Erosion and sedimentation effects on soil organic carbon redistribution in a complex landscape in western Ecuador.

Abstract

This study was conducted to evaluate how land-use changes affect the distribution of SOC within a complex tropical landscape through the processes of erosion and sedimentation. The objectives were: (i) to estimate the present SOC storage at a landscape scale using predictors such as slope, elevation, texture, land-use type and landscape position; (ii) to estimate soil redistribution under the present land-use conditions and under different land-use change scenarios using an erosion-sedimentation model; and (iii) to estimate the redistribution of SOC caused by erosion-sedimentation processes and its effect on landscape-scale SOC stocks. Implications for land-use policy options for the study area are also discussed. The study was conducted in the southern part of Manabi province in western Ecuador where 12 sites were selected in each of the three land-use systems (36 sites in total) to represent the two major physiographic soil units. The main agricultural land uses are coffee-agroforestry systems, pastures and upland rice fields. Using a general linear model with backward stepwise elimination, a model was developed for predicting SOC stocks (as the dependent variable) using the following regulatory factors (independent variables): elevation, slope, texture (as continuous variables), land-use type and soil-landform class (as categorical variables). Results showed that the significant variables that explained SOC stocks at the landscape scale were: elevation (P<0.01), texture (sand) (P<0.05), land-use type (LU1 = coffee-agroforestry; LU2 = pasture) (P<0.05), and soil-landform class (SL1 = lowland soils) (P<0.01), as reflected in the regression model. The highest SOC stocks (in the south-east corner of the area) were found in lowland soils on river valleys, river terraces and lower hills, whereas lower values were found in upland soils on higher landscape positions (north-west corner of the area). SOC stocks in the top 25 cm depth ranged from 30-87 Mg C ha-1 and the area-weighted mean was 63.6 Mg C ha-1. The SOC map illustrates that the actual SOC stocks were strongly related to topography and topography-related soil textural classes, suggesting that topography-driven water erosion and sedimentation processes play an important role in this landscape. Soil erosion losses and sedimentation gains showed stark contrasts among the four land-use change scenarios. SOC redistribution in the landscape, caused by land-use change effects on erosion and sedimentation, showed the highest impact in clay soil zones on depositional lower landscape positions and in lowland soils on river terraces, whereas the lowest impact was found in sand and loam soils on upper landscape positions.

A review of the ecosystem functions in oil palm plantations, using forests as a reference system

“…A–C) is increased soil erosion (Guillaume, Damris & Kuzyakov, ). When soil erosion and sedimentation alter the biological process of soil organic carbon (SOC) mineralization, vegetation growth, and water and nutrient availability, they can in turn affect redistribution of SOC within the landscape and its net loss from the landscape (Corre et al ., ). In a recent pan‐tropic study, lowland forest conversion to smallholder oil palm plantations caused the loss of, on average, 40% of stored SOC in the original forest soils in the top 0.1‐m depth during the first 10 years of conversion, whereafter a steady‐state condition of SOC stocks was attained (van Straaten et al ., ).…”

“…For example, LAPSUS‐based estimates of soil erosion and sedimentation have been successfully used for landscape‐scale estimates of net SOC losses in a converted landscape (e.g. Corre et al ., ). Such tools can be used to inform policies and methodologies, e.g.…”

Spatial variability in soil organic carbon in a tropical montane landscape: associations between soil organic carbon and land use, soil properties, vegetation, and topography vary across plot to landscape scales

“…The decrease in SOC c and SOC s in open land with increasing slope (Table 4) was most likely related to surface erosion, which is common in montane landscapes (e.g. Arrouays et al, 1995;Corre et al, 2015). The importance of erosion and sedimentation processes on the redistribution of SOC was shown in studies conducted in Laos (Chaplot et al, 2005) and Ecuador ; soil erosion was highest at the upper slopes and most of the eroded soil and SOC was deposited within a short distance at the lower slopes.…”

“…Within the same soil group, SOC is mainly influenced by land-use type and management (e.g. de Blécourt et al, 2013;de Koning et al, 2003;Mekuria et al, 2009;Post and Kwon, 2000), and geomorphological characteristics such as slope and slope position (Chaplot et al, 2005;Corre et al, 2015;Pennock and Corre, 2001). Spatial patterns of SOC are also greatly influenced by small-scale variability in biophysical factors that influence plant productivity and decomposition of soil organic matter (Hook et al, 1991;Stoyan et al, 2000).…”