Transport and Fate of Nitrate at the Ground‐Water/Surface‐Water Interface

Abstract

Although numerous studies of hyporheic exchange and denitrification have been conducted in pristine, high‐gradient streams, few studies of this type have been conducted in nutrient‐rich, low‐gradient streams. This is a particularly important subject given the interest in nitrogen (N) inputs to the Gulf of Mexico and other eutrophic aquatic systems. A combination of hydrologic, mineralogical, chemical, dissolved gas, and isotopic data were used to determine the processes controlling transport and fate of NO3− in streambeds at five sites across the USA. Water samples were collected from streambeds at depths ranging from 0.3 to 3 m at three to five points across the stream and in two to five separate transects. Residence times of water ranging from 0.28 to 34.7 d m−1 in the streambeds of N‐rich watersheds played an important role in allowing denitrification to decrease NO3− concentrations. Where potential electron donors were limited and residence times were short, denitrification was limited. Consequently, in spite of reducing conditions at some sites, NO3− was transported into the stream. At two of the five study sites, NO3− in surface water infiltrated the streambeds and concentrations decreased, supporting current models that NO3− would be retained in N‐rich streams. At the other three study sites, hydrogeologic controls limited or prevented infiltration of surface water into the streambed, and ground‐water discharge contributed to NO3− loads. Our results also show that in these low hydrologic‐gradient systems, storm and other high‐flow events can be important factors for increasing surface‐water movement into streambeds.

Hydrogen peroxide dynamics in an agricultural headwater stream: Evidence for significant nonphotochemical production

“…Maple Creek was identified and investigated by the USGS under the National Water-Quality Assessment Program in recent years as a representative agricultural headwater stream affected by farm-based chemicals (Fredrick et al 2006). The stream is characterized by shallow annual mean flows (2.27 m 3 s 21 ), sediment composed of fine sand and silt, and high nutrient loads (Fredrick et al 2006;Puckett et al 2008). The site was chosen for the present study due to flow and sediment conditions conducive to performing mesocosm experiments, availability of water quality and real-time gauging station data, and nutrient and temperature conditions favorable to biotic activity (Puckett et al 2008 The mesocosms were hollow cylinders made of SolacrylH SUVT (Spartech Company), standing 61 cm tall, with inner diameters of 46 cm.…”

“…The stream is characterized by shallow annual mean flows (2.27 m 3 s 21 ), sediment composed of fine sand and silt, and high nutrient loads (Fredrick et al 2006;Puckett et al 2008). The site was chosen for the present study due to flow and sediment conditions conducive to performing mesocosm experiments, availability of water quality and real-time gauging station data, and nutrient and temperature conditions favorable to biotic activity (Puckett et al 2008 The mesocosms were hollow cylinders made of SolacrylH SUVT (Spartech Company), standing 61 cm tall, with inner diameters of 46 cm. SolacrylH SUVT is a type of Plexiglas that is transparent to both visible and UV light; these properties were verified by determining light transmittance on a spectrophotometer prior to the field experiments.…”

A review of the impact of climate change on future nitrate concentrations in groundwater of the UK

“…Where residence times are sufficiently long and there are potential electron donors available denitrification can occur in this zone (Puckett et al, 2008). Krause et al (2009) showed that the distribution of the low redox zone can be very variable.…”

Fate of nitrate in seepage from a restored wetland receiving agricultural tailwater

“…3 and Table 6). Many studies report that DNP is more strongly correlated with available carbon (e.g., microbially labile C) rather than total organic carbon (D' Angelo and Reddy, 1999;Hill and Cardaci 2002;Hernandez and Mitsch, 2007;Puckett et al, 2008). Only organic carbon was measured for this study, so it is possible that there may be substantial differences in carbon availability between the environments that may affect DNP.…”