DO LANDSCAPE INDICATORS CORRELATE WITH GROUNDWATER NITRATE CONCENTRATIONS? A TRANS-BORDER AQUIFER STUDY

Nitrate contamination of groundwater is a serious concern in areas of intensive agriculture. Globally, potential health effects of excess nitrate in drinking water include reproductive problems, blue-baby syndrome, and increased cancer risk. The Abbotsford-Sumas Aquifer (ASA) spans the US-Canada border (between British Columbia and Washington) and provides drinking water for over 100,000 people. In the ASA, long-term studies indicate that elevated nitrate concentrations may be attributed to overlying land use. Because of the complexities associated with working in trans-boundary systems (such as multi-government management), few studies have quantitatively linked nitrate concentrations with changing land use and land cover across the US-Canada border.

The goal of this research was to assess the general patterns and possible correlations between land use practices and groundwater nitrate concentrations within the ASA using landscape indicators (such as percent agriculture and percent forest cover). A seamless cross-border land cover mosaic was created by harmonizing a variety of US and Canadian land use and land cover datasets. More detailed landscape indicators were created using agricultural groupings reflecting likely nutrient loading potentials of different crop types and fertilizer management practices. Nitrate concentrations in groundwater samples were examined from 41 well sites throughout the US and Canada. At each monitoring station, terrestrial zones of influence (aligned with the directional flow of groundwater) were delineated around wells and landscape indicators were calculated within this zone. To link landscape indicators with nitrate concentrations, multiple linear regression was used to test for statistical associations between landscape indicators and mean and median nitrate concentrations. Different agricultural crop types and management regimes showed different strengths of correlations with groundwater nitrate concentrations. A general goal of this work was to determine which landscape indicators could be useful to help inform future trans-boundary water management strategies.