Release of dissolved organic matter during oxic and anoxic decomposition of salt marsh cordgrass

Abstract

Chromophoric dissolved organic matter (CDOM), as the light absorbing fraction of bulk dissolved organic matter (DOM), plays a number of important roles in the global and local biogeochemical cycling of dissolved organic carbon (DOC) and in controlling the optical properties of estuarine and coastal waters. Intertidal areas such as salt marshes can contribute significant amounts of the CDOM that is exported to the ocean, but the processes controlling this CDOM source are not well understood. In this study, we investigate the production of DOM and CDOM from the decomposition of two salt marsh cordgrasses, Spartina patens, a C 4 grass, and Typha latifolia, a C 3 grass, in well-controlled laboratory experiments. During the seven-week incubation period of the salt marsh grasses in oxic and anoxic seawater, changes in dissolved organic carbon (DOC) concentrations, dissolved nitrogen (DN) concentrations, stable carbon isotopic composition of DOC (DOC- δ 13C), and CDOM fluorescence demonstrate a significant contribution of DOC and CDOM to estuarine waters from salt marsh plants, such as Spartina and Typha species. In the natural environment, however, the release processes of CDOM from different cordgrass species could be controlled largely by the in situ oxic and anoxic conditions present during degradation which affects both the production and decomposition of DOC and CDOM, as well as the optical properties of CDOM in estuarine and coastal waters.