Comparison of Water Quality Trends in Two Hydrologically Similar Iowa Watersheds

Abstract:

The Iowa Water Quality Information System (IWQIS) was established in 2014 and provides access to continuously monitored water quality data at 53 locations across Iowa in near real time. The sensors measure and collect various surface water quality data, including nitrate and nitrite (NO_x) concentration, specific conductance (SC), turbidity, dissolved oxygen (DO), pH, and water temperature. Using data from this network, water quality trends were compared for paired watersheds in eastern Iowa over the sensors’ periods of record (April 2015 – present) by comparing upstream land use composition and anthropogenic activity (e.g. point source pollution sources). Several water quality variables, including DO, pH, and water temperature, exhibited clear diurnal and seasonal patterns and high correlation with other variables. While the watersheds share similar topography, geology, and meteorology, the amount of urban and rural land use in each differ substantially. The watershed with a greater percent of row crop agriculture (23% compared to 15%) had consistently higher NO_x concentration, as expected, and greater turbidity during low flow conditions. In contrast, the watershed with more urban land use (52% compared to 11%) exhibited flashier behavior in SC and turbidity and greater levels of each over a longer duration following rain events. Additional reasons for difference in the timing and magnitude of certain water quality variables were hypothesized. These early results reveal the value of the IWQIS for monitoring the quality of Iowa’s surficial waters and helping establish baseline nutrient conditions to assist with improving water quality in the state through the Iowa Nutrient Reduction Strategy.