Interaction of alongshore sediment transport and habitat conditions at Laguna La Mancha, Veracruz, Mexico

The habitats of La Mancha Lagoon, located midway along the coast of Veracruz, Mexico, are responding to the change of sediment supply reaching its primary inlet at the Gulf of Mexico. Until several decades ago, an abundant alongshore supply of sediment created a periodic opening and closing of the La Mancha inlet. The hydrologic regime of the lagoon consisted of raised water level and lower salinity during the closures, whereas the open inlet favored lower water level, higher salinity, and sediment accumulation in the flood tidal delta. Currently, diminished alongshore sediment supply has affected the inlet morphology and the discharge regime. Associated with the reduced sediment supply, the inlet is open longer in its periodic cycle, the water level variation is reduced, the salinity contrasts are reduced, and the rate of sedimentation in the flood-tide delta is increased. This combination of alterations to the inlet area is changing the flooding regime and affecting the conditions in a very well-developed mangrove habitat at the lagoon margins as well as conditions within the aqueous portions of the lagoon. Management options produce a conflict between supporting the direction of change or preserving the existing habitats.     

Assessment of petroleum hydrocarbon in a tropical brackish water lagoon: Chilika,India

Assessment of petroleum hydrocarbon (PHC) in the Chilika Lagoon, India, revealed a significant spatio-temporal variation in surface water (analysis of variance: n?=?120, p?相似文献   

Assessment of spatial distribution of submerged vegetation in the Orbetello lagoon by means of a mathematical model

Coastal lagoons are characterized by a constant threat of eutrophication and a critical coexistence of differing submerged vegetation forms. This paper investigates the competitive equilibrium of macroalgae and phanerogams in the Orbetello lagoon in relation to physico-chemical and environmental factors, including wind, nutrients in the water column, and sediment characteristics. A mathematical model describing the evolution of the submerged vegetation as a function of the abiotic parameters is used here in conjunction with specific experimental studies to explain the relationship between phanerogams (seagrasses) prairie expansion, water movements, and sediment characteristics. The combination of specific sediment sampling and mathematical modelling shows that water circulation and the state of the upper sediment are both dominant factors in determining the phanerogams distribution in the lagoon and the mutually exclusive growth of these groups in differing parts of the lagoon. Water currents control the distribution of floating macroalgae, resulting in an uneven accumulation of decomposing biomass and phanerogams seed dispersal. The oxygenation provided by the rooted phanerogams affects the sediment characteristics, making them suitable for further prairie expansion. In addition to sediment analysis the use of a mathematical model combining the hydrodynamics and the water quality of the lagoon provides a thorough explanation of the expansion of the rooted vegetation in critical areas. A further result of this research is the validation of the model, originally calibrated with the lagoon central stations’ data, with the newly acquired data from several other parts of the ecosystem. The model predictions are in good agreement with the field observations under a number of environmental conditions and explain the observed expansion trend of phanerogams, which are beneficial for the lagoon ecology, more thoroughly than by relying on the sediment observations alone.     

Impact of rubble mound groyne structural interventions in restoration of Koggala lagoon,Sri Lanka; numerical modelling approach

Physical processes of the lagoon are influenced by structural interventions. Understanding the complex reality of physical processes sometimes difficult with field observations thus a model provides a simplified abstract view. Two dimensional hydrodynamic model is used to describe, restoration efforts to Koggala lagoon, a combined freshwater and estuarine complex of rich ecosystem on the southern coast of Sri Lanka. The lagoon mouth was naturally closed by a sand bar which controlled the seawater intrusion. Due to large-scale sand removal at lagoon mouth, formation of the sandbar shifted towards the lagoon. After the removal of natural sand barrier, rubble mound groyne structures were built to avoid sand deposition in the lagoon and to protect the highway bridge from the sea wave attack. Construction of the groyne resulted in the lagoon mouth being permanently open which in turn led to many environmental problems with saline intrusion. The aim of this study is to evaluate the current situation of the lagoon and propose alternative structural interventions for minimization of seawater intrusion and subsequently improve lagoon ecosystem. Hydrological parameters were investigated and mathematical models for hydrodynamic behavior of the lagoon were applied in order to describe the lagoon physical processes and flow characteristics. Existing rubble mound structures were redesigned in order to minimize the seawater intrusion. Numerical simulations were carried out for two different mouth widths (40 m and 20 m) with appropriate structural interventions. Existing salting factor for the lagoon is 0.68 and numerical simulation results showed salting factor for 40 m and 20 m openings are 0.61 and 0.54 respectively. This shows the mouth width can be reduced up to 20 m in order to obtain a slating factor close to 0.5, which indicates the predominant influence of fresh water which in turn leads lagoon to a fresh water ecosystem.     

