Effectiveness of narrow vegetative filter strips in regulating sediment deposition in floodplain agricultural drainage ditches.

Floodplain agroecosystems are particularly susceptible to sediment redistribution due to seasonal flooding, snowmelt, and agricultural activities. However, field-based evidence on the performance of narrow vegetative filter strips (VFS) under such dynamic hydrological conditions remains limited. This study evaluated the effectiveness of narrow VFS (2 and 4 m) in regulating sediment deposition within agricultural drainage ditches of the Lake Saint-Pierre floodplain, Québec, Canada, a cold-region agroecosystem characterized by recurrent spring flooding. From 2019 to 2023, sediment deposition dynamics were monitored across three floodplain sites using repeated total station surveys, complemented by UAV-based LiDAR measurements. Annual sediment deposition volumes were quantified and standardized by ditch length (m3 m- 1) to account for site-scale variability, and statistical analyses were used to assess VFS effects across widths and over time. Across sites, 4-m VFS consistently reduced sediment deposition by approximately 30% relative to control ditches without VFS (p < 0.10). In contrast, 2-m VFS exhibited highly site-dependent and statistically nonsignificant effects, reflecting interactions among VFS width, ditch morphology, and hydrological connectivity during flood and snowmelt periods. Differences in sediment deposition between growing and nongrowing seasons were modest, suggesting that sediment inputs are primarily controlled by episodic flood and snowmelt events rather than seasonal vegetation cover. Comparisons between LiDAR- and total station-derived ditch volumes showed strong agreement, with an average difference of approximately 10%. These results demonstrate that narrow VFS can contribute to sediment regulation in floodplain agricultural drainage networks, although their effectiveness is constrained by hydrological context and strip width.