Dowon Lee

Predicting spatial and temporal patterns of soil temperature based on topography, surface cover and air temperature

Soil temperature is a variable that links surface structure to soil processes and yet its spatial prediction across landscapes with variable surface structure is poorly understood. In this study, a hybrid soil temperature model was developed to predict daily spatial patterns of soil temperature in a forested landscape by incorporating the effects of topography, canopy and ground litter. The model is based on both heat transfer physics and empirical relationship between air and soil temperature, and uses input variables that are extracted from a digital elevation model (DEM), satellite imagery, and standard weather records. Model-predicted soil temperatures fitted well with data measured at 10 cm soil depth at three sites: two hardwood forests and a bare soil area. A sensitivity analysis showed that the model was highly sensitive to leaf area index (LAI) and air temperature. When the spatial pattern of soil temperature in a forested watershed was simulated by the model, different responses of bare and canopy-closed ground to air temperature were identified. Spatial distribution of daily air temperature was geostatistically interpolated from the data of weather stations adjacent to the simulated area. Spatial distribution of LAI was obtained from Landsat Thematic Mapper images. The hybrid model describes spatial variability of soil temperature across landscapes and different sensitivity to rising air temperature depending on site-specific surface structures, such as LAI and ground litter stores. In addition, the model may be beneficially incorporated into other ecosystem models requiring soil temperature as one of the input variables.

Geographical distribution and accumulation features of organochlorine residues in bivalves from coastal areas of South Korea.

As a part of Mussel Watch Program in Korea, the contamination levels and accumulation features of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) were assessed for 82 bivalve samples collected from 66 sites along the entire coast of Korea. The dry weight based sigmaPCBs and sigmaOCPs ranged from 4.4 ng g(-1) to 422.0 ng g(-1) (geometric mean = 36.9 ng g(-1)) and from 9.95 ng g(-1) to 131.37 (34.88) ng g(-1), respectively. PCB was predominant in Korean coast, followed by DDTs, HCHs, and Chlordanes. From the observed log normal distribution of PCB and each OCP, low- and high-levels were defined as geometric mean +/- 1 S.D., respectively. The levels at the sites near urban and/or industrial areas often exceeded the high-levels and the spatial distributions of sigmaDDTs and sigmaCHLs were correlated with that of sigmaPCBs, indicating terrestrial input pathways. Even distribution of sigmaHCHs suggested a possibility of atmospheric input pathway of HCHs. The observed isomer ratios of DDTs, HCHs, and CHLs indicated that aging has occurred.

Enzyme activities in constructed wetlands: Implication for water quality amelioration

Wetlands have been widely applied for water quality amelioration. Enzymatic analysis was applied in a study of decomposition in constructed wetlands. We hypothesise that soil enzyme activities would be lower in wetland sediment than adjacent upland and that the lower soil enzyme activities are partly responsible for the water quality amelioration. Four soil enzyme activities (β-glucosidase, β-N-acetylglucosaminidase, phosphatase, and arylsulfatase) and microbial activity (electron transport system activity) were measured across a transect from a upland soil to a wetland sediment in two constructed wetland sites in the USA. Along with the activities, hydrochemistry was determined in inflow and outflow of the wetlands. In both wetlands, the enzyme activities in the sediments were significantly lower than the adjacent upland soils. For hydrochemistry, significant decreases were observed in phosphate and nitrate concentrations in outflow water compared to inflow water. However, there were no significant changes in other anions (F-, Cl-, SO42- . For dissolved organic carbon, it seems that the wetlands would be a source rather than a sink. The results suggest that the enzymatic approach represents a valuable method to assess decomposition processes in wetland sediments, and that characteristically low enzyme activities in the sediments may be important in the water quality amelioration function.

