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 per mille. The range in δ15N of sludge samples was + 4.6 to + 7.4 per mille, while four brands of synthetic fertilizers commonly used in Gaza had δ15N ranging from + 0.2 to + 1.0 per mille. Sludge amended soil had δ15N ranging from + 2.0 to + 7.3 per mille. For both δ18O and δ15N, the ranges of groundwater NO3- were - 0.1 to + 9.3 per milleand + 3.2 to 12.8 per mille, 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