Nitrogen transport and transformations in a shallow aquifer receiving wastewater discharge: A mass balance approach

Abstract

Abstract. Nitrogen transport and transformations were followed over the initial 3 years of development of a plume of wastewater-contaminated groundwater in Cape Cod, Massachusetts. Ammonification and nitrification in the unsaturated zone and ammonium sorption in the saturated zone were predominant, while loss of fixed nitrogen through denitrification was minor. The major effect of transport was the oxidation of discharged organic and inorganic forms to nitrate, which was the dominant nitrogen form in transit to receiving systems. Ammonification and nitrification in the unsaturated zone transformed 16-19% and 50-70%, respectively, of the total nitrogen mass discharged to the land surface during the study but did not attenuate the nitrogen loading. Nitrification in the unsaturated zone also contributed to a p H decrease of 2 standard units and to an N20 increase (46-660 •g N/L in the plume). Other processes in the unsaturated zone had little net effect: Ammonium sorption removed <1% of the total discharged nitrogen mass; filtering of particulate organic nitrogen was less than 3%; ammonium and nitrate assimilation was less than 6%; and ammonia volatilization was less than 0.25%. In the saturated zone a central zone of anoxic groundwater (DO _< 0.05 mg/L) was first detected 17 months after effluent discharge to the aquifer began, which expanded at about the groundwater-flow velocity. Although nitrate was dominant at the water table, the low, carbon-limited rates of denitrification in the anoxic zone (3.0-9.6 (ng N/cm3)/d) reduced only about 2% of the recharged nitrogen mass to N2. In contrast, ammonium sorption in the saturated zone removed about 16% of the recharged nitrogen mass from the groundwater. Ammonium sorption was primarily limited to anoxic zone, where nitrification was prevented, and was best described by a Langmuir isotherm in which effluent ionic concentrations were simulated. The initial nitrogen load discharged from the groundwater system may depend largely on the growth and stability of the sorbed ammonium pool, which in turn depends on effluent-loading practices, subsurface microbial processes, and saturation of available exchange sites.

A Grey Water Footprint Assessment of Groundwater Chemical Pollution: Case Study in Salento (Southern Italy)

“…The GWF related to Ammonium (Figure 4), which reveals high values mainly in the northern area of Salento, could be the result of fertilization in agriculture, but also of human or animal defecation [28,29]. Its presence in groundwater can be related to geological factors such as the decay of material undergoing fossilization [30], but, if associated with microbiological compounds, also to sewers and/or livestock farms [31].…”

Nitrates and phosphates in cave waters of Kraków-Częstochowa Upland, southern Poland

“…In this context, groundwater pollution with nitrates is a global problem (Goodchild 1998;Joosten et al 1998;Birkinshaw and Ewen 2000;Kyllmar et al 2004;Liu et al 2005). Nitrates are characterised by a high degree of mobility and the ability to infiltrate the phreatic zone as a result of leaching processes (DeSimone and Howes 1998;Chowdary et al 2005). The leaching of nitrates from the vadose zone in cultivated areas demonstrates variation over time and space, conditioned by the quantity and the range of applied fertilisers, irrigation of the area, and types of crops (Sylvester-Bradley et al 2001;Ju et al 2006).…”

Nitrogen transformation and transport modeling in groundwater aquifers

“…Moreover, a new planctomycete has been described that is capable of anoxic ammonia oxidation by a mechanism not yet fully understood (Strous et al, 1999). DeSimone and Howes (1998) suggested that nitrification in the suboxic saturated zone, along with oxidation of the residual organic carbon, may have buffered oxygen in the plume.…”