The Effect Of Bioturbation Effects On Nitrogen Cycling Processes

Bioturbation effects on sediment properties also impact nitrogen cycling processes. In general, bioturbation increases nitrification activity by increasing the proportion of oxic sediment in which nitrification can occur (Fig.2) (Sayama and Kurihara, 1983, Tuominen et al., 1999, Welsh, 2003, Nielsen et al., 2004). Rates of denitrification also tend to be higher (Gilbert et al., 1995, Ieno et al., 2006) as bioturbation promotes coupled nitrification-denitrification (Kristensen and Blackburn, 1987, Dollhopf et al., 2005). The higher nitrification activity increases nitrate production to fuel denitrification, while burrows increase the oxic-anoxic sediment interface to bring the processes into closer proximity. Also, oscillating oxic and anoxic …show more content…
Denitrification rates can be fourfold higher in the burrows of strong bioturbators, like thalassinidean shrimp, than in unbioturbated sediment (Webb and Eyre, 2004a), but Marenzellaria sp. burrow walls suppress coupled nitrification-denitrification by promoting sulphide production (Bonaglia et al., 2013). Larger individuals also enhance nitrogen cycling processes because larger burrows have greater surface area and solute transport (Bosch et al., 2015). Bioturbation activity therefore alters the rates of sediment nitrogen cycling processes which affects nitrogen species fluxes. The presence of bioturbators tends to increase sediment ammonium release (Webb and Eyre, 2004a, Papaspyrou et al., 2010), with N.virens increasing NH4 efflux by 79% (Kristensen et al., 1985). Increased uptake of nitrate has also been observed in bioturbated sediment (Papaspyrou et al., …show more content…
Generally, nitrifying bacteria are more abundant in burrow walls than in the surrounding anoxic sediment and can be more abundant than the surficial sediment nitrifying community (Satoh et al., 2007)(Laverock et al., 2013). Yet, other research has demonstrated no change in AOB or AOA abundance in the presence or absence of particular macrofauna species (Gilbertson et al., 2012). Instead, variations in nitrification matched variations in the ratio of AOB to AOA abundance. Additionally distinct denitrifying communities have been observed around Nereis diversicolor burrows in hydrocarbon contaminated sediment (Stauffert et al., 2014a), and different temporal variations in denitrifying community structure observed between surface sediment and shrimp burrow walls (Laverock et al., 2014). Generally, there is a strong consensus that microbes are affected by bioturbation, which in turn affects the sediment functions that these microbes mediate. Yet, we lack a complete mechanistic understanding of how this occurs. There is currently limited data analysing precisely how bioturbation affects the activity of microbial functional groups. Additionally, accurate predictions of future sediment nitrogen cycling require an understanding of how microbial