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1.
The chemical forms and distribution of dissolved arsenic species in the estuary of the River Beaulieu (Hampshire, U.K.) are reported. ‘Inorganic arsenic (V)’ in both the marine and riverine estuary inputs are in true solution, passing through ultrafiltration membranes having a nominal molecular weight cut-off of 500 daltons. Extensive removal of dissolved ‘inorganic arsenic (V)’ is apparent from the distribution of arsenic in the estuary, with laboratory mixing experiments indicating that removal is favoured in the low salinity region. ‘Inorganic arsenic (III)’ and methylated arsenic species account for up to 41% and 70% of the dissolved arsenic, respectively, but are only found during the warmer months when water temperatures exceed ca. 12°C.  相似文献   

2.
Autotrophic biomass and productivity as well as nutrient distributions and phytoplankton cell populations in the James River estuary, Virginia, were quantified both spatially and temporally over a 17-month period. Emphasis was placed on the very low salinity region of the estuary in order to gain information on the fate of freshwater phytoplankters. Differing amounts of freshwater plant biomass are advected into the estuary as living material, DOC or POC and the demonstrated variability of this input must play an important role in marine biogeochemical cycling.Late summer and fall maxima in both chlorophyll a and the photosynthetic production of particulate organic carbon in very low salinity regions were inversely correlated with river discharge.During periods of low river discharge greater than 50% of the chlorophyll a biomass measured at 0‰ disappeared within a narrow range of salinity (0–2‰). Cell enumeration data suggest that species introduced from the freshwater end-member tend to comprise the bulk of the biomass removed. Confounding factors, which may contribute to the regulation of both the abundance and species of phytoplankters mid-river, include the flocculation of colloidal material with phytoplankton cells, the presence of the turbidity maximum and the growth of endemic phytoplankton populations.An inverse relationship exists between the phytoplankton abundance in very low salinity waters and the abundance of biomass measured in the lower portion of the river (estuary). Thus, autotrophic production in the fresh and very low salinity areas may indirectly regulate the onset on the spring bloom in the estuary by controlling the amount of nutrients available.  相似文献   

3.
《Marine Chemistry》2001,75(3):229-248
Dissolved and particulate mercury and methylmercury concentrations were determined in the Southern Bight of the North Sea and the Scheldt estuary in the period 1991–1999. Mercury and methylmercury concentrations are higher before 1995 than after 1995, especially in the fluvial part.The North Sea: In the offshore stations, dissolved Hg concentrations are generally higher in winter than in summer while the reverse is true for particulate Hg KD values (KD=the concentration of particulate Hg (HgP in pmol kg−1) divided by the concentration of dissolved Hg (HgD in pmol l−1)) range from 100,000 to 1000,000 l kg−1. Dissolved methylmercury concentrations vary from 0.05 to 0.25 pmol l−1 in summer and from d.l. to 0.23 pmol l−1 in winter and particulate methylmercury concentrations from 1.8 to 36 pmol g−1 in summer and from 0.9 to 21 pmol g−1 in winter. The KD ranges from 9,000 to 219,000 l kg−1.The Scheldt estuary: In winter, dissolved Hg concentrations are elevated in the upper estuary, decrease exponentially in the low salinity range followed by a very slow decrease towards the mouth. In summer, they are low in the fluvial part, increase in the low salinity range or in the mid-estuary and sometimes show an increase in the lower estuary. Particulate Hg concentrations do not show any seasonal trend.Dissolved MMHg concentrations are much lower in winter, when maximum concentrations are found in the upper estuary, than in summer. In summer, the MMHg concentrations are low at low salinity, they show a first increase in the salinity range from 3 to 12, a decrease in the mid-estuary and a second increase in the lower estuary.The highest particulate MMHg concentrations are found in the upper estuary, while in the lower estuary generally lower and more constant values are observed. The ratio of dissolved MMHg to dissolved Hg (cruise averages between 1.3% and 20%), is higher than the ratio of particulate MMHg to particulate Hg (cruise averages of 0.27–0.90%). The KD values for MMHg are lower in the summer (30,000–65,000) than in autumn and winter (77,000–114,000).The Scheldt river: In the fluvial part of the Scheldt, dissolved increases in the most upstream stations, while particulate Hg shows no particular pattern. Dissolved MMHg ranges from 0.1 to 0.39 pmol l−1 and particulate MMHg from 3.1 to 43.5 pmol g−1. The MMHg concentrations are comparable to those found in the estuary and no seasonal variations could be observed.  相似文献   

