Indicators for contaminant transport in a periodical wind-driven wetland flow

Abstract

Understanding indicators for contaminant transport in wetlands under wind is essential to agricultural pollution assessment associated with chemical fertilizers and pesticides. Presented in this paper is an analytical study of indicators for contaminant transport in a periodical wind-driven wetland flow. Analytical solutions of velocity profile, total quantity of contaminant in a streamline, position and moving velocity of mass center of contaminant cloud, and environmental dispersivity are rigorously derived and analyzed for a typical wetland flow under the combined action of periodical wind stress and superficial pressure gradient. It is found that the flow direction changes alternatively only for a large oscillatory wind stress. For instantaneous emission of multiple point sources, the total quantity of contaminant in each stream line parallel to the free surface is dependent on the initial distribution of contaminant only in the initial stage and eventually reaches a constant. For long time evolution of contaminant cloud, the mass center of contaminant cloud oscillates periodically around the origin of a coordinate system moving at a speed of the mean value of depth-averaged velocity during one period, and corresponding oscillatory amplitude enhances with the increasing oscillatory wind stress. The amplitude of environmental dispersivity increases with the increase of oscillatory wind stress, and negative environmental dispersivity appears for partial time in an oscillatory period for a large oscillatory wind stress.