Harbour Porpoises Phocoena phocoena in the Eastern Scheldt: A Resident Stock or Trapped by a Storm Surge Barrier?

Coastal protection measures are planned and executed worldwide to combat the effects of global warming and climate change, in particular the acceleration of sea level rise, higher storm surge flooding and extensive coastal inundation. The extent to which these defensive measures may impact coastal and estuarine ecosystems is still poorly understood. Since the building of a storm surge barrier, movement of harbour porpoises Phocoena phocoena in and out of the Eastern Scheldt tidal bay (SW-Netherlands) may be limited. To measure residency, porpoises stranded along the Dutch North Sea coast between 2006 and 2008 were sampled for muscle (n = 102) and bone tissue (n = 118), of which 9 muscle (8.8%) and 12 bone samples (10.2%) were collected from animals stranded within the Eastern Scheldt. Stable carbon (δ¹³C) was analysed to get insight into the habitat use and residency of porpoises in the Eastern Scheldt. Our data showed significantly higher δ¹³C values in the muscle of porpoises stranded within the Eastern Scheldt (µ = −17.7‰, SD = 0.4‰) compared to animals stranded along the Dutch coast (µ = −18.3‰, SD = 0.5‰). This suggests that most porpoises stranded in the Eastern Scheldt foraged there for a longer period. The distinct δ¹³C signature of animals from the Eastern Scheldt was not observed in bone tissue, suggesting a relatively recent shift in habitat use rather than life-long residency of porpoises within the Eastern Scheldt. The high number of strandings within the Eastern Scheldt suggests a higher mortality rate compared to the Dutch coastal zone. Our study indicates that along with other changes in the physical environment, the storm surge barrier may play an important role in determining the residency of porpoises in the Eastern Scheldt, and that the area might act as an ecological trap for porpoises entering it.     

Molluscan diversity in tidal marshes along the Scheldt estuary (The Netherlands, Belgium)

The mollusc fauna of 64 sites in 31 tidal marshes was surveyed along a salinity gradient from freshwater to marine conditions in the river Scheldt (Belgium–The Netherlands). A total of 10649 specimens involving 31 taxa were identified. Salinity turned out to be a major factor in mollusc assemblages in the Scheldt estuary, but other factors can not be excluded. In the marine part five species were common, compared to the brackish part where only Assiminea grayana was abundant. In the freshwater zone species richness was highest (24). There was a significant correlation between flooding frequency and species richness in the tidal freshwater marsh `Durmemonding'. Finally, the survey confirmed the distribution of the amphibious hygromiid snail Pseudotrichia rubiginosa, a species which in Belgium only occurs in the marshes of the tidal freshwater part of the Scheldt and its tributaries.     

Habitat and distribution of perforatella rubiginosa (Gastropoda,Pulmonata) in the freshwater tidal region of the Scheldt estuary,Belgium

The amphibious land-molluse,Perforatella rubiginosa, is a common, wide-spread and characteristic inhabitant of the freshwater tidal region of the river Scheldt and its tributaries in NW Belgium. The species occupies a rather narrow zone in the uppermost intertidal area, which is characterized by large amounts of tidal drift covering the bottom, and usually by a luxuriant vegetation of tall, nitrophilous herbs, often withUrtica dioica dominant. Other characteristic molluscs of this zone areCarychium minimum, Oxyloma pfeifferi, O. sarsi, Deroceras laeve, Vitrea crystallina andZonitoides nitidus, locally alsoNesovitrea hammonis. Communication nr. 143 of the Delta Institute for Hydrobiological Research, Yerseke, The Netherlands     

Sand dwelling Turbellaria from the Netherlands Delta area

Sand dwelling Turbellaria from the Delta of the Rivers Rhine, Meuse and Scheldt have been investigated. Thirty-eight samples taken from littoral and sublittoral stations in the Grevelingen, Eastern and Western Scheldt have been analysed.Thirty-three species were recorded (Acoela were not considered); twenty-four of them are new for the area and seven new species are described.Density and diversity of Turbellaria were higher in the Eastern Scheldt than in the Western Scheldt or in the Lake Grevelingen. A maximum density of 82 ind./100 cm³ was noted. A tentative calculation on relative abundance of the representatives of the different Turbellaria orders is established. Proseriata seem to be dominant in the localities studied.Abbreviations acg : accessory glands - aco : accessory organ - ad : atrial diverticle - b : bursa - br : brain - cil : cilia - cm : circular muscle - cn : cnidosac - co : copulatory organ - cs : cuticular spines - css : cuticular stylet sheat - de : ejaculatory duct - di : ductus intervesicularis - ds : seminal duct - dsp : spermatic duct - en : enteron - fd : female duct - fp : femal pore - ga : genital atrium - gf : glands in female duct - gg : glands - gp : genital pore - hp : adhesive papillae - ivs : intra capsular seminal vesicle - lm : longitudinal muscle - m : mouth - mp : male pore - ov : ovary - p : proboscis - pg : proboscisglands - ph : pharynx - phg : pharyngial glands - r : retractor muscle - rh : rhabdites - rhg : rhabdite glands - rs : seminal receptacle - s : stylet - sta : statocyst - ut : uterus - t : testis - v : vagina - vg : prostate vesicle - vi : vitellary - vs : seminal vesicle     

