Check-dam construction is an effective and widely used method for sediment trapping in the Yellow River Basin and other places over the world that are prone to severe soil erosion.Quantitative estimations of the dynam...Check-dam construction is an effective and widely used method for sediment trapping in the Yellow River Basin and other places over the world that are prone to severe soil erosion.Quantitative estimations of the dynamic sediment trapped by check dams are necessary for evaluating the effects of check dams and planning the construction of new ones.In this study,we propose a new framework,named soil and water assessment tool(SWAT)–dynamic check dam(DCDam),for modeling the sediment trapped by check dams dynamically,by integrating the widely utilized SWAT model and a newly developed module called DCDam.We then applied this framework to a typical loess watershed,the Yan River Basin,to assess the time-varying effects of check-dam networks over the past 60 years(1957–2016).The DCDam module generated a specific check-dam network to conceptualize the complex connections at each time step(monthly).In addition,the streamflow and sediment load simulated by using the SWAT model were employed to force the sediment routing in the check-dam network.The evaluation results revealed that the SWAT-DCDam framework performed satisfactorily,with an overestimation of 11.50%,in simulating sediment trapped by check dams,when compared with a field survey of the accumulated sediment deposition.For the Yan River Basin,our results indicated that the designed structural parameters of check dams have evolved over the past 60 years,with higher dams(37.14%and 9.22%increase for large dams and medium dams,respectively)but smaller controlled areas(46.03%and 10.56%decrease for large dams and medium dams,respectively)in recent years.Sediment retained by check dams contributed to approximately 15.00%of the total sediment load reduction in the Yan River during 1970–2016.Thus,our developed framework can be a promising tool for evaluating check-dam effects,and this study can provide valuable information and support to decision-making for soil and water conservation and check-dam planning and management.展开更多
Representativity of biota in the biosphere also have similar significance in the lithosphere after their death. Recently, taphonomic representation of biota in the lithosphere has been widely used for minimizing the b...Representativity of biota in the biosphere also have similar significance in the lithosphere after their death. Recently, taphonomic representation of biota in the lithosphere has been widely used for minimizing the biases in palaeo-environmental reconstructions including global climate change. In September 2001, a sediment trap was installed at the central area of the Loch Coire Fionnaraich （LCFR）, a small, oligotrophic mountain loch in northwest Scotland for a taphonomic study of cladoceran zooplankton. The trap was emptied on a seasonal basis, where an average 0.14 g dry material was recovered in each season, January, May and August 2002 respectively. A sediment core was also taken from near the sediment trap location. The top 0.5 cm section, the ＇core＇ was used for a comparative study with the trap sediment samples. The planktonic Cladocera consisted of Bosmina coregoni and appeared to have excellent preservation in the trap assemblages. Moreover, some common littoral Cladocera such as Alonella excisa and Aloha guttata appear to be less well preserved in the fossil assemblages. Large littoral taxa such as Eurycercus lamellatus and Aloha quadrangularis were rare in the trap but relatively common and well preserved in the sediment-water interface. It is suggested that taphonomic processes play a dominant role on deposition of fossil remains of Cladocera and caution should be taken while inferring the past environmental changes whilst using fossil assemblages recovered from the lake centre as a representation of the entire cladoceran community in the lake.展开更多
The flux of settling particles in the ocean has been widely explored since 1980s due to its important role in biogenic elements cycling,especially in the transport of particulate organic carbon(POC)in the deep sea.How...The flux of settling particles in the ocean has been widely explored since 1980s due to its important role in biogenic elements cycling,especially in the transport of particulate organic carbon(POC)in the deep sea.However,research in the seamount area of the oligotrophic subtropical Northwest Pacific Ocean is lacking.In this work,two sediment traps were deployed at the foot and another two at the hillside of Niulang Guyot from August2017 to July 2018.The magnitude and composition of particle fluxes were measured.The main factors influencing the spatial variations of the fluxes were evaluated.Our results indicated a low particulate flux from Niulang Guyot area in the Northwest Pacific Ocean,reflecting low primary productivity of the oligotrophic ocean.The total mass flux(TMF)decreased from 2.57 g/(m^(2)·a)to 0.56 g/(m^(2)·a)with increasing depth from 600 m to 4850 m.A clear seasonal pattern of TMF was observed,with higher flux in summer than that in winter.The peak flux of 26.52 mg/(m^(2)·d)occurred in August at 600 m,while the lowest value of 0.07 mg/(m^(2)·d)was shown in February at 4850 m.The settling particles at the deep layers had similar biochemical composition,with calcium carbonate(CaCO_(3))accounting for up to 90%,followed by organic matter and opal,characteristics of Carbonate Ocean.The POC flux decreased more rapidly in the twilight layer because of faster decomposition,remineralization,and higher temperature.A small fraction of POC was transported into the deep ocean by biological pump.Particle fluxes were mainly controlled by the calcareous ballasts besides the primary productivity of the surface water.The advection may be another important factor affecting the flux in the seamount area.The combination of settled matters rich in foraminiferal tests with topography and currents may be the reason for regulating the local abundance of benthos on seamounts.Our results will fill in the knowledge gap of sedimentation flux,improve the understanding of ecosystem in Niulang Guyot area,and eventually provide data support for the optimization of regional ecological modeling.展开更多
