Estimation of debris flow discharge coefficient considering sediment concentration     

Namgyun Kim  Hajime Nakagawa  Kenji Kawaike  Hao Zhang 《国际泥沙研究》2019,34(1):1-7

A sabo dam has a purpose to block the path of debris flow. However, when overflow occurs, a sabo dam works as a weir, a vertical obstruction, where the fluid must flow over. Many empirical formulas and discharge coefficients for weirs relating flow depth to discharge have been proposed to calculate overflow discharges. However, only a few studies about overflow discharge coefficients are available in the case of debris flow. In this paper, experiments and numerical simulations were done to estimate debris flow discharge coefficients by considering the sediment concentration. In the numerical simulation, a complete overflow equation and a free overfall equation were implemented to calculate debris overflow discharges at a sabo dam. To determine the discharge coefficients for each equation, single factor regression analysis was used. Laboratory experiments were done to calibrate and to compare with the simulation. Study results showed that the discharge coefficients increase as the sediment concentration increases. This finding suggests debris flow discharge coefficients are derived to calculate the debris overflow discharges at a sabo dam.  相似文献   

Influence of environmental disturbances and reproductive strategy on genetic diversity and differentiation of Zostera marina populations on the southern coast of Korea     

Young Kyun Kim  Seung Hyeon Kim  Joo Mi Yi  Sang Rul Park  Kun‐Seop Lee 《Marine Ecology》2019,40(1)

The genetic diversity and differentiation of four Zostera marina populations along the southern coast of Korea were estimated using random amplified polymorphic DNA (RAPD) markers to determine the effects of natural and anthropogenic stresses and reproductive strategy on within‐population genetic diversity. The mean number of alleles and gene diversities, indicating population genetic diversity, was highest in the Z. marina population that was exposed to repeated environmental disturbances, and lowest in the most undisturbed population. The higher genetic diversity in the disturbed population was associated with a higher contribution of sexual reproduction to population persistence. This suggests that both the level of disturbances and the reproductive strategy for population persistence contributed significantly to population genetic diversity at the study sites. According to the analysis of molecular variance (AMOVA), 76% genetic variation was attributable to differences among individuals within populations. The observed genetic differentiation (F_ST = 0.241) among Z. marina populations at the study sites appeared to result from reduced meadow size, increased genetic drift, and a high incidence of asexual reproduction. Increased population genetic diversity can enhance resistance and resilience to environmental disturbances; thus, this investigation of seagrass population genetics provides valuable new insights for the conservation, management, and restoration of seagrass habitats.  相似文献   

Competing space and place identity with landscape change analysis using Web GIS through Singapore historical maps (1828–2015)     

Ick‐Hoi Kim  Choon Piew Pow  Yi‐Chen Wang  Chen‐Chieh Feng 《Singapore journal of tropical geography》2019,40(2):181-198

The investigation of historical maps is fundamental to understanding the dynamics of landscape changes. In this study, we propose Web GIS tools as a way to compare historical maps efficiently for knowledge production. A key impetus of this article is to contribute to the ongoing efforts to broaden the appeal of ‘mixed‐methods research’ by bridging the epistemological and methodological gaps between GIS and qualitative methodologies in knowledge production. This article proposes a new visualization method for historical landscape change analysis by comparing multiple maps simultaneously with the mash‐up of Web GIS. Based on the analysis of exterior facts represented on the maps, four developmental footprints were investigated, namely, surviving place identity, disappeared place identity replaced by new identity, waning place identity overlapped with new identity, and waning identity by disconnected spatial relationships. To this end, the study argues that Web GIS applications have more potential in spatial knowledge production than traditional desktop GIS.  相似文献   

Selection of scale can reverse the importance of stochastic controls on community assembly     

Daehyun Kim 《自然地理学》2019,40(2):111-126

Reconciling the long-standing debate on the importance of niche-related and neutral factors on community assembly, recent research suggests that both deterministic and stochastic processes operate simultaneously along a continuum in many biogeographical systems. In particular, stochastic processes seem to lose importance under stressful conditions, which results in the increasing influence of deterministic counterparts. In this paper, I show that, at local scales, this stochasticity–stress relationship can be reversed along the environmental stress gradients within a salt marsh: stochasticity manifested under harshness. Here, low-lying, more stressful sites contained all of the plant species of the local pool (i.e. a greater chance of ecological drift), whereas high-elevation, less stressful sites exhibited reduced species richness due to competitive exclusion (i.e. a lower chance of ecological drift). I conclude that determining whether the importance of stochasticity in shaping community structure is greater under benign or harsh conditions depends on the scale of interest.  相似文献   

Biomarker-based Seawater Temperatures of Winter Sinking Particles and Core-top Sediment in the Ulleung Basin of the East Sea     

Park  Yu-Hyeon  Kim  Hyung Jeek  Son  Ju Won  Yoo  Chan Min  Khim  Boo-Keun 《Ocean Science Journal》2019,54(3):487-495

Ocean Science Journal - This study evaluates the application of biomarkerbased temperature proxy data (alkenone with its resultant $$U_{37}^{K'}$$ index and glycerol dialkyl glycerol tetraether...  相似文献   

R/V Isabu-Based First Ultraclean Seawater Sampling for Ocean Trace Elements in Korea     

Kim  Suk Hyun  Ra  Kongtae  Kim  Kyung-Tae  Jeong  Hyeryeong  Lee  Jihyun  Kang  Dong-Jin  Rho  Taekeun  Kim  Intae 《Ocean Science Journal》2019,54(4):673-684

Ocean Science Journal - Trace elements (Mn, Fe, Co, Ni, Cu, Zn, etc.) are essential micronutrients for marine organisms and are thus related to major issues in the ocean, such as climate change,...  相似文献   

