长江口主要阳离子随盐度变化的研究

以追踪混合水团的方式采样,并测定了长江河口混合区表层和底层中主要阳离子Mg2+、Ca2+、Na+和K+的浓度,讨论了长江口水体的pH分布特征和主要阳离子的混合特征.结果表明,长江口水体的pH状况受人为污染影响较小,河口混合区主要阳离子的浓度随着水体盐度的增大而增大,Ca/Mg比值随水体盐度的增大而迅速减小,且主要阳离子浓度相对于盐度的变化在表层和底层水体间没有显著的差别.在长江河口混合区主要阳离子的浓度及其比值随盐度的变化可用线性混合模型进行较好地预测和模拟.     

Climatic and Tidal Forcing of Hydrography and Chlorophyll Concentrations in the Columbia River Estuary

Hydrographic patterns and chlorophyll concentrations in the Columbia River estuary were compared for spring and summer periods during 2004 through 2006. Riverine and oceanic sources of chlorophyll were evaluated at stations along a 27-km along-estuary transect in relation to time series of wind stress, river flow, and tidal stage. Patterns of chlorophyll concentration varied between seasons and years. In spring, the chlorophyll distribution was dominated by high concentrations from freshwater sources. Periods of increased stream flow limited riverine chlorophyll production. In summer, conversely, upwelling winds induced input of high-salinity water from the ocean to the estuary, and this water was often associated with relatively high chlorophyll concentrations. The frequency, duration, and intensity of upwelling events varied both seasonally and interannually, and this variation affected the timing and magnitude of coastally derived material imported to the estuary. The main source of chlorophyll thus varied from riverine in spring to coastal in summer. In both spring and summer seasons and among years, modulation of the spring/neap tidal cycle determined stratification, patterns of mixing, and the fate of (especially freshwater) phytoplankton. Spring tides had higher mixing and neap tides greater stratification, which affected the vertical distribution of chlorophyll. The Columbia River differs from the more tidally dominated coastal estuaries in the Pacific Northwest by its large riverine phytoplankton production and transfer of this biogenic material to the estuary and coastal ocean. However, all Pacific Northwest coastal estuaries investigated to date have exhibited advection of coastally derived chlorophyll during the upwelling season. This constitutes a fundamental difference between Pacific Northwest estuaries and systems not bounded by a coastal upwelling zone.     

Manganese and suspended matter in the Yaquina Estuary,Oregon

The longitudinal distribution of total suspended matter and total, dissolved, and particulate manganese in a small coastal plain estuary is described. The distribution of manganese is a consequence of estuarine circulation; a within-estuary maximum is inversely correlated with river flow, and is a function of residence time in the estuary, resuspension in the upper estuary, and desorption from particles introduced from within the estuary or from the river. The turbidity maximum is similarly most pronounced during low river flows. The upper estuary (salinity <15‰), comprising a small percentage of the total estuary volume during low flow, receives material from the river and along the bottom from the lower estuary; this material is returned to the water column by resuspension and desorption from estuarine and riverine particles. The lower estuary tends to damp out these processes because of the greater volume and (residence) time available for mixing.     

Physical processes controlling bacterial distribution and variability in the upper St. Lawrence estuary

The vertical structure of the water column and the spatial distribution and semidiurnal variability of bacteria were investigated at six stations in the upper St. Lawrence estuary. The σ₁ profiles indicate that the upper St. Lawrence is a partially mixed estuary. Stratification results from buoyancy input from the freshwater outflow of the St. Lawrence River, and its variability is controlled by tidal and, to a lesser extent, wind mixing. Calculations show that tidal mixing largely exceeds mixing caused by wind. Free and attached bacteria presented different patterns of spatial distribution and temporal variability. Free bacteria exhibited highest mean concentrations at the freshwater station (3.5–4.4 10⁶ml^?1) and lowest concentrations at the downstream stations (0.3–0.5 10⁶ml^?1); their numbers declined exponentially relative to salinity. Attached bacteria had highest mean concentrations (3.2–5.5 10⁶ml^?1) at salinities between 0.5 and 5 and were virtually absent at downseam stations (<0.05 10⁶ml^?1). The importance of semidiurnal variability was demonstrated Over the idal cycle, variability of attached bacteria was always greater than that of free bacteria. The analysis of causal models between salinity and free and attached bacteria, showed that the two types of bacteria are uncoupled and that both types have a strong relationship with salimity. Physical processes are thus important controlling factors of the distribution and variability of bacteria. Results suggest that large-scale processes, such as freshwater outflow and residual circulation, largely control free bacteria, whereas short-term and more local processes (e.g., sediment resuspension caused by wind) may also be important in the control of attached bacteria.     

