STURM: Resuspension mesocosms with realistic bottom shear stress and water column turbulence for benthic-pelagic coupling studies: Design and applications

Abstract

Shear TUrbulence Resuspension Mesocosm (STURM) tanks, with high instantaneous bottom shear stress and realistic water column mixing in a single system, allow realistic benthic-pelagic coupling studies with sediment resuspension. The 1m3 tanks can be programmed to produce tidal or episodic sediment resuspension for extended time periods (e.g. 4weeks), over muddy sediments with a variety of benthic organisms. A resuspension paddle produces uniform bottom shear stress across the sediment surface while gently mixing a 1m deep overlying water column. The STURM tanks can be programmed to different magnitudes, frequencies, and durations of bottom shear stress (and thus resuspension) with proportional water column turbulence levels over a wide range of mixing settings for benthic-pelagic coupling experiments. Over ten STURM calibration settings, RMS turbulent velocity ranged from 0.26 to 4.52cms−1, energy dissipation rate from 0.0016 to 2.65cm2s−3, the average bottom shear stress from 0.0035 to 0.19Pa, and the instantaneous maximum bottom shear stress from 0.07 to 1.7Pa. We have performed four 4-week benthic-pelagic coupling ecosystem experiments with tidal resuspension and stepwise erosion experiments (both with and without infaunal bivalves), carried out experiments on oyster biodeposit resuspension, mimicked storms overlain on tidal resuspension, and studied the effects of varying frequency and duration of resuspension on sedimentary contaminant release. The large size of the tanks allows water quality and particle measurements using standard oceanographic instrumentation. The realistic scale and complexity of the contained ecosystems has revealed indirect feedbacks and responses that are not observable in smaller, less complex experimental systems.