Land Use and Nitrate Concentrations in Groundwater: Evidence from Groundwater Wells in California.

Abstract

Nitrate pollution of groundwater is a pernicious issue affecting people and ecosystems in many regions of the world. Although scientists agree that nitrogen compounds from human activity enter the groundwater system, there remains a need for estimates of the causal impacts of land use on the nitrate concentrations in well water––the location where nitrate contamination has the largest impact on human health. In this paper, we provide evidence of the link between nitrate concentrations measured in well water and local land use using a dataset of repeated cross-sectional samples of about 5,000 groundwater wells and a detailed dataset of remotely sensed land uses from 2007 to 2021. Findings show that a 10 percentage point increase in the share of land use to grow high nitrogen crops within 500 meters of a well (for example, from 5% to 15% of the land surrounding a well) relative to undeveloped land leads to a 5.8% increase in nitrate concentrations within 5 to 12 years. Compare this to a 10 percentage point increase in land developed for urban use, which leads to a 1.6% increase in nitrate concentrations over a similar time frame.