径潮共同作用对径流型河口盐水上溯的影响

为进一步认识径流型河口枯季盐水上溯距离变化的影响因素及其作用机制,将实际河口简化并在不同径流量下分别用等潮差正弦潮和主要分潮驱动,进行盐水三维数值模拟试验。结果表明:随着径流和潮汐两大基本作用的相对强度不同,平衡态下盐水形态和位置自动调整并最终达到盐输运平衡,径流量小于3 000 m3/s且潮差小于2 m时,最大上溯距离随潮差的变化规律在不同径流量下存在明显差别;大小潮半月周期内盐水呈现非平衡态,非强混合时潮周期盐水上溯最大距离围绕平衡态随潮差呈顺时针绳套关系变化。径流导致的密度环流作用和潮汐的混合作用交织,两者相互影响并协同发展,两种作用相对强度的不同是导致径流型河口盐水上溯距离变化显著的主导因素。     

Source-related classification of St. Lawrence estuary sediments based on spatial distribution of adsorbed contaminants

The St. Lawrence River upper estuary is a very large and efficient mixing zone for contaminated industrial discharges originating upstream, yet elevated levels of various toxic contaminants have persistently been reported in local biota, such as eels and Beluga whales. As part of an initial assessment of the role of bottom sediments in the fate and pathways of contaminants through the estuary ecosystem, we examine the spatial distributions of particle-reactive trace and major elements in shallow-water accumulation zones. Concentrations of more than 30 elements were determined by ICP atomic emission spectrography. A number of these (Ce, Cr, Fe, La, Ni, and Zn) proved to be useful as fine sediment tracers, despite the complicating effects of intense sediment mixing and varying grain size and salinity. Prior normalization of the concentration values with reference to aluminum was necessary in most cases to minimize bias caused by grain-size variation between samples; however, there was no means of compensating for the effect of variable salinity on trace element concentrations. Through the use of a combination of two statistical approaches, linear regression and cluster analysis (ratio-matching), two distinct depositional zones for modern sediments were resolved, each associated with a different source. The largest zone covered the western end and along the south shore of the upper estuary, while the other was confined to the northeastern shore. The western zone is characterized by high-metal-content brought in by the St. Lawrence River. The northeastern zone is distinguished by the presence of lanthanide and rare earth elements (Ce, Y), indicating that its sediment source is probably the watersheds draining the monazite-bearing Grenville Province of the Canadian Shield to the north. The statistical separation of these two sediment groupings supports the conclusion that the St. Lawrence River sediment plume follows the southern shore of the estuary. The more sparsely distributed modern sediment deposits along the north shore tend to be derived from local sources.     

近岸沉积物再悬浮期间所释放溶解有机物的荧光特征

对采自厦门湾九龙江人海河口的4个沉积物样品进行了室内再悬浮模拟实验,利用荧光激发-发射矩阵光谱(EEMs)研究了再悬浮过程中从沉积物中释放出的有色溶解有机物(CDOM)的荧光特征,同时通过与相应站位沉积物间隙水和底层水的对比分析,探讨了河口近岸海域的沉积物再悬浮作用作为水体中溶解有机物来源之一的可能性.结果表明,对给定站位,CDOM相对荧光强度和溶解有机碳(DOC)含量分布变化非常一致,均为间隙水最高,再悬浮次之,底层水最低;站位之间,底层水和再悬浮水样中CDOM相对荧光强度随盐度的降低而增加,从海端向河端增加的趋势明显.EEMs分析表明,各样品中均存在类腐殖质荧光与类蛋白质荧光团,且模拟实验也表明再悬浮作用可释放类腐殖质与类蛋白质荧光物质到底层水中,表明底质再悬浮将是近岸水体中CDOM的一个重要来源.与相应的底层水相比,间隙水的荧光峰(如峰A/C)的位置发生红移.再悬浮样品中EEMs的荧光团同时表现出相应底层水和间隙水的特征,但是荧光峰(峰A和峰C)的最大激发和发射波长更接近底层水中相应荧光团,与间隙水相比,则发生谱峰位置的蓝移.近海端样品中荧光峰M明显,随着盐度的降低,底层水和再悬浮水样的γ(M/C)值逐渐降低,且海源的峰M由海端向河端逐渐消失,表明峰M属于海洋自生来源.本研究区域DOM的荧光指数在1.61～1.93之间,表明近海端样品DOM主要为生物来源,而近河端样品DOM主要为陆源输入,或者为陆源与生物活动共同作用的结果.     

