Diagenesis and anthropogenesis of metals in the recent Holocene sedimentary record of the Ría de Vigo (NW Spain)

To contribute to establishing a historical baseline for future evaluations of the environmental quality of the Ría de Vigo (NW Spain), we report metal contents determined in eight gravity cores obtained at representative locations in 1990 - before the installation of any wastewater treatment plants - and in fractions thereof that were obtained by the BCR sequential extraction method. The results suggest that early diagenesis had been influenced by both hydrodynamic conditions and organic matter input (the latter especially in areas devoted to mariculture), and that anthropogenic inputs had also affected the concentrations and between-fraction distribution of Cu, Pb, Zn and other metals in surficial sediments.     

鳙、鲢鱼鳞作为稳定同位素研究非致命采样替代物的有效性

稳定同位素分析技术已成为食物网研究中的关键技术,通用方法是取鱼类背部白色肌肉,在实际应用过程会导致鱼类的死亡,因而有所局限.使用非致命组织作为稳定同位素研究中的替代组织越来越得到关注,但是目前国内尚未开展相关研究.比较鳙(Aristichthy nobilis)、鲢(Hypophthalmichthys molitrix)鱼鳞与肌肉组织中δ13C和δ15N比值,发现鳙、鲢的鱼鳞与肌肉组织中δ13C和δ15N比值均有显著差异.鱼鳞δ13C比值比肌肉更富集,平均高2.54‰,而δ15N比值比肌肉平均低0.7‰.对鳙、鲢的鱼鳞与肌肉组织δ15N比值含量进行相关分析发现,通过构建线性模型,可用校正后的鱼鳞δ15N比值替代肌肉组织δ15N比值.鲢的鱼鳞与肌肉组织δ13C比值存在显著线性相关,而鳙的鱼鳞与肌肉组织δ13C比值无显著相关关系.     

Variation in diet across an elevational gradient in the larvae of two Hydropsyche species (Trichoptera)

While specialized species are linked to a particular resource, omnivorous species may switch between food items according to the availability and the quality of resources. Here we use larvae of the omnivorous caddisfly genus Hydropsyche (Trichoptera) to analyse changes in diet composition across an elevational gradient. Periphyton and Hydropsyche larvae were sampled from 22 populations at stream orders from 2 to 5 on the German part of the Bohemian Forest. Elevations of sampling sites ranged between 300 m and 900 m a.s.l.. Diet composition was estimated by the analyses of the gut content of larvae as well as by stable nitrogen isotopes (δ¹⁵N). The δ¹⁵N values of the periphyton decreased and the C/N ratio of periphyton increased with increasing environmental harshness (decreasing water pH, temperature and conductivity with increasing elevation) indicating a decrease of periphyton food quality. Across individuals, the proportion of animals in the gut of Hydropsyche larvae was positively related to the difference of δ¹⁵N values between larvae and periphyton. The proportion of animals within the gut and (baseline corrected) δ¹⁵N values of Hydropsyche populations increased with increasing environmental harshness. We suggest that the (i) low primary production caused by shading, low temperatures and low nutrient levels, (ii) the low nutrient quality of periphyton and (iii) the availability of animal prey due to the input of allochthonous resources in headwaters caused the shift in the diet of Hydropsyche larvae along the river continuum.     

Bioaccumulation and trophic transfer of polybrominated diphenyl ethers (PBDEs) in a marine food web from Liaodong Bay,North China

The concentrations of 21 polybrominated diphenyl ethers (PBDEs) congeners were analyzed in organisms within a marine food web collected from the Liaodong Bay, North China. The total concentrations of PBDEs in all samples ranged from 0.87 to 91.4 ng g⁻¹ lipid weight (lw). BDE-47 was the predominant congener and had a concentration ranging from 0.30 to 36.1 ng g⁻¹ lw. The trophic magnification factors (TMF) of the PBDEs were calculated using the trophic levels obtained from the stable nitrogen isotope ratios. The TMF value of ∑PBDEs was 3.50 for the entire food web and 2.21 for the food web excluding seabirds. Four concentration ratios, BDE-99/BDE-100, BDE-99/BDE-47, BDE-153/BDE-154 and BDE-183/BDE-154, decreased linearly with the increase of the trophic levels in the invertebrates and the fishes (p < 0.01). The results suggested that the PBDEs were steadily metabolized in the trophic transfer process along the food chain.     

