The age of alluvial fan deposition at a site in the southern uplands of scotland

The age of a large alluvial fan debouching onto the valley floor of the River Tweed, in southern Scotland, and the sequence of events relating to this, are investigated using geomorphological, sedimentological, palynological, archaeological and radiocarbon dating evidence. Prior to fan deposition, the Tweed valley floor seems to have been covered by a wooded peat at a time of low fluvial activity. The fan commenced deposition in the 11th century AD, and appears to have been a local event, the Tweed showing no response to this accelerated sedimentation. Later, perhaps 200 years later, the Tweed commenced overbank deposition of the only Flandrian terrace preserved. Local proxy data are examined in order to define the causes of these events, but difficulties in temporal correlation, despite the good resolution of the radiocarbon chronology, mean that the causes of these events remain unknown.     

The stratigraphy of flandrian relative sea-level changes at a site in tayside,Scotland

Peat deposits in a gully at the inland margin of the Firth of Tay carselands contain a transgressive wedge of estuarine sediments laid down at the culmination of the Main Postglacial Transgression. In previous work, the sequence of deposits in the gully and their age have been examined at one location. The present study both extends and evaluates that previous work, employing further field work and laboratory analyses. The detailed stratigraphy of the deposits is identified, whilst from a borehole close to the limit of the transgressive deposit, diatom analysis and geochemical analyses, involving the determination of Al, Mg, C, and δ ¹³C_PDB are outlined. Eight ¹⁴C assays from peat at the transgressive and regressive contacts in four boreholes along the wedge of estuarine sediments are described. Whilst the results of diatom analysis are inconclusive, the geochemical analyses indicate that the sediment accumulated broadly continuously without major changes in the depositional environment. It is concluded that the Main Postglacial Transgression in the gully was at first rapid, then slowed and culminated between 6240 ± 80 and 6030 ± 80 (or 6170 ± 90) radiocarbon years, B.P. It is subsequently maintained that the geochemical analyses described here may be of value in determining the continuity of transgressive deposits, whilst the practice of obtaining multiple radiocarbon assays at such locations should enable assessment of age to be refined. This may in turn assist in testing the hypothesis of shoreline diachroneity in glacioisostatically affected areas.     

Holocene valley aggradation driven by river mouth progradation: examples from Australia

Since the end of the post‐glacial sea level rise 6800 years ago, progradation of river mouths into estuaries has been a global phenomenon. The responses of upstream alluvial river reaches to this progradation have received little attention. Here, the links between river mouth progradation and Holocene valley aggradation are examined for the Macdonald and Tuross Rivers in south‐eastern Australia. Optical and radiocarbon dating of floodplain sediments indicates that since the mid‐Holocene sea level highstand 6800 years ago vertical floodplain aggradation along the two valleys has generally been consistent with the rate at which each river prograded into its estuary. This link between river mouth progradation and alluvial aggradation drove floodplain aggradation for many tens of kilometres upstream of the estuarine limits. Both rivers have abandoned their main Holocene floodplains over the last 2000 years and their channels have contracted. A regional shift to smaller floods is inferred to be responsible for this change, though a greater relative sea level fall experienced by the Macdonald River since the mid‐Holocene sea level highstand appears to have been an additional influence upon floodplain evolution in this valley. Copyright © 2006 John Wiley & Sons, Ltd.     

Initiation of a multiple peat slide on Cuilcagh Mountain,Northern Ireland

In October 1998 a multiple peat slide occurred on the northern slopes of Cuilcagh Mountain, Co. Fermanagh, in response to a high‐magnitude rainfall event. Few peat slides have been recorded in Ireland, and a detailed field survey and investigation of the failure was undertaken within four weeks of the event. The morphological evidence indicated a distinct sequence of events which appeared to begin with the failure of a small segment of slope above a degraded transverse drainage ditch which was cut less than ten years previously. This segment of slope was no more than 42 m wide and 25 m long, with 0·7 m of peat overlying up to 0·5 m of a pale coloured clay, the latter containing small pipes and resting on the surface of a darker coloured loamy material. The failure surface was located at or near the base of the pale clay layer. Finite element software was used to model hydrological conditions within the upper segment of slope and to calculate factors of safety for different slope configurations including the presence or absence of a drain or a subsurface pipe. Using the peak shear strength of the pale clay, as determined in the laboratory, both the drain and subsurface pipes were required to obtain a factor of safety of 1·0 or less. Allowing for the uncertainties associated with the hydrological modelling of the pipes, it is suggested that the cutting of the drain and the hydrological impacts of its subsequent degradation are ultimately responsible for the failure. Copyright © 2001 John Wiley & Sons, Ltd.     

