Effects of organic matter degradation in cohesive sediment: linking sediment rheology to spatio-temporal patterns of organic matter degradability

Abstract Purpose Sediment organic matter (SOM) influences settling and thus the rheological behavior of suspended particles by enhancing flocculation or reducing surface charges forming organo-mineral complexes that facilitate particle–particle interactions in consolidating sediments. It was, therefore, assumed microbial degradation SOM its spatio-temporal variability would affect sediment properties enhance port maintenance dredging navigability ports waterways. Methods To investigate this effect, samples were taken at six locations along a transect 30 river kilometers through Port Hamburg, Germany, during nine sampling campaigns within two years. The collected divided into different layers based on differences visual consistency strength. For analysis degradability, incubated laboratory for 250 days glass bottles under aerobic anaerobic conditions following evolution gas composition (CH4, CO2) pressure bottle headspace over time. Yield stress was analyzed before after dissolved (DOM) decay using rheometer with Couette geometry. Standard solids pore water also analyzed. Results Shear strength decreased upon both conditions. Under conditions, reduced static fluidic yield stresses to an average 74% 79% fresh sample values. Consolidated lower depths showed highest absolute decrease up –110 Pa due larger amount degradable these connection higher bulk density. Pronounced spatial trends changes upstream downstream coincided decreasing gradient degradability from downstream. Seasonal indicated investigation area is impacted temporally changing factors. Conclusion availability easily significantly affects strength, especially even when mass loss small. indicate site-specific responses modulated overarching seasonal effects impacting entire area. decay, formation bubbles added additional physical component effect biological decay.