The Extended Kalman Filter (EKF) as a tool for the assimilation of high frequency water quality data

The Extended Kalman Filter (EKF) was applied to the analysis of high frequency field measurements of dissolved oxygen (DO), water temperature, salinity, collected by multiparametric sensors in the lagoon of Venice. This paper focuses on the practical aspects of the implementation of the EKF as a data assimilation technique and does not deal with the problems associated with the identification of the model. In this regard, the EKF has proved to be a useful tool for the updating of the estimates of the parameters of a simple DO-chlorophyll model, which can be used for linking the high frequency data to meteorological forcings, such as solar radiation and wind, and to other low frequency measurements of water quality parameters, such as the concentrations of Chlorophyll a and nutrients. The model can subsequently be used as a tool for checking the consistency of all this data, and may also be employed for controlling the quality of the data collected by the multiparametric sensors.     

Environmental conditions of Chilika Lake during pre and post hydrological intervention: an overview

Chilika Lake, the largest brackish water lagoon in Asia, is a prominent biodiversity hotspot along the Indian east coast. The geomorphology, water quality and biological productivity of the lake had undergone significant changes over the years under the influence of natural events and anthropogenic interventions. Decades of research have shown that the ecological changes of the lake system and its fisheries were influenced mainly by the water exchange between the lake and the sea that controls the salinity, siltation, macrophyte infestation and recruitment of marine forms. Depletion of fisheries and loss of biodiversity in 1980s and 1990s have been linked to the northward shifting of lake’s inlet and silting up of the outer channel. In order to improve the health of the lagoon and restoration of its biodiversity, a new mouth was dredged open in September 2000. Opening of the new mouth has resulted in some improvements with substantial increase in capture fishery, reduction in weed infestation, growth of seagrasses, appearance of dolphins and increase in the population of migratory birds. But, many stake holders claim that the problems associated with the lake ecology and its contribution to the socio-economic development of the stake holders still persist which could escalate in future.     

Relationships between nutrients and macroalgal biomass in a brazilian coastal lagoon: the impact of a lock construction

The Piratininga Lagoon is a coastal, choked, and brackish ecosystem in SE Brazil, where uncontrolled discharge of domestic sewage led to eutrophication, increasing massive proliferation of benthic macroalgae, and decrease of the lagoon mean depth. In 1992, a dam was constructed by the local Municipality at its tidal channel aiming at stabilising its water level. Main physico-chemical parameters, together with macroalgae biomass, nutrient concentrations in the water column, particulate organic carbon, and chlorophyll a were recorded monthly at 4 sampling stations within the Piratininga lagoon from April 1994 to April 1995. The data, compared with “before-lock” existing studies, show that nutrients and chlorophyll a concentrations significantly increased after the lock construction. Based on the functioning of the ecosystem, we propose to harvest the algal mats before their decomposition period in order to partly remove the nutrient stocks from the lagoon and the future ecosystem modelling to predict the impact of natural and anthropogenic eutrophication.     

Relationships between nutrients and macroalgal biomass in a brazilian coastal lagoon: the impact of a lock construction

The Piratininga Lagoon is a coastal, choked, and brackish ecosystem in SE Brazil, where uncontrolled discharge of domestic sewage led to eutrophication, increasing massive proliferation of benthic macroalgae, and decrease of the lagoon mean depth. In 1992, a dam was constructed by the local Municipality at its tidal channel aiming at stabilising its water level. Main physico-chemical parameters, together with macroalgae biomass, nutrient concentrations in the water column, particulate organic carbon, and chlorophyll a were recorded monthly at 4 sampling stations within the Piratininga lagoon from April 1994 to April 1995. The data, compared with “before-lock” existing studies, show that nutrients and chlorophyll a concentrations significantly increased after the lock construction. Based on the functioning of the ecosystem, we propose to harvest the algal mats before their decomposition period in order to partly remove the nutrient stocks from the lagoon and the future ecosystem modelling to predict the impact of natural and anthropogenic eutrophication.     

