Avaliação do estado trófico aplicando o Índice TRIX no Sistema Lagunar Manguaba (Alagoas/Brasil) acoplado ao uso de geoprocessamento

Abstract

The Manguaba Estuarine-Lagoon System is an area of relevant ecological interest, but has been under several environmental problems due to the high anthropogenic pressure on its contributor basin and surroundings area, causing water pollution and siltation, and accelerating the eutrophication process. The Manguaba Lagoon is located in the central coast of the state of Alagoas, northeastern Brazil. Artificial eutrophication is one of the biggest environmental problem at global level. Several studies were carried out in recent decades aiming to assess the trophic status throughout multiparameter models like the TRIX. The main objective of this study was to evaluate the trophic status of the Manguaba Lagoon using TRIX model, and geoprocessing techniques. The methodology was divided into the following: 1) survey of digital and analog historical data, 2) development of Geographic Information System (GIS), 3) Geoenvironmental assessment, 4) development of information plans, 5) evaluation of physical and chemical parameters, 6) definition of model equation for Manguaba Lagoon System 7) establishment of trophic status using TRIX model. Four campaigns were carried out at 21 monitoring stations to measure in situ environmental parameter and to collect water during dry season (22/02 and 12/03/2013) and rainy season (28/05 and 29/08/2016). The main environmental impact factor playing a major role in the system is the industrial/household untreated effluents input. The salinity of the lagoon is governed by the river discharge patterns which has a direct influence on the TRIX index results, with values ranging between 0.13 and 24.81 ‰. The Manguaba lagoon trophic status was classified as moderate (mesotrophic to eutrophic), varying from moderate to highly productive and highly trophic status. Dissolved inorganic nitrogen (NID) changed between 9.3 and 155.0 μg/l, while the dissolved inorganic phosphorus (PID) varied between 1.5 and 74.8 μg/l, with maximum values found in August 2016, at the stations located at the most upstream sector near the Rio Paraiba do Meio mouth. The NID and PID were the major contributors to the TRIX index. The main anthropic pressure on the Manguaba Lagoon System was the domestic sewage discharge, placing a major threat to the ecosystem.