Spatial spring distribution of the copepod Eurytemora affinis (Copepoda,Calanoida) in a restoring estuary,the Scheldt (Belgium)

The spatial spring distribution of Eurytemora affinis (adults and C5) in the Scheldt estuary (Belgium) brackish and freshwater reaches was studied in between 1996 and 2007. The bulk of the E. affinis population being generally situated in the brackish water reach (salinity > 0.5); we studied which environmental factors are responsible for its recent sporadic occurrence in the freshwater estuarine reach. Using PLS analysis, it is shown that its presence upstream is limited by a sufficient oxygen concentration (>4 mg l⁻¹) that is associated with temperature. Not only are the environmental conditions in the upstream zone important, but also the frequent presence of an O₂ minimum zone in the mid-estuary (O₂ min < 1.3 mg l⁻¹) seems to block the movement of the downstream E. affinis population in an upstream direction. Occasionally, the bulk of the population is however situated upstream. During these periods, high E. affinis abundance was also observed in the Durme tributary. Our findings suggest the possibility to use E. affinis as an “indicator” species of water quality, but also lead us to stress the necessity to consider conditions over the entire estuary when studying restoration effects, not exclusively in the zone of interest.     

Tidal exchange between a freshwater tidal marsh and an impacted estuary: the Scheldt estuary, Belgium

Tidal marsh exchange studies are relatively simple tools to investigate the interaction between tidal marshes and estuaries. They have mostly been confined to only a few elements and to saltwater or brackish systems. This study presents mass-balance results of an integrated one year campaign in a freshwater tidal marsh along the Scheldt estuary (Belgium), covering oxygen, nutrients (N, P and Si), carbon, chlorophyll, suspended matter, chloride and sulfate. The role of seepage from the marsh was also investigated. A ranking between the parameters revealed that oxygenation was the strongest effect of the marsh on the estuarine water. Particulate parameters showed overall import. Export of dissolved silica (DSi) was more important than exchange of any other nutrient form. Export of DSi and import of total dissolved nitrogen (DIN) nevertheless contributed about equally to the increase of the Si:N ratio in the seepage water. The marsh had a counteracting effect on the long term trend of nutrient ratios in the estuary.     

Contrasting behaviour of trace metals in the Scheldt estuary in 1978 compared to recent years

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 K_d (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 K_d values could be demonstrated. The sequence of K_d 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 K_d values cannot be used to describe redistribution processes.     

2011—2020年调水调沙前后黄河口海域浮游动物年间变化及影响因子

依据2011—2020年(2016年中断)黄河调水调沙工程实施前、后黄河口海域18个站位野外调查数据, 研究浮游动物种类组成和丰度变化及优势种更替, 以查明黄河口海域浮游动物的年间变动规律及调水调沙工程的影响。结果显示: 共记录浮游动物82种类(包括浮游幼体16类), 其中刺胞动物种类数最多, 共记录26种, 其次是桡足类出现23种。浮游动物种类组成的年间变化差异显著(P < 0.05), 2017年(未进行调水调沙)最低; 调水调沙前、后分别记录浮游动物69种和75种, 调水调沙前后种类数呈正相关(r=0.684, P=0.042); 调水调沙前后优势种更替率较高; 浮游动物丰度在2011—2015年较高, 2017—2020年相对较低, 调水调沙后浮游动物丰度年间变化达极显著水平(P < 0.01), 而调水调沙前后没有显著差异; 浮游动物丰度水平分布总体呈现从黄河口近岸到离岸递减趋势, 密集区位于黄河口北部近岸海域, 调水调沙后密集中心较调水调沙前向离岸海域略有推移。冗余分析表明, 对黄河口浮游动物年间变化影响较大的因子是叶绿素a浓度、溶解氧浓度和水温。研究表明: 2011—2020年调水调沙期间黄河口海域浮游动物丰度年间变动大于调水调沙前后变动, 调水调沙实施对浮游动物影响持续时间较短。     

Changes in phytoplankton diversity and community composition along the salinity gradient of the Schelde estuary (Belgium/The Netherlands)

