Evaluation of the contamination of platinum in estuarine and coastal sediments (Tagus Estuary and Prodelta, Portugal)

Platinum contamination in estuarine and coastal sediments has been evaluated in three cores collected from the Tagus Estuary and Prodelta shelf sediments. Elevated concentrations, up to 25-fold enrichment compared to background values, were found in the upper layers of the estuarine sediments. The degree of Pt enrichment in the estuarine sediments varied depending on the proximity to vehicular traffic sources, with a maximum concentration of 9.5 ng g⁻¹. A considerable decrease of Pt concentrations with depth indicated the absence of significant contamination before the introduction of catalytic converters in automobiles. Platinum distribution in the Tagus Prodelta shelf sediment core showed no surface enrichment; instead a sub-surface maximum at the base of the mixed layer suggested the possibility of post-depositional mobility, thereby blurring the traffic-borne contamination signature in coastal sediments.     

CLM4-LISSS模型对太湖多时间尺度水热通量模拟性能的评估

湖泊模型为数值天气预报模型提供热量通量、水汽通量和动量通量等下边界条件,但是不同时间尺度上湖泊水热通量变化的控制因子不同,因此有必要对湖泊模型进行多时间尺度上的离线评估.本文利用2012-2016年太湖中尺度通量网避风港站的气象资料和辐射数据驱动CLM4-LISSS模型(Community Land Model version 4-Lake,Ice,Snow and Sediment Simulator),并与涡度相关观测(Eddy Covariance,EC)结果进行对比,以年平均潜热通量模拟结果最佳为目标调整了模式中的消光系数、粗糙度长度方案,研究了该模型从半小时到年尺度上对湖表温度和水热通量的模拟性能.结果表明:模型对湖表温度的模拟在各时间尺度上均比较理想,但是模拟的日较差较小;从半小时到年尺度上潜热通量的变化趋势都能被很好地模拟出来,但在季节尺度上,潜热通量的模拟出现了秋冬季偏高、春夏季偏低的情况,季节变化模拟不准确.湖表温度和潜热通量模拟偏差的原因可能是消光系数的参数化方案.相比之下,感热通量尽管年际变化趋势的模拟值与观测值一致,但是从半小时到年尺度均被高估.特别地,冷锋过境期间,模型能较好地模拟出潜热通量和感热通量的变化趋势,但对于高风速条件下的感热通量模拟效果不佳.本文的研究结果能为湖泊模式的应用与发展提供有用信息.     

Links between saltwater intrusion and subtidal circulation in the Changjiang Estuary: A model-guided study

In this paper we discuss the links between saltwater intrusion and subtidal circulation in the Changjiang Estuary based on a 3D numerical model. We restricted our study mainly to the three major outlets of the estuary: the South Passage, the North Passage, and the North Channel. Subtidal transport is landward in the South Passage and NNW- or NW-ward on the shoals, whereas it is mainly seaward in the North Passage and North Channel. Such a residual characteristic is caused by the interaction between tide and shallow water depth. Decomposing analysis indicated that Stokes transport is the major mechanism causing this particular residual transport pattern. Under its influence, the South Passage is the most saline outlet and the North Channel is the major route discharging the Changjiang runoff. Results of a tracer experiment indicated that active water mass exchange occurs from the South Passage to the North Passage and finally to the North Channel. Thus, the salinity in each outlet is determined not only by the tidal-averaged diversion ratio around the bifurcation of the South and North Channels but also by the subtidal circulation in the waterways and on the shoals. The northerly wind produces a horizontal circulation around the river mouth, which flows into the estuary in the North Channel and out of the estuary in the South Channel and South Passage. This circulation increases the salinity in the North Channel and decreases it in the South Passage. Recent engineering projects have intensified the landward residual in the South Passage, thereby increasing the salinity in the South Passage and decreasing the salinity in the North Channel.     

