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tions from small springs and rare flood events. Currently, the only two water sources at the starting point The Lower Jordan River is located in the semiarid area of the of the Lower Jordan River are the effluent of the Bitania Jordan Valley, along the border between Israel and Jordan. The implementation of the water sections of the peace treaty between wastewater treatment plant and the Saline Water CarIsrael and Jordan and the countries’ commitment to improve the rier (Sites 1 and 2 in Fig. 1). The Bitania source includes ecological sustainability of the river system require a better under- poorly treated human and animal waste effluents. The standing of the riverine environment. This paper investigates the Saline Water Carrier contains a mixture of saline spring sources and transformations of nitrogen compounds in the Lower water diverted from the Sea of Galilee and urban sewage Jordan River by applying a combination of physical, chemical, isoto- effluent. As a result of the degradation of water quantity pic, and mathematical techniques. The source waters of the Lower and quality, the Lower Jordan River has become brackJordan River contain sewage, which contributes high ammonium loads

1 , which is about 40 times lower than the historical flow by ground water contribution (including agricultural re- rates. Our measurements and calculations indicate that ground water turn flows) and that surface inputs alone cannot account input was 20 to 80% of the river water flow, and 20 to 50% of its for the overall chemical changes. In the present study, solute mass flow. This study independently identifies the composition we quantify the ground water contribution by an integra- of possible end-members. These end-members contain high sulfate tionofflowratemeasurements withthechemicalchanges concentration and have similar chemical characteristics as were found that were observed along the Lower Jordan River. in agricultural drains and in the "saline" Yarmouk River. Future regional development plans that include the river flow rate and chem- istry should consider the interactions between the river and its shallow MATERIALS AND METHODS ground water system. Wepresentresultsofflow-ratemeasurements,chemicalanal- yses, and mass-balance calculations along the upper (northern) 20km ofthe LowerJordan River.The resultswere obtainedin W ater resourcesin arid and semiarid regions are collaboration between Jordanian, Israeli, and Palestinian re- often overexploited. Many rivers in these regions searchers between 1999 and 2001. The rainfall during these become saline and polluted, and their low flow rates years was limited (approximately 75% of the annual average) further endanger their future sustainability (Pillsburry, and thus the reported results represent base flows under 1981; Williams, 2001). The Lower Jordan River is an ex- drought conditions. treme example of such a river, where the combination of excessive water needs and lack of environmental at- The Study Area