The influence of the spectral composition of irradiance on primary production in the Eastern Scheldt (The Netherlands)

The error inin vivo ¹⁴C incubator measurements of primary production in the Eastern Scheldt when neutral density filters were used and the error obtained when no account was taken of the spectral changes in submarine irradiance that occur with increasing depth, were evaluated theoretically. By multiplying the photosynthetic action spectra of two marine algae by calculated irradiance in the euphotic layer using Kd and Kd() respectively, the gross primary production P[Ed(400–700)] and P[Ed()] was computed. In the green-brown waters of the Eastern Scheldt estuary the use of neutral density filters was sufficient to simulate the underwater light conditions. In clear waters it can cause an overestimation of the gross production.     

Numerical modelling of suspended sediment transport in tidal estuaries: A comparison between the Tagus (Portugal) and the Scheldt (Belgium-the Netherlands)

A numerical model to simulate the transport of suspended sediment in tidal estuaries is presented. The model is applied to the two large European estuaries the Tagus (Portugal) and the Scheldt (Belgium-The Netherlands). Calculated suspended sediment concentrations compare favourably with observations in the Tagus (r=0.84) and in the Scheldt (r=0.73). The parametrization scheme indicates that the bottom content of fine sediment is correlated with depth in the Tagus; but a different relationship is used in the Scheldt. Because of tidal range differences, average suspended sediment concentrations are lower in the Tagus (80 mg l⁻¹) than in the Scheldt (130 mg l⁻¹), but a larger relative variation between spring and neap tide concentrations may occur in the Tagus.     

Dynamics of dissolved and biogenic silica in the freshwater reaches of a macrotidal estuary (The Scheldt, Belgium)

Temporal evolution of dissolved and biogenic silica concentrations along the Scheldt tidal river and in its tributaries was investigated during 1 year in 2003. In the tributaries, dissolved silica (DSi) concentrations remained high and biogenic silica (BSi) concentrations were low throughout the year. In the tidal river during summer, DSi was completely consumed and BSi concentrations increased. Overall, most of the BSi was associated with living diatoms during the productive period in the tidal river. Nevertheless, the detrital BSi was a significant fraction of the total BSi pool, of which less than 10% could be attributed to phytoliths. The tidal river was divided into two zones for budgeting purposes. The highest productivity was observed in the zone that received the highest water discharge, as higher riverine DSi input fluxes induced presumably a less restrictive DSi limitation, but the discharge pattern could not explain all by itself the variations in DSi consumption. Silica uptake and retention in the tidal river were important at the seasonal time-scale: from May to September, 48% of the riverine DSi was consumed and 65% of the produced BSi was deposited, leading to a silica (DSi + BSi) retention in the tidal river of 30%. However, when annual fluxes were considered, DSi uptake in the tidal river amounted to 14% of the DSi inputs and only 6% of the riverine silica (DSi + BSi) was retained in the tidal river.     

