Nutrient limitation of the macroalgaEnteromorpha intestinalis collected along a resource gradient in a highly eutrophic estuary     

Kamer  Krista  Fong  Peggy  Kennison  Rachel  Schiff  Kenneth 《Estuaries and Coasts》2004,27(2):201-208

We conducted a laboratory experiment to quantify nutrient (nitrogen and phosphorus) limitation of macroalgae collected along a gradient in water column nutrient availability in Upper Newport Bay estuary, a relatively nutrient-rich system in southern California, United States. We collectedEnteromorpha intestinalis and water for use in the experiment from five sites ranging from the lower end of the estuary to the head. Initial algal tissue N and P concentrations and molar N∶P ratios—as well as water column NO₃ and total Kjeldahl nitrogen (TKN)—increased along a spatial gradient from the lower end toward the head. Water column soluble reactive phosphorus (SRP) varied among sites as well but did not follow a pattem of increasing from the seaward end toward the head. Algae from each site were assigned to one of four experimental treatments: control (C), nitrogen enrichment (+N), phosphorus enrichment (+P), and nitrogen and phosphorus enrichment (+N+P). Each week for 3 wk we replaced the water in each unit with the appropriate treatment water to mimic a poorly flushed estuary. After 3 wk, the degree of nutrient limitation ofE. intestinalis varied spatially with distance from the head of the estuary. Growth ofE. intestinalis collected from several sites increased with N enrichment alone and increased further when P was added in combination with N This indicated that N was limiting and that when N was sufficient, P became limiting. Sites from whichE. intestinalis exhibited nutrient limitation spanned the range of background water column NO₃ (12.9±0.4 to 55.2±2.1 μM) and SRP (0.8±0.0 to 2.9±0.2 μM) concentrations. Algae that were N limited had initial tissue N levels ranging from 1.18±0.03 to 2.81±0.08% dry weight and molar N∶P ratios ranging from 16.75±0.39 to 26.40±1.98.  相似文献   

Dissolution mechanisms of water in depolymerized silicate melts: Constraints from H and Si NMR spectroscopy and ab initio calculations     

Xianyu Xue  Masami Kanzaki 《Geochimica et cosmochimica acta》2004,68(24):5027-5057

Dissolution of water in magmas significantly affects phase relations and physical properties. To shed new light on the this issue, we have applied ¹H and ²⁹Si nuclear magnetic resonance (NMR) spectroscopic techniques to hydrous silicate glasses (quenched melts) in the CaO-MgO-SiO₂ (CMS), Na₂O-SiO₂, Na₂O-CaO-SiO₂ and Li₂O-SiO₂ systems. We have also carried out ab initio molecular orbital calculations on representative clusters to gain insight into the experimental results.The most prominent result is the identification of a major peak at ∼1.1 to 1.7 ppm in the ¹H MAS NMR spectra for all the hydrous CMS glasses. On the basis of experimental NMR data for crystalline phases and ab initio calculation results, this peak can be unambiguously attributed to (Ca,Mg)OH groups. Such OH groups, like free oxygens, are only linked to metal cations, but not part of the silicate network, and are thus referred to as free hydroxyls in the paper. This represents the first direct evidence for a substantial proportion (∼13∼29%) of the dissolved water as free hydroxyl groups in quenched hydrous silicate melts. We have found that free hydroxyls are favored by (1) more depolymerized melts and (2) network-modifying cations of higher field strength (Z/R²: Z: charge, R: cation-oxygen bond length) in the order Mg > Ca > Na. Their formation is expected to cause an increase in the melt polymerization, contrary to the effect of SiOH formation. The ²⁹Si MAS NMR results are consistent with such an interpretation. This water dissolution mechanism could be particularly important for ultramafic and mafic magmas.The ¹H MAS NMR spectra for glasses of all the studied compositions contain peaks in the 4 to 17 ppm region, attributable to SiOH of a range of strength of hydrogen bonding and molecular H₂O. The relative population of SiOH with strong hydrogen bonding grows with decreasing field strength of the network-modifying cations. Ab initio calculations confirmed that this trend largely reflects hydrogen bonding with nonbridging oxygens.  相似文献   

Tracing the protolith, UHP metamorphism, and exhumation ages of orthogneiss from the SW Sulu terrane (eastern China): SHRIMP U–Pb dating of mineral inclusion-bearing zircons     

