Incomplete mixing of soil water in the H.J. Andrews Experimental Forest. A modeling study of water and nitrogen fluxes on a hillslope

Abstract

Hillslope hydrology involves the examination of processes in the soil that influences water flowing downslope. A consensus on how water is displaced on hillslopes is still lacking, because processes involved with hillslope hydrology are difficult to observe and understand. This master thesis included a model study to estimate if incomplete mixing of soil water is present on a hillslope. Therefore a biogeochemistry-hydrological model is used, that is parameterized with data of a trenched hillslope in a headwater catchment (WS10) in the H.J. Andrews Experimental Forest (OR, USA). With the use of quantitative and qualitative (nitrogen) measures of water transport through the hillslope, two model simulations were compared. Model simulation 1 contains only complete mixing of inorganic nitrogen and model simulation 2 contains both incomplete and complete mixing of inorganic nitrogen. By comparing the results of model simulations 1 and 2 there is no clear evidence that incomplete mixing of inorganic nitrogen occurs on the hillslope. Besides model improvements, future research could include improving the dataset of nitrogen measurements, a tighter linkage between vegetation and hydrology by incorporating actual transpiration rates and a focus on both nitrogen and water-isotopes.