Historical and geographical variations of sources and transport of terrigenous organic matter within a large-scale coastal environment

Elemental and molecular analyses indicate that the sources and inputs of te rrigenous organic matter (OM) to the upper St. Lawrence system have been in fluenced by increased discharges of industrial solid organic wastes from th e pulp and paper industry following its expansion in the 1920-1940's. Moder ately altered lignin-rich particles from a combination of natural and anthr opogenic sources predominate within recent sediments of this system, with a nthropogenic fractions ranging 10-70% and 2-30% for the Fjord and the Lower Estuary, respectively. Compositional and isotopic signatures of sedimentar y OM show that the sediments within the Lower Estuary are dominated by inpu ts of allochthonous OM (60-80%), whereas terrigenous OM inputs are minor (1 5-30%) sources of OM to the Gulf/Shelf sediments. In this latter environmen t, the terrigenous OM pool is composed exclusively of highly altered lignin -poor soil OM with no substantial influence from anthropogenic lignin. A gl obal mass balance calculation suggests that about half of the global annual riverine flux is degraded, leaving only the remaining half to accumulate p redominantly (98%) within shelf and slope sediments. This estimate suggests that lignin does not behave conservatively within the marine environment b ut supports some sort of organic matter degradation. (C) 1999 Elsevier Scie nce Ltd. All rights reserved.