Contribution of climatic and anthropogenic effects to the hydric deficit of peatlands

The present study makes use of a detailed water balance to investigate the hydrological status of a peatland with a basal clay‐rich layer overlying an aquifer exploited for drinking water. The aim is to determine the influence of climate and groundwater extraction on the water balance and water levels in the peatland. During the two‐year period of monitoring, the hydrological functioning of the wetland showed a hydric deficit, associated with a permanent unsaturated layer and a deep water table. At the same time, a stream was observed serving as a recharge inflow instead of draining the peatland, as usually described in natural systems. Such conditions are not favourable for peat accumulation. Field investigations show that the clay layer has a high hydraulic conductivity (from 1·10^?7 to 3·10^?9 m.s^?1) and does not form a hydraulic barrier. Moreover, the vertical hydraulic gradients are downward between the peat and the sand aquifer, leading to high flows of groundwater through the clay layer (20–48% of the precipitation). The observed hydric deficit of the peatland results from a combination of dry climatic conditions during the study period and groundwater extraction. The climatic effect is mainly expressed through drying out of the peatland, while the anthropogenic effect leads to an enhancement of the climatic effect on a global scale, and a modification of fluxes at a local scale. The drying out of the peatland can lead to its mineralisation, which thus gives rise to environmental impacts. The protection of such wetlands in the context of climate change should take account of anthropogenic pressures by considering the wetland‐aquifer interaction. Copyright © 2011 John Wiley & Sons, Ltd.     

Morphology and modern sedimentary deposits of the macrotidal Marapanim Estuary (Amazon,Brazil)

The northern Brazilian coast, east of the Amazon River is characterized by several macrotidal estuarine systems that harbor large mangrove areas with approximately 7600 km². The Marapanim Estuary is influenced by macrotidal regime with moderate waves influence. Morphologic units were investigated by using remote sensing images (i.e., Landsat-7 ETM+, RADARSAT- 1 Wide and SRTM) integrated with bathymetric data. The modern sedimentary deposits were analyzed from 67 cores collected by Vibracore and Rammkersonde systems. Analysis of morphology and surface sedimentary deposits of the Marapanim River reveal they are strongly influenced by the interaction of tidal, wave and fluvial currents. Based on these processes it was possible to recognize three distinct longitudinal facies zonation that revels the geological filling of a macrotidal estuary. The estuary mouth contain fine to medium marine sands strongly influenced by waves and tides, responsible for macrotidal sandy beaches and estuarine channel development, which are characterized by wave-ripple bedding and longitudinal cross-bedding sands. The estuary funnel is mainly influenced by tides that form wide tidal mudflats, colonized by mangroves, along the estuarine margin, with parallel laminations, lenticular bedding, root fragments and organic matter lenses. The upstream estuary contains coarse sand to gravel of fluvial origin. Massive mud with organic matter lenses, marks and roots fragments occur in the floodplain accumulates during seasonal flooding providing a slowly aggrading in the alluvial plain. This morphologic and depositional pattern show easily a tripartite zonation of a macrotidal estuary, that are in the final stage of filling.     

既有地下结构用于地铁工程的可行性研究(I)

7381工程是70年代初哈尔滨市按照当时地铁限界标准修建的一条地下人防工程。隧道穿越粉质粘土、细砂土层,埋深10～20米。为了评价7381工程现在用于地铁运营的安全性,本文从结构承载能力、构造、变形和裂缝等方面进行了详细检测,主要内容包括混凝土强度、混凝土碳化、混凝土表面裂缝、钢筋强度及锈蚀、隧道衬砌拱顶厚度等,检测结果为旧隧道的安全性与使用性评价奠定了基础。     

Sequential radiocarbon measurement of bulk peat for high-precision dating of tsunami deposits