DOC dynamics in a small temperate estuary: Simultaneous addition and removal processes and implications on observed nonconservative behavior

Dissolved organic carbon (DOC) dynamics in the Pawcatuck River estuary, a small temperate estuary in Rhode Island, United States, were examined through the use of field transect and in situ production studies. In late summer, when river discharge was minimal, phytoplankton blooms occurred in the upper reaches of the estuary and released large amounts of autochthonous DOC that accumulated in the middle reaches of the estuary. DOC production rates in August months, calculated both by mixing diagrams and in situ DOC incubations, ranged from 6.67 to 34.7 μmol C l⁻¹ d⁻¹ and were positively correlated with DCMU-enhanced fluorescence, an estimate of phytoplankton photosynthetic activity (r²=0.796, p<0.001). The percent extracellular release (PER) of DOC from phytoplankton, calculated from measured in situ DOC production and net phytoplankton production (NPP) rates, ranged from 5.8% to 40.6% and was negatively correlated with NPP (r²=0.80, p<0.01). Accumulated DOC was principally nonhumic in nature, and the humic DOC component behaved quite differently with either conservative mixing or significant removal at the head of the estuary. Humic removal at times amounted to approximately 50% of the humic material and 25% of the total incoming riverine DOC. These large humic losses were not observed in bulk DOC-salinity mixing diagrams but required distinct analyses of the humic and nonhumic components. DOC addition and removal processes co-occur in this system and observation of bulk DOC mixing diagrams may mask the true dynamic nature of the estuarine DOC pool. The net result of the DOC addition and removal processes is a seasonally variable transformation of a humic-rich incoming riverine DOC to a nonhumic enriched bulk DOC component that varies seasonally and with river discharge.     

Rapid barium removal in the Delaware estuary

Six profiles of dissolved barium covering the entire salinity range of the Delaware River and Bay estuary from March through September 1996 were collected and analyzed. The profiles are similar to one another in both shape and magnitude except for one attribute. A sudden (≤24 days), nearly complete (>90%) removal of dissolved Ba in midestuary occurs in mid-May followed by an 80% recovery in early June. This removal appears to be temporally and spatially coupled to the end of the spring bloom. Based on such episodic behavior, and on recent work with flocculation of diatom exudates, we conclude that the Ba depletion is caused by barite precipitation in the estuary during the late stages of the bloom. This would imply that lower estuary and inner coastal margin sediments associated with eutrophic estuaries receive a seasonal pulse of barite. The suddenness of this event also implies that sedimentary barite is strongly influenced by high productivity events.Comparison of the riverine Ba concentration with the effective riverine end member after desorptive barium release yields an estimated 30–40 nM Ba available from the suspended sediments as they enter the estuary. This estimate is supported by excess barium in unfiltered samples over filtered samples taken from the river and also by calculations done elsewhere.     

Groundwater-dependent ecology of the shoreline of the subtropical Lake St Lucia estuary

The ecology of the St Lucia estuary in South Africa is of unique international importance. During droughts the estuary experiences high salinities, with values above that of seawater. Ion-poor groundwater flowing into the estuary from prominent sand aquifers along its eastern shoreline forms low-salinity habitats for salt-sensitive biota. During droughts, plants and animals can take refuge in the groundwater discharge zone until the condition in the estuary regains tolerable salinity. Simulations of the groundwater discharge indicate that the flow can persist during droughts over at least a decade, and be of great important for the resilience of the estuary. Anthropogenic activities have reduced the river inflow and made the St Lucia estuary more sensitive to droughts. The groundwater has thereby become increasingly important for the estuary’s ecology. Protection of the groundwater discharge along the shoreline itself and actions to increase the groundwater recharge are therefore important management tasks.     

