Seagrass stable isotope composition provides seascape-scale tracking of anthropogenic nitrogen inputs in a tropical marine lagoon

摘要: Anthropogenic nutrient loading has led to declines in the function and productivity of some tropical coastal ecosystems. We use the seagrass Thalassia testudinum as a sentinel for tracing nutrient inputs and movements in Ambergris Caye Lagoon, Belize, a region heavily dependent on ecotourism and in the process of expanding its network of marine protected areas. Seagrass samples were collected at stations distributed along a 24-km section of the lagoon, with stations bracketing the urban center of San Pedro. Leaf tissue carbon/nitrogen (C:N) stoichiometry, stable isotope composition (δ13C, δ15N), and epiphyte load (mg cm−2) were analyzed relative to spatial location and proximate land use conditions. Seagrass tissues showed a modal pattern in δ15N composition along the north–south axis of the lagoon, with maximum average values (1.5 ± 1.1 ‰ [SD]), occurring adjacent to or slightly down-current of the …