Analysis of Streamflow and Water-Quality Data at Two Long-Term Monitoring Sites on the St. Croix River, Wisconsin and Minnesota

Streamflow of the St. Croix River has been monitored on a long-term basis by the U.S. Geological Survey (USGS) at streamflow-gaging stations on the St. Croix River at Wisconsin State Highway 35 near Danbury, Wisconsin and below the dam at St. Croix Falls, Wisconsin. Trend analysis indicates that annual streamflow peaks, annual mean flows, and annual 7-day low flows have remained relatively stable at the Danbury (upstream) station from 1914 to 2001 but have increased by 0.45 to 0.55 percent per year at the St. Croix Falls (downstream) station from 1902 to 2001. Water-quality sampling conducted by the USGS at two associated water-quality monitoring sites from 1964 to 2001 have included analysis for nutrients, suspended sediments, metals, bacteria, and pesticides. The water-quality data at the two sites had considerable temporal variation and was often limited in extent by the data-collection needs of previous projects. The absence of consistent long-term water-quality data made detection of statistically significant trends in the water-quality data difficult. Nutrient, suspended-sediment, and major ion concentrations and field parameters were generally higher and more variable at the St. Croix Falls site than at the Danbury site. However, disparate sampling periods and strategies could cause possible biases in the comparison of water quality between sites.
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U.S. Geological Survey
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Minnesota Water Research Digital Library
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