Spatial and Temporal Variability of Groundwater Nitrate Concentrations in Irrigated Mediterranean Agriculture

Abstract

As nitrogen (N) fertilizer-use efficiency rarely exceeds 50% in most agricultural systems, the potential leaching of N to the groundwater, particularly under irrigated conditions, has economic, health, and environmental implications. Research in the Akarsu irrigation district in the Lower Seyhan Plain in southern Turkey sought to determine spatial and temporal variability of groundwater (GW) nitrate (NO₃) concentrations in 2007–2008. Shallow groundwater observation wells 3 m deep were installed at different locations to represent the whole irrigation district. Groundwater samples were collected (February, April, July, October) and analyzed for ammonium (NH₄) and NO₃ concentrations. Because NH₄ values were negligible, only NO₃ data were processed to determine spatial and temporal variability and then used to develop regional NO₃ maps using geographic information systems. Groundwater NO₃ concentrations ranged between 0.17 and 55.96 mg L^–1 during the 2 years, only exceeding the critical 50 mg L^–1 concentration in 1% of the area sampled. The areal mean of NO₃ concentration was greatest in February, indicating a potential N leaching of unused N from the early season with intensive rainfall, especially in wheat-growing areas. Groundwater NO₃ concentrations decreased after February; however, during the peak irrigation season in July, NO₃ was relatively low because of crop uptake during spring and summer. In about half the area, groundwater NO₃ concentrations ranged between 20 and 50 mg L^–1 and were thus marginal relative to the critical pollution level. As N fertilizer use will continue to increase, especially with the expanded irrigation that is now occurring in the Mediterranean region, regular monitoring of groundwater NO₃ is advisable under such conditions.

Keywords:

• Drainage observation wells
• groundwater nitrate
• irrigation schemes
• Mediterranean region
• potential nitrate pollution

Acknowledgments

The authors gratefully acknowledge funding for this work by the European Union in the context of FP6 with project acronym QUALIWATER (Project No. INCO-CT-2005-015031), and partial support was received from Cukurova University Academic Research Projects Unit (Project Numbers ZF2006KAP1 and ZF2008BAP8).