Modeling lugworm irrigation behavior effects on sediment nitrogen cycling

Abstract

Benthic infauna in marine sediments have well-documented effects on biogeochemical cycling, from individual to ecosystem scales, including stimulation of nitrification and nitrogen removal via denitrification. However, the effects of burrowing depth and irrigation patterns on nitrogen cycling have not been as well described. Here we examined the effects of lugworm behavior on sediment nitrogen cycling using a reaction-transport model parameterized with literature and laboratory data. Feeding pocket depth and pumping characteristics (flow rate and pattern) were varied, and rates of nitrification, denitrification, and benthic exchange fluxes were computed. As expected, more intense burrow irrigation stimulated denitrification and coupled nitrification−denitrification. At high pumping rates and low sediment oxygen consumption rates (~10 −6 mol m −3 s −1 ), simulation results showed a decrease in rates of nitrification and denitrification with decreasing burrow depth due to incomplete consumption of injected oxidants. Model results also suggest that discontinuous irrigation leads to temporal variability in sediment nitrogen cycling, but that the time-averaged rates do not depend on the irrigation pattern. We identify (1) the poorly constrained chemical composition of lumen fluid injected into sediments and (2) the response of microbial activity/distribution to oscillating redox conditions as critical knowledge gaps affecting estimates of sediment nitrogen removal.

Differential impact of two major polychaete guilds on microbial communities in marine sediments: a microcosm study

“…The modelled bioirrigation coefficient of 0.3-0.8 d -1 corresponds to a turnover time of 1.3-3.3 days for the entire sediment porewater in AP aquaria, and equals pumping rates of 35-93 ml individual -1 h -1 . These rates are in the range of reported pumping rates for AP and its close relative Arenicola marina based on laboratory studies (15-100 ml h -1 ; Riisgård, et al, 1996;Kristensen, 2001;Timmermann et al, 2006;Volkenborn et al, 2010;Dornhoffer et al, 2015) and field studies (Deng et al, 2022). Compared to controls, AP increases the consumption of oxygen 4to 10-fold and nitrate 8-to 20-fold.…”

The effect of redox conditions and bioirrigation on nitrogen isotope fractionation in marine sediments

“…The method described in Dornhoffer et al (2015) was used to simulate fluid flow. In short, flow velocities were calculated using the Navier-Stokes and Darcy-Brinkman equations (Le Bars and Worster, 2006), accounting for pressure forces and shear stress in the momentum balance.…”

Worldwide measurements of bioturbation intensity, ventilation rate, and the mixing depth of marine sediments

“…As sediment particle reworking often consists of a series of small particle displacement events, standard practice has been to treat the resulting vertical profile of mixing in an analogous way to that of diffusive heat transport, calculating a biodiffusion coefficient (Db, cm 2 year −1 ) that describes the rate at which the variance of the location of a particle tracer changes over time within the sediment profile 25 . Similarly, as the active transfer of fluid by infaunal organisms may be orders of magnitude greater (volumetrically) than particle reworking 26 , the non-diffusive exchange of pore-water solutes with over-lying water is routinely examined 27 , but these data have not previously been collated in an accessible archive. The combined effect of particulate and fluid transport on sediment biogeochemical processes is reflected in the vertical colour transition (from brown to olive green/black) of the sediment profile 28 , dictated by the transition from iron (oxyhydr)oxides at the surface to black sulphidic phases at depth 29 that correlate with a variety of environmental drivers 30 .…”