Terrigenous dissolved organic matter along an estuarine gradient and its ̄ux to the coastal ocean

The contribution of terrigenous organic matter (TOM) to high molecular weight dissolved and particulate organic matter (POM) was examined along the salinity gradient of the Delaware Estuary. Dissolved organic matter (DOM) was fractionated by ultra®ltration into 1±30 kDa (HDOM) and 30 kDa±0.2 mm (VHDOM) nominal molecular weight fractions. Thermochemolysis with tetramethylammonium hydroxide (TMAH) was used to release and quantify lipids and lignin phenols. Stable carbon isotopes, fatty acids and lignin content indicated shifts in sources with terrigenous material in the river and turbid region and a predominantly algal/planktonic signal in the lower estuary and coastal ocean. Thermochemolysis with TMAH released signi®cant amounts of short chain fatty acids (C9±C13), not seen by traditional alkaline hydrolysis, which appear to be associated with the macromolecular matrix. Lignin phenol distributions in HDOM, VHDOM and particles followed predicted sources with higher concentrations in the river and turbid region of the estuary and lower concentrations in the coastal ocean. TOM comprised 12% of HDOM within the coastal ocean and up to 73% of HDOM within the turbid region of the estuary. In the coastal ocean, TOM from high molecular weight DOM comprised 4% of total DOC. The annual ̄ux of TOM from the Delaware Estuary to the coastal ocean was estimated at 2.0 10 g OC yearÿ1 and suggests that temperate estuaries such as Delaware Bay can be signi®cant sources of TOM on a regional scale. # 2000 Elsevier Science Ltd. All rights reserved.