CHAPTER 3 . Coastal Lagoons of Southeastern Brazil
55
Piratininga L. Lower primary production rates were measured in Cananeia-Iguape L.
with 125 g C m- 2 ye! and in the L. Patos Estuary with 50 g C m- 2 ye!.
The choked lagoons with the least efficient tidal flushing (Table 3.2) in general exhibit the highest rates of primary production (Table 3.4). The exception is Araruama L.,
which is dominated by cyanobacterial algal mats; pelagic primary production was no
more than 10% of the benthic primary production. Maximum total daily primary production rates were very low as compared to the other choked lagoons, but the rates
were similar to those for the Patos L. Estuary. Both systems are particularly prone to
wind forcing, which is pronounced because of the long fetches of the two lagoon systems (Herz 1977; Kjerfve et al. 1996) and seemingly inhibits primary production, perhaps because of strong mixing of the water column and resuspension of fine-grained
bottom material.
Primary production and respiration rates in the lagoons were determined by different methods, but all measurements were performed in situ (Table 3-4). In the
phytoplankton-based lagoons, the methodology varied from light/dark bottle incubation techniques, using either dissolved oxygen or radioactive bicarbonate
!4C measurements, to the more time-consuming in situ diurnal curve method, measuring dissolved oxygen and carbon dioxide. Primary production of the cyanobacterial
algal mats in Araruama L. was determined by incubation of the sediment surface with
benthic chambers; macro algal primary production in Piratininga L. was determined
by the diurnal curve method. The diurnal curve method in conjunction with incubation techniques and carbon dioxide measurements is the most appropriate methodology for these lagoons, for it enables the assessment of production and respiration
of both the pelagic and benthic components, and also the whole system metabolism
for conditions where many different autotrophs prevail (Reyes and Merino 1991;
Knoppers 1994).
Abreu et al. (1994a,b) applied an interesting technique in the Patos L. Estuary, where
particulate and dissolved phytoplankton production were measured by comparing !4C
uptake rates from size fractionated filtration and the acidification bubbling method
(ABM). Production rates estimated by the ABM were equivalent to the sum of
particulate and dissolved carbon production, simultaneously determined by the filtration technique. DOC released by phytoplankton represented approximately 22% of
total dissolved and particulate carbon uptake.
The primary production estimates in the lagoons refer to the permanently aquatic
component of primary production and therefore exclude the primary production of
bordering wetland vegetation. Estimates of mangrove production from litterfall in
southeastern Brazil, including Cananeia-Iguape L., ranged from 1-5 g C m- 2 d-! on a
mean annual basis (Kjerfve and Lacerda 1993). Studies in Guarapina L. and Marica L.
revealed that the above-ground biomass production of Typha dominguensis PERS
ranged from 800 g dry weight m- 2 ye! under mesohaline conditions to 2400 g dry
weight m- 2 yr-! under oligohaline conditions (Couto 1989).
Information on the contribution by the below-ground production is not accurate
enough for these systems. Of particular interest is the impact of emergent macrophyte
vegetation upon the aquatic primary production of the lagoons. It has been documented that leachates and oxidizable particulates from mangrove forests and emerged
macrophytes may stimulate aquatic primary production in the vicinity of these habitats (Day et al. 1988). The impact by Typha dominguensis in Marica L. and Guarapina L.
55
Piratininga L. Lower primary production rates were measured in Cananeia-Iguape L.
with 125 g C m- 2 ye! and in the L. Patos Estuary with 50 g C m- 2 ye!.
The choked lagoons with the least efficient tidal flushing (Table 3.2) in general exhibit the highest rates of primary production (Table 3.4). The exception is Araruama L.,
which is dominated by cyanobacterial algal mats; pelagic primary production was no
more than 10% of the benthic primary production. Maximum total daily primary production rates were very low as compared to the other choked lagoons, but the rates
were similar to those for the Patos L. Estuary. Both systems are particularly prone to
wind forcing, which is pronounced because of the long fetches of the two lagoon systems (Herz 1977; Kjerfve et al. 1996) and seemingly inhibits primary production, perhaps because of strong mixing of the water column and resuspension of fine-grained
bottom material.
Primary production and respiration rates in the lagoons were determined by different methods, but all measurements were performed in situ (Table 3-4). In the
phytoplankton-based lagoons, the methodology varied from light/dark bottle incubation techniques, using either dissolved oxygen or radioactive bicarbonate
!4C measurements, to the more time-consuming in situ diurnal curve method, measuring dissolved oxygen and carbon dioxide. Primary production of the cyanobacterial
algal mats in Araruama L. was determined by incubation of the sediment surface with
benthic chambers; macro algal primary production in Piratininga L. was determined
by the diurnal curve method. The diurnal curve method in conjunction with incubation techniques and carbon dioxide measurements is the most appropriate methodology for these lagoons, for it enables the assessment of production and respiration
of both the pelagic and benthic components, and also the whole system metabolism
for conditions where many different autotrophs prevail (Reyes and Merino 1991;
Knoppers 1994).
Abreu et al. (1994a,b) applied an interesting technique in the Patos L. Estuary, where
particulate and dissolved phytoplankton production were measured by comparing !4C
uptake rates from size fractionated filtration and the acidification bubbling method
(ABM). Production rates estimated by the ABM were equivalent to the sum of
particulate and dissolved carbon production, simultaneously determined by the filtration technique. DOC released by phytoplankton represented approximately 22% of
total dissolved and particulate carbon uptake.
The primary production estimates in the lagoons refer to the permanently aquatic
component of primary production and therefore exclude the primary production of
bordering wetland vegetation. Estimates of mangrove production from litterfall in
southeastern Brazil, including Cananeia-Iguape L., ranged from 1-5 g C m- 2 d-! on a
mean annual basis (Kjerfve and Lacerda 1993). Studies in Guarapina L. and Marica L.
revealed that the above-ground biomass production of Typha dominguensis PERS
ranged from 800 g dry weight m- 2 ye! under mesohaline conditions to 2400 g dry
weight m- 2 yr-! under oligohaline conditions (Couto 1989).
Information on the contribution by the below-ground production is not accurate
enough for these systems. Of particular interest is the impact of emergent macrophyte
vegetation upon the aquatic primary production of the lagoons. It has been documented that leachates and oxidizable particulates from mangrove forests and emerged
macrophytes may stimulate aquatic primary production in the vicinity of these habitats (Day et al. 1988). The impact by Typha dominguensis in Marica L. and Guarapina L.