Monitoring in the Western Pacific region shows evidence of seagrass decline in line with global trends     

Frederick T. Short  Robert Coles  Miguel D. Fortes  Steven Victor  Maxwell Salik  Irwan Isnain  Jay Andrew  Aganto Seno 《Marine pollution bulletin》2014

Seagrass systems of the Western Pacific region are biodiverse habitats, providing vital services to ecosystems and humans over a vast geographic range. SeagrassNet is a worldwide monitoring program that collects data on seagrass habitats, including the ten locations across the Western Pacific reported here where change at various scales was rapidly detected. Three sites remote from human influence were stable. Seagrasses declined largely due to increased nutrient loading (4 sites) and increased sedimentation (3 sites), the two most common stressors of seagrass worldwide. Two sites experienced near-total loss from of excess sedimentation, followed by partial recovery once sedimentation was reduced. Species shifts were observed at every site with recovering sites colonized by pioneer species. Regulation of watersheds is essential if marine protected areas are to preserve seagrass meadows. Seagrasses in the Western Pacific experience stress due to human impacts despite the vastness of the ocean area and low development pressures.  相似文献   

Negative influence of burial stress on plant growth was ameliorated by increased plant density in Polygonum hydropiper     

《Limnologica》2014

Sedimentation and density are important factors influencing the growth of wetland plants. The aim of this study was to elucidate the role of plant density in acclimation to burial stress by investigating the growth, biomass allocation, and carbohydrate contents of Polygonum hydropiper L. var. flaccidum, one of the dominant species in the Dongting Lake wetland, China. Experimental treatments, conducted in a greenhouse, combined three plant densities (16, 144, and 400 plants m⁻²) with two burial depths (0 and 15 cm) in a factorial design. Greater burial depth and higher plant density had negative effects on biomass accumulation and plant height with some exceptions. Plant growth, although lower at higher densities in general, was unaffected by burial depth at medium and high densities, indicating that the negative effect of burial stress was ameliorated by increased plant density. Deeper burial led to higher stem mass fraction only in the low-density treatment. Belowground mass fraction increased significantly with increasing density in both burial treatments. Moreover, higher density and deeper burial led to higher soluble sugar content but lower starch content. These data indicate that higher density facilitates acclimation of P. hydropiper to burial stress through increased soluble sugar content.  相似文献   

A new varve thickness record from Allt Bhraic Achaidh Fan,middle Glen Roy,Lochaber: implications for understanding the Loch Lomond Stadial glaciolacustrine varve sedimentation trends     

《Proceedings of the Geologists' Association. Geologists' Association》2017,128(1):136-145

Glen Roy, Lochaber is a key UK site for understanding Late Devensian environmental change, as it contains an annually-resolved glaciolacustrine varve record. This paper develops our understanding of varve sedimentation within Glen Roy through the examination of a new varve sequence located in a more proximal position on the Allt Bhraic Achaidh Fan, one of a series of major fans within the valley. This new varve record consists of c. 203 annual layers, much fewer years than at other sites in the Lochaber area probably due to five significant hiatuses within the record. Varve sediment characteristics and thickness are comparable to, but not statistically correlated with, other varve series that were used to construct a consolidated varve record for the area, the Lochaber Master Varve Chronology. Sedimentological characteristics, analysed by thin section micromorphology, suggest that varve thickness changes within the basin are controlled mainly by distance from the valley sides rather than the position of the ice margin during the Loch Lomond Readvance, as previously proposed.  相似文献   

Numerical study of slurry consolidometer tests taking into account the influence of wall friction     

《Computers and Geotechnics》2017

Three tests of slurried Jeeropilly coal tailings in a purpose-built slurry consolidometer under three different loading sequences were numerically analysed to study the friction losses quantitatively. A simplified sedimentation-consolidation theory was proposed to link the initial suspended state and soil-like state of slurries. The numerical simulations provided good agreement with the measured, and indicated the noticeable friction losses, from 11.1% to 34.2%, due to factors such as the diameter of consolidometers and loading sequences. The average coefficient of the stress (pore water pressure) stood at 1 at the beginning, and declined to a stable value around 0.55 (0.67).  相似文献   

Basin scale distribution of organic matter in marine fine-grained sedimentary rocks: Insight from sequence stratigraphy and multi-proxies analysis in the Montney and Doig Formations     

