The influence of macrofaunal burrow spacing and diffusive scaling on sedimentary nitrification and denitrification: An experimental simulation and model approach

Abstract

The influence of burrow spacing on sedimentary nitrification and denitrification was simulated experimentally using sediment plugs of different thicknesses immersed in aerated seawater reservoirs. Different plug thicknesses mimic different distances between oxygenated burrow centers and produce similar changes in aerobic-anaerobic reaction balances as a function of diffusive transport scaling. The thicknesses used were roughly equivalent to transport scales (interburrow spacing) that could be produced by burrow abundances of ϳ400 to 50,000 m Ϫ2 , depending on burrow lumen radii (e.g., 0.05-1 cm). Following the exposure of anoxic sediment plugs to aerated water, an efficient aerobic nitrification zone was established within the first ϳ2-3 millimeters of sediment. At pseudo-steady state, the thinnest plug (2 mm) simulating highest burrow density, was entirely oxic and the denitrification rate nil. Denitrification was stimulated in anoxic regions of the thicker plugs (5, 10, and 20 mm) compared to the initial value in experimental sediment. Maximum nitrification rates and the highest denitrification/nitrification ratio between oxic nitrification and adjacent denitrification zones occurred for the intermediate plug thickness of 5 mm. Of the oxic/anoxic composites, the thickest plug showed the least efficient coupling between nitrification/denitrification zones (lowest denitrification/nitrification ratio). Both the thickness of the oxic layer and the total net remineralization of dissolved inorganic N varied inversely with plug thickness. A set of diffusionreaction models was formulated assuming a range of possible nitrification kinetic functions. All model forms predicted optimal nitrification-denitrification and ammonification-denitrification coupling with relative oxic-anoxic zonation scales comparable to intermediate plug thicknesses (5-6 mm). However, none of the commonly assumed kinetic forms for nitrification could produce the observed NO 3 Ϫ profiles in detail, implying that natural sediment populations of nitrifiers may be less sensitive to O 2 than laboratory strains. Our experimental and model results clearly show that rates of N remineralization and the balance between stimulation/inhibition of denitrification are highly dependent on sedimentary biogenic structure and the particular geometries of irrigated burrow distributions.

Denitrification in sediments as a major nitrogen sink in the Baltic Sea: an extrapolation using sediment characteristics

“…Furthermore, bioturbation is known to enhance denitrification (Pelegri et al, 1994;Gilbert et al, 2003). This issue has not been addressed, while theoretically, due to reduction of organism size with decreasing salinity, sediments further north-east in the Baltic would not bear the same potential for bioturbation-enhanced benthic denitrification as similar sediments located below saltier water in the west.…”

The role of organisms in hyporheic processes: gaps in current knowledge, needs for future research and applications

“…For example, bioturbation by aquatic invertebrates is known to modify microbial activities in fine sediments (Mermillod-Blondin et al, 2005Nogaro et al, 2007), but its consequences on microbial biofilm growing on coarse river sediment is still poorly documented and its influence on microbial diversity remains unknown. Similarly, some marine researches have demonstrated the influence of invertebrates on microbial activity and diversity via sediment reworking, grazing and bioirrigation (Aller, 1994;Gilbert et al, 1998Gilbert et al, , 2003Lo´pez-Garcı´a et al, 2002), but their role in the hyporheic zone is completely unexplored. Finally, the influence of disturbances on microbial assemblages is beginning to be understood in marine systems (Thompson et al, 2005;Atalah et al, 2007), wetlands (Ryder, 2009), and rivers (Burns and Ryder, 2001;Fischer et al, 2003), but remains understudied in the hyporheic zone.…”

Biodiversity of benthic microbial communities in bioturbated coastal sediments is controlled by geochemical microniches

“…The burrowing, ventilation and foraging activity of benthic macrofauna organisms affects key ecosystem processes of marine sediments, including organic matter remineralization, nutrient cycling, biogeochemical interactions and benthic-pelagic fluxes (Rhoads, 1974;Aller, 1982Aller, , 1988Aller, , 1994Kristensen et al, 1991Kristensen et al, , 2000Gilbert et al, 1998Gilbert et al, , 2003Banta et al, 1999). Microbial abundances and activities have been shown to increase due to the complex biogeochemical interactions induced by bioturbation activity (Hansen and Kristensen, 1998;Lohrer et al, 2004;Kogure and Wada, 2005).…”