Ballasted Flocs Capture Pelagic Primary Production and Alter the Local Sediment Characteristics in the Coastal German Bight (North Sea)

Andreas Neumann,H Christian Hass,Céline Naderipour,Jürgen Möbius

doi:10.3390/geosciences9080344

Abstract

Suspended, organic matter, especially in the form of adhesive extracellular polymers (EPS), tends to form flocs, which may also incorporate suspended lithogenic particles in coastal environments. With an increased settling velocity, these ballasted flocs form in a narrow zone along the coast and potentially represent a major source of pelagic primary production for the benthic community. We sought support for this hypothesis by examining our measurements of the mud content, porosity, permeability, pigment content, and specific respiration rate of sediment from the German Bight (North Sea) for signs that the pelagic zone of ballasted floc formation is affecting the local sediment characteristics. Based on a simple bottom-shear stress model and by employing empirical correlations of sediment characteristics we were able to find strong indications that this is actually the case. Our results demonstrate how ballasted flocs contribute to the benthic pelagic coupling in a high turbulence environment.

Highlights

The whole bottom of the German Bight in the south-eastern North Sea is covered with sediment, which by definition are particles that were deposited after transport
This study aims to examine our measurements of sediment characteristics for the putative impact of ballasted flocs
For a summary of the overall pattern, we found impermeable, muddy sediment with a high the mud content of the sediment appears approximately twofold higher than that expected via the chlorin content and high respiration rates in the deeper parts of the study area, where a low bed bed shear stress considerations

Summary

Introduction

The whole bottom of the German Bight in the south-eastern North Sea is covered with sediment, which by definition are particles that were deposited after transport. The youngest sediment includes the suspended particulate matter (SPM, see notations & abbreviations) that has settled last from the water column. This ongoing sedimentation process provides mineral particles to build up the bulk sediment, but it includes bio-available organic matter to fuel the benthic nutrient turnover. Employing the Stokes equation for the terminal sinking velocity of spheres, the settling velocities of particulate organic matter correspond to the settling velocities of quartz spheres with diameters in the range of 4–70 μm This size corresponds well to silt with a 4–63 μm grain size [6] and silt particles and POM settle under similar hydrodynamic conditions. It has been shown that POM can capture fine mineral particles into flocs [2,7], especially when extracellular polymeric substances (EPS) are present, and that these organic-inorganic flocs may settle faster than pure POM or silt [8,9,10]

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