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Search Results: 1 - 10 of 480091 matches for " J.-C. Huang "
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Temporal variation of nitrate and phosphate transport in headwater catchments: the hydrological controls and land use alteration
T.-Y. Lee, J.-C. Huang, S.-J. Kao,C.-P. Tung
Biogeosciences (BG) & Discussions (BGD) , 2013, DOI: 10.5194/bg-10-2617-2013
Abstract: Oceania rivers are hotspots of DIN (dissolved inorganic nitrogen) and DIP (dissolved inorganic phosphorus) transport due to humid/warm climate, typhoon-induced episodic rainfall and high tectonic activity that create an environment favorable for high/rapid runoff and soil erosion. In spite of its uniqueness, effects of hydrologic controls and land use on the transport behaviors of DIN and DIP are rarely documented. A 2 yr monitoring study for DIN and DIP from three headwater catchments with different cultivation gradient (0 To 8.9%) was implemented during a ~ 3 day interval with an additional monitoring campaign at a 3 h interval during typhoon periods. Results showed the DIN yields in the pristine, moderately cultivated (2.7%), and intensively cultivated (8.9%) watersheds were 8.3, 26, and 37 kg N ha 1 yr 1, respectively. For the DIP yields, they were 0.36, 0.35, and 0.56 kg P ha 1 yr 1, respectively. Higher year-round DIN concentrations and five times larger in DIN yields in intensively cultivated watersheds indicate DIN is more sensitive to land use changes. The high background DIN yield from the relatively pristine watershed was likely due to high atmospheric nitrogen deposition and large subterranean N pool. The correlations between runoff and concentration reveals that typhoon floods purge out more DIN from the subterranean reservoir, i.e., soil, by contrast, runoff washes off surface soil resulting in higher suspended sediment with higher DIP. Collectively, typhoon runoff contributes 20–70% and 47–80%, respectively, to the annual DIN and DIP exports. The DIN yield to DIP yield ratio varied from 97 to 410, which is higher than the global mean of ~ 18. Such a high ratio indicates a P-limiting condition in stream and the downstream aquatic environment. Based on our field observation, we constructed a conceptual model illustrating different remobilization mechanisms for DIN and DIP from headwaters in a mountainous river, which is analogous to typical Oceania rivers and the headwater of large rivers in similar climate zones. Our study advanced our understanding about the role of cyclones, which exert hydrological control, and land use on nutrient export in the Oceania region, benefiting watershed management under the context of climate change.
Temporal variation of nitrate and phosphate transport in headwater catchments: the hydrological controls and landuse alteration
T.-Y. Lee,J.-C. Huang,S.-J. Kao,C.-P. Tung
Biogeosciences Discussions , 2012, DOI: 10.5194/bgd-9-13211-2012
Abstract: Oceania Rivers are hotspots of high DIN (dissolved inorganic nitrogen) and DIP (dissolved inorganic phosphorus) transport. However, the effects of hydrologic controls and land use alternation on the temporal variations of DIN and DIP are rarely documented. In this study, we monitored the nitrate and phosphate concentrations from three headwater catchments with different cultivation gradients at a 3-day interval. This sampling scheme was supplemented with a 3-h interval monitoring during typhoon periods. The results showed that the DIN and DIP yields in the pristine, moderately cultivated, and intensively cultivated watersheds were 7.52/0.31, 31.17/0.30, and 40.96/0.52 kg ha 1 yr 1, respectively. The high DIN yields are comparable to the intensively and extensively disturbed large rivers around the world. These N yields may be due to a high level of nitrogen deposition, rainfall-runoff, and fertilizer application. The importance of event sampling was indicated by the contribution of the three typhoons to the annual DIN and DIP fluxes, which were 30% and 60%, respectively. Both DIN and DIP fluxes significantly increased as the cultivation gradient increased. The DIN and DIP ratio varied from 54 to 230 depending on the decrease of the cultivation gradient. This value is higher than the global mean of ~18. Thus, we speculate that nitrogen saturation occurs in the headwater catchments of Oceania Rivers. The results obtained provide fundamental clues of DIN and DIP yield of Oceania Rivers, which are helpful in understanding the impact of human disturbance on headwater watersheds.
