Water quality sampling at St. Croix National Scenic Riverway 2007

VanderMeulen, David; Elias, Joan

The Great Lakes Inventory and Monitoring Network (Network or GLKN) began monitoring water quality in the St. Croix National Scenic Riverway (SACN) in 2007. Monitoring began at eleven sites in April, with two additional sites added in May, and continued through November. In the field, we measured water temperature, pH, specific conductance, and dissolved oxygen with a multiprobe. We also measured water clarity with a transparency tube and Secchi disk, and recorded environmental conditions, such as weather and flow conditions. Water samples were collected during each sampling period and sent to contract analytical laboratories for analysis of chlorophyll-a, nutrients (total phosphorus, total nitrogen, nitrate+nitrite-nitrogen, ammonia nitrogen), total suspended solids, dissolved organic carbon, alkalinity, chloride, sulfate, cations (calcium, magnesium, potassium, sodium), and dissolved silica. We also collected surface sediment samples at five sites for analysis of diatom communities, which are a good integrator of water quality conditions. Monitoring sites were categorized into two general groups; lake sites and river sites, based mainly on hydrology and channel morphology. In general, water quality conditions were good at SACN, with somewhat degraded conditions at downstream sites in Lake St. Croix and in the Willow River, especially with respect to excess nutrient levels. These sites integrate upstream water quality conditions, which indicate that upstream nutrient additions are impacting downstream sites in a cumulative fashion. The Apple, Willow, and Kinnickinnic Rivers had very high concentrations of nitrate+nitrite-nitrogen. The watersheds associated with these tributaries are dominated by agriculture and increasing development, and have coarse-textured highly permeable soils over carbonate bedrock, which makes groundwater more susceptible to contamination from nitrate+nitrite-nitrogen fertilization associated with agriculture and increasing urbanization. Although water quality was generally good, EPA-recommended nutrient reference conditions were exceeded at most of the monitoring sites in 2007. These exceedances may only be leading to a reduction in beneficial uses at sites furthest downstream. Applicable state (Minnesota and Wisconsin) water quality standards were met at SACN throughout the season, except for low dissolved oxygen concentrations in the lower portion of the water column for two sites on Lake St. Croix in mid-summer. Additional monthly water quality monitoring is scheduled to take place in 2009 and 2011, with quarterly monitoring in the interim years dependant on additional funding. Upon completion of three full years of monthly monitoring, we will analyze the data for potential trends over time and will produce a report that synthesizes our data and those of other monitoring efforts.

Water quality sampling at St. Croix National Scenic Riverway 2007

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