Discussion
In general, water quality decreased as the river moved through the Denver metro area, which seems to imply that in this system, urban hydrology, especially impervious surfaces and engineered drainage, may be influencing the river. In addition to a general decrease in water quality through the study area, we also noted several hotspots of severely degraded water quality. The data also shows strong seasonality in water quality, with higher concentrations of nutrients and higher BOD in the winter months.
Water quality generally decreased through the Denver metro area. Specifically, DO decreased (Figure 5); the concentrations of orthophosphate (Figure 8) and ammonia-N (Figure 6) increased; and BOD (Figure 4) and temperature (Figure 9) increased from the 0 km site to the 63 km site (p < 0.05). Nitrate-N did not show the same overall trend of increasing concentration (Figure 7), but this is primarily because the 14 km and 19 km sites had excessively high concentrations. However, compared to the 0 km site (the control point), nitrate-N concentrations were elevated at all sites within the city. Compared to the other parameters measured, pH seems to be more variable and does not display a distinct trend (Figure 10). All of the measured pH values were between 6.2 – 8.9, although overall, they tended to be slightly basic.