Time series trend analysis and prediction of water quality in a managed canal system, Florida (USA)

Water quality in the Everglades canal system discharging into the St. Lucie Estuary in south Florida is greatly influenced by anthropogenic activities. We analyzed the water quality parameters trend from 1979 to 2014 using seasonal trend decomposition and LOESS of four canals (C23, C24, C25, and C44). We also predicted the value of total nitrogen (TN) and total Phosphorus (TP) and turbidity from 2016 to 2020 using exponential smoothing and additive Holt-winters method. The main goals of this paper were to reveal long-term changes trends in water quality and identify the emphasis of management in the near future. We found that the change range of water quality parameters was different, but change rules were similar. The mean of DO at each station was in the range of 5.0∼6.3 mg l-1, and the colour was in the range of 5 ∼ 400PCU. The highest specific conductivity was 2250 μS cm-1 in C24 and the lowest was 125 μS cm-1 in C44, and the minimum turbidity was only 0.4 NTU at C25 and the maximum value was 90.3 NTU at C44. The mean value of TN at each station was C24>C44 >C23>C25, and TP was C24>C23>C44>C25. Nutrient export exhibited an upward trend for TN from all the basins and downward trend was present for TP. Water quality was influenced by rainstorm and non-point source pollution. Our predictions showed that TN and TP concentrations in C23 canal were higher than other three canals every month and turbidity of C44 canal was higher than other three canals. Therefore, improved best management practices should be implemented on land that have high TN and TP concentrations in runoff and leachate flowing into the C23 canal.