Assessing hydrological model behaviors by intercomparison of the simulated stream flow compositions: case study in a steep forest watershed in Taiwan
J.-C. Huang,T.-Y. Lee,J.-Y. Lee,S.-C. Hsu
Hydrology and Earth System Sciences Discussions , 2013, DOI: 10.5194/hessd-10-855-2013
Abstract: The accurate stream flow composition simulated by different models is rarely discussed, and few studies addressed the model behaviors affected by the model structures. This study compared the simulated stream flow composition derived from two models, namely HBV and TOPMODEL. A total of 23 storms with a wide rainfall spectrum were utilized and independent geochemical data (to derive the stream composition using end-member mixing analysis, EMMA) were introduced. Results showed that both hydrological models generally perform stream discharge satisfactory in terms of the Nash efficiency coefficient, correlation coefficient, and discharge volume. However, the three simulated flows (surface flow, interflow, and base flow) derived from the two models were different with the change of storm intensity and duration. Both simulated surface flows showed the same patterns. The HBV simulated base flow dramatically increased with the increase of storm duration. However, the TOP-derived base flow remained stable. Meanwhile, the two models showed contrasting behaviors in the interflow. HBV prefers to generate less interflow but percolates more to the base flow to match the stream flow, which implies that this model might be suited for thin soil layer. The use of the models should consider more environmental background data into account. Compared with the EMMA-derived flows, both models showed a significant 2 to 4 h time lag, indicating that the base-flow responses were faster than the models represented. Our study suggested that model intercomparison under a wide spectrum of rainstorms and with independent validation data (geochemical data) is a good means of studying the model behaviors. Rethinking the characterization of the model structure and the watershed characteristics is necessary in selecting the more appropriate hydrological model.
The nitrate export in subtropical mountainous catchment: implication for land use change impact
J.-C. Huang,T.-Y. Lee,S.-J. Kao,S.-C. Hsu
Hydrology and Earth System Sciences Discussions , 2010, DOI: 10.5194/hessd-7-9293-2010
Abstract: Agricultural activity is the dominant factor affecting water quality and nitrate export, which causes eutrophication and episodic acidification in downstream water bodies (e.g., reservoirs, lakes, and coastal zones). However, in subtropical mountainous areas such environmental impact due to the land use change was rarely documented. In this study, we investigated 16 sub-catchments during 2007 and 2008 in the Chi-Chia-Wan catchment where is the sole habitat for the endemic species, Formosan landlocked salmon (Oncorhynchus masou formosanus). The results revealed that the NO3-N concentration in pristine catchments varied from 0.144 to 0.151 mg/L without significant seasonal variation. This concentration was comparable with other forestry catchments around the world. However, the annual nitrate export was around 375.3–677.1 kg/km2/yr, much higher than other catchments due to the greater amount of rainfall. This is an important baseline for comparisons with other climate areas. As for the impact of agricultural activities, the catchments with some human disturbance, ~5.2% of the catchment area, might yield 5947.2 kg N/km2/yr – over 10-times higher than that of pristine catchment. Such high export caused by such a low level of disturbance might indicate that subtropical mountainous area is highly sensitive to agricultural activities. As for the land-use effect on nitrate yield, the forestry land might yield 488.5 ± 325.1 kg/km2/yr and the vegetable farm could yield 298 465.4 ± 3347.2 kg/km2/yr – 1000-times greater than the forestry. The estimated nitrate yields for land use classes were a crucial basis and useful for the land manager to assess the possible impacts (e.g., non-point source pollution evaluation and the recovery of land expropriation).
Simulating typhoon-induced storm hydrographs in subtropical mountainous watershed: an integrated 3-layer TOPMODEL
J.-C. Huang, T.-Y. Lee,S.-J. Kao
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2009,
Abstract: A three-layer TOPMODEL is constructed by integrating diffusion wave approach into surface flow, soil moisture deficit into inter flow and exponential recession curve function into base flow. A subtropical mountainous watershed, Heng-Chi, and 22 rain storms with various rainfall types and wide ranges of total rainfall (from 81 to 1026 mm) were applied. The global best-fitted parameter set gives an average efficient coefficient of 82% for calibration and 80% for validation. Sensitivity analysis reveals that soil transmissivity dominates the discharge volume and recession coefficient dominates the hydrograph shape in TOPMODEL framework. Over 90% observed discharges of validation events falls within the 90% confidence interval derived form calibration events. The resembling performances between calibration and validation as well as good results of the confidence interval demonstrate the capability of 3-layer TOPMODEL on simulating cyclones with various rainfall intensity and pattern in subtropical watershed. Meanwhile, the upper confidence limit is suggested preferably when considering flood assessment.
