Impacts of land use change and groundwater management on long-term nitrate-nitrogen and chloride trends in groundwater of Jeju Island,Korea

Impacts of land use changes and groundwater management actions on groundwater quality were evaluated at the island scale with spatiotemporal trends of NO₃-N and Cl concentrations in groundwater of Jeju Island, Korea. The temporal trends from 1993 to 2012 in the concentrations of NO₃-N and Cl from more than 3900 wells were estimated using the Mann–Kendall trend test and Sen’s slope analysis and compared with the land use change trend for the period 1995–2009. The results indicate that the upward trends in NO₃-N were associated with the expansion of agricultural lands, whereas Cl trends were considered to be affected by other factors in addition to the land use changes. In the mid-mountainous region, the deterioration in the groundwater quality by the both NO₃-N and Cl was expected due to the continuous expansion of agricultural lands. In the lowland area, the NO₃-N and Cl components showed different trends depending on the regions. In the eastern area, increasing trends in NO₃-N were observed due to the development of new agricultural areas, while the Cl concentration was observed to decrease as a result of the regulation on groundwater extraction to reduce seawater intrusion. Our study highlights that a comprehensive interpretation of trends in NO₃-N and Cl and land use changes for long-term periods can provide useful insights to prepare for suitable groundwater management plans in the whole island perspective.     

Derivative‐Assisted Classification of Fractured Zones Crossing a Deep Borehole

In this study, the derivative analysis using the derivative of drawdown with respect to log‐time was utilized to determine candidates for hydraulic conductor domains (HCDs). At a 500‐m deep borehole in the study site, the fractured rocks crossing the borehole were first classified in fractured and nonfractured zones by core logging and geophysical loggings, such as acoustic televiewing, density, and flow loggings. After conducting the hydraulic tests such as constant head withdrawal and recovery tests at the fractured zones and the nonfractured zones, the derivative analyses were carried out, of which the results were evaluated to determine the candidates for HCDs. For the nonfractured zones, the diagnostic plot has only a big hump indicating poor connection of the background fractures to the permeable geologic media, while those of the candidates for HCDs show various flow regimes. On the basis of these results, the candidates for HCDs among the fractured zones were determined. From discussion on the results, the combination of the spacing analysis and derivative analysis following a hydraulic test is recommended for determining the candidates for HCDs rather than other geophysical loggings.     

Influence of Environmental Variables on the Distribution of Macrobenthos in the Han River Estuary, Korea

We compared environmental effects on the macrobenthic community of the Han River Estuary in summer, when freshwater input from the Han River increased, and in spring, when freshwater input decreased. Field samples were taken from the upper region of the Shingok reservoir to the southern area of Ganghwado at 18 sampling sites after rainy (August 2006) and dry (March 2007) seasons. Macrobenthic fauna were collected using a Van Veen Grab (0.025 m² and 0.1 m²) and environmental factors were measured simultaneously. Dominant species of macrobenthic fauna and the macrobenthic community were divided into two areas, the area of the Han River with no salinity (< 0.1 psu) and the southern part of Ganghwado with salinity (> 20 psu). The dominant species Byblis japonicus appeared at Junruri in the dry season. The distributions of two polychaetes, Hediste japonica and Nephtys caeca, were divided into the lower and upper areas of the Singok submerged weir. BIO-ENV (the matching of biotic to environmental patterns) analysis revealed that salinity was the most important factor affecting macrobenthic communities in the Han River Estuary, with other factors such as sediment grain size, bottom dissolved oxygen, and total organic carbon of sediment being secondary.     

