Epsilon Archive for Student Projects

Abstract

One of the ways of mitigating climate change and increasing removal of carbon dioxide
from the atmosphere is by providing forests with additional nutrients through fertilization.
However, there is a concern that fertilizer nutrients can leach into streams which in turn can
elevate risks of eutrophication. This can negatively impact aquatic life in streams, rivers and
lakes surrounding the fertilized area. This thesis explores 10-years of intensive nitrogen (N)
demand-driven fertilization in a large-scale experiment in southern Sweden. Nitrogen transport
trends for the years 2012-2021 were analysed in two catchment areas by collecting streamflow
and nutrient concentration measurements. In one of the catchments, young Norway spruce
stands was fertilized every second year starting at a mean height of 2-4 m, leading to
fertilization of in total one fifth of the area, whereas the other catchment served as an
unfertilized control. A range of streamflow estimation methods were applied to acquire
accurate N transports estimates. The results revealed that the total N transport was similar in
the stream from the control catchment as in the fertilized catchment, with an average annual
leaching of 2,04 kg N-1 ha-1 yr-1 and 1,15 kg N-1 ha -1 yr-1, respectively. The transport of
inorganic N increased over time in the fertilized catchment, but not in the control catchment.
The seasonal variation of N transport was highest in autumn and winter months, especially in
the years of fertilization. Cross-validation of streamflow estimates indicated that the N
transport may be underestimated by 8%, however this deviation is relatively minor, and equal
for both streams. Thus, the results of this thesis show that the current total N transport in the
studied streams is low and similar across catchments, indicating that the risk of eutrophication
at catchment scale is relatively minor during the first ten years of an intensive demand-driven
forest fertilization program. However, the trend of increasing inorganic N transport over the
study period indicate a gradual buildup of N in the soils in the fertilized catchment and warrant
further studies, focusing on the long-term effects of climate change and biomass harvest of
fertilized stands.