Contemporary Deposition and Long-Term Accumulation of Sediment and Nutrients by Tidal Freshwater Forested Wetlands Impacted by Sea Level Rise   总被引：1，自引：0，他引：1  

Gregory?B.?NoeEmail author  Cliff?R.?Hupp  Christopher?E.?Bernhardt  Ken?W.?Krauss 《Estuaries and Coasts》2016,39(4):1006-1019

Contemporary deposition (artificial marker horizon, 3.5 years) and long-term accumulation rates (²¹⁰Pb profiles, ~150 years) of sediment and associated carbon (C), nitrogen (N), and phosphorus (P) were measured in wetlands along the tidal Savannah and Waccamaw rivers in the southeastern USA. Four sites along each river spanned an upstream-to-downstream salinification gradient, from upriver tidal freshwater forested wetland (TFFW), through moderately and highly salt-impacted forested wetlands, to oligohaline marsh downriver. Contemporary deposition rates (sediment, C, N, and P) were greatest in oligohaline marsh and lowest in TFFW along both rivers. Greater rates of deposition in oligohaline and salt-stressed forested wetlands were associated with a shift to greater clay and metal content that is likely associated with a change from low availability of watershed-derived sediment to TFFW and to greater availability of a coastal sediment source to oligohaline wetlands. Long-term accumulation rates along the Waccamaw River had the opposite spatial pattern compared to contemporary deposition, with greater rates in TFFW that declined to oligohaline marsh. Long-term sediment and elemental mass accumulation rates also were 3–9× lower than contemporary deposition rates. In comparison to other studies, sediment and associated nutrient accumulation in TFFW are lower than downriver/estuarine freshwater, oligohaline, and salt marshes, suggesting a reduced capacity for surface sedimentation (short-term) as well as shallow soil processes (long-term sedimentation) to offset sea level rise in TFFW. Nonetheless, their potentially large spatial extent suggests that TFFW have a large impact on the transport and fate of sediment and nutrients in tidal rivers and estuaries.  相似文献   

Iron Reduction Along an Inundation Gradient in a Tidal Sedge (<Emphasis Type="Italic">Cyperus malaccensis</Emphasis>) Marsh: the Rates,Pathways, and Contributions to Anaerobic Organic Matter Mineralization     

Min?Luo  Cong-Sheng?ZengEmail author  Chuan?Tong  Jia-Fang?Huang  Kai?Chen  Feng-Qin?Liu 《Estuaries and Coasts》2016,39(6):1679-1693

Incubation experiments were adopted to characterize the rates and pathways of iron reduction and the contributions to anaerobic organic matter mineralization in the upper 0–5 cm of sediments along a landscape-scale inundation gradient in tidal marsh sediments in the Min River Estuary, Southeast China. Similar sediment characteristics, single-species vegetation, varied biomass and bioturbation, distinct porewater pH, redox potential, and electrical conductivity values have resulted in a unique ecogeochemical zonation along the inundation gradient. Decreases in solid-phase Fe(III) and increases in nonsulfidic Fe(II) and iron sulfide were observed in a seaward direction. Porewater Fe²⁺ was only detected in the upland area. High rates of iron reduction were observed in incubation jars, with significant accumulations of nonsulfidic Fe(II), moderate accumulations of iron sulfides, and negligible accumulations of porewater Fe²⁺. Most of the iron reduction was microbially mediated rather than coupled to reduced sulfides. Microbial iron reduction accounted for 20–89 % of the anaerobic organic matter mineralization along the inundation gradient. The rate and dominance of microbial iron reduction generally decreased in a seaward direction. The contributions of microbial iron reduction to anaerobic organic matter mineralization depended on the concentrations of bioavailable Fe(III), the spatial distribution of which was significantly related to tidal inundation. Our results clearly showed that microbial iron reduction in the upper sediments along the gradient is highly dependent on spatial scales controlled primarily by tidal inundation.  相似文献   

Depth classification of underwater targets based on complex acoustic intensity of normal modes     

Guang?Yang  Jingwei?YinEmail author  Yun?Yu  Zhenhua?Shi 《中国海洋大学学报(英文版)》2016,15(2):241-246

In order to solve the problem of depth classification of the underwater target in a very low frequency acoustic field, the active component of cross spectra of particle pressure and horizontal velocity (ACCSPPHV) is adopted to distinguish the surface vessel and the underwater target. According to the effective depth of a Pekeris waveguide, the placing depth forecasting equations of passive vertical double vector hydrophones are proposed. Numerical examples show that when the sum of depths of two hydrophones is the effective depth, the sign distribution of ACCSPPHV has nothing to do with horizontal distance; in addition, the sum of the first critical surface and the second critical surface is equal to the effective depth. By setting the first critical surface less than the difference between the effective water depth and the actual water depth, that is, the second critical surface is greater than the actual depth, the three positive and negative regions of the whole ocean volume are equivalent to two positive and negative regions and therefore the depth classification of the underwater target is obtained. Besides, when the 20 m water depth is taken as the first critical surface in the simulation of underwater targets (40 Hz, 50 Hz, and 60 Hz respectively), the effectiveness of the algorithm and the correctness of relevant conclusions are verified, and the analysis of the corresponding forecasting performance is conducted.  相似文献   

