沙坝—泻湖海岸动力地貌学研究进展

国内外对沙坝－泻湖海岸的研究主要采取动力地貌学的方法，本文评述了近一个半世纪以来在这一领域所取得的重要成果。波浪、潮汐、径流等特殊的动力场决定了泥沙输运的方式和路径，从而形成了与其相应的沙坝、泻湖、潮汐通道三大地貌体系。     

泻湖沉积环境——山东半岛为例

本文以山东半岛为例,系统地探讨了泻湖特征性的沉积环境——湖、海水的频繁交换,盐度多变,浅水低能和多物源。为泻湖的开发利用提供有益资料。     

Sedimentary record of redox-sensitive elements (U, Mn, Mo) in a transitory anoxic basin (the Thau lagoon, France)

In order to further document the relation between redox conditions and the sedimentary record of Mn, U and Mo in a transitory anoxic water basin, their distribution has been studied along two profiles in the Thau lagoon (France). Sediments and pore-water have been sampled at two contrasting sites located, respectively, in the shellfish-farming area and in the centre of the lagoon. In the shellfish-farming area, the particulate organic carbon (POC) data indicate a more rapid organic matter mineralisation compared to the centre of the lagoon. This results in a sharper redox gradient characterized by the appearance of H₂S in pore-water a few millimetres below the sediment–water interface. In the centre of the lagoon, H₂S appears at a depth of 35 cm.In both cores, sedimentary Mn is relatively depleted through out the whole sedimentary column and varies with the proportion of clay minerals. After an initial release into solution at the sediment–water interface in relation to Mn-oxide reductive dissolution, authigenic U is immobilized when sulphides appear. Despite the occurrence of anoxic conditions at the sediment–water interface at the site influenced by shellfish farming, the burial of U is reduced by bioturbation, which raises reducing sediments to the surface. In the centre of the lagoon, Mo profiles reflect continuous diffusion into pore water and immobilization at 15 cm probably in anoxic microenvironments. At shellfish farms, dissolved Mo undergoes removal with sulphides but contrary to U, sedimentary Mo does not appear to be strongly affected by bioturbation. The profile indicates an increase in the frequency of anoxia crises during the second half of the 20th century.     

Seasonal variation of a molluscan assemblage living in a Caulerpa prolifera meadow within the inner Bay of Cádiz (SW Spain)

The molluscan macrofauna living in shallow muddy bottoms with the green algae Caulerpa prolifera was studied monthly between February 1994 and January 1996 in the inner Bay of Cádiz (SW Spain). The molluscan assemblage followed a similar pattern over the 2 years, displaying seasonal trends in species richness, abundance and structure. During the autumn and winter months, a decrease in abundance, species richness and diversity and an increase in evenness occurred. During the spring and summer months, the molluscan assemblage was characterised by an increase in species richness, abundance and diversity. These seasonal trends were supported statistically by the presence of significantly different groupings of seasonal samples in multivariate analyses.Despite human impacts in the bay (e.g. aquaculture activities, sewage), the presence of repetitive seasonal trends, based on the qualitative and quantitative data, indicates the stability of the molluscan assemblage over 2 years. Benthic characteristics from the inner Bay of Cádiz, such as shallow soft bottoms with the presence of macrophytes and current dynamics, seem to be key factors influencing the composition and seasonality of this molluscan assemblage.     

Short-term seaward fish migration in the Messolonghi–Etoliko lagoons (Western Greek coast) in relation to climatic variables and the lunar cycle

In the present study we analysed the daily seaward migratory behaviour of four dominant euryhaline fish species (Mugilidae: Liza saliens, Liza aurata, Mugil cephalus and Sparidae: Sparus aurata) in the Messolonghi–Etoliko lagoon system (Western Greek coast) based on the daily landings' time series of barrier traps and assessed the relationship between their migratory behaviour and various climatic variables (air temperature and atmospheric pressure) and the lunar cycle. A 2-year time series of daily fish landings (1993 and 1994), a long time series of daily air temperature and daily temperature range (1991–1998) as well as a 4-year time series of the daily atmospheric pressure (1994–1997) and daily pressure range were used. Harmonic models (HM) consisting of annual and lunar cycle harmonic components explained most (R² > 0.80) of the mean daily species landings and temperature variations, while a rather low part of the variation (0.18 < R² < 0.27) was explained for pressure, daily pressure range and daily temperature range. In all the time series sets the amplitude of the annual component was highest. The model values of all species revealed two important migration periods (summer and winter) corresponding to the spawning and refuge migrations. The lunar cycle effect on species' daily migration rates and the short-term fluctuation of daily migration rates were rather low. However, the short-term fluctuation of some species' daily migration rates during winter was greater than during summer. In all species, the main migration was the spawning migration. The model lunar components of the species landings showed a monthly oscillation synchronous to the full moon (S. aurata and M. cephalus) or a semi-monthly oscillation synchronous to the new and full moon (L. aurata and L. saliens). Bispectral analysis of the model values and the model residuals' time series revealed that the species daily migration were correlated (coherencies > 0.6) to the daily fluctuations of the climatic variables at seasonal, mid and short-term scales.     

