{"title":"Erosion threshold of cohesive sediments in the German Wadden Sea: Temporal variability and comparison of in-situ and laboratory experiments","authors":"M. Witt , J. Patzke , E. Nehlsen , P. Fröhle","doi":"10.1016/j.ecss.2025.109417","DOIUrl":null,"url":null,"abstract":"<div><div>A newly developed in-situ setup of the Closed Gust Erosion Microcosm System (C-GEMS) was utilized for erosion experiments in a tidal mudflat in the mouth of the Elbe in the German Wadden Sea to investigate the temporal variability of the erosion threshold <span><math><mrow><msub><mi>τ</mi><mi>c</mi></msub></mrow></math></span> of cohesive sediments. In addition, erosion experiments with extracted sediment cores from the same site were conducted in the field and in the laboratory with the identical device to analyze the influence of sample extraction and transport on the derived erosion threshold. A total of 21 erosion experiments were carried out in four measuring campaigns between April and September 2024. The erosion thresholds derived from the in-situ experiments exhibit considerable temporal variability across campaigns, with values of <span><math><mrow><msub><mi>τ</mi><mi>c</mi></msub></mrow></math></span> = 0.1–0.27 N/m<sup>2</sup>, while repeated experiments within the individual campaigns demonstrate a high degree of reproducibility. Accompanying analyses of surface sediment particle size distribution and bulk density revealed that mud concentration (clay and silt) varied with wind conditions and the associated hydrodynamic load prior to the measurement campaigns. The observed temporal variability in <span><math><mrow><msub><mi>τ</mi><mi>c</mi></msub></mrow></math></span> is reasonably well captured by a mathematical model based on mud concentration and particle size, suggesting that <span><math><mrow><msub><mi>τ</mi><mi>c</mi></msub></mrow></math></span> can be plausibly estimated from these parameters. For campaigns with a cohesive surface sediment layer, erosion thresholds derived in the ex-situ experiments are consistently lower than those obtained in the in-situ experiments. This is attributed to the disturbance of the surface sediments due to mechanical extraction and liquefaction during transport. The findings offer insights into the transport dynamics of cohesive sediments and help guide decisions on whether future erosion experiments should be conducted in situ, despite the significant effort involved, or whether extracted sediment cores are a suitable alternative.</div></div>","PeriodicalId":50497,"journal":{"name":"Estuarine Coastal and Shelf Science","volume":"323 ","pages":"Article 109417"},"PeriodicalIF":2.6000,"publicationDate":"2025-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Estuarine Coastal and Shelf Science","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0272771425002951","RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"MARINE & FRESHWATER BIOLOGY","Score":null,"Total":0}
引用次数: 0
Abstract
A newly developed in-situ setup of the Closed Gust Erosion Microcosm System (C-GEMS) was utilized for erosion experiments in a tidal mudflat in the mouth of the Elbe in the German Wadden Sea to investigate the temporal variability of the erosion threshold of cohesive sediments. In addition, erosion experiments with extracted sediment cores from the same site were conducted in the field and in the laboratory with the identical device to analyze the influence of sample extraction and transport on the derived erosion threshold. A total of 21 erosion experiments were carried out in four measuring campaigns between April and September 2024. The erosion thresholds derived from the in-situ experiments exhibit considerable temporal variability across campaigns, with values of = 0.1–0.27 N/m2, while repeated experiments within the individual campaigns demonstrate a high degree of reproducibility. Accompanying analyses of surface sediment particle size distribution and bulk density revealed that mud concentration (clay and silt) varied with wind conditions and the associated hydrodynamic load prior to the measurement campaigns. The observed temporal variability in is reasonably well captured by a mathematical model based on mud concentration and particle size, suggesting that can be plausibly estimated from these parameters. For campaigns with a cohesive surface sediment layer, erosion thresholds derived in the ex-situ experiments are consistently lower than those obtained in the in-situ experiments. This is attributed to the disturbance of the surface sediments due to mechanical extraction and liquefaction during transport. The findings offer insights into the transport dynamics of cohesive sediments and help guide decisions on whether future erosion experiments should be conducted in situ, despite the significant effort involved, or whether extracted sediment cores are a suitable alternative.
期刊介绍:
Estuarine, Coastal and Shelf Science is an international multidisciplinary journal devoted to the analysis of saline water phenomena ranging from the outer edge of the continental shelf to the upper limits of the tidal zone. The journal provides a unique forum, unifying the multidisciplinary approaches to the study of the oceanography of estuaries, coastal zones, and continental shelf seas. It features original research papers, review papers and short communications treating such disciplines as zoology, botany, geology, sedimentology, physical oceanography.