scaricabile in rete - Enea

The lake is kept vertically well mixed by winds throughout the whole year. On the contrary,
well defined thermoclines develop in summer in the sandpit ponds, where water attains a
depth up to 25 m. Some ponds are occasionally reached by seawater and therefore develop a
permanent stratification.
Starting from the 18 th century, most of the plain between the sea and the Apuan Alps was
reclaimed and used for intensive farming. Part of the plain lies below sea level (–1 to –3 m),
and five pumping stations provide to remove the drainage water and pour it into the lake.
Sand deposits and dunes occupy the coastal belt, while more to east the cover consists mainly
of peat deposits up to several metres thick.
As a consequence of collecting the irrigation drains, eutrophication is increasing in the lake,
in spite of the natural conditions preserved in the surrounding marsh – a sanctuary for aquatic
birds. It is therefore necessary to investigate the lake balance and the organic carbon cycle in
order to evaluate the anthropogenic impact and modifications of the natural conditions, as
mandatory for setting up adequate plans to protect the lake and its environment. These are the
main objectives of a series of investigations based on hydrochemical and isotopic tracers,
which have been undertaken at the Institute of Geosciences and Georesources in collaboration
with the universities of Venice and Paris- Sud. The isotopic ratios measured include 2 H/ 1 H,
18 O/ 16 O, 13 C/ 12 C, 11 B/ 10 B, and 34 S/ 32 S. The preliminary results are reported in this paper. Last
but least, the problems described here are common to many wetlands, for which our
investigations can be of interest.
2. Field measurement and sampling
Lake water was sampled at seven stations. All the major inflowing streams were also
sampled. The samplings were performed in July-August 2004, February-March 2005, May
2005 and November 2006. A sandpit, named Incrociata, was sampled at different depths in
May 2005. The field measurements included temperature, pH, salinity, dissolved oxygen,
depth –using an automatic multi-parametric probe (Idronaut Ocean Seven, Milan, Italy) and
alkalinity. Chemical and isotopic analyses were performed in the laboratory with the usual
techniques. The results are reported in Table 1.
3. Results and discussion
3.1 Lake water balance
The water balance of Lake Massaciuccoli is quite complex. The inflow is provided by
precipitation over the lake, drainage water from the adjacent marsh and the pumping stations,
and possibly some seawater through the Burlamacca channel (mainly in summer). It is
possible, however, that most of seawater is stored in the sandpit ponds, where it sinks because
of its higher density and push out fresh water floating on the surface which eventually reaches
the lake. This effect is evident in one of the major ponds, called Incrociata.
The outflow is given by evaporation from the lake (including plant transpiration from reeds,
whose presence, however, is limited), and the water discharged into the sea through the
Burlamacca channel (mainly in winter). Furthermore, water exchanges with groundwater can
provide some additional inflow and outflow, which however are practically impossible to
estimate.
The chloride concentration of lake water, ranging from 730 mg L –1 in winter (i.e. after the
major rain period) to above 1220 mg L –1 in autumn (after the major evaporation period, with
lake surface at –0.20 m asl), confirms that seawater does not reach the lake in significant
amount.
36