Groundwater flow, nutrient, and stable isotope dynamics in the parafluvial-hyporheic zone of the regulated Lower Colorado River (Texas, USA) over the course of a small flood

Briody, Alyse C.; Cardenas, M Bayani; Shuai, Pin; Knappett, Peter S. K.; Bennett, Philip C.

Groundwater flow, nutrient, and stable isotope dynamics in the parafluvial-hyporheic zone of the regulated Lower Colorado River (Texas, USA) over the course of a small flood | Dynamiques des écoulements d’eaux souterraines, des éléments nutritifs et des isotopes stables dans la zone parafluviale-hyporhéique du Colorado inférieur régulé (Texas, Etats-Unis d’Amérique) au cours d’une petite crue Flujo de agua subterránea, de nutrientes y dinámica de isótopos estables en la zona hiporreica parafluvial regulada del Río Colorado Inferior (Texas, EE.UU.) durante el transcurso de una pequeña crecida 小的洪水过程中(美国德克萨斯州)受到管理的科罗拉多河下游准河流---伏流带地下水流、营养物和稳定同位素动力学 Dinâmicas de fluxo, nutrientes e isótopos estáveis nas águas subterrâneas em zona parafluvial hiporréica no Baixo Rio Colorado (Texas, EUA) regulado sobre curso de uma pequena cheia

2016

Briody, Alyse C. | Cardenas, M Bayani | Shuai, Pin | Knappett, Peter S. K. | Bennett, Philip C.

Periodic releases from an upstream dam cause rapid stage fluctuations in the Lower Colorado River near Austin, Texas, USA. These daily pulses modulate fluid exchange and residence times in the hyporheic zone where biogeochemical reactions are typically pronounced. The effects of a small flood pulse under low-flow conditions on surface-water/groundwater exchange and biogeochemical processes were studied by monitoring and sampling from two dense transects of wells perpendicular to the river. The first transect recorded water levels and the second transect was used for water sample collection at three depths. Samples were collected from 12 wells every 2 h over a 24-h period which had a 16-cm flood pulse. Analyses included nutrients, carbon, major ions, and stable isotopes of water. The relatively small flood pulse did not cause significant mixing in the parafluvial zone. Under these conditions, the river and groundwater were decoupled, showed potentially minimal mixing at the interface, and did not exhibit any discernible denitrification of river-borne nitrate. The chemical patterns observed in the parafluvial zone can be explained by evaporation of groundwater with little mixing with river water. Thus, large pulses may be necessary in order for substantial hyporheic mixing and exchange to occur. The large regulated river under a low-flow and small flood pulse regime functioned mainly as a gaining river with little hydrologic connectivity beyond a narrow hyporheic zone.

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