The Itamaraca Estuarine Ecosystem, Brazil
79
therefore impeded Hg removal from the water column and facilitated its
distribution throughout the ltamaraca estuary. Mercury emission decreased considerably after the construction of a precipitation basin in
1986; nevertheless, leakage continued until1991 due to a technical failure.
Today, the distribution of Hg in oysters (0.27-2.21 ppm based on dry
mass), suspended matter (0.43-5.56 ppm), and sediments (0.04-6.2 ppm,
<62 Jlm fraction 0.3-20.5 ppm) in the Santa Cruz Channel is largely a function of proximity to the original source and channel hydrodynamics
(Meyer 1996; Meyer et al.1998). Since only 10% of the total released Hg has
remained in the system, it appears that reduced trapping by mangroves,
owing to acidic water conditions, resuspension and current-controlled
export via suspended matter, and transformation processes in intertidal
sediments contributed to removal processes.
Both sea grass and mangrove habitats, which are reproduction and feeding grounds for important fishery resources, have been reduced during the
last decades. Mangrove areas in Santa Cruz Channel (36.2km 2 in 1974,
28.1 km 2 in 1988) suffered the impact of real estate expansion (5.2km 2 in
197 4, 33.0 km 2 in 1988) compounded by increasing demands for freshwater
and waste disposal sites. Non-commercial fisheries constitute the major
local economic activity for about 5,000 fishermen in Itamaraca. Although
overall catch has increased from 200 tons (Macedo 1974) to 400 tons over
the last 20 years (Borner 1994), overfishing and destructive fishing
methods have led to declining fisheries stocks in the Santa Cruz Channel.
Owing to high demand for seafood by the growing tourist industry, shrimp
stock are most affected, but oysters, crabs, and blue crabs are also in high
demand and are fished throughout the year. Under these circumstances,
extensive and semi-intensive commercial aquaculture (i.e., mullet, shrimp,
mangrove oyster) would offer an economic alternative for local communities and should reduce the fishing pressure on natural stocks. The destruction of mangrove areas and the construction of seawalls and jetties to protect real estate developments (hotels and marinas) have altered the
geomorphology around Itamaraca Island. Whereas 10 years ago Coroa do
Aviiio near the Orange inlet (Fig. 5.1) was a small sandbank and only exposed during low tide, it is now a permanently exposed, vegetated island.
As a consequence, the inlet channel has been displaced northwards and the
southern shore of Itamaraca Island is being eroded.
Despite the protection offered by state and federal laws, mangrove areas
are still rapidly diminishing. However, part of the Itamaraca drainage basin
now includes a Reserve for the Biosphere of the Atlantic Forest and a large
area of the Itamaraca estuary is under state protection. Finally, the Brazilian
Institute for the Environment (IBAMA) maintains a center for the reproduction and management of endangered manatees on ltamaraca Island.
79
therefore impeded Hg removal from the water column and facilitated its
distribution throughout the ltamaraca estuary. Mercury emission decreased considerably after the construction of a precipitation basin in
1986; nevertheless, leakage continued until1991 due to a technical failure.
Today, the distribution of Hg in oysters (0.27-2.21 ppm based on dry
mass), suspended matter (0.43-5.56 ppm), and sediments (0.04-6.2 ppm,
<62 Jlm fraction 0.3-20.5 ppm) in the Santa Cruz Channel is largely a function of proximity to the original source and channel hydrodynamics
(Meyer 1996; Meyer et al.1998). Since only 10% of the total released Hg has
remained in the system, it appears that reduced trapping by mangroves,
owing to acidic water conditions, resuspension and current-controlled
export via suspended matter, and transformation processes in intertidal
sediments contributed to removal processes.
Both sea grass and mangrove habitats, which are reproduction and feeding grounds for important fishery resources, have been reduced during the
last decades. Mangrove areas in Santa Cruz Channel (36.2km 2 in 1974,
28.1 km 2 in 1988) suffered the impact of real estate expansion (5.2km 2 in
197 4, 33.0 km 2 in 1988) compounded by increasing demands for freshwater
and waste disposal sites. Non-commercial fisheries constitute the major
local economic activity for about 5,000 fishermen in Itamaraca. Although
overall catch has increased from 200 tons (Macedo 1974) to 400 tons over
the last 20 years (Borner 1994), overfishing and destructive fishing
methods have led to declining fisheries stocks in the Santa Cruz Channel.
Owing to high demand for seafood by the growing tourist industry, shrimp
stock are most affected, but oysters, crabs, and blue crabs are also in high
demand and are fished throughout the year. Under these circumstances,
extensive and semi-intensive commercial aquaculture (i.e., mullet, shrimp,
mangrove oyster) would offer an economic alternative for local communities and should reduce the fishing pressure on natural stocks. The destruction of mangrove areas and the construction of seawalls and jetties to protect real estate developments (hotels and marinas) have altered the
geomorphology around Itamaraca Island. Whereas 10 years ago Coroa do
Aviiio near the Orange inlet (Fig. 5.1) was a small sandbank and only exposed during low tide, it is now a permanently exposed, vegetated island.
As a consequence, the inlet channel has been displaced northwards and the
southern shore of Itamaraca Island is being eroded.
Despite the protection offered by state and federal laws, mangrove areas
are still rapidly diminishing. However, part of the Itamaraca drainage basin
now includes a Reserve for the Biosphere of the Atlantic Forest and a large
area of the Itamaraca estuary is under state protection. Finally, the Brazilian
Institute for the Environment (IBAMA) maintains a center for the reproduction and management of endangered manatees on ltamaraca Island.