PRIMARY AND BACTERIAL PRODUCTION PROCESSES IN THE LOWER ITAJAÍ-AÇÚ ESTUARY , SANTA CATARINA , BRAZIL

Pereira Filho, J.; Rörig, L. R.; Hesse, K.; Poremba, K.; Schettini, C. A. F.; Proença, L. A. & Santos, J. E. 2009. Primary and Bacterial Production processes in the lower Itajaí-Açú estuary, Santa Catarina, BrazilBraz. J. Aquat. Sci. Technol. 13(1): 1-10. ISSN 1808-7035. Primary and bacterial productivity (PP and BP, respectively) were measured in the lower Itajaí-Açu estuary and in the adjacent shelf, under low river discharge conditions. The experiment was carried out in April, 2000, when physical, chemical and biological variables were recorded in five stations: three in the estuary and two in the inner shelf. Salinity, temperature, turbidity and light intensity were determined in vertical profiles; dissolved oxygen, nutrients, chlorophyll-a, primary (PP) and bacterial production (BP) were sampled at surface and near the bottom. The BP ranged from 0.5 to 11.3 mg C.m.h, and the highest values were recorded at the inner stations of the estuary, associated with lower salinity and light intensity and higher dissolved nutrients concentration. On the other hand, PP was higher in the inner shelf, with PP increasing from 2.0 to 30 mg C.m.h. The phytoplankton biomass showed the same trend, increasing from 0.2 to 8.4 μg/L at the surface. The PP was limited by light in the inner estuary and by the PO4 concentration in the inner shelf. The higher productivity zone was formed in front of the estuarine mouth, as expected, since water transparency increases leading the consumption of the rich-nutrient waters from the estuary by autotrophic organisms. The data indicated that the ecosystem metabolism shift from heterotrophic to autotrophic in a very small length scale (few kilometers) during the sampled conditions.


INTRODUCTION
Organic matter dynamics in estuaries is very complex, since it is influenced by factors such as river discharge, mixing processes due to tides and the several different effects from human activities.These factors can alter the balance between production and mineralization processes of organic matter, which can also be modified along the estuarine gradient due to changes in environment varying from fluvial to marine conditions.These changes influence the amount of particulate and dissolved organic matter and their elemental composition (carbon, nitrogen and phosphorus; C, N, P), as well as dissolved inorganic nutrients concentrations.The balance between autotrophy and heterotrophy in aquatic ecosystems is important for the assessment of the flux of organic carbon along the trophic chain.High BP/PP (Bacterial Production/ Primary Production ratio) have been shown to increase as a direct function of terrestrial carbon input and of the fraction of PP processed by bacteria (Ram et al. 2007).
Primary and bacterial production are usually correlated in aquatic systems.This behavior suggests that phytoplankton is the most important source of organic matter supporting bacterial growth in these ecosystems.On the other hand, in coastal and estuarine systems, substrates for bacterial growth can derive from sources other than phytoplankton, such as river borne material, terrestrial runoff, anthropogenic loads and watersediment fluxes (Almeida et al. 2005).Alterations induced by anthropogenic activities have modified the structure and function of coastal aquatic systems around the world (Bowen and Valiela, 2001).The metabolism of estuarine systems is greatly influenced by the entrance of nutrients and organic matter.These inputs have augmented in the last decades due to changes in land use and occupation (Revilla et al. 2002), particularly due to frequently untreated domestic and industrial effluents.In addition, the contribution of organic matter and nutrients has increased hypoxia and anoxia in estuaries and coastal environments (Diaz, 2001;Rowe, 2001), as a result of the elevated consumption of O 2 .
The bacterial activity in estuaries has not been extensively studied in Brazil.Cesar & Abreu (2001), demonstrated that a large part of the understanding of the functioning of estuaries in Brazil comes from studies of the Lagoa dos Patos Estuary, which has been the focus of various investigations on related bacterial communities (Abreu et al. ,1995;Abreu et al. 1992;Abreu, 1997).
The estuary of the Itajaí-Açú river, on Santa Catarina coast, has been subjected to several studies since 1995 (Schettini et al. 1996, 1998, Schettini, 2002;Pereira Filho et al. 2003, Rörig et al. 2003, Proença, 2004, Pereira Filho et al. 2006).Its watershed has high human population density and strong economic activity, receiving a number of impacts and discharges.As a consequence, chemical characteristics of the river and estuarine waters have been changed (Pereira Filho et al. 2003).Next to the mouth of estuary, phytoplankton blooms have been recorded with the occurrence of water discoloration and high biomass (Proença, 2004).
The Itajaí-Açu estuary presents a highly stratified circulation pattern and its transport processes is very dependent of river flow and tides .During high river discharge the river waters are directly delivered to the shelf.On the other hand, during low river discharge the salt intrusion can reach up to 30 km in the inner estuary and tides plays a major role in mixing and transport (Schettini et al. 1996(Schettini et al. , 1998(Schettini et al. , 2006;;Schettini, 2002), with direct implications on the nutrient dynamics (Pereira Filho et al. 2003, 2006) and local and nearshore biological processes (Rörig et al. 2003;Proença, 2004).The transport and transformation processes in the Itajaí-Açu/inner shelf region are reasonable understood, and its metabolism can be hypothesized following the basic rules where the autotrophy increases as river water nutrients rich becomes less turbidity areas, as it is mixed with coastal waters.
The objective of this study was to investigate and quantify primary and bacterial production along the intense physical and chemical gradients in the lower Itajaí-Açu and the adjacent shelf.It is important to emphasize that the results presented here comes from a short term experiment, although its representativeness is high since the hydrological conditions which it was performed comprises most of the time.

