Management of the nitrogen cycle is an NAE Grand Challenge. While use of nitrogen fertilizers has become essential for food production, the health and environmental consequences due to aquatic and atmospheric nitrogen released from agricultural systems are substantial. The diffuse nature of agricultural sources makes control difficult, and the spatial and temporal disconnects between cause and effect also introduce technical and social hurdles. Our work on the nitrogen problem has focused on gaining a better understanding of the microbial ecology of nitrogen management practices. It is part of a larger vision focused on identifying solutions, integrating technical and social understanding, and developing tools to assist farmers and policy makers in addressing this problem.
Our initial work focused on areas with high water tables, where tile drainage systems have been installed. These drainage systems increase the flow of nitrate to surface waters and ultimately contribute to coastal hypoxia. However, they can also serve as collection systems, and nitrate has been successfully removed from the tile drainage system effluent using wood-chip bioreactors. We have determined that the majority of the denitrification activity in the bioreactors is bacterial, although there is also a fungal contribution. To determine an appropriate sampling pattern, we performed an intensive spatial sampling of a single bioreactor and analyzed the bacterial and denitrifying bacterial communities using a modified geostatistical analysis we developed. Subsequently, we monitored the temporal dynamics of the bacterial, fungal, and denitrifying bacterial communities in three field bioreactors. This work identified cyclical seasonal patterns in the bacteria and denitrifying bacterial communities in these bioreactors; the patterns appear to be linked to moisture content.
In the second phase of the project, we applied reliability engineering approaches to model these data for the identification of design principles for the denitrifying bioreactors and other ecological engineering systems, tested the effects of water level in lab-scale reactors, and began development of hybrid models integrating process-based biogeochemical models with agent-based, farmer decision-making models to investigate the interplay between policy alternatives, farmer decisions, and control of aquatic and atmospheric nitrogen pollution. This phase of the work is either in review or in preparation for publication.
Current work is investigating a variety of agricultural management practices and nitrogen control technologies, with particular emphasis on integrating our understanding of their effects on aquatic and atmospheric emissions. Specific objectives include i) field measurements and modeling of nitrous oxide production from a variety of agricultural management strategies, ii) characterization of the microbial activity and community composition under the same management strategies, and iii) the continued development of the hybrid biogeochemical/decision-making model to support policy development and farmer decision-making.
Funding: NSF Environmental Sustainability, USDA
Collaborators: Richard Cooke (Illinois), Angela Kent (Illinois), Sotiria Koloutsou-Vakakis (Illinois), Luis Rodríguez (Illinois), and Yuanhui Zhang (Illinois)
Students: Tim Alston, Malia Andrus, Nick Bartolerio, Paul Choi, Mary Foltz, Sarah Hathaway, Yanjun Ma, Matt Porter
Related publications:
Hathaway, S. K., N. A. Bartolerio, L. F. Rodríguez, A. D. Kent, J. L. Zilles. 2017. Denitrifying bioreactors resist disturbance from fluctuating water levels. Frontiers in Environmental Science. Volume 5, article 35. doi: 10.3389/fenvs.2017.00035.
Zilles, J. L., L. F. Rodriguez, N. A. Bartolerio, and A. D. Kent. 2016. Microbial community modeling using reliability theory. The ISME Journal 10:1809-1814. advance online publication 16 February 2016. doi: 10.1038/ismej.2016.1
Hathaway, S. K., M. D. Porter, L. F. Rodriguez, A. D. Kent, J. L. Zilles. 2015. Impact of the contemporary environment on denitrifying bacterial communities. Ecological Engineering 82:469-473. published online June 9, 2015 doi:10.1016/j.ecoleng.2015.05.005
Porter, M. D., J. M. Andrus, N. A. Bartolerio, L. F. Rodriguez, Y. Zhang, J. L. Zilles, A. D. Kent. 2015. Seasonal patterns in microbial community composition in denitrifying bioreactors treating subsurface agricultural drainage. Microbial Ecology 70(3):710-23. published online April 26, 2015 DOI: 10.1007/s00248-015-0605-8
Andrus, J. M., M. D. Porter, L. F. Rodriguez, T. Kuehlhorn, R. A. C. Cooke, Y. Zhang, A. D. Kent, and J. L. Zilles. 2014. Spatial variation in the total and denitrifying bacterial community in a denitrifying biofilter treating subsurface agricultural drainage. Microbial Ecology 67(2):265-272. http://dx.doi.org/10.1007/s00248-013-0286-0 Epub 2013 Sept 29.