The construction of fully closed check dam (CD) is a conventional flood prevention mechanism implemented on rivers. Fully closed CDs trap large amounts of sediments in rivers to stabilize the river slopes and control ...The construction of fully closed check dam (CD) is a conventional flood prevention mechanism implemented on rivers. Fully closed CDs trap large amounts of sediments in rivers to stabilize the river slopes and control erosion. However, fully closed CDs cannot selectively trap sediment and may easily overflow, causing them to losing their ability to mediate and hold sediments. Previous studies proposed the concept of “breathable CDs”. The researcher introduced metal slit dam (SD) that could be assembled and disassembled quickly and conveniently. Once a CD reaches maximum capacity, operators must ensure that the water channels of the dam are free from blockage. Moreover, they must inspect the internal accumulation conditions of the dam periodically or immediately following heavy typhoon rains. When necessary, either the sediment buildup in the upriver blockage must be cleared, or the transverse structure of the dam must be removed to allow fine particles to be discharged along with a moderate amount of water. These actions can free up the sediment-storing capacity of the dam for the next heavy typhoon rains. In addition, operators should also inspect the damages inflicted on the dam, such as erosion, wear and tear, and deformation conditions. Damaged components should be disassembled and repaired if possible, or recycled and reused. The present study performed channel tests to simulate closed CDs, SDs, steel pipe dam (SPDs), and steel pipe plus slit dam (SPSDs) for 50-year and 100-year frequency floods. Results were then analyzed to determine the sediment trapping (ST) effects of various CDs, the effects of “adjustable CDs”, and the changes of moderated riverbeds.展开更多
Sediment traps are an important tool for studying the source, composition and sedimentation processes of sinking particulate matter in the ocean. An in situ observational mooring(TJ-A-1) is located in the northern Sou...Sediment traps are an important tool for studying the source, composition and sedimentation processes of sinking particulate matter in the ocean. An in situ observational mooring(TJ-A-1) is located in the northern South China Sea(20.05°N, 117.42°E) at a water depth of 2 100 m and equipped with two sediment traps deployed at 500 m and 1 950 m. Samples were collected at 18-day intervals, and 20 samples were obtained at both depths from May 2014 to May 2015. Large amounts of fecal matter and marine snow were collected in the lower trap. The fluxes of marine snow and fecal pellets exhibited a fluctuating decrease between May 2014 and early August 2014 and then stabilized at a relatively low level. Scanning electron microscopy observations revealed that the main components of the marine snow and fecal pellets were diatoms, coccolithophores, radiolarians, and other debris, all of which are planktons mostly produced in photic zone. Used in conjunction with the particle collection range estimates from the lower trap and data on ocean surface chlorophyll, these marine snow and fecal pellets were related to the lateral transport of deep water and not vertical migrations from overlying water column. Moreover, the source area might be southwest of Taiwan.展开更多
Check dams have been used worldwide for a variety of purposes.With increasing age,check dams gradually lose their sediment trapping function via the continuous deposition of material carried by debris flows and flash ...Check dams have been used worldwide for a variety of purposes.With increasing age,check dams gradually lose their sediment trapping function via the continuous deposition of material carried by debris flows and flash floods,and eventually,check dams become unable to perform the designed mitigation function.In this paper,the sediment deposit evolution in a dam with multiple debris flow surges and its influence on the sediment trapping effect were investigated.The results showed that the debris flow deposition process can be divided into three phases:the backwater-controlled deposition phase,landform-controlled deposition phase,and quasi-equilibrium phase.The sediment trapping ratio of the check dam gradually decreased as the deposit volume increased and was linearly negatively correlated with the sediment deposition rate.Moreover,a mathematical model describing the negative feedback between deposit volume and sediment trapping ratio was established,and the physical meanings of the coefficients in the model and their empirical values were clarified.Furthermore,the deposit distribution,which satisfied the Weibull distribution in the longitudinal direction,was revealed.In the cross-sectional direction,the distribution of deposition gradually became uneven with increasing sediment filling rate.展开更多
A Lagrangian model is used to evaluate source regions of particles collected in the sediment traps at the DYFAMED （Dy namique des Flux Atmospheriques en Mediterranee） station by tracking particles backwards from Mar...A Lagrangian model is used to evaluate source regions of particles collected in the sediment traps at the DYFAMED （Dy namique des Flux Atmospheriques en Mediterranee） station by tracking particles backwards from March 1 to August 31, 2001. The analysis suggests that source regions depend on the flow fields, the settling speed of the particles, and the deployment depths of the traps. Monthly variation is observed in the distribution patterns of source regions, which is caused by the currents The source regions are located around the traps and up to hundreds of kilometers away. As the settling speed increases with the particle diameters, the distance to the source regions decreases. The vertical flux can be approximately estimated in 1D for the particles with diameters larger than 500 lain. Furthermore, traps moored at various depths at the DYFAMED can collect parti- cles that originated from different regions in the Ligurian Sea.展开更多
The results of time series sediment trap experiments in the South China Sea show that particulate organic carbon (POC) fluxes are influenced by the monsoons. The increase of productivity in the northern South China Se...The results of time series sediment trap experiments in the South China Sea show that particulate organic carbon (POC) fluxes are influenced by the monsoons. The increase of productivity in the northern South China Sea is mainly due to northeast monsoon while in the central South China Sea the influence of southwest monsoon becomes more prominent. The annual primary production and export production calculated based on POC fluxes are 53 0-63 4 and 10 32-12 93 gC·m -2·a -1, respectively. The enhancement of POC flux during monsoon period suggest that higher palaeoproductivity or organic carbon accumulation rate in glacial age in the South China Sea might be the result of strengthening of the monsoons.展开更多