Tropical Atlantic climate response to different freshwater input in high latitudes with an ocean-only general circulation model     

Guang?Men  Xiuquan?WanEmail author  Zedong?Liu 《中国海洋大学学报(英文版)》2016,15(5):751-757

Tropical Atlantic climate change is relevant to the variation of Atlantic meridional overturning circulation (AMOC) through different physical processes. Previous coupled climate model simulation suggested a dipole-like SST structure cooling over the North Atlantic and warming over the South Tropical Atlantic in response to the slowdown of the AMOC. Using an ocean-only global ocean model here, an attempt was made to separate the total influence of various AMOC change scenarios into an oceanic-induced component and an atmospheric-induced component. In contrast with previous freshwater-hosing experiments with coupled climate models, the ocean-only modeling presented here shows a surface warming in the whole tropical Atlantic region and the oceanic-induced processes may play an important role in the SST change in the equatorial south Atlantic. Our result shows that the warming is partly governed by oceanic process through the mechanism of oceanic gateway change, which operates in the regime where freshwater forcing is strong, exceeding 0.3 Sv. Strong AMOC change is required for the gateway mechanism to work in our model because only when the AMOC is sufficiently weak, the North Brazil Undercurrent can flow equatorward, carrying warm and salty north Atlantic subtropical gyre water into the equatorial zone. This threshold is likely to be model-dependent. An improved understanding of these issues may have help with abrupt climate change prediction later.  相似文献   

Mechanisms of partly flooded loose sand deposits     

Gerd?GudehusEmail author 《Acta Geotechnica》2016,11(3):505-517

Partly flooded loose sand deposits are left back from lignite mining, particularly in east Germany. After flooding, gas inclusions in macropores enhance the pore pressure increase by total stress cycles without drainage, and this can cause the transition into a kind of suspension. Thus, natural and technical changes of surface loads triggered flow slides in chain reactions of sometimes catastrophic extent. Such collapsible deposits were and are stabilized by blast-induced liquefaction and densification. Successive collapse fronts in flooded grain skeletons are seismogeneous, and this appears as wavering in the near-field and leads to power-law spectra in the far-field. Apart from this evidence of mild fractality, the wild fractality of chain reactions eludes mathematical treatment. Therefore, uncommon methods of geotechnical design, operations and monitoring are required.  相似文献   

Intrinsic groundwater vulnerability determination at the aquifer scale: a methodology coupling travel time estimation and rating methods     

Vassilios?Pisinaras  Christos?Polychronis  Alexandra?GemitziEmail author 《Environmental Earth Sciences》2016,75(1):85

Groundwater vulnerability has been subject of much research due to the valuable information it provides concerning groundwater protection and exploitation potential. Up to now, most groundwater vulnerability studies adopt subjective systems of rating the various factors and subsequently, their results are often ambiguous and contradicting. Within the present study a methodology for the estimation of intrinsic groundwater vulnerability at the aquifer scale is presented. The methodology is based on travel time estimation from specified sources of pollution to the aquifer. Besides the deterministic calculation of travel times, the methodology provides a rating system for each pollution source, based on its relative severity and the estimated threat that it poses to the aquifer. Therefore, it can be regarded as a hybrid method that couples the advantages provided by the physically based methods with those of the subjective rating systems. The methodology is applied to the Neon Sidirochorion aquifer, Northeastern Greece, an overexploited aquifer where river waters, sea waters and lake waters interact, causing groundwater quality deterioration to the aquifer. The results indicated that the proposed groundwater vulnerability assessment methodology is well capturing pollution related to saltwater intrusion and agricultural activities, while it is concluded that the conceptual model is significantly affecting the vulnerability assessment results and therefore has to be previously developed.  相似文献   

Estimation of air-overpressure produced by blasting operation through a neuro-genetic technique     

Edy?Tonnizam Mohamad  Danial?Jahed ArmaghaniEmail author  Mahdi?Hasanipanah  Bhatawdekar?Ramesh?Murlidhar  Mohd?Nur?Asmawisham?Alel 《Environmental Earth Sciences》2016,75(2):174

Blasting operations usually produce significant environmental problems which may cause severe damage to the nearby areas. Air-overpressure (AOp) is one of the most important environmental impacts of blasting operations which needs to be predicted and subsequently controlled to minimize the potential risk of damage. In order to solve AOp problem in Hulu Langat granite quarry site, Malaysia, three non-linear methods namely empirical, artificial neural network (ANN) and a hybrid model of genetic algorithm (GA)–ANN were developed in this study. To do this, 76 blasting operations were investigated and relevant blasting parameters were measured in the site. The most influential parameters on AOp namely maximum charge per delay and the distance from the blast-face were considered as model inputs or predictors. Using the five randomly selected datasets and considering the modeling procedure of each method, 15 models were constructed for all predictive techniques. Several performance indices including coefficient of determination (R ²), root mean square error and variance account for were utilized to check the performance capacity of the predictive methods. Considering these performance indices and using simple ranking method, the best models for AOp prediction were selected. It was found that the GA–ANN technique can provide higher performance capacity in predicting AOp compared to other predictive methods. This is due to the fact that the GA–ANN model can optimize the weights and biases of the network connection for training by ANN. In this study, GA–ANN is introduced as superior model for solving AOp problem in Hulu Langat site.  相似文献   

