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Mass balance for inorganic nutrients (N and P) in the Iajai-Açu river estuary, SC

ABSTRACT

This work aimed to determine the dissolved inorganic nutrient flows and calculate a budget for N and P in the Itajai-Açu River Estuary, SC, Brazil. Flows were calculated according to the method developed by LOICZ (Land Ocean Interactions in the Coastal Zone), based on the balance of water, salt and N and P in the estuary. Data were collected weekly at seven sampling sites between 2003 and 2004 and the balances were calculated for the lowest and highest period of the river discharge (97 and 228 m3.s-1). The results showed a hydraulic residence time ranging between 12.4 h and 23 h for the surface layer of the system and between 58 h and 65 h for the bottom layer. The estuary was a sink for phosphate, removing 50% of the computed entries and this was attributed to adsorption to suspended particulate material, since the primary productivity is low. The estuary showed no conservative increase of ammonia and nitrite, related to mineralization and nitrification of organic matter, and low variation for nitrate. The sewage was shown to be an important component of the flows, accounting for 28-42% of P inputs and 23-30% of N inputs to the estuary.

Keywords:
Nitrogen; Phosphorus; Water resources; Santa Catarina; Sewage

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