Date of Degree


Document Type


Degree Name



Earth & Environmental Sciences


Pengfei Zhang

Committee Members

Karin Block

Zhongqi Cheng

Kevin Kroeger

Subject Categories

Environmental Microbiology and Microbial Ecology | Other Life Sciences


nitrogen cycle, antibiotics, denitrification, nitrogen pollution


Following a comprehensive review of the occurrence and impacts of antibiotics and related pharmaceutical compounds on the terrestrial N-cycle, three experiments were performed to explore the topic of biogeochemistry as a source or a sink for N-pollution. The first of these experiments addresses the question of whether environmentally relevant concentrations of antibiotics (µg·kg-1) have a significant effect on denitrification or N2O production, a question that has not been well addressed in previous studies. Having determined that there is a significant shift, the second study aims to comprehensively follow changes to soil N pools and N2O flux alongside biogeochemical reaction rates under different soil moisture conditions. The final chapter of this research, Chapter 5, looks to biogeochemistry as a solution for some of the water quality issues associated with excess N by quantifying the rate at which sand columns inoculated with lake sediment biodegrade undesirable taste/odor compounds and toxins produced by cyanobacterial algae that proliferate in nitrogen-rich waters.

The results of this work show that the balance between soil as a source or a sink of N pollutants can be significantly disturbed by sources beyond the obvious, i.e. antibiotics. It further shows that biogeochemical activity can serve as an effective treatment for secondary N-pollution. Additional research is encouraged to test the effects of additional antibiotics and by extending the incubation period to longer time periods. In particular, there also exists a need to examine the short and long-term effects of antibiotics on soil microbial community structure. While the present work shows that endemic bacteria can degrade nuisance compounds in N-polluted waters, the efficacy of this activity may also be affected by long-term antibiotic exposure in sediment. Genetic tools including GeoChip, will help to better constrain changes that are relevant to all aspects of these findings.



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