Transport and dispersion of particulate Hg associated with a river plume in coastal Northern Adriatic environments

The role of suspended particulate matter (SPM) as an important carrier of mercury (Hg) dispersed into the Gulf of Trieste and in the adjacent Grado lagoon (Northern Adriatic Sea) was studied during a high Isonzo River inflow and the resulting river plume formation. Despite the fact that extreme flood events are rare during the year, they account for most of the PHg influx (37-112 ngL(-1)) into the Gulf of Trieste. When the river plume is diverted to the SW under the influence of an E-NE wind, the tidal flux acts as a "transport belt" carrying the PHg, mostly inorganic, into the Grado lagoon. A preliminary estimation indicates that the amount of PHg entrapped in the lagoon basin following a tidal semi-cycle accounts for 1.4 kg/12h, which corresponds to about 49% of the total Hg carried by the tidal flow. These findings should be considered in future remediation strategies in the lagoon environment.     

The Mar Menor lagoon (SE Spain): A singular natural ecosystem threatened by human activities

The Mar Menor lagoon is one of the most important ecological singularities in the Mediterranean area. At the same time, it is an area where many economic and industrial activities meet. The sum of the impacts of mining, agriculture and urban development in the surroundings to the lagoon during the last decades has affected its ecosystem. In this paper, we have reviewed the studies done by researchers over two decades regarding the impacts of human activities in the lagoon, reporting data of contamination levels and the effects generated in the ecosystem of the lagoon. The discharge of enriched nutrient waters seems to be the most important input in the lagoon. Changes to more friendly agricultural techniques in the surrounding areas are therefore necessary. After our review, we can conclude that it is necessary to have higher efforts from the public administrations and stricter environmental regulations in order to preserve, on one hand, the important ecological values of the lagoon, and on other hand, public health.     

A model of sand transport in Treporti channel: northern Venice lagoon

The origin of the sands in the Venice lagoon has been the subject of an extensive field survey in parallel with numerical modelling. Four transects along Treporti and Burano canals were conducted from which 33 bottom sediment samples were collected. These samples were analysed for grain size and sorting to examine any trends in the granulometry of these sediments that might shed light on transport paths. The modelling study consists of three parts: the sediment transport model sedtrans96 was used with a finite-element hydrodynamic model (Shyfem) and an empirical wave model (US Army Corps of Engineering) to simulate sand transport in the Treporti canal. A type of link box model was created where finite elements of the hydrodynamic model have been combined to macro-boxes on which the water and sediment flux over the sections, and a mass balance has been computed. Several grain size classes were simulated; the distributions before and after the simulation were examined. Idealised wind and tidal values were initially used to force 12 h simulations to test the sediment transport sensitivity. Finally, a full-year simulation (1987) has been carried out using measured tidal and wind data. Only a part of Venice lagoon was covered by the simulation: a major channel (Treporti) running from Lido inlet towards the northern lagoon. The total sand transport through all of the sections was computed for 1 year. Sediment mass balance was determined, and the resulting trends of erosion and deposition were computed. There were no trends in the median grain diameter and sorting of bottom samples from the Treporti canal; all sands were fine (120 μm, one outlier of 300 μm was removed). The absence of a trend in grain size suggests that there is no significant import of sand to the lagoon through the Lido inlet. The results from the simulations seem therefore to confirm the hypothesis of reworking of sand within the lagoon. The computed erosion is some centimeters per year diagnostic of channel scouring and enlargement with time. The Treporti canal is subject to strong current velocities of around 1 m/s, which hold fine sand in suspension and thus prevent sedimentation.     

ROBUST: The ROle of BUffering capacities in STabilising coastal lagoon ecosystems

“Buffer capacities” has been defined in ecology as a holistic concept (e.g., Integration of Ecosystem Theories: A Pattern, second ed. Kluwer, Dordrecht, 1997, 388pp), but we show that it can also be worked out in mechanistic studies. Our mechanistic approach highlights that “buffering capacities” can be depleted progressively, and, therefore, we make a distinction between current and potential “buffering capacities”. We have applied this concept to understand the limited “local stability” in seagrass ecosystems and their vulnerability towards structural changes into macro-algal dominated communities. We explored the following processes and studied how they confer buffering capacities to the seagrass ecosystem: (i) net autotrophy is persistent in Zostera noltii meadows where plant assimilation acts as a sink for nutrients, this contrasted with the Ulva system that shifted back and forth between net autotrophy and net heterotrophy; (ii) the Z. noltii ecosystem possesses a certain albeit rather limited capacity to modify the balance between nitrogen fixation and denitrification, i.e., it was found that in situ nitrogen fixation always exceeded denitrification; (iii) the nitrogen demand of organoheterotrophic bacteria in the sediment results in nitrogen retention of N in the sediment and hence a buffer against release of nitrogen compounds from sediments, (iv) habitat diversification in seagrass meadows provides shelter for meiofauna and hence buffering against adverse conditions, (v) sedimentary iron provides a buffer against noxious sulfide (note: bacterial sulfide production is enhanced in anoxic sediment niches by increased organic matter loading). On the other hand, in the coastal system we studied, sedimentary iron appears less important as a redox-coupled buffer system against phosphate loading. This is because most inorganic phosphate is bound to calcium rather than to iron. In addition, our studies have highlighted the importance of plant–microbe interactions in the seagrass meadows.