PNNL

Abstract

There exists a substantial amount of research on abiotic (e.g. photochemical) degradation pertaining to OM in the marine realm. While recent research has shown its importance in the degradation of terrestrial particulate organic matter (TPOM), the mechanisms involved in the induction of autoxidation in estuaries remain unclear. In this study, we propose for the first time the involvement of lipoxygenase (LOX) activity in the induction of autoxidation in mixed waters. The observation of unusual profiles of palmitoleic acid oxidation products and the presence of jasmonic acid in suspended particulate matter (SPM) collected close to the Rhône River as well as in samples from the Mackenzie and Amazon rivers is attributed to strong LOX activity. We show the role played by salinity in the induction of this LOX activity and provide an explanation for the differences in estuarine autoxidation levels. At high latitudes, lower temperatures and irradiances favor photooxidative damage to higher plant debris and, consequently, hydroperoxide production. High hydroperoxide contents strongly contribute to LOX activation in mixed waters. The high resulting LOX activity enhances alkoxyl radical production and thus autoxidation. On the contrary, at low latitudes, photooxidative effects are limited, while riverine autoxidation is favored. The higher hydroperoxide content of TPOM may, as a consequence, thereby also contribute to a high level of LOX activity and autoxidation in estuaries. In temperate zones, land and riverine photooxidative and autoxidative damage is limited, unlike estuaries where we observe significant LOX-induced and autoxidative damage.