Watershed Scaling Effects Measured Via Nested High Frequency Sensors
- Marty St. Clair, University of Iowa
Issue
Measurement of nutrient concentrations in Iowa surface waters has informed ongoing efforts to reduce nutrient loading through the Iowa Nutrient Reduction strategy. However, much of that monitoring takes place near the outlet of a watershed. While this strategy allows comparisons of watersheds and assessments of changes in concentrations over time, it does not allow for insights into the dynamics of nutrient processing within the watershed.
Objective
The work proposed involves placement of in situ water quality instrumentation near the mouth, in the middle and in the headwaters of several Iowa watersheds. These sets of instruments will allow scientists to assess how nutrients react within the watershed, and, in combination with flow measurements, determine where nutrients originate. In addition, the high time resolution of these instruments will allow study of the impact of extreme precipitation events on nutrient and sediment movement.
Approach
This grant will also support development of a method combining the use of the in situ nitrate sensors with a USGS statistical model to provide a standard method of calculating annual nutrient and sediment loads for the state. Different forms of nutrients (nitrate, ammonia, organic nitrogen, orthophosphate and particulate phosphorus) will be included in the output.
Project Update
December 2025
Activities completed since the last report include collecting data at the field sites in each of the five watersheds, maintenance of those sites as water levels fluctuated over the season, and removal of the sensors for the winter. Sensors will be serviced and calibrated prior to reinstallation in the spring.
Data analysis is underway including plotting of hysteresis curves and quantification of hysteresis metrics for events at each site. Preliminary analysis indicates that the 2025 season, with elevated precipitation in July, should provide a rich data set for analysis.
Related Activities and Accomplishments
Multiple presentations about the water quality sensor network to various civic groups.
One proposal was submitted and has been funded to continue related work, starting in early 2026 :"Growing Resilience in the Middle Cedar Watershed " - submitted by Middle Cedar WMA/city of Cedar Rapids to EPA Farmer to Farmer program. $436,305, subcontract to Iowa Geological Survey includes water monitoring and practice installations.
Two other related grants have been submitted.
- Integrating NASA Earth Observations and In Situ Sensor Networks to Predict Nitrate Dynamics in Iowa's Streams and Rivers; PI Jesus Gomez Velez. Submitted to NASA. 3.
- Support for Water Quality Sensor Network, Polk County, Request for $200,000 for direct support for sensor network.
August 2025
Primary activities have been installation of additional field sites, reinstallation of established sites, and maintenance/troubleshooting of problems as they occur. It has been a challenging year for keeping all sites functioning with low-water levels and high-water levels occurring at different times and places, cell reception changes from previous years, and vandalism causing problems with data acquisition. However, we are actively collecting data at present and will continue through the field season. We are also beginning preliminary analysis of data as described in the proposal with an eye toward determining the most appropriate analytical tools and procedures.
Related accomplishments and activities
- 3 presentation
- Analysis of existing data and development of water monitoring plan for Linn County, "Growing Resilience in the Middle Cedar Watershed",
- EPA Farmer to Farmer grant; subcontract from City of Cedar Rapids to Iowa Geological Survey
January 2025
The primary activity since receipt of the grant has been preparing equipment and site selection for the actual research. Nitratax sensors are undergoing preventive maintenance and re-calibration. The maintenance and site-selection are ongoing and will be complete within the next 1.5 months. We anticipate installation of equipment in March/April (depending on weather).
Related accomplishments and activities
1 proposal was submitted: CIROH White Paper (pre-proposal) - Connecting Hydrology and Public Health: Iowa as a Water Quality Testbed.