Water and nitrogen processes along a typical water flowpath and streamwater exports from a forested catchment and changes after clear-cutting: a modelling study

• Published in: Hydrology and earth system sciences Vol. 9; no. 6; pp. 657 - 674
• Main Authors: Lauren, A, Finer, L, Koivusalo, H, Kokkonen, T, Karvonen, T, Kellomaki, S, Mannerkoski, H, Ahtiainen, M
• Format: Journal Article
• Language: English
• Published: Copernicus Publications 01.01.2005
• Subjects: ammonium nitrogen; biogeochemical cycles; biological activity in soil; clearcutting; coniferous forests; dissolved organic matter; dissolved organic nitrogen; environmental models; FEMMA model; forest soils; forested watersheds; Freshwater; immobilization in soil; logging; losses from soil; nitrate nitrogen; nitrates; nitrification; slope; soil microorganisms; watershed hydrology; Finland
• ISSN: 1027-5606; 1607-7938; 1607-7938
• DOI: 10.5194/hess-9-657-2005

A two dimensional model, FEMMA, to describe water and nitrogen (N) fluxes within and from a forested first-order catchment (Kangasvaara in Eastern Finland) was constructed by linking the most significant processes affecting the fluxes of water, ammonium, nitrate and dissolved organic nitrogen along a hillslope from the water divide to the stream. The hillslope represents the average flowpath of water in the catchment and the model was used to estimate the N fluxes for a catchment in eastern Finland before and after clear-cutting. The simulated results were in reasonable agreement with the nitrate, dissolved organic N and dissolved total N measurements from the study catchment and with other results in the literature. According to the simulations, the major sinks of N after clear-cutting were immobilisation by soil microbes, uptake by ground vegetation and sorption to soil. These sinks increased downslope from the clear-cut area, indicating the importance of an uncut buffer zone between the stream and the clear-cut area in reducing N exports. The buffer zone retained 76% of the N flux coming from the clear-cut area. Nitrification was a key process in controlling the N export after clear-cutting and N increases were mainly as nitrate. Most of the annual N export took place during the spring flood, when uptake of N by plants was minimal.