Catastrophic hurricane history revealed by organic geochemical proxies in coastal lake sediments: a case study of Lake Shelby,Alabama (USA)

We developed a new method for reconstructing millennia-long hurricane records from coastal environments that uses Organic Geochemical Proxies (OGPs) of organic carbon and nitrogen concentrations and their δ¹³C and δ¹⁵N compositions. The new method is independent of presence/absence of sand layers and improves significantly the severe-storm history resolution. The subject of this investigation is a 1.5 m long sediment core raised at 2.8 m water depth from the center of Lake Shelby, Alabama, a freshwater lake located approximately 250 m from the Gulf of Mexico, from which an overwash sand-layer based record was previously derived. The core contains two distinct sediment units; an upper 62 cm thick, fine-grained, organic-rich lacustrine sapropel (gyttja) that shows no visible structures except one sand lamina at 23.7 cm depth, and an underlying 90 cm thick, organic-poor lagoon/estuary clay unit. The sapropel unit was deposited over a 682 ± 30 cal year time interval (1320–2002 A.D.) with a mean sedimentation rate of 0.79 ± 0.04 mm/year. Lake Shelby’s water column exhibits two contrasting states based on water chemistry surveys (i) an “isolated”, stratified, mode under calm weather conditions with a relatively low trophic state, and (ii) a “flooded” mode occurring during storm surges when nutrient-rich seawater floods the lake. Statistically significant δ¹³C and δ¹⁵N positive excursions in organic matter, up to maximum values of −25 (‰ PDB) and 4 (‰ Air N₂), respectively, are interpreted as geochemical responses to the marine intrusions that fertilize the lake, increase light availability, and cause eutrophication spikes. Detailed OGPs analyses crossing a sand layer that offers visual evidence of a catastrophic hurricane overwash event at 1717 A.D. exhibit large δ¹³C and δ¹⁵N positive shifts bounded by rapid returns to base values, thus confirming the validity of the hurricane identification by the OGPs model. Our data indicate that 11 catastrophic hurricanes hit the Alabama coast over the past 682 years with a rough recurrence interval of one in 62 years.     

Characterization of Risks in Coastal Zones: A Review

Interest in sustainable development for the natural, socio‐economic, and cultural resources of coastal zones is growing worldwide. On the other hand, the range of threats to coastal zones increasingly posed by hydro‐meteorological natural phenomena has led to a trend in the analysis and assessment of risks to these areas. The available literature dealing with coastal risk assessment is quite wide, focusing mainly on the risk evaluation of coastal flooding and erosion resulting directly from the occurrence of extreme natural events. The risk assessment methodologies are usually specific to the conditions and available data of each country, society or location, though most have evolved to assess the risk concept more precisely and rigorously. However, there are still very few studies that present feasible and effective methodologies, which lead to the effective integration of risk analysis at all levels. In Mexico coastal risk analysis has barely begun despite our extensive coastline, which is highly vulnerable to the threat of tropical cyclones. This paper aims to give a broad view of the risk assessment methodologies which already exist, in order to provide a starting point for future efforts in Mexico and elsewhere.     

Evaluation of a proposed damage index for a set of earthquakes

A damage index computed for a set of ground motions recorded in 11 earthquakes, including the 1985 Mexico City earthquake, the 2010 Chile earthquake, the 2011 Christchurch earthquake, and the 2011 Great East Japan earthquake, is proposed in this paper. The proposed damage index uses some basic parameters of the response of an SDOF system including the maximum hysteretic energy per unit mass that a structure can dissipate under strong ground motions. Control of lateral displacements, especially roof drift ratio of buildings, was found to be important in minimizing seismic damage. The values and distribution of the computed damage index are consistent with global building damage observations for the selected earthquakes. Copyright © 2014 John Wiley & Sons, Ltd.     