Study of water renewal and sedimentation of a square harbor encapsulated in a coastal front with seawalls due to wind-induced hydrodynamic circulation

In the current study in the middle of a coastal zone,a harbor basin in the form of a square area recessed to the front is considered.A breakwater of variable length and position offers protection from waves.The water renewal time and the self-purification capacity of the harbor under the influence of alongshore currents due to wind-induced water circulation of varying intensities were examined.Furthermore,the transport of particulate matter released from the upstream side of the coastal zone and the possible influence(via sedimentation)on the lateral basin was investigated.The current study was based on the use of a two-dimensional depth-averaged hydrodynamic model and a quasi-three-,dimensional transport model while the effect of partial closing of the harbor's entrance was examined.The(1)adjustment and(2)validation of the reliability of the numerical model at a laboratory level were done using a recent research based on the use of a particle image velocimetry(PIV)measurements ensuring very good agreement between numerical and experimental results.The current study showed that the partial closing of the opening between the harbor basin and the extended coastal zone,with a breakwater of length equal to 1/3 of the opening,seems to be the most acceptable technical solution.     

Equilibrium and time scales in geomorphology: Application to sand-bed alluvial streams

Equilibrium is defined as a single-valued, temporally invariant functional relationship between the values of an output variable and the values of the input variable(s) in a geomorphic system. Disequilibrium occurs if the output deviates from the functional relationship by more than a consensual degree. Natural geomorphic variables are characterized by a relaxation time. Output variables are insensitive to cyclical inputs with frequencies much greater than the relaxation time, but can respond completely for sufficiently low frequencies. Rapid trends, recent step changes or pulse inputs, and intermediate frequency inputs can cause disequilibrium. The gradient of sand-bed alluvial channels (the output variable) is determined by sediment and water delivery from slopes (the input variables), and changes in this hydraulic regime require regrading by erosion and deposition. Initial stages of adjustment to changed regime in a long, unbranched channel with sediment and water delivery only at the upstream end propagate downstream, but later stages of adjustment occur simultaneously throughout the reach. In a dendritic channel network the gradient responds rather uniformly throughout the network to changes in regime during all stages of adjustment. The time scale of adjustment to changed regime depends upon the size of the channel network (or stream length), the sediment and water discharges, and to a lesser degree upon the magnitude of the change. Grade as defined by Mackin (1948) is synonymous with equilibrium as used in this paper if ‘a period of years’ is replaced by ‘a time period commensurate with the relaxation time of the gradient’. The use of the term grade is best restricted to a single-valued relationship between channel gradient and the hydraulic regime.     

Transient oceanic and tidal contributions to water exchange and residence times in a coastal upwelling system in the NE Atlantic: the Pontevedra Ria, Galicia

An analysis of the intra-annual variability of hydrographic residence times, tau, is presented for the Pontevedra Ria--a large coastal system in NW Spain with a deep, unobstructed connection with the Atlantic Ocean. Ria-offshore water exchange and tau were quantified with an iterative approach to the fraction of freshwater method using 23 quasi-steady state water-salt budgets. Excluding prolonged flushing due to downwelling events at the end of the upwelling season, mean was 6 +/- 2 day in the central ria and 2 +/- 1 day in the internal ria. The tidal contribution, equal to 10-25% of total water renewal, was quantified for the first time for a Galician ria with the hydrodynamic model estuarine contaminant simulator (ECoS). The relationship between tau and residual freshwater input, Qz, was atypical, since Qz played a minor role in water exchange in comparison to periodic upwelling of East North Atlantic Central Water (ENACW) from the continental shelf mainly during spring and summer. During positive upwelling stress, the intrusion of ENACW into the ria produced enhanced flushing and tau < 4 day in the central ria and < 2 days in the internal ria. Under downwelling favourable conditions, water was retained and tau prolonged to >8 and >5 days, respectively. A quantitative parameterisation of tau with upwelling and Qz was weakly significant, due to the short-term variability in ria salinity. This paper elucidates problems associated with the use of water budgets to transient coastal systems such as the Pontevedra Ria.     