4.
Dissolved and particulate trace metals (Cu, Cd, Pb, Zn, Ni, Fe and Mn) measured at six stations along the Scheldt estuary in October/November 1978 are compared with more recent data. Based on Ca content in the suspended matter, three distinct geochemical regions could be distinguished: the upper estuary (salinity 1–7) dominated by fluvial mud, mid-estuary (salinity 7–17) where the composition of the suspended matter remained relatively constant, and the lower estuary where marine mud prevailed. Re-suspension of sediments is the major factor controlling the composition of the particles in the upstream region. Anoxic conditions prevailed in the upper part of the estuary extending to a salinity of 15 in 1978, while at present the seaward boundary of the anoxic water body is located at less saline waters. Furthermore, the present-day metal load is much lower than in 1978. As a consequence of the changed situation, maxima in dissolved concentrations of redox-sensitive metals in the mid/lower estuary have moved as well, which affects the trace metal re-distribution pattern. In the anoxic zone, exchange processes between dissolved and particulate metal fractions were strongly redox regulated, with Fe and Mn as excellent examples. Iron was removed from the dissolved phase in the early stages of mixing resulting in an increase in the suspended particulate matter of the leachable ‘non-residual' Fe fraction from 2 to 3.5%. Due to its slower kinetics, removal of Mn from solution occurred in mid-estuary where oxygen concentrations increased. Cu, Cd and Zn on the contrary were mobilised from the suspended particles during estuarine mixing. External inputs of Pb, and to a lesser extent of Cu, in the lower estuary resulted in the increase of their particulate and the dissolved concentrations. Calculated Kd (distribution coefficient) values were used to assess the redistribution between the dissolved and particulate phase of the investigated metals. Due to the existence of the anoxic water body in the upper estuary, the importance of redox processes in determining the Kd values could be demonstrated. The sequence of Kd values in the upper estuary (Fe, Cd, Zn, Pb > Cu > Ni, Mn) is significantly different from that in the lower estuary (Fe > Mn > Pb, Ni, Zn, Cu, Cd). Thus, in such a dynamic estuary single metal-specific Kd values cannot be used to describe redistribution processes.  相似文献   

5.
Phytoplankton chlorophyll concentrations in the Delaware estuary range over two orders of magnitude and display several maxima over the seasonal cycle. These maxima were found to be regulated both spatially and temporally by light availability. Both the spring chlorophyll maximum, which reaches 50–60 μg chlorophyll l?1 during a Skeletonema costatum dominated bloom, and transient fall blooms (15–20 μg l?1) are focused in mid-estuary. These blooms are regulated spatially by settling out of suspended sediment below the turbidity maximum and both spatially and temporally by physical factors (e.g. river flow) that cause vertical stratification in mid-estuary. In freshwater regions, chlorophyll concentrations display seasonal periodicity correlated with solar irradiance; summer chlorophyll concentrations average 30 μg l?1. These freshwater and mid-estuarine biomass maxima may be correctly predicted using a steady-state light-limitation model. In contrast, summer chlorophyll concentrations in the lower estuary remain below 10 μg l?1 and are not correctly modeled, despite minimum turbidity, and non-nutrient limiting conditions. These chlorophyll concentrations appear to be regulated by a combination of light availability and grazing.Although extremely high anthropogenic nutrient inputs in the freshwater region of the Delaware River provide non-limiting nutrient concentrations throughout the estuary, regulation of phytoplankton growth by light-limitation restricts chlorophyll concentrations below the nuisance levels found in many eutrophic systems.  相似文献   

