Quantifying Organic Nitrogen and Other Suspended Solids at High Resolutions to Investigate Nutrient Transport Patterns in Iowa Rivers

Issue

The nutrient nitrogen is one of Iowa’s most problematic pollutants. Most traditional research on waterborne nitrogen has focused on nitrate—a dissolved form of nitrogen with significant implications for drinking water. However, new studies have demonstrated that a considerable presence of organic nitrogen, which is the form nearly all suspended (i.e., non-dissolved) nitrogen takes, exists within Iowa’s surface waters. In certain regions of Iowa, organic nitrogen levels are higher than those of nitrate. Differentiating between organic nitrogen and nitrate is important because most pollution control strategies are more effective for certain types of nitrogen.

Objective

The widespread presence of organic nitrogen means that accurately modeling its transport is critical. This project will investigate the ability of turbidity (a measurement of water clarity) to predict levels of organic nitrogen throughout 40+ Iowa’s rivers. Turbidity has successfully been used in numerous efforts to model phosphorus and sediment—two other pollutants of concern in Iowa—and we will test whether these same techniques can also be applied to model organic nitrogen. Turbidity is routinely monitored throughout Iowa using devices installed alongside rivers that measure turbidity every 15 minutes. Using these measurements to predict pollutant concentrations can result in big improvements to historical datasets, which consist of samples collected once per month.

Approach

This project will also explore the potential of these turbidity datasets to simultaneously predict several pollutants, including sediment, phosphorus and organic nitrogen. Furthermore, many nitrate sensors have traditionally been deployed alongside turbidimeters in Iowa. In these cases, this project will pair nitrate records with predictions of organic nitrogen to generate estimates of nitrogen’s overall presence in a stream, which has not been estimated before. These new records of total nitrogen will provide a fuller picture of nitrogen transport in Iowa over short timeframes.