Change of nitrate concentration in groundwater

What do you see: The change in the average nitrate concentration in groundwater at a depth of 5-15 m for the period 2004-2010. Change is reflected as the difference between the averages for the period 2004-2007 and the period 2008-2010. The change in nitrate concentration is divided into classes. Important for: Early warning system for groundwater sources used for the production of drinking water.