6.
Mass fluxes of diatom opal, planktonic foraminifera carbonate and coccolithophorid carbonate were measured with time-series sediment traps at six sites in the Arabian Sea, Bay of Bengal and Equatorial Indian Ocean (EIOT). The above fluxes were related to regional variations in salinity, temperature and nutrient distribution. Annual fluxes of diatom opal range between 3 and 28 g m−2 yr−1, while planktonic foraminifera carbonate fluxes range between 6 and 23 g m−2 yr−1 and coccolithophorid carbonate fluxes range between 4 and 24 g m−2 yr−1. Annual planktonic foraminifera carbonate to coccolithophorid carbonate ratios range between 0.8 and 2.2 and coccolithophorid carbonate to diatom opal ratios range between 0.5 and 3.3.In the western Arabian Sea, coccolithophorids are the major contributors to biogenic flux during periods of low nutrient concentrations. Coccolithophorid carbonate fluxes decrease and planktonic foraminiferal carbonate and diatom opal fluxes increase when nutrient-rich upwelled waters are advected over the trap site. In the oligotropic eastern Arabian Sea, coccolithophorid carbonate fluxes are high throughout the year. Planktonic foraminiferal carbonate fluxes are the major contributors to biogenic flux in the EIOT. In the northern and central Bay of Bengal, when surface salinity values drop sharply during the SW monsoon, there is a drastic reduction in planktonic foraminiferal carbonate fluxes, but coccolithophorid carbonate and diatom opal fluxes remain steady or continue to increase. Distinctly higher annual molar Sibio/Cinorg (>1) and Corg/Cinorg (>1.5) ratios are observed in the northern and central Bay of Bengal mainly due to lower foraminiferal carbonate production as a result of sharp salinity variations. We can thus infer that the enhanced freshwater supply from rivers should increase oceanic CO2 uptake. Its silicate supply favours the production of diatoms while the salinity drop produces conditions unfavourable for most planktonic foraminifera species.  相似文献   

7.
Sinking particles were collected using time-series sediment traps deployed at 350 and 20 mab at Site SB (34° 58.5’N, 139° 20.9’E, 1544 m depth) near the center of Sagami Bay, off Japan with high time resolutions of 5-8 days (March 1997 to August 1998) and 3-4.5 days (March 1998 to August 1998), respectively. The major components (CaCO3, OM, opal, and clay) of these sinking particles and surface bottom sediments were determined using a stepwise leaching method combined with gravimetry. Average total mass fluxes were 1480, 5560 and 3068 mg/m2/year at 350 mab, at 20 mab, and in the surface sediments, respectively, indicating an enhanced collection of sinking particles at 20 mab. Clay was the dominant component and biogenic components (opal+OM+CaCO3) were dominated mainly by opal and secondly by OM. On average, opal and CaCO3 contents decreased gradually as clay content increased with increasing depth from 350 mab-20 mab and in the surface sediments, indicating dissolution of opal and CaCO3 through sinking, rebound, resuspension or sedimentation processes. Thirteen total mass flux peaks at 17--40-day intervals were observed at 350 mab during the period from March 1997 to August 1998 except for winter, while eight peaks were observed at 20 mab for the period from March 1998 to August 1998. Two types of total mass peaks can be distinguished: one with a clear increase in biogenic flux (opal+OM+CaCO3) and little or no increase in clay flux and termed a bloom type (B-type), and the other with a clear increase in clay flux, little increase in biogenic flux and termed a resuspension type (R-type). Some R-type peaks, but not all, coincided with total mass flux peaks observed at the mouth of Tokyo Bay and suggested the possibility of the effect of particulate materials transported from Tokyo Bay to site SB. The enormously large peak observed at 20 mab in late May 1998 and that at 350 mab in early June 1998 were considered to be due to some physical perturbations from an earthquake swarm near site SB during the period from April to June 1998. The 17--40-day periodicity was associated clearly with the change in biogenic flux dominated by opal flux and is thought to reflect the periodicity of biological productivity dominated by diatoms in the euphotic zone of Sagami Bay.  相似文献   

