Nitrogen cycling in sediments with different organic loading

Abstract

Sediment cores from an intertidal marine area were experimentally loaded with different amounts of organic material, in order to investigate regulation of the processes in the nitrogen cycle, and the fate of the inorganic and organic N (NH4+, No3-, DON, and urea) released through mneralization. The particulate orgamc matenal was added in amounts of 30 g dw m-2 (30MIX) and 100 g dw m 2 (100MIX) mixed into the sediment, and as 100 g dw rrr2 (100SURF) to the sediment top layer. Processes and pools were related to unamended controls (CTRL). The cores were incubated with low (0 to 2 pM) N O 3 in the overlymg water, and measurements were made after 1 wk. Total sediment respiration rate measured as 0; uptake and CO; release were 10 and 18 mmol m 2 d l , respectively, in the CTRL, gradually increasmg m the order of treatments (30MIX, IOOMIX, 100SURF) to 62 and 64 mrnol m-' d-' respectively in 100SURF. Higher loading resulted in increasing effluxes of NH4+. DON effluxes were quantitatively significant only from the 100SURF sediment cores. There was an accumulation of dissolved N-species in the sediment amounting to 12 to 28 % of the loading, with most increase where the organic matter was mixed into the sediment. Nitrification and denitrification rates were highest in the moderately loaded sediment (30MIX), followed by control cores and the 100MIX. There was no nitrification or denitrification activity in the 100SURF cores, and NO3" was completely absent in this sediment. Dissimilative N o 3 reduction to NH4+ was insignificant in all treatments. The experiment showed that moderate loading increased N removal through denitrification, while high loading decreased denitrification. The marked differences in the fate of nitrogen, due to organic matter distribution, demonstrated the importance of bioturbation and other physical mixing processes.

Nitrogen fluxes, denitrification and the role of microphytobenthos in microtidal shallow-water sediments:an annual study

“…The lack of major differwater interface (e.g. Sloth et al 1995). Our results sugences in the magnitude of measured rates was somegest that, although sediment type may well determine what unexpected considering the different sediment the major composition of the microalgal community, its type (particle size, porosity, organic matter content, biomass and function are less affected, the range of oxygen penetration; Table 1).…”

Coupled nitrification‐denitrification in autotrophic and heterotrophic estuarine sediments: On the influence of benthic microalgae

“…Sedimentary O 2 consumption is linked to mineralization of organic bound nitrogen and hence to NH generation. Therefore, low O 2 ϩ 4 consumption rates reflect low NH generation and limitation ϩ 4 of nitrification by the availability of electron donors, whereas higher O 2 consumption rates reflect better NH availability ϩ 4 for the nitrifiers (Sloth et al 1995).…”

Eutrophication in shallow coastal bays and lagoons: the role of plants in the coastal filter

“…Trimmer et al (2000) found that both direct denitrification, using nitrate (NO 3 -) supplied from the water column, and denitrification coupled to sedimentary nitrification were low in sediments underlying macroalgal mats. High free sulfide concentrations in organic-rich sediments underlying macroalgal accumulations may inhibit nitrification (Henriksen & Kemp 1988, Sloth et al 1995 and partially account for the low denitrification rates. It appears that the net effect of dense macroalgal mats is to move the zone of denitrification from the sediments up into the oxic-anoxic interface in the mat, but not to influence the rates significantly compared to 'bare' sediments with benthic microalgae (Krause-Jensen et al 1999, Dalsgaard 2003.…”