Simulating typhoon-induced storm hydrographs in subtropical mountainous watershed: an integrated 3-layer TOPMODEL
J.-C. Huang,T.-Y. Lee,S.-J. Kao
Hydrology and Earth System Sciences Discussions , 2008,
Abstract: A three-layer TOPMODEL is here constructed by integrating three components, diffusion wave approach into surface flow, soil moisture deficit into interflow and exponential recession curve function into base flow. Sensitivity analysis reveals that D (soil depth), K (hydraulic conductivity), and mi (soil moisture decay) predominate simulated hydrograph shape and total discharge, yet, there are distinct effects on the three flows. A subtropical mountainous watershed, Heng-Chi and eighteen typhoon-induced storms with various rainfall type and wide-ranged total rainfall (81 to 1026 mm) were applied. The global best-fitted combination gives an average efficient coefficient of 75.1% and 76.0% for calibration (14 cases) and validation (4 cases), respectively. Most discharges of validation events fall within the 90% confidence interval derived from calibration events. Those results demonstrate the capability of the 3-layer TOPMODEL in subtropical watershed. Meanwhile, the upper confidence limit is suggested preferably when considering the flood assessment.
Influence of Specific Contributing Area algorithms on slope failure prediction in landslide modeling
J.-C. Huang,S.-J. Kao,M.-L. Hsu,Y.-A. Liu
Natural Hazards and Earth System Sciences (NHESS) & Discussions (NHESSD) , 2007,
Abstract: This study anatomized algorithm effects of specific contributing area (SCA) on soil wetness estimation, consequently landslide prediction, in SHALSTAB. A subtropical mountainous catchment during three typhoon invasions is targeted. The peak 2-day rainfall intensity of the three typhoons: Haitang, Mindulle and Herb are 144, 248 and 327 mm/day, respectively. We use modified success rate (MSR) to retrieve the most satisfying mean condition for model parameters in SHALSTAB at three rainfall intensities and respective pre-typhoon NDVI themes. Simulation indicates that algorithm affects the prediction of landslide susceptibility (i.e. FS, Factor of Safety) significantly. Based on fixed NDVI and the mean condition, we simulate by using full scale rainfall intensity from 0 to 1200 mm/day. Simulations show that predicted unstable area coverage increases non-linearly as rainfall intensity increases for all algorithms yet with different increasing trends. Compared to Dinf, D8 always gives lower coverage of predicted unstable area during three typhoons. By contrast, FD8 gives higher coverage areas. The absolute difference (compared to Dinf) in predicted unstable area ranges from ~ 3% to +4% (percent watershed area). The relative difference (compared to Dinf) ranges from 15% to as high as +40%. The maximum absolute and relative differences in unstable area prediction occur around the condition of 100–300 mm/day, which is common in subtropical mountainous region. Theoretical relationship among slope, rainfall intensity, SCA and FS value was derived in which FS values are very sensitive to algorithms in the field of slope from 37 to 52degree. Results imply any comparison among SCA-related landslide models or engineering application of rainfall return period analysis must base on the same algorithm to obtain comparable results. This study clarifies the SCA algorithm effect on FS prediction and deepens our understanding on landslide modeling.
ACTA MATHEMATICA UNIVERSITATIS COMENIANAE
J.-C. Puchta
ACTA MATHEMATICA UNIVERSITATIS COMENIANAE , 2001,
Abstract: . We improve bounds of A. Fujii concerning the distribution of zeros of Riemann's $\zeta$-function with respect to logarithms of prime numbers.
Organic synthesis applied to space sciences
Guillemin J.-C.
EPJ Web of Conferences , 2012, DOI: 10.1051/epjconf/20111806004
Abstract: About 160 molecules have been detected in the interstellar medium, the comae and the atmospheres of planets. The presence of these compounds leads to imagine a chemistry of these media to explain the formation of these species and to predict the possible presence of other ones. Many of them have never been synthesized or isolated in labs and their preparation can be challenging, up to necessitate news reactions or special equipments.
Le classement automatique des sceaux: solutions manuelles et problèmes d'informatique. Essai méthodologique appliqué à l'Orient Latin
J.-C. POUTIERS
Byzantina Symmeikta , 1981,
Abstract: No abstract
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