Co-Supervisor: Alberto Barausse Co-Supervisor: Daniele Brigolin
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UNIVERSITY OF PADUA DEPARTMENT OF INDUSTRIAL ENGINEERING Second Cycle Degree Environmental Engineering Thesis work SEASONAL AND SPATIAL FOOD WEB ANALYSIS IN THE LAGOON OF VENICE USING LINEAR INVERSE MODELLING Supervisor: Luca Palmeri Co-Supervisor: Alberto Barausse Co-Supervisor: Daniele Brigolin Student: VERONICA ZANATTA ACADEMIC YEAR 2013 – 2014 II If you enter this world knowing you are loved and you leave this world knowing the same, then everything that happens in between can be dealt with. Michael Jackson III IV ABSTRACT As a matter of fact anthropogenic pressures on ecosystems are increased in several parts of the world and a preservation and conservation of their natural status are issues of concern. A description of the interactions between the compartments of a trophic network is fundamental in order to obtain a general picture of the state of the ecosystem. The trophic network modelling approach is a useful tool to study the ecosystem state because it collects a large amount of ecological and biological information. This way the food web model describes the relationships among the components of the system. Moreover mass balance models allow to look at the ecosystem through a steady state condition which is a snapshot image of the behaviour of the system in the period under study. For these reasons the first goal of this study is to quantify the flow network of carbon in different food webs models in the Lagoon of Venice using the Linear Inverse Modelling (LIM) approach. LIM ensures that the quantified trophic network satisfies the basic biological constraints and that the experimentally observed composition of the food web is conserved as much as possible. As for the area investigated is the Venice Lagoon which is situated along the coast of the North-Western Adriatic sea. The northern part of Lagoon is the least influenced by external negative human effects, although it is also affected by several pressures (e.g. erosion). On the contrary, the central part of Lagoon is the most influenced by anthropogenic impact due to the very close industrial area of Marghera near Mestre. In particular, this approach is applied in three different parts of the Venice Lagoon, Palude della Rosa, Fusina, Sacca Sessola and in three different periods of the year: winter, spring and summer. Then, the second aim of this study is the seasonal and spatial analysis of the food web models obtained by the LIM approach, using ecological network analysis which permits to calculate the key indicators of ecosystem status. The results show that the Venice Lagoon is not a single, large ecosystem, but it is composed by markedly different, interconnected ecosystems. Palude della Rosa is a sort of control site due to its sheltered position and network analysis confirm its good ecological performance. Fusina is again situated in a confined area (a protected area far from sea influences) for this reason it has the same trend of growth and development over seasons as Palude della Rosa, that is, it is characterized by low activity in winter and boom activity in summer season. Different impacts are disturbing the two sites and this explains the difference of the boom intensity in spring and in summer for Fusina. In summer, Sacca Sessola has a different behaviour due to the influence of sea water, instead in winter it shows the same trend as in the rest of the Lagoon. Finally, Fusina suffers of high import of nutrients and V pollutants, and of hot water inflow arriving from the cooling water of electrical generation power plant. However these imports guarantee a quick resilience in the case of external perturbation in Fusina with respect to the rest of Lagoon. In general, this study demonstrates the importance of carefully constructed food web models, whose analysis can yield key ecological insights into the functioning of transitional ecosystem, such as the Lagoon of Venice. VI INDEX INTRODUCTION .................................................................................................................................. 9 AIM OF THE STUDY .................................................................................................................................... 9 WHAT ARE ECOSYSTEMS? ......................................................................................................................... 11 Holistic and phenomenological approaches ................................................................................. 11 LINEAR INVERSE MODELLING .................................................................................................................... 14 Estimation of trophic network flows ............................................................................................. 14 MATERIALS AND METHODS ............................................................................................................. 17 THE LAGOON OF VENICE, AN ECOSYSTEM OF GREAT ECOLOGICAL AND CULTURAL VALUE ........................................ 17 Environmental conservation of the lagoon of Venice ................................................................... 18 Temperature and Tide excursion .................................................................................................. 19 Bathymetry ................................................................................................................................... 19 Chemical and physical parameters ............................................................................................... 20 Primary producers in the lagoon ................................................................................................... 21 Nekton, Benthos and Zooplankton in the Venice Lagoon ............................................................. 21 Fishing activity .............................................................................................................................. 22 Negative human impacts on the Venice lagoon ........................................................................... 23 STUDY AREAS DESCRIPTION ....................................................................................................................... 24 Description and location of the study areas.................................................................................. 24 DATA SOURCE ........................................................................................................................................ 27 MODELLING APPROACH ........................................................................................................................... 28 Mass balance – undetermined problem ....................................................................................... 29 Diet composition, Biomass ............................................................................................................ 30 Metabolic parameters .................................................................................................................. 31 Description of the compartments ................................................................................................. 33 Structure of LIM INPUT file............................................................................................................ 38 NETWORK AND MODEL BALANCING ............................................................................................................ 43 Biomass ranges ............................................................................................................................. 43 Diet composition. .......................................................................................................................... 46 ECOLOGICAL NETWORK ANALYSIS ............................................................................................................... 48 Flows indices ................................................................................................................................. 49 Whole system status indices: ........................................................................................................ 49 Indirect effect: Mixed trophic impact and total dependency matrixes ......................................... 52 Cycle analysis ................................................................................................................................ 54 Trophic structure ........................................................................................................................... 55 RESULTS ........................................................................................................................................... 57 DIET AND FLOW ..................................................................................................................................... 57 Fusina ............................................................................................................................................ 58 Palude della Rosa .......................................................................................................................... 59 TROPHIC LEVEL AND LINDEMAN SPINE ......................................................................................................... 70 Seasonal trend of Trophic Levels ................................................................................................... 70 Lindeman spine line: ....................................................................................................................