USGS Continuous Nutrient Monitoring in the Mississippi River Basin video
The Mississippi River is the fourth largest river in the world and with its tributaries,
the Mississippi drains all or part of 31 States or about 41% of the continental United States.
This central artery of the US connects the Great Lakes to the Heartland to the Gulf.
The U.S. Geological Survey is working with water, industrial, and agricultural groups,
as well as cities, States, Federal and non-governmental organizations to better understand the river
and monitoring data.
One such collaboration is with mayors of the Mississippi River Cities and Towns Initiative.
“We are actually a group of 76 mayor's from Minnesota to Louisiana who have come together
to protect our water way and make sure that the economies that depend on the river are
more sustainable.
We know in government, especially, what gets measured, gets managed.
In March of this year, the mayors signed a memorandum of common understanding with the
USGS and we are working together to deploy a comprehensive nutrient monitoring network
for the entire Mississippi River Valley.
That might not sound like what would expect for a group of Mayors and cities but we do
understand that it all starts with water quality.”
The USGS historically has collected both discreet and continuous water-quality data.
Both discreet and continuous data have provided a rich foundation of information for science
analyses such as determining trends in water quality to assess the health of our Nation’s
rivers and streams.
Recent advances in nitrate sensors are now providing an opportunity to measure changes
in concentration many times per hour or day and can be deployed in many types of rivers
and lakes.
The USGS has 3,894 real-time stream gages in the Mississippi River basin that monitor
the flow in the Mississippi and its tributaries.
About 60 sites have continuous monitoring for nitrates and about 10 sites monitor for
continuous phosphate, but some are temporary monitoring sites that are deployed for assessing
site specific nutrient issues.
A dedicated long-term nutrient monitoring or “supergage” network is needed that
will provide a cost effective, consistent, unbiased regional approach to evaluate the
changes in nutrient loads.
Significant resources are invested by farmers, industry, and the public to reduce nutrient
pollution to the river and a long-term network will help us assess the changes that are occurring.
But, setting up and maintaining these continuous monitoring “supergages” is complex as
Elizabeth Murphy explains.
A USGS “supergage” is a gauge station with real-time, continuous measurements of
streamflow, other parameters ( such as pH, Specific Conductance, turbidity, and Dissolved
Oxygen), and at least one chemical constituent such as nitrate or phosphate.
Discrete samples of nitrate and phosphate are still collected but the continuous nutrient
sensors help fill in the gaps between samples.
The supergages also collect data when it isn’t safe to collect discrete samples, such as
during extreme flood events when the largest loads of nutrients are being flushed through
the basin.
We are here at the USGS supergage to collect continuous water quality.
This site is on the Green River near Geneseo Illinois where the station is housed along
the edge of the river.
We can see that nitrate and turbidity are being continuously recorded at this site from
instruments that are deployed in the river.
Solar power allows these supergages to be positioned in remote locations.
Integrating cellular and satellite modems into the supergage also supports remote sites
and allows real-time data upload to the Web along with remote system monitoring.
(put NWIS web address at bottom of screen).
The long pipes going down to the stream house the four instruments for measuring nitrate,
phosphate, turbidity, and general water quality.
The USGS makes monthly maintenance trips to most water-quality sites to clean the sensors
and calibrate them against known standards.
This helps insure that there has been no degradation to the instrument and the data available on
the web are accurate.
Additionally, the hydrologic technicians collect samples at the extreme flow events (high and
low) to make sure the instruments are recording accurately at the extremes.
The largest loads of nutrients to the river occur during storm and high flow events.
Since the sensors are located at one point in the river, the technicians will visit the
site for periodic cross-sections of water quality.
These measurements across the river will allow us to understand how the measurement at the
instrument relates to variability across the channel.
By monitoring and analyzing the nutrient data from a regional network of supergages we are
taking the first steps in understanding how actions by farmers, industry and governments
on the landscape are changing the conditions in the river and the actions we may need to
take to preserve this vital resource for generations to come.