SACCA DI GORO  - ITALY

P. Viaroli¹, G. Giordani¹, J.M. Zaldívar², E. A. Fano³, G. Castaldelli³ S. Bencivelli^4
1Department of Environmental Sciences, University of Parma, Italy
²European Commission, Joint Research Centre, Environment Institute, Ispra (VA), Italy
³Department of Biology, University of Ferrara, Italy.
⁴Servizio Ambiente, Provincia di Ferrara, Italy

Sacca di Goro (Italy). This lagoon is an important environmental as well as economical area. Fish and shellfish production provides work, directly or indirectly, for five thousand people. The economical annual revenue has been oscillating during the last few years around 10 MEuro. Due to the larger supply of nutrients, organic matter and sediments, which arrive from the fresh water agricultural catchment, the limited water circulation characterised by little water exchange with the sea, and the intensive shellfish production; water quality is a major problem. Indeed from 1987 the Sacca di Goro experienced an abnormal proliferation of macroalgae (Ulva rigida). The oxygen depletion and anoxic crises.

Figure 1: Sacca di Goro on the Adriatic coast

The lagoon of Sacca di Goro is located in the southern part of the Po River delta in the province of Ferrara. The Sacca di Goro lagoon is approximately triangular in shape with a surface area of 26 Km², an average depth of 1.5 m, and it is connected to the sea by a mouth about 1.5 Km wide. The watershed, Burana-Volano, is a lowland, flat basin, which is in some parts below the sea level. The watershed on the northern and eastern side is bordered by a branch of the Po river entering the Adriatic sea, and it covers an area of about 3000 Km². About 80 % of the watershed is dedicated to agriculture.

Figure 2: Sacca di Goro

The lagoon is surrounded by embankments. The main freshwater inputs are the Po di Volano River (approximately 350^.10⁶ m³ yr^-1), the Canal Bianco and Giralda, which have approximately the same discharge rates (20-55 ^x 10⁶ m³ yr^-1). Freshwater inlets are also located along the Po di Goro River and are regulated by sluices. There are no direct estimates of the freshwater input from the Po di Goro, which is usually assumed to be equivalent to that of the Po di Volano. The freshwater system is mostly located in a subsident area and is regulated by a system of pumping stations (scooping plants). The fresh water or hydraulic residence time oscillates monthly between 2.5 and 122 days with a mean value of 24.5 days, whereas the water exchange time ranges from 2 to 4 days.

Figure 3: Satellite image of land-use around the Sacca di Goro

The tidal amplitude is approximately 80 cm. The bottom of the lagoon is flat and the sediment is alluvial mud with high clay and silt content in the northern and central zones. Sand is more abundant near the southern shoreline, whilst sandy mud occurs in the eastern area.

The climate of the region is Mediterranean with some continental influence (wet Mediterranean). Precipitation is approximately 600 mm yr^-1, with late spring and autumn peaks. However, this pattern is undergoing significant changes with an increase of short-term intense events.

Figure 4: Map of the sacca di Goro lagoon with the farming areas indicated

The catchment is heavily exploited for agriculture, whilst the lagoon is one of the most important aquacultural systems in Italy.  About 10 km² of the aquatic surface are exploited for farming of the Manila clam (Tapes philippinarum), with an annual production of about 15000 tons. The annual revenue has been oscillating during the last few years around 50 million Euros.

TIn the last decade the N loading has been persistently high, about 2000 t yr^-1, whilst the P loading has decreased from ca 200 to ca 60 t yr^-1. The lagoon is subjected to anthropogenic eutrophication, which causes extensive growth of seaweeds, especially the chlorophyceans (Ulva sp. and Cladophora sp.) in the sheltered eastern area and phytoplankton in the deeper central zone. Macroalgal growth is responsible for summer anoxia and dystrophy (Fig. 2), which usually take place in the eastern area. Recent studies have also demonstrated that the clam stock can contribute to the oxygen depletion and internal loading.

Figure 5: The Sacca di Goro lagoon during a dystrophic crises in which water assume the typical white colour ( in the background)

Due to its characteristics and its economic importance, the Sacca di Goro has been the object of a continuous study and, hence, long-term data is available. However, a biogeochemical model able to capture the essential dynamics of the lagoon, correlate the different compartments (clams, macroalgae, bacteria, etc.) as well as predict its future behaviour was missing.