NATURAL AND CONSTRUCTED WETLANDS ARE NOW USED EXTENSIVELY ACROSS THE UNITED STATES AS A MEANS FOR MITIGATING NITRATE LOSSES TO BOTH SURFACE WATER AND GROUNDWATER. HOWEVER, PROPERTY AND MANAGEMENT REQUIREMENTS LIMIT WETLAND USE. FLOATING TREATMENT WETLANDS, FLOATING MACROPHYTE MATS, POSITIONED IN ADJACENT WATER STORAGE PONDS HAVE THE POTENTIAL TO A WIDE RANGE OF CONTAMINANTS (I.E., NITRATE, PHOSPHATE, ANTIBIOTICS) FROM SOURCE WATER WITHOUT THE LIMITATIONS OF PROPERTY AND MANAGEMENT REQUIREMENTS. WHILE THE USE OF FLOATING TREATMENT WETLANDS AS A TREATMENT APPROACH FOR NITRATE IN RUN-OFF IS AN EMERGING PRACTICE, NITRATE-N IS NOT THE SOLE CONSTITUENT COMING FROM AGRICULTURAL FIELDS. OTHER BIOLOGICALLY ACTIVE CONTAMINANTS REGULARLY CO-OCCUR WITH NITRATE AND MANY CAN AFFECT THE EFFICIENCY OF NITRATE REMOVAL. THIS PROJECT WILL EVALUATE THE DISCRETE AND COMBINED EFFECTS OF SPECIFIC VETERINARY ANTIBIOTICS AND AN INCREASINGLY USED NITRIFICATION INHIBITOR (NITRAPYRIN) TO NITROGEN TRANSFORMATIONAND ITS POTENTIAL EFFECT ON NITRATE-N TREATMENT EFFICIENCY IN SATURATED SEDIMENTS AND FLOATING TREATMENT WETLANDS. SPECIFIC RESEARCH OBJECTIVES OF OUR PROJECT ARE TO: 1) SIMULATE AND QUANTIFY THE COMBINED EFFECTS OF ANTIBIOTICS AND A COMMERCIAL NITRIFICATION INHIBITOR ON THE NITROGEN CYCLE IN FLOATING TREATMENT WETLANDS; AND 2) DETERMINE THE OVERALL EFFECT OF TRACE LEVELS OF ANTIBIOTICS AND NITRIFICATION INHIBITORS ON THE NITRATE-N REMOVAL POTENTIAL OF FLOATING TREATMENT WETLANDS RECEIVING CONTAMINATED AGRICULTURAL RUN-OFF. WE WILL FIRST CONDUCT MICROCOSM INCUBATIONS AT A USGS RESEARCH LABORATORY TO ESTABLISH THE CONCENTRATION LEVELS WHERE NITRAPYRIN AND ANTIBIOTIC MIXTURES AFFECT NITRATE TRANSFORMATION. NITROGEN AND ANTIBIOTIC TRANSFORMATION, AND NITRAPYRIN INTERACTIONS WILL BE ASSESSED IN TWO SETS OF MESOCOSM FLOATING TREATMENT WETLAND EXPERIMENTS USING METHODS FROM PAST SUCCESSFUL SIMULATIONS. THE TRANSFORMATION AND FATE OF SELECTED VETERINARY ANTIBIOTICS WILL ALSO BE TRACKED IN THE MESOCOSMS. FINDINGS WILL PROVIDE NEW INSIGHT INTO WHETHER RESIDUES OF NITRIFICATION INHIBITORS AND VETERINARY ANTIBIOTICS IN THESE ENVIRONMENTS WILL AFFECT PROPOSED MITIGATION STRATEGIES FOR CONTROLLING NITROGEN LOSSES FROM FERTILIZED CROPS AND MANAGING NITRATE CONTAMINATION OF GROUND AND SURFACE WATER.THE INTERDISCIPLINARY TEAM ASSEMBLED FOR THIS PROJECT PROVIDES A RARE OPPORTUNITY TO EVALUATE A COMPLEX ECOSYSTEM FROM AN INTEGRATED MICROBIOLOGY, BIOGEOCHEMISTRY, ANALYTICAL HYDROCHEMISTRY, AND ENVIRONMENTAL ENGINEERING PERSPECTIVE. COLLABORATION WITH A USGS AND A USDA SCIENTIST WHOSE RESEARCH EXPERTISE IN NITROGEN TRANSFORMATION IN SEDIMENTS AND AQUATIC ENVIRONMENTS, ALONG WITH THE USE AND MANAGEMENT OF LIVESTOCK MANURE IN SEDIMENTS, WILL FURTHER ENHANCE AND EXPAND THE SCOPE OF THIS PROJECT. THIS PROJECT WILL ACCELERATE RESEARCH PROGRAMS OF TWO EARLY CAREER SCIENTISTS AT THE UNIVERSITY OF NEBRASKA, FOSTER COLLABORATIONS WITH AN ESTABLISHED USGS BIOGEOCHEMIST AND USDA-ARS MICROBIOLOGIST, AND WILL TRAIN A PHD STUDENT IN ENVIRONMENTAL ANALYTICAL AND STABLE ISOTOPE METHODS. ALL ACTIVITIES WILL HELP TO FURTHER OUR UNDERSTANDING OF THE POTENTIAL EFFECTS OF SPECIFIC CONTAMINANT MIXTURES ON NITROGEN BIOTRANSFORMATION IN FLOATING TREATMENT WETLAND DESIGN TO TREAT RUN-OFF FROM URBAN AND AGRICULTURAL WATERSHEDS. FINDINGS FROM THIS STUDY WILL BE DISSEMINATED THROUGH RESEARCH PRESENTATIONS, HIGH IMPACT JOURNAL ARTICLES, LOCAL SEMINARS, NATIONAL CONFERENCES, TECHNICAL WORKSHOPS, A PUBLIC MAGAZINE ARTICLE, PUBLIC OUTREACH PRESENTATIONS, AND AN UNDERGRADUATE WETLANDS CLASS.