Effect of land cover and hydro-meteorological controls on soil water leachate doc concentrations in a high-elevation tropical environment

Abstract

Páramo soils store high amounts of organic carbon. However, climate change and changes in land cover/use may cause a decrease in their carbon storage capacity. As such, a better understanding of the factors influencing the páramo soils carbon storage and export is urgently needed. To fill this knowledge gap we selected the Quinuas Ecohydrological Observatory (91.3 km²) in south Ecuador, and study the hydro-meteorological conditions controlling the dissolved organic carbon (DOC) content in the soil water for the four main land cover types (tussock grass, natural forest, pine plantations and pasture). Weekly soil water samples for DOC analysis, as well as meteorological variables and soil water content and temperature probes (5-min intervals) from various depth and slope positions were monitored within the soils’ organic and mineral horizons between October 2014 and January 2017. These data was used to generate regression trees and random forest statistical models in order to identify controllers of soil water DOC concentrations. Our results evidenced that land cover is the most important predictor in the models, followed by sampling depth and soil moisture. Natural forest have been identified with the higher DOC concentrations in soil water followed by pasture, tussock grass and pine forest. DOC concentrations also increase with decreasing soil moisture (except when soil moisture is >0.56 m³ m-³ in natural forest). The latter shows that land cover change and factors that affect soil moisture conditions over time, are very likely to lead significant changes in DOC concentrations in soil water and therefore in streams.