Seasonal contribution of living phytoplankton carbon to vertical fluxes in a coastal upwelling system (Ría de Vigo, NW Spain)

The aim of this study is to explore the contribution of living phytoplankton carbon to vertical fluxes in a coastal upwelling system as a key piece to understand the coupling between primary production in the photic layer and the transfer mechanisms of the organic material from the photic zone. Between April 2004 and January 2005, five campaigns were carried out in the Ría de Vigo (NW Iberian Peninsula) covering the most representative oceanographic conditions for this region. Measurements of particulate organic carbon (POC), chlorophyll-a (chl a), phaeopigments (phaeo), and identification of phytoplankton species were performed on the water column samples and on the organic material collected in sediment traps.The POC fluxes measured by the sediment traps presented no seasonal variation along the studied period ranging around a mean annual value of 1085±365 mg m⁻² d⁻¹, in the upper range of the previously reported values for other coastal systems. The fact that higher POC fluxes were registered during autumn and winter, when primary production rates were at their minimum levels points to a dominant contribution of organic carbon from resuspended sediments on the trap collected material. On the contrary, fluxes of living phytoplankton carbon (C_phyto) and chl a clearly presented a seasonal trend with maximum values during summer upwelling (546 mg m⁻² d⁻¹ and 22 mg chl a m⁻² d⁻¹, respectively) and minimum values during winter (22 mg m⁻² d⁻¹ and 0.1 mg chl a m⁻² d⁻¹, respectively). The contribution of C_phyto to the vertical flux of POC ranged between 2% and 49% in response to the pelagic phytoplankton community structure. Higher values of C_phyto fluxes were registered under upwelling conditions which favour the dominance of large chain-forming diatoms (Asterionellopsis glacialis and Detonula pumila) that were rapidly transferred to the sediments. By contrast, C_phyto fluxes decreased during the summer stratification associated with a pelagic phytoplankton community dominated by single-cell diatoms and flagellates. Minimal C_phyto fluxes were observed during the winter mixing conditions, when the presence of the benthic specie Paralia sulcata in the water column also points toward strong sediment resuspension.     

鄱阳湖湿地典型中生植物水分利用来源的同位素示踪

水分是维持植物生长、决定种群分布的关键因子,研究植物水分利用来源是揭示水文过程与植被演替作用机制的基础,作为中国最大的淡水湖泊系统,鄱阳湖水文情势的显著改变已直接影响到湿地生态系统的水分补给来源.本文通过测定降水、土壤水、地下水、湖水和植物茎水中δ¹⁸O、δD同位素组成,识别鄱阳湖湿地典型中生植被——茵陈蒿（Artemisia capillaris）群落的土壤水分补给来源,并应用直接对比法和IsoSource多源混合模型估算优势种茵陈蒿的主要吸水区间及水源利用比例.结果发现：（1）与降水同位素相比,湖水和湿地土壤水同位素较为富集,地下水同位素较少发生分馏;（2）湿地地下水主要受历史长期降水和湖水共同补给,土壤水在雨季4—6月和秋季9—10月主要受降水补给,夏季7—8月深层土壤水受湖水侧向入渗和地下水的共同补给,并在蒸发作用下水分向浅层土壤传输;（3）茵陈蒿主要利用0~80 cm深度的土壤水,且能够在不同土层水源间灵活转换.当土壤含水量较高时（4—5月）,主要利用0~40 cm浅层土壤水,利用率约49%~68%;当浅层土壤含水量较低时（6—8月）,主要利用40~80 cm深层土壤水,利用率高达74%~95%;当植物进入生长后期（9—10月）,主要利用0~15 cm表层土壤水,利用率介于41%~70%.总体发现,湖水是鄱阳湖湿地中生植物群落土壤水分的重要补给来源,优势种茵陈蒿能够响应土壤含水量的变化改变吸水深度,具有较强的干旱适应能力.研究结果可为鄱阳湖湿地植被生态系统演变和科学保护提供理论参考.     

