Nutrient retention in the sediments and the submerged aquatic vegetation of the coastal lagoon of the Ria de Aveiro,Portugal |
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| Institution: | 1. IPMA - Instituto Português do Mar e da Atmosfera, Rua Alfredo Magalhães Ramalho, 6, 1495-006 Lisboa, Portugal;2. CQE - Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal;3. C2TN - Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10 (ao km 139,7), 2695-066 Bobadela, Lisboa, Portugal;4. FCUL - Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016, Lisboa, Portugal;1. Bioxeoquímica Mariña, Instituto de Investigacións Mariñas IIM-CSIC, Eduardo Cabello 6, 36208 Vigo, Pontevedra, Spain;2. Instituto Español de Ocenaografía, Centro Oceanográfico de Murcia, Varadero 1, 30740 San Pedro del Pinatar, Murcia, Spain;3. IPMA—Portuguese Institute of Sea and Atmosphere, Av. Brasilia, 1449-006 Lisbon, Portugal;4. CIIMAR, Marine and Environmental Research Center, Rua dos Bragas, 289, 4050-123 Porto, Portugal;1. IPMA - Portuguese Institute for the Sea and Atmosphere, R. Alfredo Magalhães Ramalho, 6, 1495-006 Lisbon, Portugal;2. CIIMAR, Interdisciplinary Centre of Marine and Environmental Research, Terminal de Cruzeiros do Porto de Leixões, Av. General Norton de Matos s/n, 4450-208 Matosinhos, Portugal;1. IPMA, Portuguese Institute of Sea and Atmosphere, Rua Alfredo Magalhães Ramalho, 6, 1495-006 Lisboa, Portugal;2. CIIMAR, Marine and Environmental Research Centre, Rua dos Bragas, 289, 4050-123 Porto, Portugal;3. Instituto de Investigaciones Marinas (CSIC), 36208 Vigo, Spain |
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| Abstract: | A decrease in the areas covered by seagrasses within the Ria de Aveiro, Portugal, has been observed over the past five decades, resulting in a corresponding increase of the areas of uncovered sediment supporting the growth of sparse macroalgae populations only. Presently, several macroalgae (Ulva spp., Gracilaria sp.) and one seagrass species (Nanozostera noltii (Hornem.) Toml. & Posl.) comprise the submerged aquatic vegetation (SAV) adapted to this shallow, high-energy environment, characterised by fast tidal currents and turbid waters and in which large areas of the bed are exposed during low tide. This study shows that there is a strong inter-relation between the SAV and the surface sediment in intertidal areas. The sediment covered by N. noltii was finer (median grain size 95 µm) and had a high percentage of organic matter (mean value 7.6%), compared with the sediment colonised by macroalgae (median grain size 239 µm; mean organic content 3.2%). The concentrations of both total nitrogen and phosphorous were significantly greater (P < 0.001) in surface sediments covered by N. noltii. Thus, sediments within N. noltii appear to act as a large reservoir of N and P by accumulating greater concentrations of fine sediment particles (silt and clay) and organic matter when compared with the coarser sediment covered with macroalgae only. Hence, the reduction in the area covered by seagrasses will likely result in a gradual loss of nutrients and fine sediment from the Ria de Aveiro channels. |
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