Vegetation cover and rainfall seasonality impact nutrient loss via runoff and erosion in the Colombian Andes

Mountain ecosystems provide key services to a large portion of the population in the tropics. However, they are particularly vulnerable to regional environmental changes such as soil degradation, via soil erosion and associated nutrient loss, both dissolved in runoff and suspended in sediment. Current trends in land use conversion combined with projections of intensified hydrological extremes potentially amplify these threats. We analyze the interactive effects of rainfall characteristics (at three time scales) and vegetation cover on the runoff–erosion–nutrient loss progression for a group of vegetation cover types that represent different land use conversion stages. After a year of observations we found, as expected, that natural forests have the highest potential for regulating precipitation–runoff–erosion–nutrient loss. The highest amounts of runoff occurred in pasturelands, and croplands had the highest erosion losses. Croplands showed the highest concentrations of soluble nutrients in runoff and in sediment. However, due to higher runoff amounts, pasturelands had the greatest loss of dissolved nutrients. Precipitation seasonality significantly influenced both erosion and nutrient loss. This is particularly critical in managed agricultural and pasture systems where increased runoff and erosion rates, combined with unsustainable management practices, may lead to alterations in soil and water quality. Our results indicate how agricultural practices need to adapt fertilization scheduling to rainfall seasonality to minimize potential environmental impacts. Collectively, our results highlight a fundamental management need in tropical mountains where the combination of rapid land use change and altered climate threatens ecosystem integrity and ecosystem services.