Ecological investigations in sublittoral biocenoses on hard substrates

Summary In 1979 the Environment Research Division of the Delta Service of the Dutch Department of Public Works and Waterways instructed Bureau Waardenburg to investigate the distribution of biocenoses on and near hard substrates in the Eastern Scheldt and Lake Grevelingen. The instruction was issued in connection with the progress of the so-called Delta Works, a large engineering project aiming at a maximal protection of the southwest Netherlands against stormfloods. In this project dykes are made higher, some estuaries have been closed off from the sea, and the Eastern Scheldt area will be protected by means of a storm surge barrier.The intention of the investigation presented here is to describe the biocenoses of the hard substrates in such a way, that changes caused by the engineering project can be established. This means that these biocenoses must be described in terms of a list of species visible to the naked eye, of which the percentage of coverage of the substrate is estimated.Is is attempted to obtain an impression of seasonal changes in the biocenoses, and to distinguish these from phenomena that are not connected with the seasonal changes. Diatoms, microscopical algae, small crustaceans (like Gammaridea) and worms and molluscs which normally live in concealment were not studied. Underwater observations in this investigation are done by divers with SCUBA equipment. In winter and spring, when water temperatures are low, dry constant-volume diving suits are being used.Apart from stony materials also wood and peat are studied because of their suitability as settling substrate for various organisms. Three times a year, in February–March, June–July, and October–November, recordings of flora and fauna are made at a number of fixed points in Lake Grevelingen and the Eastern Scheldt. The recordings are made according to the method of Braun-Blanquet, much used in vegetation analysis, and slightly modified to fit the circumstances under water.Apart from the sessile benthos and algae, semi-mobile organisms like mussels and sea-anemones, and mobile animals like starfish, crabs, bottom-dwelling fish are recorded. At every point samples are collected from the flora and fauna. The various organisms are identified in the laboratory since many of them cannot be identified during the underwater recordings.If it appears that changes in the biocenoses occur by the influence of the engineering works, the latter can be executed with necessary modifications to control those changes. Also specified management measures can be taken to prevent or diminish negative effects on flora and fauna.     

Restoration of the Sieperda Tidal Marsh in the Scheldt Estuary, The Netherlands

Because of land reclamation, reinforcement of dikes, and the deepening of shipping channels, large areas of tidal marshes have been removed or eroded from the Scheldt estuary during the last two centuries. Tidal wetland restoration contributes toward compensating this loss of habitat. Not all restoration projects are meticulously planned, however; some are forced by nature. During a severe storm in 1990, a dike was breached in the brackish part of the Scheldt estuary and returned tidal influence to the Sieperda polder. In the 10 years since the dike breach, the former polder has changed into a brackish tidal marsh. Here we report on the geomorphologic and ecological developments that have taken place in the marsh. Tidal intrusion into the former polder turned crop fields into mudflats and changed pastures into salty marsh vegetation. The digging of a new creek improved marsh hydrology and enhanced tidal intrusion further into the marsh. Macrofauna typical of estuarine mudflats established rapidly in the developing marsh. Vegetation succession took place rapidly. Within 5 years, large areas of mudflats became covered with marsh vegetation. Birds characteristic of salt marshes were observed breeding or seen foraging in the marsh. The number of wading birds declined as areas of mudflat became overgrown. It is demonstrated that tidal flow is the engine to tidal marsh restoration. Tidal influence caused geomorphologic changes, which directed ecological developments in the former polder.     

Average annual growth and condition of mussels as a function of food source

Prior to 1986, before completion of a storm surge barrier, the average annual condition of mussels at culture plots in the Eastern Scheldt was better in the western part near the North Sea, than in the central part of the estuary. No such difference was observed in 1986 and 1987.To predict the effects of the barrier on mussel culture, the condition of the mussels, which is an index of growth rate, is analysed and correlated with food sources for the period 1981–84. In the western and central part of the Eastern Scheldt, mussel condition correlates strongly with average annual primary production, but not with chlorophyll-a concentrations. This suggests a direct link between primary production and the growth of mussels.In the western part of the estuary, the relation between condition and primary production has a less steep slope than in the central part. Import of food from the North Sea is suggested to act as an additional food source in the west of the Eastern Scheldt; hence the better condition values of the mussels, also in years with relatively low primary production.The storm surge barrier reduces the water exchange with the North Sea. Reduced import of food and consequently lower mussel condition are expected in the western part of the estuary. Preliminary data from 1987 confirm this prediction.     

Potential re-establishment of diadromous fish species in the River Scheldt (Belgium)

This study (2002) documents on the inland penetration off diadromous fish species into the tidal and non-tidal part of the River Scheldt and on the impact of two lock-weir complexes. Long-term trends in oxic conditions show the river is undergoing a natural recovery process, nevertheless five of ten diadromous species recorded were still restricted to the brackish part of the estuary. Despite poor conditions, five species reached the upper freshwater part of the estuary. Erratic free-flowing conditions at the tidal weir offered limited opportunities for some diadromous species to migrate into the non-tidal part of the river. Upstream migration over the second barrier is almost completely blocked. Rehabilitation schemes to restore self-sustaining populations of diadromous fish in the cross-border River Scheldt need to include the building of fish bypasses and improved wastewater treatment and habitat restoration programmes. Guest editors: S. Dufour, E. Prévost, E. Rochard & P. Williot Fish and diadromy in Europe (ecology, management, conservation)     

Distribution and ecology of anthozoa in the estuarine region of the rivers Rhine,Meuse and Scheldt

Data on the ecology and distribution in the estuarine region of the rivers Rhine, Meuse and Scheldt are given for ten species of Anthozoa. These data have been correlated with several environmental variables, but especially salinity. Communication nr. 142 of the Delta Institute for Hydrobiological Research.     

