Seasonality
Water quality in this study showed strong seasonality. BOD and the concentrations of ammonia-N, nitrate-N, and orthophosphate were highest in the fall and winter (Figures 4, 6, 7, 8, respectively). These times coincide with the lowest flows in the river (Figure 3). Low flow can result in higher concentrations of nutrients as there is less water for dilution. In addition, biological uptake of nutrients is lower during the cold months of the year (Olatunde et al., 2015; Rolls et al., 2012). Not surprisingly, water temperature also showed strong seasonality, with temperatures reaching their maximum values in July (max 25.9oC) (Figure 9). DO saturation is inversely related to temperature but is also influenced by hydrology, BOD, and pH. In this study, we measured the lowest DO values in early fall when temperatures were still relatively high and flow in the river was low (Figure 5).