Terrestrial Nutrients and Dissolved Organic Matter Input to the Coral Reef Ecosystem via Submarine Springs

Submarine groundwater discharge (SGD)
transports terrestrial nutrients
and dissolved organic matter (DOM) to the ocean. An elevated concentration
of nutrients and DOM can act as stressors enhancing coral disease
and mortality, but only a few studies address the impacts of groundwater-borne
nutrients and DOM on coral reef ecosystems. This study quantifies
and characterizes nutrients, nitrate (NO3–) stable isotopes, and DOM molecular composition of coastal groundwater
discharging to the reef ecosystem via submarine springs in Lombok,
Indonesia. NO3– isotopic values point
to both natural (soil) and anthropogenic (wastewater and fertilizer)
origins of nutrients in the coastal aquifer. Submarine springs are
fed by different groundwater sources and deliver land-based NO3–, dissolved silica, phosphate, and labile
DOM to the reef water column. Terrestrial nutrients and DOM undergo
rapid turnover in the reef water column due to biogeochemical processes
and biological uptake. Meanwhile, reef and offshore water likely act
as sources of more stable, reworked DOM formulas and its mineralization
product, ammonium. We observed that submarine springs consistently
deliver similar nutrient loadings, creating a long-term environmental
threat to coral reef sustainability. This study emphasizes the importance
of understanding coastal biogeochemistry and hydrological processes
in sensitive tropical ecosystems, particularly those adjacent to modified
land-use watersheds.