Dates of tsunami deposits have been used to estimate paleotsunami recurrence intervals in areas affected by these natural events. The depositional age of tsunami deposits is commonly constrained by the radiocarbon (¹⁴C) dating of sediments above and below the geological event. However, because of calibration curve fluctuations, the depositional age sometimes has a wide error range. In this study, we conducted millimeter-scale high-resolution radiocarbon measurements of tsunami deposits at Urahoro in southern Hokkaido, Japan. The site faces the Pacific Ocean along the Kuril Trench. Eight event deposits were identified within peat at this site. We took sequential measurements for ¹⁴C dating using bulk peat samples. The results were validated based on comparison with the absolute and radiometric ages of tephra layers. Dating results were further constrained by stratigraphic order using statistical methods. We constrained the depositional age of the paleotsunami deposits better using this method than we did when using conventional methods. We proposed an efficient measurement strategy with respect to the radiocarbon calibration curve. This method is also applicable for other deposits formed by any natural hazard if bulk peat is obtainable so it can contribute to better hazard assessment worldwide.     

闽南沿海晚更新世地层的初步研究

本文对闽南沿海晚更新世沉积的分布特征和主要的地层剖面进行了描述,并根据野外沉积与地貌观察及~(14)、微体古生物与孢粉分析资料,对上述地层与沉积的年代、成因与古气候状况进行了分析与讨论     

Research on Dynamic Parameters of Soil Site in the Tianjin Coastal Area

The Tianjin coastal area is a typical soft soil region,where the soil is a marine deposit of the late Quaternary.The soil dynamic parameters from seismic risk assessment reports are collected,and drilling of 15 holes was carried out to sample the soils and measure their dynamic characteristics.The data was divided into 7 types based on lithology,namely,muddy clay,muddy silty clay,silt,silty clay,clay,silty sand and fine sand.Statistics of the dynamic parameters of these soils are collected to obtain the mea...     

Mid‐Holocene sub‐blanket‐peat alluvia and sediment sources in the upper Liffey valley,Co. Wicklow,Ireland

A recently exposed section across a ?rst‐order valley buried beneath the regional blanket peat on hillside slopes in the upper Liffey valley, Co. Wicklow, is described. The section shows two alluvia within a shallow valley form underlain by an extensive boulder and stone line over regional till and weathered granite. ¹⁴C dates from wood in the alluvia indicate the older alluvium to have formed between 4324 ± 53 BP and 4126 ± 45 BP and the younger between 3217 ± 53 BP and 2975 ± 53 BP . The basal layer of the overlying peat yielded a date of 2208 ± 61 BP . The younger alluvium shows the effects of soil paludi?cation prior to the peat expansion. Dated pollen analyses elsewhere in the upper catchment con?rm the spread of blanket peat over most areas above 350 m after 4000–3600 BP . The buried valley was contributing sediments to the mid‐Holocene ?oodplains in the upper Liffey valley prior to the extension of blanket peat over the catchment after which sediment yields from it and the other catchment slopes declined. Copyright © 2003 John Wiley & Sons, Ltd.     

Upper Pleistocene‐Holocene geomorphic changes dictating sedimentation rates and historical land use in the valley system of the Chifeng region,Inner Mongolia,northern China

This study focuses on the late Quaternary landscape evolution in the Chifeng region of Inner Mongolia, China, its relations to the history of the Pleistocene‐Holocene loess accumulation, erosion and redeposition, and their impact on human occupation. Based on 57 optically stimulated luminescence (OSL) ages of loess sediments, fluvial sand and floodplain deposits accumulated on the hill slopes and floodplains, we conclude that during most of the Pleistocene period the region was blanketed by a thick layer of aeolian loess, as well as by alluvial and fluvial deposits. The loess section is divided into two main units that are separated by unconformity. The OSL ages at the top of the lower reddish loess unit yielded an approximate age of 193 ka, roughly corresponding to the transition from MIS 7 to 6, though they could be older. The upper gray loess unit accumulated during the upper Pleistocene glacial phase (MIS 4–3) at a mean accumulation rate of 0·22 m/ka. Parallel to the loess accumulation on top of the hilly topography, active fans were operating during MIS 4–2 at the outlet of large gullies surrounding the major valley at a mean accumulation rate of 0·24 m/ka. This co‐accumulation indicates that gullies have been a long‐term geomorphic feature at the margins of the Gobi Desert since at least the middle Pleistocene. During the Holocene, the erosion of the Pleistocene loess on the hills led to the burial of the valley floors by the redeposited sediments at a rate that decreases from 3·2 m/ka near the hills to 1–0·4 m/ka¹ in the central part of the Chifeng Valley. This rapid accumulation and the frequent shifts of the courses of the river prevented the construction of permanent settlements in the valley floors, a situation which changed only with improved man‐made control of the local rivers from the tenth century AD. Copyright © 2010 John Wiley & Sons, Ltd.     

