| Muddy tidal flats are widely distributed in estuarine and coastal areas,and are the most sensitive areas of land-sea interaction and human activity response,and are also hotspots research on global climate change.As an important land reserve resource in coastal areas,muddy tidal flats have ecological functions and economic value,such as carbon sequestration,flood control,water purification,wave dissipation and revetment,tourism development and so on.However,under the current background of global warming,sea-level rise and intensified human activities,muddy tidal flats in estuarine and coastal areas are facing the risk of erosion.The erosion of muddy tidal flats will not only cause damage to the tidal flat ecosystem,but also increase the difficulty of coastal protection and threaten people’s lives and property.Studying the stability of muddy tidal flat is a prerequisite to reveal the mechanism of coastal erosion.At the same time,studying the influence of vegetation roots on sediment stability to resist the erosion in the salt marsh-bare flat transition zone can deepen the understanding of the role of tidal salt marsh vegetation in coastal protection.It provides important scientific support for the rational planning and utilization of tidal flats,ecological environmental protection and sustainable land development,and has important scientific value and application value.In this study,the typical muddy tidal flats in China-Chongming Dongtan in the Yangtze River Estuary and Qingshuigou and Diaokou River tidal flats in the Yellow River Delta are selected as the research objects.The advanced sediment stability to resist the erosion measuring instrument CSM(Cohesive Strength Meter)was used to quantitatively evaluate the sediment stability to resist the erosion of salt marsh-bare flat transition zone of Chongming Dongtan,Qingshuigou and Diaokou River tidal flats.And summarize the spatiotemporal variation characteristics of sediment stability to resist the erosion in Chongming Dongtan and the Yellow River Delta.By measuring the vegetation biomass and physical characteristics of sediments in laboratory experiments,the influence of vegetation root system on sediment stability to resist the erosion in vegetation area and the influence of sediment physical characteristics on sediment stability to resist the erosion in bare flat were systematically analyzed.The main conclusions are as follows:(1)There are significant spatial differences in sediment stability to resist the erosion in Chongming Dongtan.On different sections,the sediment stability to resist the erosion in the north section(Critical shear stress:2.80 Pa)>middle section(2.67Pa)>south section(1.60 Pa);On different geomorphological units,the sediment stability to resist the erosion in the vegetation zone(3.30 Pa)>the transition zone(2.28Pa)>the bare flat(1.50 Pa);At different depths,sediment stability to resist the erosion increases with depth:0-5 cm(1.62 Pa)<5-10 cm(1.94 Pa)<10-15 cm(2.34 Pa)<15-20 cm(2.85 Pa)<20-25 cm(3.06 Pa)(The stability to resist the erosion is expressed by the critical shear stress).Affected by vegetation types,the seasonal variation of sediment stability to resist the erosion in different sections is different.The vegetation on the north section is Spartina alterniflora community,and the sediment stability to resist the erosion is strong in spring and winter,but weak in summer and autumn.The vegetation on the middle and south sections is Scirpus mariqueter community,and the sediment stability to resist the erosion is strong in spring and autumn,but weak in summer and winter.The stability of sediments on the bare flat does not change significantly throughout the year.(2)The sediment stability to resist the erosion of the Qingshuigou and Diaokou River tidal flats in the Yellow River Delta has non-uniform distribution characteristics.On different geomorphological units,Qingshuigou tidal flat sediment stability to resist the erosion in the transition zone(1.90 Pa)>the bare flat(1.24 Pa)>the vegetation zone(0.87 Pa).While Diaokou River tidal flat sediment stability to resist the erosion in the bare flat(1.25 Pa)>the transition zone(1.24 Pa)>the vegetation zone(1.05 Pa).At different depths,the sediment stability to resist the erosion of Qingshuigou gradually weakened with the increase of depth,while the sediment stability to resist the erosion of Diaokou River remained unchanged at first and then increased with the increase of depth.(3)The research results show that the sediment stability to resist the erosion in the Chongming Dongtan vegetation zone is greater than that of the bare flat,which may be due to the"reinforcement"effect of vegetation roots on sediments.Moreover,chemical substances such as multivalent cations and extracellular polymers produced by vegetation roots may also enhance sediment stability to resist the erosion.For the same type of vegetation zone,the higher the underground biomass,the more stable the sediment.When the underground biomass of Spartina alterniflora was high(860 g/m~2),its corresponding sediment stability to resist the erosion was 1.32 times that when it was low(708 g/m~2).And when the underground biomass of Scirpus mariqueter was high(1323 g/m~2),its corresponding sediment stability to resist the erosion was 1.32times that when it was low(1103 g/m~2).In different types of vegetation zones,the sediment stability to resist the erosion is affected by the characteristics of the root system.Compared with Scirpus mariqueter,the thicker root system of Spartina alterniflora had a poor effect on enhancing sediment stability to resist the erosion,and the shorter root system of Suaeda salsa had no obvious effect on sediment stability to resist the erosion.(4)The research shows that the stability to resist the erosion in the north and middle sections of Chongming Dongtan bare flat is stronger than that in the south section.The reason may be the clay content(average value is 18.93%)of the north and middle sections is higher than that of the south section(average value is only 4.55%),the gravitational effect of sediment particles is small,and the bonding effect is large.At the same time,the clay particles are adsorbed on the surface of the silt and sand particles,filling the gaps between the silt and the sand particles.So that the porosity inside the sediment is reduced and the density is increased,forming a tighter whole with stronger stability to resist the erosion. |
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