Aquifer-scale controls on the distribution of nitrate and ammonium in ground water near La Pine, Oregon, USA

Abstract

Summary Geochemical and isotopic tools were applied at aquifer, transect, and subtransect scales to provide a framework for understanding sources, transport, and fate of dissolved inorganic N in a sandy aquifer near La Pine, Oregon. NO 3 is a common contaminant in shallow ground water in this area, whereas high concentrations of NH 4 -N (up to 39 mg/L) are present in deep ground water. N concentrations, N/Cl ratios, tracer-based apparent ground-water ages, N isotope data, and hydraulic gradients indicate that septic tank effluent is the primary source of NO 3 . N isotope data, N/Cl and N/C relations, 3H data, and hydraulic considerations point to a natural, sedimentary organic matter source for the high concentrations of NH 4 , and are inconsistent with an origin as septic tank N. Low recharge rates and flow velocities have largely restricted anthropogenic NO 3 to isolated plumes within several meters of the water table. A variety of geochemical and isotopic data indicate that denitrification also affects NO 3 gradients in the aquifer. Ground water in the La Pine aquifer evolves from oxic to increasingly reduced conditions. Suboxic conditions are achieved after about 15-30 y of transport below the water table. This article is a U.S. government work, and is not subject to copyright in the United States.denitrified near the oxic/suboxic boundary. Denitrification in the La Pine aquifer is characterized well at the aquifer scale with a redox boundary approach that inherently captures spatial variability in the distribution of electron donors. ª

Linking groundwater dissolved organic matter to sedimentary organic matter from a fluvio-lacustrine aquifer at Jianghan Plain, China by EEM-PARAFAC and hydrochemical analyses

“…Subsequent studies in West Bengal showed that DOM originated from the sediments of aquifers (McArthur et al, 2004) and arsenic concentrations corresponded to younger sediments with more biodegradable organic carbon (Postma et al, 2012). In addition, ammonium occurrence in groundwater was related to the release of C and N due to degradation of sedimentary organic matter (SOM) (Hinkle et al, 2007) or OM from buried paleosols of geological age (Glessner and Roy, 2009). Finally, studies of SGD generally ascribed dissolved nutrients (C, N and P) to release from coastal sediments (Gleeson et al, 2013).…”

Tracing freshwater nitrate sources in pre-alpine groundwater catchments using environmental tracers

“…Thus, the local hydrogeology needs to be part of any investigation tracing nitrate origin in groundwater. Considering the time delay between infiltration of nitrate pollution and its appearance in groundwater (Diédhiou et al, 2011;Hinkle et al, 2007), groundwater studies struggle with an appropriate temporal assignment of nitrate contamination. Vice versa, reducing nitrate input affects the groundwater quality only after a certain time lag due to nitrogen turnover processes in soil and the mean transit time of groundwater recharge (Sebilo et al, 2013).…”

Geochemical reactivity of subsurface sediments as potential buffer to anthropogenic inputs: a strategy for regional characterization in the Netherlands

“…These studies predominantly focus on water chemistry and include topics such as groundwater (redox) zonation and gradients; degree and scale of, and controls on water quality variability and spatial distribution; source apportionment; (bio)geochemical controls on contaminant degradation; reactive transport modelling; aquifer vulnerability mapping; and the determination of background/threshold concentrations (for recent papers, see, e.g. Vissers 2005;Park et al 2006;Hinkle et al 2007;Robins et al 2007;Báez-Cazull et al 2008Hinsby et al 2008;McMahon andChapelle 2007, Sochaczewski et al 2008;Spiteri et al 2008).…”