High-resolution multivariate analysis of the hydrochemical signature of water corridors in the upper Rio de la Plata estuary, Argentina

Major world river-estuaries integrate the hydrochemical characteristics of the basin with specific signatures which are maintained until complete mixing or discharge to the sea. The chemical signature of distinct water masses and the anthropogenic impact in the Upper Rio de la Plata estuary (RLP) were evaluated by high -resolution continuous monitoring (i.e. every 200 m) of conductivity, turbidity, pH, temperature, chlorophyll a and coloured dissolved organic matter (CDOM), discrete analysis of suspended particulate matter (SPM) grain size composition combined with multivariate analysis (K-means clustering, Principal Component Analysis). The characteristic signatures of main RLP tributaries such as the Paran ' a River, yielding higher conductivity, CDOM, turbidity and coarser SPM, and the Uruguay River, with clearer, more eutrophic waters enriched in very fine SPM, were maintained 60 km seaward from the estuary head. Across the river, three water corridors with distinct signatures and variable widths (3-20 km) were identified reflecting the transition from Paran ' a to Uruguay River waters. Multivariate techniques also allowed the identification of a polluted coastal corridor (higher conductivity and CDOM and lower turbidity) impacted by wastewater discharges from the metropolitan Buenos Aires and La Plata cities extending 100 km seaward. The combined strategy of high-resolution monitoring, discrete sampling and multivariate techniques was a useful tool to identify water masses, corridors of flow and anthropogenic sources in a heavily urbanized estuary.

Automated summary

The hydrochemical characteristics of the Upper Rio de la Plata estuary were studied using high-resolution continuous monitoring and multivariate analysis. Distinct signatures of the main tributaries and anthropogenic impact were identified and maintained up to 60 km from the estuary head. A polluted coastal corridor affected by wastewater discharges from urban areas was also identified. The combined strategy of monitoring, sampling, and multivariate analysis proved to be a useful tool for studying heavily urbanized estuaries.