Nutrient dynamics in a hyporheic zone in response to a severe and prolonged dry period in a semi-arid river (Tafna wadi)

Abstract

Against the backdrop of recent climate change issues, the intensity of dry periods is increasing in semi-arid environments due to high temperatures, evaporation and a shortage of precipitation in summer. The Tafna catchment, which is located in north-western Algeria and is characterised by a Mediterranean climate with a sub-dry tendency, has been subject to severe and prolonged dry periods. In order to understand the impact of prolonged dry periods on biogeochemical processes and nutrient exchange between surface water (SW) and hyporheic water (HW) within the (study) catchment, four sets of samples were taken upstream of the Tafna wadi during low-water (LW) periods over two years (2014–2015). Nitrate, nitrite, ammonium and chloride were measured in surface water (SW) and hyporheic water (HW) at depths of 30, 60 and 100 cm. The results showed a significant loss of nitrate and a considerable increase in ammonium in the hyporheic zone (HZ) during these severe conditions. This could be related to (i) high rates of denitrification and (ii) the process of dissimilatory nitrate reduction to ammonium (DNRA). This study indicated that a severe drought directly affects the nitrogen cycle that occurs in a hyporheic zone (HZ), and thus affects the functioning of this area relative to the wadi system as a whole.