The role of dynamic surface water‐groundwater exchange on streambed denitrification in a first‐order, low‐relief agricultural watershed

Abstract

The role of temporally varying surface water-groundwater (SW-GW) exchange on nitrate removal by streambed denitrification was examined along a reach of Leary Weber Ditch (LWD), Indiana, a small, first-order, low-relief agricultural watershed within the Upper Mississippi River basin, using data collected in 2004 and 2005. Stream stage, GW heads (H), and temperatures (T) were continuously monitored in streambed piezometers and stream bank wells for two transects across LWD accompanied by synoptic measurements of stream stage, H, T, and nitrate (NO 3 ) concentrations along the reach. The H and T data were used to develop and calibrate vertical two-dimensional, models of streambed water flow and heat transport across and along the axis of the stream. Model-estimated SW-GW exchange varied seasonally and in response to high-streamflow events due to dynamic interactions between SW stage and GW H. Comparison of 2004 and 2005 conditions showed that small changes in precipitation amount and intensity, evapotranspiration, and/or nearby GW levels within a low-relief watershed can readily impact SW-GW interactions. The calibrated LWD flow models and observed stream and streambed NO 3 concentrations were used to predict temporal variations in streambed NO 3 removal in response to dynamic SW-GW exchange. NO 3 removal rates underwent slow seasonal changes, but also underwent rapid changes in response to high-flow events. These findings suggest that increased temporal variability of SW-GW exchange in low-order, low-relief watersheds may be a factor contributing their more efficient removal of NO 3 . Key Points:Low-order, low-relief watersheds experience dynamic streambed SW-GW exchange Streambed hyporheic and GW flow vary with season, streamflow, and climate Dynamic exchange may enhance streambed denitrification in headwater streams Supporting Information:Supporting Information S1 Correspondence to: H. I. Essaid, hiessaid@usgs.gov Citation: Rahimi, M., H. I. Essaid, and J. T. Wilson (2015), The role of dynamic surface water-groundwater exchange on streambed denitrification in a first-order, low-relief agricultural watershed, Water Resour. Res., 51, 9514-9538,

Hyporheic exchange controlled by dynamic hydrologic boundary conditions

“…This type of coupled surface and subsurface flow response could be considered as part of the design of nonemergency flow releases for dams and possibly as a mitigation measure as part of dam relicensure. For example, by controlling the timing of stream stage fluctuations relative to aquifer withdrawals, such as riverbank filtration for drinking water or irrigation withdrawals downstream of a hydropower dam, a manager could manipulate hyporheic exchange to achieve timescales that would enable desirable functions (e.g., denitrification [e.g., Harvey et al ., ; Rahimi et al ., ] or creation of thermal refugia for fish [e.g., Bowerman et al ., ; Mathes et al ., ]). Alternatively, exchange could be intentionally reduced to provide environmental benefits.…”

“…These up-and down-valley boundaries are periodic only in space to approximate an infinite domain and do not vary in time. The sinusoidal components of the stream and hillslope boundary conditions are taken as uniform along the 36 m model domain, which is assumed short enough to not warrant downstream wave routing of the stream boundary condition [after Perkins and Koussis, 1996]. A homogeneous, isotropic hydraulic conductivity of 10 À3 m s À1 was assigned to the entire model domain to eliminate the possibility of heterogeneity in the hydraulic conductivity field as a control on groundwater flow [e.g., Salehin et al, 2004;Sawyer et al, 2014b;Ward et al, 2011].…”

Flux dynamics at the groundwater-surface water interface in a tropical catchment

“…However, water cycling in river beds and banks during storms also has the possibly to drive nutrient cycling and nitrate removal from riverbed processes (McCallum and Shanafield, 2016;Rahimi et al, 2015). These processes might function differently for intermittent compared to perennial river systems (Costigan et al, 2015;Datry et al, 2014).…”

The importance and challenge of hyporheic mixing

“…These transients strongly affect the hyporheic zone, but most are damped considerably before they reach deeper groundwater, with greater damping expected at shorter durations/higher frequencies [Liu et al, 2016]. At larger spatial and temporal scales, such transients can be periodic (e.g., daily such as flow peaking for hydropower generation, snowmelt, evapotranspiration, and tides; or annual seasons) or nonperiodic (e.g., storms and other meteorological events) Swanson, 1996, 1999;Peterson and Connelly, 2001;Arntzen et al, 2006;Boano et al, 2007b;Fritz and Arntzen, 2007;Loheide and Lundquist, 2009;Boano et al, 2013;Azinheira et al, 2014;Larsen et al, 2014;Pool et al, 2014;Dudley-Southern and Binley, 2015;Rahimi et al, 2015;Malzone et al, 2016;Schmadel et al, 2016]. Such transient hydraulic perturbations propagate downward into the sediment, which based on studies that vary the hydraulic boundary conditions of hyporheic processes [e.g., Cardenas and Wilson, 2006;Boano et al, 2008;Trauth et al, 2013;Fox et al, 2014;Marzadri et al, 2016], would thereby change the size of hyporheic flow cells, move hyporheic flow cells longitudinally along riverbeds, and move mixing zones around within the sediment [Boano et al, 2007b[Boano et al, , 2013Schmadel et al, 2016;Stegen et al, 2016].…”