Phytoplankton diversity and community composition were studied along the Schelde river–estuary–coastal zone continuum during the summer of 2003. DCA analysis indicated a gradual compositional turnover of the phytoplankton community within the estuary. GAM modelling of species response curves along the estuarine gradient was used to identify taxa that had their population maximum in the river, the coastal zone or within the estuary. Taxa that had their population maximum within the estuary did not form a homogenous community but comprised species with different salinity optima and rather restricted salinity tolerances. The observed changes in community composition along the estuarine transition zone correspond more closely to an ecocline than to an ecotone model. Despite the fact that few taxa had their population maximum at or near the salinity gradient, alpha diversity did not display a minimum around the salinity gradient. This lack of a diversity minimum within the estuary was ascribed to an important contribution of taxa of riverine or coastal origin to alpha diversity within the estuary contributed. On average 55% of the alpha diversity in the estuarine samples was due to riverine or coastal taxa. Beta diversity displayed a clear maximum around the salinity gradient. For planktonic organisms which are subject to mass effects, beta diversity is probably a better indicator for the impact of the salinity gradient on diversity in estuaries than alpha diversity.     

Organic complexation and its control of the dissolved concentrations of copper and zinc in the Scheldt estuary

Cathodic stripping voltammetry (CSV) is used to determine total (after UV-irradiation) and labile dissolved metal concentrations as well as complexing ligand concentrations in samples from the river Scheldt estuary. It was found that even at high added concentrations of catechol (1 m for copper and 0·4 m for iron) and of APDC (1 m for zinc) only part of the dissolved metal was labile (5–58% for copper, 34–69% for zinc, 10–38% for iron); this discrepancy could be explained by the low solubility of iron which is largely present as colloidal material, and by competition for dissolved copper and zinc by organic complexing ligands. Ligand concentrations varied between 28 and 206 n for copper and between 22 and 220 n for zinc; part of the copper complexing ligands could be sub-divided into strong complexing sites with concentrations between 23 and 121 n and weaker sites with concentrations between 44 and 131 n . Values for conditional stability constants varied between (logK′ values) 13·0 and 14·8 for strong and between 11·5 and 12·1 for weaker copper complexing ligands, whereas for zinc the values were between 8·6 and 10·6. The average products of ligand concentrations and conditional stability constants (a-coefficients) were 6 × 10² for zinc and 6 × 10⁶ for copper.The dissolved zinc concentration was found to co-vary with the zinc complexing ligand concentration throughout the estuary. It is argued that the zinc concentration is regulated, in this estuary at least, by interactions with dissolved organic complexing ligands. A similar relationship was apparent between the dissolved copper and the strong copper complexing ligand concentration. The total copper complexing ligand concentrations were much greater than the dissolved copper concentrations, suggesting that only strongly complexed copper is kept in solution.These results provide evidence for the first time that interactions of copper and zinc with dissolved organic complexing ligands determine the geochemical pathway of these metals.     

长江口浮游动物生态分布特征及其与环境的关系

采用2002年8月监测资料,对长江口海域的浮游动物生态分布特征(种类组成、群落结构及多样性等)分四个区域进行了分析,并探讨了浮游动物个体数、生物量分布与环境因子的关系。结果表明,调查海域共鉴定出浮游动物74种,桡足类28种,水母类7种,毛颚类6种,另外还鉴定出多种浮游虾类和浮游幼体。长江口外海区浮游动物种类最多,为55种,长江口混合区其次,为42种,长江口南支和南汇嘴附近海域种类较少,分别为11种和13种。长江口南支和南汇嘴附近海域优势种类为火腿许水蚤(Schmackeria poplesia)和虫肢歪水蚤(Tortanus vermiculus),长江口混合区为背针胸刺水蚤(Centropages dorsispinatus)、真刺唇角水蚤(Labidocera euchaeta),而中华哲水蚤(Calanus sinicus)和肥胖箭虫(Sagitta enflata)为长江口外海区的优势种类。浮游动物个体数大小为:长江口南支<长江口混合区<长江口外海区<南汇嘴;而生物量高低依次为:长江口外海区>长江口混合区>南汇嘴>长江口南支。长江口外浮游动物种类丰富,多样性指数较高,均匀度较好。经相关分析结果表明,浮游动物个体数与生物量存在明显的正相关,个体数与Hg呈正相关,与化学需氧量呈负相关;生物量与盐度、酸碱度、叶绿素a呈正相关,与溶解氧、化学需氧量、活性磷酸盐、无机氮表现为负相关。     

Distribution pattern of zooplankton in the han river estuary with respect to tidal cycle

