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61.
E. Molinaroli S. Guerzoni G. De Falco A. Sarretta A. Cucco S. Como S. Simeone A. Perilli P. Magni 《Sedimentary Geology》2009,219(1-4):196-207
A comparison was made of shallow water sediments from the Lagoon of Venice (LV) and the Lagoon of Cabras (LC), comparing depositional environments and exploring the relationships between hydrodynamics and sedimentological parameters. The two water bodies are very different in size (LV: 360 km2; LC: 22 km2), and the sediments predominantly consist of silty-clay (LV: Mz ≈ 26 μm; LC: Mz ≈ 6 μm). However, there are large differences between the two lagoons with respect to sand (LV: mean 19%; LC: mean ~ 3%) and clay (LV: mean 20%; LC: mean 45%) contents. The Lagoon of Venice (mean depth ~ 1 m) can be considered a tidal basin, whereas the Lagoon of Cabras (mean depth ~ 2 m) has the character of a coastal lake in which wind is the main hydrodynamic forcing factor. A comparison of sediment grain-size distributions with water circulation patterns in different parts of the lagoons highlighted some interesting differences. Grain-size analyses of samples reveal a deficiency of particles around 8 μm in the LC, which is interpreted as reflecting the transition between cohesive flocs/aggregates and non-cohesive coarser silt particles, while the transition limit in the LV is ~ 20 μm. Thus, particles are cohesive below 8 μm in the LC and below ~ 20 μm in the LV. This is probably because of the differences in the clay/silt ratio, which is much lower in the LV (~ 0.3) than in LC (~ 1), conferring a “silt-dominated network structure” on most of the LV sediments.The hydrographical data used were root mean square velocity (RMSV) and water residence time (WRT), computed under the main forcing conditions. The results show a general correlation between RMSV and sortable silt in the LC, and between RMSV and coarser sediments (63–105 μm) in the LV. Some significant differences between the lagoons were detected in the degree of correlation between WRT and grain size. Root mean square velocity (~ 7 cm s− 1 in the LV and ~ 3 cm s− 1 in the LC) was a greater forcing factor in the LC than in the LV. Conversely, WRT, which is on average ~ 16 days in the LV and ~ 19 days in the LC, has more influence in the LV. This study highlights the usefulness of comparing environments with different hydrodynamic energies, e.g., tidal and/or wind-driven currents, to elucidate and thereby improve our understanding of the processes governing the spatial distribution of sedimentological features, the transport mechanisms of sediments, and the relationship between them. The results demonstrate that the approach outlined in this study has the potential to provide a universal hydro-sedimentological classification scheme. 相似文献
62.
Occurrence and levels of polybrominated diphenyl ethers (PBDEs) in recent sediments and marine organisms from Xiamen offshore areas, China 总被引:3,自引:0,他引:3
Surface sediments and porewater from 12 sites within Xiamen offshore areas and organisms from a heavily contaminated site Yuandang Lagoon were sampled and analyzed for eight polybrominated diphenyl ethers (PBDEs) congeners (-28, -47, -99, -100, -153, -154, -183 and -209). The total concentrations of eight PBDEs (∑8PBDEs) and BDE-209 in sediments ranged from 0.27 to 76.54 ng/g with an average of 16.31 ng/g and from 0.10 to 70.11 ng/g with an average of 14.94 ng/g, respectively. Concentrations of ∑8PBDEs in porewater ranged from 2.5 to 34.1 ng/L, with a mean value of 15.3 ng/L. In this study, the partition coefficients (log ) of PBDE congeners (without -209) were significantly correlated with their octanol-water partition coefficients (log KOW) (r2 = 0.74, P < 0.01). ∑8PBDE concentrations ranged from 0.33 to 1.26 ng/g (lipid weight) in marine organisms, and PBDE congener patterns were significantly different between fish and clam, crab. 相似文献
63.
