• Journal of Wetlands Research
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• v.7 no.4
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• pp.33-42
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• 2005

Wetlands often function as a nutrient sink. It is well known that increased input of nutrient increases the primary productivity but it is not well understood what is the fate of produced biomass in wetland ecosystem. Water and sediment quality, decomposition rate of cellulose, and sediment accumulation rate in 11 montane marshes in northern Sierra Nevada, California were analyzed to trace the effect of nitrogen and phosphorus content in water on nutrient dynamics. Concentrations of ammonium, nitrate, soluble reactive phosphorus (SRP) in water were in the range of 27 to 607, 8 to 73, and 6 to 109 ppb, respectively. Concentrations of ammonium, calcium, magnesium, sodium, and potassium in water were the highest in Markleeville, which has been impacted by animal farming. Nitrate and SRP concentrations in water were the highest in Snow Creek, which has been impacted by human residence and a golf course. Cellulose decomposition rates ranged from 4 to 75 % per 90 days and the highest values were measured in Snow Creek. Concentrations of total carbon, nitrogen, and phosphorus in sediment ranged from 8.0 to 42.8, 0.5 to 3.0, and 0.076 to 0.162 %, respectively. Accumulation rates of carbon, nitrogen, and phosphorus fluctuated between 32.7 to 97.1, 2.4 to 9.0, and 0.08 to $1.14gm^{-2}yr{-1}$, respectively. Accumulation rates of carbon and nitrogen were highest in Markleeville and that of phosphorus was highest in Lake Van Norden. Correlation analysis showed that decay rate is correlated with ammonium, nitrate, and SRP in water. There was no correlation between element content in sediment and water quality. Nitrogen accumulation rate was correlated with ammonium in water. These results showed that element accumulation rates in montane wetland ecosystems are determined by decomposition rate rather than nutrient input. This study stresses a need for eco-physiological researches on the response of microbial community to increased nutrient input and environmental change because the microbial community is responsible for the decomposition process.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.320-329
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• 2008

The influence of thermodynamic transition associated with transcritical nitrogen injection upon the flow structure was investigated to explore numerical simulation of the injectant dynamics of oxygen/hydrogen coaxial jet in liquid rocket engines. Single and coaxial nitrogen jets were treated by comparing the transcritical and perfect-gaseous conditions, wherein the numerical model was accommodative to the real-fluid thermodynamics and transport properties at supercritical pressures. The model was in the first place validated by comparing the results of transcritical nitrogen injection between calculations and available experiments. For a single jet under the transcritical condition, the nitrogen kept a relatively high density up to its pseudo-critical temperature inside the mixing layer, since it remains less expanding until heated up to its pseudo-critical temperature. Numerical analysis revealed that cryogenic jets exhibit strong dependence of specific enthalpy profile upon the associated density profile that are both dominated by turbulent thermal diffusion. In the numerical model, therefore, exact evaluation of turbulent heat fluxes becomes very important for simulating turbulent cryogenic jets under supercritical pressures. Concerning the coaxial jets due to transcritical/gaseous nitrogen injections, the density profile inside the mixing layer was again affected by the thermodynamic transition of nitrogen. However, hydrodynamic instability modes of the inner jet did not show significant differences by this thermodynamic transition, so that further study is needed for the mixing process downstream of the near injection position.

• Asian-Australasian Journal of Animal Sciences
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• v.23 no.4
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• pp.491-500
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• 2010

