Patterns in Soil Chemical Weathering Related to Topographic Gradients and Vegetation Structure in a High Andean Tropical Ecosystem

Abstract

Although climate exerts a major control on mineral weathering and soil formation processes, the combined effect of vegetation and topography can influence the rate and extent of chemical weathering at the hillslope scale. In this paper, we examined spatial patterns in volumetric strain and soil weathering extent associated with topographic gradients and vegetation patterns. In a high Andean catchment, we selected 10 soil toposequences on andesitic flows: 5 under tussock grasses, 3 under cushion forming plants, and 2 under native forest. Along each toposequence, one pit was excavated at the shoulder, backslope, and toeslope resulting in 30 soil profiles. Depth‐weighted total soil porosity of the 30 soil profiles averaged 64 ± 6%. The association between volumetric strain and soil organic C indicates that biotic agents can be effective in dilating the regolith during weathering. The young, postglacial volcanic soils were depleted in mono‐divalent and divalent cations, with total mass losses ranging between 793 and 1610 kg/m2. The accumulation of Al‐humus complexes in the soil matrix plays an essential role in chemical transformation of the nonallophanic soils. Beyond the marginally significant topographic control on chemical weathering extent, our data show highly significant differences in chemical weathering extent between vegetation communities with total mass losses in forest soils being, respectively, 19% and 22% higher than in grasslands and cushion‐forming plants. The vegetation mosaic in alpine ecosystems might therefore provide essential clues to understand soil chemical weathering patterns caused by spatially varying soil particle and water residence times.

Land use impacts on soil erosion and rejuvenation in Southern Brazil

“…The potential impact of agricultural activities on tropical and subtropical soils is of particularly concern because of their low mineral nutrient reserve (Godfray et al, 2010;Foley, 2011). In humid tropical and subtropical environments, soils are characterised by intense chemical weathering and leaching of soluble components (e.g., Chadwick et al, 2003;Hewawasam et al, 2013;Molina et al, 2019). The development of the soil mantle is the result of in-situ weathering, atmospheric input and downhill transport of weathering products (Carson and Kirkby, 1972;Mudd and Furbish, 2006).…”

Post‐fire changes in plant growth form composition and diversity in Andean páramo grassland

“…High vegetation cover of tussock grasses is often associated with protecting and promoting the ecosystem function of páramo soils, i.e., providing water regulation, storing and sequestering soil carbon (Minaya Maldonado, 2017; Bremer et al, 2019). For example, Molina et al (2019) demonstrated higher rates of chemical weathering in páramo zone soil under trees compared with soil beneath tussock grassland in southern Ecuador.…”

Distribución espacio-temporal de los deslizamientos y erosión hídrica en una cuenca Andina tropical

“…Soils are developed in volcanic and meta-sedimentary rocks, and are classified as Andisols, Histosols and Mollisols following the USDA soil taxonomy. They are characterised by high organic matter contents and high fertility when undisturbed (henry et al, 2013;Molina et al, 2019). The land use pattern is the result of several decades of anthropogenic land use changes: at mid and low altitudes, one can observe a patchwork of small agricultural plots, remnants of subalpine cloud forest, and patches of abandoned land with regeneration of shrubs.…”