Evaluating the Relation of Total Phosphorus to Turbidity During High Flow Events to Improve Quantification of Phosphorus Export from Iowa Rivers

Aug 2020


The presence of phosphorus in waterways is a major concern in the state of Iowa. Although this nutrient is essential for biological processes, excessive quantities sourced from anthropogenic origins disrupt the ecological balance of both fresh and marine aquatic systems. Human activity has historically elevated the amount of P discharged into Iowa’s waterbodies. The state has set targets to ameliorate this P load via the Iowa Nutrient Reduction Strategy, and a key benchmark of the INRS is the reduction of annual P load exported from Iowa by the state’s major rivers. To assess this reduction, it is necessary to routinely monitor P concentrations in the waters leaving the state and to improve quantification of P export.


The primary goal of the project is to gather data to support development of regression equations to predict Total Phosphorus (TP) concentrations using turbidity as a surrogate during high-flow conditions in major rivers leaving the state.


The primary activities to achieve the objective include:

  1. collecting water samples at 16 terminal monitoring sites during high flow conditions;
  2. measuring turbidity and particulate P (Part P) levels in the samples;
  3. using the sample data to update the established turbidity-Part P regression relationships for each site; and 
  4. combining the high-flow monitoring with IDNR-supported low-flow analysis to quantify TP export from Iowa at hourly to annual scales.

The TP export data from the 16 sites will be displayed on the Iowa Water Quality Information Site (IWQIS).

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