Decadal morphological evolution of the mouth zone of the Yangtze Estuary in response to human interventions

The morphology of the Yangtze Estuary has changed substantially at decadal time scales in response to natural processes, local human interference and reduced sediment supply. Due to its high sediment load, the morphodynamic response time of the estuary is short, providing a valuable semi-natural system to evaluate large-scale estuarine morphodynamic responses to interference. Previous studies primarily addressed local morphologic changes within the estuary, but since an overall sediment balance is missing, it remains unclear whether the estuary as a whole has shifted from sedimentation to erosion in response to reduced riverine sediment supply (e.g. resulting from construction of the Three Gorges Dam). In this paper we examine the morphological changes of two large shoals in the mouth zone (i.e. the Hengsha flat and the Jiuduan shoal) using bathymetric data collected between 1953 and 2016 and a series of satellite images. We observe that the two shoals accreted at different rates before 2010 but reverted to erosion thereafter. Human activities such as dredging and dumping contribute to erosion, masking the impacts of sediment source reduction. The effects of local human intervention (such as the construction of a navigation channel) are instantaneous and are likely to have already resulted in new dynamic equilibrium conditions. The morphodynamic response time of the mouth zone to riverine sediment decrease is further suggested to be >30 years (starting from the mid-1980s). Accounting for the different adaptation time scales of various human activities is essential when interpreting morphodynamic changes in large-scale estuaries and deltas. © 2019 John Wiley & Sons, Ltd.     

A Model of PCB Bioaccumulation in the Sea Bass Food Web from the Seine Estuary (Eastern English Channel)

A bioaccumulation model was developed to simulate the PCB contamination in the sea bass food web from the Seine Estuary. The model relies upon a contaminant mass balance budget for each biological species. Biological processes determine the extent of bioaccumulation: respiration and feeding rates control the uptake of contaminants whereas excretion, spawning, and growth act on the chemicals removal. A step-by-step modelling approach was followed. A first version was a steady-state model validated for the bioaccumulation processes. In the second version seasonal variation was taken into account, and finally in the third version, the model was coupled with a population dynamics model to describe PCB contamination in each age class.     

噪声HVSR法在OBS探测中的应用——以珠江口外海OBS台阵为例

噪声谱比法(horizontal-to-vertical spectral ratio, HVSR)通常用于确定沉积层的厚度, 而应用于海底地震仪(OBS)以获取海底沉积厚度的研究较少.本文将HVSR法应用于珠江口外海域OBS台阵中, 验证了该方法用于OBS探测中的可靠性.通过对珠江口外海27台OBS收集的三分量地震噪声记录进行处理, 得到了所有台站的HVSR曲线.有23台OBS的HVSR曲线可获取与沉积层厚度相关的峰值频率, 通过经验公式可以计算得到沉积层厚度.结果显示, 珠江口外海域沉积层(新生代地层)厚度范围为100~3500 m, 研究区东南部沉积层远厚于西北部, 且沉积厚度受到NEE向滨海断裂带控制.本文获得的结果与以往依靠反射地震剖面和钻井等获得的沉积层厚度结果基本一致.进一步分析发现研究区新生代地层具有多层结构, 大部分HVSR曲线在5~12 Hz存在振幅最大的波峰, 认为是与第四系厚度相关的峰值频率, 继而确定第四系厚度为20~50 m.本研究拓展了HVSR法的应用领域, 为获取海底沉积层厚度提供了一种新的可靠方法.

     

Thermocline characterisation in the Cariaco basin: A modelling study of the thermocline annual variation and its relation with winds and chlorophyll-a concentration

