Executive Summary : | Studies have shown that macropores enhance flow and transport in the subsurface, with most studies using artificially created macropores. However, some major scientific questions remain unanswered, such as the role of macropores in the spatial distribution of bacteria and associated activity in the subsurface. This has implications for the fate and transport of pesticides and organic matter, as bacterial activity may be concentrated along preferential flow paths. This proposal aims to experimentally characterize enhanced transport of nutrients, pesticides, and bacteria through the preferential flow paths created by roots using artificial analogue and natural root networks. Experiments will be conducted with artificial root networks and various agricultural plants, both in a controlled environment of a plant growth chamber and in the field. Pesticide and degradation products will be extracted using the Soxhlet technique and analyzed in a GCMS. Bacteria will be characterized in terms of activity and bacterial protein. Flow and transport through the soil matrix without the preferential flow network will be characterized through similar experiments with no plants. A dual permeability model will be formulated to simulate flow, and a two-zone composite transport model will be used to simulate preferential transport through macropores. Dispersion in the two zones will be characterized using conservative tracer experiments, and retardation parameters will be estimated from experimental data through reverse simulation. |