| | Description: | The long-term temporal trends of water quality in the Illinois Waterway system upstream of Peoria are described in this report. The time period investigated was from 1965 to 1995. The seasonal Kendall trend test was used to detect statistically significant trends. A related test, the seasonal Kendall slope estimator, was used to calculate the magnitude of the trend. Box plots were also used to visualize differences in data over time. The water quality analytes considered in this report include dissolved oxygen, ammonia-nitrogen, nitrate and nitrite-nitrogen, total Kejeldahl nitrogen, total phosphorous, sulfate, turbidity, total suspended solids, fecal coliform, cyanide, and phenol. Water quality was generally found improved at all stations. Substantial improvements were found at most stations for dissolved oxygen, the nitrogen species, phenol, and cyanide concentrations. Fecal coliform densities generally decreased at most locations. Little or variable change was found for turbidity, total suspended solids, and total phosphorus concentrations. Increasing trends were detected for sulfate concentrations. | |
