Bastiaan Knoppers . Bjorn Kjerfve
included in this review, using the method of Kjerfve et al. (1996). The concept of the
flushing half-life or the time that it takes to replace half of the lagoon water volume is
a robust measure of water renewal, and serves as a good comparative indicator of the
hydrodynamic flushing lagoons for trophic state analysis (Knoppers et al. 1991). The
hydrological data and results are summarized in Table 3.2.
All the Brazilian lagoons exhibit a positive annual hydrological balance (Knoppers
et al. 1991; Miyao et al. 1986) with the exception of the permanently hypersaline
Araruama L. Araruama L. is hypersaline as a result of a semi-arid climate with high
evaporation and low rainfall rates and an extremely small fresh water input in relation to the lagoon water volume (Kjerfve et al. 1996). The mean flushing half-lives of
the lagoons vary from 1-84 days. The shortest flushing half-life occurred in the tidally
dominated Itaipu L. (1 day) and the Patos L. Estuary (3 days). The external cells of the
choked systems with long tidal channels exhibited flushing half-lives of 5-7 d<:J.Ys, while
the interior lagoon cells located furthest from the sea without significant tidal exchange
had flushing half lives of 15-28 days. The longest flushing half-lives were computed
for Araruama L.(84 days) and the Patos L. proper (82 days).
3.9
Nutrient Standing Stock and Particulate Organic Matter
The majority of choked and restricted coastal lagoons in Brazil and other tropical and
sub-tropical regions with humid climates are rich in organic materials. Some are entirely detritus-based during some stage of the annual cycle (Nixon 1982; Nichols 1989).
The majority are also marked by seasonal changes in their standing stock of biogenic
matter and autotrophic biomass (Nixon 1982; Knoppers 1994). However, extreme seasonal variability, as encountered in the coastal lagoons of the west coast of Mexico
(Flores-Verdugo 1985; Flores-Verdugo et al. 1988), western Australia, and the Mediterranean, is not encountered in the coastal lagoons of Brazil (Mee 1978; Nixon 1982; Vaulot
and Frisoni 1986; Y
the coastal lagoons of Brazil is limited to distributions of dissolved inorganic nitrogen (DIN) and phosphorus (DIP), a phytoplankton biomass indicator (chlorophyll a),
particulate organic carbon (POC), and total suspended solids. Some information has
also been published on annual cycles of dissolved organic carbon (DOC), dissolved
organic nitrogen (DON), and dissolved organic phosphorous (DOP) for Urussanga L.,
Fora L., Barra L., Cananeia-Iguape L., and the estuary of Patos L. (Mesquita and Peres
1985; Carmouze et al. 1991; 1993; Abreu et al. 1994a,b). The mean annual concentrations
and ranges of values for some nutrient parameters for the eight lagoon systems included in this comparison are summarized in Table 3.3.
The standing stock of particulates generally attains peak concentrations in the late
austral summer and early fall, reflecting a trend towards a unimodal seasonal pattern
in the development of autotrophic biomass, i.e., chlorophyll a (Fig. 3.9). This is true
for all the lagoons of this study with the exception of the Patos L. Estuary. In most of
the lagoons, the highest fraction of suspended detrital organic matter is encountered
during the less productive period during late fall and winter. Most of the suspended
detritus originates from autotrophic production, as indicated by the relatively low
particulate organic carbon to nitrogen ratios, with C: N by weight less than 9 : 1, and
included in this review, using the method of Kjerfve et al. (1996). The concept of the
flushing half-life or the time that it takes to replace half of the lagoon water volume is
a robust measure of water renewal, and serves as a good comparative indicator of the
hydrodynamic flushing lagoons for trophic state analysis (Knoppers et al. 1991). The
hydrological data and results are summarized in Table 3.2.
All the Brazilian lagoons exhibit a positive annual hydrological balance (Knoppers
et al. 1991; Miyao et al. 1986) with the exception of the permanently hypersaline
Araruama L. Araruama L. is hypersaline as a result of a semi-arid climate with high
evaporation and low rainfall rates and an extremely small fresh water input in relation to the lagoon water volume (Kjerfve et al. 1996). The mean flushing half-lives of
the lagoons vary from 1-84 days. The shortest flushing half-life occurred in the tidally
dominated Itaipu L. (1 day) and the Patos L. Estuary (3 days). The external cells of the
choked systems with long tidal channels exhibited flushing half-lives of 5-7 d<:J.Ys, while
the interior lagoon cells located furthest from the sea without significant tidal exchange
had flushing half lives of 15-28 days. The longest flushing half-lives were computed
for Araruama L.(84 days) and the Patos L. proper (82 days).
3.9
Nutrient Standing Stock and Particulate Organic Matter
The majority of choked and restricted coastal lagoons in Brazil and other tropical and
sub-tropical regions with humid climates are rich in organic materials. Some are entirely detritus-based during some stage of the annual cycle (Nixon 1982; Nichols 1989).
The majority are also marked by seasonal changes in their standing stock of biogenic
matter and autotrophic biomass (Nixon 1982; Knoppers 1994). However, extreme seasonal variability, as encountered in the coastal lagoons of the west coast of Mexico
(Flores-Verdugo 1985; Flores-Verdugo et al. 1988), western Australia, and the Mediterranean, is not encountered in the coastal lagoons of Brazil (Mee 1978; Nixon 1982; Vaulot
and Frisoni 1986; Y
the coastal lagoons of Brazil is limited to distributions of dissolved inorganic nitrogen (DIN) and phosphorus (DIP), a phytoplankton biomass indicator (chlorophyll a),
particulate organic carbon (POC), and total suspended solids. Some information has
also been published on annual cycles of dissolved organic carbon (DOC), dissolved
organic nitrogen (DON), and dissolved organic phosphorous (DOP) for Urussanga L.,
Fora L., Barra L., Cananeia-Iguape L., and the estuary of Patos L. (Mesquita and Peres
1985; Carmouze et al. 1991; 1993; Abreu et al. 1994a,b). The mean annual concentrations
and ranges of values for some nutrient parameters for the eight lagoon systems included in this comparison are summarized in Table 3.3.
The standing stock of particulates generally attains peak concentrations in the late
austral summer and early fall, reflecting a trend towards a unimodal seasonal pattern
in the development of autotrophic biomass, i.e., chlorophyll a (Fig. 3.9). This is true
for all the lagoons of this study with the exception of the Patos L. Estuary. In most of
the lagoons, the highest fraction of suspended detrital organic matter is encountered
during the less productive period during late fall and winter. Most of the suspended
detritus originates from autotrophic production, as indicated by the relatively low
particulate organic carbon to nitrogen ratios, with C: N by weight less than 9 : 1, and