Study Area
The Itajaí-Açú Estuary is located in the state of Santa Catarina,Southern Brazil (Lat. 26.9ºS and Lon. 48.66º) .The regional climate is humid subtropical without water deficit, with rains well distributed throughout the year, a typical Cfa, according to the classification system of Köpenn.Mean temperature is about 18ºC, with mean annual precipitation and evapotranspiration rates of approximately 1400 mm and 1080 mm, respectively (Gaplan, 1986).
The Itajaí-Açu river basin is the most important in the Santa Catarina State, presenting high human population density and strong economic activity, receiving a number of impacts and discharges.It presents watersheds area of 15,500 km 2 , where the cities of Blumenau, Brusque and Rio do Sul are located.In the lower river state the Itajaí and Navegantes harbors, and an active fishery industry.As a consequence of all these human activities, chemical characteristics of the river and estuarine waters have been changed (Pereira Filho et al. 2003).
The Itajaí-Açu river accounts with 90 % of the fresh water input to the estuary, while the remaining 10% is mainly from two smaller tributaries named Luis Alves river and Itajaí Mirim river.The averaged annual discharge of Itajaí river is 228 m 3 .s - , with historical minimum and maximum of 17 m 3 .s - and 5390 m 3 .s - , respectively (Schettini, 2002).The regional tidal regime is microtidal semi-diurnal, ranging from 0.4 to 1.2 m during neap and spring tide periods, respectively (Schettini, 2002).The physical setting of (i) small tidal range, (ii) highly variable river discharge regime and (iii) the deep and uniform channel morphology results in a highly stratified estuarine structure (Schettini et al. 1996).A two water layers structure separated by an intense halocline is observed most of the time, being stronger during neap tide periods.The salt intrusion during low discharge periods extends up to 30 km from the mouth, meanwhile all salt water is flushed out when the river discharge exceeds about 1000 m 3 .s - .The former situation usually lasts for weeks until a couple months; meanwhile the latter usually lasts for hours to few days.

