The main idea behind this research, the two scientists said, was to identify regions where nitrate problems can be expected as well as where they might not occur.

“The Rolling Plains has been identified as the nitrate hotspot of the state since the 1960s,” Ale said. “In Haskell and Knox counties, all observations exceeded the maximum contaminant level in the 2000s. In addition, in Wilbarger, Wichita, Baylor and Fisher counties, the median nitrate concentrations exceeded the maximum contaminant level in the 2000s.”

This indicates substantial groundwater quality degradation in recent times, he said.

Various factors influence the origin and migration of nitrate in Texas, Chaudhuri said. It can originate from natural (soil nitrogen and atmospheric deposition) and anthropogenic (mostly mixture of nitrate and ammonium fertilizers) sources. Due to its solubility and mobility, nitrate can easily leach to groundwater and persist for decades depending on the hydrologic regime.

“For the Texas Rolling Plains, we found a close association between nitrate contamination and agricultural activities, such as fertilizer application and irrigation with high-nitrate groundwater,” he said.

A variety of factors influence nitrate entry to groundwater, including climate, land use, aquifer characteristics and groundwater-table depth and recharge patterns, the researchers said.

A critical review of potential factors that affect fate and transport of nitrates in soils is essential to address groundwater nitrate contamination issues and determining corrective actions, they said.

“We want to emphasize the need for accounting for nitrogen present in irrigation water, soil, manure applied and crop residue recycled, while deciding the fertilizer application rates for various crops in this region to reduce nitrate leaching to groundwater systems,” Ale said.

Ale said the highly transmissive geologic and soil media in the Rolling Plains has also facilitated faster movement of nitrate, causing the widespread groundwater contamination.

They said while groundwater nitrate concentrations continue to increase in different parts of the state, adequate groundwater quality data necessary to support research or decision making is significantly lacking as indicated by lack of nitrate data from seven counties in the 2000s.

As an example, in the Rolling Plains region, nitrate concentration data was available for about 2,400 and 1,800 wells in the 1960s and the 1970s, respectively, but that dropped to 422 and 213 wells in the 1990s and the 2000s, respectively.

Similarly, in the 1970s, about 440 and 480 groundwater wells were monitored for water quality in Haskell and Knox counties, which recorded the highest nitrate concentrations in the state, respectively, as compared to only 19 and 60 wells, respectively, in the 2000s.

This indicates a significant reduction in the intensity of nitrate monitoring in recent years, Ale said.

With the importance of groundwater as a major water source continuing to increase in Texas, more frequent and spatially intensive groundwater quality monitoring and more critical review of the groundwater resources in different parts of the state will be necessary, he said.