Abstract
Embankments are common structures along rivers or lakes in riparian zones in plain areas. They should have natural slopes instead of slopes covered by concrete or other hard materials, in order to rebuild sustainable ecosystems for riparian zones. This study was conducted to evaluate the effects of vegetative slopes on water flow and pollutant transport through the embankments. Three embankments with different slope treatments (a bare slope, a slope covered in centipede grass, a slope covered in tall fescue) were examined, and three inflow applications of pollute water with different concentration of total nitrogen (TN) and total phosphorus (TP) used to simulate different agricultural non-point pollution levels. The results showed that the water flux rates of the three embankments were relatively stable under all inflow events, and almost all values were higher than 80%. The embankments with vegetative slopes had better nitrogen removal than the bare slope under all events, and the one with tall fescue slope was best, but the benefits of vegetative slopes decreased with increasing inflow concentration. Moreover, there were no significant differences between the embankments on phosphorus removal, for which the reductions were all high (above 90%) with most loads remaining in the front third of embankment bodies. Overall, the embankments with vegetative slopes had positive effects on water exchange and reducing non-point pollutant into lake or river water, which provides a quantitative scientific basis for the actual layout of lakeshores.
Highlights
Agricultural non-point source pollution is one of the important reasons for water eutrophication because of the excessive use of fertilizers, which results in large residual nitrogen and phosphorus transportation into water bodies [1,2]
Our experiment showed that total nitrogen (TN) reductions in the embankments with the centipede grass and tall fescue slopes were better than for in the bare slope when polluted water flowed through the banks (Table 4, Figures 2a and 3a)
The results show that banks with partial natural slopes are effective zones for the exchange between surrounding water and lake water and perform well in retarding pollutants discharge into lake water
Summary
Agricultural non-point source pollution is one of the important reasons for water eutrophication because of the excessive use of fertilizers, which results in large residual nitrogen and phosphorus transportation into water bodies [1,2]. Riparian zones are often considered effective at retarding pollutants from surrounding agricultural areas before they enter lake water [3,4]. In the plain areas in China, embankments are common structures distributed widely in riparian zones along the rivers and lakes. Some researchers have suggested that the concrete slopes should be restored to more natural slopes (vegetation protected and biotechnical slopes) in order to rebuild the connection between the river and surrounding lands [8]. Many researchers have given attention to new covered materials and methods of balancing the stabilization and ecological effects of embankments [9,10,11,12]. Current ecological revetment methods can be divided into three categories: (1) simple vegetation revetment, using vegetation roots to protect slopes; (2) vegetation revetment combined with engineering measures such as geonets, ecological concrete grids, planting grooves, prefabricated pieces, filled geotextile or fiber bags, etc., to enhance the anti-erosion abilities of vegetative slopes; (3) ecological material revetment such as cylinder molds, stone cages, ecological concrete, ecological grids, etc
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