Three experiments were conducted to investigate the effects of polyurethane coated urea on in vitro ruminal fermentation, ammonia release dynamics and lactating performance of Holstein dairy cows fed a steam-flaked corn-based diet. In Exp. 1, a dual-flow continuous culture was run to investigate the effect of polyurethane coated urea on nutrient digestibility, rumen fermentation parameters and microbial efficiency. Three treatment diets with isonitrogenous contents (13.0% CP) were prepared: i) feedgrade urea (FGU) diet; ii) polyurethane coated urea (PCU) diet; and iii) isolated soy protein (ISP) diet. Each of the diets consisted of 40% steam-flaked corn meal, 58.5% forages and 1.5% different sources of nitrogen. PCU and FGU diets had significantly lower digestibility of NDF and ADF (p<0.01) than the ISP diet. Nitrogen source had no significant effect (p = 0.62) on CP digestibility. The microbial efficiency (expressed as grams of microbial N/kg organic matter truly digested (OMTD)) in vitro of the PCU diet (13.0 g N/kg OMTD) was significantly higher than the FGU diet (11.3 g N/kg OMTD), but comparable with the ISP diet (14.7 g N/kg OMTD). Exp. 2, an in vitro ruminal fermentation experiment, was conducted to determine the ammonia release dynamics during an 8 h ruminal fermentation. Three treatment diets were based on steam-flaked corn diets commonly fed to lactating cows in China, in which FGU, PCU or soybean meal (SBM) was added to provide 10% of total dietary N. In vitro $NH_3-N$ concentrations were lower (p<0.05) for the PCU diet than the FGU diet, but similar to that for the SBM diet at all time points. In Exp. 3, a lactation trial was performed using 24 lactating Holstein cows to compare the lactating performance and blood urea nitrogen (BUN) concentrations when cows were fed PCU, FGU and SBM diets. Cows consuming the PCU diet had approximately 12.8% more (p = 0.02) dietary dry matter intake than those consuming the FGU diet. Cows fed the PCU diet had higher milk protein content (3.16% vs. 2.94%) and lower milk urea nitrogen (MUN) concentration (13.0 mg/dl vs. 14.4 mg/dl) than those fed the FGU diet. Blood urea nitrogen (BUN) concentration was significantly lower for cows fed the PCU (16.7 mg/dl) and SBM (16.4 mg/dl) diets than the FGU (18.7 mg/dl) diet. Cows fed the PCU diet had less surplus ruminal N than those fed the FGU diet and produced a comparable lactation performance to the SBM diet, suggesting that polyurethane coated urea can partially substitute soybean meal in the dairy cow diet without impairing lactation performance.

• Korean Journal of Agricultural and Forest Meteorology
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• v.20 no.4
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• pp.357-365
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• 2018

This study was carried out to evaluate the weight loss rates, carbon and nitrogen dynamics of wood stakes following soil amendment treatments (CLB: compound fertilizer + lime + biochar; LB: lime + biochar) in a post-fire restoration area, Ulsan Metropolitan city, southern Korea. Soil amendments in the fire-disturbed area were applied to two-times (Mar. and Jun. 2015, 2016) during the study period. Wood stakes on Mar. 2015 were buried at a top 15cm of mineral soil in two soil amendment and control treatments of Liriodendron tulipifera, Prunus yedoensis, Quercus acutissima, Pinus thunbergii plantations and an unplanted area in the post-fire restoration area. Wood stakes were collected at Oct. 2015, Mar. 2016 and Oct. 2016 to measure weight loss rates, organic carbon and nitrogen concentrations. Weight loss rates of wood stakes were not significantly affected by soil amendment treatments. However, remaining carbon of wood stakes were lowest in the control treatment (43.7%), followed by the CLB (71.3%) and the LB (71.6%) treatments. Remaining nitrogen of wood stakes was less in the control treatment (29.7%) compared with the LB treatment (52.6%). The results indicate that carbon and nitrogen mineralization of wood stakes in post-fire restoration area were delayed by soil amendment treatments.

• Journal of The Korean Society of Agricultural Engineers
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• v.52 no.3
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• pp.65-71
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• 2010

This study was conducted to investigate the dynamics of nutrients such as total nitrogen (TN), nitrate nitrogen ($NO_3$-N) total phosphorous (TP), and phosphate phosphorous ($PO_4$-P) in outflow from a cabbage farmland in a mixed land-use watershed. The TN concentrations in groundwater showed twice peaks in late July 2006 and late March 2007 (3.8, 4.7 mg/L, respectively), when it rained shortly after fertilizer application, indicating that nitrogen leaching is greatly influenced by fertilization and rainfall. The mean concentrations of TN and $NO_3$-N in surface water were not significantly higher than those in groundwater, while the mean concentrations of TP and $PO_4$-P in surface water were significantly (p < 0.05) were higher than those in groundwater. The TN concentrations in groundwater were generally higher than those in surface water during fertilization and early growing season due to the effect of fertilization, but vice versa in the other periods. In contrast, the TP concentrations in groundwater were always lower than those in surface water due to the sorption of particulate phosphorous by soil. The ratio of TN load in baseflow to that in total TN load (39 %) was much greater than the TP ratio (7 %), suggesting that baseflow contribute to nitrogen export. Therefore, proper fertilization management should be taken to reduce nitrogen load through baseflow.

