FREQUENCY-DURATION ANALYSIS OF DISSOLVED-OXYGEN CONCENTRATIONS IN 2 SOUTHWESTERN WISCONSIN STREAMS

Historically, dissolved-oxygen (DO) data have been collected in the sa me manner as other water-quality constituents, typically at infrequent intervals as a grab sample or an instantaneous meter reading. Recent years have seen an increase in continuous water-quality monitoring wit h electronic dataloggers. This new technique requires new approaches i n the statistical analysis of the continuous record. This paper presen ts an application of frequency-duration analysis to the continuous DO records of a cold and a warm water stream in rural southwestern Wiscon sin. This method offers a quick, concise way to summarize large time-s eries data bases in an easily interpretable manner. Even though the tw o streams had similar mean DO concentrations, frequency-duration analy ses showed distinct differences in their DO-concentration regime. This type of analysis also may be useful in relating DO concentrations to biological effects and in predicting low DO occurrences.