Investigating “net” provenance, N source, transformation and fate within hydrologically isolated grassland plots

E. Clagnan, S.F. Thornton, S.A. Rolfe, N.S. Wells, K. Knoeller and O. Fenton

Agricultural Water Management, 2018, vol. 203, issue C, 1-8

Abstract: Agricultural landscapes contain many different soil types with heterogeneous nitrogen (N) attenuation capacity. Typically, a zone of contribution (ZOC) surrounding a borehole is used to interpret subsurface hydro-biogeochemical functional capacity. This presents a “net” interpretation of source and attenuation within these calculated areas. Herein, we use the concept of ZOC commonly used for borehole screen intervals but for an end-of-pipe location within four hydrologically isolated plots. Water samples from end-of-pipe and piezometer locations are examined for nitrogen (N), biogeochemical, dissolved gas and isotopic viewpoints to elucidate multi-layered “net” water provenance, N source, transformations and fate. Results showed a nitrate (NO3−-N) plume migrating in shallow groundwater (between 0.39 and 8.07 mg N/L), with low concentrations in the shallow artificial drainage system (below 3.22 mg N/L). Water provenance data showed distinct signatures of: precipitation and deep groundwater at 3–4 m below ground level (bgl) and water entering, migrating and discharging at the end of pipe location. The latter signature was caused by enrichment of δ18O-H2O during migration. This means there was disconnectivity on site with no interaction between water migrating through the drainage pipe at 1 m and deeper groundwater migrating at 3–4 m depth. The analysis of NO3−-N concentration and its isotopic signature (δ15N-NO3− and δ18O-NO3) identified further connections between screen interval depths and an up-gradient organic point source with elevated NO3−-N migrating at this depth and different transformation processes occurring at different depths. Temporally NO3−-N concentrations at this depth have decreased over time. Fenton et al. documented an average of 7.5 (±4.5) mg N/L whereas Ibrahim et al. documented an average of 6.8 (±3.7) mg N/L at this depth. The point source was removed in 2006 and NO3−-N concentration in the present study have further reduced to an average of 3.9 (±2.8) mg N/L. End-of-pipe data at 1 m bgl highlighted connectivity with the overlying plot and showed different water attenuation functionality than the deeper system. End-of-pipe locations clustered together along the denitrification line. This highlighted a consistency of signals across the four plots in terms of what occurs in the soil profile above the drain installation depth of 1 m. At 3–4 m bgl however, samples varied spatially showing inconsistency between the end-of-pipe locations and plots indicating the occurrence of different processes.

Keywords: Land drainage; Agriculture; Nitrogen; Natural isotopic abundances; Dissolved gases (search for similar items in EconPapers)
Date: 2018
References: View references in EconPapers View complete reference list from CitEc
Citations:

Downloads: (external link)
http://www.sciencedirect.com/science/article/pii/S0378377418301264
Full text for ScienceDirect subscribers only

Related works:
This item may be available elsewhere in EconPapers: Search for items with the same title.

Export reference: BibTeX RIS (EndNote, ProCite, RefMan) HTML/Text

Persistent link: https://EconPapers.repec.org/RePEc:eee:agiwat:v:203:y:2018:i:c:p:1-8

DOI: 10.1016/j.agwat.2018.02.031

Access Statistics for this article

Agricultural Water Management is currently edited by B.E. Clothier, W. Dierickx, J. Oster and D. Wichelns

More articles in Agricultural Water Management from Elsevier
Bibliographic data for series maintained by Catherine Liu ().