A STATISTICAL ASSESSMENT OF THE IMPACT OF AGRICULTURAL LAND USE INTENSITY ON REGIONAL SURFACE WATER QUALITY AT MULTIPLE SCALES - Agricultural Resource Use and Management - page 20

1.3 RESULTS
1.3.1 WATER QUALITY ASSESSMENT
Table 8 shows the 2000 yearly mean concentration of NO 3 -N and COD Mn .
The concentration of NO 3 -N in the samples ranged from 0.46 to 12 mg/L,
while COD Mn ranged from 1 to 7.4 mg/L. Only the concentration of NO 3 -
N for Site 12 exceeded to 10 mg/L, which is the Chinese surface drinking
water standard limit. Different from NO 3 -N, there are five types of surface
water environmental quality standard for COD Mn . Since type IV and V
cannot be acceptable for drinking water, the type III recommended value
of 6 mg/L is considered as the surface drinking water standard limit for
COD Mn . According to this standard limit of 6 mg/L, Site 12 was faced
with organic contaminant and reducible inorganic substance drinking wa-
ter pollution. Since Sites 10, 11, 17 and 22 were close to the standard limit
of 6 mg/L, especially Site 10, they also had a pollution risk caused by
COD Mn .
1.3.2 LINKAGE MODEL RESULTS AT MULTIPLE SCALES
The regression models of NO 3 -N and COD Mn at the various watershed
scales are shown in Table 9 and Table 10, respectively. The log-trans-
formed NO 3 -N exhibited a relationship with WI-IPC 1 and WI-IPC 2 at the
scale of Zone 1, while no statistically significant relationships were found
between agricultural land use intensity and nitrate level at the other water-
shed scales. The regression equation in the Zone 1 model, with the value
0.374 of R 2 and the level 0.004 of statistical significance, is as follows:
ln(NO 3 -N) = −0.026 − 0.901WI-IPC 1 + 0.418WI-IPC 2 (3)