Agriculture Reference
In-Depth Information
input intensity of pesticide and agricultural plastic mulch in the Beijing
mountainous areas watersheds has increased drastically between 1984 and
2000, which resulted in the permanganate index pollution risk. Several
studies have indicated that the proportion of vegetable-planted land exhib-
ited a positive correlation with permanganate index [28]. For the Beijing
mountainous areas, vegetable outputs depended principally on the abun-
dant inputs of pesticide and agricultural plastic mulch in 2000, according
to our previous research [24].
1.4.2 WATERSHED ADAPTIVE RESPONSE UNIT
The significant scales at which there were statistically significant rela-
tionships between agricultural land use intensity and each water quality
variable were identified on the basis of the multi-scale regression analy-
sis, which were considered as the watershed adaptive response units for
each water quality variable. Thus, the first order watershed (Zone 1) of
27 monitoring points was the adaptive response unit for nitrate-nitrogen,
while the fifth order watershed (Zone 5) was the adaptive response unit for
the permanganate index.
In the Beijing mountainous study area, watershed adaptive response
units differ with the water quality variables being assessed, which are re-
lated with transformation regularity of nitrate-nitrogen and permanganate
index. After the use of nitrate fertilizer that is the source of nitrate-nitrogen
on agricultural fi elds, nitrate-nitrogen formed by nitrifi cation is either ab-
sorbed and utilized by plants or transformed into gaseous nitrogen through
denitrifi cation under reducing conditions. Therefore, only the agricultural
inputs inside the fi rst order watershed zones can make a signifi cant con-
tribution to the concentration of nitrate-nitrogen at the pour-point, while
that inside other order watershed zones has little infl uence on the nitrate-
nitrogen level at the pour-point with the action of long distance transport.
Compared to nitrate-nitrogen, permanganate index contamination is
relatively steady. As the main source, the transformation time of agricul-
tural plastic mulch and pesticides is relatively long. It could not make a
signifi cant contribution to the concentration of permanganate index until it
accumulates. Therefore, the smaller area basins, such as fi rst order water-
