Modelling nitrification in the river Zarka of Jordan

The Zarka, a shallow, relatively small river flowing through a semi-arid region of Jordan is the countryʹs main water course. Its prime source is discharge from a large overloaded waste treatment plant centred on stabilization ponds. Between May 1990 and January 1992, NH4---N concentrations of up to 130 mg/l were recorded at the river source, and an average 76 mg/l NO3---N at the discharge into a strategically vital supply reservoir. Proposed revisions to the structure of a model to simulate nitrification, take into account the influence of very high algal and bacterial populations (106–107 cfu/ml), as their activities are both important factors. With respect to algae, high solar radiation intensities appeared to inhibit activity, such that for modelling, activity was related to the maximum/minimum diurnal DO ratio, rather than measured biomass or chlorophyll a.