Sulfate reduction in fine-grained sediments in the Eastern Scheldt,southwest Netherlands

Sulfate reduction and sulfide accumulation were examined in fine-grained sediments from rapidly accreting abandoned channels and mussel culture areas in the Eastern Scheldt, which covered 4 and 5% of the total surface area, respectively.Reduction rates were measured in batch experiments in which the SO₄ ^2– depletion was measured during anoxic incubation. The reduction rates in summer varied between 14–68 mmol SO₄ ^2– m^–2 day^–1 and were related to the sedimentation rate. In the most rapidly accreting channels, SO₄ ^2– was exhausted below 15–50 cm and methanogenesis became the terminal process of organic carbon oxidationOne-dimensional modelling of sulfate profiles in mussel banks indicated that the subsurface influx of SO₄ ^2– was almost of the same order as the diffusive flux at the sediment-seawater interface, during the initial stages of the mussel bank accretion. The energy dissipation of waves and tidal currents on the mussel bank surface increased the apparent sediment diffusivity up to 3-fold, especially in the winterThe results indicate that acid volatile sulfide (AVS) was the major, in-situ reduced, sulfur compound in the sediment. The sulfidation of easily extractable iron was nearly complete. Pyrite concentrations (40–80 M S cm^–3) were as high as the AVS concentrations, but there was apparently no in-situ transformation of AVS into pyrite. The detrital pyrite originated from eroding marine sediments elsewhere     

Description of Proales litoralis sp. nov. (Rotifers, Monogononta: Proalidae) from the marine littoral

Proales litoralis sp. nov. (Rotifers, Monogononta: Proalidae) collected from littoral algae and psammon of the Channel (France) and the Eastern Scheldt (the Netherlands) is described. The affiliation of the new species is discussed.     

城市土地利用变化对生态系统服务价值影响的多情景模拟——以深圳市为例

深圳市作为粤港澳大湾区城市化水平最高、经济最为发达区域,其快速变化的土地利用方式对生态系统服务价值产生了深刻影响。基于1995—2015年深圳市土地利用和生态系统服务价值(ESV)变化规律,运用FLUS模型与ESV算法,设定自然发展、城市发展、耕地保护和生态保护4种情景,模拟不同情景下土地利用变化对ESV的影响。结果表明：(1) 1995—2015年转出量最高的地类是草地,草地与林地间存在密切相互转化关系,除建设用地外,其余地类均呈“入不敷出”态势;(2) 1995—2015年ESV总价值的下降趋势由迅猛变化为和缓,调节服务是深圳市最主要的生态系统服务功能,其次则是支持服务功能;(3)秉持粤港澳大湾区建设基本原则,以2035年为目标年,设定了自然发展、城市发展、耕地保护和生态保护四种情景,发现自然发展和城市发展的ESV总价值损失量较高,建筑面积的增加和草地面积的大规模减少成为两情景下生态系统服务价值减少的关键。生态保护情景下,虽然ESV总价值减少趋势并未有效遏制,但减少量明显少于其余三种情景,成为未来深圳市土地利用优化的最优情景。     

海平面上升对粤港澳大湾区沿海生境脆弱性评估

全球气候变暖所导致的海平面上升和快速城镇化将对沿海生境的分布和景观格局造成重大影响。评估海平面上升影响下的滨海湿地的脆弱性是对区域生态环境进行修复治理的重要依据。以粤港澳大湾区为例,基于SLAMM模型和Fragstas模型,针对六种海平面上升和土地利用耦合情景,对红树林、盐沼和潮滩三类海岸生境在2100年的面积变化、分布状况和脆弱程度进行了预测和分析。结果表明:1) 随着海平面上升,红树林和潮滩生境遭受严重退化。其中,红树林高脆弱性区主要分布在西江口、珠江口和黄茅海东岸。潮滩高脆弱性区则平均分布在大湾区沿海地带。相比之下,盐沼生境受海平面上升的影响较小。2) 与红树林和潮滩相比,土地利用模式对盐沼生境的影响最为显著。在保护已开发用地的情景下,珠江口西侧的盐沼面积大幅增加,脆弱性程度低。在保护所有旱地的情景下,盐沼生境面积虽然基本维持,但景观格局破坏严重,脆弱性程度高。本研究建议针对高脆弱区,动态调整土地利用策略,清理沿海湿地向内迁移的空间,增强沿海生境应对海平面上升的适应性。本研究可为沿海湿地的管理和保护提供科学支持。     

