Biological influences on coastal muddy sediment structure following resuspension

Abstract

AbstractShallow coastal muddy sediments are important for global nutrient cycling and carbon storage and provide a habitat for diverse communities of organisms. Bottom shear stress from physical disturbances such as storms and hurricanes resuspend coastal muds, disrupting their cohesive structure. How biological vs. physical processes affect reconsolidation of physically disturbed natural muds, however, is poorly understood. We compare the recovery of sediment properties related to compaction and cohesion of muds following physical disturbance. We hypothesized that recovery of cohesion would take longer than compaction and that changes in surface and subsurface cohesion would occur on different timescales. We collected muddy sediment cores and resuspended the top 5 cm in the lab to simulate storm disturbance. At several timepoints following resuspension (1–30 d), we measured sediment properties providing metrics of compaction (sediment height, porosity, grain size distribution, sound speed) and of surface and subsurface cohesion (erodibility, fracture behavior, exopolymeric substances [EPS]). Compaction and cohesion increased rapidly over the first 1–2 d after resuspension and continued to slowly increase for 2 weeks. Between 2 and 4 weeks, however, subsurface cohesion increased and turbidity decreased, consistent with sediment restabilization. In contrast, subsurface compaction decreased and eroded mass increased, suggesting destabilization. We attribute this apparent destabilization to delayed activity of small‐bodied infauna. Surprisingly, EPS concentration did not explain cohesion changes. These results highlight the importance of including biological parameters when predicting the recovery of sediment structure following a physical disturbance. This work has implications for understanding coastal sediment transport dynamics in frequently disturbed sediments.