The Exper Imental Study Of Water And Solute Preferential Transport In Sediments On Yellow River Estuary

Preferential flow is the rapid migration that the inflow boundary in the soil to accept the supplies, but the supplies only by a small part of the soil. Nowadays, the pollution problems of the offshore waters become more and more serious, the serious pollution caused by land-based sources of material is occuring infiltration, migration and transformation under the wave induced motion of water and seepage in intertidal sediments, and preferential flow caused by biological caves accelerates migration and transformation of these substances, increases pollution of coastal waters. So the study on preferential flow path caused by the biological cave has important theoretical and practical value for the transformation and migration law of contaminants in sediments.Firstly, we revealled the characteristics of the preferential flow in the soil and took preliminary study on the preferential transport of non-adsorption solute through homogeneous soil columns and columns with artificial macropores comparative test, and further studied the effects of the initial soil water content, clay content, solute application method, influent concentration, different valence cations on the solute preferential transport process, and finally reserched the spatial and temporal distribution law of solute preferential transport through the two-dimensional soil bin tests.By comparing nitrate breakthrough curves of the homogeneous soil column and soil column with artificial macropore, earlier initial penetration time, earlier peak times and higher recovery rates show that preferential flow presents in soil column with artificial macropores. Soil preferential flow is characterized by penetrating the soil quickly, the breakthrough curves show asymmetry, tailing and the flow rate has large fluctuation.Dry soil conditions make more contributions of large pores to water flow and solute transport, and reduce the interactions between the flow and the matrix, and make the characteristics of solute preferential transport clearer; clay content also has great effects on the transport of water and solute. With the decrease of clay content, the initial penetration time becomes earlier, as well as the time when the solute concentration reach the peak value. Moreover, the peak value gets bigger.the more obvious of the characteristics of preferential flow; in the gap phase of the intermittent solute application method, solute in low-permeability medium can diffuse to preferential flow channel boundary, when the next cycle starts, it can be resumed a part of the downward infiltration of water, then gets a higher solute recovery rates compared to the continuous solute application method; the bigger the influent concentration, the bigger the solute potential of solute transport process, resulting in faster flow, shorter total time, while speeding up the solute transport rate in the soil, Thus advances the effluent time, reduces the time to balance and complete the migration; the migration of nitrate in the soil samples is little affected by the cations of different valence.Using two-dimensional soil tank to study solute preferential transport, we investigated the temporal and spatial distribution law of the preferential migration of the non-adsorption solute (NO3-N) and adsorption solute (H2PO4-P).When NO3-N transported in the sediment, surface nitrate concentrations decreased with time, which indicated that water and solutes moved downward over time, and nitrate concentration become more uniform with time, andwith the depth increase the distribution is more uneven in the cross section; H2PO4- was adsorpted by soil particles when migrated in soil samples, so surface total phosphorus concentration was higher, when to the second layer of the soil profile, total phosphorus concentrations were lower, and so do the others. Be similar to the Nitrate transport law, total phosphorus concentration is more uniform over time, and more uneven with depth. By the two-dimensional image we can seen nitrate and total phosphorus concentration distribution in the soil tank more directly.