Water flow and nitrate transport through a lakeshore with different revetment materials

摘要

As an important part of a transition zone surrounding a lake, lakeshore plays a critical role in connecting hydrology and biochemistry between surface water and groundwater. The shape, slope, subsurface features, and seepage face of a lakeside slope have been reported to affect water and nutrient exchange and consequently the water quality of near-shore lake water. Soil tank experiments and Hydrus-2D model simulations were conducted to improve our understanding of the influence of slope revetment materials (SRMs) on water flow and solute transport in a lakeshore zone. The low hydraulic conductivity of SRMs affected flow patterns in the lakeshore zone and resulted in a local increase of the groundwater table near the slope face. Water and solute flux distributions on the slope face under bare-slope conditions followed an exponential function. Fluxes were concentrated within a narrow portion of the slope surface near the intersection point between the lake water level and the slope face. Surface pollutants (for example from fishponds and paddy fields surrounding a lake) were transported into the lake along shallow groundwater through both unsaturated and saturated zones. The SRMs on the slope face affected the ratio of water and solute fluxes in the unsaturated zone, increasing along with the decline of the hydraulic conductivity of SRMs. Furthermore, as the hydraulic conductivity of SRMs decreased, the retention time and the potential for oxygen reduction correspondingly increased, which affected the nitrogen transport and transformations in the lakeshore zone. Simulated and experimental results indicate that if concrete along the shoreline of Lake Taihu is replaced with a relatively high-conductivity lime or the slope is left bare, water fluxes will increase less than solute fluxes, which will rise significantly, in particular in the unsaturated zone and along the seepage face. On the other hand, the largest water and solute fluxes along the shoreline for the bare and lime-slope conditions will be located higher at the slope than for the concrete-slope conditions. Hydrus-2D provided a good description of complicated hydrodynamic and solute transport/transformation conditions in the lakeshore zone. (C) 2014 Elsevier B.V. All rights reserved.