Sampling and Sample Processing
The field surveying and incubation experiments were performed on April 17, 18 and 19 of 2000 at five stations located along a transect comprising the lower stretch of Rio Itajaí-açu estuary and the adjacent shelf area (Fig. 1), and under low river discharge condition.The estuary stations #1, #2 and #3 were sampled on April 17; the adjacent shelf stations #4 and #5 were sampled on the follow days, on April 18 and 19, respectively.
Vertical profiles of salinity, temperature, turbidity and irradiance were taken in all stations in the beginning of the experiments, for every 0.5 m of water column.Salinity, temperature and turbidity were recorded with a CTD probe model SD-202 by Saiv™ A/S, where the turbidity was an optical backscatter probe by SeaPoint™.The turbidity was converted to mass concentration of suspended sediments (mg.L -1 ) by a calibration curve.The light irradiance was recorded with a direct reading probe by Licor™.
Water samples were taken at near surface and near bottom for the determination of pH, alkalinity, dissolved inorganic nutrients, chlorophyll-a, and qualitative and quantitative analysis of phytoplankton.Further water samples were taken for the incubation experiments of primary and bacterial productivity.The pH was measured with an Orion™ pHmeter.Alkalinity was analyzed by titration with HCl.The incubations for primary and bacterial production were limited by the number of racks.The incubations experiments were carried out at near surface and near bottom at the estuarine stations #3, #4 and #5, and only at near surface level at station #1, the in the shelf area.
The aliquots for nutrients determinations were kept on ice until processing in the laboratory (up to 3 h).In the laboratory, the samples were filtered (Whatman ® GF/F) and frozen for later determination of NH 4 + , NO 2 -, NO 3 -, PO 4 3-and Si(OH) 4 using standard colorimetric methods (Strickland & Parsons, 1972).The filters were also frozen and later utilized for the determination of Chl a after extraction with 90% acetone v/v.The pigment quantification was carried out by reverse-phase high efficiency liquid chromatography (HPLC) according to Mantoura et al. (1997).Aliquots of the samples were preserved in Lugol's solution for later identification and quantification of phytoplankton organisms with an inverted microscope according to Utermöhl (1958).Total CO 2 was calculated from pH and alkalinity data, using a model of ionic interaction (Carmouze, 1994).Alkalinity was measuremed by HCl titration.
River discharge data for the Itajaí-Açu river was obtained with the Brazilian Water Agency for the Indaial linmetric gauge station.This station is located nearly 90 km upstream from the estuarine mouth, although is the closest which does not influenced by tides, and represents nearly 70% of the total drainage basin.The discharge data are available at daily basis since 1929.To characterize the hydrological conditions of discharge and assess the representativeness of the present experiment, it was used the period from 1991 until 2000.

Primary and bacterial productivity
Water samples of 50 ml were transferred to polycarbonate bottles (Zenoko) containing 4.5 mCi NaHC 14 O 3 and incubated at different intensities of natural light (in situ incubation).After the incubation period, the samples inoculated with C-14 were filtered, transferred to vials that received scintillation cocktail, after elimination of NaHC 14 O 3 from filters with HCl.Sample radioactivity was later read in a Packard ® scintillation counter.The results obtained were converted to mg C.m -3 .h - , based on the radioactivity measured (dpm) using the formula described in IOC/UNESCO (1994), for incubation times of 3 to 3.5 h.The results were plotted as Photosynthesis vs. Irradiance curves (PxI curves) and adjusted to generate mathematical models by using Sigma-plot ® software routines.The best model was chosen based on the best equation fitting the PxI curves, using calculated adjustment coefficients.
During the incubation period, irradiance at the surface was recorded with a Licor ® Radiometer.Integrated surface irradiance (Io) for the period was calculated, considering the total irradiance determined during incubation, which was expressed as mE.m -2 .s - .The light profile, integrated by the incubation period, was obtained by combining the integrated irradiance at the surface (Io) with the light profile in the water column at each station.The productivity profile in the water column was calculated by combining the light profiles in the water column and the PxI curves obtained at each station.From the primary productivity profile, the potential primary productivity was determined for each sample, integrated by depth, expressed in mg C.m -2 .h - .
For bacterial production, subsamples of 10 ml were supplemented with 7.5 nmol (the pre-checked saturation level) ( 3 H) methyl-thymidine (TdR purchased from NEN Dupont, specific activity 80 mCi.µmol -1 ) and incubated in a water bath under in situ temperatures.Each determination consisted of 3 replicates and 1 formalin-fixed control.After 45 min, incubation was stopped by adding 200 µl of 35 % formaldehyde.In the laboratory, samples were filtered through 0.2 µm polycarbonate membranes.The filters were rinsed 1 time with cooled, pre-filtered (0.2 µm) seawater and 5 times with 2 ml of a cooled solution of 5 % trichloroacetic acid (TCA) before being transferred to 6 ml vials.Scintillation counting was done in a Packard LSC after a 2 days storage in the scintillation cocktail (Lumagel, Packard).Calibration with a known amount of labelled thymidine allowed the calculation of incorporated thymidine.Bacterial carbon biomass production was estimated by using a conversion factor of 1.5 x 10 18 cells mol -1 thymidine (Admiraal et al. 1985) and 20 fg C cell -1 (Lee and Fuhrmann, 1987).

