Effects of watershed land use on coastal marine environments: A multiscale exploratory analysis with multiple biogeochemical indicators in fringing coral reefs of Okinawa Island

Sakamaki, Takashi; Morita, Akiko; Touyama, Shouji; Watanabe, Yasushi; Suzuki, Shouhei; Kawai, Takashi

Effects of watershed land use on coastal marine environments: A multiscale exploratory analysis with multiple biogeochemical indicators in fringing coral reefs of Okinawa Island

2022

The analytical spatial scale and selection of biogeochemical indicators affect interpretations of land-use impacts on coastal marine environments. In this study, nine biogeochemical indicators were sampled from 36 locations of coral reefs fringing a subtropical island, and their relationships with watershed land use were assessed by spatial autoregressive models with spatial weight matrixes based on distance thresholds of a few to 30 km. POM-relevant indicators were associated with agricultural and urban lands of watersheds within relatively small ranges (6–14 km), while the concentrations of inorganic nutrients were associated with watersheds within 20 km or more. The macroalgal δ¹⁵N showed a strong relationship with agricultural lands of watersheds within 7 km and urban/forest lands of watersheds within 24 km. These results demonstrate significant effects of land use on the coral reef ecosystems of the island, and the importance of appropriate combinations of analytical scales and biogeochemical indicators.

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