Avaliação do estado trófico de um sistema estuarino tropical a partir do índice trófico TRIX

Abstract

The estuarine ecosystem is located in the interface continent - ocean, with hydrodynamic, morphological, biological and sedimentary characteristics influenced by freshwater discharge from the drainage basin, and oceanographic processes. The Piraquê–açu and Piraquê–Mirim’s Estuarine System (SEPAPM) (7,48 km2), located in the district of Santa Cruz (Aracruz, ES), is predominantly situated in the valleys of Formação Barreiras. The SEPAPM has great importance, providing many goods and services to the local economy, as well as having a predominantly natural setting with no history of significant dredging and engineering works. Thus, is necessary to investigate it characteristics understanding the ecological processes to contribute to coastal zone management. Therefore, this study aimed to assess the trophic conditions of SEPAPM through environmental variables chlorophyll a, total phosphorus (TP), dissolved inorganic nitrogen (DIN), percentage of oxygen combined into a Trophic State Index (TRIX). Influence of river discharge were considered on TRIX. Samples were taken at 10 sampling stations in the rainy and dry periods of 2012. Point data variables were interpolated in Geographic Information System - GIS using the Spline method. As a result, the trophic condition of SEPAPM show eutrophic trends (TRIX > 6). The SEPAPM showed significant spatial variation of chlorophyll a and salinity in the rainy season and percentage of oxygen and salinity in the dry season; Significant temporal variation of TP, dissolved inorganic nitrogen, oxygen percentage and salinity. There was a negative significant correlation using the Spearman test between chlorophyll a and salinity (dry and rainy), chlorophyll a and flow (dry), TP and salinity (dry), NID and percent oxygen (dry), TRIX and percent oxygen (dry), salinity and flow (dry and rainy) chlorophyll a and oxygen percentage (rainy), TF and NID (rainy) and TRIX and TP (rainy). There was a significant positive correlation for percentage of oxygen and chlorophyll a (dry), TRIX and NID (dry and rainy), oxygen percentage and flow (rainy), salinity and TRIX (rainy) and TP and flow (rainy). This work appears as a management tool for the steering committee of the North Coast Regional Hydrographic Center.