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Review
Nitrate attenuation in groundwater: A review ofbiogeochemical controlling processes
Michael O. Rivetta,*, Stephen R. Bussb, Philip Morganb,1,Jonathan W.N. Smithc,d, Chrystina D. Bemmentb
aSchool of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UKbESI Ltd, New Zealand House, 160 Abbey Foregate, Shrewsbury SY2 6FD, UKcEnvironment Agency, Olton Court, 10 Warwick Road, Olton, Solihull, West Midlands B92 7HX, UKdCatchment Science Centre, University of Sheffield, Broad Lane, Sheffield S3 7HQ, UK
a r t i c l e i n f o
Article history:
Received 10 December 2007
Received in revised form
11 July 2008
Accepted 15 July 2008
Available online 23 July 2008
Keywords:
Nitrate
Denitrification
Groundwater
Natural attenuation
Nitrates Directive
Water Framework Directive
* Corresponding author. Tel.: 44 (0) 1214143E-mail address: [email protected] (M
1 Present address: Sirius Geotechnical & En0043-1354/$ see front matter 2008 Elsevidoi:10.1016/j.watres.2008.07.020
a b s t r a c t
Biogeochemical processes controlling nitrate attenuation in aquifers are critically
reviewed. An understanding of the fate of nitrate in groundwater is vital for managing risks
associated with nitrate pollution, and to safeguard groundwater supplies and ground-
water-dependent surface waters. Denitrification is focused upon as the dominant nitrate
attenuation process in groundwater. As denitrifying bacteria are essentially ubiquitous in
the subsurface, the critical limiting factors are oxygen and electron donor concentration
and availability. Variability in other environmental conditions such as nitrate concentra-
tion, nutrient availability, pH, temperature, presence of toxins and microbial acclimation
appears to be less important, exerting only secondary influences on denitrification rates.
Other nitrate depletion mechanisms such as dissimilatory nitrate reduction to ammonium
and assimilation of nitrate into microbial biomass are unlikely to be important in most
subsurface settings relative to denitrification. Further research is recommended to improve
current understanding on the influence of organic carbon, sulphur and iron electron
donors, physical restrictions on microbial activity in dual porosity aquifers, influences of
environmental condition (e.g. pH in poorly buffered environments and salinity in coastal or
salinized soil settings), co-contaminant influences (particularly the contrasting inhibitory
and electron donor influences of pesticides) and improved quantification of denitrification
rates in the laboratory and field.
2008 Elsevier Ltd. All rights reserved.
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42162. Denitrification: overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4217
2.1. Electron acceptor context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42172.2. Denitrification process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4218
957; fax: 44 (0) 1214144942..O. Rivett).vironmental Ltd, The Heath Business Park, Runcorn WA7 4QX, UK.
er Ltd. All rights reserved.
mailto:[email protected]://www.elsevier.com/locate/watres
w a t e r r e s e a r c h 4 2 ( 2 0 0 8 ) 4 2 1 5 4 2 3 24216
2.2.1. Transformation products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42182.3. Denitrification occurrence in the subsurface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4219
3. Electron donors used in denitrification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42193.1. Organic carbon (heterotrophic denitrification) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42193.2. Organic contaminant carbon sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42213.3. Reduced iron (autotrophic denitrification) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42223.4. Reduced sulphur (autotrophic denitrification) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42223.5. Other electron donors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4222
4. Denitrification activity: effects of environmental conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42234.1. Nitrate concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42234.2. Oxygen concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42234.3. Nutrient and micro-nutrient availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42244.4. pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42244.5. Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42244.6. Salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42254.7. Inhibitory substances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42254.8. Sediment pore size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42254.9. Microbial acclimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4225
5. Nitrate depletion mechanisms other than denitrification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42265.1. Dissimilatory nitrate reduction to ammonium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42265.2. Assimilation of nitrate into microbial biomass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42265.3. Nitrate removal via phreatophytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4226
6. Conclusions and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4227Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4227References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4227
1. Introduction The European approach to the problem has increasingly
Since the 1970s, nitrate (NO3) contamination of groundwater
has become a significant environmental problem, with
many parts of the world now reporting groundwater nitrate
pollution (Burden, 1982; Spalding and Exner, 1993; Beeson
and Cook, 2004; European Environment Agency (EEA), 2000;
Rao, 2006; Rivett et al., 2007; Roy et al., 2007; Organisation
for Economic Co-operation and Development (OECD), 2008).
The consequences include long-debated health concerns
arising from increased risks of methaemoglobinaemia and
cancer (Fan and Steinberg, 1996; WHO, 1999; WHO, 2004;
Horing and Chapman, 2004), and environmental impacts
such as the eutrophication of surface waters due to excess
nutrients (Vitousek et al., 1997; WHO, 1999; Mason, 2002).
Diffuse pollution from intensive agriculture since the mid-
20th century has largely been blamed for these problems
(Foster, 2000). It has been estimated that 7080% of the
nitrate in English surface and groundwaters is derived from
agricultural activities (