Reservoirs are usually exposed to sediment accumulation problems that will lead to reduction in their storage capacity. This problem directly affects the performance of the dams and causes shortage of their useful lif...Reservoirs are usually exposed to sediment accumulation problems that will lead to reduction in their storage capacity. This problem directly affects the performance of the dams and causes shortage of their useful life. The simplest technique to estimate sediment deposition rate is using sediment rating curve with sediment trapping efficiency (TE) of the reservoir. Many empirical and semi-empirical approaches have been suggested for to determine this term depending on the annual inflow rate, reservoir characteristics and features of the catchments area. In this study six different empirical methods depending on the residence time principle (water retention time) were used. These approaches were reviewed and applied to determine TE of Mosul dam reservoir (MDR) for period 1986 to 2011. The monthly operating data for inflow, outflow and water elevations for MDR were used to determine monthly TE and long-term TE for whole period of MDR using the mentioned methods. Furthermore, the monthly inflow rate for River Tigris upstream MDR, its sediment rating curve and sediment feeding from valleys around MDR were used to estimate the amount sediment coming to the reservoir. The results provided by these methods for TE with sediment coming to MDR were used to compute the amount of sediment deposited in MDR on monthly bases during this period. The results obtained were evaluated using observed bathymetric survey data that had been collected in 2011 after 25 years of the operation of the dam. The results showed all the mentioned methods gave convergent results and they were very close to bathymetric survey results for estimating the volume of sediment deposited especially that proposed by Ward which gave 0.368% percentage error. Furthermore, the result computed using monthly TE gave good agreement if compared with that long-term TE where the percentage error was ranging between –3.229% to 1.674% for monthly adopted data and –4.862% to?–2.477% for whole period data. It is believed that this work will help others to use this procedure on other reservoirs.展开更多
A rare occurrence of a microspherule has been found in the infratrappean sediments,encountered below338 m thick Deccan volcanic cover in KLR-1 scientific borehole,drilled in the epicentral zone of the 1993 Killari ear...A rare occurrence of a microspherule has been found in the infratrappean sediments,encountered below338 m thick Deccan volcanic cover in KLR-1 scientific borehole,drilled in the epicentral zone of the 1993 Killari earthquake(Maharashtra,India).Palynological studies of the sediments indicate their age as Early Permian(Asselian,298-295 Ma) for deposition.Transmission electron microscope studies reveal that the spherule from the infratrappeans,is having a similar composition to that of the Neoarchean amphibolite to granulite facies mid crustal basement.The spherule is non-spherical in nature,containing mostly FeO(10.70±0.20 wt.%),CaO(13.8±0.5 wt.%),Al203(7.78±0.30 wt.%),MgO(6.47±0.3 wt.%),Si02(47,46±0.50 wt.%),Ti02(2.47±0.3 wt.%).K20(1.89±0.20 wt.%).and Cl(0.33±0.05 wt.%).Since the Fe composition of the spherule is almost same as the basement rock(10.5 wt.%),and the chlorine content is also in the same range as the basement(0.04-0.24 wt.%),it would suggest possibility of an extraterrestrial impact over the Indian terrain during the erstwhile Gondwana sedimentation period that may be associated with the Permian-Triassic mass extinction,the most severe one in the Earth's history.展开更多
The purpose of this study is to investigate the control function and mechanisms of natural river notches. Physical and numerical experiments are analyzed in this study for two representative types of sediment events：...The purpose of this study is to investigate the control function and mechanisms of natural river notches. Physical and numerical experiments are analyzed in this study for two representative types of sediment events： high intensity and short duration Type A sediment disaster events, and low intensity and long duration Type B moderate non-disaster events. Two dimensionless parameters, sediment trapping rate and reduction rate of peak sediment transport, are defined to evaluate the sediment control function of river notches. Study results indicate that the contraction ratio of the notch has a significant influence on sediment control function, with high contraction ratios resulting in both high sediment-trapping and high reduction rates. River notches provide better sediment control during Type A events than Type B events. The sediment control mechanism of river notches is the result of multiple interactions among river flow, sediment transport, and riverbed variation. Analysis of these interactions supports the significant protection role of river notches on sediment control for disaster events.展开更多
Illegal deforestation changes in land use and climate change have resulted in increased runoff and surface erosion from the upper areas of watersheds, affecting directly the lower lands where human settlements are com...Illegal deforestation changes in land use and climate change have resulted in increased runoff and surface erosion from the upper areas of watersheds, affecting directly the lower lands where human settlements are common. Such is the case of Angangueo in the state ofMichoacam, Mexico, where in 2010 an unusual weather event caused substantial damage to infrastructure, and unfortunately human deaths. Against disasters, the government has carried out actions such as implementing infrastructure to alleviate flooding and mudslides. Gabions dams were used to control erosion and runoff, as they are considered environmentally friendly as compared to most of the constructed impermeable weirs. This study was carried out to evaluate the effectiveness of gabions dams in sediment retention in a small watershed East of Michoacan. Eight gabions dams and five masonry dams two years after of construction were studied. The results indicated that the gabions dams retained less gravel than masonry dams, more sand, but no significant differences were found for fine sediments. Regarding the efficiency of gabions dams, there were not identified relationships since the building volume and contribution area is different in each one of them.展开更多