Dissolved aluminum in four Chinese estuaries: evidence of biogeochemical uncoupling of Al with nutrients

Four Chinese estuaries, the Jiaojiang, Luanhe, Shuangtaizihe, and Yalujiang were investigated to determine Al geochemistry and inter-relations between Al and nutrients. These estuaries are characterised by low particulate organic carbon and high turbidity, with various tidal regimes. Dissolved Al was determined by fluorescence method after liquid–liquid extraction into n-hexanol. Concentrations of Al in the Luanhe estuary are relatively high (1.5–2.0 μM) and approximately uniform over the salinity range sampled, suggesting the influence of in situ sources/processes. In the Shuangtaizihe estuary, riverine concentrations of Al (1.8–2.2 μM) decrease with higher chlorinity, indicating the predominance of simple dilution by seawater. The Jiaojiang and Yalujiang provide evidence that Al is removed from water column at early stages of estuarine mixing, owing to probably the particle–solution reactions (e.g. flocculation) in the estuary. The Al data are further compared with total suspended matter and nutrients in these estuaries. The data sets indicate that aluminum is not dominantly coupled to the cycle of nutrients.     

Distribution of colloidal trace metals in the San Francisco Bay estuary

The size distribution of trace metals (Al, Ag, Cd, Cu, Fe, Mn, Ni, Sr, and Zn) was examined in surface waters of the San Francisco Bay estuary. Water samples were collected in January 1994 across the whole salinity gradient and fractionated into total dissolved (<0.2 μm colloidal (10 KDa–0.2 μm) and < 10 kDa molecular weight phases. In the low salinity region of the estuary, concentrations of colloidal A1, Ag, and Fe accounted for ≥84% of the total dissolved fraction, and colloidal Cu and Mn accounted for 16–20% of the total. At high salinities, while colloidal Fe was still relatively high (40% of the dissolved), very little colloidal Al, Mn, and Cu (<10%) and no colloidal Ag was detectable. Colloidal Zn accounted for <3% of the total dissolved along the estuary, and colloidal Ni was only detectable (<2%) at the river endmember. All of the total dissolved Cd and Sr throughout the estuary consisted of relatively low molecular weight (<10 kDa) species. The relative affinity of metals for humic substances and their reactivity with particle surfaces appear to determine the amounts of metal associated with colloids. The mixing behavior of metals along the estuary appears to be determined by the relative contribution of the colloidal phase to the total dissolved pool. Metals with a small or undetectable colloidal fraction showed a nonconservative excess (Cd, Cu, Ni, and Mn) or conservative mixing (Sr) in the total dissolved fraction, relative to ideal dilution of river water and seawater along the estuary.

The salt-induced coagulation of colloidal A1, Fe, and Cu is indicated by their highly nonconservative removal along the salinity gradient. However, colloidal metals with low affinity for humic substances (Mn and Zn) showed conservative mixing behavior, indicating that some riverine colloids are not effectively aggregated during their transport to the sea. While colloidal metal concentrations correlated with dissolved organic carbon, they also covaried with colloidal Al, suggesting that colloids are a mixture of organic and inorganic components. Furthermore, the similarity between the colloidal metal:A1 ratios with the crustal ratios indicated that colloids could be the product of weathering processes or particle resuspension. Distribution coefficients for colloidal particles (K_c) and for large, filter-retained particles (K_d) were of the same magnitude, suggesting similar binding strength for the two types of particles. Also, the dependence of the distribution coefficients on the amount of suspended particulate matter (the so-called particle concentration effect) was still evident for the colloids-corrected distribution coefficient (K_p+c) and for metals (e.g., Ni) without affinity for colloidal particles.     

