Abstract. Two different in situ spectrophotometers are compared that were used in the field to determine nitrate-nitrogen (NO 3 -N) concentrations at two distinct spring discharge sites. One sensor was a double wavelength spectrophotometer (DWS) and the other a multiple wavelength spectrophotometer (MWS). The objective of the study was to review the hardware options, determine ease of calibration, accuracy, influence of additional substances and to assess positive and negative aspects of the two sensors as well as troubleshooting and trade-offs. Both sensors are sufficient to monitor highly time-resolved NO 3 -N concentrations in emergent groundwater. However, the chosen path length of the sensors had a significant influence on the sensitivity and the range of detectable NO 3 -N. The accuracy of the calculated NO 3 -N concentrations of the sensors can be affected if the content of additional substances such as turbidity, organic matter, nitrite or hydrogen carbonate significantly varies after the sensors have been calibrated to a particular water matrix. The MWS offers more possibilities for calibration and error detection but requires more expertise compared with the DWS.

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Abstract. Two different in-situ spectrophotometers are compared that were used in the field to determine nitrate-nitrogen (NO3-N) concentrations at two distinct spring discharge sites. One sensor was a double wavelength spectrophotometer (DWS) and the other a multiple wavelength spectrophotometer (MWS). The objective of the study was to review the hardware options, determine ease of calibration, accuracy, influence of additional substances and to assess positive and negative aspects of the two sensors as well as troubleshooting and trade-offs. Both sensors are sufficient to monitor highly time-resolved NO3-N concentrations in emergent groundwater. However, the chosen path length of the sensors had a significant influence on the sensitivity and the range of detectable NO3-N. The accuracy of the calculated NO3-N concentrations of the sensors can be affected, if the content of additional substances such as turbidity, organic matter, nitrite or hydrogen carbonate significantly varies after the sensors have been calibrated to a particular water matrix. The MWS offers more possibilities for calibration and error detection, but requires more expertise compared with the DWS.

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Urban karst aquifers are threatened by anthropogenic activities, especially in semiarid developing countries. Recent water-sampling campaigns assessed the extent of groundwater-quality impairment in the Wadi Shueib in Jordan by a comprehensive hydrogeological and hydrochemical characterization of groundwater, wastewater, and imported water with its endmembers Lake Tiberias, Yarmouk River and Mukheiba wellfield. The results of a ternary mixing model with the mass ratios of Cl−/Br− and Ca2+/Mg2+ indicate that Lake Tiberias and Yarmouk River provide most of the imported water at the time of sampling in 2017 and Mukheiba wellfield provided minor amounts. The similarity in seasonal variations of Br− concentrations in the springs and the imported water revealed that imported water has generally a greater impact on groundwater than wastewater. However, the Br− concentrations also showed that the spatial wastewater impact is more visible towards urbanized areas due to increased infiltration of pollutants. The analysis of historical data series demonstrated the long-term urban impact on groundwater by an electrical conductivity increase over several decades, particularly since the mid-1990s, which is related to a doubling of Jordan’s population since that time and the associated urban growth. In this context, increased chloride and sulfate concentrations are noticeable due to the increased impact of more highly mineralized imported water and wastewater and decreasing recharge of low-mineralized rainwater. This study showed the hydrochemical differences in the Wadi Shueib groundwater system and serves as an example for the spatial and long-term response of karst aquifers to anthropogenic, seasonally variable input of imported water and wastewater.

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