Linking crop structure, throughfall, soil surface conditions, runoff and soil detachment: 10 land uses analyzed in Northern Laos

Lacombe, Guillaume; Valentin, Christian; Sounyafong, Phabvilay; Rouw, Anneke de; Soulileuth, Bounsamay; Silvera, Norbert; Pierret, Alain; Sengtaheuanghoung, Oloth; Ribolzi, Olivier

doi:10.1016/j.scitotenv.2017.10.185

Cited by 69 publications

(63 citation statements)

References 38 publications

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“…However, in recent years, acid-tolerant cash crops (e.g., corn, cassava) have been introduced in these areas [29], resulting in the loss of forest area at the annual rate of about 0.4%, according to [30]. Government incentives to limit shifting cultivation have led to an increase of teak, rubber, and biofuel tree plantations in many parts of the basin [31]. In the lowland areas of the Khorat Plateau, Tonle Sap sub-basin, and central to southern parts of Lao PDR, the availability of fertile soil allows a permanent form of agriculture.…”

Section: Study Area Characterizationmentioning

confidence: 99%

“…Shifting cultivation practices cause erosion (i.e., approximately 5.7 Mg/ha/year of topsoil are lost during cultivation, and about 0.7 Mg/ha/year during fallow years, according to [12], though they are not the only land use practice to be blamed for soil erosion in the LMB. Incentives for eliminating shifting cultivation (see Section 2.1) have led to a conversion of upland rice areas to tears, mazes, and tree plantations (teak, rubber, palm trees) [31,49,56]. Changes from upland rice to mazes and job's tears, for example, have been found to almost double the rate of sediment production, from about 6 to about 11 Mg/ha/year [12].…”

Section: Land Management Influencing Tss and Nitrate Depositionmentioning

confidence: 99%

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Linking Changes in Land Cover and Land Use of the Lower Mekong Basin to Instream Nitrate and Total Suspended Solids Variations

Metternicht

Marshall

2020

Sustainability

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Population growth and economic development are driving changes in land use/land cover (LULC) of the transboundary Lower Mekong River Basin (LMB), posing a serious threat to the integrity of the river system. Using data collected on a monthly basis over 30 years (1985–2015) at 14 stations located along the Lower Mekong river, this study explores whether spatiotemporal relationships exist between LULC changes and instream concentrations of total suspended solids (TSS) and nitrate—as proxies of water quality. The results show seasonal influences where temporal patterns of instream TSS and nitrate concentrations mirror patterns detected for discharge. Changes in LULC influenced instream TSS and nitrate levels differently over time and space. The seasonal Mann–Kendall (SMK) confirmed significant reduction of instream TSS concentrations at six stations (p < 0.05), while nitrate levels increased at five stations (p < 0.05), predominantly in stations located in the upper section of the basin where forest areas and mountainous topography dominate the landscape. Temporal correlation analyses point to the conversion of grassland (r = −0.61, p < 0.01) to paddy fields (r = 0.63, p < 0.01) and urban areas (r = 0.44, p < 0.05) as the changes in LULC that mostly impact instream nitrate contents. The reduction of TSS appears influenced by increased forest land cover (r = −0.72, p < 0.01) and by the development and operation of hydropower projects in the upper Mekong River. Spatial correlation analyses showed positive associations between forest land cover and instream concentrations of TSS (r = 0.64, p = 0.01) and nitrate (r = 0.54, p < 0.05), indicating that this type of LULC was heavily disturbed and harvested, resulting in soil erosion and runoff of nitrate rich sediment during the Wet season. Our results show that enhanced understanding of how LULC changes influence instream water quality at spatial and temporal scales is vital for assessing potential impacts of future land and water resource development on freshwater resources of the LMB.

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Section: Study Area Characterizationmentioning

confidence: 99%

Section: Land Management Influencing Tss and Nitrate Depositionmentioning

confidence: 99%

Linking Changes in Land Cover and Land Use of the Lower Mekong Basin to Instream Nitrate and Total Suspended Solids Variations

Metternicht

Marshall

2020

Sustainability

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“…Numerous studies have reported the quantitative relationships between soil loss and rainfall and vegetation cover using various modeling approaches, such as regression, conceptual, and physics-based models (de Vente & Poesen, 2005), using observations made at microplots (less than 10 m 2 ; e.g., Ha et al, 2012;Lacombe et al, 2018) and/or rainfall simulation experiments (Ollobarren Del Barrio, Giménez, & Campo-Bescós, 2017). The low data requirement, small number of variables, and extrapolation to the same region increase the applicability of regression models on annual erosion at the slope scale, though the process dynamics are not precisely presented.…”

mentioning

confidence: 99%

Runoff and soil erosion responses to rainfall and vegetation cover under various afforestation management regimes in subtropical montane forest

