Complex land cover change, water and sediment yield in a degraded Andean environment

Abstract

Exotic forest plantations Hydrology Water yield s u m m a r yRapid land use/-cover change has increasingly transformed the hydrological functioning of tropical Andean ecosystems. The hydrological response to forest cover change strongly depends on the initial state of the ecosystem. Relatively little is known about human-disturbed ecosystems where forest plantations have been established on highly degraded land. In this paper, we analyze the impact of forest change on water and sediment fluxes for a highly degraded Andean catchment. Different pathways of land cover change are observed in the Jadan catchment, with deforestation taking place in remote uplands and recovery and reforestation in the middle and lower parts where agricultural and bare lands are prevalent. Time series analyses of streamflow and rainfall data (1979/1982-2005/ 2007) show significant shifts in the distribution of rainfall and flow data. Changes in discharge are not resulting from changes in precipitation, as the direction of change is opposite. The removal of native forest for rangeland or croplands (by À20 km 2 ) is likely to have contributed to the increase in total annual water yield, through an increase in annual baseflow by 25 mm. The observed changes in peakflow are important as the 1st percentile highest flow rates were 54% lower, while the 1st percentile rainfall amounts increased by 52%. The observed decrease in peakflow cannot be explained by clearcut of native forest, but is likely to be related to reforestation of degraded lands as well as spontaneous recovery of vegetation on remaining grazing lands. Over the same time period, a major decrease in specific sediment yields and suspended sediment loads was observed. Although deforestation in the upper parts led to increased landslide activity, this change is not reflected in an increased sediment yield. Small upland rivers are often nearly completely blocked by landslide material, thereby reducing their potential to transport sediment. In contrast, the reduction in estimated erosion is likely to be caused by the reduction of the degraded areas in areal extent as well as to the (partial) recovery of the vegetation in these areas.

Patterns and Implications of Hydrologic Regime Change in Chongwe River, Zambia

“…They pointed out that base flow increase was due to reduced evapotranspiration losses following the removal of native forest, and their (native forest) subsequent replacement by grass and crops. Therefore the findings of this study are not in agreement with those of Molina et al (2012). This is an example regarding the conflicting evidence on the impact of forest cover change on dry season flows.…”

“…Elsewhere, scholars such as Molina et al (2012) observed an increase in dry season flows after deforestation, while at Chongwe 5025 in this study, these flows have decreased significantly in the period with high deforestation. Molina et al (2012) attributed the increase in dry season flows to the increase in base flow after deforestation. They pointed out that base flow increase was due to reduced evapotranspiration losses following the removal of native forest, and their (native forest) subsequent replacement by grass and crops.…”

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

“…Direct anthropogenic impact associated with land cover change is rapidly transforming the hydrological functioning of tropical Andean ecosystems (Vanacker et al, 2003;Farley et al, 2004;Molina et al, 2012;Harden et al, 2013). The hydrological response is diverse, as changes in vegetation affect various components of the hydrological cycle including evapotranspiration (Nosetto et al, 2005), infiltration (Molina et al, 2007), and surface runoff (Bathurst et al, 2011;Restrepo et al, 2015).…”

“…A full coverage of aerial photographs at the scale of 1/60000 was obtained for November 1963 and1977, and land cover mapping was realized following the orthorectification procedure described by Molina et al (2012). Three Landsat scenes (1991,2001,2009, from the same season) with 1T level of pre-processing were acquired from the USGS (U.S. Geological Survey) archive, and images were atmospherically and topographically corrected with ATCOR3 (Atmospheric and Topographic Correction; Balthazar et al, 2012).…”

Effects of Productive Activities on the Water Quality for Human Consumption in an Andean Basin, a Case Study

“…Different land cover histories assess the effect of land use change on the erosion process. Additionally, changes in the area and crop yield distribution can relate to increases in runoff (Molina et al 2012). Inputs of pollutants in different zones help to establish critical areas of land management.…”