The regulating ecosystem services, such as water purification, that tidal flats provide by nitrogen (N) burial are being increasingly recognized; yet, quantitative estimates remain limited. Here, we first present nationwide evaluation of total N stocks and burial rates in the Korean tidal flats, based on a 3 year long monitoring assessment combined with remote sensing approach. A total of 20 intertidal flats representing 7 provinces of South Korea were extensively surveyed in 2018-20. The sediment textural type (sand, mixed, and mud) classified from remotely sensed imagery was significantly correlated to that identified from field data (p < 0.01), warranting a nationwide estimate of total N stocks. The estimated total N stocks and burial rates in the tidal flats of Korea were 1.5 Tg N and 8,192 Mg N yr-1, respectively. Total N stocks significantly varied by region, province, morphology, salinity, and land use type adjacent to the corresponding tidal flats. In general, the N stocks of tidal flats were influenced by the degree of terrestrial N inputs to the ocean. The N stocks were significantly correlated with several physical parameters, such as precipitation (p < 0.05) and tide (p < 0.01). Among the sediment properties, the mud content was found to be the key factor determining the total N stocks across the 20 intertidal flats (p < 0.01). Finally, by applying the environmental value for N removal (USD km-2 yr-1) to the tidal flat area (km2), the economic value of the total N removal was estimated as ~233 Million USD yr-1 in Korea and ~15 Billion USD yr-1 globally. Overall, the present work confirms the valuable ecosystem service of tidal flat's cost-efficient N removal capacity, highlighting marine ecosystem service.
Keywords: Intertidal flat; Nitrogen burial rates; Regulating ecosystem services; Remote sensing classification; Total nitrogen stocks.
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