Ecotope mapping for landscape ecological assessment of habitat and ecosystem

An ecotope (spatial eco-space) map that considers topography and bio-organism-relevant variables emerges as an important basic framework when landscape-scale characteristics for ecosystem management and wildlife conservation are needed. A spatio-geoecological framework based on geographic information systems (GIS) and a vegetation survey were developed for wildlife habitat evaluation of national parks and applied to a representative rugged valley area of Mt. Sorak National Park in Korea. An ecotope map was classified into hundreds of types and dozens of groups by combining biological and geophysical variables. Variables included: forest vegetation type, topographic solar radiation, normalized difference vegetation index (NDVI), elevation, and anthropogenic factors, such as, streams and roads. Layers of GIS variables were produced by field surveys, modeling, satellite images, or digitalization. Vegetation surveys were carried out to identify finer-scale distribution of vegetation types in the rugged valley area. Digital forest vegetation maps from the Forestry Administrator were then modified using the field-surveyed vegetation maps. Topographic solar radiation was predicted with a daily topographic radiation model. The NDVI was calculated from the satellite imagery of a Landsat Thematic Mapper. A digital elevation model (DEM) was used and the other layers were digitized using topographical maps with a scale of 1:25 000. The aim of this study is to determine the geoecological factors relating to the spatial pattern of plant community. It was cleared by the spatial pattern of environmental variables and vegetation characteristics by detrended correspondence analysis using plant species and the environmental variables of each plot. The ordination component value of the first axis shows significant regression to some environmental variables. A case study of habitat evaluation was carried out using the resultant ecotope map. The spatial distribution of potential goral habitat and vegetation characteristics were predicted and the impact of human trails on the neighboring vegetation was also examined for restoration planning. The GIS-based framework developed for wildlife habitat evaluation is useful for natural resource management and human activity control in national parks in Korea.

Nitrogen removal from a riverine wetland: a field survey and simulation study of Phragmites japonica

Because Phragmites japonica is one of the dominant plant species in riverine wetlands in South Korea, we constructed an individual-based plant growth model to determine management strategies for maximizing nitrogen removal by P. japonica for water quality improvement purposes. We calibrated our model using field data on the growth, reproduction, and mortality of P. japonica individuals collected over one growing season in 1997 (May–October). The model effectively predicted seasonal changes in the number of the individuals (r 2 = 0.89), aboveground biomass (r 2 =0.85), and nitrogen concentration (r 2 =0.91). Total nitrogen, however, was poorly explained by our model (r 2 =0.53). To evaluate the effects of biomass removal (e.g. harvest or grazing) on Phragmites management strategies, removal was simulated by manipulating the intensity and period of biomass loss. Distinct patterns in population density and biomass were produced in intensity-period phase planes, suggesting that population dynamics are influenced by a strong relationship between disturbance intensity and period. In addition, the highest rates of nitrogen removal by P. japonica occurred for high-density populations that maintained relatively low biomass levels.

Transformation of resource management institutions under globalization: the case of songgye community forests in South Korea.

The context in which many self-governed commons systems operate will likely be significantly altered as globalization processes play out over the next few decades. Such dramatic changes will induce some systems to fail and subsequently to be transformed, rather than merely adapt. Despite this possibility, research on globalization-induced transformations of social-ecological systems (SESs) is still underdeveloped. We seek to help fill this gap by exploring some patterns of transformation in SESs and the question of what factors help explain the persistence of cooperation in the use of common-pool resources through transformative change. Through the analysis of 89 forest commons in South Korea that experienced such transformations, we found that there are two broad types of transformation, cooperative and noncooperative. We also found that two system-level properties, transaction costs associated group size and network diversity, may affect the direction of transformation. SESs with smaller group sizes and higher network diversity may better organize cooperative transformations when the existing system becomes untenable.

Ecological Assessment of Plant Succession and Water Quality in Abandoned Rice Fields

