Water and Nutrient Budgets of Organic Layers and Mineral Topsoils Under Tropical Montane Forest in Ecuador in Response to 15 Years of Environmental Change

Abstract

We quantified the changes in macronutrient storages of the soil in a remote Andean tropical montane rain forest on the rim of the Amazon basin from 1998 to 2013. In the studied 15 years, the N, P, and S fluxes in throughfall+stemflow increased significantly, while those of Ca decreased and of Mg and K remained unchanged. The main reasons for increasing nutrient inputs were Amazonian forest fires. Ca inputs decreased because of a particularly strong Sahara dust deposition event in 1999/2000. On average of the 15 budgeted years, P and K accumulated in the organic layer at a rate doubling their current storages in 197 and 27 years, respectively. The other macronutrients were on average leached from the organic layer, depleting it in 38 (Mg) to 281 years (N). Nutrient leaching was likely favored by enhanced mineralization driven by climate warming. In the upper 30 cm of the mineral soil, all macronutrients accumulated at rates doubling their storages in 57 (Ca) to 601 years (P). Our results demonstrate that the current environmental change increased the nutrient supply of the studied ecosystem. Increased nutrient supply might shift the ecosystem to a new state and change the chemistry of headwater streams.