A new patent registered device- suspended flexible curtain （SFC） for sedimentation enhancement is proposed in this paper, which consists of two parts： a light-weight curtain with sediment-passing windows and a heav...A new patent registered device- suspended flexible curtain （SFC） for sedimentation enhancement is proposed in this paper, which consists of two parts： a light-weight curtain with sediment-passing windows and a heavy pillar for the device stability. The mechanism of trapping nearbed sediment by the SFC is such that a primary and a secondary circulations with horizontal hubs would be formed at the leeside when it is placed on beds in running flow; the velocities within the sediment-passing windows are locally accelerated, the nearbed sediments would be brought by the flow through the windows, and then settled down within the primary circulation zone. Experimental tests on hydraulic characteristics are conducted in a laboratory flume with rigid bed. It is found that the dimensions of the curtain and the sediment-passing windows determine the characteristics of the primary and the secondary circulations. The intensity of the primary and the secondary circulations is dominated by the size of the sediment-passing window. Whether the secondary circulation would contact the bed or not depends on the level of the sediment-passing window. The length and the height of the primary circulation zone demonstrate quasi linear relationships with the effective height of the SFC. And the tests on sandy bed flume show that the sediment deposition happens just in the primary circulation zone.展开更多
Earlier investigators have numerically carried out performance analysis of the invert trap fitted in an open channel using the stochastic discrete phase model(DPM) by assuming the open channel flow to be closed condui...Earlier investigators have numerically carried out performance analysis of the invert trap fitted in an open channel using the stochastic discrete phase model(DPM) by assuming the open channel flow to be closed conduit flow under pressure and assuming zero shear stress at the top wall.This is known as the fixed lid model.By assuming the top wall to be a shear free wall,they have been able to show that the velocity distribution looks similar to that of an open channel flow with zero velocity at the bottom and maximum velocity at the top,representing the free water surface,but no information has been provided for the pressure at the free water surface.Because of this assumption,the validation of the model in predicting the trap efficiency has performed significantly poorly.In addition,the free water surface subject to zero gauge pressure cannot be modeled using the fixed lid model because there is no provision of extra space in the form of air space for the fluctuating part of the water surface profile.It can.however,be modeled using the volume of fluid(VOF) model because the VOF model is the appropriate model for open channel or free surface flow.Therefore,in the present study,three-dimensional(3D) computational fluid dynamics(CFD) modeling with the VOF model,which considers open channel flow with a free water surface,along with the stochastic DPM.was used to model the trap efficiency of an invert trap fitted in an open rectangular channel.The governing mathematical flow equations of the VOF model were solved using the ANSYS Fluent 14.0 software,reproducing the experimental conditions exactly.The results show that the 3D CFD predictions using the VOF model closely fit the experimental data for glass bead particles.展开更多
The melting of seasonal sea ice in Antarctica plays a pivotal role in the region’s carbon cycle,influencing global carbon storage and the exchange of carbon between the atmosphere and the ocean.However,the impact of ...The melting of seasonal sea ice in Antarctica plays a pivotal role in the region’s carbon cycle,influencing global carbon storage and the exchange of carbon between the atmosphere and the ocean.However,the impact of variability in the timing of seasonal sea ice retreat on the flux and composition of sinking particulate matter remains to be elucidated.In this study,we deployed sediment traps in Prydz Bay during the austral summers of 2019/2020 and 2020/2021,noting that sea ice melting occurred approximately one and a half months earlier in the former summer compared to the latter.We analyzed sediment trap data,which included total mass flux(TMF),particulate organic carbon(POC),biogenic silica(BSi),particulate inorganic carbon,and lithogenic particle(Litho)fluxes,as well as the stable isotopesδ^(13)C andδ^(15)N of particulate organic matter(POM).Additionally,we incorporated remote sensing data on sea ice concentration and chlorophyll a.This dramatic delay in sea ice melting timing could result in a significant increase in TMF,BSi and POC fluxes in the summer of 2020/2021 compared to 2019/2020.Elevated BSi fluxes and more ^(13)C-depleted POC in the austral summer of 2020/2021 suggest that the delayed melting of sea ice may have stimulated the productivity of centric diatoms.Furthermore,the higher BSi/POC ratio and more negativeδ^(15)N values of POM,along with a reduced presence of krill in the traps,indicate a diminished grazing pressure from zooplankton,which collectively enhanced the sedimentation efficiency of POC during the austral summer of 2020/2021.These findings highlight the critical role of sea ice melting timing in regulating productivity,flux and composition of sinking particulate matter in the Prydz Bay ecosystem,with significant implications for carbon cycling in polar oceans.展开更多
基金funded by the Strategic Priority Research Program of Chinese Academy of Sciences(XDB40020205)the National Natural Science Foundation of China(U2243210,42041006,42207401,42271025,and 31961143011)+8 种基金Key Laboratory of Degraded and Unused Land Consolidation Engineering of the Ministry of Natural Resources of the People’s Republic of China(SXDJ2019-5)the Key Research and Development Program of Shaanxi Province(2022ZDLSF06-04)the Innovation Team of Shaanxi Province(2021TD-52)the Technology Innovation Center for Land Engineering and Human Settlements,Shaanxi Land Engineering Construction Group Co.,Ltd.and Xi’an Jiaotong University(201912131-B2)the Foundation of Development on Science and Technology by Yellow River Institute of Hydraulic Research(HKF202205)the Scientific Research Foundation of Yellow River Institute of Hydraulic Research(HKY-JBYW-2022-09)the"Light of the West"talent program of the Chinese Academy of Science,the Key Research and Development Project in Shaanxi Province(S2020-YF-GHZD-0061)the National Thousand Youth Talent Program of Chinathe Shaanxi Hundred Talent Program。
