## 3 Results and Discussion
### Septic System Density
Land use is the most likely explanation for differences in FIB concentrations among the studied watersheds since river flow (Table 3) and salinity (all freshwater watersheds) were similar. [PERSON] et al. [24] found that watersheds with a low density of septic systems (<1 system ha\({}^{-1}\)) exhibited more variability in FIB concentration due to variable sources of fecal pollution (e.g., livestock, wildlife, and septic systems), which they attributed to an even distribution of land use between agriculture, forested, and developed area. In the current study, forested and developed area accounted for >75% of land cover (Table 1). Forested areas provide a habitat for wildlife, which can be a significant non-point source of FIB to surface waters, especially during warmer months when they are most active and FIB survivability is greater [44]. These additional microbial inputs made it more difficult to differentiate trends in _E. coli_ and enterococci concentrations based on septic system density during warmer months (Figure 2). During colder months, both _E. coli_ (median: >700 MPN 100 mL\({}^{-1}\)) and enterococci (median: >100 MPN 100 mL\({}^{-1}\)) concentrations were elevated in the higher density watersheds (SF3 and CS3) (Figure 2). _E. coli_ concentrations in the SF2 watershed were also elevated during colder months (Figure 2). The SF3, CS3, and SF2 watersheds were predominantly residential (\(\geq\)53%), with lesser percentages of forested and agricultural land classes ranging from 26-45% and 0-5%, respectively (Table 1). Median values of _E. coli_ and enterococci were <200 and <100 MPN 100 mL\({}^{-1}\), respectively, in the CS1, CS2, and SF1 watersheds. Forest accounted for \(\geq\)60% of land cover in CS1 and CS2, whereas forest and residential development in SF1 was approximately equal (Table 1). Thus, land cover data suggest that differences in FIB concentrations during colder months were likely due to differing septic system densities when other major non-point sources of FIB were limited. Figure 2: Concentrations of _Escherichia coli_ and _Enterococcus_ spp. from watersheds grouped by wastewater treatment approach (**A**,**B**) and comparison of cold (**C**) vs. warm (W) months showing increased fecal indicator bacteria during warmer months (**C**,**D**). Pooled data are shown for each group as CS = conventional septic; SF = sand filter; SEW = sewer. The asterisks (*) denote outliers. Specific conductance and chloride data in the CS3 and SF3 watersheds were also elevated relative to the other watersheds (Figure 3; Table 3), potentially indicating wastewater effects [45, 46]. These differences were statistically significant for both specific conductance and chloride at \(p<0.01\). Waters downgradient from wastewater inputs tend to contain elevated specific conductance and chloride [45, 46]. Furthermore, elevated specific conductance in water may indicate a continuous source of dissolved ions, such as septic systems, and increased septic system densities are often associated with elevated specific conductance [47, 48]. Past studies [45, 46, 49] reported specific conductance and chloride values ranging from approximately 500\(-\)2000 \(\upmu\)S cm\({}^{-1}\) and 50-300 mg L\({}^{-1}\), respectively, in wastewater, which were similar to values reported in the CS3 and SF3 watersheds (Figure 3; Table 3). The other watersheds in the current study contained similar specific conductance (approximately 30-250 \(\upmu\)S cm\({}^{-1}\)) and chloride (approximately 10 mg L\({}^{-1}\)) values to groundwater and surface water unaffected by wastewater inputs reported in [PERSON] et al. [46]. Runoff from roads treated with salt to prevent ice accumulation during winter weather can contain specific conductance and chloride values