Groundwater Nitrate Vulnerability

Nitrate vulnerability assessments often focus on soil characteristics observable at the surface with limited consideration of the subsurface. A recent airborne electromagnetic survey was used to map large-scale variation in sediment type in the Central Valley, providing the missing depth dimension. The goal of this study was to evaluate whether electrical resistivity measurements could be used for nitrate vulnerability assessment in California’s Central Valley. One criterion often used in nitrate vulnerability assessment is soil coarseness because pollution percolates faster through coarse than fine soil, more readily reaching groundwater. This reasoning suggests that fine soils characterized by low depth-averaged resistivity are correlated with low nitrate concentration. However, we found reduced nitrate concentration only at very low resistivity, likely representing high clay content. Beyond very-low resistivity, we found no correlation between nitrate concentration and resistivity. Our findings suggest that local soil characteristics alone are insufficient to identify areas vulnerable to nitrate pollution.

Research published is under review at GRL.