B057-03
WHEN ARTIFICIAL CONNECTIONS TO THE SEA DO NOT CONTROL EUTROPHICATION: LESSONS FOR URBAN COASTAL MANAGEMENT FROM THE MARICÁ LAGOON (BRAZILIAN SOUTHEAST)

Thursday, 10 December 2020: 19:08
Virtual
Leonardo Amora Nogueira1, Joseph Smoak2, Rodrigo Coutinho Abuchacra3, Carla Regina Alves Carvalho4, Andre Luiz Carvalho da Silva5, Kevin Campos Martins6, Anderson de Almeida Castro6, Alex Enrich-Prast Dr.7, Christian J Sanders8 and Humberto Marotta Dr.9, (1)Universidade Federal Fluminense, Niteroi, Brazil, (2)University of South Florida, Sain Petersburg, United States, (3)Universidade Estadual do Rio de Janeiro, Geography, São Gonçalo, Brazil, (4)Universidade Federal Fluminense, Geochemistry, Niterói, Brazil, (5)Universidade do Estado do Rio de Janeiro, São Gonçalo, Brazil, (6)Universidade Federal Fluminense, Niterói, Brazil, (7)Change, Linkoping University, Linkoping, Sweden, Department of Environmental, Linkoping, Sweden, Sweden, (8)National Marine Science Centre, School of Environment, Science and Engineering, Southern Cross University, Coffs Harbour, NSW, 2450, Australia, Coffs Harbour, Australia, (9)Universidade Federal de Fluminense, Geography Department, Niteroi - RJ, Brazil
Recorded Presentation
Abstract:
Coastal eutrophication and flood risks are increasingly recognized as global change impacts. Although artificial connections to the sea are frequent interventions used to mitigate nutrient enrichment and water level, long-term data on their effects in coastal lagoons are still scarce. To support urban coastal management, we evaluated the relationships between flood control interventions (i.e., channeling in the catchment or artificial connections to the sea) and land use/cover change directly related to eutrophication in a tropical urban lagoon (Maricá lagoon, Brazilian Southeast). We determined sediment, nutrient, and carbon burial rates over the past 135 years (derived from 210Pb dating) in two sediment cores, relating to historical records and geoinformation data. The enormous increase in the infilling and eutrophication revealed by both sedimentary profiles were linked to deforestation and untreated sewage discharge, as well as anthropogenic interventions in water flow designed to reduce eutrophication in the lagoonal ecosystems. In addition, increases in total sediment and total phosphorus (TP) burial over the entire record indicated sediment focusing and preferential deposition in the central area of the lagoon as compared with the region near the river mouth. Comparing rates pre- and post-intense urbanization (i.e., pre and post-1974), we found the total sediment and TP burial rates increased by 5 and 6 fold, respectively in the central lagoon, while the region near the river mouth increased by 12 and 20 fold, respectively. While drastic shifts were observed early in the sediment record, those shifts were temporary. A persistent increase in nutrient burial had not occurred until the most recent opening of the sandy barrier in 2010. Our centennial geochemical record and historical findings reveal a more comprehensive understanding of lagoonal functioning as lessons for urban coastal management. Therefore, without forest conservation and sewage treatment, artificial connections to the sea could be important management tools to reduce floods, however, they may, in turn, reduce the dilution capacity and limit efforts to control eutrophication.
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