Hindered erosion : the biological mediation of noncohesive sediment behavior
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Extracellular polymeric substances (EPS) are ubiquitous on tidal flats but their impact on sediment erosion has not been fully understood. Laboratory-controlled sediment beds were incubated with Bacillus subtilis for 5, 10, 16 and 22 days before the erosion experiments, to study the temporal and spatial variations in sediment stability caused by the bacterial secreted EPS. We found the bio-sedimentary systems showed different erosional behaviour related to biofilm maturity and EPS distribution. In the first stage (5 days), the bio-sedimentary bed was more easily eroded than the clean sediment. With increasing growth period, bound EPS became more widely distributed over the vertical profile resulting in bed stabilisation. After 22 days, the bound EPS was highly concentrated within a surface biofilm, but a relatively high content also extended to a depth of 5 mm and then decayed sharply with depth. The biofilm increased the critical shear stress of the bed and furthermore, it enabled the bed to withstand threshold conditions for an increased period of time as the biofilm degraded before eroding. After the loss of biofilm protection, the high EPS content in the sub-layers continued to stabilise the sediment (hindered erosion) by binding individual grains, as visualized by electron microscopy. Consequently, the bed strength did not immediately revert to the abiotic condition but progressively adjusted, reflecting the depth profile of the EPS. Our experiments highlight the need to treat the EPS-sediment conditioning as a bed-age associated and depth-dependent variable that should be included in the next generation of sediment transport models.
Chen , X D , Zhang , C K , Paterson , D M , Thompson , C E L , Townend , I H , Gong , Z , Zhou , Z & Feng , Q 2017 , ' Hindered erosion : the biological mediation of noncohesive sediment behavior ' Water Resources Research , vol 53 , no. 6 , pp. 4787-4801 . DOI: 10.1002/2016WR020105
Water Resources Research
© 2017. American Geophysical Union. All Rights Reserved. This work has been made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at: https://doi.org/10.1002/2016WR020105
This work was supported by the National Natural Science Foundation of China (NSFC, Grant Nos. 51579072, 51620105005, 51379003, 41606104), the Fundamental Research Funds for the Central Universities of China (Grant Nos. 2015B24814, 2016B00714, 2015B15814, 2015B25614), and the Jiangsu Provincial Policy Guidance Programme (BY2015002-05). Z. Zhou acknowledges the funding from Natural Science Foundation of Jiangsu Province (No. BK20160862). D. M. Paterson received funding from the MASTS pooling initiative (The Marine Alliance for Science and Technology for Scotland) and their support is gratefully acknowledged. MASTS is funded by the Scottish Funding Council (grant reference HR09011) and contributing institutions.
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