Watering or buffering? Runoff and sediment pollution control from furrow irrigated fields in arid environments
Surface irrigated agriculture in arid and
semi-arid regions contributes to downstream environmental degradation. Changes
in irrigation system operational scenarios (ISOS) can represent an economic
alternative to reduce surface runoff impacts. At the same time the use of
vegetative filter strips (VFS) can have a positive impact on the ecological
health of rural landscapes by reducing erosion, improving water quality,
increasing biodiversity, and expanding wildlife habitat. The goal of this paper
is, using a combination of field data and mechanistic modeling results, to
evaluate and COMPARE the spatial effectiveness of improvements in ISOS and
introduction of VFS to reduce surface runoff pollution in the semi-arid/arid
furrow irrigation agroecosystem that exceeds current regulatory turbidity
limits (25 NTU). Five main factor interactions were studied: four soil textures,
two field slopes, three ISOS, six filter vegetation types, and ten filter
lengths. Slope and runoff volume were identified as the two main drivers of
sediment export from furrows. Shifting from current ISOS to less water
consumptive irrigation practices reduce runoff in addition to sediment delivery
to comply with environmental regulations. The implementation of 3–9 m
vegetative buffers on experimental parcels were found to mitigate sediment
delivery (greater than 90% sediment reduction) on tail drainage ditches but had
limited effect in the reduction of runoff flow that can transport other
dissolved pollutants. These findings were insensitive to filter vegetation
type. Thus, introduction of improved ISOS is desirable while VFS may be
targeted to specific hot spots within the irrigation district. This study shows
that the adoption of dense vegetation buffers in vulnerable semi-arid irrigated
regions can be effective to mitigate agricultural impacts and provide
environmental protection. However, it should not be adopted as an alternative
to proper on-site irrigation practices, rather as a complementary off-site
pollution control practice.
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