The spatial and temporal evolution of the thermocline depth and width of the Cariaco basin (Venezuela) is analysed by means of a three-dimensional hydrodynamic model. The thermocline depth and width are determined through the fitting of model temperature profiles to a sigmoid function. The use of whole profiles for the fitting allows for a robust estimation of the thermocline characteristics, mainly width and depth. The fitting method is compared to the maximum gradient approach, and it is shown that, under some circumstances, the method presented in this work leads to a better characterisation of the thermocline. After assessing, through comparison with independent in situ data, the model capabilities to reproduce the Cariaco basin thermocline, the seasonal variability of this variable is analysed, and the relationship between the annual cycle of the thermocline depth, the wind field and the distribution of chlorophyll-a concentration in the basin is studied. The interior of the basin reacts to easterly winds intensification with a rising of the thermocline, resulting in a coastal upwelling response, with the consequent increase in chlorophyll-a concentration. Outside the Cariaco basin, where an open ocean, oligothrophic regime predominates, wind intensification increases mixing of the surface layers and induces therefore a deepening of the thermocline. The seasonal cycle of the thermocline variability in the Cariaco basin is therefore related to changes in the wind field. At shorter time scales (i.e. days), it is shown that other processes, such as the influence of the meandering Caribbean current, can also influence the thermocline variability. The model thermocline depth is shown to be in good agreement with the two main ventilation events that took place in the basin during the period of the simulation.     

Reactivity of transparent exopolymeric particles: A key parameter of trace metal cycling in the lagoon of Nouméa, New Caledonia

Seawater samples were collected in the lagoon of Nouméa (New Caledonia) along two transects from coastal bays to the oligotrophic barrier reef. Dissolved (<0.2 μm) and sub-micrometer (0.2–0.8 μm) concentrations of chromium, nickel and zinc were measured. Concentrations in the 0.2–0.8 μm size range were correlated with transparent exopolymeric particles (TEP) turnover rates, suggesting that a TEP pool rapidly cycling in the system is more reactive toward metals. The role of TEP reactivity in the transfer efficiency of metals from dissolved to particulate phases was estimated through variations of the metal partitioning coefficient K between sub-micrometer TEP and solution, as a function of the water mass residence time. The log K (6.0–8.0) increased from high to low residence time, suggesting that TEP reactivity increases when water masses renew rapidly. This suggests that hydrodynamics control TEP reactivity toward metals. The characteristics (adsorption vs. complexation) of TEP-metal association are discussed.     

A new approach to the Nd residence time in the ocean: the role of atmospheric inputs

Concentrations of rare earth elements (REE) and Nd isotopic ratios were analyzed for seawater, filtered suspension and sediment trap samples collected in the tropical Atlantic Ocean (EUMELI program, EUtrophic, MEsotrophic and oLIgotrophic sites, 20°N, 18°–21°W). This is the first REE/Nd dataset on solution and different-sized particles collected at the same site. We present direct evidence of the Nd isotopic exchange between particulate lithogenic fraction and seawater without significant mass transfer. This exchange is probably one of the main factors that simultaneously constrains the Nd concentration and isotopic ratio budget. We propose a new approach to estimate the residence time of Nd in the ocean (τ_Nd) based on isotopic exchange: 200 yr < τ_Nd< 1000 yr. The exchange requires a partial dissolution of lithogenic Nd. We estimate that the fraction of soluble Nd proportion in atmospheric dust is of the order of 20% based on the isotopic ratios. We suggest that the partial dissolution of atmospheric fallout is probably one of the main REE sources of the ocean.     

Using lithium isotopes to quantitatively decode continental weathering signal: A case study in the Changjiang (Yangtze River) Estuary

