By Hannah Reents

Faculty Mentor: Dr. Tyler Frankel

Abstract

Total coliforms are a broad group of bacteria commonly found in vegetation, soil, and warm-blooded animal intestinal tracts that can be used as a water sanitary indicator. Fecal coliforms are a specific subgroup of coliform bacteria found solely in the intestinal tracts of warm-blooded organisms that are strongly correlated with gastrointestinal illnesses and other health effects on both humans and wildlife. Sources of contamination include wastewater treatment plant overflows, leaking septic systems, agricultural runoff, and wildlife or pet waste. While the Rappahannock River is commonly utilized for recreational activities including fishing and swimming, few studies have been conducted to examine the presence, concentrations, potential sources, and long-term patterns of coliform contamination in commonly utilized areas. As such, this study was designed to 1) generate baseline data to track contamination levels in correlation with rainfall, temperature, and seasonality, and 2) provide the public with easily accessible information regarding the cleanliness of recreational areas. Surface water samples were collected weekly from five frequently utilized locations along the Rappahannock River with dissolved oxygen (DO), pH, temperature, total dissolved solids, and salinity measurements taken. Total and fecal coliform concentrations were quantified using the IDEXX Colilert-18/ Quantitray 2000 system. Samples were incubated at 35°C for 18-22 hours, after which total and fecal coliform most probable number (MPN) values were measured under UV light using an IDEXX 2000 MPN Table. Results were then released to the Potomac Riverkeeper Network Swim Guide and the Chesapeake Monitoring Cooperative Data Explorer websites for public access. While this study is currently ongoing, preliminary data has shown fecal coliform levels are correlated to seasonality. Several sites exceeded the EPA single sample maximum contaminant limit of 410 MPN/100 mL during the summer season, with precipitation over 1.29 inches. Under similar conditions (1.22 inches of precipitation) in the winter, all sites were reported below the maximum contaminant limit. In addition to fluctuations due to temperature changes, we expect to find DO levels decrease when coliform levels are elevated due to increased bacterial respiration. Collectively, the results of this study will help to better inform the public and create a reliable dataset for future research.