Modelling extraordinary floods and sedimentological processes in a large channel-floodplain system of the Lower Paran River(Argentina)

A quasi-2D unsteady flow and sediment transport model suitable for the simulation of large lowland river systems,including their floodplains,is presented.The water flow and sediment equations are discretised using an interconnected irregular cells scheme,in which different simplifications of the 1D de Saint Venant equations are used to define the discharge laws between cells.Spatially-distributed transport and deposition of fine sediments throughout the river-floodplain system are simulated.The model is applied over a 208-km reach of the Parana River between the cities of Diamante and Ramallo(Argentina) comprising a river-floodplain area of 8100 km~2.After calibration and validation,the model is applied to predict water and sediment dynamics during synthetically generated extraordinary floods of100,1000,and 10,000 years return period.The potential impact of a 56-km long road embankment constructed across the entire floodplain is simulated and compared to model results without the embankment.The embankment results in increases in upstream water levels,inundation extent,flow duration,and sediment deposition.     

Salt Marsh and Fringing Oyster Reef Transgression in a Shallow Temperate Estuary: Implications for Restoration,Conservation and Blue Carbon

The importance of intertidal estuarine habitats, like salt marsh and oyster reef, has been well established, as has their ubiquitous loss along our coasts with resultant forfeiture of the ecosystem services they provide. Furthering our understanding of how these habitats are evolving in the face of anthropogenic and climate driven changes will help improve management strategies. Previous work has shown that the growth and productivity of both oyster reefs and salt marshes are strongly linked to elevation in the intertidal zone (duration of aerial exposure). We build on that research by examining the growth of marsh-fringing oyster reefs at yearly to decadal time scales and examine movement of the boundary between oyster reef and salt marsh at decadal to centennial time scales. We show that the growth of marsh-fringing reefs is strongly associated to the duration of aerial exposure, with little growth occurring below mean low water and above mean sea level. Marsh-shoreline movement, in the presence or absence of fringing oyster reefs, was reconstructed using transects of sediment cores. Carbonaceous marsh sediments sampled below the modern fringing oyster reefs indicate that marsh shorelines within Back Sound, North Carolina are predominantly in a state of transgression (landward retreat), and modern oyster-reef locations were previously occupied by salt marsh within the past two centuries. Cores fronting transgressive marsh shorelines absent fringing reefs sampled thinner and less extensive carbonaceous marsh sediment than at sites with fringing reefs. This indicates that fringing reefs are preserving carbonaceous marsh sediment from total erosion as they transgress and colonize the exposed marsh shoreline making marsh sediments more resistant to erosion. The amount of marsh sediment preservation underneath the reef scales with the reef’s relief, as reefs with the greatest relief were level with the marsh platform, preserving a maximum amount of carbonaceous sediments during transgression by buffering the marsh from erosional processes. Thus, fringing oyster reefs not only have the capacity to shelter shorelines but, if located at the ideal tidal elevation, they also keep up with accelerating sea-level rise and cap carbonaceous sediments, protecting them from erosion, as reefs develop along the marsh.     

秘鲁南部阿雷基帕段海岸岩基带找矿方向探讨

通过详细的岩相学和锆石U-Pb年龄的研究,秘鲁海岸岩基带阿雷基帕段的填图工作得到了补充,该岩基带岩浆活动可分为7个阶段和4个旋回,各阶段都显示出不同的岩浆容量,其地貌主要表现为岩基和岩脉。旋回Ⅰ和旋回Ⅱ代表侏罗纪岩浆活动阶段（201~145Ma）,岩浆分异为辉长岩到花岗岩;旋回Ⅲ和旋回Ⅳ代表白垩纪岩浆,岩浆分异为英云闪长岩-二长花岗岩、闪长岩与花岗闪长岩及英云闪长岩-花岗闪长岩。对角闪石和黑云母矿物晶体的数量关系研究表明,旋回Ⅰ的侵入岩有大量辉石和角闪石结晶,并伴随金-铁成矿作用;旋回Ⅱ有大量的群集角闪石晶体和呈定向排列或群集的六边形黑云母,且伴随铜-金-铁成矿作用;旋回Ⅲ侵入岩内发育角闪石和黑云母,伴随着金-铜和铁成矿作用;旋回Ⅳ发育大量角闪石和六边形黑云母,岩石更偏长英质,并伴随铜-锌-金-银-铁和铜-金-钼成矿作用。     

