Fluxes and reactivities of organic matter in a coastal marine bay

Abstract

Vertical fluxes of bulk particulate material, organic carbon, nitrogen, lignin-derived phenols, and neutral sugars through the water column and into surface sediments of Dabob Bay, Washington, were determined monthly for 1 yr by sediment trap deployments at 30, 60, and 90 m at a site 110 m deep. Vertical fluxes of sinking bulk particulate material in this marine bay were elevated during winter and increased in consistent proportion to sediment trap deployment depth throughout the year. Although annual average particle fluxes at 30 and 60 m bracketed the mean accumulation rate of the underlying sediment, the flux at 90 m was higher by a factor of 2 due to resuspension, horizontal advection, or both.The monthly fluxes of lignin-derived phenols paralleled those of total particulate material, indicating a common riverine origin. The annual average fluxes of vanillyl and cinnamyl phenols through the water column closely matched the corresponding accumulation rates in the underlying sediment, whereas about a third of the total syringyl phenol input was degraded at the watersediment interface. Although p-hydroxyacetophenone exhibited a stability typical of lignin-derived phenols, the distinctly higher reactivities (> 60% degradation) ofp-hydroxybenzaldehyde and p-hydroxybenzoic acid indicate a predominantly nonlignin source.On average, 60 and 70%, respectively, of the total particulate organic carbon and nitrogen and 65-75% of all neutral sugars settling through the midwater column were degraded at the watersediment interface. The elemental and carbohydrate composition of the degraded material was similar to that of local net plankton except for higher percentages of glucose and total neutral sugars. Land-derived organic material accounted for about one-third of the total organic carbon passing through the midwater column and two-thirds of the organic carbon accumulating in the underlying sediments. The amounts of plankton-derived organic matter sinking through the midwater column and being preserved in the sediments below corresponded to 14 and 3% of the annual mean primary productivity. Plankton-derived organic matter exhibited about 5 times the reactivity of local land-derived organic matter at the water-sediment interface of Dabob Bay and supported essentially all of the benthic respiration.

Increases in terrestrially derived carbon stimulate organic carbon processing and CO2 emissions in boreal aquatic ecosystems

“…It has long been recognized that terrestrial DOC is susceptible to photochemical degradation in the water 23 , but it has traditionally been assumed that this DOC is generally recalcitrant to biological degradation [24][25][26] , and therefore that the contribution of this latter pathway to aquatic CO 2 production is modest. This view is rapidly changing 24,25 , and a growing volume of evidence indicates that terrestrial DOC may be readily degraded by biological processes in aquatic environments, such as the Amazon basin 27 and the Arctic 8,28 , temperate 29,30 and boreal 31,32 biomes.…”

Compositional heterogeneity within oceanic POM : a study using flow cytometry and mass spectrometry

“…For organic matter within a particular size class (e.g., sediment trap samples or ultrafiltered dissolved organic matter (UDOM), this view appears correct and has yielded valuable insights into the relative lability of different compound classes (e.g., Wakeham et al, 1984;Hedges et al, 1988;. However, this view begins to change when one looks across the spectrum of organic matter size classes at a particular depth, as shown by .…”

“…Fluxes within compound classes have also been determined (e.g., for aldoses, Hernes et al, 1996; for lignin-derived phenols and for neutral sugars, Hedges et al, 1988; for lipids, continuum" models (Middelburg, 1989;and Boudreau and Ruddick, 1991). In addition to the monitoring of bulk organic matter degradation, laboratory degradation studies have also monitored the preferential degradation of various compound classes.…”

“…Depth has been considered a proxy for extent of diagenesis, allowing the effects of diagenesis to be monitored by sediment trap deployments and/or filtration of particles at different depths (e.g., Wakeham et al, 1984;Hedges et al, 1988;Wakeham and Canuel, 1988; Wakeham and Lee, 1993;Hernes et al, 1996;. Such work has led to a general measure of the reactivity of different components of POM.…”

“…Vertical profiles of organic matter composition and flux have been used to obtain estimates of diagenetic reactivity (e.g., Wakeham et al, 1984;Hedges et al,1988;. Laboratory degradation experiments using phytoplankton cultures and various combinations of bacteria and heterotrophs have been used to monitor remineralization of organic matter (Westrich and Berner, 1984), the conversion of phytoplankton organic material into bacterial and/or grazer biomass (e.g., Harvey et al, 1987;Harvey and Macko, 1997) and the chemical composition of the remaining "detritus."…”