Preprints
https://doi.org/10.5194/egusphere-2022-1233
https://doi.org/10.5194/egusphere-2022-1233
 
09 Dec 2022
09 Dec 2022
Status: this preprint is open for discussion.

When climate and human interactions threaten soil and water resources through hyper sedimentation: example of El Niño events (1978–2019 period), Poechos Reservoir, Northern Peru

Anthony Foucher1, Sergio Morera2,3,4, Michael Sanchez2, Jhon Orrillo2, and Olivier Evrard1 Anthony Foucher et al.
  • 1Laboratoire des Sciences du Climat et de l’Environnement (LSCE-IPSL), UMR 8212 (CEA/CNRS/UVSQ), Université Paris-Saclay, 91191 Gif-sur-Yvette Cedex, France
  • 2Instituto Geofísico del Perú, Calle Badajoz, 169, Lima, Peru
  • 3Universidad Nacional Agraria La Molina, Av. La Molina, s/n, Lima, Peru
  • 4Universidad Nacional Autónoma de Huanta, Jr. Manco Cápac, 497 Ayacucho, Peru

Abstract. Although Extreme El Niño Events (EENE) have always impacted hydrology in South America, their intensification by global warming and their association with changes in human activities and land cover may lead to the acceleration of sediment transfers in river systems and dam reservoirs. This situation may threaten soil and water resources in a region highly dependent on freshwater originating from large dams. In this study, we investigated the sediment sequence accumulated in the Poechos reservoir (Northern Peru) and provided a retrospective reconstruction of the interactions of El Niño-Southern Oscillation (ENSO), agricultural practices and vegetation cover changes on sediment dynamics (1978–2019). To this end, a sediment core was dated and characterized by physical and chemical analyses (e.g. scanner tomography, X-ray fluorescence, particle size analysis) for estimating the evolution of sedimentation rates and changes in sediment sources during the last five decades.

Sediment tracing results indicated the occurrence of changes in sediment sources associated with positive and negative phases of the Central and East Pacific Index (C and E index), with a greater contribution of the lowland dry forest biome in comparison to that of the Andean source to sediment during the warm periods (El Niño events, ENE), (mean contribution of 76 %, up to 90 % during the Coastal El Niño Events (CENE) of 2016–2017). Overall, the development of agriculture within the fluvial plains of the dry forest biome upstream of the Poechos dam induced an acceleration of sedimentation rates by 140 % after 1997, with an accumulation of coarser sediment in the reservoir during ENE and EENE.

This study suggests that the expansion of agriculture (e.g. agriculture in floodplains, deforestation) associated with a higher frequency of extreme rainfall events amplified the consequences of ENE, EENE and CENE on the quantity and quality of sediment transported by this river system, which will significantly decrease the lifespan of the dam reservoir essential to meet freshwater demands of the farmers and the populations living in this region.

Anthony Foucher et al.

Status: open (until 09 Mar 2023)

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  • RC1: 'Comment on egusphere-2022-1233', Anonymous Referee #1, 03 Feb 2023 reply

Anthony Foucher et al.

Anthony Foucher et al.

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Short summary
The current research investigated, as a representative study case, the sediment accumulated in the Poechos reservoir (Northern Peru) for retrospectively reconstructing the impact of the El Niño-Southern Oscillation and agriculture expansion along the riverine system of the dry tropical forest biome on sediment dynamics and sources (1978–2019).