Aplicação do índice de TRIX e O'Boyle em estuários amazônicos

Abstract

The Brazilian Amazonian coastal zone represents approximately 35% of the country's coast, extending for more than 2500 km, From the mouth of the Oiapoque River, in Amapá, until the Bay of São Marcus, in Maranhão, in this region is the largest estuarine area of the world, located on the continental shelf of the Amazonas (CSA) In addition to numerous estuaries such as the Furo of Muriá – FM in Curuçá and the Furo of Laura – FL in Vigia that comprise the local landscape and favor the primary productivity as rich in nutrients considered essential, such as nitrogen, phosphorus and silicon. For the evaluation of this process are required studies involving the assessment of the trophic state of the estuarine and marine environments. This segment this work has as objective to use the index trophic (TRIX) and O’Boyle to determine the trophic state in the area of CSA and we in order to compare the results and relate them with the fluvial discharge in the area of SCA and the seasonality of furos. In CSA the collection was performed aboard the ship ANTARES between the Orange Cable/ AP and the mouth of the river Pará/PA. The data were obtained in the campaign America III in the period from 28 May to 13 June 1999 of maximum discharge of the Amazon River and North IV where he was the smallest discharge the Amazon River between 11 July and 10 September 2001. In the course of the collection of water were distributed along 11 profiles, totaling 41 stations. The FL is located in the village of Vigia, distant 93 km from Belém. The samples were collected during the period of higher rainfall and lower precipitation totaling 6 months of collection in the flood and ebb tide totaling 8 samples per campaign in the year of 2011 and 2012. The FM It is located in the municipality of Curuçá, 140 km from the capital Belém. Water samplings were performed in 21 points distributed along the hole during 9 months covering the dry season and rainy and flood and ebb tide totaling 42 samples per campaign in the year 2015. In the three estuaries collected were obtained from the data of temperature, salinity, pH, dissolved oxygen, dissolved oxygen saturation in situ later in the laboratory samples were filtered for the analyzes of nitrite, nitrate, ammonia, phosphate and chlorophyll a content to fit the indexes TRIX and O’Boyle. For the TRIX the highest values were found in the FL and CSA and lower values were in FM. For the index of O’Boyle, the greatest value was in FL and FM and lower in CSA. To compare the index of O'Boyle with the TRIX it was possible to observe that the classification was similar for both indexes only in SCA in the period of maximum discharge of the Amazon River (eutrófizado) and varied a bit at the minimum discharge (potentially to eutrófizado O'Boyle and eutrófizado for TRIX). This difference can be explained by the additional variables in the TRIX, as for example, the nutrients and chlorophyll a. For the holes in the scenario was totally different, where it is evident that the TRIX obtained greater variation due present in its composition the dissolved inorganic nutrients (DIN and DIP) and to be calculated punctually oscillating differently for each hole. While the index of O'Boyle is calculated with the use of percentiles of 5 and 95% with this by removing outliers. However, the index of O'Boyle has the advantage of not having the need of so many variables for application, but in environments that occur high variations of the components that make up the index tend to have high values, which was observed in this study. Both indices can be applied to explain in a simple and direct the conditions of eutrophication of estuarine areas so that the joint approach and MMS extension of indices brings additional information about the dynamics of the studied environments through its degree of trophic.