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1777 . ";." ~~~~.;~~~:?::~~.~:t ~~.:~ ..~..\ ~ -.. ;:':"~~~4':! ~ U'll;,'':'&'."'::;'' ....Q,i.J'~...~ '" . ~ wl...... ~ s~l~~ a~ ..~ Data Presentation . S:Jbj9d tc R3vision DO r~OT QLlOTE OR REleASE P'.!ir.ding Approval by Director, Water-quality data in this repolt are routinely presented in a seasonal !t~~~~!~l~~vided into three seasonal periods that are closely associated with streamflow regimes in the Arkansas River Basin. The three seasons are defined as: low flow (October-April), snowmelt runoff (May-June), and post-snowmelt runoff and reservoir release (July-September). However, seasonal analysis of trace elements in the upper basin were defined somewhat differently because of the transpolt mechanisms in the upper watershed. For trace element analysis in the upper basin the seasons were defined as: low flow (October-March), pre-snowmelt runoff (April), snowmelt runoff (May-June), and post-snowmelt runoff and reservoir release (July-September). The transport characteristics for trace metals are discussed in greater detail in the trace-elements section. This repolt uses box plots for downstream comparisons of water-quality data. These boxplots can show the concentration variability at a site and allows comparisons of variations that occur between sites. Box plots are useful .cause all the data are rep_resented and are easily displayed. Figure 3 shows an example of a box plot: The horizon- tal line within the box represents the median (50th percentile) value. The lower line of the box represents the lower quartile (25th percentile) value while the upper line represents the upper quartile (75th percentile) value. The inter- quartile range (IQR) is the difference between the upper and lower quartiles and is represented by the height of the box. As such, the height of the box or the IQR represents fifty percent of the data. The top of the verricallines or "whiskers" are values within 1.5 times the IQR of the box. Outside points, represented as a star (*), are values greater than 1.5 times the IQR but less than 3 times the IQR. Far outside points, represented by an open circle (0) are values greater than 3 times the IQR. Statistical comparisons of selected water-quality properties and concentrations of constiruents were made between sites in the Arkansas River Basin. Most statistical comparisons were made using Tukey's studentized range test (SAS Instirute Inc., 1995) and an alpha level of 0.05 was used to determine whether the variations in concentra- .ns that occurred between sites were significantly diiferent. 7