Impact of maintenance operations on the seasonal evolution of ditch properties and functions

Abstract

International audienceDitch networks were traditionally designed to protect fields from soil erosion or control waterlogging. They are still frequently managed by either mowing, chemical weeding, dredging or burning to ensure their optimal hydraulic capacity. Ditches were recently reported also to improve water quality and sustain biodiversity. These ditch functions are related to specific ditch properties. By contrastingly modifying ditch properties, maintenance operations were supposed to regulate these functions. There is, therefore, a need to re-examine the design and maintenance strategies of ditches to optimize the whole range of ecosystem services that they provide. In this study, we address the innovator question of how maintenance operations affect the yearly evolution of ditch properties, and in turn, the panel of functions that ditches support. During one year, we monitored the vegetation, litter, soil properties, and ash cover of five ditches that were being unmanaged, dredged, mowed, burned, and chemically weeded, respectively, with timing and frequency as generally operated by farmers in the study area. We then used indicators to evaluate the effect that the evolution of these properties has on the ditch water conveyance, herbicide retention and biodiversity conservation functions. We found that the evolution of these properties significantly contrasted among the 5 maintenance strategies. All the maintenance operations cleared the vegetation, which improves the hydraulic capacity by up to 3 times. The optimal hydraulic capacity is maintained longer after chemical weeding and dredging, but these operations have negative impacts on the herbicide retention and biodiversity conservation functions. The litter and ash layers generated by mowing and burning, respectively, improve the herbicide retention by up to 45%. Our results confirm that maintenance can be an efficient tool for optimizing ditch functions. The choice of maintenance operation and timing are key to successfully optimizing most of the functions that ditches can support

The Use of Photogrammetry to Construct Time Series of Vegetation Permeability to Water and Seed Transport in Agricultural Waterways

“…However, this effect could be counterbalanced by the presence of small plants below the canopy. For example, the decrease in vegetation height occurring in December 2016 suggests a washing out of the dead vegetation [15,56] and a probable reconfiguration of vegetation due to the flow [57]. It is worth mentioning that the vegetation height estimated with our method showed lower error (0.1 m) across treatments and surveys than that in the study of [15] (0.2 m), confirming the robustness of the SfM-MVS surveys for vegetation monitoring.…”

“…The SfM-MVS technique used in this study provides access to vegetation characteristics with a higher accuracy than that of other manual surveys [15] but requires preparation of the survey area. The two indicators of porosities could not be measured visually in the field because they are based on fine monitoring of vegetation cover and channel topography.…”

“…The experimental design has been described in detail in [15]. In brief, five treatments were applied from upstream to downstream in 4-m-long quadrats separated by 2-m-long unmanaged buffers: (1) non-managed (control), (2) dredged, (3) mowed, (4) burned, and (5) chemically weeded ( Figure 1).…”

“…According to the maintenance schedule and depending on cropping practices, vegetation cover significantly varies throughout the year. Recently, it has been demonstrated that vegetation cover exhibited great variations after being managed by farmers, with direct consequences on water conveyance capacities [15]. The agricultural channels are mainly used for channelizing overland flow, and the water level is highly dynamic throughout the year and depends on the frequency of rainfall or irrigation events [16,17].…”

Promoting adoption of two-stage agricultural drainage ditches: A change agent perspective

“…In the Western Lake Erie Basin (WLEB) region of Ohio, these individuals include government agents involved closely with advising farmers/landowners about their drainage management practices. Among others, this advice pertains to maintenance of drainage ditches, a practice that has implications for water conveyance, nutrient retention, and biodiversity conservation [15]. Given their involvement in decisions related to drainage management, change agents play a crucial role in promoting two-stage ditches.…”