Biogeochemistry of Nutrients and Trace Metals in the Estuarine Region of the Patos Lagoon (Brazil)

The major aim of this research was to assess processes occurring in the low (0-5) salinity region and the role of biological processes (i.e. uptake and remineralization in the transport and fate of trace metals in a coastal lagoonal system. The characteristics of Patos Lagoon which provide sufficient resolution to evaluate these processes are the long residence time/slow mixing rate of the system and the high utilization of the riverine supply of nutrients within the system. Samples were collected from approximately 24 stations over an approximately 80 nautical mile transect through the estuarine region of the Patos Lagoon over the two day period, 14-15 December 1995. Based on the results, Patos Lagoon can be divided into three zones within each of which certain processes dominate the fate and transfer of materials. In the first zone (salinity zero toc. 5-7) nutrient and particle removal, as fresh water mixes with seawater, are the dominant features and reflect high primary production, flocculation and particle scavenging. The second zone (up to salinityc. 25-27) is characterized by rapidly increasing salinity with distance along the transect. Within this region, nutrient regeneration suggests that organic matter remineralization is a dominant process and that metal release, in association with this process, may account for metal distributions in this region. However, other processes, such as mobilization from bottom sediment, may also explain these observations. The third zone (salinities greater thanc. 27) is dominated by conservative mixing.