Trophic functioning of the St. Lucia estuarine lake during a drought phase assessed using stable isotopes

The St. Lucia Estuary is Africa’s largest estuarine system and is currently experiencing the stress of prolonged freshwater deprivation, manifested by extremely low water levels and hypersalinity. These unprecedented conditions have raised questions regarding the trophic functioning of the ecosystem. Despite the substantial amount of research previously undertaken within this system, no studies of food web structure and function have yet been documented. This study therefore aimed to examine the food web structure of the St. Lucia estuary system through the use of carbon and nitrogen stable isotope analysis. Analysis of carbon isotope ratios indicates that benthic carbon sources are most utilised at sites with low water levels and generally higher salinity (Catalina Bay, Charter’s Creek). Conversely, the estuarine region of the mouth and Narrows, with its elevated water levels and lower salinity, still sustains a viable pelagic food web. Analysis of δ¹⁵N ratios indicates that the number of trophic transfers (food chain length) might be related to water levels. Overall, the study provides a greater understanding of the ecological processes of this complex estuarine lake, which may allow for future comparisons of trophic functioning under drought and normal/wet conditions to be made.     

Origin of resources and trophic pathways in a large SW Atlantic estuary: An evaluation using stable isotopes

The Río de la Plata (34° 36′ S, 55° 58′ W; Argentina and Uruguay) estuary, one of the most important South American estuarine environments, is characterized by weak seasonal freshwater discharge, low tidal amplitude (<1 m), a wide and permanent connection to the sea, and a salt-wedge regime. Using stable isotope analysis, we explored the relative importance of the different sources of primary production in the food web. Our results show that phytoplankton and macrodetritus from terrestrial salt and freshwater marshes both contribute to the food web of the Río de la Plata estuary. On the basis of the sampled species, we identified four trophic levels. The clam Mactra isabelleana, the calanoid copepod Acartia tonsa, and the opossum shrimp Neomysis americana are the primary consumers. The rays Atlantoraja castelnaui and Squatina guggenheim and the shark Galeorhinus galeus are the top predators. The Río de la Plata food web shows an important input of nutrients derived from phytoplankton. Rays, sharks, and predatory gastropods reveal an important contribution of C4 plants (likely Spartina spp.). However, production derived from C3 plants is also important for some species. The fishes Brazilian menhaden, Brevoortia aurea; the stripped weakfish Cynoscion guatucupa; and the whitemouth croaker, Micropogonias furnieri, showed differences in their isotopic signatures as juveniles and adults, indicating different food sources, and they were therefore treated as different components of the food web. Our data suggest that detritus from salt and freshwater marshes is reaching the Río de la Plata estuary and can be an important allocthonous source of energy to this environment.     

Sea,freshwater or saltpans? Foraging ecology of terns to assess mercury inputs in a wetland landscape: The Ebro Delta

The Ebro catchment, the largest river basin in Spain, includes various heavily industrialized areas. Among these is the Flix site, where a chemical plant has been operating since the beginning of the 20th century. This extended operational period, together with the construction of a dam next to the factory around 1960, resulted in the accumulation of large amounts of heavily polluted sediments in the adjacent riverbed, many of which are contaminated by mercury. Pollutants from Flix are carried downstream by the Ebro River to its delta. In order to assess the transfer of mercury to the complex river estuary ecosystem, we studied the ecology of the tern community living there as these birds segregate into a range of habitats. For this purpose, first we used stable isotope analysis (SIA) (δ³⁴S, δ¹³C, δ¹⁵N) of eggs to determine the trophic ecology and habitat partitioning of several tern species (Common, Sandwich, Little, Gull-Billed and Whiskered Tern) breeding sympatrically, in order to link their foraging ecology with habitat types. Next we measured mercury concentrations in eggs to monitor the input of this metal into the diverse habitats. With the exception of the Little Tern, the other terns used a restricted habitat range in the Ebro Delta, as shown by C and S isotopes; the Gull-Billed and Whiskered Tern foraged in freshwater habitats, while the Common and Sandwich Tern used marine habitats. This restricted feeding behavior of the Gull-Billed and Common Tern contrasts with previous reports in other breeding sites. The Little Tern, which showed a wide range of isotopic values, was found to be an opportunistic forager but fed mainly in saltpans, a feeding habitat not reported previously for this species in this area. We found that mercury concentrations are related to foraging habitat and diet, and are unexpectedly higher in species feeding on demersal prey in marine habitats and also higher in birds feeding in saltpans than in those feeding in freshwater habitats. The mercury concentrations found in the Little and Common Tern eggs sampled in “Punta de la Banya” may be sufficiently high to endanger breeding success.     