Modeling flood dynamics in a temporary river draining to an eutrophic reservoir in southeast Portugal

Enxoé is a small temporary river with a flushy regime, which flash floods carry significant loads to the reservoir. As a result, the reservoir, which supplies 25,000 inhabitants, exhibits a high trophic state and cyanobacteria blooms since its construction in 1998, with water abstractions requiring extensive treatment. This study aimed to understand the contribution of flash floods to the Enxoé’s reservoir high trophic state using a modeling approach. This was the first time the river was monitored and that a modeling study was carried out. The MOHID-Land model was implemented to assess the water path in the catchment, and was integrated with field data to compute river loads. Results confirmed the importance of flash events. During flash floods, water properties were determined by soil surface and river bottom wash out, and depended mostly on the flush sequence and intensity. Model simulations showed that soil surface permeability reduction was an important factor regulating surface runoff while soil moisture was low. The first flood after the dry period contributed to 2% of the yearly discharge, 3% of yearly N load, and 7% of the yearly P loads. Winter floods contribution differed, producing 10% of both yearly discharge and loads. However, concentration of particulate matter and organic compounds in the first flood were one order of magnitude higher than in winter floods. This was due to river bottom resuspension and erosion of riparian areas, representative dynamics of a flushy regime. During subsequent winter floods, nutrient concentrations tended to remain constant as the watershed surface and respective soils were washed. Further work should link a watershed model to a reservoir model to depict the flood impact in the reservoir, and test management strategies to reduce the reservoir trophic state.     

Amphipod intersex, metals and latitude: A perspective

Intersexuality has been widely reported in crustaceans with several mechanisms being directly or indirectly held responsible for its occurrence, amongst which pollution. No mechanistic relationship between metals and intersex has ever been established. Also the incidence of intersex in populations of the same invertebrate species in a latitudinal gradient has never been studied so far. Three populations (Iceland, Scotland and Portugal) of the amphipod Echinogammarus marinus were scrutinized. Intersex females from Iceland registered the highest fecundity loss. Only in Scottish samples females with two genital papillae and males with only one genital papillae were observed. Nevertheless, water, biota and sediment samples pointed to equivalent metal levels, and in consonance the prevalence of intersex was not significantly different between locations. An unequivocal relationship between metal presence and intersex induction cannot be presented, but our results advocate the potential role of metals as a direct cause of intersexuality in E. marinus.     

Inversion of Multiconfiguration Complex EMI Data with Minimum Gradient Support Regularization: A Case Study

Mathematical Geosciences - Frequency-domain electromagnetic instruments allow the collection of data in different configurations, that is, varying the intercoil spacing, the frequency, and the...     

Evaluation of a distributed model for urban catchments using a 7‐year continuous data series

The documentation existing on both land use and the delineation of pervious and impervious zones in urban areas tends to be rather complete. In addition, topographical information (altitudes, slopes) is generally available, although contours are not drawn in detail on urban‐area maps. The development of urban databases has provided a convenient means of accessing this information for the purpose of hydrological modelling. The objective of this paper is to evaluate a recent model, ‘SURF’ (semi‐urbanized runoff flow), specifically developed for coupling with a GIS based on a digital terrain representation. This model was evaluated by use of an original approach from the field of urban hydrology. A 7‐year continuous data series, which includes the dry periods, has been used as input to run the model. The principles behind the SURF model are briefly described herein. A sensitivity analysis is then performed in order to select the most influential parameters. Following the calibration stage, the model's validation is discussed. This validation is conducted not only by comparing observed and simulated hydrographs, but also by comparing the SURF model with a more conventional model in urban hydrology, called the URBAN model. It is demonstrated that the SURF model provides useful simulation results and does outperform the URBAN model. Copyright © 2000 John Wiley & Sons, Ltd.