《Marine and Petroleum Geology》2017

The occurrence of hydrocarbons in self-sourced reservoirs strongly depends on the concentration and maturity of organic matter in sediments. Therefore, understanding the distribution of organic heterogeneity at the time of deposition is key to reduce the risk in exploration and development of unconventional resources. This study focuses on the Lower and Middle Triassic Montney and Doig Formations (Alberta and British Columbia). Samples from outcrops, cores and cuttings were analyzed for organic content with a Rock-Eval VI and for major and trace element concentration using ICP-MS and ICP-AES techniques. The interpretation of the analysis results in relation with the stratigraphic architecture provides a mean to better understand the distribution of the organic heterogeneities and the variations of primary productivity, sedimentation rates and anoxia that control the development of source rocks.The key findings of this analysis are:- The basin-scale distribution of the organic matter suggests that the two major source-rock intervals of the Lower and Middle Triassic correspond to the sequence 3 (Spathian Montney unit) and to the transgressive systems tract of sequence 4 (Doig phosphate zone).- The dominant controls on organic matter accumulations vary through time. The Montney source-rock interval is interpreted to be associated with a major basin restriction triggering anoxia during a second-order falling stage of relative sea level. The organic accumulation of the Doig phosphate zone is interpreted as being controlled by a sharp decrease of the sedimentation rate, combined with an increase of the primary productivity.- The spatial and temporal variations of anoxia, primary productivity and dilution reflect the geodynamic evolution of the basin that ultimately controls the basin physiography as well as the sources of nutrient and sediments.  相似文献   

Deep-sea terrigenous organic carbon transfer and accumulation: Impact of sea-level variations and sedimentation processes off the Ogooue River (Gabon)     

《Marine and Petroleum Geology》2017

Sedimentary, isotopic and bulk geochemical proxies measured in sediment samples of five gravity cores collected in the distal part of the Ogooue turbidite system (around 4000 m-depth) were used to develop a conceptual model to describe the accumulation of terrigenous organic matter (OM) during the last 200,000 yrs BP in the eastern part of the Gulf of Guinea. This model takes into account the influence of the different depositional processes (turbiditic vs hemipelagic sedimentation), geomorphological features and sea-level variations.Total organic carbon (TOC) and the stable organic carbon isotopes of the OM (δ¹³C) variability follow the highstand/lowstand (interglacial/glacial) cyclicity with a very low accumulation rate of terrigenous OM during periods of high sea-level and higher accumulation rate during period of low sea-level. A sea-level of 80–120 m below present day seems to favor the transfer of terrigenous sediments to the deep offshore environment through the turbidite system and thanks to the connection of the canyons heads with the river system presently located at the shelf edge at −120 m water depth.In this system, terrigenous OM matter delivered by the river accumulate in the sediments via two main processes. Indeed, a part of the terrigenous OM settles in combination with the finest particles forming hemipelagites, while another part, formed of very well preserved land plant debris, is transported and deposited far offshore with turbidity currents. The proportion of terrigenous OM accumulated due to turbidity currents is important as it can represent more than 70% of the carbon accumulated during sea-level lowstand. Moreover, terrigenous OM seems to preferentially accumulate in the levees and the lobes of the system notably due to the higher frequency of organic-rich turbidites.This study demonstrates that gravity flows, influenced by the sea-level variations, can significantly affect the terrigenous OM budget of the deep offshore Atlantic margins and that channel-levee complexes as well as turbidite lobes can be regarded as good sink for terrestrial organic carbon. These processes should be taken into consideration in the context of source rocks exploration but also for the estimation of the general carbon accumulation in ocean sediment.  相似文献   

Petrographic and geochemical characteristics of the lacustrine black shales from the Upper Triassic Yanchang Formation of the Ordos Basin,China: Implications for the organic matter accumulation     

《Marine and Petroleum Geology》2017

The lacustrine black shales in the Chang7 Member from the Upper Triassic Yanchang Formation of the Ordos Basin in Central China are considered one of the most important hydrocarbon source rocks. However, the mechanism of organic accumulation in the black shales remains controversial. To resolve the controversy, with the former paleontological data of Yanchang Formation and sedimentation rate data of the Chang7 black shales, we investigated the typical intervals of the Chang7 black shales (TICBS) which were obtained by drilling in Yaowan at the southern margin of the Ordos Basin and performed various sedimentary, isotopic and geochemical analysis, including the sedimentary petrography, pyrite morphology, total organic carbon (TOC) and total sulfur (TS), the ratio of pyritic Fe to total Fe (DOP_T), major and trace elements, together with pyritic sulfur isotopes (δ³⁴S_py). The high sulfur content, enrichment of redox-sensitive trace metals, and the lower sedimentation rate of the TICBS in addition to the presence of marine spined acritarchs and coelacanth fossils indicate that the TICBS were deposited in a lacustrine environment possibly influenced by seawater. The petrographic observations show a thick layer of black shale with interlayers of thin layered siltstone (silty mudstone) and laminated tuff, which were related to the turbidity currents and volcanism, respectively. The U/Th, C-S, and Mo-U covariations, pyrite morphology, DOP_T, combined with the δ³⁴S_py, suggest that the deposition occurred beneath the anoxic-sulfidic bottom waters, which was intermittently influenced by the oxygen-containing turbidity. The Ni/Al and Cu/Al possibly show extremely high to high primary productivity in the water column, which might be connected with the substantial nutrients input from seawater or frequently erupted volcanic ash entering the lake. In addition, the coincidence of an increased abundance of TOC with increased P/Al, Ni/Al, Cu/Al and U/Th, as well as relatively consistent Ti/Al suggest that the accumulation of the organic matter might be irrelevant to the clastic influx, and was mainly controlled by the high primary productivity and anoxic-sulfidic conditions. Further, the covariations of TOC vs. P/Al and TOC vs. Ba/Al indicate that the high primary productivity led to the elevated accumulation and burial of organic matter, while the anoxic to sulfidic conditions were likely resulted from an intense degradation of the organic matter during the early diagenesis. In summary, the organic matter accumulation is ultimately attributed to the high primary productivity possibly resulted from seawater or volcanic ash entering the lake.  相似文献   

