Controls on the Chemical and Isotopic Compositions of Urban Rainwater and Stormwater in a Semiarid Zone

Analyses of regional-scale synoptics and air-mass trajectories, local-scale atmospheric measurements (wind direction and speed, air temperature, dust load, SO 2 and NO x concentrations in the air, rain amount and intensity), and chemical and isotopic compositions of rainwater collected in the coastal city of Ashdod, Israel, were used to identify the various contributing sources to rainwater salts and their timing. During this period, the temporal variations in the chemical and isotopic compositions of the city's stormwater were investigated under different land use, and their dependence on physical parameters such as precipitation intensity, stormwater discharge, cumulative stormwater volumes or the size of the drainage area were evaluated. Fourty six events were intensively monitored for precipitation distribution and intensity at three stations across the city and for stormwater discharge at seven stations draining 85% of the city area. A total of 39 and 202 precipitation samples were collected and analyzed for chemical and isotopic compositions, respectively. 149 stormwater samples, collected from the drains during 10 of these events, were analyzed for chemical and isotopic compositions. Because the stormwater stations drained areas of different size and land use, their impact on the stormwater chemistry could be evaluated. Rainwater affected by the sea was characterized by a large marine fraction of salts, high Cl concentrations and low values of δ 18 O and δD. These rain events were associated with Mediterranean trajectories (the Cyprus Low system), which typically prevail in midwinter. Rainwater affected by continental sources had a very small contribution of marine salts, high HCO 3 and Ca concentrations, low nitrate and ammonia concentrations, and high values of δ 18 O and δD. These rain events were associated with continental trajectories from the Red Sea, Arabian Desert and North African coast, usually during the fall and spring. Rainwater affected by anthropogenic (urban) sources was characterized by a very low marine fraction, high sulfate, nitrate and ammonia concentrations, sulfate as the dominant anion, and low values of δ 34 S. This was shown to be a steady source, unrelated to any specific synoptic pattern or air-mass trajectory, and was dominant when other sources were less prominent. Land use had only a minor effect on the concentrations of major ions and trace elements. Conversely, the concentrations and variety of volatile and semi-volatile organic compounds were significantly higher in stormwater generated in the industrial area than in that draining from residential areas. Ion and trace metal …