SOURCES AND EARLY DIAGENESIS OF LIGNIN AND BULK ORGANIC-MATTER IN THESEDIMENTS OF THE LOWER ST.-LAWRENCE ESTUARY AND THE SAGUENAY FJORD

Elemental and molecular organic matter concentrations were analyzed in sediments from the Lower St. Lawrence Estuary and the Saguenay Fjord in order to evaluate the historic evolution of pulp and paper mills so lid-waste inputs in the system in the last decades and the relative re activities of lignin and bulk organic materials in coastal sediments. A qualitative estimation of vascular plant sources to the Saguenay Fjo rd shows that the sedimentary terrigenous plant material is comprised predominantly of gymnosperm woods. In the deeper sediment horizons of the upper Saguenay basin, low intensive lignin parameters (C/V and S/V ) and high percentages of lignin to total sedimentary organic carbon(> 20%) all indicate elevated concentrations of woody gymnosperm tissues unprecedented in coastal sediments and directly related to the intens e activity of the region's pulp and paper industries. The increased co ntrol on solid organic wastes from industrial effluents into the Sague nay river in the late 1980s to early 1990s is clearly apparent from in creasing intensive parameter values and decreasing lignin fractions to the total sedimentary organic carbon (approximate to 6-8%) in the upp er basin surface sediments, Elemental and molecular analyses of fjord sediments, all indicate that most of the solid-phase discharge of lign ified material by the pulp and paper industry is deposited rapidly clo se to the mouth of the river without reaching the downstream basins. I n the St. Lawrence Estuary, intensive lignin parameters indicate that gymnosperm tissues are a major component of the sedimentary vascular p lant material but with a significant fraction composed of angiosperm a nd nonwoody tissues. These latter types of organic tissues are particu larly important components of terrigenous material in sediments deposi ted prior to the 1910-1920s. Acid/aldehyde ratios in most cores studie d do not indicate clear-cut oxidative degradation of lignin material p rior to its introduction in the aquatic system, The only exceptions ar e the two estuarine cores, where slightly elevated acid/aldehyde ratio s relative to the range for fresh vascular plant tissues, might indica te mild aerobic fungal degradation of the sedimentary lignin material, Organic carbon, total nitrogen, organic phosphorus and lignin derived phenols all exhibited decreasing concentrations with core depth in th e sediments of the Lower St. Lawrence Estuary. First-order degradation rate constants for all four chemical categories ranged between 0.02-0 .05 yr(-1). The order of apparent reactivity among the different organ ic compounds is TN greater than or equal to C-org > P-org > lignin at the head of the Laurentian channel and lignin approximate to TN = C-or g > P-org further downstream. The surprising diagenetic selectivity ob served at the upstream station is probably due to a higher flux of fre sh, labile organic matter that reaches the sediment-water interface an d degrades preferentially to more refractory materials such as lignin. Further downstream, little diagenetic selectivity was observed below the sediment-water interface indicating an overall refractory nature o f the sedimentary organic matter. Finally, the differences in reactivi ty observed between C-org and P-org at both stations contradict earlie r assumptions that no fractionation occurs between organic carbon and phosphorus during anaerobic degradation. (C) 1997 Elsevier Science B.V .