Assessing the influence of sewage outfalls on seagrass meadows using nitrogen isotopes
Matheus F Andrade1, Joel C Creed2, Ana Cecília R de Albergaria-Barbosa3
1Laboratório de Oceanografia Biológica, Departamento de Oceanografia, Instituto de Geociência, Universidade Federal da Bahia, Rua Barão de Jeremoabo, s/n, Campus Universitário de Ondina, Sala 403D.6, Salvador, Bahia CEP: 40170-115, Brazil; Programa de Pós-Graduação em Ecologia: Teoria, Aplicação e Valores, Endereço: Rua Barão de Jeremoabo, 147, Campus de Ondina Salvador, Bahia CEP: 40170-115, Brazil.
Abstract:
Untreated sewage discharged increases the nutrient loads and changes ecosystem functions. It increases the values of the nitrogen isotopic signature (δ15N) of primary producers such as seagrasses. Itaparica Island (Bahia, Brazil) has undergone extensive urbanization over 50 years. Most of the island has no sewage treatment, and a bridge's construction could increase its population ten times. We evaluated the effects of sewage inputs on the δ15N of seagrass (Halodule wrightii) across Itaparica Island in 14 areas of the island with different degrees of urbanization. Average values of δ15N ranged from -3.95 ‰ (±1.04 SD) to 2.73 ‰ (±1.61). The highest human occupation site also has the highest mean value of δ15N, and seagrass shoot density. The significant correlation (p < 0.05) between δ15N values and shoot density may indicate a possible anthropogenic pressure impacting meadow abundance. Despite a positive correlation, increased anthropogenic nutrient supply can support algae growth and harm seagrass ecosystems.
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