Now, I assume that an elevated nitrate content in the groundwater is due to fertilizer runoff, damaged sewer systems or similiar and unrelated to the saltwater problem, the author of the article simply mixed those problems up. But I'm not sure, hence this question: Is there any causal link between sea-water inflitration and groundwater nitrate?
An answer not specific to Gaza would be ok as I want to understand possible mechanisms.
There has been reported incidence of sewage draining into the Mediterranean, which would explain nitrate contamination in conjunction with sea-water intrusion.