Hydrography and circulation of the Chubut River estuary (Argentina)

The hydrography and circulation of the Chubut River were investigated under exceptionally low river discharge. The frontal zone formed by the entrance of the tide in the estuary may be observed as far as 4.5 km from the mouth, showing that the salt intrusion due to tidal effects reaches further inland than during normal river discharge. Based on the classification of Hansen and Rattray (1966), the estuary corresponds to Type 1 with some vertical stratification observed on the seaward side of the frontal zone. A lateral salinity gradient was found, which was not the result of Coriolis force. The general morphology of the estuary and the consequent secondary circulation due to meanders and interchannel bars may explain the lateral variation. Wind effect is a major component of the circulation and mixing of this shallow estuary.     

Response times of salinity in relation to changes in freshwater inflows in the Lower Hillsborough River, Florida

The Lower Hillsborough River, Florida is a short (16 km) riverine estuary which has a dam located at its upstream end. Salinity below the dam is influenced by freshwater that flows over or through the structure. Depending on location in the estuary, the response of salinity to changes in upstream freshwater inflows is normally not instantaneous, but lags behind the freshwater release. An analytical approach and a laterally averaged two-dimensional hydrodynamic model were used to examine the response time of salinity in the Lower Hillsborough River to changes in freshwater inflows from the upstream reservoir. A series of case studies were conducted using the model to determine how salinity in the river within one kilometer below the dam would respond to changes in freshwater inflows. The model results suggest that the time lag of salinity in the river depends on whether the upstream freshwater inflows are increasing or decreasing, as well as their magnitude. While the time lag for salinity is about six to eight days for decreasing inflows, it is much shorter for increasing inflows depending on the magnitude of the flow release.     

黄河三角洲浅层地下水盐分来源及咸化过程研究

黄河三角洲地下水咸化已成为区域最突出的生态环境问题之一。识别地下水补给及盐分来源是有效控制和改善地下水咸化问题的关键。本研究采集了研究区浅层地下水、地表水和海水等不同类型水样,利用离子比、Piper三线图、吉布斯图等方法对八大离子浓度、δD和δ¹⁸O 组成、Br和Sr 浓度等进行地下水补给研究与盐分来源辨析。结果表明:(1)黄河三角洲浅层地下水以总溶解性固体(TDS)为338 g/L的咸水为主,地下水水化学类型较为单一,主要为Cl-Na型。(2)三角洲区域地下水以大气降水补给为主,并且在补给过程中经历了不同程度的蒸发作用的影响,黄河现行流路区域地下水主要来源于河水侧渗补给,但浅层地下水含水层水平渗透性较差限制了黄河侧渗补给范围。(3)海洋是黄河三角洲浅层地下水盐分的主要来源,黄河现行流路区域及近岸地下水盐分来源于海水混合,三角洲北部刁口河等古河道区域地下水盐分主要来源于海相蒸发盐淋滤溶解。     

Seasonal Variability and Estuary–Shelf Interactions in Circulation Dynamics of a River-dominated Estuary

The long-term response of circulation processes to external forcing has been quantified for the Columbia River estuary using in situ data from an existing coastal observatory. Circulation patterns were determined from four Acoustic Doppler Profilers (ADP) and several conductivity–temperature sensors placed in the two main channels. Because of the very strong river discharge, baroclinic processes play a crucial role in the circulation dynamics, and the interaction of the tidal and subtidal baroclinic pressure gradients plays a major role in structuring the velocity field. The input of river flow and the resulting low-frequency flow dynamics in the two channels are quite distinct. Current and salinity data were analyzed on two time scales—subtidal (or residual) and tidal (both diurnal and semidiurnal components). The residual currents in both channels usually showed a classical two-layer baroclinic circulation system with inflow at the bottom and outflow near the surface. However, this two-layer system is transient and breaks down under strong discharge and tidal conditions because of enhanced vertical mixing. Influence of shelf winds on estuarine processes was also observed via the interactions with upwelling and downwelling processes and coastal plume transport. The transient nature of residual inflow affects the long-term transport characteristics of the estuary. Effects of vertical mixing could also be seen at the tidal time scale. Tidal velocities were separated into their diurnal and semidiurnal components using continuous wavelet transforms to account for the nonstationary nature of velocity amplitudes. The vertical structure of velocity amplitudes were considerably altered by baroclinic gradients. This was particularly true for the diurnal components, where tidal asymmetry led to stronger tidal velocities near the bottom.     