The monthly distribution of zooplankton communities in Han River estuary was investigated at two stations from July 1998 to June 1999. Monthly mean abundance of total zooplankton varied remarkably, with the range from 20 indiv.·m^-3 to 19,600 indiv.·m^-3. During the study period, dominant species of zooplankton community were dinoflagellateNoctiluca scintillans, copepodsParacalanus indicus, Paracaanus crassirostris, Acartia hongi, Acartia ohtsukai, and meroplanton cirriped larvae. According to tidal states, relative high abundance occurred at high tide without regard to season. The temporal distribution of abundance implied that the reduced salinity probably limited the zooplankton populations and the fluctuations of salinity were an important factor in the variation of abundance. However, the results of salinity tolerance test shows that the variations in salinity do not directly influence the decrease of abundance. This study shows that the relatively high abundance of zooplankton near high tide seems to be related with the expansion of abundant zooplankton inhabiting Incheon coastal waters through tidal currents.     

A finite-element,multi-scale model of the Scheldt tributaries,river, estuary and ROFI

We report on the development and validation of a coupled two- and one-dimensional finite-element model for the Scheldt tributaries, river, estuary and region of fresh water influence (ROFI). The hydrodynamic equations are solved on a single, unstructured, multi-scale mesh stretching from the shelf break to the Scheldt tributaries. The tide is forced on the shelf break and propagates upstream in the riverine network. Upstream boundaries lie on sluices or outside of the region of tidal dominance where daily averaged discharges are imposed. Two-dimensional, depth-averaged shallow water equations are solved by means of the discontinuous Galerkin (DG) method over the marine and estuarine parts of the computational domain. In the rivers, however, one-dimensional equations are dealt with using the DG method with the addition of a technique to cope with confluence points. Model parameters are carefully calibrated, leading to the simulation of wind- and tide-forced flows that are in excellent agreement with available data. The diffusivity in the transport equation is calibrated using time series of salinity at various locations in the estuary. Finally, the Lagrangian residual transport in the estuary and the adjacent coastal zone is investigated. This work is a major step towards an integrated model for studying the dynamics of waterborne contaminants and the water renewal timescales in the Scheldt land-sea continuum.     

A diagnostic modelling framework to construct indices of biotic integrity: A case study of fish in the Zeeschelde estuary (Belgium)

We propose a coherent regression model building framework to construct fish-based indices. More specifically, we concentrate on the selection of an optimal set of metrics which remains a difficult problem. The paper departs from the observation that an index of biotic integrity (IBI) is analogous to a diagnostic model in medicine assessing the health condition of a patient from a series of biomarkers. In the same vein, an IBI is a diagnostic model predicting the ecosystem condition of a site from a set of (scored) metrics. Metrics are community attributes sensitive to anthropogenic pressure and their scores express the “distance to target” to a reference condition. In a medical context, Receiver Operating Characteristic (ROC) curves are commonly used to assess the diagnostic accuracy of laboratory tests. An ROC curve plots the sensitivity of a test (Se; the capacity to detect a disease or degradation) as a function of its false positive fraction (FPF) which is the complement of the specificity (Sp = 1 - FPF; the capacity to recognise a healthy person or a reference condition). The ROC curve represents the strength of the index to discriminate between degraded and reference sites. Higher curves correspond to stronger tests as then a higher sensitivity can be combined with a lower false positive fraction. Hence, it is intuitively clear to use summary statistics of the ROC curve as criteria to optimise medical tests or biotic indices. In this paper, we illustrate the value of this modelling framework with a case study in the Zeeschelde estuary in Belgium. In essence, a “traditional” IBI is an average of metrics scoring relevant properties of the ecosystem. We demonstrate this average score model (AVG) is a special member of the more flexible predictive logistic model (PLM) family. The selection of a set of metrics becomes equivalent to variable selection in statistical model building. We apply model building techniques as best subsets regression to facilitate the search for an optimal suite of metrics from a candidate set and use cross-validation to avoid overfitting. The results show that a few metrics suffice to discriminate between most-impacted and least-impacted sites.     