文摘Check-dam construction is an effective and widely used method for sediment trapping in the Yellow River Basin and other places over the world that are prone to severe soil erosion.Quantitative estimations of the dynamic sediment trapped by check dams are necessary for evaluating the effects of check dams and planning the construction of new ones.In this study,we propose a new framework,named soil and water assessment tool(SWAT)–dynamic check dam(DCDam),for modeling the sediment trapped by check dams dynamically,by integrating the widely utilized SWAT model and a newly developed module called DCDam.We then applied this framework to a typical loess watershed,the Yan River Basin,to assess the time-varying effects of check-dam networks over the past 60 years(1957–2016).The DCDam module generated a specific check-dam network to conceptualize the complex connections at each time step(monthly).In addition,the streamflow and sediment load simulated by using the SWAT model were employed to force the sediment routing in the check-dam network.The evaluation results revealed that the SWAT-DCDam framework performed satisfactorily,with an overestimation of 11.50%,in simulating sediment trapped by check dams,when compared with a field survey of the accumulated sediment deposition.For the Yan River Basin,our results indicated that the designed structural parameters of check dams have evolved over the past 60 years,with higher dams(37.14%and 9.22%increase for large dams and medium dams,respectively)but smaller controlled areas(46.03%and 10.56%decrease for large dams and medium dams,respectively)in recent years.Sediment retained by check dams contributed to approximately 15.00%of the total sediment load reduction in the Yan River during 1970–2016.Thus,our developed framework can be a promising tool for evaluating check-dam effects,and this study can provide valuable information and support to decision-making for soil and water conservation and check-dam planning and management.
基金supported by the ORS Award to Giri Kattel, ENSIS Ltd Trust Fund,Department of Geography and UCL Graduate School Research Scholarships
文摘Representativity of biota in the biosphere also have similar significance in the lithosphere after their death. Recently, taphonomic representation of biota in the lithosphere has been widely used for minimizing the biases in palaeo-environmental reconstructions including global climate change. In September 2001, a sediment trap was installed at the central area of the Loch Coire Fionnaraich （LCFR）, a small, oligotrophic mountain loch in northwest Scotland for a taphonomic study of cladoceran zooplankton. The trap was emptied on a seasonal basis, where an average 0.14 g dry material was recovered in each season, January, May and August 2002 respectively. A sediment core was also taken from near the sediment trap location. The top 0.5 cm section, the ＇core＇ was used for a comparative study with the trap sediment samples. The planktonic Cladocera consisted of Bosmina coregoni and appeared to have excellent preservation in the trap assemblages. Moreover, some common littoral Cladocera such as Alonella excisa and Aloha guttata appear to be less well preserved in the fossil assemblages. Large littoral taxa such as Eurycercus lamellatus and Aloha quadrangularis were rare in the trap but relatively common and well preserved in the sediment-water interface. It is suggested that taphonomic processes play a dominant role on deposition of fossil remains of Cladocera and caution should be taken while inferring the past environmental changes whilst using fossil assemblages recovered from the lake centre as a representation of the entire cladoceran community in the lake.
基金The Global Change and Air-sea Interaction II Project under contract Nos GASI-04-HYST-01 and GASI-01-NPACSTsumthe Eastern Pacific Eco-environment Monitoring and Protection Project under contract No.DY135-E2-5-02+1 种基金the Fund of COMRA-45 Cruise under contract No.DY-HC-135-45the Scientific Research Foundation of Third Institute of Oceanography,Ministry of Natural Resources of the People’s Republic of China under contract No.2017014。
文摘The flux of settling particles in the ocean has been widely explored since 1980s due to its important role in biogenic elements cycling,especially in the transport of particulate organic carbon(POC)in the deep sea.However,research in the seamount area of the oligotrophic subtropical Northwest Pacific Ocean is lacking.In this work,two sediment traps were deployed at the foot and another two at the hillside of Niulang Guyot from August2017 to July 2018.The magnitude and composition of particle fluxes were measured.The main factors influencing the spatial variations of the fluxes were evaluated.Our results indicated a low particulate flux from Niulang Guyot area in the Northwest Pacific Ocean,reflecting low primary productivity of the oligotrophic ocean.The total mass flux(TMF)decreased from 2.57 g/(m^(2)·a)to 0.56 g/(m^(2)·a)with increasing depth from 600 m to 4850 m.A clear seasonal pattern of TMF was observed,with higher flux in summer than that in winter.The peak flux of 26.52 mg/(m^(2)·d)occurred in August at 600 m,while the lowest value of 0.07 mg/(m^(2)·d)was shown in February at 4850 m.The settling particles at the deep layers had similar biochemical composition,with calcium carbonate(CaCO_(3))accounting for up to 90%,followed by organic matter and opal,characteristics of Carbonate Ocean.The POC flux decreased more rapidly in the twilight layer because of faster decomposition,remineralization,and higher temperature.A small fraction of POC was transported into the deep ocean by biological pump.Particle fluxes were mainly controlled by the calcareous ballasts besides the primary productivity of the surface water.The advection may be another important factor affecting the flux in the seamount area.The combination of settled matters rich in foraminiferal tests with topography and currents may be the reason for regulating the local abundance of benthos on seamounts.Our results will fill in the knowledge gap of sedimentation flux,improve the understanding of ecosystem in Niulang Guyot area,and eventually provide data support for the optimization of regional ecological modeling.