8.
In April 1996, a massive algal bloom of the coccolithophorid Gephyrocapsa oceanica developed in both Chita Bay and Atsumi Bay which comprise the bay known as Mikawa Bay of Japan. It was the first record of such a bloom in this area. In Chita Bay, the bloom persisted until the middle of May, however in Atsumi Bay, it remained until early June. From the analysis of salinity, water temperature, and current velocity and direction data, it is considered that the following mechanism accounts for the occurrence and maintenance of the bloom: Before the bloom, the standing crop of phytoplankton was poor, resulting in relatively rich nutrients throughout the bay. Thereafter, with the influx of oceanic water into Mikawa Bay, high salinity occurred firstly in Chita Bay. Under these hydrographic conditions, the bloom occurred first in Chita Bay, and extended throughout the bay with the clockwise circulation of water into Atsumi Bay. In Chita Bay, the bloom was influenced by rainfall and G. oceanica flowed out from this area. Whereas, in Atsumi Bay, the bloom persisted for longer due to the clockwise circulation and another influx of oceanic water.  相似文献   

9.
The hydrological and hydrochemical parameters of the Tumen River estuary were collected at 13 stations in May and October 2015. Vertical temperature, conductivity, dissolved oxygen, chlorophyll fluorescence, and turbidity profiles were obtained. Water was sampled from the surface and bottom layer. The water samples were analyzed for major ions, pH, salinity, concentrations of dissolved oxygen, major nutrients, dissolved organic carbon, humic matter, and δ18О and δD isotopes. This estuary is attributed to microtidal type with a flushing time of about 10 h. A phytoplakton bloom occurred in the top layer of the estuary. For surface horizons, the hydrochemical parameters show a linear correlation with salinity. In the bottom horizons, all these parameters, except for major ions and δ18О and δD isotopes, reveal substantial nonconservative behavior. The nonconservative behavior of the hydrochemical parameters in the bottom waters was mainly caused by degradation of the phytoplankton biomass at the water/sediment interface. Hypoxic conditions were established in the bottom waters of the estuary in May.  相似文献   

10.
象山港水体的磷酸盐及其对赤潮的潜在影响   总被引：1，自引：0，他引：1  
根据2012年5月和2017年10月在象山港海域的调查结果，研究了象山港磷酸盐的来源、分布和消耗。磷酸盐浓度在两次的调查中均呈现由港顶向湾口逐渐降低的趋势，说明港顶区有较高浓度磷酸盐的输入，可能主要来自生活污水和海水养殖。磷酸盐、硝酸盐和盐度在象山港外湾的分布特征说明长江和钱塘江是外湾水体磷酸盐的一个重要来源；此外，磷酸盐、硝酸盐和盐度在牛鼻山水道和佛渡水道的差异分布说明，陆地径流可能经由佛渡水道向象山港贡献了一部分的磷酸盐。内湾水体的磷酸盐分布受控于内外湾水体混合和浮游植物的同化作用，磷酸盐在水体停留时间较长的内湾发生了明显的消耗，相比于保守混合模型的估算值，磷酸盐在象山港内湾中的净消耗比例在2012年5月和2017年10月分别约为20%和9%。2017年秋季观测到的磷酸盐浓度[（1.88±0.31）μmol/L]与2002-2005年在同季节观测到的结果相比增加超过了50%，N/P值下降明显，这一变化可能会导致象山港内引发藻华的藻类种群发生变化，同时也可能会引发更为严重的赤潮。  相似文献   

11.
秋季湛江港和入海口温盐结构及生态特征   总被引：2，自引：1，他引：1  
采用2015年10月采集的湛江港海域水体叶绿素a浓度、温度、盐度等参数,分析了秋季湛江港和入海口温盐结构及生态特征。研究结果表明,湛江港海域盐度的水平分布上由湾内往湾外逐渐递增,叶绿素a浓度由湾内往湾外逐渐递减,水深比较浅的区域水温较高,同时在航道入海口底层存在着“高盐低温低叶绿素”的相对稳定的冷水团结构。该水团的形成是由于湛江港出海口独特的地形构造促进区域性水体层化,同时底部水体透明度低,限制航道入海口区域底层的浮游植物的生长等因素所致。  相似文献   

