Effect of tidal resuspension with oyster biodeposits on nutrient and oxygen dynamics

To test the effect of biodeposit resuspension on nutrient and oxygen dynamics, we performed a 30 d experiment in three 1000 l shear turbulence resuspension mesocosm (STURM) tanks (R) and three 1000 l non-resuspension (NR) tanks. All tanks contained defaunated muddy sediment and brackish estuarine water, received daily additions of oyster biodeposits, and had similar water column root mean square turbulent velocities (similar to 1 cm s(-1)), energy dissipation rates (similar to 0.08 cm(2) s(-3)), and tidal cycles (4 h mixing-on; 2 h mixing-off). While bottom shear stress was low in NR tanks, high instantaneous bottom shear produced sediment and biodeposit resuspension in R tanks during the mixing-on cycles. Resuspension and biodeposit addition resulted in complex nutrient and oxygen dynamics in the water column as well as altered seabed fluxes. Modeled biodeposit diagenesis demonstrated that added resuspended biodeposit nitrogen in R tanks was nitrified, resulting in high water column nitrate and nitrite concentrations, as well as increasing water column dissolved oxygen demand. Water column dissolved oxygen concentrations were 2.3 times lower in the R tanks than in the NR tanks, whereas deposited organic matter from biodeposits resulted in sediment dissolved oxygen uptake 3 times higher in NR versus R tanks. Sediment dissolved inorganic nitrogen uptake in NR tanks and efflux in R tanks, respectively, were mediated by microphytobenthos abundance and biodeposit deposition. Seabed and water column biogeochemical processes, as mediated by biodeposit resuspension, controlled the nutrient and oxygen balances. Biodeposit resuspension is important when evaluating oysters as support for eutrophication control.

Automated summary

In this 30-day experiment, we investigated the effect of biodeposit resuspension on nutrient and oxygen dynamics. By comparing tanks with resuspension and tanks without resuspension, we found that resuspended biodeposits resulted in higher nitrate and nitrite concentrations in the water column, as well as increased dissolved oxygen demand. Water column dissolved oxygen concentrations were lower in tanks with resuspension, while sediment dissolved oxygen uptake was higher in tanks without resuspension. Overall, biodeposit resuspension plays a significant role in controlling nutrient and oxygen balances in the water column and seabed.