Multi-scale Modeling of Nutrient Pollution in the Rivers of China

Chinese
surface waters are severely polluted by nutrients. This
study addresses three challenges in nutrient modeling for rivers in
China: (1) difficulties in transferring modeling results across biophysical
and administrative scales, (2) poor representation of the locations
of point sources, and (3) limited incorporation of the direct discharge
of manure to rivers. The objective of this study is, therefore, to
quantify inputs of nitrogen (N) and phosphorus (P) to Chinese rivers
from different sources at multiple scales. We developed a novel multi-scale
modeling approach including a detailed, state-of-the-art representation
of point sources of nutrients in rivers. The model results show that
the river pollution and source attributions differ among spatial scales.
Point sources accounted for 75% of the total dissolved phosphorus
(TDP) inputs to rivers in China in 2012, and diffuse sources accounted
for 72% of the total dissolved nitrogen (TDN) inputs. One-third of
the sub-basins accounted for more than half of the pollution. Downscaling
to the smallest scale (polygons) reveals that 14% and 9% of the area
contribute to more than half of the calculated TDN and TDP pollution,
respectively. Sources of pollution vary considerably among and within
counties. Clearly, multi-scale modeling may help to develop effective
policies for water pollution.