Escherichia coli was used as a bacterial tracer for the development, calibration, and validation of a watershed scale fate and transport model to be extended to a suite of reference pathogens (Cryptosporidium, Giardia, Campylobacter, E. coli O157:H7). E. coli densities in water and sediments from the Blackstone River Watershed, Massachusetts, were measured at three sites for a total of five wet weather events and three dry weather events covering three seasons. The confirmed E. coli strains were identified by ribotyping for tracking the sources of E. coli and for determining the association of downstream E. coli isolates with isolates from upstream sediments. A large number of downstream samples were associated with upstream sediment sources of E. coli. E. coli densities ranged from 71 to 6,401 MPN ⁄ 100 ml in water samples and from 2 to 335 MPN ⁄ g in sediments. Pearson correlation analysis revealed significant correlations between E. coli and total coliforms in water (r = 0.777, p < 0.01) and sediments (r = 0.728, p < 0.01). In addition, E. coli concentrations in water were weakly correlated with sediment particle size and sediment concentrations (r = 0.298, p < 0.01). A hydrologic model, WATFLOOD ⁄ SPL9, was used to predict the temporal and spatial variation of E. coli in the Blackstone River. The rapid rise of stream E. coli densities was more accurately predicted by the model with the inclusion of sediment resuspension, thus demonstrating the importance of the process.

A series of field and laboratory investigations was conducted aimed at characterizing disinfection byproduct (DBP) precursor levels in the Wachusett Reservoir watershed. Samples were collected from spatial based and storm event sampling campaigns, as well as laboratory leaching experiments. These were analyzed for DOC, TOC and DBP precursors in an effort to characterize the changes in precursor levels and natural organic matter (NOM) character in this watershed. Based on these data, it was proposed that freshly leached NOM is relatively poor in DBP precursors due to the abundance of non-reactive carbohydrates. As these compounds undergo biodegradation within the watershed, the measured specific DBP precursor level rises, because the more reactive materials (e.g. lignins, phenolics) are also more persistent.

The objective of this study was to characterize the variability of Escherichia coli density and sources in an urban watershed, particularly to focus on the influences of weather and land use.E. coli as a microbial indicator was measured at fourteen sites in four wet weather events and four dry weather conditions in the upper Blackstone River watershed. The sources of E. coli were identified by ribotyping. The results showed that wet weather led to sharp increases of E. coli densities. Interestingly, an intense storm of short duration led to a higher E. coli density than a moderate storm of long duration (po0.01). The ribotyping patterns revealed microbial sources were mainly attributed to humans and wildlife, but varied in different weather conditions and were associated with the patterns of land use. Human sources accounted for 24.43% in wet weather but only 9.09% in dry weather. In addition, human sources were more frequently observed in residential zones (430% of the total sources), while wildlife sources were dominant in open land and forest zones (54%). The findings provide useful information for developing optimal management strategies aimed at reducing the level of pathogens in urban watersheds.Key words 9 9 9 9 E. coli, land use, microbial source tracking, urban watershed, variability, wet weather

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