基于1998～2011年调查数据的长江口海域浮游动物群落划分

长江口海域是受人类活动以及自然变动多重压力影响下的典型水域。为研究长江口海域浮游动物群落动态, 作者基于1998～2011年每年5月(春季)和11月(秋季)长江口海域(30°30′～32°00′N、121°00′～123°20′E)浮游动物调查资料, 利用多元统计分析方法, 开展了该水域浮游动物群落结构分析。基于物种组成及相对丰度进行聚类, 春、秋季长江口海域的浮游动物可分为3个群落: A(淡水/半咸水群落、B(过渡群落)、C(外海群落)。群落的地理分布与海域的盐度梯度分布相对应, 其中: 浮游动物群落A与群落B的地理分界一般在盐度等值线14～18, 群落B与群落C的地理分界一般在盐度等值线24～28。淡水种以及半咸水种只在群落A中占优势; 水母类只在群落C中优势度值较高。比较分析1998～2011年各群落的物种多样性的年间变化, 发现秋季群落A的物种多样性呈现显著升高的趋势, 而群落B的物种多样性呈现显著降低的趋势; 春季, 群落B的物种多样性呈现显著升高的趋势, 而群落C则呈现显著降低的趋势。     

象山港冬季浮游动物的分布

对2002年12月象山港海区的浮游动物种类组成和数量分布特征及其与环境的关系进行了研究。结果表明,象山港海区出现浮游动物44种,可以划分为4个生态类群,其中近岸低盐性类群的种类较多,其优势种有真刺唇角水蚤Labidoceraeuchaeta、驼背隆哲水蚤Acro-calanusgibber、中华哲水蚤Calanussinicus、中华假磷虾Pseudeuphausiasinica和拿卡箭虫Sagittanagae等,半咸水河口类群、暖水性外海类群和广盐暖水性类群的种数均较少。浮游动物生物量的分布趋势与丰度的一致。湾顶部水域浮游动物的生物量和丰度都出现最高值,从湾顶部往湾口方向,浮游动物的生物量和丰度均呈逐渐降低的趋势。象山港海区周日连续站观测的结果显示,夜间半日潮时浮游动物的生物量和丰度均高于白昼半日潮时,低平潮时浮游动物的生物量与丰度均出现了最高值。     

杭州湾浮游动物群落与水团的相关性研究

1 引言海洋浮游动物是一个生态学范畴的概念,是依据其生活方式而划分的一类生物类群.浮游动物在海洋食物网中处于枢纽位置,担负着将单细胞藻类通过光合作用固定的能量向高营养层次传递的任务,在海洋物质循环中起着承上启下的作用,是一类对能量和物质循环起调控作用的关键功能群[1-3].     

Spatial and temporal distribution of cadmium and copper in water and zooplankton in the Bahía Blanca estuary,Argentina

Cadmium and copper in the dissolved and particulate phase and in zooplankton were determined in the Bahía Blanca estuary during six surveys from March to December 2005. Temperature, pH, salinity, dissolved oxygen, suspended particulate matter, particulate organic matter and chlorophyll-a were also considered. Dissolved Cd was below the detection limit (0.2 μg L⁻¹) for almost the entire study period whereas Cu concentrations (0.5–2.4 μg L⁻¹) indicated a continuous dissolved Cu input. Particulate Cd concentrations ranged from below the detection limit (<0.01) to 28.6 μg g⁻¹ d.w. while particulate Cu ranged from below the detection limit (<0.04) to 53.5 μg g⁻¹ d.w. Cd in mesozooplankton ranged from below the detection limit (<0.01) to 37.4 μg g⁻¹ d.w. Some of the Cd levels were higher than those reported for other aquatic ecosystems. Cu in the mesozooplankton ranged from 1.3 to 89.3 μg g⁻¹ d.w., values which were within the reported values or higher than other studies. The log of the partition coefficients (log (K_d)) of Cd was 0.04, while log (K_d) for Cu ranged from −0.39 to 2.79. These values were lower than both those calculated for other estuaries and the typical coefficients for marine environments. The log of the bioconcentration factor (log BCF) of Cd was 1.78, indicating that Cd concentration was higher in the zooplankton than in the dissolved phase. Log BCF of Cu ranged from 1.15 to 3. The logs of the biomagnification factors (log BMF) of Cd were low, with a range between −3.45 and 2.21 and those for Cu ranged from −0.1 to 3.35. Positive values indicate biomagnification while negative values indicate biodiminution. In general, no significant dissolved Cd concentration appeared to be present in the Bahía Blanca estuary and Cu values did not indicate a critical environmental status. The particulate phase seemed to be the major carrier for Cd and Cu and TPCu values were within the normal values for an anthropogenically stressed estuary but not for a strongly polluted system. This fraction was the most important metal source for the mesozooplankton. Moreover, the highest metal concentrations were in the mesozooplankton since most of the bioconcentration and biomagnification factors were positive, especially for Cu.     

