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Water quality in
fee-fishing ponds located in the metropolitan region of São Paulo city,
Brazil: an analysis of the eutrophication process
MERCANTE, C.T.J.1;
CABIANCA, M.A.1; SILVA, D.1; COSTA, S.V.1
& ESTEVES, K.E.1
1
Instituto de Pesca/São Paulo, Av Francisco Matarazzo, 455 CEP 05010-000
e-mail:
cthais@pesca.sp.gov.br
ABSTRACT:
This
study intended to evaluate the eutrophication process of fee-fishing
ponds located in the Metropolitan region of São Paulo city. Samples from
30 of such fishing ponds were taken during the dry
(winter)
and rainy (summer) seasons in
order to measure the following variables: phosphorous, water
transparency and chlorophyll-a. The modified Carlson trophic
state index was applied to evaluate the “trophic status”. Considering
both seasons, the total phosphorous concentrations ranged from 0.03 to
0.35 mg/L, and were 10 times higher than the recommendated values of the
National Council of Environment (CONAMA, 1986). Reactive soluble phosphorus varied from
0.01 to 0.05 mg/L; chlorophyll-a from 0.001 to 0.43 mg/L and
water transparency from 0.10 to 0.80 m. The analysis of variance showed
that there were no significant differences between the two seasons for
the variables, suggesting that management strategies have more influence
on the system dynamics rather than seasonal variations. In general, the
high phosphorous load derived from ration distribution increased the
phytoplankton biomass, indicating an intense eutrophication process in
these sites. Concerning the Trophic State Index, the fee-fishing ponds
were classified as eutrophic or hyper-eutrophic environments. Nitrogen
and phosphorus intake control by means of the preliminary knowledge of
the quantity and quality of the introduced ration, bait intake, as well
as water flow are necessary for maintaining water quality. The control
of fish densities, especially the smaller ones may contribute to reduce
the internal phosphorus release. Finally, from the water quality point
of view, the fee-fishing ponds shall be seen through an approach
different from the pisciculture management practices. It means that this
activity deals neither with fish production nor with their reproduction,
thus invalidating some management practices, such as plankton production
increase and high protein content ration.
Key-words:
fee-fishing; eutrophication; Modified Trophic State Index; water
quality; freshwater. |
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