『Abstract
In agricultural areas, fertilizer application is the main source
of nitrate contamination of groundwater. To develop fertilizer
management strategies to combat this problem, arable land in Hokkaido,
Japan was evaluated using geographic information system techniques
for intrinsic groundwater vulnerability to nitrate contamination.
The DRASTIC method was modified to adapt it to the Hokkaido environment
and used for the evaluation. Of the seven original DRASTIC factors,
the depth of water (D), net recharge (R), soil media (S), topography
(T), and impact of vadose zone media (I) were selected and used
to explain the vertical movement of contaminants to the aquifer.
The rating for the net recharge factor was also modified to a
dilution factor for contaminants, rather than as a transporter.
The frequency of wells with nitrate concentrations exceeding the
Japanese environmental standard (10 mg/L) was reasonably explained
by vulnerability evaluation results )GLM: logit-link, quasi-binomial
distribution, Y = [1 + exp(6.873765 - 0.045988 × X]-1,
p＜0.001). However, in the paddy fields and pastures, vulnerability
did not exhibit a clear relationship with the frequency of wells
exceeding the standard. This suggests that the modified DRASTIC
method is applicable for fertilizer application management in
upland fields. In addition, under the ongoing policy for acreage
allotment for rice production, this method will be useful for
deciding the arrangement of arable land and crop rotation taking
into consideration the potential risk of fertilizer-induced nitrate
contamination of groundwater.
Keywords: Groundwater; Nitrate contamination; Fertilizer application;
GIS; Hydrogeology; DRASTIC』
Introduction
Problems of nitrate contamination of groundwater
Nitrate sources in groundwater
DRASTIC and a brief review of its modifications
Necessary modifications of DRASTIC to adapt Hokkaido region
Goal of this study
Materials and methods
Site description
Description of DRASTIC
Modification to DRASTIC
Selection of factors
Modification of net recharge rating
Individual parameters
Depth to water
Net recharge
Soil media
Topography
Impact of vadose zone
Output of vulnerability map and validation
GIS and statistic analysis
Results
Discussion
Vulnerability evaluation and its validation
Application to fertilizer management
Acknowledgments
References