Fulai Liu  Zhiqin Xu  Huaimin Xue 《Lithos》2004,78(4):411-429

Orthogneisses are the major country rocks hosting eclogites in the Sulu UHP terrane, eastern China. All of the analyzed orthogneiss cores from the main drilling hole of the Chinese Continental Scientific Drilling Project (CCSD-MH) have similar major and trace element compositions and a granite protolith. These rocks have relatively high LREE/HREE ratios, strong negative Eu anomalies (Eu/Eu*=0.20–0.39), and negative Ba anomalies (Ba/Ba*=0.25–0.64). Coesite and coesite-bearing UHP mineral assemblages are common inclusions in zircons separated from orthogneiss, paragneiss, amphibolite, and (retrograded) eclogite of the CCSD-MH. This suggests that the eclogite, together with its country rocks, experienced in situ ultrahigh-pressure (UHP) metamorphism. Laser Raman spectroscopy and cathodoluminescence (CL) images show that zircons from the orthogneisses are zoned and that they have distinct mineral inclusions in the different zones. Most zircons retain early magmatic cores with abundant low-pressure mineral inclusions, which are mantled with metamorphic zircon-containing inclusions of coesite and other UHP minerals. The outermost rims on these grains contain low-pressure mineral inclusions, such as quartz and albite. SHRIMP U–Pb dating of the zoned zircons gives three discrete and meaningful groups of ages: Proterozoic ages for the protolith, 227±2 Ma for the coesite-bearing mantles, and 209±3 Ma for the amphibolite facies retrograde rims. The widespread occurrence of UHP mineral inclusions in zircons from the Sulu metamorphic belt dated at about 227 Ma suggests that voluminous continental crust experienced late Triassic subduction to depths of at least 120 km and perhaps more than 200 km. Eighteen million years later, the terrane was rapidly exhumed to midcrustal levels, and the UHP rocks were overprinted by amphibolite facies metamorphism. The exhumation rate deduced from the zircon age data and previously obtained metamorphic P–T data is estimated to be 5.6–11.0 km/Ma. Such rapid exhumation of the Sulu UHP terrane may be due to the buoyancy forces produced by subduction of low-density continental material into the deep mantle.  相似文献   

金坛市开发区的数字影像测图     

王立兴  薛炜  王训霞 《现代测绘》2004,27(3):41-42

为完善数字化测图功能，通过全数字摄影测量系统(VirtuoZo)的数字影像测图模块(IGS)在金坛市开发区1：500测区中的应用，总结提高测图精度和速度的体会。  相似文献   

西安市冬季冷暖的历史演变对采暖的影响          下载免费PDF全文

庞文保 《山西气象》2005,(3):27-28

本文针对CAPPS2.0系统在业务化自动运行过程中的一些问题,提供了一套具体可行的解决方案,实现了CAPPS系统的全自动运行,具有很高的实用价值。  相似文献   

侯马市酸雨概况及其气象条件分析          下载免费PDF全文

薛廷枝  王智娟  史海平  张红安  贾海燕 《山西气象》2005,(4):14-15

通过对侯马近14a酸雨观测资料分析,发现侯马出现酸雨的概率较大,强度较强,时间变化特征明显,与气象条件关系密切。  相似文献   

Correlation between magnetic susceptibility and heavy metals in urban topsoil: a case study from the city of Xuzhou, China   总被引：7，自引：0，他引：7  

Xue Song WANG  Yong QIN 《Environmental Geology》2005,49(1):10-18

Anthropogenic influence, mainly due to urban and industrial activities and traffic exhaust, may affect urban topsoil via atmospheric contamination and solid waste. Magnetic susceptibility measurements were conducted on 21 urban topsoil samples from the city of Xuzhou, China. High intensities of magnetic susceptibility were detected in the majority of the samples. SEM analysis shows that magnetic minerals are in the form of spherules and mainly due to anthropogenic inputs. The heavy metals Pb, Cu, Zn, Se, Sc, Mo, Fe, and Bi show strong correlations with magnetic susceptibility, and Ag, Ba, Cd, Ni, Cr, Sb, and Sn, on the other hand, show a weak correlation with magnetic susceptibility. Whereas, of these metals studied, only Hg has no significant correlation with the susceptibility. The Tomlinson pollution load index (PLI) also shows significant correlation with the susceptibility (χ). The present study shows that magnetic susceptibility is a fast, inexpensive, and non-destructive method for the detection and mapping of contaminated soils.  相似文献   