Spatial and temporal variations of nutrient concentration in the groundwater of a floodplain: effect of hydrology,vegetation and substrate

Spatio‐temporal variations in nitrogen and phosphorus concentrations in groundwater were analysed and related to the variations in hydrological conditions, vegetation type and substrate in an alluvial ecosystem. This study was conducted in the Illwald forest in the Rhine Plain (eastern France) to assess the removal of nutrients from groundwater in a regularly flooded area. We compared both forest and meadow ecosystems on clayey‐silty soils with an anoxic horizon (pseudogley) at 1·5–2 m depth (eutric gley soil) and a forest ecosystem on a clayey‐silty fluviosoil rich in organic matter with a gley at 0·5 m depth (calcaric gley soil). Piezometers were used to measure the nutrient concentrations in the groundwater at 2 m depth in the root layer and at 4·5 m depth, below the root layer. Lower concentrations of nitrate and phosphate in groundwater were observed under forest than under meadow, which could be explained by more efficient plant uptake by woody species than herbaceous plants. Thus NO₃‐N inputs by river floods were reduced by 73% in the shallow groundwater of the forested ecosystem, and only by 37% in the meadow. Compared with the superficial groundwater layer, the lowest level of nitrate nitrogen (NO₃‐N) and the highest level of ammonium nitrogen (NH₄‐N) were measured in the deep layer (under the gley horizon at 2·5 m depth), which suggests that the reducing potential of the anoxic horizon in the gley soils contributes to the reduction of nitrate. Nitrate concentrations were higher in the groundwater of the parcel rich in organic matter than in the one poorer in organic matter. Phosphate (PO₄‐P) concentrations in both shallow and deep groundwater are less than 62 to 76% of those found in surface water which can be related to the retention capacity of the clay colloids of these soils. Moreover, the temporal variations in nutrient concentrations in groundwater are directly related to variations in groundwater level during an annual hydrological cycle. Our results suggest that variations in groundwater level regulate spatio‐temporal variations in nutrient concentrations in groundwater as a result of the oxidation–reduction status of soil, which creates favourable or unfavourable conditions for nutrient bioavailability. The hydrological variations are much more important than those concerning substrate and type of vegetation. Copyright © 1999 John Wiley & Sons, Ltd.     

Quantitative relationships between uplift and relief parameters for the Southern Alps,New Zealand,as determined by fission track analysis

The Southern Alps mountain chain, New Zealand, has formed as a consequence of late Cenozoic collision of the continental parts of the Pacific and Australia plates. Fission track analysis has yielded estimates of the amount, age of initiation, and rate of late Cenozoic rock uplift for 82 surface samples taken from transects across the Southern Alps. The mean surface, summit and valley elevations in the vicinity of each of the rock sample sites have also been measured. Regression of the geomorphic variables on the uplift variables has been used to establish quantitative relationships between uplift and geomorphology. There are strong and consistent linear associations between uplift and the elevations of the mean surface, summits and valleys. The preferred regression models have uniform slope but varying elevation response between transects. Substitution of space for time has allowed the evolution of landforms to be studied. To the east of the Main Divide, elevation and relief are proportional to, and closely related to, the age of initiation of rock uplift (‘uplift age’) and the amount of rock uplift (r² > 0·8). Mean surface uplift was delayed for ～2 Ma after the start of rock uplift, a result of the stripping of a soft cover rock succession that, prior to rock uplift, overlaid the harder greywacke basement. Inter-transect variations in regression response and x-intercept are inferred, therefore, to reflect the variable preuplift thickness of cover rocks. However, the regular regression slope for the transects reflects the consistent nature of the interaction between uplift and the erodibility of greywacke basement. Uplift of the mean surface proceeded at 0·4 km/km and 0·4 km/Ma of rock uplift, while the rock uplift rate was 0·8 km/Ma. Summit elevations have increased at a rate of 0·6 km/Ma and valley elevations have increased at 0·2 km/Ma. Regression lines relating mean surface, summit and valley elevations to rock uplift and uplift age diverge from common intercepts; it is concluded, therefore, that the mountains east of the Main Divide have continued to increase in elevation and relief and change in form over time since the start of mean surface uplift. Mountain elevation has little relationship with late Cenozoic mean rock uplift rates of 0·8–1·0 km/Ma or inferred contemporary rock uplift rates (r² ～ 0·3). In contrast, to the west of the Main Divide, elevation is shown to be closely related to rock uplift rate (r² > 0·3). In contrast, to the west of the Main Divide, elevation is shown to be closely related to rock uplift rate (r² > 0·8). Transects with higher rock uplift rates support higher topography. Landforms are therefore in a stable equilibrium with rock uplift rate, and the landscape contains no residual evidence of the total amount of rock uplift, or the age of uplift. Lithological variation appears to have no relationship with elevation.     