Physical and chemical variable
The experiment was conducted during low river discharge (average 211 m 3 s -1 ), s and after a prolonged period without significant discharge peaks (Fig. 2a).The 10-year averaged discharge (1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000) was 300 ± 302 m 3 .s - , and discharge values bellow the average occurs nearly 75% of the time (Fig. 2a).As pointed out by other studies in the Itajaí-Açu estuary, the system presents high hydrological variability (Schettini, 2002;Schettini et al., 2006).This variability rises from two main factors: the meso-thermic climate with rains uniformly distributed along the year (Gaplan, 1996), and the reduced size of the drainage basin, what results in short concentration time, i.e. the time elapsed from the beginning of a rain to the peak of discharge, in the order of hours.Table 1: Calculated equations used to obtain the light profiles and the primary production profile on each sampling site.Iz: Light intensity (µE.m -2 .s - ) on the depth z (m), Io: integrated light intensity in the surface (µE.m -2 .s - ).Calculated PxI equations (n=7) showing the relationship between Primary Productivity (PP) and Light Intensity (I) on each sample; the determination coefficients (r 2 ).Additionally, the regional climatology can be interannually affected by large-scale phenomena such as El Niño (Grimm et al., 2000).Therefore, river discharge is usually below the averaged value, intercalated with randomly occurrences of high discharge peaks.The periods of low discharge can last for several weeks, or even for several months.Thus, in spite of the present experiment is time limited in terms of observation, it presents reasonable representativeness taking into account the hydrologic conditions.

Samples
Salinity ranged from 4 (#5 at surface) to 35 (# 1 at bottom), presenting strong longitudinal and vertical gradient (Fig. 3a), typically observed under the low river discharge condition (Schettini, 2002;Schettini and Toldo, 2006).The temperature did not present significant horizontal or vertical gradient (Fig. 2b).The salinity distribution in the estuary presented a highly stratified/ salt wedge pattern, where the salinity increases tens of unities from surface to bottom.The vertical salinity gradient was not so strong at the shelf stations, although with a vertical variation of several unities, indicating the influence of estuarine water in forming a estuarine plume (Schettini et al., 1998;Trochimczuk & Schettini, 2003).
The suspended particulate matter (SPM) concentration ranged from ~10 to higher than 150 mg.L -1 , with the highest values being observed near the bottom and in the estuary (Fig. 3c).Benthic material ressuspension by tidal currents and/or mechanical perturbation caused by ship traffic or dredging are the main factors controlling the SPM distribution in the lower estuary (Schettini and Toldo, 2006).This scenario is strongly modified during river discharge peaks, when the river borne SPM can increase up to 1000 mgL -1 .This invert the SPM vertical structure as the higher concentrations are associated with lighter fresh water, which flows over the heavier coastal saline waters.Nevertheless, such events last shortly from several hours until few days.
The light profiles for each station showed that only the first meters of the water column presented sufficient light for phytoplankton primary production.The attenuation of light was particularly high at the estuarine inner most stations (#4 and #5), meanwhile the influence of coastal waters resulted in deeper euphotic layers in the shelf stations and in the near estuarine mouth station (#1 to #3).The equations that best described the light profiles at each sampling station are shown in Table 1.
The concentrations of dissolved oxygen varied between 3.7 and 7.8 mg.L -1 O 2 .The highest values were associated with the surface and with the outermost portion of the estuary, and the lowest were recorded at the inner stations, at the bottom (Fig. 4a).The dissolved inorganic nutrients presented inverse relationship with salinity.The highest values occurred at the surface and at the inner most stations (#4 and #5), meanwhile the inorganic nitrogen (DIN= NH 4 + + NO 2 -+ NO 3 -), phosphorus (DIP= PO 4 3-) and Silica (Si = Si(OH) 4 ) decreased seawards (Fig. 4b, c and d).The concentrations of DIN varied between 12.0 and 63.3 mmol.L -1 .NH 4 + was the main form of DIN (76%) at all the stations, followed by NO 3 -and NO 2 -(Figs.5a, b and  c).The predominance of ammonium over the other nitrogenous nutrients has already been observed in previous studies for this environment (Pereira Filho et al. 2003).
The concentrations of DIP varied between 0.1 and 0.8 µmol.L -1 , and the concentrations of Si varied between 12 and 87 µmol.L -1 .DIP, Si and NH 4 + presented nonconservative increases at a salinity range of 10 to 30 (Figs. 6a, b, c, d and e) and suggest decomposition of organic matter along the estuarine gradient.The organic matter would be related to anthropogenic sources, as indicated by the high levels of ammonium.The high turbidity in the estuary favors the predominance of mineralization processes over those associated with phytoplankton primary production, resulting in an increase in nutrients at the inner most stations.The concentrations of Si and DIP were particularly low in the shelf stations, what increases the N:P ratio.At the station #1 the N:P ratio was higher than 200.

