Relationships Between Land Use and Terrestrial Organic Matter Transfer to the Baltic Sea Over the Last 500 Years

Abstract

AbstractTerrestrial organic matter (OM) plays a key role in coastal organic carbon burial. However, few studies focus on the relationship between land use in the watershed and the transport of terrestrial OM to coasts from a long‐term perspective. In this study, we compared terrestrial OM deposition between an inlet of the Baltic Sea and an upstream lake within the same watershed over the last 500 years, using lignin biomarkers in the sediments. In combination with pollen‐based quantitative land cover reconstruction, we assessed the impacts of semicentennial‐scale changes in land use on terrestrial OM export. The results indicated that the concentration, composition, and degradation state of the lignin‐derived OM differed substantially between the two sites. The lake received larger amounts of lignin‐derived OM during periods of intensified agriculture, but the coastal site did not. The composition of lignin in the coastal sediment did not directly reflect variations in vegetation cover in the watershed. The reason could be that the OM was settled in the upstream basins. Furthermore, the terrestrial OM that did reach the coastal sediments was modified through degradation during the transport, and only the refractory component was deposited at the coast in a relatively unaltered form.