Nutrient budgets in the Piratininga-Itaipu lagoon system (southeastern Brazil): effects of sea-exchange management

Abstract

The Piratininga-Itaipu Lagoon System and its drainage basin, located on the southeastern coast of Brazil, Niterói (RJ), has been the target of an intense process of urbanization over the last four decades. As a result of this process, both the lagoon and the adjacent sea area have shown signs of eutrophication due to the release of large quantities of domestic sewage semi (or not) treated. In an attempt to minimize these effects, in 2008 the government re-established a connection between the Piratininga lagoon and the sea. To evaluate changes and variations in the balance of dissolved inorganic nutrients, before and after interventions, the geochemical model of two stoichiometric mass balance boxes of the "LOICZ Program” (Land-Ocean Interactions in the Coastal Zone) was used. The salt and water balance showed different water residence times in the Piratininga lagoon for the two periods: 2005-2006 (before the opening of the connection between the Piratininga lagoon and the sea) and 2009-2010 (after the opening of the connection with the sea). The first period showed a value about two times higher than that obtained for 2009-2010, τ = 83 and 39 days respectively. The water residence time of the Itaipu lagoon did not show great variations between the two periods (τ = 9 and 8 days). For the period of 2005-2006, before the opening of the connection with the sea, both the lagoons were autotrophic (∆DIP > 0) and nitrogen loss was predominant (∆DIN < 0). The second period (2009-2010) was characterized by changes only in the trophic state of the Piratininga lagoon, which became heterotrophic (∆DIP > 0).

Phosphorus spatial distribution and mass balance in the Itaipu lagoon (Rio de Janeiro, Brazil)

“…Human interventions in the Itaipu lagoon system have caused a strong imbalance in biogeochemical cycles over the past decades. The resulting eutrophication has led to a change from meso-to hypertrophic conditions (Cerda et al 2013), although P loads are not particularly high compared to other eutrophic coastal lagoon systems. Factors related to the spatial distribution of P, the main sources that control the mass balance, and their effects on eutrophication are discussed below.…”

“…A recent assessment, using the LOICZ model (Dupra, et al 2000), has shown that residence time can currently reach three days (Angelini et al, 2021). In the lagoon, two water channels were built to reduce flooding, the Camboatá channel connected to the Piratininga lagoon in the 1940s and the Itaipu channel connected to the sea, which has been permanently open since 1979 (Cerda et al, 2013). Thus, the waters flow from the Piratininga lagoon to the Itaipu lagoon, through which the Itaipu channel reaches the sea.…”

Estado trófico, dinámica de nutrientes y metabolismo neto de una laguna costera subtropical (Golfo de California) receptora de aguas residuales

“…Otras lagunas costeras de esta región árida subtropical (i.e., Guaymas, Lobos) mostraron baja susceptibilidad a la eutrofización debido a sus tasas de renovación del agua < 15 días, las cuales favorecen la dilución de nutrientes y limitan el aumento de la biomasa de fitoplancton (Ruiz-Ruiz et al 2016. Asimismo, diversos estudios han aportado evidencia de que cuerpos de agua costeros con tasas de renovación del agua de varios días son más susceptibles a procesos de eutrofización; por ejemplo, el estuario Támesis, Inglaterra (Devlin et al 2011); el sistema lagunar Piratininga-Itaipu, Brasil (Cerda et al 2013), y el sistema lagunar Chantuto-Panzacola, México (Gómez et al 2014).…”

Spreading Eutrophication and Changing Co2 Fluxes in the Tropical Coastal Ocean: a Few Lessons From Rio De Janeiro

“…The degradation of urban organic matter nearby sewage outlet leads to a rapid degassing of wastewater carbon as CO 2 (as well as CH 4 ; Cotovicz et al, 2016Cotovicz et al, , 2021a, whereas the nitrogen and phosphorus accumulate within the system, being further assimilated by phytoplankton and recycled in waters and sediments (Figure 5). The loss of nitrogen to the atmosphere through denitrification (Souza et al, 2003;Cerda et al, 2013) is apparently much lower than the loss of carbon by aquatic respiration coupled to CO 2 and CH 4 outgassing. Increases in the rate of organic carbon and nutrient burial in sediments have been reported on decadal scales in Guanabara Bay (Carreira et al, 2002) and Itaipu Lagoon (Cerda et al, 2016).…”

“…An abundant literature has described the decadal changes of nutrient and organic carbon fluxes in waters and sediments of coastal ecosystems during eutrophication (e.g. Turner & Rabalais, 1994), including the region of Rio de Janeiro (Souza et al, 2003;Cerda et al, 2013Cerda et al, , 2016Ramos, 2016;Fistarol et al, 2015). In addition, changes in the phytoplankton biomass and the spreading of eutrophication can be inferred from ocean color satellite data, which now allow for a synoptic monitoring of coastal waters Chl a concentration continuouly since 1997 (Groom et al, 2019, and references therein).…”