CHAPTER 3 . Coastal lagoons of Southeastern Brazil
51
stock of particulate organic carbon (PaC) and phytoplankton carbon (PPC). The
pac: PPC ratio varies between 10 : 1 and 4: 1, depending on the lagoon and season,
and may inverse to 0.5 : 1 during exponential growth phases close to the peak of extreme phytoplankton blooms in summer. The pac stock varies between 4 and 15 g C m- 2
(Knoppers et al. 1984; Odebrecht and Caruso 1987; Moreira 1988; Moreira and Knoppers 1990; Knoppers and Moreira 1990; Carmouze et al. 1993).
In contrast, dissolved inorganic nutrient concentrations are generally low and lack
clear seasonal trends, mainly as a result of uptake by primary producers throughout
the year. With the exception of the hypersaline Araruama L. (Landim de Souza 1993),
the polyhaline anoxic central Concei<;:3.o L. basin (Knoppers et al. 1984), and the limnic
sections of the Patos L. Estuary (Proen<;:a et al. 1988), the inter- and intraspecific DIN
varies from 2-10 flM and DIP varies from 0.3-1.5 flM in the Brazilian lagoons
(Table 3-3). This corresponds to the range established for the majority of tropical and
subtropical coastal lagoons with low cultural eutrophication (Nixon 1982). In Flora L.
and Piratininga L., the nutrient concentration reaches the upper limit of this range,
with ammonia dominating DIN as a consequence of domestic effluent discharge and
low tidal flushing. In Araruama L., DIN may attain 20-30 flM, and in Patos L., 20-50 flM
close to the discharge of the Guaiba River. In Araruama L., DIP concentrations are frequently at the detection level (Landim de Souza 1993), because phosphorous dynamics are additionally controlled by calcium carbonate reactions (Atkinson 1987;
Knoppers et al. 1996). Except for Araruama L. and Patos L. proper, which are limited
by phosphorous, the DIN: DIP atomic ratios in the other lagoons remain well below
the Redfield ratio of 16 : 1 (Table 3.3). Thus, irrespective of their natural or cultural
nutrient loading, the lagoons are nitrogen limited.
Short-term variability in nutrient concentrations occurs in most of the choked lagoons due to changes in nutrient loading from wash-out from the drainage basins in
response to climatic events (Knoppers et al. 1991; Niencheski and Windom 1994), nutrient release from the sediments by wind-induced mixing, and density displacement
of pore water during tidal intrusion (Knoppers and Moreira 1988; Knoppers and
Moreira 1990; Machado 1989). In Barra L. and Piratininga L., sporadic dystrophic crises and fish kills induce nutrient pulses (Carmouze et al. 1993). Of particular interest
is the short temporal variability from intrusion of nutrient-rich coastal water into the
Patos L. Estuary. Ocean salinity waters at the surface near the mouth of the lagoon
yielded up to 3 flM NH 4 -N, 13 flM N0 3 -N, and 3 flM P0 4 -P in spring and markedly
enhanced phytoplankton primary production (Abreu et al. 1995). Similar nutrient
enrichment by marine waters has been documented for San Quentin Bay during
upwelling events (Alvarez-Borrego and Alvarez-Borrego 1982).
3.10
Primary Producers
Most of the Brazilian coastal lagoons are phytoplankton-based systems. The exceptions are Araruama L., which is dominated by microphytobenthic cyanobacterial mats
(Knoppers et al. 1996), and Piratininga L. and Tramandaf-Imbe L., which are dominated
by macrophytobenthos (Carneiro et al. 1993; 1994). Macroalgae and submerged macrophytes also grow at shallow depths in some parts of the Patos L. Estuary (Coutinho
and Seeliger 1986). The majority of primary producers in the phytoplankton-based
51
stock of particulate organic carbon (PaC) and phytoplankton carbon (PPC). The
pac: PPC ratio varies between 10 : 1 and 4: 1, depending on the lagoon and season,
and may inverse to 0.5 : 1 during exponential growth phases close to the peak of extreme phytoplankton blooms in summer. The pac stock varies between 4 and 15 g C m- 2
(Knoppers et al. 1984; Odebrecht and Caruso 1987; Moreira 1988; Moreira and Knoppers 1990; Knoppers and Moreira 1990; Carmouze et al. 1993).
In contrast, dissolved inorganic nutrient concentrations are generally low and lack
clear seasonal trends, mainly as a result of uptake by primary producers throughout
the year. With the exception of the hypersaline Araruama L. (Landim de Souza 1993),
the polyhaline anoxic central Concei<;:3.o L. basin (Knoppers et al. 1984), and the limnic
sections of the Patos L. Estuary (Proen<;:a et al. 1988), the inter- and intraspecific DIN
varies from 2-10 flM and DIP varies from 0.3-1.5 flM in the Brazilian lagoons
(Table 3-3). This corresponds to the range established for the majority of tropical and
subtropical coastal lagoons with low cultural eutrophication (Nixon 1982). In Flora L.
and Piratininga L., the nutrient concentration reaches the upper limit of this range,
with ammonia dominating DIN as a consequence of domestic effluent discharge and
low tidal flushing. In Araruama L., DIN may attain 20-30 flM, and in Patos L., 20-50 flM
close to the discharge of the Guaiba River. In Araruama L., DIP concentrations are frequently at the detection level (Landim de Souza 1993), because phosphorous dynamics are additionally controlled by calcium carbonate reactions (Atkinson 1987;
Knoppers et al. 1996). Except for Araruama L. and Patos L. proper, which are limited
by phosphorous, the DIN: DIP atomic ratios in the other lagoons remain well below
the Redfield ratio of 16 : 1 (Table 3.3). Thus, irrespective of their natural or cultural
nutrient loading, the lagoons are nitrogen limited.
Short-term variability in nutrient concentrations occurs in most of the choked lagoons due to changes in nutrient loading from wash-out from the drainage basins in
response to climatic events (Knoppers et al. 1991; Niencheski and Windom 1994), nutrient release from the sediments by wind-induced mixing, and density displacement
of pore water during tidal intrusion (Knoppers and Moreira 1988; Knoppers and
Moreira 1990; Machado 1989). In Barra L. and Piratininga L., sporadic dystrophic crises and fish kills induce nutrient pulses (Carmouze et al. 1993). Of particular interest
is the short temporal variability from intrusion of nutrient-rich coastal water into the
Patos L. Estuary. Ocean salinity waters at the surface near the mouth of the lagoon
yielded up to 3 flM NH 4 -N, 13 flM N0 3 -N, and 3 flM P0 4 -P in spring and markedly
enhanced phytoplankton primary production (Abreu et al. 1995). Similar nutrient
enrichment by marine waters has been documented for San Quentin Bay during
upwelling events (Alvarez-Borrego and Alvarez-Borrego 1982).
3.10
Primary Producers
Most of the Brazilian coastal lagoons are phytoplankton-based systems. The exceptions are Araruama L., which is dominated by microphytobenthic cyanobacterial mats
(Knoppers et al. 1996), and Piratininga L. and Tramandaf-Imbe L., which are dominated
by macrophytobenthos (Carneiro et al. 1993; 1994). Macroalgae and submerged macrophytes also grow at shallow depths in some parts of the Patos L. Estuary (Coutinho
and Seeliger 1986). The majority of primary producers in the phytoplankton-based