Bastiaan Adriaan Knoppers

Regional geochemical baselines for sedimentary metals of the tropical São Francisco estuary, NE-Brazil

River catchments of the humid tropics deliver a large amount of the world’s particulate suspended matter and associated elements to the coastal zone (Hay, 1998; Meybeck, 1993). The estuaries and mangrove habitats set along this transport pathway transform, retain and accumulate a fraction of the river-borne particulates and metals in their sediments (Lee, 1995; Jennerjahn and Ittekkot, 2002; Machado and Lacerda, 2004). The metals are preferentially buried with fine-grained sediments and also affected by the mineralogy and content of organic matter (Hornberger et al., 1999). Many metal accumulation studies in coastal systems focused on the establishment of geochemical baselines for the evaluation of the degree of natural and/or anthropogenic metal loadings in the system. The tropical and sub-tropical coastal zone of Brazil has been subject to manifold metal contamination studies of its embayments, estuaries, coastal lagoons and mangrove habitats embedded in these systems affected by a varying degree of multiple human impacts, such as urbanization, industrialization, deforestation, land erosion and agricultural practices (Patchineelam et al., 1988; Lacerda et al., 1992, 1999, 2006; Marins et al., 2004). However, consistent geochemical baselines are still relatively scant and in practice may also only be established on a regional basis, as the grain size, mineralogical and chemical composition of suspended matter of Brazils tropical rivers varies greatly in accor-

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.”

Changes in nutrient loads (N, P and Si) in the São Francisco estuary after the construction of dams

The aim of this study was to investigate the post-d am conditions of the loads and yields of dissolved inorganic nitrogen (DIN), orthophosphate (DIP, silicate (DSi) and total phosphorous (TP) in the Lower Sao Franci sco riverestuary (NE-Brazil) after the river was regulated t o a constant flow by the dams. Loads and yields of monthly measurements performed from November 2000 to March 2002 at a gauging station downstream of the dams (8 0 km from the coast) showed 4.1 x 10 3 t/yr and 0.006 t/km 2 /yr of DIN, 0.2 x 10 3 t/yr and 0.002 t/km 2 /yr of DIP, and 448 x 10 3 t/yr and 0.71 t/km 2 /yr of DSi, respectively. Over the last 15 years, D IN loads reduced by 94 % and DSi by 31%. The river turned into an oligotrophic system with p rimary production limited by nitrogen and nutrient yields being among the lowest of Brazilian coastal rivers.

Suspended Matter and Nutrient Gradients of a Small-Scale River Plume in Sepetiba Bay, SE-Brazil

Coastal river plumes represent one of the final sta ges of material transport across the land-sea inter face. Most studies, however have focused on the behavior of me dium to large sized river plumes of coastal-shelf w aters, whereas small sized river plumes acting within estu aries have been neglected. This study addressed the behavior of suspended particulate matter (SPM), dissolved inorg anic nutrients (DIN, DIP and DSi) and Chlorophyll a (Chl. a) of a small sized river plume derived from the close ly lain Sao Francisco and Guandu river channels, se t in the Sepetiba Bay estuary, SE-Brazil. Two surface water sampling campaigns were conducted, one in January 2 (humid summer conditions) and the other in June 200 3 (dry winter conditions). On both occasions, the p lumes dispersed in a SE direction towards the inner porti on of the bay. The “wet” event plume was more turbi d, nutrient rich and dispersed beyond nearshore waters, whereas the “dry” event plume proliferated as a narrow, le ss turbid and more nutrient poor film alongshore. Both exhibi ted a marked degree of patchiness, induced by the d ifferential input of materials from the river sources and resus pension processes from the shallow nearshore bottom . The Sao Francisco river channel was the main source of fres hwater, SPM and nutrients, except for ammonia (NH 4 + -N) derived from domestic effluents of the Guandu river . The mesohaline portion of the estuarine mixing zo ne of the plumes behaved as a slight source for SPM, DSi and DIP, due to bottom resuspension processes. N:P mo lar ratios ranged between 80:1 and 20:1 along the estuarine gr adient, being higher in the summer than in the win ter event, indicating that DIP was the potential nutrient limi ting primary production. Chl. a concentrations incr eased at the outer premises of the plume, suggesting that the sh ort residence times and turbidity of the plume wate rs, hampered primary production nearshore, particularly during t he summer occasion. The small sized plume lacked th e spatial decoupling between the estuarine mixing and turbidi ty zones, generally observed in larger sized coasta l-shelf plumes.

A satellite view of riverine turbidity plumes on the NE-E Brazilian coastal zone

Turbidity plumes of Sao Francisco, Caravelas, Doce, and Paraiba do Sul river systems, located along the NE/E Brazilian coast, are analyzed for their dispersal patterns of Total Suspended Solids (TSS) concentration using Landsat images and a logarithmic algorithm proposed by Tassan (1987) to convert satellite reflectance values to TSS. The TSS results obtained were compared to in situ collected TSS data. The analysis of the satellite image data set revealed that each river system exhibits a distinct turbidity plume dispersal pattern. The behavior, dimension and degree of turbidity of the Sao Francisco River plume have been greatly altered by the construction of a cascade of hydroelectric dam reservoirs in its hydrological basin. The plume has lost its typical unimodal seasonal pattern of material dispersion and its turbidity has decreased due to the regulation of river flow by the dams and TSS retainance by the reservoirs. In contrast, the Doce and Paraiba do Sul river plumes are still subject to seasonal pulsations and show more turbid conditions than the SF plume, as dams are less numerous, set in the middle river sections and the natural river flow has been maintained. The Caravelas Coastal System river plume is restricted to near shore shallow waters dominated by resuspension processes. During austral spring and summer when NE-E winds prevail, all plumes generally disperse southward. Short-term northward reversals may occur in winter with the passage of atmospheric cold fronts. The Sao Francisco and Doce river plumes tend to disperse obliquely to the coast and transport materials further offshore, while the Caravelas and Paraiba do Sul plumes tend to disperse mainly parallel to the coast, enhancing TSS retention nearshore.

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.

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).