Determination of groundwater discharge rates and water residence time of groundwater‐fed lakes by stable isotopes of water (18O, 2H) and radon (222Rn) mass balances

Lacustrine groundwater discharge (LGD) and the related water residence time are crucial parameters for quantifying lake matter budgets and assessing its vulnerability to contaminant input. Our approach utilizes the stable isotopes of water (δ¹⁸O, δ²H) and the radioisotope radon (²²²Rn) for determining long‐term average and short‐term snapshots in LGD. We conducted isotope balances for the 0.5‐km² Lake Ammelshainer See (Germany) based on measurements of lake isotope inventories and groundwater composition accompanied by good quality and comprehensive long‐term meteorological and isotopic data (precipitation) from nearby monitoring stations. The results from the steady‐state annual isotope balances that rely on only two sampling campaigns are consistent for both δ¹⁸O and δ²H and suggested an overall long‐term average LGD rate that was used to infer the water residence time of the lake. These findings were supported by the good agreement of the simulated LGD‐driven annual cycles of δ¹⁸O and δ²H lake inventories with the observed lake isotope inventories. However, radon mass balances revealed lower values that might be the result of seasonal LGD variability. For obtaining further insights into possible seasonal variability of groundwater–lake interaction, stable water isotope and radon mass balances could be conducted more frequently (e.g., monthly) in order to use the derived groundwater discharge rates as input for time‐variant isotope balances.     

Recharge sources and hydrogeological effects of irrigation and an influent river identified by stable isotopes in the Motril‐Salobreña aquifer (Southern Spain)

Measurement of the stable isotopes oxygen‐18 and deuterium in water is an important tool to characterize aquifer recharge sources. In the driest areas of the Mediterranean, this application is of special interest due to the scarcity of water and the resulting common incidence of human influence on natural hydrological systems. The Motril‐Salobreña detrital aquifer (southern Spain) is a clear example of such an impact as inhabitants have designed irrigation systems and a dam was recently built across the course of the Guadalfeo River, which feeds the aquifer. The sampling of (river or ground) water has allowed the determination of stable isotope contents (oxygen‐18 and deuterium), both temporally and spatially, and the relative importance of the main recharge sources in certain sectors. In addition, we were able to infer seasonal trends and to improve existing knowledge of the main flow paths and the position of a seasonal groundwater divide. Data analysis shows evaporation plays a minor role (despite the high temperatures in the zone), scarce rainwater influence, and the overwhelming contribution of recharge from the Guadalfeo River and from the carbonate aquifer (Escalate aquifer) in contact with the Motril‐Salobreña aquifer. Irrigation return flow during the summer months comprises the main recharge due to the significant volumes of water that infiltrate. The construction of the dam will almost certainly entail great changes in the current dynamics of the hydrogeology of the Motril‐Salobreña aquifer; therefore, knowledge of its behaviour is crucial in order to carry out sustainable use of its groundwater resources. Copyright © 2011 John Wiley & Sons, Ltd.     

Mining lakes as groundwater‐dominated hydrological systems: assessment of the water balance of Mining Lake Plessa 117 (Lusatia,Germany) using stable isotopes

In the present study, the stable isotopes δ¹⁸O and δ²H were used for assessment of the water balance in a heterogeneously structured catchment area in the Lusatian Lignite Mining District, in particular, for estimation of the annual groundwater inflow and outflow (I_GW and O_GW) of Mining Lake Plessa 117. The application of stable isotopes was possible since the water exchange in the catchment area had reached steady‐state conditions after the abandonment of mining activities in 1968 and the filling of the voids and aquifers by re‐rising groundwater in the years thereafter. Diverging slopes of the Evaporation Line and the Global Meteoric Water Line manifested as evaporation from the lake catchment area. The calculated isotope water balance was compared with the commonly used surface water balance, which is unable to differentiate between I_GW and O_GW, and with a local groundwater model. The groundwater model calculated an I_GW of about 811 000 m³ yr^?1 and an O_GW close to zero, whereas the isotope water balance showed fluxes of about 914 000 and 140 000 m³ yr^?1, respectively. Considering the contribution of the groundwater inflow to the total annual input into the lake (ΔI_T) and the mean residence time (τ), where the groundwater model and the isotope water balance calculated 42 and 47% for ΔI_T and 4·3 and 3·9 years for τ, respectively, it was shown that both water balance calculation methods led to comparable results despite the differences in I_GW and O_GW. Copyright © 2008 John Wiley & Sons, Ltd.