12.
Accurate knowledge of the extent of biogenic opal preservation in marine sediment cores is important for paleoceanographic reconstructions. The alkaline leaching method is widely employed for %biogenic opal analysis due to its ease and speed. In this study, a revised method for measuring %biogenic opal in sediment from arctic coring expedition samples was suggested. The studied middle Eocene sediments from the central Arctic Ocean presented a problem in insufficiently leaching biogenic opal with a Na2CO3 solution. Based on XRD analysis, it was suggested that such an alkaline resistance results from slight diagenesis of biogenic opal. In order to solve this problem, an alkaline leaching method utilizing a 2 M NaOH solution was suggested for the accurate measurement of %biogenic opal in the Eocene sediments from the central Arctic. Furthermore, dissolution rates from lithogenic matter by NaOH solution were measured in order to correct the %biogenic opal values.  相似文献   

13.
The temporal and spatial distribution of total and organic particulate matter is investigated in the Bideford River estuary. Particulate matter is homogenously distributed in both the water column and the surface sediment, due to high rates of resuspension and lateral transport. The measured mean sedimentation rate for the estuary is 183·5 g of particulate matter m?2 day?1, of which more than half is due to resuspension.The surface sediment of the estuary is quantitatively the dominant reservoir of organic matter, with an average of 902·5 g of particulate organic carbon (POC) m?2 and 119·5 g of particulate organic nitrogen (PON) m?2. Per unit surface area, the sediment contains 450 times more POC and 400 times more PON than the water column. Terrestrial erosion contributes high levels of particulate matter, both organic and inorganic, to the estuary from the surrounding watershed. Low rates of sediment export from the estuary result in the accumulation of the terrigenous material. The allochthonous input of terrigenous organic matter masks any relationship between the indigenous plant biomass and the organic matter.In the water column, a direct correlation exists between the organic matter, i.e. POC and PON, concentration and the phytoplankton biomass as measured by the plant pigments. Resuspension is responsible for the residual organic matter in the water column unaccounted for by the phytoplankton biomass.The particulate content of the water column and the surface sediment of the estuary is compared to that of the adjacent bay. Water-borne particulate matter is exported from the estuary to the bay, so that no significant differences in concentration are noted. The estuarine sediment, however, is five to six times richer in organic and silt-clay content than the bay sediment. Since sediment flux out of the estuary is restricted, the allochthonous contribution of terrigenous particulate matter to the bay sediment is minor, and the organic content of the bay sediment is directly correlated to the autochthonous plant biomass.  相似文献   

14.
The dominant physical and chemical processes that control Fe, Mn and Zn are explored by comparing the compositions of sediments and their sources. The MnFe and ZnFe ratios in sediment are found to be largely unaffected by local hydraulic sorting (unlike the actual concentrations of Fe, Mn and Zn) and thus are useful indicators of origin. The sediments in northern Chesapeake Bay have markedly lower MnFe and ZnFe ratios than those found in the Susquehanna River (dissolved plus suspended) under ordinary flow, but not under high flow conditions. Since high flow conditions dominate sediment transport, seaward loss of a major fraction of the river-derived Mn and Zn need not be invoked to reconcile sediment and river compositions. Sediments in the seaward end of the northern bay have higher MnFe and ZnFe ratios than their principal external source, the eroding shore deposits. The excess Zn appears to be derived from the atmosphere; the required depositional flux of Zn is consistent with measurements of the total atmospheric flux. The excess Mn can be explained by remobilization of roughly 5% of the river-borne Mn from sediments in the landward part of the northern bay. Because rare floods influence sediment composition markedly, comparing suspended particles in the river at ordinary stages with resuspended sediment in the estuary would lead to the false interpretation that Mn and Zn were being desorbed in the saltwater.  相似文献   

