Science Serving Maryland's Coasts

Caroline Rodriguez, Duke University

Class Year: 

Project Title: 

Identifying Nitrogen Sources and Antibiotic Resistance within Microbial Contaminants in Tributaries of Johnson Bay, Maryland Coastal Bays


Water quality in Maryland's Coastal Bays has been declining dramatically due to land runoff. In Johnson Bay, nutrient levels are quite high considering low-density land usage. We hypothesize that nutrients and microbial contaminants may be from runoff of poultry manure from feeding operations and agricultural fields. We also hypothesize that microbes from these sources will exhibit resistance to common antibiotics used in nearby feeding operations. This study seeks to measure water quality parameters to identify nitrogen sources and assess antibiotic resistance and abundance of isolated indicator species of bacteria (e.g. Escherichia coli and Enterococcus spp.). Surface water samples were collected at three sites along three creeks that flow into Johnson Bay in order to measure water quality parameters and determine bacterial abundance. Specific agar plates were used to assess bacterial contaminant abundance and a modified chromogenic agar impregnated with four different antibiotics (tetracycline, ciprofloxacin, gentamicin, and oxacillin) were used to assess E. coli antibiotic resistance. Nutrient levels were very high, particularly nitrogen at the head of Powell, which was in excess of 600 M and fecal bacterial abundances were extremely high at the majority of sites. High nutrient levels and contaminant bacterial abundances measured in Powell Creek indicate it is the main source of pollutants. Finally, bacteria demonstrated the highest resistance to oxacillin, but overall the data was inconclusive because it did not decisively identify the sources of nutrient pollutants. These findings will help to better understand how land use patterns affect water quality and sources of contamination from runoff.