Nilva Brandini

Assessment of the trophic status of four coastal lagoons and one estuarine delta, eastern Brazil

Anthropogenic eutrophication of aquatic ecosystems continues to be one of the major environmental issues worldwide and also of Brazil. Over the last five decades, several approaches have been proposed to discern the trophic state and the natural and cultural processes involved in eutrophication, including the multi-parameter Assessment of Estuarine Trophic Status (ASSETS) index model. This study applies ASSETS to four Brazilian lagoons (Mundaú, Manguaba, Guarapina, and Piratininga) and one estuarine delta (Paraíba do Sul River), set along the eastern Brazilian coast. The model combines three indices based on the pressure–state–response (PSR) approach to rank the trophic status and forecast the potential eutrophication of a system, to which a final ASSETS grade is established. The lagoons were classified as being eutrophic and highly susceptible to eutrophication, due primarily to their longer residence times but also their high nutrient input index. ASSETS classified the estuary of the Paraíba do Sul river with a low to moderate trophic state (e.g., largely mesotrophic) and low susceptibility to eutrophication. Its nutrient input index was high, but the natural high dilution and flushing potential driven by river flow mitigated the susceptibility to eutrophication. Eutrophication forecasting provided more favorable trends for the Mundaú and Manguaba lagoons and the Paraíba do Sul estuary, in view of the larger investments in wastewater treatment and remediation plans. The final ASSETS ranking system established the lagoons of Mundaú as “moderate,” Manguaba as “bad,” Guarapina as “poor,” and Piratininga as “bad,” whereas the Paraíba do Sul River Estuary was “good.”

Assessment of remotely sensed chlorophyll-a concentration in Guanabara Bay, Brazil

Abstract. The Guanabara Bay (GB) is an estuarine system in the metropolitan region of Rio de Janeiro (Brazil), with a surface area of ∼346  km2 threatened by anthropogenic pressure. Remote sensing can provide frequent data for studies and monitoring of water quality parameters, such as chlorophyll-a concentration (Chl-a). Different combination of Medium Resolution Imaging Spectrometer (MERIS) remote sensing reflectance band ratios were used to estimate Chl-a. Standard algorithms such as Ocean Color 3-band, Ocean Color-4 band, fluorescence line height, and maximum chlorophyll index were also tested. The MERIS Chl-a estimates were statistically compared with a dataset of in situ Chl-a (2002 to 2012). Good correlations were obtained with the use of green, red, and near-infrared bands. The best performing algorithm was based on the red (665 nm) and green (560 nm) band ratio, named “RG3” algorithm (r2=0.71, chl-a=62,565*x1.6118). The RG3 was applied to a time series of MERIS images (2003- to 2012). The GB has a high temporal and spatial variability of Chl-a, with highest values found in the wet season (October to March) and in some of the most internal regions of the estuary. Lowest concentrations are found in the central circulation channel due to the flushing of ocean water masses promoted by pumping tide.

COMPARAÇÕES ENTRE MEDIÇÕES EM TEMPO REAL DA pCO2 AQUÁTICA COM ESTIMATIVAS INDIRETAS EM DOIS ESTUÁRIOS TROPICAIS CONTRASTANTES: O ESTUÁRIO EUTROFIZADO DA BAÍA DE GUANABARA (RJ) E O ESTUÁRIO OLIGOTRÓFICO DO RIO SÃO FRANCISCO (AL)

Carbon dioxide (CO2) fluxes from aquatic systems are generally derived from the gradient in the partial pressure of CO2 (pCO2) between air and surface waters. In this study, we compare real-time measurements of water pCO2 using an equilibrator and non-dispersive infrared gas detector, with calculations based on pH and total alkalinity (TA) in two contrasting Brazilian estuaries: Guanabara Bay (Rio de Janeiro) and the Sao Francisco River Estuary (Alagoas). In Guanabara Bay, the measured and calculated values showed an excellent agreement (R2 = 0.95, p < 0.0001), without significant statistical differences between the two methods. In the Sao Francisco River Estuary, where the entire gradient from freshwaters to seawater could be sampled, important overestimates were found for the calculated pCO2. The overestimation was on average 71%, and reached up to 737%. This large bias in pCO2 calculation was verified at low pH and TA concentrations in freshwaters (pH < 7.5; TA < 700 µmol kg-1) possibly due to the contribution of organic alkalinity, lowering the buffer capacity of the carbonate system. As such, direct measurements of pCO2 should be considered as a priority for CO2 studies conducted in estuarine systems, particularly tropical systems where physical and biological processes are prone to significant spatial and temporal variability.