Yang

Qian

et al. 2019

Land Degrad Dev

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Soil erosion and runoff generation are a major concern in forest and agricultural ecosystem management. However, the tangled coeffects of rainfall and vegetation on runoff and erosion generation are regionally dependent and remain unclear in regions with high erosivity, such as Southeast China where the large‐scale afforestation is being implemented. Here, we present the 4‐year observations of runoff and erosion responses to various storms following three afforestation (assisted natural regeneration [ANR; windrowing harvest residues on surface]; Chinese fir cultivation [YCF]; and Castanopsis carlesii cultivation [YCP] after slash‐and‐burn) since 2012. Stepwise power‐law regressions were used to identify the key variables and formulate the responses. Results show that the YCF and YCP following slash and burn have extremely high erosion rates, over 20 t ha−1 yr−1 (twofold higher than the global tolerable threshold), during the first year. In contrast, the erosion rate is only approximately 1.3 t ha−1 yr−1 in the ANR. The high erosion rates reveal the environmental vulnerability and the necessity of management in this region. Stepwise regressions suggest total rainfall rather than rainfall intensity as key variable probably because the forest canopy substantially offsets raindrop kinetics. The nonlinear runoff and erosion responses indicate that the risk of soil erosion is extremely high when vegetation cover is less than 40% and rainfall is greater than 80 mm. This study, therefore, suggests that windrowing harvest residues into strips or maintaining a vegetation cover greater than 40% is a sound management practice for mitigating land degradation in this region.

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“…With respect to simulating hydrology, soil, and bacteria, first, Lacombe et al (2017) and Ribolzi et al (2017) found that the teak plantation increased the amount of surface runoff because the raindrops, which are stored on the surface of the broad leaves of these tall trees, could fall with higher kinetic energy. 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.…”

Section: Resultsmentioning

confidence: 99%

“…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).…”

mentioning

confidence: 99%

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

et al. 2018

Self Cite

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Land use change from annual crops to commercial tree plantations can modify flow and transport processes at the watershed scale, including the fate and transport of fecal indicator bacteria (FIB), such as Escherichia coli. The Soil and Water Assessment Tool (SWAT) is a useful means for integrating watershed characteristics and simulating water and contaminants. The objective of this study was to provide a comprehensive assessment of the impact of land use change on microbial transfer from soils to streams using the SWAT model. This study was conducted for the Houay Pano watershed located in northern Lao People's Democratic Republic. Under the observed weather conditions, the SWAT model predicted a decrease from 2011 to 2012 and an increase from 2012 to 2013 in surface runoff, suspended solids, and E. coli transferred from the soil surface to streams. The amount of precipitation was important in simulating surface runoff, and it subsequently affected the fate and transport of suspended solids and bacteria. In simulations of identical weather conditions and different land uses, E. coli fate and transport was more sensitive to the initial number of E. coli than to its drivers (i.e., surface runoff and suspended solids), and leaf area index was a significant factor influencing the determination of the initial number of E. coli on the soil surface. On the basis of these findings, this study identifies several limitations of the SWAT fertilizer and bacteria modules and suggests measures to improve our understanding of the impacts of land use change on FIB in tropical watersheds. Core Ideas Watershed‐scale processes influence land use change impact on FIB transport. The amount of precipitation significantly influences bacteria transport. FIB transport is sensitive to FIB number on soil surface, itself determined by LAI. We report several limitations of the SWAT model when describing FIB transfer. We suggest model improvements to understand the impact of land use change on FIB.

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Linking crop structure, throughfall, soil surface conditions, runoff and soil detachment: 10 land uses analyzed in Northern Laos

Cited by 69 publications

References 38 publications

Linking Changes in Land Cover and Land Use of the Lower Mekong Basin to Instream Nitrate and Total Suspended Solids Variations

Linking Changes in Land Cover and Land Use of the Lower Mekong Basin to Instream Nitrate and Total Suspended Solids Variations

Runoff and soil erosion responses to rainfall and vegetation cover under various afforestation management regimes in subtropical montane forest

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

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