The mechanism of bottom water DO variation in summer at the northern mouth of Isahaya Bay,Japan     

Sangyeob Kim  Yuichi Hayami  Akira Tai  Akihide Tada 《Journal of Oceanography》2018,74(6):595-605

Recently, bivalves have been massively killed by anoxia or hypoxia in summer at the northern part of Isahaya Bay, Japan, which constituted a major problem for fisheries. However, the mechanism behind the occurrence of hypoxic water masses is unclear. It is known that the bottom water dissolved oxygen (DO) in this area is affected by the inflow of seawater into the northern mouth of Isahaya Bay. To understand the mechanism of hypoxia, it is necessary to determine the physical processes that cause changes in the bottom DO concentrations in this area. This study shows that there is a neap-spring tidal variation in bottom DO due to a change in vertical tidal mixing, and it also suggests that the decrease in bottom DO was generated by a baroclinic flow, which is due to the internal tide, and a shear flow, which is induced by the external tide in the bottom boundary layer. In addition, our study suggests that the source of cold and hypoxic water that appears in the bottom layer at low tide is the inner area of the Ariake Sea.  相似文献   

Sinking Particle Flux in the Subtropical Oligotrophic Northwestern Pacific from a Short-term Sediment Trap Experiment     

Hyung Jeek Kim  Jonguk Kim  Dongseon Kim  Michael T. Chandler  Seung Kyu Son 《Ocean Science Journal》2018,53(2):395-403

Time-series sediment traps were deployed in the subtropical oligotrophic northwestern Pacific (SONP) at three depths from August to September 2015 to better understand vertical flux of sinking particles. Sinking particles were collected at 5-day intervals over the sediment trap deployment period. The average total mass flux at water depths of 400 m, 690 m, and 1,710 m was 9.1, 4.4, and 4.1 mg m^-2day^-1, respectively. CaCO₃ materials constituted 50 to 70% of sinking particles while in comparison particulate organic carbon (POC) constituted up to 20%. A synchronous variation of total mass flux was observed at the three depths, indicating that calcite-dominated particles sank from 400 to 1,710 m within a 5-day period. POC flux at these water depths was 2.4, 0.38, and 0.31 mg m^-2day^-1, respectively. Our results indicate low transfer efficiencies of 16% from 400 to 690 m and 13% for the 400 to 1,710 m depth range. The estimated transfer efficiencies were significantly lower than those observed at the K2 station in the northwest Pacific subarctic gyre, presumably because of a prevalence of pico-cyanobacteria in the SONP. Because cyanobacteria have a semi-permeable proteinaceous shell, they are more readily remineralized by bacteria than are siliceous phytoplankton in the northwest Pacific subarctic gyre. Continued surface water warming and expansion of the SONP will likely have a profound impact on ocean acidification in the northwest Pacific, possibly affecting the transfer efficiency of sinking POC to the deep-sea.  相似文献   

A Length-based Analysis of Recruitment Variability in the Korean Pollock Population under Data-limited Conditions     

Kyuhan Kim  Saang-Yoon Hyun 《Ocean Science Journal》2018,53(3):535-555

The walleye pollock (Gadus chalcogrammus) population in Korean waters had thrived until the mid-1980s, but this fish population has been depleted since the late 1990s. Limited data and lack of ecological research about the population prevented us from revealing the mechanism or material cause that resulted in the population’s collapse. Instead, we intended to examine possible hypotheses for the collapse, and built a statistical linear model, where juvenile fish, adult fish, and environmental factors were explored as variables. Because actual data on fish ages were not available, we estimated age compositions of the fish sample, applying the length-frequency analysis suggested by Schnute and Fournier (1980) to data on their lengths. Then we used the estimates of age compositions to determine adequate time lags between juvenile and adult stages in the statistical linear model. The selected final model suggested that the depletion of the fish population was associated with changes in water temperatures during April, June, and October and with adult abundance, but was not with the other species (e.g., sandfish (Arctoscopus japonicus) and flatfishes (Pleuronectidae sp.)) considered in the model. We further interpreted the results from ecological perspectives, referring to previous studies and ecological hypotheses.  相似文献   

Physiological Characteristics and Related Biochemical Parameters of Snow Algae from King George Island,Antarctica     

Bo?Kyung?Kim  HyoungMin?Joo  Boyeon?Lee  Dong-Hun?Lee  In-Young?Ahn  Sun-Yong?HaEmail author 《Ocean Science Journal》2018,53(4):621-630

Red and green snow caused by snow algal blooms is common on glaciers and snowfields worldwide. Reddish and greenish snow samples containing algae were collected at the vicinity of penguin rockeries on King George Island (62°13′S, 58°47′W, near the King Sejong Station), Antarctica in February 2017 to investigate their physiology. Eight pigments and six fatty acids were detected from the samples. No difference in pigment and fatty acid (FA) composition was found between reddish and greenish snow samples. In contrast, spectral profiling and mycosporine-like amino acids (MAAs) were different between reddish and greenish snow. Particularly in greenish snow, a high absorbance between 450–600 nm was observed. The average MAA concentration was 316.0 μg g^-1 in greenish snow, which was higher than that of reddish snow (278.2 μg g^-1). The MAA to Particulate organic carbon (POC) ratio (mg (g C)^-1) for reddish snow (6.2 mg (g C)^-1) was higher than that of greenish snow (2.6 mg (g C)^-1). These results suggest that reddish and greenish snow are considered to be the same species based on pigment and FA composition. Compared with photoprotective pigments, MAAs offer snow algae a more effective photoprotection strategy to promote tolerance of natural levels of ultraviolet radiation (UVR).  相似文献