Using ion-exchange resins to monitor nitrate fluxes in remote semiarid stream beds

Monitoring in remote areas can represent a real challenge in environmental studies. Numerous techniques have been developed over the last decades to monitor nutrients and other elements in different systems. However, not all of them are suitable for field applications, particularly when the locations are difficult to access or its accessibility depends on seasonal climate conditions. This study was aimed to test the applicability and efficiency of resin samplers and resin bags to monitor nitrates fluxes (NO₃-N) in two small semi-arid catchments in Northwestern Mexico. Resin samplers were installed in the hyporheic zone below the river bed in order to monitor the vertical fluxes of NO₃-N and remained there for 5 months (during the summer rains). Resin bags were anchored in rock outcrops upstream of the resin samplers before the onset of the summer rainfall season and replaced every 2 weeks during 4 months to capture pulses of NO₃-N in ephemeral streams. NO₃-N pulses in the stream are a potential source of NO₃-N that can infiltrate into the soil. Results of the resin samplers found a difference of up to 12 kg ha^-1 season^-1 between the two catchments. The resin bags showed a higher accumulation of NO₃-N in the catchment with lower vegetation cover (160.3 mg L^-1 season^-1) compared to the one with higher vegetation (67.8 mg L^-1 season^-1). Measured nitrate fluxes at both sites responded to rainfall pulses recorded during the monitoring period. Resin samplers and resin bags can be used together, to assess nutrient fluxes on the surface and in the soil and can be tested in any type of ecosystem. In this particular case, these methods demonstrated an efficient way of determining spatio-temporal nitrate fluxes in semi-arid ecosystems in remote areas that are difficult to access, monitor, and collect data.