Effects of tide range alterations on salt marsh sediments in the Eastern Scheldt,S. W. Netherlands

The construction of three dams induced large changes in the tide range in the Eastern Scheldt, a tidal inlet in the southwestern part of the Netherlands. In 1986 the mean high tide level was reduced by almost one metre. This excluded the greater part of the medium-high marshes almost completely from tidal flooding.The absence of tidal flooding in the summer of 1986, combined with a net precipitation deficit, increased the bulk density of the sediment irreversibly from 400 to 530 kg m^–3 in the top 5 cm. The subsidence of the backmarshes varied from 1 to 8 cm.The loss of moisture allowed oxygen to diffuse into the initial reducing sediment. This altered the geochemistry of the sediment significantly. The redoxcline was lowered from a mean depth of about 15 cm in 1985 to 20–30 cm in the summer of 1986. Evidence of pyrite oxidation within a narrow depth interval of 15–30 cm was obtained from the change in the composition of pore waters. The rapid increase in redox potentials (up to 600 mV) and total dissolved iron (up to 5 mM 1^–1) and SO _inf4 ^sup2– (up to 65 mM 1^–1) and the decrease in pH (up to 4.5–2.5) all suggest a rapid oxidation of pyrite. Acidic conditions were found only in sediments with low contents of calcium carbonate and high contents of pyrite. The importance of seasonal changes in redox processes on the partial decalcification of the salt marsh sediments is discussed.The established of a new tide range was reflected in the pH and Eh of the sediment. In December 1987 the depth profiles of pH and Eh were again close to those observed in 1985.     

Central estrogen inhibition of angiotensin II-induced hypertension in male mice and the role of reactive oxygen species

It has been shown that reactive oxygen species (ROS) contribute to the central effect of ANG II on blood pressure (BP). Recent studies have implicated an antihypertensive action of estrogen in ANG II-infused female mice. The present study used in vivo telemetry recording and in vitro living mouse brain slices to test the hypothesis that the central activation of estrogen receptors in male mice inhibits ANG II-induced hypertension via the modulation of the central ROS production. In male wild-type mice, the systemic infusion of ANG II induced a significant increase in BP (Delta30.1 +/- 2.5 mmHg). Either central infusion of Tempol or 17beta-estradiol (E2) attenuated the pressor effect of ANG II (Delta10.9 +/- 2.3 and Delta4.5 +/- 1.4 mmHg), and the protective effect of E2 was prevented by the coadministration of an estrogen receptor, antagonist ICI-182780 (Delta23.6 +/- 3.1 mmHg). Moreover, the ganglionic blockade on day 7 after the start of ANG II infusions resulted in a smaller reduction of BP in central Tempol- and in central E2-treated males, suggesting that estrogen inhibits the central ANG II-induced increases in sympathetic outflow. In subfornical organ slices, the application of ANG II resulted in a 21.5 +/- 2.5% increase in ROS production. The coadministration of irbesartan, an ANG II type 1 receptor antagonist, or the preincubation of brain slices with Tempol blocked ANG II-induced increases in ROS production (-1.8 +/- 1.6% and -1.0 +/- 1.8%). The ROS response to ANG II was also blocked by E2 (-3.2 +/- 2.4%). The results suggest that the central actions of E2 are involved in the protection from ANG II-induced hypertension and that estrogen modulation of the ANG II-induced effects may involve interactions with ROS production.     

黄河三角洲滨海湿地潮沟分布与植被覆盖度的关系

基于黄河三角洲滨海湿地2005、2010与2017年3个时期的Landsat TM/OLI影像,利用遥感和地理信息技术,对黄河三角洲滨海湿地的潮沟与植被覆盖度的分布格局与动态变化进行了分析,并运用网格搜索法,对研究区的潮沟与植被覆盖度进行相关分析。结果表明:(1) 2005—2017年黄河三角洲滨海湿地植被覆盖度不断提高,低植被覆盖度的面积减少了233.73 km2,高植被覆盖度的面积增加了165.85 km2;(2) 2005—2017年黄河三角洲滨海湿地的潮沟长度和面积不断增加,频数也在增加,其中2017年滨海湿地东南部的潮沟长度达到216.13 km,面积为22.23 km2,长度和面积分别比2005年增加了36.91%和49%;(3) 2005—2017年黄河三角洲潮沟分布与植被覆盖度呈负相关,其中2010年、2017年的潮沟与植被覆盖度呈显著相关(P<0.05),这说明黄河三角洲的潮沟的空间分布与区域植被的长势密切相关。