Sammendrag
Phosphorus (P) loss from diffuse sources
remains as the main cause of freshwater eutrophication
in agricultural regions. The amount of land used
for different agricultural practices may be a strong
explanatory factor for the P loading to runoff waters.
A prerequisite is that the effect of changes in land use
on P levels in surface waters needs to be ascertained
and quantified. In this study, a comprehensive approach
has been developed to explore the environmental
consequences of P levels in receiving water
with corresponding land use change in a heavily
agriculturally influenced watershed. A coupled simulation
using Dyna-CLUE model with grey relational
analysis (GRA) and grey model GM (1,1) model
was employed to stimulate spatial distribution and
area demand. Besides, a comprehensive land use
index with degree of P saturation (DPS%) as weight
coefficient was developed to examine the statistical
and spatial relationships of land use and P levels in
receiving waters on regional watershed. Moreover, in
order to evaluate the practical impact of land use
change on water quality, a planned emigration and
watershed ecological reconstruction planning were
designed into the scenarios. The potential of changes
in land use as an abatement action to curb eutrophication
was evaluated by modelling the effect of issued
emigration and ecological restoration programs
in the local watershed of the Yuqiao water reservoir
in northeastern China. Kappa indexes above 0.85 for
the validation period verify that the coupled land use
change model is able to simulate the effect of the
abatement actions on land use. Scenario predictions
reveals that local emigration and a comprehensive
ecological restoration project as abatement actions
could significantly decrease contents of P in receiving
surface waters: Relative to year 2012, total P and
orthophosphate could be reduced by 36 and 45 %,
respectively, by the end of year 2018. This modelling
approach can, with moderate modifications, also be
adapted to other watersheds. The model developed in
this study can thus be used by environmental managers
as a tool to identify risk for P loss from diffuse
sources within a watershed and assist policy makers
to assess the effect on P losses by implementing
abatement actions that changes land use.
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