Sediment trapping by a tree belt: processes and consequences for sediment delivery |
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| Authors: | Sophie Leguédois Tim W Ellis Peter B Hairsine David J Tongway |
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| Institution: | 1. INRA, UR272‐Science du sol, BP 20619, F‐45166 Olivet, France;2. CSIRO Land and Water, GPO Box 1666, Canberra ACT 2601, Australia;3. CSIRO Sustainable Ecosystems, GPO Box 284, Canberra City ACT 2601, Australia |
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| Abstract: | Restoring belts of perennial vegetation in landscapes is widely recognized as a measure of improving landscape function. While there have been many studies of the transport of pollutants through grass filter strips, few have addressed sediment related processes through restored tree belts. In order to identify these processes and quantify their relative contribution to sediment trapping, a series of rainfall simulations was conducted on a 600 m2 hillslope comprising a pasture upslope of a 15 year old tree belt. Although the simulated events were extreme (average recurrence intervals ～10 and 50 yr), the trapping efficiency of the tree belt was very high: at least 94% of the total mass of sediments was captured. All the size fractions were trapped with a minimum Sediment Trapping Ratio (STR) of 91% for the medium‐sized fragments. Fractions < 1·3 µm and > 182 µm were totally captured (STR = 100%). Through the joint analysis of sediment budgets and soil surface conditions, we identified different trapping processes. The main trapping process is the sedimentation (at least 62% of trapped sediment mass) with deposits in the backwater and as micro‐terraces within the tree belt. Modelling results show that the coarsest size fractions above 75 µm are preferentially deposited. Joint infiltration of water and sediments has also been noticed, however, this process alone cannot explain the selective trapping of the finest fractions. We suggest that the finest fractions transported by the overland flow may be trapped by adsorption on the abundant litter present within the tree belt. Copyright © 2008 John Wiley & Sons, Ltd. |
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| Keywords: | runoff size selectivity sediment delivery tree litter backwater sedimentation macropores |
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