Time-varying impacts of different management regimes on vegetation cover in agricultural ditches

Man-made drainage networks consisting primarily of ditches have been constructed by farmers for centuries to remove excess water from fields. In addition to removing water, ditch networks are involved in other hydrological processes, such as redistributing soil or pesticides. To maintain the hydraulic capacity of ditches, farmers apply various management regimes to regulate ditch vegetation cover that can impact the aforementioned hydrological processes. The objective of this study was to characterise the time-varying impacts of ditch management regimes on vegetation cover and to discuss the resulting hydrological impacts. The vegetation associated with the surveyed ditches was observed and used to define the different ditch management regimes and to quantify their impacts on ditch vegetation cover. The management regimes were heterogeneous and involved a combination of dredging, chemical weeding, mowing and burning. The variety of management practices and the frequency with which they were applied to the ditches resulted in strong spatial variability in the vegetation cover and in strong temporal variability for a given ditch. Finally, it is probable that the surveyed management regimes had time-varying and contrasting impacts on the hydraulic capacity of ditches, the erosion of ditch banks, sedimentation and pesticide retention in the ditches, as indicated by the extensive literature on these topics.