| The structure and spatial distribution of root channels, the hydrochemistry in the lake (ditch) water and subsurface water within the reed-bed/ditch system, and the matter transport affected by root channels were studied in the land/inland water ecotones with reed domination in Baiyangdian Lake, China.(1) It is found, as the first report, that the root channels formed by hydrophytes thrive in the ecotone soil. According to the statistical results from 17 field profiles, the root channels of reeds are mainly distributed above 120cm along the profile and particularly concentrated at 20-70cm. The area of root channels over 40-60cm section occupies more than 2.2% of the profile section area. The ratios of dead root channels to living ones account for 48.4% and 51.6%, respectively. Over 50% root channels have a diameter of less than 5mm. However, 90% of the root channel area is composed of root channels with diameter of more than 10mm. The wetland root channels spread predominantly along horizontal direction underground. The dye tracer experiment and hydraulic conductivity determination consistently show that the wetland root channels can quickly transport water to far distance within ecotones and consequently provide the transport, adsorption and transformation interface for pollutants such as nitrogen and phosphorus.(2) Field work well verified the new purification mechanism by root channels in the land/inland water ecotone. The purification mechanism of ecotone indicates that the root channels can freely exchange the water between land and water body as far as 4-8 m when the lake water level fluctuates, which considerably increases the purification efficiency by reed bed system. Here the soluble pollutants may be adsorbed or degraded by ecotone soil minerals. The reed-bed/ditch system can achieve best self-purification efficiency at sea level of 8 m. When the lake level rises from 7.3 m to 8.1 m, the concentrations of ammoniacal nitrogen (NH4+-N), total...
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