psychrobacter strains were identified as psychrophilic, with optimal growth tempera- tures of 10~C or 15~C Psychrobacter cryohalolentis PAMC 21807 with a high growth rate at 4~C was selected for transposon mutagenesis. Tri-parental conjugation with a plasmid containing Tn5 produced 13 putative recombinants containing the selectable marker. Genomic Southern hybridization confirmed Tn5 existed as episomes for seven recombinants, and for a single recombinant, Tn5 was integrated into the genome of Psychrobacter cryohalolentis PAMC 21807. The result indicates that the mutagenesis method, although successful, has a relatively low rate. The psychrophilic bacteria isolated in this study may be a useful resource for studying cold adaptation mechanisms, and the mutagenesis method can be applied to genetic analysis.     

Meta-heuristic maximum likelihood parameter estimation of the mixture normal distribution for hydro-meteorological variables

In the water resources field, there are emerging problems such as temporal changes of data and new additions of water sources. Non-mixture models are not efficient in analyzing these data because these models are developed under the assumption that data do not change and come from one source. Mixture models could successfully analyze these data because mixture models contain more than one modal. The expectation maximization (EM) algorithm has been widely used to estimate parameters of the mixture normal distribution for describing the statistical characteristics of hydro meteorological data. Unfortunately, the EM algorithm has some disadvantages, such as divergence, derivation of information matrices, local maximization, and poor accuracy. To overcome these disadvantages, this study proposes a new parameter estimation approach for the mixture normal distribution. The developed model estimates parameters of the mixture normal distribution by maximizing the log likelihood function using a meta-heuristic algorithm—genetic algorithm (GA). To verify the performance of the developed model, simulation experiments and practical applications are implemented. From the results of experiments and practical applications, the developed model presents some advantages, such as (1) the proposed model more accurately estimates the parameters even with small sample sizes compared to the EM algorithm; (2) not diverging in all application; and (3) showing smaller root mean squared error and larger log likelihood than those of the EM algorithm. We conclude that the proposed model is a good alternative in estimating the parameters of the mixture normal distribution for kutotic and bimodal hydrometeorological data.     

Improved fog detection from satellite in the presence of clouds

This study analyzes radiative effect of the higher clouds over the fog layer and presents the improvement of fog detection over the Korean peninsula, utilizing satellite data of the Multi-functional Transport SATellite (MTSAT)-1R and the MODerate resolution Imaging Spectroradiometer (MODIS) and the Look-Up Table (LUT) based on Radiative Transfer Model (RTM) simulations. Fog detection utilizing the satellite data from visible (0.68 µm) and infrared (3.75 µm and 10.8 µm) channels has been evaluated in comparison with ground-based observations over 52 meteorological stations in the Korean Peninsula from March 2006 to February 2007. The threshold values for fog sensing have been derived from the difference (i.e., T_3.7–11) in brightness temperature between 3.75 µm (T_3.7) and 10.8 µm (T₁₁) during day and night, and also from the reflectivity at 0.68 µm (R_0.68) in the daytime. In the twilight, however, the difference between the temperature values at 10.8 µm and their maximum within previous 15 days (i.e., T_11max-11) are used instead, because the 3.75 µm channel is inaccurate for the fog detection at dawn/dusk. The sensitivity of the T_3.7–11 values with respect to the clouds is investigated based on the cloud variables such as its height, optical thickness, and amount. The values of T_3.7–11 are the most sensitive to cloud height, followed by cloud optical thickness and effective radius, while R0.68 is insensitive to cloud height. The sensitivity is examined with various conditions of cloud phases and day/night. Sixteen cases among eighteen fog occurrences, which have been unable to be sensed by using only the conventional threshold values, are successfully detected with the additional LUT corrections, indicating a significant improvement. The method of fog detection in this study can be useful to the Communication, Ocean, and Meteorological Satellite (COMS) Meteorological Data Processing System (CMDPS) by reducing the cloud effect on fog sensing.     

Characterization of chemical properties of atmospheric aerosols over Anmyeon (South Korea), a super site under Global Atmosphere Watch

This paper reports aerosol chemical properties for the first time over a Korean Global Atmosphere Watch (GAW) supersite, Anmyeon (36°32′N; 126° 19′E), during 2003–2004 period. Total suspended Particulates (TSP) showed significant seasonal variation with consistent higher mass concentrations during spring season (average of up to 230?±?190 μg/m³). PM₁₀ also followed similar trend with higher concentrations during spring (average of up to 170?±?130 μg/m³) and showed reduced concentrations during summer. PM_2.5 showed a significant increase during summer (average of up to 60?±?25 μg/m³), which could be due to the influx of fine mode sea salt aerosols associated with the Changma front (summer monsoon). Chemical composition analysis showed enhanced presence of acidic fractions, majorly contributed by sulphates (SO ₄ ^2- ) and nitrates (NO ₃ ^- ) in TSP, PM₁₀ and PM_2.5 during different seasons. Enhanced presence of Calcium (Ca²⁺) was observed during sand storm days during spring. The high correlation obtained on matrix analysis between crustal ions and acidic ions suggests that the ionic compositions over the site are mainly contributed by terrestrial sources of similar origin. The neutralization factors has been estimated to find the extend of neutralization of acidicity by main basic components, and found to have higher value for Ammonium (up to 1.1) in different seasons, indicating significant neutralization of acidic components over the region by NH ₄ ⁺ . Back trajectory analysis has been performed during different seasons to constrain the possible sources of aerosol origin and the results are discussed in detail.     

Spatial distribution and comparative evaluation of phosphorus release rate in benthic sediments of an estuary dam

A series of experiments and simulations were performed to ascertain the rate at which phosphorus is released using a water quality model in Saemangeum Lake, an artificially constructed lake located in an estuary. The general inflow of seawater once a day contributed to the formation of a halocline in the lake water, which caused variation in the vertical concentration of dissolved oxygen. The halocline was mainly observed in the deep downstream regions of Saemangeum Lake that are close to the op...     

Fluidization Process in Submarine Landslides: Physical and Numerical Considerations

Fluidization processes in submarine landslides were studied by physical and numerical means. To examine soil-water interactions in the fluidization process, the computer axial tomography (CAT)-scan imaging techniques and laboratory vanes were utilized with a focus on the transition from failure to post-failure. Based on the results that were obtained from the scanning images and laboratory vane tests after the process of water infiltration into the soil sample, it appears that a gradual decrease in shear strength is unavoidable with increasing water content in a shear zone. From the numerical results, which were based on the dam-break problem using the transport equation coupled with the Navier-Stokes equation, if the slide is assumed to be initially unstable, a possible transition of fluidization processes that are dependent upon a change in density occurs. The density of the mud decreases with time during the flow at the interface between mud and water. The upper part of the mud pushes the lower part of the mud and then induces a rotation of mud that moves substantial distances. These results emphasize the importance of the soil-water interaction, the need for sediment rheology and the influence of the water circulation on the motion of the landslide.