15.
Measurements of salinity perturbations in a partially mixed estuary have been used to evaluate the usefulness of an inductive salinometer and to determine some of the characteristics of the salinity perturbations. The salinometer performed satisfactorily under most conditions. Although internal wave like effects were present, the turbulence fluctuations were dominant. The salinity fluctuations and the turbulent fluxes sw and su were found to behave in a manner similar to the density fluctuations in a thermally stratified atmospheric boundary layer and a laboratory open channel flow. A quadrant analysis suggested that the contribution of each quadrant to the turbulent flux changed with Ri. The turbulence parameters ν and cγ were found to decrease and increase respectively as Ri increases.  相似文献   

16.
The timing and magnitude of phytoplankton blooms have changed markedly in Narragansett Bay, RI (USA) over the last half century. The traditional winter–spring bloom has decreased or, in many years, disappeared. Relatively short, often intense, diatom blooms have become common in spring, summer, and fall replacing the summer flagellate blooms of the past. The annual and summer mean abundance (cell counts) and biomass (chl a) of phytoplankton appear to have decreased based on almost 50 years of biweekly monitoring by others at a mid bay station. These changes have been related to warming of the water, especially during winter, and to increased cloudiness. A significant decline in the winter wind speed may also have played a role. The changes in the phenology of the phytoplankton and the oligotrophication of the bay appear to have decreased greatly the quantity and (perhaps) quality of the organic matter being deposited on the bottom of the bay. This decline has resulted in a very much reduced benthic metabolism as reflected in oxygen uptake, nutrient regeneration, and the magnitude and direction of the net flux of N2 gas. Based on many decades of standard weekly trawls carried out by the Graduate School of Oceanography, the winter biomass of bottom feeding epibenthic animals has also declined sharply at the mid bay station. After decades of relatively constant anthropogenic nitrogen loading (and declining phosphorus loading), the fertilization of the bay will soon be reduced during May–October due to implementation of advanced wastewater treatment. This is intended to produce an oligotrophication of the urban Providence River estuary and the Upper Bay. The anticipated decline in the productivity of the upper bay region will probably decrease summer hypoxia in that area. However, it may have unanticipated consequences for secondary production in the mid and lower bay where climate-induced oligotrophication has already much weakened the historically strong benthic–pelagic coupling.  相似文献   

17.
《Marine Chemistry》2005,93(1):21-32
We investigated distributions of surface water CO2 partial pressure (pCO2), dissolved oxygen (DO) and associated carbonate parameters in the Pearl River estuary, a large subtropical estuary under increasingly anthropogenic pressure in China, in the summer of 2000 and late spring of 2001. pCO2 levels, measured underway using a continuous measurement system, were high during both seasons, with levels of >4000 μatm at salinity <0.5. pCO2 distribution overall mirrored DO across the salinity gradient. Using the linear relationship between excess CO2 and apparent oxygen utilization (AOU) in surface water, we conclude that aerobic respiration is the most important process in maintaining such high pCO2 measured upstream. The material being respired is likely in a close association with the organic pollutants discharged into the system. Based on the measured excess CO2 vs. AOU plots, we estimate that the upper limit of pCO2 should be ∼7000 μatm in the Pearl River estuary assuming that CO2 was produced solely by aerobic respiration.  相似文献   

18.
Three estuaries with differing catchment use and freshwater input were investigated in terms of their nutrient status, phytoplankton biomass, freshwater inflow and salinity between 1993 and 1995. The nutrients analysed include phosphate, nitrate, nitrite, ammonia and total particulate nitrogen. All the parameters were investigated for their relationship with land-use and freshwater abstraction. The Kromme River catchment area is relatively pristine, the river is impounded for ca. 133% of its mean annual runoff, and consequently, freshwater input into the estuary is only episodic. Nutrient and chlorophyll-a concentrations are low, but become elevated when freshwater does reach the estuary. The Geelhoutboom tributary contributes nutrients to the Kromme estuary during high freshwater inflow conditions, but is not a viable nutrient contributor during low flow conditions. Freshwater abstraction from the Swartkops River catchment is limited, and it is characterised by urbanisation and industrial development. The Swartkops River was the main source of phosphate in the estuary, whereas other small tributaries along the estuary were additional point sources for nitrate, ammonia and nitrite. The third system, the Sundays estuary, has no tributaries or other point sources except the Sundays River, where the catchment is extensively used for agriculture and freshwater input relatively high. The phytoplankton biomass (in terms of chlorophyll-a) was highest in the Sundays estuary, although phosphate concentrations were as low as in the Kromme estuary. Trends over time indicated a decrease in phosphate concentrations and showed variations for inorganic dissolved nitrogen concentrations since the previous 15 years in all the three estuaries. Nutrient stochiometry had changed in favour of inorganic dissolved nitrogen.  相似文献   