Inter-annual variability on the water quality in the Lower São Francisco River (NE-Brazil)

Aim This study characterized the water quality in the lower Sao Francisco River (NE-Brazil).This research represents the first work to be carried out in the lower sector of the Sao Francisco river aiming to quantify and compare limnological variables, during three different years (2001, 2004 and 2007). Methods Water samples were collected in a transversal section of the river at monthly intervals period on surface layer. Temperature, conductivity, pH, and dissolved oxygen were obtained using a multiparameter probe YSI-6600. The dissolved inorganic nutrients (ammonium, nitrite, nitrate, dissolved phosphorus and silicates), chlorophyll-a and total suspended sediment (TSS) were also determined. Results The three hydrological years showed differences in precipitation rates and discharge conditions. The year 2001 had precipitation rates below the historical series of rainfall. The mean annual water temperature showed negligible differences among the three years. Dissolved inorganic nutrient concentrations were highest in 2004, with ammonia and nitrate differing statistically between the years (p<0.05); the later showed the largest concentration of dissolved inorganic nitrogen. Chlorophyll-a showed a slight difference among years. Conclusions Precipitation intensity has a direct impact on the Sao Francisco River discharge, but the geographical distribution of the precipitation is also a determinant factor for alterations of the chemical and physical characteristics of the water that reaches the lower sector of the Sao Francisco River.

Dams Impacts upon the fluxes of biogenic matter

Dams impacts are usually associated with the formation of artificial lakes, population displacements and loss of continental habitats. However, but not less significant, are the impacts upon the fluxes of water and materials to the coastal zone with severe quantitative and qualitative alterations which may cause saline water intrusion and coastal erosion, loss of estuarine and coastal zone fertility and the alterations of regional and global biogeochemical cycles. The present article, presents a brief review on the theme by incorporating Brazilian examples addressed by the work group from the Instituto Nacional de Ciência e Tecnologia de Transferência de Materiais Continente-Oceano (INCT-TMCOcean).

COMPARISONS BETWEEN REAL-TIME pCO2 MEASUREMENTS WITH INDIRECT ESTIMATES IN TWO CONTRASTING BRAZILIAN ESTUARIES: THE EUTROPHIC GUANABARA BAY (RJ) AND THE OLIGOTROPHIC SÃO FRANCISCO RIVER ESTUARY (AL).

Carbon dioxide (CO2) fluxes from aquatic systems are generally derived from the gradient in the partial pressure of CO2 (pCO2) between air and surface waters. In this study, we compare real-time measurements of water pCO2 using an equilibrator and non-dispersive infrared gas detector, with calculations based on pH and total alkalinity (TA) in two contrasting Brazilian estuaries: Guanabara Bay (Rio de Janeiro) and the Sao Francisco River Estuary (Alagoas). In Guanabara Bay, the measured and calculated values showed an excellent agreement (R2 = 0.95, p < 0.0001), without significant statistical differences between the two methods. In the Sao Francisco River Estuary, where the entire gradient from freshwaters to seawater could be sampled, important overestimates were found for the calculated pCO2. The overestimation was on average 71%, and reached up to 737%. This large bias in pCO2 calculation was verified at low pH and TA concentrations in freshwaters (pH < 7.5; TA < 700 µmol kg-1) possibly due to the contribution of organic alkalinity, lowering the buffer capacity of the carbonate system. As such, direct measurements of pCO2 should be considered as a priority for CO2 studies conducted in estuarine systems, particularly tropical systems where physical and biological processes are prone to significant spatial and temporal variability.

Sediment Oxygen and Nutrient Fluxes in Three Estuarine Systems of South-Eastern Brazil

Shallow water ecosystems, such as estuaries and coastal lagoons, are characterised by a tight pelagic-benthic coupling of biogeochemical processes. The sediment-water interface supplies a substantial fraction of regenerated nutrients for the sustenance of pelagic primary production and plays an important role in total community metabolism (Pamatmat 1971; Rowe et al. 1975; Florek and Rowe 1983). In organic-rich phytoplankton-based systems, the relation between sediment oxygen consumption (SOC) and pelagic primary production (PP) generally lies between 25 and 50%, and the benthic supply of dissolved inorganic nitrogen (DIN) and phosphate (DIP) sustains up to 30% of the annual demand by primary production, or even 100% at some stage of the annual cycle (Nixon et al. 1976, 1980; Zeitzschel 1980); Knoppers 1994). These systems are potentially limited by nitrogen, partly because of nitrogen loss from denitrification at the sediment-water interface (Seitzinger 1988). In contrast, hypersaline carbonate-rich systems are usually dominated by benthic primary production and phosphorous limitation (Jorgensen et al. 1979 1983; Bauld 1984; Javor and Castenholz 1984; Smith 1988). Nutrient release rates from the benthic interface are intrinsically related to the activity of microphytobenthic primary producers and the additional control of phosphorous by calcium carbonate reactions. Benthic DIP release rates compared to DIN are usually low or negligible (Hines and Lyons 1982; Atkinson 1987; Smith and Atkinson 1994).