From shifting cultivation to teak plantation: effect on overland flow and sediment yield in a montane tropical catchment

Abstract

Soil erosion supplies large quantities of sediments to rivers of Southeastern Asia. It reduces soil fertility of agro-ecosystems located on hillslopes, and it degrades, downstream, water resource quality and leads to the siltation of reservoirs. An increase in the surface area covered with commercial perennial monocultures such as teak plantations is currently observed at the expanse of traditional slash-and-burn cultivation systems in steep montane environments of these regions. The impacts of land-use change on the hydrological response and sediment yields have been investigated in a representative catchment of Laos monitored for 13 years. After the gradual conversion of rice-based shifting cultivation to teak plantation-based systems, overland flow contribution to stream flow increased from 16 to 31% and sediment yield raised from 98 to 609 Mg km−2. This result is explained by the higher kinetic energy of raindrops falling from the canopy, the virtual absence of understorey vegetation cover to dissipate drop energy and the formation of an impermeable surface crust accelerating the formation and concentration of overland flow. The 25-to-50% lower 137Cs activities measured in soils collected under mature teak plantations compared to soils under other land uses illustrate the severity of soil erosion processes occurring in teak plantations.

Modeling the Impact of Land Use Change on Basin‐scale Transfer of Fecal Indicator Bacteria: SWAT Model Performance

“…Consequently, the temporal variation in suspended solids was consistent with the variation in surface runoff because both surface runoff and peak runoff rate determine the temporal variation in soil erosion in SWAT. Similar trends in both simulated surface runoff and simulated suspended solids were also reported in Ribolzi et al (2017).…”

“…Therefore, we suggest further development of the hydrology submodule of SWAT to simulate the effect of the kinetic energy of raindrops falling from the canopy on soil erosion. Second, SWAT separates soil and land use management parameters, although previous studies revealed that different land use can change soil properties, such as saturated hydraulic conductivity (SOL_K) or bulk density (SOL_BD) (Patin et al, 2012; Ribolzi et al, 2017; Ziegler et al, 2004). In this study, we found that SOL_BD was highly ranked in the sensitivity analysis, but because of the model concept, it remained constant while land use changed.…”

“…The four major land use types include annual crops (Job's tears [ Coix lacryma‐jobi L.], upland rice [ Oryza sativa L.], corn [ Zea mays L.], or sesame [ Sesamum orientale L.]), fallow, forests, and teak ( Tectona grandis L.f.) plantations (Ribolzi et al, 2017). Chemical fertilization is not used.…”

“…The fate and transport of FIB are influenced by the environment, including climate, hydrology, pollution, topography, soil type, and land use (Boithias et al, 2016; Cho et al, 2016; Coffey et al, 2016; Rochelle‐Newall et al, 2016). Land use change is thought to be influential in FIB transfers due to alteration in hydrology and erosion processes in watersheds (Lacombe et al, 2017; Ribolzi et al, 2017; Valentin et al, 2008), which consequently influence the export of bacteria. Nevertheless, most studies have focused on the transport of bacteria in streams rather than the impact of land use on FIB due to the complexity and heterogeneity of land uses in watersheds (Liang et al, 2013).…”

The transition from arable lands to rubber tree plantations in northern Thailand impacts weed assemblages and soil physical properties

“…They found that in flat areas, RT monocultures decrease insect, bird and plant species richness and soil quality compared to forests (Beukema et al ., ), but are similar to or have slightly higher biodiversity and soil conditions than other tree plantations (Gnanavelrajah & Shrestha, ; Guillaume et al ., ). Various studies found that in mountainous areas tree plantations increased overland flow and sediment loss (Ribolzi et al ., ) and overall exacerbated soil degradation (Janeau et al ., ; Podwojewski et al ., ; Valentin et al ., ; Paiboonvorachat & Oyana, ). The processes and social implications of such trajectories have been discussed elsewhere (Fox & Castella, ; Ahrends et al ., ).…”