Application of bivariate frequency analysis to the derivation of rainfall–frequency curves

Bivariate distributions have been recently employed in hydrologic frequency analysis to analyze the joint probabilistic characteristics of multivariate storm events. This study aims to derive practical solutions of application for the bivariate distribution to estimate design rainfalls corresponding to the desired return periods. Using the Gumbel mixed model, this study constructed rainfall–frequency curves at sample stations in Korea which provide joint relationships between amount, duration, and frequency of storm events. Based on comparisons and analyses of the rainfall–frequency curves derived from univariate and bivariate storm frequency analyses, this study found that conditional frequency analysis provides more appropriate estimates of design rainfalls as it more accurately represents the natural relationship between storm properties than the conventional univariate storm frequency analysis.     

A new methodology for measuring coastline recession using buffering and non‐linear least squares estimation

Coastline recession is one of the best indicators of coastal erosion. Three methods for computing coastline recession – the baseline approach, the dynamic segmentation approach and the area‐based approach – have been used, each of which has one or more drawbacks. To overcome these problems, a new methodology for measuring coastline recession is proposed, using buffering and non‐linear least squares estimation. The proposed method was compared with the three existing methods with respect to two simulated cases and two real coastlines. Test results confirmed that the new method is more reliable than the three other methods, all of which are susceptible to variability of recession, scale, number of line segments, length of coastlines and direction of the baseline. The proposed method, incorporating two physically meaningful values – magnitude and variability of coastline recession according to the mean and standard deviation of coastline offsets, respectively – presents itself as an effective alternative method of assessing coastline recession.     

Evidence for significant clockwise rotations of the Korean Peninsula during Cretaceous

In an effort to evaluate the Cretaceous magnetostratigraphy for the Korean Peninsula and to establish the tectonic coherence of its various elements, we collected paleomagnetic data from 121 samples from 20 sites within the Chilgok Formation (108.3–109.9 Ma) in the Gyeongsang Basin. Together with previously published data, we evaluate the results from a total of 163 sites in the basin.We combine our age model with results from recent stratigraphic, paleomagnetic and radiometric geochemical studies. In this study, we found that two distinct declination shifts decrease with younging direction, indicating two clockwise rotational events of the Korean Peninsula with respect to the Eurasia continent. The earlier event took place during 130–100 Ma (Phase I, newly termed “Goguryeo Disturbance”) and a later one during 80–50 Ma (Phase III, belonging to “Bulguksa Orogeny”). The mean rotation rate in the interval from 115.2 to 103.8 Ma (Phase I) is about 0.74°/Ma, while the rate from 90.9 to 79.8 Ma (Phase II) is 0.19°/Ma. Based on paleolatitude change during Phase I, we infer that the Korean Peninsula (eastern part of the Sino-Korea Block) migrated southward about 300 km after the complete amalgamation of the Sino-Korea Block into the Eurasian continent resulting in N–S compression within the Korean peninsula and Manchuria. Large-scale strike-slip faults (e.g., Tan-Lu Fault, Okcheon Boundary Fault) were probably rejuvenated in the Sino-Korea Block during Phase I.     

Secondary production of the eusirid amphipod <Emphasis Type="Italic">Pontogeneia rostrata</Emphasis> Gurjanova, 1938 (Crustacea: Peracarida) on a sandy shore in Korea

The secondary production of the eusirid amphipod Pontogeneia rostrata Gurjanova, 1938, was examined on a sandy shore in Korea. Secondary production was estimated using a size-frequency method. The biomass structure of P. rostrata included one peak in spring, with maximum biomass occurring in April. The annual secondary production of this species was 0.57 g DW m⁻² yr⁻¹ with an annual P/B ratio of 6.97. Secondary production of P. rostrata fell within the range observed for other amphipods on intertidal sandy shores, although the production/biomass (P/B) ratio was higher than those recorded previously from the sampling site and from other tidal and estuary areas, as the number of generations increases the P/B ratio. The results showing high abundance and P/B ratios suggest that P. rostrata plays an important role in the sandy shore ecosystem as a trophic link between primary producers and higher consumers.     

