Environmental quality of transitional waters: The lagoon of Venice case study

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Abstract

The health status of European aquatic environments, including transitional waters such as coastal lagoons, is regulated by the Water Framework Directive (WFD), which requires the classification of the water bodies' environmental quality and the achievement of a good ecological status by 2015. In the Venice lagoon, a transitional water body located in the northeastern part of Italy, the achievement of a good ecological status is hampered by several anthropogenic and natural pressures, such as sediment and water chemical contamination, and sediment erosion. In order to evaluate the lagoon's environmental quality according to the WFD (i.e. 5 quality classes, from High to Bad), an integrated Weight-of-Evidence methodology was developed and applied to classify the quality of the lagoon water bodies, integrating biological, physico-chemical, chemical, ecotoxicological, and hydromorphological data (i.e. Lines of Evidence, LOE). The quality assessment was carried out in two lagoon habitat typologies (previously defined on the basis of morphological, sediment, and hydrodynamic characteristics) which were selected taking into account the ecological gradient from sea to land, and the differences in anthropogenic pressure and contamination levels. The LOE classification was carried out by using indicators scored by comparing site specific conditions to reference conditions measured in lagoon reference sites, or provided by local, national or European regulations (e.g. Environmental Quality Standards, EQS, for chemicals). Finally, the overall quality status for each water body was calculated by a probabilistic approach, i.e. by reporting the final result as the frequency distribution of quality classes. The developed procedure was applied by using data and information concerning selected LOE and collected from monitoring programs and research studies carried out in the last 15 years in the lagoon of Venice. A set of sampling stations characterized by spatially and temporally coherent information for each LOE was selected, and among these stations, potential reference sites for each water body typology were identified. The quality assessment highlighted that there are specific lagoon areas, especially those located near the industrially developed area, which are highly affected by anthropogenic activities, and that chemical contamination is one of the main pressures affecting ecological status (e.g. macro-benthonic biodiversity) in the Venice lagoon. The integrated quality assessment procedure that was developed provided a new tool supporting decision making, as well as lagoon assessment and management.

Introduction

The European Water Framework Directive 2000/60/CE (WFD; European Community, 2000) established a framework for protecting and improving ecological status of European surface waters. The WFD gives emphasis to the site-specific evaluation of ecological effects (Vighi et al., 2006), assessing how the structure of the biological communities and the overall ecosystem functioning are altered by multiple anthropogenic stressors (Heiskanen et al., 2004). Therefore, biology as main quality element is supported by hydromorphological and chemical/physico-chemical quality parameters, within the water quality classification process. The overall classification procedure is based on the “one-out, all-out” conservative principle and follows an appropriate flow chart as recommended by the CIS ECOSTAT working group (European Community, 2005).

Quality elements to be considered are selected on the basis of surface waters classification (e.g. river, lake and coastal). Coastal lagoons can be classified either as transitional waters or coastal waters depending on the substantial, or not significant, influence of freshwater flow (European Community, 2003a). However, coastal lagoons were suggested to be included in a specific category of the transitional water domain, taking into consideration lagoons peculiar characteristics, such as the tidal range, coastal morphology, and climate conditions (Tagliapietra and Volpi Ghirardini, 2006). Therefore, to address WFD principles (i.e. ratio-to-reference), homogeneous habitat typologies (and water bodies) within the lagoon have to be identified (Tagliapietra and Volpi Ghirardini, 2006).

To evaluate surface waters (i.e. rivers, lakes, coastal and transitional waters) environmental quality, different indicators and indices (Solimini et al., 2006) are currently applied. The indices which were already developed and applied are mainly focused on the assessment of aquatic biological communities (e.g. Biological Monitoring Working Party for macroinvertebrates; Armitage et al., 1983). Other indices analyze water bodies' physicochemical conditions (e.g. Trophic Status Index; Carlson, 1979) and habitat characteristics (e.g. River Habitat Survey; Raven et al., 1997).

As far as transitional waters are concerned, the WFD requires the monitoring of macroinvertebrates, fish, phytoplankton, macroalgae and angiosperms communities. Benthic invertebrates respond rapidly to anthropogenic and natural stress (Munari & Ministri, 2008, Rosenberg et al., 2004, Ruellet & Dauvin, 2007, Borja et al., 2007), while the macroalgae assemblages (e.g. Ecological Evaluation Index; Orfanidis et al. 2001) have a relatively long life span and are sessile or quite sedentary organisms (Sfriso et al., 2007).

Since the enforcement of the WFD, research efforts have included the development of assessment methods to evaluate and classify the water body ecological status integrating different quality elements. The integration of heterogeneous information, often synthesized into indices, is generally achieved by using the Ecological Risk Assessment (ERA) procedure (US EPA, 1998) based on a Weight of Evidence (WOE) approach (Burton et al., 2002, Smith et al., 2002, Chapman, 2009). WOE allows to integrate multiple lines of evidence (LOE) to estimate the impact of stressors on the environment: the overall risk is higher if more evidences indicate a larger impact.

In this paper, a WOE methodology integrating WFD tools and approaches to assess the quality of the lagoon water bodies was developed, taking into account different LOE: i.e. Biology, Chemistry, Physico-chemistry, Hydromorphology and Ecotoxicology. The methodology was applied to the lagoon of Venice, a coastal lagoon which was classified as transitional water (Tagliapietra and Volpi Ghirardini, 2006). The environmental quality was estimated for the water bodies of two selected habitat typologies, by evaluating and integrating data collected at different sampling sites. In the next sections, a description of the case study, the environmental database, the integrated quality assessment methodology and the obtained results are presented.

Section snippets

Materials and methods

In order to estimate the environmental quality in the lagoon of Venice, a WOE methodology was developed on the basis of the environmental risk assessment paradigm and the WFD requirements for transitional waters. To support the application of the WOE methodology, available monitoring and literature environmental data were used.

Results and discussion

For each assessment step, from category evaluation at sampling site scale to LOE aggregation at water body scale, presented in the Methods section, the results obtained were showed both as tables and as GIS maps, as discussed in the next paragraphs.

Conclusions

The environmental quality integrated assessment methodology developed and applied to the lagoon of Venice is a first step towards a full implementation of the Water Framework Directive. The results obtained in this paper by integrating different types of information confirm previous ecological risk assessment outcomes for benthic community, thus linking the sediment contamination to the observed ecological status and environmental quality. Moreover, the probabilistic approach supports an

Acknowledgments

This work was funded by the CORILA consortium. Part of the experimental data was provided by the Venice Water Authority. Jonathan Rizzi provided technical support for the environmental data collection, as well as for data elaboration and representation in GIS.

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