Study sites were chosen based on the location of marine stations within the JAMBIO network that would allow for ease of access and use of facilities for sampling. In 2020, five marine stations were visited in western Japan from 13 October to 2 November; In 2021, three stations located in northern Japan were visited from 19 July to 4 August; In 2022 stations located on the coast of the Sea of Japan were visited; In September 2022 a station at the entrance of Tokyo was visited and in June 2023 stations at southern island of Okinawa were visited. (See Supplementary Information Figure ) At each station a major river was identified, and samples were taken along a transect from the estuary to the bay and offshore areas. A minimum of three neuston samples and three sediment sample were taken at each marine station.