Stable C and N isotope analysis elucidated the importance of zooplankton in a tropical seagrass bed of Santiago Island,Northwestern Philippines

The role of zooplankton in a tropical seagrass ecosystem was investigated in milkfish farms pollution-impacted and -unimpacted seagrass beds in Santiago Island coral reefs, Northwestern Philippines. The aim was to compare between the two sites: (1) abiotic factors and zooplankton community parameters, and (2) the trophic structure using C and N stable isotopes. Low water (98–119?mV) and sediment (–121 to ?138?mV) Oxidation Reduction Potential values indicated a reducing environment in the impacted site. Zooplankton in the impacted site showed the typical community response to eutrophication (low diversity, but high total abundance due to the dominance of the cyclopoid copepod Oithona oculata), generally few elevated δ¹⁵N values, but a significant shift towards depleted ¹³C due to the organic enrichment of fish-farm feeds. Apart from suggesting a highly complex food web with POM and zooplankton as main food sources in the unimpacted site, the Bayesian mixing model simulation generated reduced complexity in feeding interactions between basal sources, zooplankton, and fish including adults of a key fish species, Siganus fuscescens, in the impacted sites. In this study, C and N stable isotope analysis has clarified the importance of zooplankton as fish prey in a seagrass bed food web.     

Prenatal diagnosis of 47,XX,der(15)t(15;16)(q13;p13.2)

A case of prenatally detected partial trisomy 15 and 16 is reported. Amniocentesis was performed at 14 weeks' gestation because a 6-mm nuchal translucency was detected on a dating ultrasound evaluation. Karyotype from amniocytes was suspect of an aberration concerning a marker chromosome. FISH analysis demonstrated that this marker chromosome was a der(15). A maternal chromosomal rearrangement t(15;16)(q13;p13.2) was confirmed. At birth, the proband was severely hydropic and had dysmorphic features, which included hypertelorism, micrognathia, incomplete separation of the maxilla and mandible, hyperflexed hands with overlapping fingers, hyposegmented right lung, and a single umbilical artery. Copyright © 2004 John Wiley & Sons, Ltd.     

Transformations of nitrogen at the interface between the topsoil and an impervious clay subsoil

Much work has been done on gaseous emissions and leaching of nitrogenous compounds from whole soil profiles and also from soil surface measurements which are assumed to be mainly due to topsoil activity. In soils with an impervious clay subsoil, the boundary between the topsoil and subsoil may provide an interface for microbial activity, including N transformations. In this study, we investigated movement and transformations of two reactive N species (nitrate and urea) at the subsoil interface using a series of replicate, intact soil blocks, under two contrasting watering regimes. We measured fluxes in both liquid and gaseous phases and demonstrated that nitrate reaching the subsoil interface does not necessarily leach into water systems, but may denitrify immediately and could, therefore, add to atmospheric pollution through N₂O production. On the other hand, ammonium reaching the subsoil interface either directly, or after mineralization, appears to be more mobile than expected and has the potential to pollute watercourses.     

Correlating the Spatial Distribution of Atmospheric Ammonia with δ15N Values at an Ammonia Release Site

A field ammonia (NH₃) release experiment and open top chambers containing moorland monoliths continuously fumigated with NH₃ or sprayed with NH₄Cl were used to assess the potential for using ¹⁵N values in determining the area of influence around a point NH₃ emission source. ¹⁵N values are being increasingly used as environmental tracers and we tested the hypothesis that the ¹⁵N signal from an NH₃ emission source is observable in nearby vegetation. Using modified monitoring devices, atmospheric NH₃ concentrations were found to decrease with distance from source, with ¹⁵N values also reflecting this trend, producing a signal shift with changing concentration. Open top chamber studies of ¹⁵N values of Calluna vulgaris (L.) Hull indicated a correlation with deposition treatments in current year shoots. Analysis of Calluna shoots from the NH₃ release showed a similar trend of ¹⁵N enrichment. Significant linear correlations between ¹⁵N and percent N in plant material were found, both in the controlled conditions of the open top chambers and at the NH₃ release site, illustrating the possible use of this technique in N deposition biomonitoring.     

