Growing Season Surface Water Loading of Fecal Bacteria within a Rural Watershed

Abstract

Water quality within the Thomas Brook watershed, a 750 ha mixed land-use catchment located in the headwaters of the Cornwallis River drainage basin, was assessed using an integrated monitoring program. The research objective was to examine spatial and temporal characteristics of fecal bacteria loading from a watershed during the growing season. Fecal coliform, Escherichia coli, total suspended solids (TSS) concentrations and stream flow were monitored at five points in the watershed during a six growing season period (May to Oct, 2001-2006). A nested watershed monitoring approach was used to determine bacterial loading from distinct source types (residential vs. agricultural). Daily loading was further differentiated into stormflow and baseflow. Bacterial loading per hectare increased in each nested watershed moving downstream through the watershed and were highest in the three subcatchments dominated by agricultural activities. Upper watershed bacterial loading from an agricultural subcatchment (Annual Avg 8.92x1010 CFU/ha) was consistently higher than a residential subcatchment (Annual Avg 8.43x109 CFU/ha). Annual stormflow bacterial loads were higher than baseflow loads. The highest daily fecal bacteria load per annum ranged from 8.1 to 20.1% of the total annual growing season load and were all preceded by at least 38 mm of precipitation. Annual fecal bacteria loads were found to be greater during growing seasons with greater annual precipitation. A positive linear relationship was observed between E. coli and TSS loading during the 2005 and 2006 growing seasons when both parameters were monitored. The E. coli and TSS loading relationship was weakest during baseflow periods (R2=0.40), higher for stormflow periods (R2=0.50), and strongest (R2=0.60) when all flow conditions were included in the regression. Further year round watershed and intensive stormflow monitoring are required to expand the understanding of fecal bacteria loading in the Thomas Brook watershed.