Sedimentology and Sequence Stratigraphy of Marine to Lacustrine Deltaic Deposits in a Craton Basin and Their Controlling Factors: Shan 2 Member–He 8 Member (Guadalupian–Lopingian, Permian), Southeast Ordos Basin, North China     

SHAN Xin  YU Xinghe  Peter ?CLIFT  LI Yalong  JIN Lin  SU Dongxu  DU Yonghui  ZHOU Jinsong  HAN Xiaoqin 《《地质学报》英文版》2018,92(1):268-285

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Structure and stratigraphy of Rumbli and Panjar areas of Kashmir and Pakistan with the aid of GIS     

Omer Iqbal  Mirza Shahid Baig  Shahab Pervez  Muhammad Iqbal Siddiqi 《Journal of the Geological Society of India》2018,91(1):57-66

The project area lies in the southern part of the Hazara Kashmir syntaxis. The Hazara Kashmir syntaxis is an antiformal structure. The project area includes Rumbli, Namb, Chatrora, Chachan, Panjar, Barathian and Utrinna areas of Rawalpindi and Sudhnoti districts. The southeastern limb of the Hazara Kashmir syntaxis is imbricated along Punjal thrust, Main Boundary thrust and Riasi fault. The Jhelum fault truncates the western limb of Hazara Kashmir syntaxis. The core of syntaxis comprises of Himalayan molasse deposits. These molasse deposits represent the part of cover sequence of Indian plate. These Himalayan molasse deposits include the Early to Middle Miocene Kamlial Formation, Middle to Late Miocene Chinji Formation, Late Miocene Nagri Formation and Late Miocene Dhok Pathan Formation. The area is highly deformed resulting folds and faults. The major folds in the project area are the Panjar anticline, Barathian syncline, Barathian anticline, Rumbli anticline, Chatrora antiformal syncline and Namb syncline. The folds are either northwest-southeast trending or southwestnortheast trending. The folds are asymmetric, open, and gentle and close in nature. The folds are southwest, northeast or southeast vergent. The Jhelum fault truncates the northeast and northwest trending structures. The folds and faults are the result of northeastsouthwest or northwest-southeast Himalayan compression.  相似文献   

Formation by silicate–fluoride + phosphate melt immiscibility of REE-rich globular segregations within aplite dikes     

Charles?R.?SternEmail author  Julien?M.?Allaz  Markus?B.?Raschke  G.?Lang?Farmer  M.?Alexandra?Skewes  Jeremy?T.?Ross 《Contributions to Mineralogy and Petrology》2018,173(8):65

Aplite dikes intruding the Proterozoic 1.42(±?3) Ga Longs Peak-St. Vrain Silver Plume-type peraluminous granite near Jamestown, Colorado, contain F, P, and rare earth element (REE)-rich globular segregations, with 40–46% REE, 3.7–4.8 wt% P₂O₅, and 5–8 wt% F. A combination of textural features and geochemical data suggest that the aplite and REE-rich globular segregations co-existed as two co-genetic liquids prior to their crystallization, and we propose that they are formed by silicate–fluoride?+?phosphate (+?S?+?CO₂) melt immiscibility following ascent, cooling, and decompression of what was initially a single homogeneous magma that intruded the granite. The REE distribution coefficients between the silica-rich aplites and REE-rich segregations are in good agreement with experimentally determined distribution coefficients for immiscible silicate–fluoride?+?phosphate melts. Although monazite-(Ce) and uraninite U–Th–Pb microprobe ages for the segregations yield 1.420(±?25) and 1.442(±?8) Ga, respectively, thus suggesting a co-genetic relationship with their host granite, ε_Nd1.42Ga values for the granites and related granitic pegmatites range from ??3.3 to ??4.7 (average ??3.9), and differ from the values for both the aplites and REE-rich segregations, which range from ??1.0 to ??2.2 (average ??1.6). Furthermore, the granites and pegmatites have (La/Yb)_N <50 with significant negative Eu anomalies, which contrast with higher (La/Yb)_N >100 and absence of an Eu anomaly in both the aplites and segregations. These data are consistent with the aplite dikes and the REE-rich segregations they contain being co-genetic, but derived from a source different from that of the granite. The higher ε_Nd1.42Ga values for the aplites and REE-rich segregations suggest that the magma from which they separated had a more mafic and deeper, dryer and hotter source in the lower crust or upper mantle compared to the quartzo-feldspathic upper crustal source proposed for the Longs Peak-St. Vrain granite.  相似文献