Simulations of water movement and solute transport through different soil texture configurations under negative‐pressure irrigation

This study examined the effects of different soil texture configurations on water movement and solute transport to provide a reliable scientific basis for the application of negative‐pressure irrigation (NPI) technology. HYDRUS‐2D was used to analyse water movement and solute transport under NPI. The main results are as follows: (a) HYDRUS‐2D can be used to simulate water movement and solute transport under NPI, as there was good agreement between the simulated and measured values for water contents, NaCl concentrations, cumulative water infiltration, and wetting distances in the horizontal and vertical directions; the Nash–Sutcliffe efficiency coefficients were in the range of 0.94–0.97. (b) Layered soils have obvious effects on water movement under NPI. With the emitter position in the loam layer, when a coarse texture of loamy sand was present below the loam layer (namely, L‐LS), irrigation water accumulated in the topsoil, and this led to an increase in evaporation compared with the homogeneous loam profile. However, fine texture silty loam or silty clay loam layers beneath the loam layer (namely, L‐SiL or L‐SiCL, respectively) was more conducive to water infiltration into the lower layer, and this increased the amount of water infiltration and simultaneously reduced the surface evaporation effectively. (c) Layered soils have obvious effects on solute transport under NPI, and salt accumulation will readily occur in the clay‐rich soil layer at the interface. The maximum soil salt accumulation of L‐LS occurred above the soil interface between the two soil layers with a value of 21.80 g/kg; however, for L‐SiCL and L‐SiL, the maximum salt accumulation occurred below the soil interface between the two soil layers, with values of 23.80 g/kg and 20.08 g/kg, respectively. (d) Interlayered soils showed remarkable changes in the water infiltration characteristics and salt‐leaching intensities under NPI, and the properties for the soil profile with a silty loam interlayer were better than those for the soil profile with a silty clay loam interlayer. The soil profile with a loamy sand interlayer had the lowest amount of water infiltration, which resulted in reductions of the salt‐leaching intensities. Thus, NPI is clearly not suitable for loamy sand soil. Overall, the results demonstrated that soil texture configurations affected water movement and solute transport under NPI. Therefore, careful consideration should be given to the use of NPI to achieve target soil water and solution conditions and reduce water loss.     

Estuarine Habitat Assessment for Construction of a Submarine Transmission Line

The present paper describes a submarine survey using the acoustic discrimination system QTC VIEW (Series V) as an exploratory tool to adjust final route alignment of a new pipeline. By using acoustic sound survey as an exploratory tool described in this paper to adjust final route alignment of a new pipeline to minimize the environmental impact caused and ultimately to avoid any mitigation measures. The transmission pipeline extended from the shore line of Abu-Qir Bay, on the Mediterranean Sea in Egypt, out to 70 nautical miles at sea (60 m water depth). Four main surface sediment types were defined in the study area, namely fine sand, silty sand, silt and clay. Results of the acoustic classification revealed four acoustic classes. The first acoustic class corresponded to fine sand, absence of shell debris and very poor habitats characteristics. The second acoustic class is predominant in the study area and corresponds to the region occupied by silt. It is also characterized by intermediate diversity of macrobenthic invertebrate community which is mainly characterized by polychaeta. The third acoustic class is characterized by silt to silty clay. It is characterized by a high diversity of macrobenthic invertebrate community which is mainly polychaeta with an intermediate diversity of gastropoda and bivalvia. The final acoustic class is characterized by clay and high occurrence of shell debris of gastropoda, bivalvia and polychaeta.     

