NITROGEN, PHOSPHORUS AND SESTON TRANSPORT BY THREE PRE-AMAZONIAN RIVERS, MARANHÃO STATE, BRAZIL
Keywords:
load, flux, river, seston, nutrientAbstract
The watershed of the Pindaré, Mearim and Itapecuru rivers is located in Maranhão State, encompassing more than 50 % of its area. The objective of this work is preliminary to determine the seston and total nitrogen and total phosphorus contents transported by these rivers. For each river samples of the superficial water with three units where taken at three-month intervals (November/1996 to August/1998). The rivers presented similar seasonal variations of temperature (29.0 to 32.7o C). The dissolved oxygen ranged from 0.78 to 8.35mg/l. The highest electric conductivity was verified in the Pindaré River (153 to 410mS/cm) and the smallest ones in the Itapecuru River (40 to 90mS/cm). The pH ranged from 6.1 to 7.6. The load ranged from 346.07 to 528.38ton/day (seston), 2.43 to 3.64ton/day (total nitrogen), 393.71 to 623.71kg/day (total phosphorus). The fluxes ranged from 2.27 to 6.52 ton/km2/year (seston), 17.78 to 45.04kg/km2/year (total nitrogen), 2.89 to 6.35kg/km2/year (total phosphorus). The data suggest that separately the Pindaré River is the one which contributes more with seston and total nitrogen and phosphorus to the São Marcos and São José Bays. The Mearim River, after receiving the waters of the Pindaré River, transports about 3 times more seston, total nitrogen and total phosphorus than the river Itapecuru.
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