19.
Ecotone or Ecocline: Ecological Boundaries in Estuaries   总被引：1，自引：0，他引：1  
Two main ecological boundaries, ecotone and ecocline, have been defined in landscape ecology. At this scale, the estuary represents a boundary between rivers and the sea, but there has been no attempt to fit empirical data for estuaries to these boundary models. An extensive data set from the Thames estuary was analysed using multivariate techniques and species-range analysis, in order to investigate whether the ecocline or the ecotone model was most relevant to this estuary. Data for periods of high and low freshwater flow allowed the impact of large-scale fluctuations implicit in both models to be determined.A continuum of assemblages existed along the salinity gradient from freshwater river to the North Sea, with shifts in the ranges of organisms apparent in response to changes in freshwater flow. This pattern closely fits an ecocline model. However, the estuary differs from previously defined ecoclines in having two overlapping gradients in the major stressor: from river to mid-estuary for freshwater species and from sea to mid-estuary for marine species. We propose, therefore, that the estuary represents a two-ecocline model, with fauna inhabiting the mid-estuary being either freshwater or marine species at the edge of their range, rather than ‘ true estuarine organisms ’. This allows a redefinition of the Remane diagram, with estuarine species removed, and supports previous arguments that brackish-water species do not exist. Such two-ecocline models may also exist in other marine systems, such as rocky shores.  相似文献   

20.
Radionuclides (i.e., 7Be and 210Pb) can be used to trace particle and sediment dynamics and to quantify coastal oceanic processes with time scales ranging from a few days to a hundred years. Here, we study the settling dynamics of suspended particles and the implication by sedimentary heavy metals in the Wenjiao/Wenchang River and Wanquan River estuaries through the measurement of the particulate 7Be and 210Pb nuclides. Activity in the particulate phase had a range of 2.1–54.5 and 4.6–67.9 Bq kg−1 for 7Be and excess 210Pb (210Pbxs), respectively, in the Wenjiao/Wenchang River estuary. In the Wanquan River estuary, activity is in the range of 1.2–43.5 Bq kg−1 for 7Be and 6.2–194.5 Bq kg−1 for 210Pbxs. At the same time, activity in the dissolved phase had a range of 0.46–1.26 and 0.30–1.17 Bq m−3 for 7Be and 210Pb, respectively, in the Wenjiao/Wenchang River estuary; ranges of 0.10–2.31 and 0.09–1.87 Bq m−3 for 7Be and 210Pb, respectively, were observed in the Wanquan River estuary. The distribution coefficients (Kd) for the two nuclides decreased within increased in suspended particle matters (SPM) concentration and/or salinity in Wanquan River estuary. The residence times of particulate 7Be and 210Pbxs had ranges of 0.4–1.6 and 1.65–5.15 days, respectively, in the Wenjiao/Wenchang River estuary; and ranges of 0.02–3.2 and 0.61–4.44 days, respectively in the Wanquan River estuary. All residence times for the two nuclides increased in the seaward direction. In the Wenjiao/Wenchang River estuary, we found that 11.8–21.0% of Cu, 3.0–9.0% of Zn and 43.2–69.9% for Cd is removed from the water column and deposited into the estuary, and 24.2–34.8% for Cu, 7.2–23.8% for Zn, and 70.0–82.5% for Cd in the Wanquan River estuary, respectively.  相似文献   

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