基于MODIS数据的渤海海冰遥感探测系统的设计

为了满足渤海海冰预报业务化的需求,针对渤海海冰和MODIS数据的特点,结合MO-DIS-TERRA数据,编程实现了基于MODIS数据的渤海海冰遥感探测系统.系统以IDL和VisualC++作为开发语言,为海冰信息提取提供了一个统一的平台,实现了海冰面积、海冰外缘线、海冰厚度和海冰密集度信息提取,并以专题图和数值的形式输...     

稳定同位素方法在海洋N_2O研究中应用展望

氧化亚氮(N2O)是大气中重要和微量的温室气体,且在平流层N2O形成NO自由基与O3发生反应破坏臭氧层.海洋是大气中N2O净源,但由于海洋中生物化学过程的复杂性,有关N2O形成机制至今是人们研究的重点和难点.应用稳定同位素分馏原理对海洋中N2O形成机制的研究,区分海洋中通过硝化和反硝化过程不同途径产生的N2O过程,为深入研究海洋中N2O循环、估算将来大气中N2O浓度变化提供有用工具.     

Differential utilization of a shallow-water pulse by six shrub species in the Patagonian steppe

A field experiment was performed to improve understanding of the functional diversity of western Patagonian shrubs. Anarthrophyllum rigidum, Adesmia volckmanni, Berberis heterophylla, Mulinum spinosum, Schinus poligamus and Senecio filaginoides were compared in their capacity to absorb water from a 10-mm pulse enriched in deuterium and applied at the beginning of the dry summer. Xylem-water enrichment 14 days after watering was rather subtle, but the upper-soil signal was clear enough to distinguish shallow from deeper absorption. According to a linear mixing model, the proportion of surface-pulse water relative to total water uptake was maximum for Senecio (29-38%) and Mulinum (22-32%), both relatively shallow-rooted species, intermediate for Berberis (16-17%) and Schinus (6-9%), and negligible for the two N-fixing Fabaceae: Adesmia (<1%) and Anarthrophyllum (<3%), despite this last one having a dimorphic (tap + shallow) root system. It is hypothesized that shallow-water pulses may be more profitable in terms of nitrogen than of water, and thus constitute a higher-quality resource for those species only able to use N from soil sources.     

Late Cretaceous paleoenvironmental evolution of the Tarfaya Atlantic coastal Basin,SW Morocco

Lithological evidence, benthic foraminiferal census counts, and X-ray fluorescence (XRF) scanner-derived elemental data were integrated with planktonic foraminiferal biostratigraphy and bulk carbonate stable isotopes to retrace the Turonian to early Campanian paleoenvironmental evolution and sea-level history of the Tarfaya Atlantic coastal basin (SW Morocco). The lower Turonian is characterized by laminated organic-rich deposits, which contain impoverished benthic foraminiferal assemblages, reflecting impingement of the oxygen minimum zone on the shelf during a sea-level highstand. This highstand level is correlated to the global transgressive pulse above the sequence boundary Tu1. The appearance of low-oxygen tolerant benthic foraminiferal assemblages dominated by Gavelinella sp. in the middle to upper Turonian indicates an improvement in bottom water oxygenation, probably linked to offshore retraction of the oxygen minimum zone during a regressive phase. This interval is marked by major regressive events expressed by a series of erosional truncations associated with the prominent sequence boundaries Tu3 and/or Tu4. Dysoxic–anoxic conditions recorded in the upper Santonian of the Tarfaya Basin coincide with the eustatic sea-level rise prior to Sa3 sequence boundary. The lower Campanian transgression, only recorded in the southern part of the Tarfaya Basin, coincided with substantial deepening, enhanced accumulation of fine-grained clay-rich hemipelagic sediments and improved oxygenation at the seafloor (highest diversity and abundance of benthic foraminiferal assemblages). Stable isotope data from bulk carbonates are tentatively correlated to the English Chalk carbon isotope reference curve, in particular the Hitch Wood Event in the upper Turonian, the Navigation Event in the lower Coniacian, the Horseshoe Bay Event in the Santonian and the Santonian/Campanian Boundary Event.     