Chl a and Phytoplankton
The Chl a concentration decreased towards the estuary (Fig. 7a).The highest value was 8.0 µg.L -1 , at the surface of station #2 , similarly to the phytoplankton abundance, which also revealed higher values of cells density at the surface, with a maximum at station #2 (Fig. 7b).Autotrophic organisms were dominant in the stations #1 (surface and bottom), #2 (surface) and #3 (surface), represented by chain forming diatoms (Bacillariophyceae, > 20µm) (Figs.8a and b).There was a predominance of the nanoplankton fraction (Fig. 8b) and higher influence of heterotrophic organisms in samples #3 (bottom) and #4 (surface and bottom).
The qualitative and quantitative analysis of the phytoplankton showed various characteristic patterns along the estuarine gradient.The higher cells densities were found at stations with lower turbidity, with the maximum occurring in the outer station (#1).A similar finding had already been recorded in the region under high river discharge condition; however, in that case the maximum values occurred farther from the mouth (Rörig et al. 2003).The lowest abundances were found in bottom samples, supporting the notion that light is a critical factor for phytoplankton in the inner estuary, since relatively high levels of nutrients occurred in all water column of most stations.The higher abundance of heterotrophic and nanoplanktonic organisms in bottom samples is a further indication of this process.The  predominance of diatoms in almost all the samples indicates a favorable condition for organisms, which benefit from relatively high concentrations of nutrients.However, in the shelf (station #1) the phytoplankton biomass decreased (Figs.7a and  b).This was probably related to dilution effect and decrease in the nutrient concentrations, mainly DIP (Fig. 4d), what increases the N:P ratio, suggesting a limitation of phosphorus to phytoplankton growth in the coastal water.

Primary Productivity
The primary production profiles for each station, are shown in Fig. 9.There was sufficient light for primary production only in the first meters of the water column, mainly in the inner most stations of the estuary (#4 and #5), what can be attributed to the higher turbidity levels.The bottom samples, when exposed to light, showed values of productivity comparable to those obtained at the surface, suggesting that light is a limiting factor for productivity at the bottom for inner most stations and that populations at the bottom are physiologically capable of producing when eventually exposed to high levels of irradiance.
The highest level of primary productivity was recorded at station #1, of the order of 30 mg C.m -3 .h - , decreasing to less than 2 mg C.m -3 .h - at the inner most stations (Fig. 9).This result was expected on the basis of physical, chemical and biological gradients previously described, and resulted from mixing of estuarine water, rich in nutrients although more turbid, with coastal water of low turbidity, resulting in an increase in productivity.A increasing phytoplankton productivity along the estuarine/shelf salinity gradient has been reported in other estuarine systems (e.g., Filardo and Dunstan, 1985;Fisher et al.1988;Robertson et al. 1998;Pereira Filho et al. 2001).In the present case the localization of the maximum productivity was between stations nearby station #2, where the salinity was 32.The localization of the region of highest productivity differs among different estuaries and within the same estuary under different flow conditions (Dagg et al. 2004).In this case, the region of biggest phytoplankton biomass and abundance was situated in the shelf just in front the estuarine mouth.In an study carried out along the Itajaí-Açu estuary and shelf during a period of high river discharge, the gradients were located several kilometers offshore (Schettini et al., 1998;Rörig et al. 2003).
The integrated productivity in the water column presented maximum value ( 5.9 mg C.m -2 .h - ) at station #1, and decreased towards the estuary where it was of 1.1 mg C.m -2 .h - (Fig. 10a).The same tendency was observed for Chl a (Fig. 7a), however, the peak of Chl a was recorded at station #2, where primary productivity was not determined.The distribution of phytoplankton abundance has the same pattern as the productivity, i.e., showing an increase in phytoplankton biomass in the transition of coastal and estuarine waters, with  greater concentration of organisms in the front of estuarine and coastal water masses.