• Journal of the korean society of oceanography
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• v.37 no.1
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• pp.35-44
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• 2002

To assess the relative contribution of bacterial and phytoplankton biomasses to particulate organic matter (POM) in the water column, microbial abundance and biomass were from two transects in the western channel of the Korea Strait in 1996. Bacterial abundance had a mean value of $5.9{\times}10^5$ cells/ml and chlorophyll-a averaged 0.14 ${\mu}g/l$. Bacterial abundance in the Korea Strait showed a positive relationship with chlorophyll-a concentration, while the distribution of POM did not covary with chlorophyll-a. Particulate organic carbon (POC) and nitrogen (PON) concentrations were greater in August than in October. Bacterial carbon (POC) and nitrogen (PON) concentrations were greater in August than in October. Bacterial carbon and nitrogen biomasses were 7.29 ${\mu}gC/l$ and 1.24 ${\mu}gN/l$, respectively, during the study periods. Bacterial biomass was larger in October than in August due to the autumn phytoplankton bloom. Phytoplankton biomass based on chlorophyll-a was 7.67 ${\mu}gC/l$ for carbon and 1.10${\mu}gN/l$l for nitrogen. The ratio of bacterial carbon (BC) to phytoplankton carbon (Cp) averaged 0.95 in the Korea Strait in 1996. Bacteria may play a more significant role in the dynamics of POM than phytoplankton do in August, with BC/Cp ratio of 1.26. The ratio of BC to Cp increased with a decrease in chlorophyll-a concentration. Averaged over all the samples in both cruises, the contribution of microbial biomass to POC and PON was about 43% and 51%, respectively. Bacterial assemblage constituted a significant fraction of POC (21%) and PON (27%). Phytoplankton accounted for 22% of POC and 24% of PON. Microbial biomass played a more important role in the dynamics of POC and PON in October than in August due to a significant increase in microbial biomass in the southern transect (transect-B) in October by the autumn phytoplankton bloom. This study showed that marine microbes may constitute a significant part in the reservoir of POM in the Korea Strait.

• Animal cells and systems
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• v.14 no.4
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• pp.297-303
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• 2010

To document the basic ecological aspects of Chaoborus species, which has never been reported in Korea, we attempted to identify the species, to monitor seasonal and vertical dynamics, and to elucidate trophic relations of the species in Sang-Chun reservoir. Using morphological characteristics, we identified the collected samples as C. flavicans. Also, we compared the distribution of C. flavicans, Daphnia rosea and chlorophyll a to observed seasonal dynamics. The increase of C. flavicans was observed 1-2 weeks after the increase of D. rosea. Survey of diel vertica migration patterns in the summer season showed that C. flavicans were in hypolimnion at daytime, but moved to the epilimnion at night. Finally, to determine trophic relationships in Sang-Chun reservoir, additional studies on the food web were undertaken by stable isotope analysis. Chaoborus flavicans I-II instars appear to be filter feeders based on carbon isotope values. Trophic levels of C. flavicans III-IV instars were shown to be higher than other zooplankto based on nitrogen isotope values.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.257-261
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• 2004

Computational fluid dynamics analysis was carried out for thermo-chemical flow field in Arcjet thruster with mono-propellant Hydrazine ($N_2$H$_4$) as a working fluid. The theoretical formulation is based on the Reynolds Averaged Navier-Stokes equations for compressible flows with thermal radiation. The electric potential field governed by Maxwell equation is loosely coupled with the fluid dynamics equations through the Ohm heating and Lorentz force. Chemical reactions were assumed being infinitely fast due to the high temperature field inside the arcjet thruster. An equilibrium chemistry module for nitrogen-hydrogen mixture and a thermal radiation module for optically thin media were incorporated with the fluid dynamics code. Thermo-physical process inside the arcjet thruster was understood from the flow field results and the performance prediction shows that the thrust force is increased by amount of 3 times with 0.6KW arc heating.

• Proceedings of the Korean Society of Crop Science Conference
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• 1994.06a
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• pp.164-165
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• 1994

• Journal of Wetlands Research
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• v.12 no.2
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• pp.59-65
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• 2010

Wetlands are a well known ecosystem which have high spatial-temporal heterogeneity of chemical characteristics. This high heterogeneity induces diverse biogeochemical processes, such as aerobic decomposition, denitrification, and plant productivity in wetlands. Understanding the dynamics of dissolved organic carbon (DOC) and inorganic nitrogen in wetlands is important because DOC and inorganic nitrogen are main factors controlling biological processes in wetlands. In this study, we assessed spatial distribution of DOC and inorganic nitrogen with relation to the different hydrology and vegetation in created wetlands. Both DOC and nitrate contents were significantly higher in vegetated areas than open areas. Different water levels also affected DOC contents and their quality. Average DOC contents were $0.37mg{\cdot}g^{-1}$ in deep riparian (DR) and $0.31mg{\cdot}g^{-1}$ in shallow riparian (SR). These results appeared to be related to the interaction between carbon supply by vegetation and microbial decomposition. On the other hand, inorganic nitrogen contents were not affected by water level differences. This result indicates that presence/absence of vegetation could be a more important factor than hydrology in the spatial dynamics of inorganic nitrogen. In conclusion, we observed that vegetation and hydrology differences induced spatial distribution of carbon and nitrogen which are directly related to biogeochemical processes in wetlands.