Simulation tools to support bathing water quality management: Escherichia coli bacteria in a Baltic lagoon

Insufficient hygienic water quality and bathing prohibitions are still a serious problem in the Szczecin Lagoon (southern Baltic). In our study we focus on the southern lagoon coast and analyse the causes and consequences of high Escherichia coli bacteria concentrations. For this purpose we carry out laboratory experiments on the behaviour of E.coli in the lagoon, a literature review and apply a three-dimensional flow model together with a Lagrangian particle tracking routine. Three major E.coli sources, the Uecker river, the wetlands with cattle as well as sea gulls with bathing and fisheries were allocated, quantified and compiled into an emission scenario. This serves as input for transport simulations under different wind conditions and for the development of a spatial contamination map. Reasons for high E.coli concentrations in the lagoon are a permanent supply from different sources and the special environmental situation in the lagoon. The availability of organic matter, either in form of reed stems or as muddy sediments, has a positive effect on bacteria survival. Very important, too, are the prevailing wind and flow conditions, which cause water and organism transport in narrow ribbons along the coastline and promote near-shore accumulations. Even in our shallow lagoon, the application of a 3D-model is beneficial. Heavy rains are, very likely, responsible for the outstanding high total-coliform concentrations of 11,000?cfu/100?ml on August 21, 2006. The model system proved to be a valuable tool for spatial analysis and is suitable to support the development of bathing water profiles according to the EU Bathing Water Directive (2006/7/EC).     

Assessment of the aquatic biodiversity of a threatened coastal lagoon at Bimini, Bahamas

Coastal biodiversity is threatened worldwide by both direct and indirect anthropogenic activities. To more effectively manage and protect coastal biodiversity, accurate assessments of genetic, species, and ecosystem level diversity are required. We present the results from an assessment of the aquatic species diversity of a small (3?km²), shallow, mangrove-fringed Bahamian lagoon (the North Sound) subject to ongoing anthropogenic development. The assessment was conducted through a collation of field observations and data in published literature. We found that eight angiosperm species, 30 macroalgal species, and 370 animal species (including 95 fishes, 69 arthropods, 56 birds, and 45 mollusks) were documented within the lagoon. At least 11 of these species are of conservation concern, such as the critically endangered smalltooth sawfish (Pristis pectinata) and hawksbill turtle (Eretmochelys imbricata). Comparisons of community similarity indicated that the North Sound has a relatively distinct fauna and flora, but available data suggest that the species found there are most similar to those found in nearby habitats in Cuba. The lagoon forms a key nursery habitat for many species, including lemon sharks (Negaprion brevirostris), Caribbean spiny lobsters (Panulirus argus), and queen conch (Strombas gigas). Recently, the lagoon was included as part of a new marine protected area (MPA), but much of the habitat has already experienced considerable anthropogenic disturbance and the MPA boundaries have yet to be established. We have therefore analyzed the lagoon biodiversity and expect the data presented here to serve as a baseline for future comparisons.     

Retrospective analysis of spatial and temporal variability of chlorophyll-a in the Curonian Lagoon

The Curonian Lagoon, the largest in Europe (total surface area 1584?km²), is located in the southern part of the Baltic Sea, from which it is separated by a narrow sand bar and to which it is connected by the Klaipeda Straits. It is characterised by shallow eutrophic waters (mean depth 3.8?m) with average low salinity (<5??) due to the nutrient-rich freshwaters discharged by the river Nemunas. Cyanobacteria blooms, including species producing toxic metabolites, have been a frequent phenomenon in summer. In this study a series of MERIS Full Resolution (FR) satellite images acquired between 2004 and 2009 during summer periods were used to assess the temporal evolution and spatial variability of the lagoon water quality in terms of chlorophyll-a. The models/algorithms were calibrated/validated with field data collected in 2009, based on in situ radiometric (remote sensing reflectance -Rrs-) and limnological (chlorophyll-a concentrations -chl-a-) measurements. The chl-a concentrations were estimated by developing a semi-empirical band ratio (Rrs(708)/Rrs(664)) equation applied to MERIS images after correction for atmospheric effects with the 6S code. Results from this study suggest elevated spatial and temporal variability of chl-a. Spatial variability probably arises from the mosaic of situations within the Curonian lagoon in terms of bottom sediment features, nutrient availability in the water column, water depth and hydrodynamics. Temporal variability is probably linked to complex and interplaying metereological and environmental constraints such as the length of the ice cover period, average water temperatures, wind-induced sediment re-suspension, the pattern of precipitations and river-associated nutrient transport to the lagoon. This study stresses the importance of remote sensing as a valid tool for long-term whole ecosystem studies. The preliminary results need more through analyses and intersection with other environmental data in order to better comprehend algal bloom determinants in complex and extremely dynamic systems such as coastal lagoons.     

