Temporal and spatial variability of water and sediment composition in the Middle Paraná River system

MAINE, M. A.; HADAD, H. R.; SÁNCHEZ, G.; CAFFARATTI, S.; PEDRO, M. C.

Floodplains: Physical Geography, Ecology and Societal Interactions

NOVA Publishers

Lugar: New York; Año: 2011; p. 79 - 98

The physicochemical and chemical characteristics of water and sediment of representative points of the Middle Paraná River and its floodplain were analysed during a flood peak and its receding stage. Limnological parameters in water, phosphorus (P) forms (Psorb, PFe-Al, PCa, Pres), Fe, Al and Ca concentrations in sediment were evaluated. Data were analysed by principal component analyses (PCA). A downstream increasing pollution gradient was not observed in the studied rivers as determined by PCA. Contrarily, PCA showed downstream SRP (soluble reactive phosphate-phosphorus) and nitrate reduction in the Paraná River main channel suggesting retention in the floodplain. River-borne nutrients sustain a high macrophyte production within floodplain lakes. According to inorganic N to SRP ratios, P is a limiting factor for primary production. Middle Paraná floodplain environments represent a natural buffer system that partially counteracts anthropogenic nutrient loads. Highly significant correlations between sediment Fe or Al and total phosphorus (TP) (p<0.001) and sediment Fe or Al and PFe-Al (p<0.001) were obtained, denoting the significance of this fraction. In this aquatic system, oxygen depletion is uncommon and P bound Fe and Al oxy-hydroxides are not released back into the water column, but remain stored in the sediment of the lakes contributing to the P retention within the floodplain. The development of a man-made lake project has been proposed for the area studied. If the dam is constructed, a vast area will be flooded and a large mineralization of organic matter will be produced with the consequent diminution of dissolved oxygen (DO). As a consequence, P could be released from the PFe-Al sediment fraction causing eutrophication.