Patchiness in groundwater nitrate removal in a riparian forest

Our ability to identify and manage riparian sites for groundwater nitrate (NO3(-)) removal is limited by uncertainty surrounding the relative importance of plant uptake vs. microbially mediated removal processes. Microcosm studies often demonstrate negligible transformation rates in the subsoil of r...

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Bibliographic Details
Published in:Journal of environmental quality 1998-01, Vol.27 (1), p.146-155
Main Authors: Gold, A.J, Jacinthe, P.A, Groffman, P.M, Wright, W.R, Puffer, R.H
Format: Article
Language:English
Subjects:
Agronomy. Soil science and plant productions
Animal, plant and microbial ecology
Applied ecology
AZOTE
Biological and medical sciences
CONTROL DE LA CONTAMINACION
Ecotoxicology, biological effects of pollution
Fundamental and applied biological sciences. Psychology
GROUNDWATER POLLUTION
LUTTE ANTIPOLLUTION
NITRATE
NITRATES
NITRATOS
NITROGEN
NITROGENO
Nutrient removal
POLLUTION CONTROL
POLLUTION DE L'EAU SOUTERRAINE
POLUCION DE AGUAS SUBTERRANEAS
Riparian forests
Soil and water pollution
Soil science
Terrestrial environment, soil, air
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Summary:Our ability to identify and manage riparian sites for groundwater nitrate (NO3(-)) removal is limited by uncertainty surrounding the relative importance of plant uptake vs. microbially mediated removal processes. Microcosm studies often demonstrate negligible transformation rates in the subsoil of riparian forests, even in situations where groundwater well networks showed substantial groundwater NO3(-) removal during the winter and a decline in dissolved oxygen (DO) in ambient groundwater moving through the site. We hypothesize that microcosm studies may miss groundwater transformations that occur within microsites, that is, "hotspots" of riparian subsoils. We created mesocosms of large (15 cm diam. X 40 cm length), undisturbed cores from the seasonally saturated zone of poorly dried (PD) and moderately well drained (MWD) sandy soils from a forested riparian area in southern New England. We dosed the mesocosms for 130 d with ambient groundwater amended with NO3(-)-N and Br(-). Changes in the NO3(-)-N/Br(-) ratios were used to calculate groundwater NO3(-)-N removal rates. The PD treatment demonstrated substantial groundwater NO3(-)-N removal rates. The PD mesocosms contained patches of dark-stained material that often surrounded roots in various stages of decay. The dry mass of patches in the PD treatment ranged from 0.07 to 1.4% of the mesocosms. The MWD treatment contained no patches and exhibited no groundwater NO3(-)-N removal. Further investigations on the relationships between the extent of subsurface patchiness, water table dynamics and plant characteristics might yield fruitful insights into the management of vegetated riparian zones for groundwater NO3(-)-N removal
ISSN:0047-2425
1537-2537
DOI:10.2134/jeq1998.00472425002700010021x