Storm-triggered landslides in the Peruvian Andes and implications for topography, carbon cycles, and biodiversity

Abstract

Abstract. In this study, we assess the geomorphic role of a rare, large-magnitude landslide event and consider the effect of this event on mountain forest ecosystems and the erosion of organic carbon in an Andean river catchment. Proximal triggers such as large rain storms are known to cause large numbers of landslides, but the relative effects of such low-frequency, high-magnitude events are not well known in the context of more regular, smaller events. We develop a 25 year duration, annual-resolution landslide inventory by mapping landslide occurrence in the Kosñipata Valley, Peru, from 1988 to 2012 using Landsat, Quickbird and Worldview satellite images. Catchment-wide landslide rates were high, at 0.076 % yr−1 by area, indicating landslides may completely turn over hillslopes every ~ 1320 years and strip 28 tC km−2 yr−1 of soil (73 %) and vegetation (27 %). A single rain storm in March 2010 accounted for 27 % of all landslide area observed during the 25 year study and removed 26 % of the organic carbon that was stripped from hillslopes by all landslides during the study. An approximately linear magnitude–frequency relationship for annual landslide areas suggests that large storms contribute an equivalent landslide failure area to the sum of smaller frequency landslides events occurring over the same period. However, the spatial distribution of landslides associated with the 2010 storm is distinct. On the basis of precipitation statistics and landscape morphology, we hypothesize that spatial focusing of storm-triggered landslide erosion at lower elevations in the Kosñipata catchment may be characteristic of longer-term patterns. These patterns may have implications for the source and composition of sediments and organic material supplied to river systems of the Amazon basin, and, through focusing of regular ecological disturbance, for the species composition of forested ecosystems in the region.

Erosion of organic carbon from the Andes and its effects on ecosystem carbon dioxide balance

“…The climate and tectonic setting combine to produce moderate‐to‐high denudation rates of ~0.4 mm yr −1 in the central Andes according to cosmogenic radionuclide concentrations in detrital quartz [ Wittmann et al ., ] and decadal river gauging [ Guyot et al ., ]. The slopes are steep and prone to landslides, which harvest sediment and POC [ Blodgett and Isacks , ; Clark et al ., ]. In this part of the Andes, rivers drain large areas of sedimentary and meta‐sedimentary melanges that comprise ~80% of the Kosñipata River drainage area [ Clark et al ., ].…”

“…(a) San Pedro gauging station (yellow circle) and catchment area (purple line) and the subcatchment at the Wayqecha gauging station (yellow square) overlain on topography from the Shuttle Radar Topographic Mission (SRTM) digital elevation model at 90 × 90 m resolution. (b) Landslides were mapped from satellite imagery at annual resolution from 1988 to 2012, for nontopographic shadow areas (shown in light grey, where landslides were not visible) [ Clark et al ., ]. (c) The Kosñipata River feeds the Madre de Dios River (basin outlined in red), a tributary of the Madeira River draining to the Amazon River.…”

“…The catchment is located in Manu National Park and the adjacent buffer zone (Table ). The forest contains significant stores of organic carbon (total 35,000 ± 5000 t C km −2 ), with 28,000 ± 4000 t C km −2 in soils and 5300 ± 800 t C km −2 in vegetation [ Clark et al ., ]. Total carbon stocks increase slightly with elevation due to an increase of soil stocks and woody necromass with elevation, accompanied by a smaller reduction in standing live biomass [ Zimmermann et al ., ; Gurdak et al ., ; Clark et al ., ].…”

“…We aim to provide new insight into the impact of physical erosion on carbon budgets by quantifying the source and magnitude of river discharge of POC from the steep, eastern flank of the Peruvian Andes, characterized by predominantly sedimentary bedrock with relatively high concentrations of petrogenic organic carbon. We focus on a catchment where previous work has established the hydrological water balance [ Clark et al ., ]; rates of geomorphic processes such as landslides [ Clark et al ., ]; and forest productivity, respiration, and carbon stocks across the landscape [ Zimmermann et al ., ; Zimmermann et al ., ; Marthews et al ., ; Girardin et al ., ; Clark et al ., ; Malhi et al ., ]. We use a detailed set of suspended sediment samples and hydrometric river gauging measurements over a 12 month period and analyze the stable isotopes of POC (δ 13 C org ), the nitrogen to organic carbon ratio ([N]/[OC total ]), and the radiocarbon activity of POC to distinguish POC petro derived from sedimentary rocks and to study the source and age of POC biosphere .…”

Connectivity of earthquake‐triggered landslides with the fluvial network: Implications for landslide sediment transport after the 2008 Wenchuan earthquake

“…Fluvial evacuation of landslide‐derived sediment removes mass from mountains, influencing landscape evolution [ Pearce and Watson , ; Malamud et al ., ; Korup et al ., ; Hovius et al ., ; Parker et al ., ; Egholm et al ., ; Li et al ., ]. Landslides also impact the terrestrial biosphere [ Garwood et al ., ; Allen et al ., ; Clark et al ., ], and delivery of eroded material to river channels can redistribute essential nutrient elements (e.g., carbon and nitrogen), contributing to tectonic forcing of global biogeochemical cycles [ Hilton et al ., ; Ramos Scharrón et al ., ; Jin et al ., ]. Furthermore, sediment supply from landslides to rivers may cause prolonged secondary natural hazards, via channel aggradation and enhanced flooding, and may reduce the storage capacity of downstream reservoirs [ Korup et al ., ; Glade and Crozier , ; Huang and Fan , ; Wang et al ., ].…”