文摘The construction of fully closed check dam (CD) is a conventional flood prevention mechanism implemented on rivers. Fully closed CDs trap large amounts of sediments in rivers to stabilize the river slopes and control erosion. However, fully closed CDs cannot selectively trap sediment and may easily overflow, causing them to losing their ability to mediate and hold sediments. Previous studies proposed the concept of “breathable CDs”. The researcher introduced metal slit dam (SD) that could be assembled and disassembled quickly and conveniently. Once a CD reaches maximum capacity, operators must ensure that the water channels of the dam are free from blockage. Moreover, they must inspect the internal accumulation conditions of the dam periodically or immediately following heavy typhoon rains. When necessary, either the sediment buildup in the upriver blockage must be cleared, or the transverse structure of the dam must be removed to allow fine particles to be discharged along with a moderate amount of water. These actions can free up the sediment-storing capacity of the dam for the next heavy typhoon rains. In addition, operators should also inspect the damages inflicted on the dam, such as erosion, wear and tear, and deformation conditions. Damaged components should be disassembled and repaired if possible, or recycled and reused. The present study performed channel tests to simulate closed CDs, SDs, steel pipe dam (SPDs), and steel pipe plus slit dam (SPSDs) for 50-year and 100-year frequency floods. Results were then analyzed to determine the sediment trapping (ST) effects of various CDs, the effects of “adjustable CDs”, and the changes of moderated riverbeds.
基金The National Natural Science Foundation of China under contract Nos 91528304 and 41376043.
文摘Sediment traps are an important tool for studying the source, composition and sedimentation processes of sinking particulate matter in the ocean. An in situ observational mooring(TJ-A-1) is located in the northern South China Sea(20.05°N, 117.42°E) at a water depth of 2 100 m and equipped with two sediment traps deployed at 500 m and 1 950 m. Samples were collected at 18-day intervals, and 20 samples were obtained at both depths from May 2014 to May 2015. Large amounts of fecal matter and marine snow were collected in the lower trap. The fluxes of marine snow and fecal pellets exhibited a fluctuating decrease between May 2014 and early August 2014 and then stabilized at a relatively low level. Scanning electron microscopy observations revealed that the main components of the marine snow and fecal pellets were diatoms, coccolithophores, radiolarians, and other debris, all of which are planktons mostly produced in photic zone. Used in conjunction with the particle collection range estimates from the lower trap and data on ocean surface chlorophyll, these marine snow and fecal pellets were related to the lateral transport of deep water and not vertical migrations from overlying water column. Moreover, the source area might be southwest of Taiwan.
基金supported by the National Natural Science Foundation of China(No.41925030)the Second Tibetan Plateau Scientific Expedition and Research Program(No.2019QZKK0904)+1 种基金the Chinese Academy of Sciences“Light of West China”ProgramSupport from the Dongchuan Debris Flow Observation and Research Station(DDFORS),Chinese Academy of Sciences,is acknowledged.
文摘Check dams have been used worldwide for a variety of purposes.With increasing age,check dams gradually lose their sediment trapping function via the continuous deposition of material carried by debris flows and flash floods,and eventually,check dams become unable to perform the designed mitigation function.In this paper,the sediment deposit evolution in a dam with multiple debris flow surges and its influence on the sediment trapping effect were investigated.The results showed that the debris flow deposition process can be divided into three phases:the backwater-controlled deposition phase,landform-controlled deposition phase,and quasi-equilibrium phase.The sediment trapping ratio of the check dam gradually decreased as the deposit volume increased and was linearly negatively correlated with the sediment deposition rate.Moreover,a mathematical model describing the negative feedback between deposit volume and sediment trapping ratio was established,and the physical meanings of the coefficients in the model and their empirical values were clarified.Furthermore,the deposit distribution,which satisfied the Weibull distribution in the longitudinal direction,was revealed.In the cross-sectional direction,the distribution of deposition gradually became uneven with increasing sediment filling rate.
基金supported by the National Natural Science Foundation of China(Grant No.40821004)Public Science and Technology Research Funds Projects of Ocean(Grant No.201005030)+1 种基金the National Natural Science Foundation of China(Grant No.41276186)the Program of Nanjing University of Information Science and Technology(Grant No.S8111005001)
文摘A Lagrangian model is used to evaluate source regions of particles collected in the sediment traps at the DYFAMED （Dy namique des Flux Atmospheriques en Mediterranee） station by tracking particles backwards from March 1 to August 31, 2001. The analysis suggests that source regions depend on the flow fields, the settling speed of the particles, and the deployment depths of the traps. Monthly variation is observed in the distribution patterns of source regions, which is caused by the currents The source regions are located around the traps and up to hundreds of kilometers away. As the settling speed increases with the particle diameters, the distance to the source regions decreases. The vertical flux can be approximately estimated in 1D for the particles with diameters larger than 500 lain. Furthermore, traps moored at various depths at the DYFAMED can collect parti- cles that originated from different regions in the Ligurian Sea.
