Statistical Analysis of Trends in the Red River Over a 45 Year Period

livestock data for the Red River are reported by the National Agricultural Statistics
Service, this available data can be incorporated into QWTREND and allows one to
have more of an explanation as to why certain fitted trends make sense. For example,
if there has been an increase in the amount of cattle in an area surrounding the Red
River, does that explain a certain percent increase in phosphorus concentration?
Parametric time series analysis should be considered when complex trends appear
in flow-adjusted concentrations and if sampling is highly variable from year to
year. There are advantages and disadvantages to both methods for trend detection,
they are summarized below:
Advantages of Non-Parametric Methods using WQSTAT:
• Easy to compute
• Requires few assumptions
• Robust to outliers
• Simple to use
Disadvantages of Non-Parametric Methods using WQSTAT:
• Not as powerful in detecting trends
• “Hydrologic” seasons must be clearly defined
• Assumes monotonic trend
• No flexibility for defining trend lengths
Advantages of Parametric Methods using QWTREND:
• Can model complex trends
• Good for explanatory and exploratory analysis
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