Phytoplankton composition and trophic
status assessment
Over the four studied years, the
trophic status assessment of the reservoir
has been performed following different
methods. The significant correlation
between phytoplankton biomass
and Chl-a suggests that these two metrics
could be appropriate to assess the
trophic status of the NT2 Reservoir.
Both Chl-a and biomass generally experienced
medium values, corresponding
with an oligo-mesotrophic status. Highest
values have been observed during
the WD season. Similar tendency has
been observed for physico-chemical
features which classified the trophic
status of the NT2 Reservoir as oligomesotrophic
(Tab. VII).
The Secchi values indicate a trophic
status higher than the classical Chl-a/
biomass based qualification. Its ranges
of values remained shallow, corresponding
to a meso-eutrophic status.
Nevertheless, the total phytoplankton
biomass has also a significant correlation
with the Secchi depth suggesting
that the water transparency might be
dictated by phytoplankton biomass as
Secchi values significantly respond to
the biomass. The higher phytoplankton
biomass might lead to a contraction of
the euphotic zone at the WD season
(Naselli Flores & Barone, 1998). However,
no clear relationship between
Secchi depth, Chlorophyll a or TP and
trophic status could explain such low
water transparency. This study confirms
the results of Brazilian studies
which revealed that many of the trophic
status classification developed for temperate
areas could not be applied to the
tropics (Huszar et al., 1998).