Use of real-time and continuous water quality monitoring in Iowa streams

Christopher S. Jones, Caroline A. Davis, Sea-Won Kim, and Thomas V. Stoeffler

IntroductionAgricultural watersheds in the Midwestern U.S. are major contributors of nutrients to the Mississippi River Basin and the Gulf of Mexico. Many states within the Upper Mississippi River Basin, including Iowa, are

developing nutrient reduction strategies to reduce non-point and point source loads of nitrogen and phosphorous in an effort to reverse degradation of streams and lakes.

David, et al., 2010. JEQ 39:1657-67

N loss in the Mississippi River Basin

MonitoringQuantifying nutrient loads in Iowa and assessing loads transported within Iowa rivers are important components of Iowa's strategy. Nutrient loads estimated with data collected using traditional methods of

grab sampling are expensive and have met with limited usefulness to the agricultural community when assessing the effectiveness of implemented conservation practices.

Equipment

New sensor technology is allowing for real-time measurement of nutrient loads in many Iowa rivers. IIHR Hydroscience and Engineering has deployed 22 nitrate-nitrogen sensors in several Iowa rivers to provide accurate measure of nutrient loads. Combined with 17 sensors operated by the USGS, the sensor network captures nutrient transport and loading patterns in rivers across the state. Sensors use background-corrected UV absorbance to quantify nitrate-N.

Objectives

• Establish Water Quality Information System (WQIS) to disseminate data

• Compare and Contrast Load Calculations Obtained Using Continuous Monitors with those from Grab Sampling Programs

• Demonstrate how Continuous Monitoring Informs Watershed Hydrology

• Assessment of Implemented Conservation Practices Designed to Reduce N Transport to Streams

• Cost Comparisons

Water Quality Information System

Load Comparisons

With rainfall overlay

User can manipulate data to look at N loads, N yield (load per unit area), or concentration as a function of discharge.

Raccoon River, Iowa

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2010 2011 2012 2013 2014

N Load per Day (Mg)

Bi-weekly Grab Continuous

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2008 2009 2010 2011 2012 2013 2014

N Load per Day (Mg)

Bi-weekly Grab Continuous

Average annual load difference between grab sample continuous monitoring was >10% at each location. Overall, grab samples predicted 11% higher loading than continuous monitoring.

This difference may seem small, but in the context of tracking progress for the Iowa Nutrient Reduction Strategy, it is huge.

The Iowa Nutrient Reduction Strategy targets conservation and best management practices (BMPs) with the objective of reducing N loading from the state by 45%.

Can we accurately and precisely track load reductions linked to improved agricultural practices with bi-weekly grab samples?

Cost of real time monitor (~$20,000) is small compared to the millions of dollars invested in BMPs.

Assessment of BMPs

Real time continuous N and other water quality monitors on wetland outlet

Conservation Reserve Enhancement Program

(CREP) Constructed Wetland to Process N in Agriculture

Drainage Water

Continuous monitoring demonstrates seasonality of N processing, and the effect of precipitation events. Site is >100 miles from testing laboratory; continuous monitoring may actually be more cost effective than regular grab samples in the long term.

In-Stream Processing of Nitrogen

Question: how much in-stream processing of nitrogen in headwater streams can we expect?

Obstacle: intrusion of groundwater, drainage water, and small streams confound ability to quantify N processing.

Project: deploy real-time continuous nitrate monitors 5 km apart in stream stretch with few of other water intrusions.

Results: variations between upstream and downstream discharge and nitrate-N illustrate and quantify the effects of weather and in-stream processing of nitrogen.