The shrimp culture (shrimp farms) is one of the activities of aquaculture widely
employed in Brazilian estuaries and mangroves. The shrimps are fed with phosphate
enriched compounds. Thus, the effluent produced by farms can accelerate the
eutrophication process. An increase of shrimp farming has been seen in Coreaú River
Estuary, state of Ceará, but data about environmental quality are scarce to allow
monitoring of the region. The aim of the present research was to assess the contribution
of the shrimp farms on phosphorus input to the Coreaú River Estuary. The main forms
of phosphorus: bioavailable (P-Exch); bound to iron oxy-hydroxides (P-Fe), on the
biogenic, autigênica carbonates and apatite (P-CFAP), on the detrital apatite (P-FAP)
and organic phosphorus (P-Org) and as well as total organic carbon (%TOC) and
chlorophyll-a were determined in samples of surface sediments and cores from the
margins of the Coreaú River Estuary. The high concentrations of P-Total in surface
sediments indicated the need for monitoring studies. The larger fraction was P-Fe,
composing 30% of P-Total, approximately. These results indicate the ability of the iron
oxy-hydroxides to immobilize or release phosphorus. The contribution of the farm’s
effluents was evidenced by higher concentrations of P-Org in points adjacent to
discharge areas. In sediment cores, the highest P-Total concentrations were found
predominantly in fine sediments (silt and clay), with the P-Fe, P-CFAP and P-FAP
fractions being the main contributors. The sedimentation rates and concentration
increases of P-Total indicate the possible period of deforestation and starting or
maximum activity of shrimp farms in the end of the 1980 and mid 1990, respectively.
High phosphorus concentrations as well as %TOC and chlorophyll-a levels suggested a
significant anthropogenic contribution, associated with a high potential for
eutrophication.
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