Contributions of nitrogen deposition and forest regrowth to terrestrial carbon uptake     

Galina Churkina  Kristina Trusilova  Mona Vetter  Frank Dentener 《Carbon balance and management》2007,2(1):5-7

Background  

The amount of reactive nitrogen deposited on land has doubled globally and become at least five-times higher in Europe, Eastern United States, and South East Asia since 1860 mostly because of increases in fertilizer production and fossil fuel burning. Because vegetation growth in the Northern Hemisphere is typically nitrogen-limited, increased nitrogen deposition could have an attenuating effect on rising atmospheric CO₂ by stimulating the vegetation productivity and accumulation of carbon in biomass.  相似文献   

Sedimentary evolution and environmental history of Lake Van (Turkey) over the past 600 000 years   总被引：1，自引：0，他引：1  

Mona Stockhecke  Michael Sturm  Irene Brunner  Hans‐Ulrich Schmincke  Mari Sumita  Rolf Kipfer  Deniz Cukur  Ola Kwiecien  Flavio S. Anselmetti 《Sedimentology》2014,61(6):1830-1861

The lithostratigraphic framework of Lake Van, eastern Turkey, has been systematically analysed to document the sedimentary evolution and the environmental history of the lake during the past ca 600 000 years. The lithostratigraphy and chemostratigraphy of a 219 m long drill core from Lake Van serve to separate global climate oscillations from local factors caused by tectonic and volcanic activity. An age model was established based on the climatostratigraphic alignment of chemical and lithological signatures, validated by ⁴⁰Ar/³⁹Ar ages. The drilled sequence consists of ca 76% lacustrine carbonaceous clayey silt, ca 2% fluvial deposits, ca 17% volcaniclastic deposits and 5% gaps. Six lacustrine lithotypes were separated from the fluvial and event deposits, such as volcaniclastics (ca 300 layers) and graded beds (ca 375 layers), and their depositional environments are documented. These lithotypes are: (i) graded beds frequently intercalated with varved clayey silts reflecting rising lake levels during the terminations; (ii) varved clayey silts reflecting strong seasonality and an intralake oxic–anoxic boundary, for example, lake‐level highstands during interglacials/interstadials; (iii) CaCO₃‐rich banded sediments which are representative of a lowering of the oxic–anoxic boundary, for example, lake level decreases during glacial inceptions; (iv) CaCO₃‐poor banded and mottled clayey silts reflecting an oxic–anoxic boundary close to the sediment–water interface, for example, lake‐level lowstands during glacials/stadials; (v) diatomaceous muds were deposited during the early beginning of the lake as a fresh water system; and (vi) fluvial sands and gravels indicating the initial flooding of the lake basin. The recurrence of lithologies (i) to (iv) follows the past five glacial/interglacial cycles. A 20 m thick disturbed unit reflects an interval of major tectonic activity in Lake Van at ca 414 ka bp . Although local environmental processes such as tectonic and volcanic activity influenced sedimentation, the lithostratigraphic pattern and organic matter content clearly reflect past global climate changes, making Lake Van an outstanding terrestrial archive of unprecedented sensitivity for the reconstruction of the regional climate over the last 600 000 years.  相似文献   

The Gol-e-Zard Zn-Pb Deposit,Lorestan Province,Iran: a Metamorphosed SEDEX Deposit     

Alireza ZARASVANDI  Mona SAMETI  Martiya SADEGHI  Fatemeh RASTMANESH  Hooshang POURKASEB 《《地质学报》英文版》2014,88(1):142-152

The Gol-e-Zard Zn-Pb deposit is one of several sediment-hosted Zn-Pb deposits found in the central part of the Sanadaj-Sirjan Zone, known as the Isfahan-Malayer belt, western Iran. Mineralization occurs in Upper Triassic to Jurassic phyllites and meta-sandstones. Sphalerite and galena are the most abundant metallic ores, with minor chalcopyrite. Calcite and quartz are the main gangue minerals. Fissure filling, replacement textures and especially mineralized faults, suggest an epigenetic stage in the Gol-e-Zard deposit formation. Geochemical studies of mineralized rocks show high concentrations of Zn, Pb and Cu, (Zn and Pb > 10000 ppm and Cu average 3000 ppm). LREE enrichment (LREE>HREE, La/Lu average 1.44) and positive Eu anomalies (Eu/Eu*>1 average 1.67) indicate reducing conditions during the deposition of deposit. However, some samples do not display negative Ce anomalies, which indicate that localized oxidizing conditions are also present. This study indicates that the Gol-e-Zard deposit formed due to circulating hydrothermal fluids in a marine environment. A SEDEX-type genesis, which is defined by circulating hydrothermal fluids through sediments in a marine environment, and syngenetic precipitation of Zn and Pb sulphides, is suggested for the Gol-e-Zard deposit. Emplacement of some granitoid intrusions such as the Aligudarz granitoid intrusion remobilized mineralizing fluids and metamorphosed the Gol-e-Zard deposit.  相似文献   

Phytoplankton and bacterial community structures and their interaction during red-tide phenomena     

Mona Mohamed Ismail  Hassan Abd Allah Ibrahim 《Ocean Science Journal》2017,52(3):411-425

Phytoplankton and bacteria diversity were studied before, during and after red tide phenomena during spring season 2015 in the Eastern Harbour (E.H.) of Alexandria, Egypt. Fifty five species of phytoplankton were identified and represented different distinct classes “Bacillariophyceae; Dinophyceae, Chlorophyceae, Cyanophyceae and Eugelenophyceae”. Also, Diatom formed the most dominant group. The average number of the phytoplankton density varied from 4.8 × 10⁴ to 1.1 × 10⁶ cell l^-1 during the study period and Skeletonema costatum was the agent causing the red tide. The existence percentages of bacteria ranged from 2.6 to 17.9% on all media tested. The bacterial isolates on the nutrient agar medium represented the highest existence with a total percentage of 43.6%, followed by MSA medium (25.7%), while the lowest percentage was for the AA medium at 7.8%. However, twelve isolates were selected as representative for bacterial community during study interval. Based on the morphological, biochemical, physiological and enzymatic characteristics, the bacterial strains were described. Depending on the 16S rDNA gene sequence, three common antagonists were aligned as: Vibrio toranzoniae strain Vb 10.8, Ruegeria pelagia strain NBRC 102038 and Psychrobacter adeliensis strain DSM 15333. The interaction between these bacteria and S. costatum was studied. The growth of S. costatum was significantly lower whenever each bacterium was present as compared to axenic culture. More specifically, 30% (v/v) of the all tested bacteria showed the strongest algicidal activities, as all S. costatum cells were killed after two days. 10% of R. pelagia and P. adeliensis also showed significant algicidal activities within six days.  相似文献