洋山深水港入境船舶压载水浮游动物种类组成分析

2008年10月至2009年4月采集了19艘停靠在上海洋山深水港的入境船舶压载水水样,对其浮游动物的种类组成进行了分析,共检出压载水中浮游动物39种,其中桡足类37种、淡水枝角类1种、海洋枝角类1种.结果显示,压载水中浮游动物的密度及种类组成与水样压载地的环境直接相关,不同航线船舶压载水中浮游动物的种类差异较大.调查发...     

Response of Nereis diversicolor (Polychaeta, Nereidae) populations to reduced wastewater discharge in the polluted estuary of Oued Souss, Bay of Agadir, Morocco

Field investigations on the population dynamics of Nereis diversicolor were carried out from January 2002 to December 2003 in the estuary of Oued Souss (southwestern Morocco) to determine the changes caused by setting up of a domestic and industrial wastewater purification plant (M'zar) before and after by the end of wastewater discharges in November 2002 on the structure of the ecosystem. Samples of N. diversicolor were collected monthly in the intertidal zone at low tide before (during 2002) and after (during 2003) the end of wastewater discharges.Separation of cohorts using the Algorithm EM method (McLachlan, G.J., Krishnan, T., 1997. The EM algorithm and extensions. Wiley Series in Probability and Statistics. Wiley, New York, 274 pp.) allowed determination of the growth rate (mm day⁻¹) by cohort and the annual production. The data showed significant differences between populations of Nereis diversicolor before and after the end of wastewater discharges. During the wastewater discharge period (2002), the population had a mean annual density of 1992 ind m⁻², a mean annual biomass of 75.52 g DW m⁻² and an annual secondary production of 141.3 g DW m⁻² with a P/B ratio of 1.87. After the end of discharges (2003), density, biomass and secondary production decreased significantly. The annual averages for these parameters were 740 ind m⁻², 14.16 g DW m⁻² and 23.83 g DW m⁻², respectively, with a P/B ratio of 1.68.The important decrease observed in density, biomass and secondary production of Nereis diversicolor may be attributed (a) to the environmental changes observed after the end of wastewater discharges in the estuary of Oued Souss, namely the increase of salinity and the decrease of organic matter content, and (b) to the migration of this species towards other areas.     

Interstitial water chemistry of the inner continental shelf sediments off the gironde estuary

The interstitial water composition ( , alkalinity, Ca²⁺, Mg²⁺, Sr²⁺, Na⁺, K⁺) and the cation exchange capacity (CEC) were determined for the muddy sediments of the continental shelf off the Gironde Estuary (France), in the area where the sediment represents the deposit of the muddy suspension of the river. In comparison with seawater concentrations, the pore waters below 10 cm depth, show depletions of and Ca²⁺ and below a 30 cm depth show depletions of Mg²⁺. Inversely, the upper 10 cm an enrichment of Ca²⁺ concentration, and an increase of K⁺ concentration to a 40 cm depth. High values of are observed at the top 4 cm. Alkalinity enrichment is observed along the length of the core. Applying the alkalinity models for the sediment below a 10 cm depth demonstrates generally that calculated alkalinities are higher than the measured ones. Ca²⁺ dissolution occurs at the first 10 cm and authigenic carbonate precipitation starts beneath that level. Mg²⁺ depletion is accompanied by bicarbonate loss. This proves that Mg²⁺ depletion is due to a Mg-silicate reaction. The result of the CEC does not confirm the Mg²⁺ uptake by clay minerals in exchangeable site, under reducing conditions. Diffusion and bioturbation play an important role in the pore water concentration at the top of the core.     

Statistical analysis of estuarine profiles: II application to arsenic in the Tamar estuary (S.W. England)

By combining field observations with a statistical approach and a simple but effective estuarine analogue, the main features of the cycling of arsenic in the Tamar estuary have been elucidated. As(III) and As(V) enrichment in the water column is due to a combination of localized inputs and effective recycling of sediment interstitial waters. The profiles of As(V) are similar to those of NH₄⁺ and are dominated by an estuarine maximum resulting from an input from the sediments. As(III) profiles are correlated with those of dissolved manganese and exhibit both fresh water and estuarine maxima. As(III) appears to be effectively removed at the freshwater/brackish water interface by a combination of heterogenous oxidation, catalysed by hydrous manganese dioxide, and adsorption on to iron oxyhydroxide. The estuarine distribution of As(III) within the water column is consistent with the published rates of oxidation of As(III) to As(V) by both inorganic and microbiological processes. The reduction of As(V) to As(III) in the sediments is incomplete. On the basis of our observations a tentative estuarine arsenic cycle is presented.