As the key link connecting the earth's spheres, continental weathering plays an important role in regulating the global biogeochemical cycle and long-term climate change. Siliciclastic sediments derived from large river basins can record continental weathering and erosion signals, and are thus widely used to investigate weathering processes. However, sediment grain size, hydrodynamic sorting and sedimentary recycling complicate the interpretation of sediment weathering proxies. This study presents elemental and lithium isotope compositions of estuarine surface sediments(SS) and suspended particulate matters(SPM) collected from the Changjiang(Yangtze River) Estuary. Based on a simple mass balance model, the proportions of different end-members(i.e., igneous rocks, modern weathering products and inherited weathering products) in sediments were quantitatively calculated and thus the silicate weathering process can be estimated. Overall, the sediments in the Changjiang Estuary are mainly eroded from un-weathered rock fragments(60%), while modern weathering products account for less than40%. The fine-grained SPM contain more shale components(52–66%), and the modern weathering products account for 21–40%. Comparatively, the coarse-grained surface sediments contain more un-weathered igneous rock fragments(63–84%) and less modern weathering products(only 4–18%). The comparison of δ7 Li values with the weathering proxy(Chemical Index of Alteration, CIA) suggests that sediment weathering intensity declines with increasing proportion of un-weathered igneous rock fragments. Additionally, the occurrence of inherited weathering products(i.e., shale) in modern sediments makes it a challenge to simply use CIA and δ7 Li as indicators of weathering intensity. This study confirms that fine-grained particles are more suitable for tracing contemporary weathering process, albeit with the influence of sedimentary recycling. Lithium isotopes combining with the mass balance model can quantitatively constrain the continental weathering processes in large river basins.     

Long-term SMOS soil moisture products: A comprehensive evaluation across scales and methods in the Duero Basin (Spain)

The European Space Agency’s Soil Moisture and Ocean Salinity (SMOS) Level 2 soil moisture and the new L3 product from the Barcelona Expert Center (BEC) were validated from January 2010 to June 2014 using two in situ networks in Spain. The first network is the Soil Moisture Measurement Stations Network of the University of Salamanca (REMEDHUS), which has been extensively used for validating remotely sensed observations of soil moisture. REMEDHUS can be considered a small-scale network that covers a 1300 km² region. The second network is a large-scale network that covers the main part of the Duero Basin (65,000 km²). At an existing meteorological network in the Castilla y Leon region (Inforiego), soil moisture probes were installed in 2012 to provide data until 2014. Comparisons of the temporal series using different strategies (total average, land use, and soil type) as well as using the collocated data at each location were performed. Additionally, spatial correlations on each date were computed for specific days. Finally, an improved version of the Triple Collocation (TC) method, i.e., the Extended Triple Collocation (ETC), was used to compare satellite and in situ soil moisture estimates with outputs of the Soil Water Balance Model Green-Ampt (SWBM-GA). The results of this work showed that SMOS estimates were consistent with in situ measurements in the time series comparisons, with Pearson correlation coefficients (R) and an Agreement Index (AI) higher than 0.8 for the total average and the land-use averages and higher than 0.85 for the soil-texture averages. The results obtained at the Inforiego network showed slightly better results than REMEDHUS, which may be related to the larger scale of the former network. Moreover, the best results were obtained when all networks were jointly considered. In contrast, the spatial matching produced worse results for all the cases studied.These results showed that the recent reprocessing of the L2 products (v5.51) improved the accuracy of soil moisture retrievals such that they are now suitable for developing new L3 products, such as the presented in this work. Additionally, the validation based on comparisons between dense/sparse networks and satellite retrievals at a coarse resolution showed that temporal patterns in the soil moisture are better reproduced than spatial patterns.     

Bacterioplankton dynamics along the gradient from highly eutrophic Pearl River Estuary to oligotrophic northern South China Sea in wet season: implication for anthropogenic inputs

Bacterioplankton abundance (BA) and biomass (BB) from the eutrophic Pearl River Estuary (PRE) to the oligotrophic northern South China Sea (NSCS) were studied in the wet season. BA was significantly higher (p < 0.05) in PRE (12.51 ± 3.52 × 10⁸ cells L⁻¹), than in the continental shelf neritic province (CSNP, 4.95 ± 2.21 × 10⁸ cells L⁻¹) and in the deep oceanic province (OP, 3.16 ± 1.56 × 10⁸ cells L⁻¹). Nutrient-replete PRE waters (DIN > 100 μM and PO₄ > 1 μM) resulted in high chl a and BB, whereas nutrient-depleted offshore waters (DIN <5 μM and PO₄ < 0.5 μM) had low biomass. Temperature (>26 °C) was not the controlling factor of BA. BB was significantly correlated with chl a biomass both in PRE and NSCS. The bacteria to phytoplankton biomass (BB/PB) ratio increased clearly along the gradient from near-shore PRE (0.15) to offshore CSNP (0.93) and deep OP (2.75), indicating the important role of small cells in the open ocean compared to estuarine and coastal zones.     

