Sediment trap efficiency of paddy fields at the watershed scale in a mountainous catchment in northwest Vietnam
Composite agricultural systems with permanent maize cultivation in the uplands and irrigated rice in the valleys are very common in mountainous southeast Asia. The soil loss and fertility decline of the upland fields is well documented, but little is known about reallocation of these sediments withi...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-06-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/13/3267/2016/bg-13-3267-2016.pdf |
| Summary: | Composite agricultural systems with permanent maize cultivation in the
uplands and irrigated rice in the valleys are very common in mountainous
southeast Asia. The soil loss and fertility decline of the upland fields is
well documented, but little is known about reallocation of these sediments
within the landscape. In this study, a turbidity-based linear mixed model
was used to quantify sediment inputs, from surface reservoir irrigation
water and from direct overland flow, into a paddy area of 13 ha.
Simultaneously, the sediment load exported from the rice fields was
determined. Mid-infrared spectroscopy was applied to analyze sediment
particle size. Our results showed that per year, 64 Mg ha<sup>−1</sup> of
sediments were imported into paddy fields, of which around 75 % were
delivered by irrigation water and the remainder by direct overland flow
during rainfall events. Overland flow contributed one-third of the received
sandy fraction, while irrigated sediments were predominantly silty. Overall,
rice fields were a net sink for sediments, trapping 28 Mg ha<sup>−1</sup> a<sup>−1</sup>
or almost half of total sediment inputs. As paddy outflow consisted almost
exclusively of silt- and clay-sized material, 24 Mg ha<sup>−1</sup> a<sup>−1</sup> of
the trapped amount of sediment was estimated to be sandy. Under continued
intensive upland maize cultivation, such a sustained input of coarse
material could jeopardize paddy soil fertility, puddling capacity and
ultimately food security of the inhabitants of these mountainous areas.
Preventing direct overland flow from entering the paddy fields, however,
could reduce sand inputs by up to 34 %. |
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| ISSN: | 1726-4170 1726-4189 |