文摘The results of time series sediment trap experiments in the South China Sea show that particulate organic carbon (POC) fluxes are influenced by the monsoons. The increase of productivity in the northern South China Sea is mainly due to northeast monsoon while in the central South China Sea the influence of southwest monsoon becomes more prominent. The annual primary production and export production calculated based on POC fluxes are 53 0-63 4 and 10 32-12 93 gC·m -2·a -1, respectively. The enhancement of POC flux during monsoon period suggest that higher palaeoproductivity or organic carbon accumulation rate in glacial age in the South China Sea might be the result of strengthening of the monsoons.
文摘Reservoirs are usually exposed to sediment accumulation problems that will lead to reduction in their storage capacity. This problem directly affects the performance of the dams and causes shortage of their useful life. The simplest technique to estimate sediment deposition rate is using sediment rating curve with sediment trapping efficiency (TE) of the reservoir. Many empirical and semi-empirical approaches have been suggested for to determine this term depending on the annual inflow rate, reservoir characteristics and features of the catchments area. In this study six different empirical methods depending on the residence time principle (water retention time) were used. These approaches were reviewed and applied to determine TE of Mosul dam reservoir (MDR) for period 1986 to 2011. The monthly operating data for inflow, outflow and water elevations for MDR were used to determine monthly TE and long-term TE for whole period of MDR using the mentioned methods. Furthermore, the monthly inflow rate for River Tigris upstream MDR, its sediment rating curve and sediment feeding from valleys around MDR were used to estimate the amount sediment coming to the reservoir. The results provided by these methods for TE with sediment coming to MDR were used to compute the amount of sediment deposited in MDR on monthly bases during this period. The results obtained were evaluated using observed bathymetric survey data that had been collected in 2011 after 25 years of the operation of the dam. The results showed all the mentioned methods gave convergent results and they were very close to bathymetric survey results for estimating the volume of sediment deposited especially that proposed by Ward which gave 0.368% percentage error. Furthermore, the result computed using monthly TE gave good agreement if compared with that long-term TE where the percentage error was ranging between –3.229% to 1.674% for monthly adopted data and –4.862% to?–2.477% for whole period data. It is believed that this work will help others to use this procedure on other reservoirs.
基金PLANEX,Physical Research LaboratoryISRO-Space Application center,Ahmedabad for financial supportingsupported by the CSIR-Emeritus Scientist project sanctioned to O.P.Pandey
文摘A rare occurrence of a microspherule has been found in the infratrappean sediments,encountered below338 m thick Deccan volcanic cover in KLR-1 scientific borehole,drilled in the epicentral zone of the 1993 Killari earthquake(Maharashtra,India).Palynological studies of the sediments indicate their age as Early Permian(Asselian,298-295 Ma) for deposition.Transmission electron microscope studies reveal that the spherule from the infratrappeans,is having a similar composition to that of the Neoarchean amphibolite to granulite facies mid crustal basement.The spherule is non-spherical in nature,containing mostly FeO(10.70±0.20 wt.%),CaO(13.8±0.5 wt.%),Al203(7.78±0.30 wt.%),MgO(6.47±0.3 wt.%),Si02(47,46±0.50 wt.%),Ti02(2.47±0.3 wt.%).K20(1.89±0.20 wt.%).and Cl(0.33±0.05 wt.%).Since the Fe composition of the spherule is almost same as the basement rock(10.5 wt.%),and the chlorine content is also in the same range as the basement(0.04-0.24 wt.%),it would suggest possibility of an extraterrestrial impact over the Indian terrain during the erstwhile Gondwana sedimentation period that may be associated with the Permian-Triassic mass extinction,the most severe one in the Earth's history.
基金financial support were provided by the Disaster Prevention Research Center, National Cheng Kung University
文摘The purpose of this study is to investigate the control function and mechanisms of natural river notches. Physical and numerical experiments are analyzed in this study for two representative types of sediment events： high intensity and short duration Type A sediment disaster events, and low intensity and long duration Type B moderate non-disaster events. Two dimensionless parameters, sediment trapping rate and reduction rate of peak sediment transport, are defined to evaluate the sediment control function of river notches. Study results indicate that the contraction ratio of the notch has a significant influence on sediment control function, with high contraction ratios resulting in both high sediment-trapping and high reduction rates. River notches provide better sediment control during Type A events than Type B events. The sediment control mechanism of river notches is the result of multiple interactions among river flow, sediment transport, and riverbed variation. Analysis of these interactions supports the significant protection role of river notches on sediment control for disaster events.
