Gianmarco Giordani

Nutrient and iron limitation to Ulva blooms in a eutrophic coastal lagoon (Sacca di Goro, Italy)

Growth patterns and bloom formation of the green seaweed Ulva rigida were analysed in the eutrophic Sacca di Goro lagoon (Po River Delta, Italy). Variations of standing biomasses and elemental composition of Ulva were analysed through an annual cycle with respect to nitrogen, phosphorus and iron. Growth rates, nutrient and iron uptake and nitrate storage by macroalgal thalli were also assessed with field experiments during the formation of a spring bloom. The control of Ulva growth and the bloom formation depended on multiple factors, especially on nitrogen availability and iron deficiency. In the nitrate rich waters of the Sacca di Goro lagoon, nitrate accumulation in Ulva thalli was inversely related with Fe uptake, indicating an influence of Fe limitation on N acquisition. Since length and magnitude of nitrate luxury uptake are inversely related to the size of the intracellular nitrate pools, in nitrate rich waters the fast growing Ulva may face risk of N-limitation not only when exposed to low N concentrations or at high biomass levels, but also when exposed to pulsed dissolved nitrate concentrations at low iron availability. The potential Fe limitation could be affected by processes controlled by geochemical reactions and by macroalgal growth and decomposition. Both Fe oxidation during the active macroalgal growth and the formation of insoluble FeS and FeS2 during bloom collapse can result in a drastic decrease of soluble iron. Thus, a potential limitation of Fe to macroalgae can occur, determining positive feedbacks and potentially controlling the extent of bloom development and persistence.

Assessment of ecological quality of coastal lagoons with a combination of phytobenthic and water quality indices.

Coastal lagoons are ecotones between continents and the sea. Coastal lagoons of Western Greece, subjected to different human pressures, were classified into four different types based on their hydromorphological characteristics and monitored over a three year period for their biotic and abiotic features. Six ecological indices based on water quality parameters (TSI-Chl-a, TSI-TP, TRIX), benthic macrophytes (E-MaQI, EEI-c) and an integrated index TWQI, were applied to assess the ecological status of studied lagoons under real conditions. The trophic status ranged from oligotrophic to hypertrophic according to the index applied. The ecological quality of transitional water ecosystems can be better assessed by using indices based on benthic macrophytes as changes in abundance and diversity of sensitive and tolerant species are the first evidence of incoming eutrophication. The multi-parametric index TWQI can be considered appropriate for the ecological assessment of these ecosystems due to its robustness and the simple application procedure.

Short term changes of benthic fluxes during clam harvesting in a coastal lagoon (Sacca di Goro, Po River Delta)

In this paper the relationships between the Manila clam (Ruditapes philippinarum) fanning and benthic fluxes in the eutrophic Sacca di Goro lagoon (Po River Delta, Italy) are studied considering (1) the analysis of spatial patterns of sedimentary organic matter, acid volatile sulphide (AVS), chromium reducible sulphur (CRS) and labile amorphous iron in a grid of nine stations; (2) an assessment of the short-term oxygen consumption caused by sediment resuspension in oxygen-rich water; (3) a mesocosm experiment for evaluating the potential effects of sediment dredging on benthic fluxes of oxygen, soluble reactive phosphorus (SRP), ammonium, nitrate and dissolved reactive silica (DRSi). Our data suggest that in the farming area benthic fluxes of oxygen, ammonium and silica are driven mainly by clam respiration, whilst harvesting causes only transient modification of benthic fluxes. Therefore, we expect that clam metabolism is responsible for a persistent impact at the lagoon scale, whilst harvesting activities induce local and acute effects.

Trade-off between conservation and exploitation of the transitional water ecosystems of the northern Adriatic Sea

Transitional waters (TWs) provide ecosystem goods and services that are essential for the well-being of human populations. These unpredictable aquatic systems, characterised by large environmental fluctuations, are under severe stress due to human activities. Increasing pressures (e.g. over-harvesting, eutrophication, habitat loss) inevitably lead to the degradation of these ecosystems. Analysis of the complexity of species distribution patterns within and among TW habitats is relevant to understanding the underlying processes and promoting appropriate management strategies. Assessment of the trophic status is one of the most critical aspects of TWs. Untangling the relevance of anthropogenic nutrient inputs from internal biogeochemical processes is of primary importance in defining appropriate restoration strategies. Biotic indices have been suggested as an operational tool to assess environmental quality in TWs. However, the application in TWs of indices developed for coastal waters can give distorted results (e.g. low species diversity and high abundance are natural features). The BITS approach provides a rapid assessment of ecological quality, although its sensitivity in reflecting field conditions remains to be assessed. The major challenge to TWs management is to couple long-term conservation with productive activities. This goal can be achieved using an integrated approach, forecasting conservation of TW ecosystem functioning together with sustainable economic development. North-western Adriatic TW habitats have been exploited for centuries and major shifts in ecological processes have occurred. In this study, knowledge of the ecological features of these habitats is summarised and analysed using recent ecological tools. Based on these findings, possible strategies for conservative management have been discussed.

