Carbon and nitrogen cycling in intertidal sediments near Doel, Scheldt Estuary

Abstract

Carbon and nitrogen cycling in intertidal mud flat sediments in the Scheldt Estuary was studied using measurements of carbon dioxide, methane and nitrous oxide emission rates and pore-water profiles of ECO 2 , ammonium and nitrate . A comparison between chamber measured carbon dioxide fluxes and those based on ECO2 pore-water gradients using Fick's First law indicates that apparent diffusion coefficients are 2 to 28 times higher than bulk sediment diffusion coefficients based on molecular diffusion . Seasonal changes in gaseous carbon fluxes or ECO2 pore water concentrations cannot be used directly, or in a simple way, to determine seasonal rates of mineralization, because of marked seasonal changes in pore-water storage and exchange parameters .The annual amount of carbon delivered to the sediment is 42 mol m -2, of which about 42% becomes buried, the remaining being emitted as methane (7%) or carbon dioxide (50%) . Each year about 2 .6 mol N m -2 of particulate nitrogen reaches the sediment ; 1 .1 mol m-2 is buried and 1 .6 mol m-2 is mineralized to ammonium . Only 0 .42 mol m-2 yr1 of the ammonium produced escapes from the sediments, the remaining being first nitrified (1 .2 mol m -2 yr-1 ) and then denitrified (1 .7 mol m' 2 yr 1). Simple calculations indicate that intertidal sediments may account for about 14% and 30% of the total estuarine retention of nitrogen and carbon, respectively .

Vertical Distribution of Denitrification in an Estuarine Sediment: Integrating Sediment Flowthrough Reactor Experiments and Microprofiling via Reactive Transport Modeling

“…The integrated N 2 O production rates determined in the acetylene block core incubations, the direct nitrate flux determinations, and the reactive transport modeling results all point to the high capacity for nitrate removal by the intertidal estuarine sediments in the upper Scheldt Estuary (21). High rates of benthic denitrification supported by nitrate uptake from the water column, similar to those at Appels (37 to 60 nmol N cm Ϫ2 h Ϫ1 ), have been reported for nitrate-rich streams (ϳ120 nmol N cm Ϫ2 h Ϫ1 ) (7) and eutrophic estuaries in Denmark (40 to 140 nmol N cm Ϫ2 h Ϫ1 ) (4,20).…”

“…The excess denitrifying capacity also implies that there is efficient utilization by the denitrifying community of nitrate produced by nitrification. In the mid-Scheldt Estuary downstream from Appels, up to 85% of total denitrification in intertidal sediments may be coupled to nitrification (21). The ability to rapidly respond to changes in the NO 3 Ϫ concentration should be a useful adaptation in intertidal estuarine sediments where the pore water composition and redox state can vary substantially on short time scales due to tidal flooding and irrigation by benthic infauna.…”

Transport and degradation of a dinoflagellate bloom in permeable sublittoral sediment

“…In coastal sediments, average Q 10 values of 3 are typically observed (e.g. Middelburg et al 1995, andMoodley et al 2005 reported that the Q 10 of freshly added algal material was 5). Therefore, it is conceivable that our reaction constants measured at 8°C would increase to ~23-29 yr -1 (assuming a Q 10 of 3) or possibly higher at 18°C.…”

Carbon and nitrogen cycling on intertidal mudflats of a temperate Australian estuary. II. Nitrogen cycling

“…As such, mudflats may act as both sources and sinks of dissolved inorganic nitrogen. Recently, much attention has been focused on the role of intertidal sediments in attenuating high inorganic nitrogen loads from the land to the sea in temperate European estuaries (Middelburg et al 1995b, Ogilvie et al 1997, Trimmer et al 1998, Cabrita & Brotas 2000, Dong et al 2000, Trimmer et al 2000, Magalhães et al 2002.…”