Environmental factors controlling spatial variation in sediment yield in a central Andean mountain area

Abstract

A large spatial variability in sediment yield was observed from small streams in the Ecuadorian Andes. The objective of this study was to analyze the environmental factors controlling these variations in sediment yield in the Paute basin, Ecuador. Sediment yield data were calculated based on sediment volumes accumulated behind checkdams for 37 small catchments. Mean annual specific sediment yield (SSY) shows a large spatial variability and ranges between 26 and 15,100 Mg km − 2 year − 1 . Mean vegetation cover (C, fraction) in the catchment, i.e. the plant cover at or near the surface, exerts a first order control on sediment yield. The fractional vegetation cover alone explains 57% of the observed variance in ln(SSY). The negative exponential relation (SSY = a × e −b C ) which was found between vegetation cover and sediment yield at the catchment scale (10 3 -10 9 m 2 ), is very similar to the equations derived from splash, interrill and rill erosion experiments at the plot scale (1-10 3 m 2 ). This affirms the general character of an exponential decrease of sediment yield with increasing vegetation cover at a wide range of spatial scales, provided the distribution of cover can be considered to be essentially random. Lithology also significantly affects the sediment yield, and explains an additional 23% of the observed variance in ln(SSY). Based on these two catchment parameters, a multiple regression model was built. This empirical regression model already explains more than 75% of the total variance in the mean annual sediment yield. These results highlight the large potential of revegetation programs for controlling sediment yield. They show that a slight increase in the overall fractional vegetation cover of degraded land is likely to have a large effect on sediment production and delivery. Moreover, they point to the importance of detailed surface vegetation data for predicting and modeling sediment production rates.

Multidecadal change in streamflow associated with anthropogenic disturbances in the tropical Andes

“…Soil erosion measurements based on fallout radionuclides for the Chimbo catchment (central Ecuadorian Andes) by Henry et al (2013) clearly illustrate that soil erosion rates highly depend on land cover and management: erosion rates in páramo grasslands are estimated at 9 t ha −1 yr −1 , and are significantly higher in forest plantations, pastures, and croplands with erosion rates of, respectively, 21, 24, and 150 t ha −1 yr −1 . The latter values are similar to soil erosion estimates for highly degraded Andean environments in southern Ecuador (Molina et al, 2008;Vanacker et al, 2014). Accelerated soil erosion after land cover change has been shown to alter soil hydrological conditions, e.g., through a reduction of soil water infiltration rates and soil water retention capacity (Podwojewski et al, 2002;Molina et al, 2007).…”

Land‐Use and Land‐Cover Change in the Páramo of South‐Central Ecuador, 1979–2014

“…These dramatic changes in native vegetation in the high Andes in the late 20th and early 21st Centuries have been attributed to changes in land-use practices after the 1954 land reform [31]. These changes have increased soil erosion rates and negatively impacted on the hydrological and carbon cycles [8,9,14,[31][32][33][34][35][36][37][38][39]. It has been argued that land-use policies, deforestation, urbanization, and the movement of people are the root causes of degradation in this ecoregion [40].…”

Landslide susceptibility near highways is increased by 1 order of magnitude in the Andes of southern Ecuador, Loja province

“…Tropical mountain ecosystems are especially sensitive and respond quickly to any change (Vanacker et al, 2007). In the Andes of southern Ecuador, accelerated human pressure has increased sediment yield manifold (Molina et al, 2008), and areas adjacent to highways have proved to be most susceptible to landsliding (Muenchow et al, 2012).…”