Elevated nitrate levels in the groundwater of the Gaza Strip: Distribution and sources

Seven years of monitoring groundwater in the Gaza Strip has shown that nitrate was and still is a major groundwater pollutant. The objectives of this research were to study the distribution of NO₃^- in the groundwater of the Gaza Strip and to identify the sources of NO₃^- in the Gaza aquifer system by assessing nitrogen and oxygen isotopes. The most recent samples collected in 2007 showed 90% of the wells having NO₃^- concentrations that are several times higher than the WHO standards of 50 mg/L. Potential NO₃^- source materials in Gaza are animal manure N, synthetic NH₄ based fertilizers, and wastewater/sludge. The average concentrations of N in the sludge, manure and soil of Gaza were 2.9%, 1% and 0.08%, respectively. The range in δ¹⁵N of solid manure samples was + 7.5 to + 11.9‰. The range in δ¹⁵N of sludge samples was + 4.6 to + 7.4‰, while four brands of synthetic fertilizers commonly used in Gaza had δ¹⁵N ranging from + 0.2 to + 1.0‰. Sludge amended soil had δ¹⁵N ranging from + 2.0 to + 7.3‰. For both δ¹⁸O and δ¹⁵N, the ranges of groundwater NO₃^- were - 0.1 to + 9.3‰ and + 3.2 to 12.8‰, respectively. No significant bacterial denitrification is taking place in the Gaza Strip aquifer. Nitrate was predominantly derived from manure and, provided δ¹⁵N of sludge represents the maximum δ¹⁵N of human waste, to a lesser extent from septic effluents/sludge. Synthetic fertilizers were a minor source.