Stable isotope analysis of carbon cycling in the Perdido estuary, Florida

Stable carbon isotope (δ¹³C) analysis was used in the Peridido Estuary, Florida U.S. to determine the predominant carbon source that supports the bacterial assemblage. Stable carbon isotope values were measured in the suspended particulate matter (SPM), dissolved organic and inorganic matter, and bacteria. Stable nitrogen isotope (δ¹⁵N) ratios were measured in SPM and nitrate to assist in understanding carbon cycling through the estuary. Analyses were conducted on samples from riverine, coastal, and anthropogenic sources and compared with samples from the bay. Stable isotope ratio analysis was coupled with estimates of mixing of riverine and coastal waters into the bay. Preliminary observation of the °¹³C data indicates that terrestrial organic matter is the primary carbon source that is assimilated by bacteria in the ecosystem. Stable isotope data from carbon and nitrogen pools in combination with analysis of estuarine current velocities indicates that primary production is an important factor in the carbon cycle. This study demonstrates the importance of stable isotope analysis of multiple carbon and nitrogen pols to assess sources and cycling of organic matter.     

Seasonal changes in the depth distributions of interstitial salinities in the Fraser River estuary,British Columbia

The vertical distribution of interstitial salinities to a depth of 6 cm in subtidal estuarine sediments was measured monthly from June 1977 to August 1978 in mud substrates in the Fraser River estuary, British Columbia. Measurements were made at six stations ranging from oligohaline to polyhaline. The results of this study demonstrated that vertical salinity gradients were present, particularly in the mesohaline zone of the estuary, in the sediments and that the magnitude of these gradients changes seasonally.     

Comparison of Estuarine Salinity Gradients and Associated Nekton Community Change in the Lower St. Johns River Estuary

Salinity is an important determinant of estuarine faunal composition; previous studies, however, have indicated conflicting accounts of continuous vs. relatively rapid change in community structure at certain salinities from geographically distinct estuaries. This study uses a large fisheries monitoring database (n?>?5,000 samples) to explore evidence for estuarine salinity zonation by nekton in the lower St. Johns River estuary (LSJR). There was little evidence to support the presence of estuarine salinity zones except at the extremes of the salinity gradient (i.e., 0.1?C1.0 and 34?C39). The LSJR estuarine nekton community exhibits progressively slow ecological change throughout most of the salinity gradient with rapid change at the interfaces with fresh and marine waters??an ecoline bounded by ecotones. This study affirms the rapid change that occurs at the extremes of the salinity spectrum in certain estuaries and is relevant to efforts to manage surface water resources and estuarine ecosystems. Given the disparity in the results of the studies examining biological salinity zones in estuaries, it would be wise to have, at minimum, a regional understanding of how communities are structured along the gradient from freshwater to marine.     

Modeling of the Cape Fear River Estuary plume

The Environmental Fluid Dynamic Code, an estuarine and coastal ocean circulation model, is used to simulate the distribution of the salinity plume in the vicinity of the mouth of the Cape Fear River Estuary, North Carolina. The individual and coupled effects of the astronomical tides, river discharge, and atmospheric winds on the spatial and temporal distributions of coastal water levels and the salinity plume were investigated. These modeled effects were compared with water level observations made by the National Oceanic and Atmospheric Administration and salinity surveys conducted by the Coastal Ocean Research and Monitoring Program. Model results and observations of salinity distributions and coastal water level showed good agreement. The simulations indicate that strong winds tend to reduce the surface plume size and distort the bulge shape near the estuary mouth due to enhanced wind-induced surface mixing. Under normal discharge conditions, tides, and light winds, the southward outwelling plume veers west. Relatively moderate winds can mechanically reverse the flow direction of the plume. Under conditions of weak to moderate winds the water column does not mix vertically to the bottom, while in strong wind cases the plume becomes vertically well mixed. Under conditions of high river discharge the plume increases in size and reaches the bottom. Vertical mixing induced by strong spring tides can also enable the plume to reach the bottom.