Distribution patterns of nutrients and symptoms of eutrophication in the Rio de la Plata River Estuary System

• Published in: Hydrobiologia Vol. 475; no. 1; p. 125
• Main Authors: Nagy, Gj, Gómez-erache, M, López, Ch, Perdomo, Ac
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Nature B.V 01.05.2002
• Subjects: Biological stress; Brackish; Chlorophyll; El Nino; Estuaries; Eutrophic environments; Eutrophication; Hypoxia; Nitrogen; Nutrient concentrations; Nutrient dynamics; Nutrient loading; Organic matter; Oxygen; Particulate matter; Phytoplankton; Rivers; Tidal rivers; Water inflow
• ISSN: 0018-8158; 1573-5117
• DOI: 10.1023/A:1020300906000

In this paper we discuss nutrient dynamics and the effects of eutrophication in the Rio de la Plata River Estuary System since 1980. The tidal river was characterized by high suspended particulate matter (SPM), nutrients, and N:P ratio (>25), moderate chlorophyll a values, an inverse relationship between SPM and phosphate, and cianobacteria blooms. Seaward of the salinity front, where both SPM and nutrient concentrations are lower and chlorophyll a values greater, the net ecosystem metabolism is positive. Permanent stratification controls nutrient, organic matter and oxygen dynamics leading to biological stress and hypoxia below the halocline. Non conservative behavior of nitrogen in the estuary leads to a low N:P ratio (<3) because of both phytoplankton assimilation of nitrogen and denitrification, and benthic flux of phosphate. Periodic nuisance and toxic blooms occur at high salinities along the Uruguayan coast (Canal Oriental). Over the recent decades, changes in freshwater inflow, point and non-point nutrient load, and stratification, triggered by ENSO events, seem to have controlled the ecosystem metabolism, nutrient-oxygen dynamics, and the development of harmful blooms. The assessment of the regional and overall ranking of eutrophic conditions determines that the system is moderately eutrophied. Nevertheless, increasing trends in quantity of freshwater and nutrient loads, and the low potential to dilute and flush nutrients, suggest that the Rio de la Plata, in particular the Canal Oriental is prone to worsening eutrophication conditions like oxygen stress and harmful blooms.[PUBLICATION ABSTRACT]