Anthropogenic nutrient inputs in the NW Iberian Peninsula estuaries determined by nitrogen and carbon isotopic signatures of Zostera noltei seagrass meadows

Abstract

Coastal watersheds of the NW Iberian Peninsula have undergone increases in population densities and urbanization over the past decades. However, the effect of altered nutrient inputs to estuarine Zostera noltei ecosystems associated to these anthropogenic pressures remains largely unknown. Eleven Zostera noltei meadows located in the NW Iberian Peninsula were studied to assess the relationship between the anthropogenic pressure over coastal watersheds and the nitrogen and carbon isotopic signatures of Z. noltei meadows. Anthropogenic pressure on the watersheds was estimated from human population data and land cover classes. Carbon and nitrogen stable isotopic analyses were performed on Z. noltei leaves and in the sediments surrounding the rhizospheres. Our results indicate that the N and C isotopic signatures of Z. noltei meadows from the NW Iberian Peninsula reflect the impact of anthropogenic pressures. Nevertheless, these relationships are complex due to several processes acting simultaneously altering the expected isotopic responses.

Keywords: Eutrophication; Land use; Seagrass; Sediments; Sewage; Stable isotopes.