334
V. Bombelli and M. Lenzi
From the 1980s to the 1990s, the annual number of tourists has doubled
from 0.5 to 1 million. According to Cossu and coworkers (1992), such
data allow the evalutation of the human, in particular, tourist contribution to the lagoon's eutrophication, which was estimated as 54 t year- I
nitrogen and 11 t year - I phosphorus for the residents, 65 t year - I nitrogen and 13 t year - I phosphorus for the tourists, respectively (Bombelli
et al. 1993).
With regard to other economic activities, only intensive aquaculture
has undergone significant development. According to the Local Sanitary
Agency and ENEA Agency, the contribution from these activities to the
lagoon's eutrophication is about 37 t year- I nitrogen and 1.2 t year- I
phosphorus, respectively (Lenzi 1992). Total contribution of nutrients to
the lagoon's budget as a result of human activities has been estimated as
68 g m - 2 year -I nitrogen and 1 gm - 2 year -] phosphorus, respectively.
14.2.3 Benthic Vegetation
Behveen 1976 and the present, a large reduction of eelgrass beds has
been observed, while some seaweed species, typical of this ecosystem in
the past (Valonia aegagropila, Lamprothamnion papulosum) have disappeared (Cognetti et al. 1978; Lenzi and Angelini 1985; Naviglio et al.
1988; Lenzi unpubl. data 1988). Other species (Gracilaria verrucosa,
Chaetomorpha linum, Cladophora vagabunda) are now dominating in
turn. In the last 4 - 5 years, the occurrence of these seaweeds has become
totally unpredictable, both in quantity and quality.
14.2.4 Seasonal Environmental Events
The development of seaweeds and microphytes are the dominant events
for the Orbetello Lagoon. Macroalgal growth occurs between winter and
spring. In the latter part of spring, the biomass decays and piles up on
the bottom. After the decomposition of the seaweed masses and further
remineralization in the spring/summer period, the lagoon becomes subject to frequent distinct blooms of microphytes (Lenzi and Angelini
1985). Despite an sample supply of nutrients from the decaying seaweeds, the availability of additional nutrients from domestic wastes during the tourist season is important for many micro algae, including Dinophycea.
Decomposition of the seaweed masses in the summer heat, and the
subsequent sulphate reduction processes (Izzo 1988; Lenzi 1988) cause a
drastic decrease of dissolved oxygen and development of toxic reducing
V. Bombelli and M. Lenzi
From the 1980s to the 1990s, the annual number of tourists has doubled
from 0.5 to 1 million. According to Cossu and coworkers (1992), such
data allow the evalutation of the human, in particular, tourist contribution to the lagoon's eutrophication, which was estimated as 54 t year- I
nitrogen and 11 t year - I phosphorus for the residents, 65 t year - I nitrogen and 13 t year - I phosphorus for the tourists, respectively (Bombelli
et al. 1993).
With regard to other economic activities, only intensive aquaculture
has undergone significant development. According to the Local Sanitary
Agency and ENEA Agency, the contribution from these activities to the
lagoon's eutrophication is about 37 t year- I nitrogen and 1.2 t year- I
phosphorus, respectively (Lenzi 1992). Total contribution of nutrients to
the lagoon's budget as a result of human activities has been estimated as
68 g m - 2 year -I nitrogen and 1 gm - 2 year -] phosphorus, respectively.
14.2.3 Benthic Vegetation
Behveen 1976 and the present, a large reduction of eelgrass beds has
been observed, while some seaweed species, typical of this ecosystem in
the past (Valonia aegagropila, Lamprothamnion papulosum) have disappeared (Cognetti et al. 1978; Lenzi and Angelini 1985; Naviglio et al.
1988; Lenzi unpubl. data 1988). Other species (Gracilaria verrucosa,
Chaetomorpha linum, Cladophora vagabunda) are now dominating in
turn. In the last 4 - 5 years, the occurrence of these seaweeds has become
totally unpredictable, both in quantity and quality.
14.2.4 Seasonal Environmental Events
The development of seaweeds and microphytes are the dominant events
for the Orbetello Lagoon. Macroalgal growth occurs between winter and
spring. In the latter part of spring, the biomass decays and piles up on
the bottom. After the decomposition of the seaweed masses and further
remineralization in the spring/summer period, the lagoon becomes subject to frequent distinct blooms of microphytes (Lenzi and Angelini
1985). Despite an sample supply of nutrients from the decaying seaweeds, the availability of additional nutrients from domestic wastes during the tourist season is important for many micro algae, including Dinophycea.
Decomposition of the seaweed masses in the summer heat, and the
subsequent sulphate reduction processes (Izzo 1988; Lenzi 1988) cause a
drastic decrease of dissolved oxygen and development of toxic reducing