Quaternary evolution of the intermontane Val d'Agri Basin, Southern Apennines     

Irene Zembo  Laura Panzeri  Anna Galli  Riccardo Bersezio  Marco Martini  Emanuela Sibilia 《Quaternary Research》2009,72(3):431-442

Optically Stimulated Luminescence (OSL) enables the chronology of the late Pleistocene evolution for the Val d'Agri intermontane basin of Southern Apennines to be defined in the frame of Mediterranean geodynamic and climate changes. Quartz sand from braided floodplain and alluvial fan depositional systems was analyzed using the coarse-grained, single-aliquot regenerative-dose (SAR) technique. The obtained optical ages are mostly consistent with other assessments (radiocarbon, tephrochronology) and stratigraphic constraints. OSL allows for the dating to 56–43 ka of an asymmetric subsidence stage that forced alluvial fan progradation, filling of a former lacustrine area, and development of an axial alluvial plain. A short period of Mediterranean-type pedogenesis, recorded at the top of the prograding-aggrading fans (OSL age bracket 43–32 ka), corresponds with MIS 3. During the subsequent stage of decline of vegetation cover, possibly corresponding to MIS 2, the latest progradation of alluvial fans occurred. The subsequent uplift and breakthrough of the basin threshold during the latest Pleistocene and Holocene induced entrenchment of the drainage network. The results presented here provide an example of the usefulness of OSL dating in intermontane continental settings where other geochronological constraints are scarce.  相似文献   

Analysis of non climatic origins of floods in the downstream part of the Kura River,Azerbaijan   总被引：1，自引：1，他引：0  

R. K. Abbasov  R. N. Mahmudov 《Natural Hazards》2009,50(2):235-248

Over the past century, there is an increased contribution of non climatic factors to the flood formation processes in the Kura River. Non climatic factors of floods refer to factors that are related to reductions in channel capacity and result in floods. More recently, there are numerous non climatic factors occurring in and around the Kura River basin that have increased the frequency of floods. Sediment accumulation in the riverbed over a long period of time has led to the reduction of channel capacity and has raised the elevation of the riverbed above the surrounding territory. It is illustrated that construction of dykes and levees do not actually prevent flooding, where hydrologic connections between groundwater and surface water are high, since infiltrated waters from channel results in raising of ground waters, causing an effect of “underground flood.” Since underground floods occur when water going from channels raises the level of ground waters, there is an urgent need to carefully investigate the groundwater–surface water connections. With the purpose of predicting floods, the authors suggest defining maximal acceptable flows (MAFs) rather than channel capacities. Results show that high rates of hydraulic conductivity of soils will decrease MAF rates. MAF computations before high-water season allow for further regulation of outlets further downstream in order to prevent flooding and enable flood forecasting. While the study focuses on a specific region, the overall approach suggested is generic and may be applied elsewhere.  相似文献   

Does Glacial-Interglacial Transition Affect Sediment Accumulation in Monsoon-Dominated Regions?     

Dharmendra Pratap SINGH  Rajeev SARASWAT  Dinesh K. NAIK 《《地质学报》英文版》2017,91(3):1079-1094

The spatio-temporal changes in sedimentation rate along the continental margin of the monsoon-dominated eastern Arabian Sea during the last 24 kyr have been estimated from a compilation of 58 radiocarbon dated cores, in order to understand the effect of glacial-interglacial variation on sedimentation. The sedimentation rate has been computed for four-time slices, viz. the last glacial maximum, glacial-interglacial transition, early Holocene and late Holocene. We report that the average sedimentation rate in the slope to the abyssal region of the entire eastern Arabian Sea, although higher during the Holocene as compared with that during the last glacial maximum and glacial-interglacial transition, does not significantly vary during all four-time intervals. The sedimentation rate during any particular time interval, however, varies from core to core, thus indicating zonal changes. We report four zones of relatively high sedimentation rate, viz. the northeastern Arabian Sea, the region off the Gulf of Khambhat, the region off Goa and Mangalore, and off the southern tip of India. We suggest that a complex interaction of land-ocean-atmospheric processes controlled sedimentation rate in the eastern Arabian Sea during the last 24 kyr in such a way that the average sedimentation rate does not vary significantly, even during highly contrasting climatic conditions.  相似文献