Environmentally associated spatial changes of a macrozoobenthic community in the Saemangeum tidal flat,Korea

Estuarine tidal flats are both ecologically and economically important, hence developing methods to reliably measure ecosystem health is essential. Because benthic fauna play a central role in the food web of tidal flats, in this study we set out to quantitatively describe the intertidal zonation of macro-invertebrates and their associations with specific environmental parameters along three transects in the Saemangeum tidal flat, Korea. The abundance and biomass of intertidal fauna with respect to five environmental parameters (i.e., shore level, mud content, coarse sand content, water content, and organic content) were measured, to identify environmental factors that influence macrofaunal distribution in intertidal soft bottom habitats. A total of 75 species were identified, with dominant species showing distinct zones of distribution along all transects. The number of species recorded in each transect was found to be dependent on sediment characteristics and salinity. Cluster analysis classified the entire study area into three faunal assemblages (i.e., location groups), which were delineated by characteristic species, including (A) ‘Periserrula–Macrophthalmus’, (B) ‘Umbonium–Meretrix’, and (C) ‘Prionospio–Potamocorbula’. Four environmental variables (i.e., shore level, water content, mud content, and organic content) appeared to determine factors that distinguished the three faunal assemblages, based on the discriminant analysis. The faunal assemblage types of the sampled locations were accurately predicted from environmental variables in two discriminant functions, with a prediction accuracy of 98%. It should be noted that the zonation of benthos in the lower section (C) of Sandong had been affected by the construction of a nearby dike, while this parameter had remained essentially unchanged at the other two location groups (A–B). Overall, the zonation of benthos from the Saemangeum tidal flat was explained adequately by the measured environmental variables, implying that faunal assemblages are closely associated with certain combinations of abiotic factors. The identification of such reliable associations may facilitate the development of statistical models to predict faunal distributions based on environmental variables at both local and regional scales. The entire study area was embanked in 2006 (one year after this study), and an integrated plan was set into force to develop claimed land into industrial, residential and agricultural districts, which also included a partial restoration program of the tidal flats located near to the study area.     

Comparison of the Ordovician-Carboniferous Boundary Between Korea and NE China: Implications for Correlation and Tectonic Evolution

There is a great hiatus between Ordovician and Carboniferous strata in the Northeast China and Korean Peninsula. In order to understand geology and tectonic evolution, and to find out the similarities and differences in both regions, two sections in the Western Hill near Beijing in NE China and several sections in the Korean Peninsula were selected to examine their geologic boundaries between Lower and Upper Paleozoic strata to compare their characteristic features. At four sites in the two sections in the Western Hill near Beijing were examined their contact relations. The Hui Yu section is the same horizon where one site is top of a quarry hill and the other of down hill. Mid-Carboniferous Qingshuijian Formation rests on the Ordovician Majiagou Formation. Limestone beds are more commonly intercalated with shale and sandstone at site 2 of the Hui Yu section, while at site 1, conglomerate beds are dominant. Site 1 of the Se Shu Fen section shows eroded and concealed karst topography and conglomerate beds are intercalated within shale beds. Silurian and Devonian strata are absent in these areas. In the Korean Peninsula, most O-C contacts occur between Ordovician limestone formation and Carboniferous strata, although Silurian strata occur beneath the Carboniferous strata in the Jeongseon area and Pyeongnam Basin. Most contact relations are parallel unconformity and angular unconformity is rarely seen. The O-C relations in both regions are similar to each other, and these indicate that the Korean Peninsula was located near or belonged to the Sino-Korean paraplatform during Paleozoic time.     

Statistical prediction of heavy rain in South Korea

1. Introduction In recent decades, extreme weather events seem to be growing in frequency and risk due to water-related disasters. According to the World Meteorological Or- ganization report (ISDR and WMO, 2004) on World Water Day, 22 March 2004, the economic losses caused by water-related disasters, including floods, droughts and tropical cyclones, are on an increasing trend as follows: the yearly mean in the 1970s was about 131 billion US dollars, 204 billion dollars in the 1980s, and …