| dc.description.abstract | Nitrogen (N) fluxes show a substantial variability at the landscape scale.
Emissions are transferred by atmospheric, hydrological and anthropogenic dispersion
between different landscape elements or ecosystems, e.g. farms, fields, forests or
moorland. These landscape N fluxes can cause impacts to the environment, such as
loss of biodiversity. The aim of this study is to illustrate how landscape N fluxes can
be quantified by integrating atmospheric and fluvial fluxes in a Scottish landscape of
6 km x 6 km that contains intensively managed poultry farming, extensively
managed beef and sheep farming, semi-natural moorland and woodland.
Atmospheric ammonia (NH3) emissions of two deep pit free range layer poultry
houses were estimated by high time-resolution measurements of NH3 concentrations
and meteorological variables downwind of layer poultry houses and the application
of an inverse Gaussian plume model. Atmospheric NH3 concentrations and
deposition fluxes across the study landscape were studied at a resolution of 25 m x
25 m. The approach combined a detailed landscape inventory of all farm activities
providing high resolution NH3 emission estimates for atmospheric dispersion
modelling and an intensive measurement programme of spatial NH3 concentrations
for verifying modelled NH3 concentrations. The spatially diverse emission pattern
resulted in a high spatial variability of modelled mean annual NH3 concentrations
(0.3 to 77.9 μg NH3 m-3) and dry deposition fluxes (0.1 to >100 kg NH3-N ha-1 yr-1)
within the landscape.
Annual downstream fluxes and variation in spatial concentration of dissolved
inorganic nitrogen (NH4
+ and NO3
-) and dissolved organic nitrogen (DON) were
studied in the two main catchments within the study landscape (agricultural grassland
vs. semi-natural moorland catchment). The grassland catchment was associated with
an annual downstream total dissolved nitrogen (TDN) flux of 14.4 kg N ha-1 yr-1,
which was 66% higher than the flux of 8.7 kg ha-1 yr-1 from the moorland catchment.
This difference was largely due to the NO3
- flux being one order of magnitude higher
in the grassland catchment. The contribution of DON to the TDN flux varied
between the catchments with 49% in the grassland and 81% in the moorland
catchment. Fluvial and atmospheric N fluxes were combined to derive N budgets of the two
catchments. Agricultural activities accounted for the majority of N input to the
catchments, with atmospheric deposition also playing a significant role, especially in
the moorland catchment. Both catchments showed large stream export fluxes
compared to their net import which suggests that their capacity of N storage is
limited.
This thesis quantifies major N fluxes in a study landscape and shows their large
spatial variability. Agricultural activities dominate landscape N dynamics. The work
demonstrates the importance of considering landscape N variability when attempting
to reduce the environmental impact of agricultural activities. | en |