Trophic food web and ecosystem attributes of a water reservoir of the Ria Formosa (south Portugal)

Using a top-down modelling approach, a balanced trophic food web model of a water reservoir of the Ria Formosa lagoonal system was constructed. Few adjustments of input data were necessary to run the model since most of the parameters were estimated at the study site and the characteristics of the water reservoir allowed a high degree of control and precision in terms of sampling and data collection. Trophic levels of the 14 compartments included in the model varied between 1.0 for primary producers and detritus to 3.4 for carnivorous fish and the 14 groups were aggregated in a food chain with six trophic levels. The water reservoir has a detritus based food chain, with the majority of the biomass concentrated in the first two levels, the producers level and the herbivore/detritivore level (97.6%). The transfer efficiencies were low, and decreased with increasing level number, varying between 6.0 and 0.2%. The degree of “ecosystem maturity” was difficult to establish, but several parameters indicate that it could be high. The water reservoir studied, which has similar environmental and ecological characteristics as the Ria Formosa lagoon, is near its carrying capacity.     

Nitrogen and plankton dynamics in the lagoon of Venice

The nitrogen cycle in the lagoon of Venice, which is the largest Italian lagoon, was investigated by means of a 3D fully coupled transport – water quality model, which had been validated against a substantial amount of real-world data. Nitrogen fluxes among different ecosystem compartments were computed for each month of a reference year, and for each one of the three sub-basins into which the lagoon is conventionally subdivided. The computation included the loads of nitrogen discharged by the tributaries, the direct inputs from the industrial area and the city of Venice, the atmospheric loads, the fluxes at the three lagoon inlets and the internal fluxes between sediment and water compartments and among the three sub-basins. The results of the analysis show that the lagoon, as a whole, exports nitrogen towards the sea. Approximately 4000 tN/year are recycled by the system, while 4640 tN/year is the net input from the drainage basin and the other sources, thus leading to about 8640 tN/year of dissolved inorganic nitrogen that enter the water compartment. Around half of the this amount is used by primary producers, one fourth is exported towards the sea, and one fourth is transferred into the sediment compartment, or lost to atmosphere. These findings suggest that the exchanges through the inlets play an important role in keeping nitrogen concentration at an acceptable level. A more detailed analysis of the model results shows that the non-homogeneous spatial distribution of tributary discharges and point sources is the main cause of the differences in the ecosystem response and water quality among the three sub-basins. Nutrient poorer sub-basins fix a ration of available inorganic nutrient higher than nutrient rich ones. However, they are more efficient in transferring the biomass to the highest trophic levels. Results also include estimates of fluxes that were not quantified so far (such as grazing and recycling), and a validated model, which could have a practical use, for example for assessing implications of reduction of nutrient loads.     

A preliminary model of nutrient cycling in sediments of a Mediterranean lagoon

A model of nitrogen and phosphorus cycles in the sediment of a lagoon has been developed. This model was applied to the Thau lagoon (southern France). Sediment was sliced in three layers to reproduce the oxygen profile, which is simulated within the model. Following an equilibrium hypothesis, the model was calibrated against field data. State variables and fluxes were estimated in the sediment and across the sediment-water interface. A Monte Carlo sensitivity analysis was performed to determine the most sensitive parameters and sediment state variables. A dynamic simulation with varying oxygen concentrations then showed the influence of anoxia on the phosphorus and nitrogen fluxes between water and sediment.     