An improved algorithm to estimate the surface soil heat flux over a heterogeneous surface: A case study in the Heihe River Basin

Surface soil heat flux(G0) is an indispensable component of the surface energy balance and plays an important role in the estimation of surface evapotranspiration(ET). This study calculated G0 in the Heihe River Basin based on the thermal diffusion equation, using the observed soil temperature and moisture profiles, with the aim to analyze the spatial-temporal variations of G0 over the heterogeneous area(with alpine grassland, farmland, and forest). The soil ice content was estimated by the difference in liquid soil water content before and after the melting of the frozen soil and its impact on the calculation of G0 was further analyzed. The results show that:(1) the diurnal variation of G0 is obvious under different underlying surfaces in the Heihe River Basin, and the time when the daily maximum value of G0 occurs is a few minutes to several hours earlier than that of the net radiation flux, which is related to the soil texture, soil moisture, soil thermal properties, and the vegetation coverage;(2) the net radiation flux varies with season and reaches the maximum in summer and the minimum in winter, whereas G0 reaches the maximum in spring rather than in summer, because more vegetation in summer hinders energy transfer into the soil;(3) the proportions of G0 to the net radiation flux are different with seasons and surface types, and the mean values in January are 25.6% at the Arou site, 22.9% at the Yingke site and 4.3% at the Guantan site, whereas the values in July are 2.3%, 1.6% and 0.3%, respectively; and(4) G0 increases when the soil ice content is included in thermal diffusion equation, which improves the surface energy balance closure by 4.3%.     

A probabilistic framework to evaluate the uncertainty of design hydrograph: case study of Swannanoa River watershed

ABSTRACT

This study presents a probabilistic framework to evaluate the impact of uncertainty of design rainfall depth and temporal pattern as well as antecedent moisture condition (AMC) on design hydrograph attributes – peak, time to peak, duration and volume, as well as falling and rising limb slopes – using an event-based hydrological model in the Swannanoa River watershed in North Carolina, USA. Of the six hydrograph attributes, falling limb slope is the most sensitive to the aforementioned uncertainties, while duration is the least sensitive. In general, the uncertainty of hydrograph attributes decreases in higher recurrence intervals. Our multivariate analysis revealed that in most of the return periods, AMC is the most important driver for peak, duration and volume, while time to peak and falling limb slope are most influenced by rainfall pattern. In higher return periods, the importance of rainfall depth and pattern increases, while the importance of AMC decreases.     

Prediction of regional-scale groundwater recharge and nitrate storage in the vadose zone: A comparison between a global model and a regional model

Extensive nitrogen loads at the soil surface exceed plant uptake and soil biochemical capacity, and therefore lead to nitrogen accumulation in the deep vadose zone. Studies have shown that stored nitrogen in the vadose zone can eventually reach the water table and affect the quality of groundwater resources. Recently, global scale models have been implemented to quantify nitrate storage and nitrate travel time in the vadose zone. These global models are simplistic and relatively easy to implement and therefore facilitate analysis of the considered transport processes at a regional scale with no further requirements. However, the suitability of applying these models at a regional scale has not been tested. Here, we evaluate, for the first time, the performance and utility of global scale models at the regional scale. Applied to the Loess Plateau of China, we compare estimates of groundwater recharge and nitrate storage derived from global scale models with results from a regional scale approach utilizing the Richards and advection-dispersion equations. The estimated nitrate storage was compared to nitrate observations collected in the deep vadose zone (>50 m) at five sites across the Loess Plateau. Although both models predict similar spatial patterns of nitrate storage, the recharge fluxes were three times smaller and the nitrate storage was two times higher compared with the regional model. The results suggest that global scale models are a potentially useful screening tool, but require refinement for local scale applications.