Bacterial Production
The bacterial activity in estuaries has not been extensively studied in Brazil.César and Abreu (2001) demonstrated, based on a compilation of data, that a large part of the understanding estuaries in Brazil comes from studies of the Lagoa dos Patos Estuary, which has been the focus of various investigations on bacterial communities (Abreu et al. ,1995;Abreu et al. 1992;Abreu, 1997).In the present study, the bacterial activity increased upstream at stations of intermediate salinity (Fig. 10b).The lowest values were recorded at the bottom, with a minimum of 0.5 mg C.m -3 .h - , at a salinity of 34.5, while the highest values occurred in samples of the surface with a maximum level of bacterial production of 11.3 mg C.m -3 .h - at a salinity of 11.Dagg et al. (2004) showed that bacterial production in river plumes, corresponding to a salinity between 8 and 32, is typically higher than that of fresh/brackis (salinity < 2) and coastal (salinity > 33) waters.Meanwhile, the low river flow during this study resulted in the penetration of coastal saline waters into the estuary, differing from the previous situations reported by Schettini et al. (1998) and Rörig et al. (2003), where equivalent salinities were found at the river plume in the adjacent coastal zone.
The values obtained were higher than those found for the plume of Lagoa dos Patos, which varied between 0.1 and 6.5 mg C.m -3 .h - (Abreu et al. 1995), but within the typical range observed for several river plumes (Dagg et al. 2004).This pattern can be explained by the influence of salinity, exerting an inhibitory effect on bacterial activity, and by the drop of organic substrates once the estuarine waters mixes with coastal waters.Moreover, the diminution of inorganic nutrients also means a decrease in substrates for bacterial activity.This tendency was also found by Abreu et al. (1995) in the region of the estuarine plume of Lagoa dos Patos, in the extreme south of Brazil.They suggested that the decrease in bacterial activity in the region of the estuarine plume was associated with stress caused by the rapid change in salinity in this type of system.
The pattern of variation of bacterial production was inverse to that of Chl a (Figs.7a and 10b), suggesting that phytoplankton biomass does not support bacterial activity, as occurs in oceanic environments (Cole et al. 1988).On the other hand, being an estuarine region, the bacterial production was probably sustained by material of allochtonous origin, such as domestic and industrial effluents, and detritus from the drainage of the basin.The increase in bacterial activity coincided with increases in nutrients in the estuary, mainly NH 4 + , and with a decrease in dissolved O 2 , which also was  related to the decomposition of organic matter throughout the salinity gradient in the estuary.

CONCLUDING REMARKS
The bacterial and primary production rates showed a shift in the lower Itajaí-Açu estuary and the adjacent shelf present from a heterotrophic metabolism (estuary) to an autotrophic metabolism (adjacent shelf) under low discharge condition.The formation of a region of higher productivity occurred in the shelf just in front the estuary mouth, where there was increase in the levels of primary productivity and phytoplankton biomass.This increase in phytoplankton primary production was the result of an increase in light intensity in the water column, associated with the availability of nutrients from the estuarine water.This pattern was observed in many estuarine ecosystems and their location has been attributed to differences in salinity, and where suspended particulate matter concentration decreased to less than 10 mg.l -1 (Dagg et al, 2004).
The phytoplankton photosynthesis showed a pattern strongly dependent on the irradiance in the estuary, being relevant wherever irradiance was significant.Where the high turbidity prevented light penetration, phototrophic phytoplankton was rare, indicating increased importance of heterotrophic processes.The considerable variability of nutrients and organic matter in almost all transect probably generated the transition between autotrophic to heterotrophic condition.However, phytoplankton was limited by light at the bottom and at the inner most stations and bacterial activity was limited by dilution and osmotic stress produced by the salt influence.On the other hand, in the outer estuary, the low levels of phosphorus and high N:P ratio suggested that the phytoplankton growth was nutrient limited in the coastal waters.

Figure 2
Figure 2 -(A) Hydrogram of daily Itajaí-Açu river discharge for the Jan-May period of 2000, with indication of the period or the experiment.(B) Accumulative frequency distribution of river discharge for the period 1991-2000, with indication of the mean discharge.

73 Figure 3 -Figure 4 -
Figure 3 -Spatial distributions of (A) salinity, (B) temperature and (C) particulate suspended matter during the experiment.The hollow circles in the upper panel indicate the location of the incubation experiments.

Figure -
Figure -Dissolved inorganic nitrogen as: (A) N-ammonium, (B) Nnitrite and (C) N-nitrate in surface and bottom samples.

Figure 7 -
Figure 7 -(A) Chl a concentrations (mg/l) and (B) phytoplankton density (cell/ml) in the Itajaí Açú River Estuary in surface and bottom samples.

Figure 9 -
Figure9-Profiles of primary productivity estimated for each sampling point.The profiles were calculated using PxI curves obtained from each sample and from the light profile at each station.S: Surface, B: Bottom.

Figure 10 -
Figure 10 -(A) Potential area of productivity and (B) bacterial production for each sampling site in the Itajaí-Açú River Estuary.