Evaluating the source and seasonality of submarine groundwater discharge using a radon-222 pore water transport model 总被引:1,自引:0,他引:1
Christopher G. Smith Jaye E. Cable Jonathan B. Martin Moutusi Roy 《Earth and Planetary Science Letters》2008,273(3-4):312-322
Pore water radon (222Rn) distributions from Indian River Lagoon, Florida, are characterized by three zones: a lower zone where pore water 222Rn and sediment-bound radium (226Ra) are in equilibrium and concentration gradients are vertical; a middle zone where 222Rn is in excess of sediment-bound 226Ra and concentration gradients are concave-downward; and an upper zone where 222Rn concentration gradients are nearly vertical. These 222Rn data are simulated in a one-dimensional numerical model including advection, diffusion, and non-local exchange to estimate magnitudes of submarine groundwater discharge components (fresh or marine). The numerical model estimates three parameters, fresh groundwater seepage velocity, irrigation intensity, and irrigation attenuation, using two Monte Carlo (MC) simulations that (1) ensure the minimization algorithm converges on a global minimum of the merit function and the parameter estimates are consistent within this global minimum, and (2) provide 90% confidence intervals on the parameter estimates using the measured 222Rn activity variance. Model estimates of seepage velocities and discharge agree with previous estimates obtained from numerical groundwater flow models and seepage meter measurements and show the fresh water component decreases offshore and varies seasonally by a factor of nine or less. Comparison between the discharge estimates and precipitation patterns suggests a mean residence time in unsaturated and saturated zones on the order of 5 to 7 months. Irrigation rates generally decrease offshore for all sampling periods. The mean irrigation rate is approximately three times greater than the mean seepage velocity although the ranges of irrigation rates and seepage velocities are the same. Possible mechanisms for irrigation include density-driven convection, wave pumping, and bio-irrigation. Simulation of both advection and irrigation allows the separation of submarine groundwater discharge into fresh groundwater and (re)circulated lagoon water. 相似文献
64.
Lucas O. Bianchi Juan Antonio Rivera Facundo Rojas Mauro Britos Navarro Ricardo Villalba 《水文科学杂志》2017,62(4):533-545
In the Central Andes of Argentina (30–37°S), snowmelt is the main source of freshwater, an essential natural resource for ~2.2 million people in the adjacent arid lowlands. In this region, Laguna Llancanelo collects the water inputs from the Malargüe endorheic basin. Previous studies concerning the annual and intra-annual variations of this lagoon and its relationship with regional climate are rare. We obtained a monthly record for the Laguna Llancanelo area (LLA, 1984–2013) using the modified normalized difference water index derived from Landsat images. Monthly LLA ranges between 35 km2 and 411 km2 and is significantly related to variations of the Río Malargüe, the main snow-fed tributary to the lagoon. There is no long-term relationship between LLA and local rainfall, but rapid increases in LLA result from heavy rainfall around the lagoon. Conversely, rapid reductions in LLA encompass periods with both reduced discharge from the Río Malargüe and low local rainfall. The LLA integrates moisture of both Pacific (snowfall in the upper Andes) and Atlantic (lowland rainfall) origins; therefore, we propose using LLA as an indicator of regional water balance. 相似文献
65.
66.
67.
The Manzala Lagoon in Egypt's Nile Delta has become a sediment sink of reduced area and depth, with increased contaminant
levels. Loss of much-needed fresh to brackish water reserves and decreased fish catches have serious ramifications. Herein,
maps of temporal and regional sediment distributions in Manzala incorporate petrological and statistical analyses of 200 surficial
and short core samples. These provide baseline information needed to help implement protection measures for this vital wetland.
Four periods are considered: 1920s, 1940s, ∼1965, and 1990. Important depositional changes between 1940s and ∼1965 resulted
from anthropogenic effects on this quasi-closed lagoon system, including industrial buildup, wetland conversion to agricultural
land, and irrigation waterway development. Further modification from ∼1965 to 1990 is associated with closure of the Aswan
High Dam, continued construction of waterways that discharge waste water into lagoon margins, and marine incursion into the
northern lagoon. If current practices continue, the lagoon could be reduced to about one-third of its present area by 2050
AD.
