## 3 Results and Discussions  
### The Dataset Overview  
The concentrations (MPN/L) of L. _monocytogenes_ and _S. enterica_ at each sampling date by month over two years are shown in Figure 1. Over the entire observation period, the mean concentration value of \(L\). _monocytogenes_ at MA05 was significantly (\(p<0.05\)) higher than at the other three sampling sites (MA04, MA10, and MA11). _S. enterica_ levels were significantly greater in stream water (1.29 MPN/L at MA04 and 1.08 MPN/L at MA05) compared to pond water sites (0.05 MPN/L at MA10 and 0.20 MPN/L at MA11). _S. enterica_levels measured in ponds agree with results from [34]. In that work, S. _ enterica_ values in the ponds were relatively low (geometric mean 0.3 MPN/L). Conditions in ponds appear to be less conducive for the survival of S. _enterica_ and L. _monocytogenes._  
Figure 1: Concentrations of \(L\). _monocytogenes_ and _S. enterica_ for four sites in this study from October 2016 to September 2018. (**a**) \(L\). _monocytogenes_ at MA04, (**b**) S. _enterica_ at MA04, (**c**) \(L\). _monocytogenes_ at MA05, (**d**) \(S\). _enterica_ at MA10, (**e**) \(L\). _monocytogenes_ at MA11 and (**h**) \(S\). _enterica_ at MA11. The mean levels of pathogens and prevalence data by season are shown in Table 1. The prevalence of both pathogens was higher in stream water samples (sites MA04 and MA05) than in pond samples (sites MA10 and MA11). These results can be partially explained by the fact that pathogens can be more readily exposed to solar UV radiation in shallow and slow-flowing pond waters than in streams. The prevalence of _L. monocytogenes_ was higher in the non-growing season at all sampling sites except at stream site MA05. A similar seasonality was observed in Nova Scotia, Canada, where the prevalence of L. _monocytogenes_ in surface waters was higher in winter (72%) in comparison to summer (55%) months [35]. Analogous results were reported in [36]. In that work, the prevalence of L. _monocytogenes_ along the Salinas River in California was found greater in the winter and spring, and lower in the fall. _L. monocytogenes_ prevalence in water was higher during colder seasons in agricultural regions in New York [21]. No significant differences in L. _monocytogenes_ and S. _enterica_ levels were observed between the non-growing season (cold season) and growing season (warm season) at each sampling site. These results agree with Southern Ontario and New York reports, where _Salmonella_ levels did not significantly differ by season [37; 38]. Studies in other US geographic regions showed that the prevalence of _Salmonella_ in surface water in California followed a noticeable seasonal trend [36; 39]. Similarly, _S. enterica_ levels were significantly higher during warmer seasons than during colder seasons in stream water samples from the Suwannee River basin in Georgia [19]. Correlation analysis between rainfall and prevalence of pathogen for each sampling site yielded a biserial correlation coefficient for _L. monocytogenes_ in ponds versus streams (Table 2). _L. monocytogenes_ prevalence positively correlated with rainfall in ponds but not in streams. That may be related to the proximity of ponds to the agricultural lands and the resulting pathogen transport in runoff to ponds. We note that the effect of direct runoff from farmlands on the _L. monocytogenes_ prevalence was suggested earlier by [40; 41] based on observations at streams of different orders. Streams MA04 and MA05 were likely not directly affected by the agricultural runoff. The prevalence of _L. monocytogenes_ was probably affected by the dilution effect that manifested itself in a negative biserial correlation (Table 2). This assumption is supported by the fact that a significant negative correlation of the _L. monocytogenes_ prevalence was observed with the Rain1 but not with the Rain7, as the dilution should be affected by the recent precipitation rather than weekly cumulative precipitation for a week. _Salmonella_ prevalence correlated with precipitation in streams