文摘Illegal deforestation changes in land use and climate change have resulted in increased runoff and surface erosion from the upper areas of watersheds, affecting directly the lower lands where human settlements are common. Such is the case of Angangueo in the state ofMichoacam, Mexico, where in 2010 an unusual weather event caused substantial damage to infrastructure, and unfortunately human deaths. Against disasters, the government has carried out actions such as implementing infrastructure to alleviate flooding and mudslides. Gabions dams were used to control erosion and runoff, as they are considered environmentally friendly as compared to most of the constructed impermeable weirs. This study was carried out to evaluate the effectiveness of gabions dams in sediment retention in a small watershed East of Michoacan. Eight gabions dams and five masonry dams two years after of construction were studied. The results indicated that the gabions dams retained less gravel than masonry dams, more sand, but no significant differences were found for fine sediments. Regarding the efficiency of gabions dams, there were not identified relationships since the building volume and contribution area is different in each one of them.
基金supported by the Nationnal Natural Science Foundation of China (Grant No.50579036)the National High Technology Research and Development Program of China (863 Program, Grant No.2007AA09Z312)
文摘A new patent registered device- suspended flexible curtain （SFC） for sedimentation enhancement is proposed in this paper, which consists of two parts： a light-weight curtain with sediment-passing windows and a heavy pillar for the device stability. The mechanism of trapping nearbed sediment by the SFC is such that a primary and a secondary circulations with horizontal hubs would be formed at the leeside when it is placed on beds in running flow; the velocities within the sediment-passing windows are locally accelerated, the nearbed sediments would be brought by the flow through the windows, and then settled down within the primary circulation zone. Experimental tests on hydraulic characteristics are conducted in a laboratory flume with rigid bed. It is found that the dimensions of the curtain and the sediment-passing windows determine the characteristics of the primary and the secondary circulations. The intensity of the primary and the secondary circulations is dominated by the size of the sediment-passing window. Whether the secondary circulation would contact the bed or not depends on the level of the sediment-passing window. The length and the height of the primary circulation zone demonstrate quasi linear relationships with the effective height of the SFC. And the tests on sandy bed flume show that the sediment deposition happens just in the primary circulation zone.
文摘Earlier investigators have numerically carried out performance analysis of the invert trap fitted in an open channel using the stochastic discrete phase model(DPM) by assuming the open channel flow to be closed conduit flow under pressure and assuming zero shear stress at the top wall.This is known as the fixed lid model.By assuming the top wall to be a shear free wall,they have been able to show that the velocity distribution looks similar to that of an open channel flow with zero velocity at the bottom and maximum velocity at the top,representing the free water surface,but no information has been provided for the pressure at the free water surface.Because of this assumption,the validation of the model in predicting the trap efficiency has performed significantly poorly.In addition,the free water surface subject to zero gauge pressure cannot be modeled using the fixed lid model because there is no provision of extra space in the form of air space for the fluctuating part of the water surface profile.It can.however,be modeled using the volume of fluid(VOF) model because the VOF model is the appropriate model for open channel or free surface flow.Therefore,in the present study,three-dimensional(3D) computational fluid dynamics(CFD) modeling with the VOF model,which considers open channel flow with a free water surface,along with the stochastic DPM.was used to model the trap efficiency of an invert trap fitted in an open rectangular channel.The governing mathematical flow equations of the VOF model were solved using the ANSYS Fluent 14.0 software,reproducing the experimental conditions exactly.The results show that the 3D CFD predictions using the VOF model closely fit the experimental data for glass bead particles.
基金The National Key Research and Development Program of China under contract No.2022YFE0136500the Scientific Research Fund of the Second Institute of Oceanography,Ministry of Natural Resources,under contract Nos JG2212 and JG2211+2 种基金the National Natural Science Foundation of China under contract Nos 42276255,41976228,and 42176227the National Polar Special Program“Impact and Response of Antarctic Seas to Climate Change”under contract Nos IRASCC 01-01-02 and IRASCC 02-02the China Scholarship Council under contract No.201704180017.
文摘The melting of seasonal sea ice in Antarctica plays a pivotal role in the region’s carbon cycle,influencing global carbon storage and the exchange of carbon between the atmosphere and the ocean.However,the impact of variability in the timing of seasonal sea ice retreat on the flux and composition of sinking particulate matter remains to be elucidated.In this study,we deployed sediment traps in Prydz Bay during the austral summers of 2019/2020 and 2020/2021,noting that sea ice melting occurred approximately one and a half months earlier in the former summer compared to the latter.We analyzed sediment trap data,which included total mass flux(TMF),particulate organic carbon(POC),biogenic silica(BSi),particulate inorganic carbon,and lithogenic particle(Litho)fluxes,as well as the stable isotopesδ^(13)C andδ^(15)N of particulate organic matter(POM).Additionally,we incorporated remote sensing data on sea ice concentration and chlorophyll a.This dramatic delay in sea ice melting timing could result in a significant increase in TMF,BSi and POC fluxes in the summer of 2020/2021 compared to 2019/2020.Elevated BSi fluxes and more ^(13)C-depleted POC in the austral summer of 2020/2021 suggest that the delayed melting of sea ice may have stimulated the productivity of centric diatoms.Furthermore,the higher BSi/POC ratio and more negativeδ^(15)N values of POM,along with a reduced presence of krill in the traps,indicate a diminished grazing pressure from zooplankton,which collectively enhanced the sedimentation efficiency of POC during the austral summer of 2020/2021.These findings highlight the critical role of sea ice melting timing in regulating productivity,flux and composition of sinking particulate matter in the Prydz Bay ecosystem,with significant implications for carbon cycling in polar oceans.
