Effect of tidal resuspension on benthic–pelagic coupling in an experimental ecosystem study
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Porter ET, Mason RP, Sanford LP
Marine Ecology Progress Series
Tidal resuspension, Benthic–pelagic coupling, Shear stress, Shear velocity, STURM, mesocosm, 1 m3, Maryland, USA, Ecosystem
To test the effect of sediment resuspension on the nutrient and ecosystem dynamics weperformed a 4 wk experiment in three 1000 l shear-turbulence-resuspension-mesocosm (STURM)resuspension (R) tanks and three 1000 l non-resuspension (NR) tanks. All tanks contained defaunatedmuddy sediment and brackish estuarine water and had similar water-column turbulence intensities(~1 cm s–1), energy dissipation rates (~0.08 cm2 s–3), and tidal cycles (4 h mixing-on and 2 h mixingoff).However, while bottom shear velocity (stress) was low in the NR tanks, high instantaneousbottom shear produced resuspension in the R tanks during the mixing-on cycles. Tidal resuspensionin the R tanks resulted in concentrations of 120 to 220 mg l–1 total suspended solids when mixing wason, decreasing to between 10 and 20 mg l–1 when mixing was off. Particulate nitrogen, phosphorus,and carbon concentrations, as well as dissolved inorganic nitrogen, nitrate + nitrite, and phosphatelevels were higher in the R tanks. Phytoplankton biomass was also higher in the R tanks, though lightwas limiting. Tidal resuspension affected water-column algal and zooplankton community compositionand induced significantly higher concentrations of brown tide Aureococcus anophagefferens.Microphytobenthos biomass was significantly higher in the NR tanks. Dissolved inorganic nitrogensediment effluxes were similar in both tanks; however, polychaetes and amphipods developed in theNR, but not in the R tank sediments. Tidal resuspension shifted processes from the benthos to thewater column. Regular tidal resuspension profoundly affected ecosystem structure and function,often through indirect pathways and linkages.
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