Modelling partitioning and distribution of micropollutants in the lagoon of Venice: a first step towards a comprehensive ecotoxicological model

The model presented in this paper integrates a large amount of recent and ad hoc collected data concerning environmental contamination from micropollutants in the lagoon of Venice. This model represents the first step in setting up of an ecotoxicological model for the Venice lagoon, to simulate fate of contaminants from abiotic matrices to organisms. Distribution and partitioning of organic and inorganic contaminants are modelled by a two-dimensional model, based both on deterministic and empirical submodels and adapted to a large spectrum of different substances (polychlorinated dibenzo-dioxins/polychlorinated dibenzo-furans (PCDD/F), polychlorinated biphenyls (PCBs), heavy metals). The model was successfully calibrated on a wide set of experimental data. Sensitivity analysis showed that the model is generally not very sensible to parameters values but it is sensible to external conditions (e.g., pollutants loads). Distribution of dissolved and total concentrations of contaminants was obtained for a series of PCDD/F and PCBs congeners and for eight heavy metals. These distributions represent integrated information on ecosystem health, complementary to monitoring data and they are useful to be used for comparisons with various water quality criteria. Simulation scenarios under different external conditions are proposed as examples of use of the model for management purposes.     

Use of Mytilus galloprovincialis and Tapes philippinarum as sentinel organisms for the development of a biosurveillance program in the Pialassa Baiona coastal lagoon (Ravenna, Italy)

The Pialassa Baiona is an intertidal lagoon located north from the town of Ravenna (Italy). It shows a certain degree of contamination caused by past uncontrolled discharges, and we aim at developing a bioassessment program to be used for future monitoring and conservation plans. A battery of six biomarkers (lysosome membrane stability, lipofuscin and neutral lipid accumulation, hsp70 expression, metallothionein levels and acetylcholinesterase (AChE) activity) was investigated in Mytilus galloprovincialis transplanted for 30 days in different sites. Tapes philippinarum are widely distributed within the lagoon, and we explored the possibility to use resident clams for future biosurveillance programs. Adenylyl cyclase (ACase) activity was also assessed in tissues of both bivalves as a future possible biomarker. Taken together, our results indicate that mussels are suitable sentinel organisms also within such a peculiar environment; alteration of four biomarkers was observed in tissues of mussels transplanted in two sites out of the five analyzed, indicating their low water quality. T. philippinarum showed a barely detectable AChE activity and absence of neutral lipids in digestive glands, therefore appeared unsuitable for our purpose, at least using the selected battery of biomarkers. ACase activity was not different among animals collected from the different sites.     

Resident mysids: community structure,abundance and small-scale distributions in a coral reef lagoon

Seasonal and diel variations in community structure and abundance of coral-reef lagoon mysids were examined at Davies Reef in the central region of the Great Barrier Reef (GBR) between June 1980 and May 1981. Twenty-five mysid species belonging to three subfamilies of the family Mysidae were captured during the study, with six new records for the GBR. The epibenthic mysid community differed from that in the overlying water, was faunistically uniform, but formed characteristic seasonal and diel groupings. The dominant epibenthic species were Erythrops sp., Anisomysis pelewensis, Doxomysis littoralis, A. laticauda, Prionomysis stenolepis, A. lamellicauda, and A. australis, five of which formed schools. Total mysid abundances ranged between 110 and 790 m^-3 with peak abundance in October. Schooling species occurred at local densities of up to 500 000 m^-3. Mysids were absent from shallow and midwater depths during the day, but were distributed throughout all depths at night with peak abundances in mid-water and deep layers. The dominant species in the water column at night were Pseudanchialina inermis, A. laticauda and Gastrosaccus indicus, in descending order of abundance. Lagoonal mysids contribute little to the food of sessile reef planktivores, as all but three species remain concentrated near or on the lagoon floor both day and night. The contribution of resident lagoon mysids to reef trophodynamics is probably through remineralization of lagoon detritus. Given the vast reef areas comprised of sandy lagoons, the large populations and relatively large size of lagoon mysids, this trophodynamic role may be of considerable importance.A.I.M.S. Contribution No. 477     

Faunal relationships among the near-reef zooplankton at three locations on heron reef,great barrier reef,and seasonal changes in this fauna

