Changes in discharge and solute dynamics between hillslope and valley-bottom intermittent streams

Abstract

Abstract. To gain understanding on how alluvial zones modify water and nutrient export from semiarid catchments, we compared monthly discharge as well as stream chloride, carbon, and nitrogen dynamics between a hillslope catchment and a valley-bottom catchment with a well-developed alluvium. Stream water and solute fluxes from the hillslope and valley-bottom catchments showed contrasting patterns between hydrological transitions and wet periods, especially for bio-reactive solutes. During transition periods, stream water export decreased >40 % between the hillslope and the valley bottom coinciding with the prevalence of streamto-aquifer fluxes at the alluvial zone. In contrast, stream water export increased by 20-70 % between the hillslope and valley-bottom catchments during wet periods. During transition periods, stream solute export decreased by 34-97 % between the hillslope and valley-bottom catchments for chloride, nitrate, and dissolved organic carbon. In annual terms, stream nitrate export from the valley-bottom catchment (0.32 ± 0.12 kg N ha −1 yr −1 [average ± standard deviation]) was 30-50 % lower than from the hillslope catchment (0.56 ± 0.32 kg N ha −1 yr −1 ). The annual export of dissolved organic carbon was similar between the two catchments (1.8 ± 1 kg C ha −1 yr −1 ). Our results suggest that hydrological retention in the alluvial zone contributed to reduce stream water and solute export from the valley-bottom catchment during hydrological transition periods when hydrological connectivity between the hillslope and the valley bottom was low.

The influence of riparian evapotranspiration on stream hydrology and nitrogen retention in a subhumid Mediterranean catchment

“…The relatively low ET values, together with the fact that the riparian forest occupied a small area of the catchment (6 %), resulted in a minimal contribution (4.5 %) of riparian transpiration to the annual water budget for this catchment. This estimate is similar to values reported for tropical (Cadol et al, 2012), temperate (e.g., Petrone et al, 2007;Salemi et al, 2012), and Mediterranean (e.g., Bernal and Sabater, 2012;Folch and Ferrer, 2015;Wine and Zou, 2012) systems, while being several folds lower than values reported for semiarid and dry land regions (Contreras et al, 2011;Dahm et al, 2002;Doble et al, 2006) (Fig. 6).…”

“…Thus, riparian trees could affect the strength, location, and duration of the predominant flow path, and consequently, influence the capacity of riparian zones to reduce N not only from upland groundwater inputs, but also from stream water. In this line of thought, previous studies have reported decreases in stream N concentration along losing stream reaches attributed to N uptake at the stream-riparian edge (Bernal and Sabater, 2012;Dent et al, 2007;Rassam et al, 2006). Yet, there has been little research focused on the influence of riparian ET on upland-riparian-stream hydrological exchange and its potential to promote variations in stream N concentrations and fluxes.…”

“…NO − 3 was analyzed by the cadmium reduction method (Keeney and Nelson, 1982) using a Technicon Autoanalyzer (Technicon, 1976). NH + 4 was manually analyzed by the salicilate/nitropruside method (Baethgen and Alley, 1989) using a spectrophotometer (PharmaSpec UV-1700 SHIMADZU).…”

“…Second, we expected that differences in stream N concentration between the headwater and valley reach will reflect differences in riparian N cycling coupled to the dominant direction of water flow between the riparian zone and the stream. Based on longitudinal changes observed in semiarid streams (Bernal and Sabater, 2012;Dent et al, 2007), we expected decreases in N concentration along the two reaches, but especially at the valley reach because of higher stream hydrological retention. The results of this study contribute to our understanding of the interaction between riparian ET and fluxes of water and nutrients at the stream-riparian edge.…”

Responses of microbial activity in hyporheic pore water to biogeochemical changes in a drying headwater stream

“…Drying and its consequences, such as disconnection of flow paths laterally and longitudinally, as well as longer water residence times (Fisher, Grimm, Martí, & Gómez, 1998;Harvey, Conklin, & Koelsch, 2003) provoked a decrease in SRP and NO 3 concentrations that is also observed in other studies from intermittent streams (Bernal & Sabater, 2012;Martí, Grimm, & Fisher, 1997;von Schiller et al, 2008). Additionally, in intermittent streams, the absence of surface flow can involve the diffusion of oxygen into the pore space of the hyporheic zone that triggers ammonia oxidation (Merbt et al, 2016).…”