Allogenic and autogenic effects on mangrove dynamics from the Ceará Mirim River,north‐eastern Brazil,during the middle and late Holocene

It is possible that climate changes and sea level fluctuations (allogenic processes) are and will cause major changes in mangrove dynamics. However, other driving forces may be significantly affecting this system. Distinguishing allogenic and autogenic influence on mangroves is a challenging question, because mechanisms related to the natural dynamics of depositional environments (autogenic processes) have strong influences on the establishment and degradation of mangroves. Thus, impacts on mangroves caused by autogenic processes may be erroneously attributed to allogenic mechanisms. Therefore, it is imperative to identify the ‘fingerprint’ of global changes in modern mangrove dynamics. In order to characterize the influence of these forces on mangroves, this work has used geomorphology and vegetation maps integrated with sedimentological and palynological data, radiocarbon dating, as well as δ¹³C, δ¹⁵N and C/N from sedimentary organic matter. The inter‐proxy analyses reveal an estuarine influence with mangrove development along the Ceará Mirim River, north‐eastern Brazil, since ~6920 cal yr bp , after the post‐glacial sea level rise. Relative sea level (RSL) has been stable during the middle and late Holocene. Mangrove establishment along this fluvial valley begins at about 6920 cal yr bp , caused by the sea‐level stabilization, an allogenic influence. However, after its establishment, wetland dynamics were mainly controlled by autogenic factors, related to channel migrations, instead of allogenic process. Some influence of sea‐level and climate changes on mangrove dynamics in this estuarine channel have been weakened by more intense tidal channels activities. Therefore, the expansion and contraction of mangrove areas along the estuary of the Ceará Mirim River since 6920 cal yr bp has been mainly influenced by channel dynamics that regulate the accretion and erosion of mangrove substrates. Copyright © 2018 John Wiley & Sons, Ltd.     

A field study of estuarine pollution in Madras,India

A field study has been made of the quality of water in three estuaries in Madras, India, receiving a variety of human and industrial wastes. Among the three estuaries, the Buckingham canal is grossly polluted with no surface flow. The Cooum estuary, though grossly polluted, because of the flow and flushing into the sea may be recovered if precautions are taken. The Ennore estuary, with a large volume of water flowing, has a peculiar problem at the mouth due to continuous formation of a sand bar due to long-shore currents. This sand bar prevents the flushing of the estuarine water. As a result, the pollutants discharged either in the estuary or in the sea accumulate at the mouth. This pollution, together with impaired self-purification of the estuary, resulted in a decrease in fish production.     

黄土微观参数指标与阻尼比关联度研究

对岷县地震台、庆阳黄土塬2~12m深度土层的粉土、粉质黏土样品,利用室内动三轴试验和扫描电镜试验,测定阻尼比和微观结构特征,研究了粉土、粉质黏土的阻尼比随深度的变化及应力应变关系,采用灰色关联度方法,分析了黄土竖向（沉积方向）和横向（垂直于沉积方向）的微观结构参数对阻尼比影响的主次关系及其权重。研究结果表明:小应变下,粉土和粉质黏土阻尼比随着深度的增加而减小;粉土和粉质黏土的微观参数与阻尼比有一定的关联性,粉土竖向的微观参数对阻尼比的影响较为敏感;粉质黏土横向的微观参数对阻尼比的影响更加敏感;影响权重方面,粉质黏土的平均形状系数影响权重最大,对阻尼比的影响最大;粉土的平均形状系数、分形维数和概率熵影响权重最大,对阻尼比影响最敏感。平均面积无论在关联度还是影响权重方面对阻尼比影响最小,该结论粉土与粉质黏土保持一致。     

Numerical determination of residence time and age in a partially mixed estuary using three-dimensional hydrodynamic model

This paper documents a numerical modeling study to calculate the residence time and age of dissolved substances in a partially mixed estuary. A three-dimensional, time-dependent hydrodynamic model was established and applied to the Danshuei River estuarine system and adjacent coastal sea in Taiwan. The model showed good agreement with observations of surface elevation, tidal currents and salinity made in 2002. The model was then applied to calculate the residence time and age distribution response to different freshwater discharges with and without density-induced circulations in the Danshuei River estuarine system. Regression analysis of model results reveals that an exponential equation can be used to correlate the residence time to change of freshwater input. The simulated results show it takes approximately 10, 4.5, and 3 days, respectively, for a water parcel that has entered the headwaters of the estuary to be transported out of the estuary under low, mean, and high flow conditions with density-induced circulation. The calculated age with density-induced circulation is less than that without density-induced circulation. The age of the surface layer is less than that at the bottom layer. Overall the study shows that freshwater discharges are the important factors in controlling the transport of dissolved substances in the Danshuei River estuarine system.