Samples of zooplankton were collected using a light trap at 5 sites in 3 locations on Heron Reef: (a) near the surface of open water 300 m south of the reef crest; (b) near the surface and at the substratum on the upper reef slope; (c) near the surface and at the substratum on a patch reef in the Heron lagoon. The collections made were analysed with respect to: (a) distribution and abundance of the taxa present; (b) faunistic relationships among samples from the 5 sites; (c) seasonal changes in both of these factors. A total of 181 taxa were recognised, many of which are identified to species, and many of which are demersal or epi-benthic in habits. At all sites, the abundance of animals increases from May to November, and faunal similarity between sites also changes. In May, reef collections are generally similar to one another and, with the exception of the slope surface collection, distinct from the open water collection. In September this pattern is enhanced, but in November slope collections more closely resemble the open water collection, while the lagoon collections are quite distinct from slope and open water collections. Lagoon surface and substratum collections also differ considerably from each other at this time. A MULTCLAS cluster analysis of the samples confirms the pattern of change in faunal relationships seen from examination of the collections. Dark-trap samples were used to assess the bias introduced by using a light to attract the animals, as well as to estimate the density of the fauna sampled. Lighttrap samples over-represent calanoid and harpacticoid copepods and gammarid amphipods, but the bias is minor and does not prevent use of a light trap as an efficient sampling tool for near-reef plankton. The density of the fauna is approximately 700 animals m^-3 at all sites. This may be a lower density than in more tropical regions. Pronounced seasonal changes occur in faunal composition of collections from open water and from surface sites. The substratum collections show more constant faunas throughout the year. Major changes are primarily in the proportions of copepods and cumaceans present. Changes in amphipod numbers are also important at lagoon sites.     

斑马鱼幼鱼运动行为测试评价饮用水安全

饮用水安全直接关乎人类的健康与安全,当前迫切需要全新的毒性测试方法对饮用水的潜在人类健康风险进行全面、准确和灵敏的评估和预警。本研究以反渗透技术(RO)取代常用的固相萃取,分别浓缩饮用水厂的进厂水、出厂水和管网水进行毒性试验水样的前处理。反渗透技术前处理方法可以避免传统固相萃取方法中使用的有机溶剂对行为学测试体系的干扰。RO浓缩后的饮用水对斑马鱼胚胎进行持续暴露,采用Viewpoint行为测试软件量化分析出生后第6天(6 dpf)斑马鱼幼鱼的运动行为,选择运动距离和转向行为作为测试终点,分析进厂水、出厂水及管网水的潜在毒性及可能变化。结果表明,暴露在进厂水的幼鱼出现了明显的行为变化,尤其在较高浓度(20倍浓缩)暴露时,运动距离相比对照组显著减少,同时伴有剧烈的转向等异常行为;管网水对斑马鱼幼鱼行为存在一定程度的影响,而出厂水对幼鱼的运动行为没有显著影响。研究结果反映出当前饮用水厂深度处理工艺可以有效降低进厂水的潜在毒性和健康风险,但是经供水管网输送后,其水质可能发生了改变,导致管网水可能存在潜在的毒性。本研究所采用的反渗透技术前处理技术及斑马鱼幼鱼的运动行为学测试方法,可用于未来建立评估饮用水水质安全的早期预警系统。     

Modelling seasonal dynamics of biomasses and nitrogen contents in a seagrass meadow (Zostera noltii Hornem.): application to the Thau lagoon (French Mediterranean coast)

Anumerical deterministic model for a seagrass ecosystem (Zostera noltii meadows) has been developed for the Thau lagoon. It involves both above- and belowground seagrass biomasses, nitrogen quotas and epiphytes. Driving variables are light intensity, wind speed, rain data and water temperature. This seagrass model has been coupled to another biological model in order to simulate the relative contributions of each primary producer to: (i) the total ecosystem production, (ii) the impact on inorganic nitrogen and (iii) the fluxes towards the detritus compartment. As a first step in the modelling of seagrass beds in the Thau lagoon, the model has a vertical structure based on four boxes (a water box on top of three sediment boxes) and the horizontal variability is neglected until now. This simple box structure is nevertheless representative for the shallow depth Z. noltii meadows, spread over large areas at the lagoon periphery.After calibration, simulation results have been compared with in situ measurements and have shown that the model is able to reproduce the general pattern of biomasses and nitrogen contents seasonal dynamics. Moreover, results show that, in such shallow ecosystems, seagrasses remain the most productive compartment when compared with epiphytes or phytoplankton productions, and that seagrasses, probably due to their ability in taking nutrients in the sediment, have a lower impact on nutrient concentration in the water column than the phytoplankton. Furthermore, in spite of active mechanisms of internal nitrogen redistribution and reclamation, the occurrence of a nitrogen limitation of the seagrass growth during summer, already mentioned in the literature, have also been pointed out by the model. Finally, simulations seems to point out that epiphytes and phytoplankton could compete for nitrogen in the water column, while a competition for light resources seems to be more likely between epiphytes and seagrasses.