Integrated modelling in coastal lagoons: Sacca di Goro case study

A coupled 3D hydrodynamic-biogeochemical model was developed and implemented for the Sacca di Goro coastal lagoon. The model considers nutrient and oxygen dynamics in water column and sediments. Among the biological elements, phytoplankton, zooplankton, bacteria, Ulva sp. and commercial shellfish (Tapes philippinarum) were taken into consideration. Nutrients fluxes from the watershed and open sea, as well as atmospheric inputs, heat flux, light intensity and wind shear stress at the water surface constituted the model forcing functions. The comparison of numerical results with available measurement data indicated that the model was able to capture the essential dynamics of the lagoon. This model has also been used to estimate clam productivity and its impacts on water quality and lagoon properties.

A bioaccumulation model for herbicides in Ulva rigida and Tapes philippinarum in Sacca di Goro lagoon (Northern Adriatic)

A bioaccumulation model to predict concentrations of s-triazine herbicides in the macroalgae Ulva rigida and in clams Tapes philippinarum has been implemented, calibrated and validated. The model uses input data from a 3D biogeochemical model that provides biomasses in the different compartments, i.e. phytoplankton, zooplankton and bacteria; and from a 3D fate model that provides the herbicides concentrations in the water column as well as in the sediments. Simulated data were compared with experimental data collected during a set of sampling campaigns carried out in 2004 and 2005 in the Sacca di Goro lagoon (Northern Adriatic). The model predicts correctly the concentrations of herbicides measured in Ulva rigida and reproduces with good agreement the values of concentration of herbicides found in clams. Furthermore, the simulated spatial and temporal dynamics in the biota compartment, following those of the water and sediments, are also in agreement with the experimental data. This integrated approach combining biogeochemical, fate and bioaccumulation models provide an overall assessment of the importance of the different environmental compartments and it can also support the testing of different management strategies to improve ecosystem state and functioning. Further research is necessary to elucidate the role and importance of the metabolism of these compounds by clams.

A Decision Support System for the Management of the Sacca di Goro (Italy)

This chapter addresses some results concerning the development of a Decision Support System (DSS) for the management of Southern European lagoons, and is particularly focused on the application of the proposed DSS to the management of clam farming in the Sacca di Goro lagoon (Italy). After having established a reference framework for the study and management of coastal lagoons, a general model-based decision support structure is introduced. The development of this tool, obtained within the EU project DITTY, was motivated by the need for a common and flexible framework to ease the integration of the outputs of different models and analyses, as well as to deal with the diversity of socio-economic and environmental characteristics of several application sites. The proposed structure helps integrate and manage in a clear and structured fashion the information provided by different kinds of mathematical and analytical models of a lagoon ecosystem, such as biogeochemical, hydrodynamic, ecological and socio-economic models. Data and information obtained from the models can be used to accomplish the decision task by application of multicriteria analysis. Finally, robustness of the decision with respect to external factors beyond the control of the decision maker is considered in the proposed DSS.

Ecosystem Alteration and Pollution in Southern European Coastal Lagoons

The Conference on “Southern European Coastal Lagoons: The Influence of River Basin– Coastal Zone interactions” was held in Ferrara, 10–12, November 2003. The conference aimed at debating on Southern European coastal lagoons as important ecosystems which are of considerable ecological and economical value, and are under great anthropogenic pressure. The conference themes were the Water Framework Directive and the integrated river basin and coastal zone management; structure, functions, natural value, and ecosystem alterations of Southern European coastal lagoons; modelling of watershed-coastal lagoons interactions; socio-economic implications with emphasis on aquaculture; the use of indicators for assessing ecosystem trends and health. This special issue, which composes of eight papers, is dedicated to studies of water and sediment pollution. Spatial dependent and time-lagged processes of contamination by heavy metals and persistent organic pollutants are analysed in sediments and benthic macrofauna. Sediment contamination and ecosystem quality are then analysed with bioindicator tools and integrated biomonitoring techniques. Attention is also paid to geomorphologial alterations, nutrient loadings, and eutrophication processes.