Received: 2 October 1997 · Accepted: 13 January 1998 相似文献
68.
In this study we examined the spatial and temporal dynamics of planktonic bacterial assemblages at four different sites in the Lagoon of Venice. Samples were collected in January, April, July and October 2005 and several parameters (temperature, salinity, dissolved oxygen, chlorophyll a, dissolved macronutrients, dissolved and particulate organic carbon, viral and heterotrophic nanoplanktonic abundances) were determined in order to highlight the most important factors which are implied in shaping such assemblages. Furthermore we tested the relationship between similar assemblages and the patterns of activities (prokaryotic carbon production and several hydrolytic activities) that they perform in order to establish if, in this highly variable environment, similar assemblages behave in analogous ways. Results indicate that seasonality act as the main forcing on the communities. Moreover, we found a mismatch between community structure and patterns of activity possibly as a consequence of the heterogeneity of the lagoon which can affect in turn the assemblages' metabolic requirements (and thus their responses). 相似文献
69.
Emmanuil Koutrakis Georgios Sylaios Nikolaos Kamidis Dimitrios Markou Argyris Sapounidis 《Estuarine, Coastal and Shelf Science》2009,83(4):505-515
Drana Lagoon, located at the NW site of Evros River Delta, was drained in 1987 and re-flooded in 2004 within the framework of an integrated wetland restoration project. This study presents the results of a monitoring program of the lagoon's oceanographic, water quality and fish fauna characteristics, during the pre- and post-restoration period. Results depict the presence of high salinity water (up to 41) due to seawater intrusion, strong evaporation in its interior and inadequate freshwater inflows. Overall, nutrient levels were low depicting local changes. Tidal variability at the mouth was approximately 0.2 m, producing high velocity tidal currents (up to 0.75 m/s). Eleven fish fauna species were collected; seven species were caught in both the inlet channel and the lagoon during the pre-restoration period and nine species in the post-restoration period. Atherina boyeri (37.6%) and Pomatoschistus marmoratus (31.7%) dominated the lagoon during the post-restoration period. Most of the A. boyeri specimens (88.5%) were caught inside the lagoon, while P. marmoratus had an almost equal distribution in the inlet channel and the lagoon (56.3% and 43.7% respectively). The presence of species of the Mugilidae family (5.2% total average catches after lagoon re-flooding) was mainly in the inlet channel (12.6% of the average catches) and not inside the lagoon (only 1.3% of the average catches). The small number of fish species inhabiting the lagoon might be the result of the recent restoration or it could be related with the increased water flow observed at the lagoon mouth during the flood and ebb tidal phases, and also in the presence of a smooth bank in the concrete waterspout that connects the entrance channel with the lagoon. The limited presence of the Mugilidae juveniles inside the lagoon could be related to the prevailing tidal inlet dynamics (i.e. strong ebb flow at lagoon inlet), thus preventing the species to enter the lagoon. In order to restore the lagoon environment, careful and gradual steps should be undertaken under the basis of continuous monitoring of hydrologic, environmental and fisheries system's status. 相似文献
70.
通过在高度富营养化的海水泻湖——厦门贸彗湖开展龙须菜(Gracilaria lemaneiformis)的延绳夹苗挂养与网笼挂养实验和室内端足类啃食海藻实验,探讨了影响筼筜湖龙须菜生长的主要因素。结果显示,筼筜湖龙须菜的表观生长率为0.42%/d,实际生长率为4.80%/d,强壮藻钩虾(Ampithoe valida)的摄食量占龙须菜总生长量的91.4%。而且,筼筜湖的水流缓慢,使藻体附着最高可达2.32g/gFw的颗粒物,明显抑制了龙须菜的生长。以上研究表明,端足类的啃食作用和不良的水动力条件是导致筼筜湖龙须菜表观生长率低的主要原因。 相似文献