Element mobility during pyrite weathering: implications for acid and heavy metal pollution at mining-impacted sites   总被引：1，自引：0，他引：1  

Long Lu  Rucheng Wang  Fanrong Chen  Jiyue Xue  Peihua Zhang  Jianjun Lu 《Environmental Geology》2005,49(1):82-89

Based on back scattered electron images and electron micro-probe analysis results, four alteration layers, including a transition layer, a reticulated ferric oxide layer, a nubby ferric oxide layer and a cellular ferric oxide layer, were identified in the naturally weathering products of pyrite. These layers represent a progressive alteration sequence of pyrite under weathering conditions. The cellular ferric oxide layer correlates with the strongest weathering phase and results from the dissolution of nubby ferric oxide by acidic porewater. Leaching coefficient was introduced to better express the response of element mobility to the degree of pyrite weathering. Its variation shows that the mobility of S, Co and Bi is stronger than As, Cu and Zn. Sulfur in pyrite is oxidized to sulfuric acid and sulfate that are basically released into to porewater, and heavy metals Co and Bi are evidently released by acid dissolution. As, Cu and Zn are enriched in ferric oxide by adsorption and by co-precipitation, but they would re-release to the environment via desorption or dissolution when porewater pH becomes low enough. Consequently, Co, Bi, As, Cu and Zn may pose a substantial impact on water quality. Considering that metal mobility and its concentration in mine waste are two important factors influencing heavy metal pollution at mining-impacted sites, Bi and Co are more important pollutants in this case.  相似文献   

A new bounding surface model for thermal cyclic behaviour          下载免费PDF全文

C. Zhou  K.Y. Fong  C.W.W. Ng 《国际地质力学数值与分析法杂志》2017,41(16):1656-1666

To accurately predict soil volume changes under thermal cycles is of great importance for analysing the performance of many earth structures such as the energy pile and energy storage system. Most of the existing thermo‐mechanical models focus on soil behaviour under monotonic thermal loading only, and they are not able to capture soil volume changes under thermal cycles. In this study, a constitutive model is proposed to simulate volume changes of saturated soil subjected to cyclic heating and cooling. Two surfaces are defined and used: a bounding surface and a memory surface. The bounding surface and memory surface are mainly controlled by the preconsolidation pressure (a function of plastic volumetric strain) and the maximum stress experienced by the soil, respectively. Under thermal cycles, the distance of the two surfaces and plastic modulus increase with an accumulation of plastic strain. By adopting the double surface concept, a new elastoplastic model is derived from an existing single bounding surface thermo‐mechanical model. Comparisons between model predictions and experimental results reveal that the proposed model is able to capture soil volume changes under thermal cycles well. The plastic strain accumulates under thermal cycles, but at a decreasing rate, until stabilization. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

海水温度对衰亡期浒苔释放生源硫影响的模拟研究   总被引：1，自引：0，他引：1  

韩露  邓雪  李培峰  高先池  刘春颖 《海洋学报》2018,40(10):110-118

为研究浒苔释放生源硫的特征，本文对采集于黄海绿潮中期和末期的浒苔进行了实验室模拟培养，探讨了不同温度对衰亡期浒苔释放生源硫化物的影响。实验结果表明，在10~25℃温度范围内，温度升高能够加速浒苔的衰亡。二甲基硫（DMS）的平均释放速率范围为2.79~150.70 nmol/（L·g·d），二甲基硫基丙酸内盐（DMSP）的平均释放速率范围为2.16~113.26 nmol/（L·g·d）。温度升高能够使DMS和DMSP的释放速率加快，释放量增加，DMS最大平均释放速率在25℃条件下比10℃条件下升高了约60%，培养液中DMS浓度升高了2~3倍。采集于绿潮末期的浒苔培养液中的DMS和DMSP和采集于绿潮中期的浒苔相比，浓度有所增加，采集于浒苔绿潮末期浒苔培养液中DMS的最高平均浓度为418.41 nmol/L，约为中期的4倍；DMSP的最高平均浓度为316.14 nmol/L，是中期的3倍。浒苔绿潮的爆发会对水体中的硫体系循环产生影响，进而影响该海域生态环境。  相似文献