The increasing area of abandoned rice fields could provide new opportunities for wetland restoration in Asia. However, it is unknown how quickly or completely abandoned rice fields will recover from agricultural disturbances. We assessed water quality and plant community succession in abandoned rice fields with different hydrology in a mountain valley to understand the effects of hydrological regime on recovery. Water level, soil redox potential, water quality, plant composition, and primary production were measured. The sites, coded as D6, N13, and N16, had been recovering for 6, 13, and 16 years by 2006. N13 and N16 have been recovering naturally whereas D6 has been drained with a nearby dike and was tilled in 2001. The typical hydroperiods of D6, N13, and N16 were no surface water, permanently flooded, and seasonally flooded, respectively. The major change in vegetation structure of both D6 and N13 was the replacement of herbaceous species by woody species. Drawdown accelerated this change because Salix koreensis grew better in damp conditions than in flooded conditions. Phragmites japonica reduced plot-level plant species richness. The removal efficiency of , , and from water varied seasonally, ranging between -78.8 to 44.3%, 0 to 97.5%, and -26.0 to 44.4%, respectively. In summary, abandoned rice fields quickly became suitable habitat for native wetland plant species and improved regional water quality. Variation among our sites indicates that it is likely possible to manage abandoned rice fields, mostly through controlling hydrology, to achieve site-specific restoration goals.

Inhibition of Extracellular Enzyme Activities in a Forest Soil by Additions of Inorganic Nitrogen

Abstract Forest ecosystems are known to be nitrogen (N) limited, and productivity often increases with N additions. However, recent studies have suggested that additions of excessive N through atmospheric deposition may affect soil processes adversely. In this study, we conducted a laboratory‐based manipulation experiment to reveal the effects of N additions on extracellular enzyme activities in a temperate forest soil. Three different levels of N additions (water‐only control, low N addition, and high N addition) were applied to soil columns (2.5‐cm diameter×12 cm height) over 4 weeks. Overall, the additions of N decreased specific activities (enzyme activity per log bacterial cell number) of urease, glutaminase, phosphatase, and arylsulfatase significantly. However, dehydrogenase activity was increased with the high N addition. The results suggest that N deposition may impede nutrient cycling, particularly mineralization of organic nutrients. In addition, this enzyme inhibition may be one of the mechanisms for N retention observed in forest floors.

Significance of aspect and understory type to leaf litter redistribution in a temperate hardwood forest

Annual production and redistribution of leaf litter were compared among three distinct understory patches in a temperate hardwood forest dominated by Quercus mongolica, Kalopanax pictus, Acer pseudo‐sieboldianum, and Carpinus cordata. Two patches were located on a southwest‐facing slope: one with an understory dominated by herbaceous plants (Patch S), and the other covered with evergreen dwarf bamboo, Sasa borealis (Patch SS). The third patch was on the opposite slope with an understory dominated by herbaceous plants (Patch N). Annual leaf litterfall was averaged 330 gm‐2 yr‐1 in the three patches from 1994 to 1998. From mid‐September 1996 to mid‐September 1997, net transport of leaf litter over patch boundaries was 1,824 g m‐1 from Patch S to SS, 1,465 g m‐1 from Patch S to N, and 886 g m‐1 from Patch SS to N. The amounts moving downslope out of Patch S, SS, and N were 2,548, 471, and 588gm‐1, respectively. When a mass balance approach was employed for the data of leaf litter transport, the results were ...

Parametric image of myocardial blood flow generated from dynamic H215O PET using factor analysis and cluster analysis

Algorithm-based parametric imaging of myocardial blood flow (MBF), as measured by H215O PET, has been the goal of many research efforts. A method for generating parametric images of regional MBF by factor and cluster analysis on H215O dynamic myocardial PET was validated by its comparison with gold-standard MBF values determined invasively using radiolabelled microspheres. Right and left ventricular blood pool activities and their factor images were obtained by the application of factor analysis to dynamic frames. By subtraction of the factor images multiplied by their corresponding values on the factors from the original dynamic images for each frame, pure tissue dynamic images were obtained, from which arterial blood activities were excluded. Cluster analysis that averaged pixels having time-activity curves with the same shape was applied to pure tissue images to generate parametric MBF images. The usefulness of this method for quantifying regional MBF was evaluated using canine experiment data. H215O PET scans and microsphere studies were performed on seven dogs at rest and after pharmacological stress. The image qualities and the contrast of parametric images obtained using the proposed method were significantly improved over either the tissue factor images or the parametric images obtained using a conventional method. Regional MBFs obtained using the proposed method correlated well with those obtained by the region of interest method (r=0.94) and by the microsphere technique (r=0.90). A non-invasive method is presented for generating parametric images of MBF from H215O PET, using factor and cluster analysis.