Accumulation of pollutant nitrogen in calcareous and acidic grasslands: Evidence from N flux and 15N tracer studies

Semi-natural calcareous and acidic grasslands are known to be sensitive to increased atmospheric N deposition. However, the fate of pollutant N within these systems is unknown. This paper reports on the first studies to determine the fate of added N within a calcareous and an acidic grassland subject to long-term simulated enhanced N deposition. Intact soil/turf cores were removed from field plots treated for six years with enhanced N deposition (ambient +0, +35 and +140 kg N ha^–1 year^–1). Cores were inserted into lysimeters and output fluxes of N were monitored in detail. Complete N budgets—calculated from the N flux data—showed considerable accumulation of N within the treated grasslands, up to 76% and 38% of pollutant N in the calcareous and acidic grasslands respectively. In the second study, the short-term (21 day) fate of pollutant N was determined by tracing ¹⁵N labelled ammonium nitrate (+35 kg N ha^–1 year^–1) though the acidic and calcareous lysimeters into plant, soil and leachate pools. Up to 91% and 59% of ¹⁵N was recovered in soils and vegetation of the calcareous and acidic grasslands respectively, with negligible amounts recovered in soil extractable ammonium and nitrate (<0.3%) and in leachate (<0.02%). This rapid short-term immobilisation of pollutant N supports the long-term accumulation of the element calculated from the N flux study.     

Estimating the Relative Efficiency of Brazilian Publicly and Privately Owned Water Utilities: A Stochastic Cost Frontier Approach1

Abstract: This paper assesses cost efficiencies of Brazilian public and private companies of water supply. To measure the efficiency, we used a stochastic frontier model derived from the translog family – a specification similar to a Cobb‐Douglas including a quadratic term in log output. The model parameters are estimated by maximum likelihood using Brazilian data for the year 2002. Statistical inference leads to the conclusion that there is no evidence that private firms and public firms are significantly different in terms of efficiency measurements.     

共聚苯胺/邻氨基苯酚介孔硅复合材料对Hg(Ⅱ)的吸附动力学研究

利用共聚苯胺邻氨基酚与介孔硅SBA-15的复合材料进行了汞离子的吸附性能试验研究,发现该复合材料对Hg(Ⅱ)具有较优异的吸附去除效果,对几种不同初始浓度的汞离子的去除率均可达到95%以上;对初始浓度为100mg/L的汞溶液的吸附动力学分别进行了一级和二级动力学模型拟合,结果表明该吸附材料对汞的吸附符合准二级动力学模型。     

基于15N 同位素示踪技术的地下河硝态氮来源时空变化特征分析

根据2007年10月至2008年10月每月对青木关地下河水的监测,利用~(15)N 同位素示踪技术并结合水化学指标,分析地下河硝态氮来源的时空变化特征.结果表明,地下河出口S2硝态氮浓度(20.35 mg/L)比入口D1(3.20 mg/L)高6倍多.受农业生产施肥和降雨冲刷稀释效应的影响,地下河水硝态氮浓度2007年10月至2008年3月较低且比较稳定,2008年4月至7月较高但受降雨冲刷稀释影响变化较大,2008年8月至9月随降雨减少,土壤中残留的化肥造成地下河水硝态氮浓度偏高.根据NO_3~--δ~(15)N 值识别出了地下河硝态氮来源变化特征为:D1处2007年10月至2008年3月以及2008年7月至10月NO_3~--δ~(15)N 值为-0.857‰±2.01‰(n=9),其硝态氮来源为稻田中残留的化肥;2008年4月、6月中下旬NO_3~--δ~(15)N 值为2.50‰±0.29‰(n=3),其来源为稻田中施用的化肥与土壤有机氮的混合;2008年5月下旬至6月上旬NO_3~--δ~(15)N 值分别为-3.74‰和0.52‰,其来源为稻田中施用的化肥.S2处硝态氮不仅来自上游的化肥,更主要的是来自中下游的耕地、林地土壤渗透水或侧向裂隙水带来的土壤有机氮与化肥,其中2007年10月至2008年3月以及2008年7月至10月NO_3~--δ~(15)N 值为4.77‰±0.73‰(n=9),其硝态氮主要来自于土壤有机氮;2008年4～6月NO_3~--δ～15N 值为3.16‰±0.39‰(n=5),其硝态氮来自于土壤有机氮与化肥的混合.     

基于碳氮稳定同位素组成分析的孔石莼对氨氮的吸收

氨氮(NH4-N)是水体中能被藻类直接吸收利用的无机氮。利用稳定同位素技术研究了不同浓度下孔石莼(Ulvapertusa)对NH4-N的吸收,藻类体内δ15N、δ13C的变化。结果显示:试验初始阶段,孔石莼大量吸收水体中的14NH4-N、12CO2用于自身组织的合成,导致水体中氨氮浓度、δ15N和δ13C急剧下降,约在5～25 h,这一阶段水体中氨氮浓度变化很小,藻体15N缓慢降低,达到平缓期;约在25 h后,氨氮浓度缓慢下降,海水中的底物浓度很低,水体中14NH4-N几乎被吸收殆尽,孔石莼开始大幅吸收15NH4-N,δ15N上升。δ13C在4 h后呈现无规律波动。