河南新县花岗岩岩基的岩石成因、来源及对西大别构造演化的启示

本文对新县花岗岩岩基进行了系统的锆石U-Pb定年,全岩元素地球化学、Sr-Nd-Pb-Hf同位素测试,研究探讨其成岩年龄、岩石成因、物质来源以及地球化学动力学背景。锆石U-Pb年龄为125.5±1.5Ma,属于早白垩世产物。全岩元素地球化学成分表现为高硅、富碱,贫镁、铁和钙,富集轻稀土元素、大离子亲石元素（Rb、K、Th、U）和Pb,亏损重稀土元素、高场强元素(Nb、Ta、Ti)和Sr、Ba。全岩同位素具有中等略偏高的Sr 初始比值(87Sr/86Sr)i=0.706949~0.707086;低的放射性Pb同位素组成[ (206Pb/204Pb)i=16.611～17.152,(207Pb/204Pb)i=15.304～15.432,(208Pb/204Pb)i=37.316～37.702]; 低的Nd初始比值（εNd(t)=-13.65～-13.51）和老的Nd模式年龄（TDM2=2.12～2.13Ga）。锆石原位Hf同位素具有较低的初始比值（εHf(t)=-22.92～-19.40）和老的Hf二阶段模式年龄（TDM2=2.39~2.61 Ga）。综合以上元素地球化学特征、锆石U-Pb定年结果及Sr-Nd-Pb-Hf同位素组成,新县花岗岩岩基应属于分异的高钾钙碱性I型花岗岩,是化学成分类似于扬子板块北缘新元古代TTG型岩浆岩的扬子下地壳在非加厚下地壳（深度小于35km）环境下部分熔融的产物。     

黄河流域大气降水氢、氧稳定同位素时空特征及其环境意义

大气降水δ18O值的变化是一个蒸发和凝结的物理过程,与纬度、海拔、距海岸的距离、季节和降水量等因素有关,具有规律变化的特征。根据黄河流域上中下游地区取得的降水同位素数据和降水气象资料,分析了该区域降水中δ18O的时空变化特征。研究了流域上中下游降水中稳定同位素与温度和降水量的关系,揭示了流域降水中稳定同位素的变化规律。结果表明,流域上游和中下游降水中稳定同位素具有不同的季节变化特征,上游地区表现为夏季富集、冬季贫化,中游和下游则与之相反;在空间变化上,流域降水稳定同位素自上而下整体趋于逐渐贫化,波动明显,存在显著的极值区;黄河流域上、中下游具有不同的同位素过程,上游地区受海拔效应和内陆循环影响显著,而中下游则主要受季风系统和局地因素的影响。局地大气水线以及d与大气水汽压关系的分析表明,流域降水在从云层底部降落到地面的过程中,具有明显的二次蒸发现象,并伴随着同位素的分馏。     

Spatial variability of watermass conditions within the European Epicontinental Seaway during the Early Jurassic (Pliensbachian–Toarcian)

In order to constrain spatial variability in watermass conditions within the European Epicontinental Seaway prior to, during and after the Toarcian Oceanic Anoxic Event, carbon (δ¹³C_bel, δ¹³C_carb) and oxygen (δ¹⁸O_bel, δ¹⁸O_carb) isotope records were obtained from three sections in the Grands Causses Basin (southern France). These data were then compared with similar records along a north–south transect across the European Epicontinental Seaway. As the conclusions reached here strongly depend on the reliability of belemnite calcites as archives of palaeoceanographic changes, an attempt was made to improve the understanding of isotope signals recorded in belemnite calcite. Intra‐rostral carbon and oxygen‐isotope data from six belemnite specimens belonging to the genus Passaloteuthis were collected. Intra‐rostral carbon‐isotopes are influenced by vital effects, whereas oxygen‐isotopes reflect relative changes in temperature and salinity. Palaeotemperatures calculated from δ¹⁸O_bel‐isotope records from the Grands Causses Basin confirm relatively low temperatures throughout the Late Pliensbachian. Similar cool water conditions have previously been shown in Germany, England, Spain and Portugal. A temperature increase of up to 6 °C is observed across the Pliensbachian–Toarcian boundary. A pronounced negative shift of at least ?3‰ (Vienna‐Pee Dee Belemnite) is recorded in bulk carbonate carbon during the lower Harpoceras serpentinum zone, typical of the Toarcian Oceanic Anoxic Event. Before and after the Toarcian Oceanic Anoxic Event, a good correlation between δ¹³C_carb and δ¹³C_bel exists, indicating well‐ventilated bottom‐waters and normal marine conditions. Instead, data for the Toarcian Oceanic Anoxic Event indicate the development of a strong north–south gradient in salinity stratification and surface‐water productivity for the Western Tethyan realm. This study thus lends further support to a pronounced regional overprint on carbon and oxygen‐isotope records in epicontinental seaways.