Proceedings available at: http://www.extension.org/67730 Elevated phosphorus concentrations in the Illinois River Watershed (IRW) have long been an environmental issue between the states of Arkansas and Oklahoma, which has led to the development of a watershed-reservoir model and future TMDL by the U.S. Environmental Protection Agency. Here, we examine phosphorus concentrations from multiple sources, including the Arkansas Water Resources Center and the U.S. Geological Survey, to evaluate trends in flow-adjusted concentrations. Flow-adjusted phosphorus concentrations have been decreasing in the Illinois River at Arkansas Highway 59, and this translates into decreases further downstream to Tahlequah, Oklahoma. However, flow-adjusted concentrations in Flint Creek have been increasing over time until the last few years. These decreases are tied to the reductions in effluent phosphorus, which have occurred over the last couple decades. But, the application of poultry litter has also likely decreased within the IRW. A nutrient mass balance of the Watershed Research and Education Center in Fayetteville, Arkansas showed that reduced litter applications and increased forage export (i.e., hay being removed from fields) can result in phosphorus export at the farm-scale. The missing piece of this study would be understanding legacy phosphorus, and how this influences source apportionment and changes over time. Presentation by: Brian Haggard

1. Phosphorus concentrations have
been declining in the Illinois River:
was it point sources, farm-level
nutrient management, or what?
Brian E. Haggard and J. Thad Scott
Arkansas Water Resource Center

2. Wewantameasuringstick
totelluswhatphosphorus
concentrationsaredoing?
• We want to be able to
quantify increases and
or decreases.
• We want to know when
variation (or deviation)
occurred.
• We want to know why
changes occurred…
• This gets difficult at the
large watershed scale.
• Lots of things happen
as phosphorus moves
downstream.

3. It’s not always as simple as looking at
changes in concentrations over time…
A
Year
97 98 99 00 01 02 03 04 05 06 07 08 09 10 11
TotalPhosphorus,TP(mg/L)
0.0
0.5
1.0
1.5
2.0
2.5
Example from Illinois River at
Arkansas Highway 59, South of
Siloam Springs.
We need consider all exogenous parameters that might influence changes.

4. We used two statistical methods to
evaluatetrends in concentrations.
• The analysis was performed
using three steps:
• STEP 1 – Log-transform the
water-quality data
• STEP 2 – Plot log-
concentration as a function
of log-discharge
• STEP 3 – Use LOESS
regression to remove the
effects of discharge on
concentration
• The residuals from the LOESS
regression are used in the
two statistical methods.
Example from Illinois River

5. The residuals represent the flow-
adjustedconcentrations, FACs.
Example from Illinois River

6. The two most popular trend analysis
techniques out there are:
• The first technique is semi-parametric, where FACs are plotted over
time and simple linear regression is used to evaluate changes.
• The second technique is non-parametric (Seasonal Kendall Test),
which compares the FACs at separate time periods or seasons and
determines if there is a trend.
Example from Illinois River This methods assumes
a monotonic change
in FACS, which might
hide step changes or
separate trends over
the long-term.

7. Base on our analysis, the percent changes
were similar for either technique…
SEN SLOPE, PERCENT CHANGE
REGRESSIONSLOPE,PERCENTCHANGE
y = 0.921x + 1.024
R² = 0.891
-25
-20
-15
-10
-5
0
5
-25 -20 -15 -10 -5 0 5
When trends were significant, the slopes were significantly related with a slope near one.

8. This presentationwill focus on trends
using the semi-parametric technique…
• This technique provides an
good visual assessment with
statistical significance.
• It is a published method and
used in the scientific literature.
• Haggard, 2010 – JEQ
• Scott et al., 2011 - JEQ
• It is somewhat easier to
communicate the methods to
stakeholder groups.
• The percent change calculated
was also related to the Sen
slope from the non-parametric
Seasonal Kendal Test.

9. Phosphorus concentrations in the
Illinois River have been decreasing, both
in Arkansas and Oklahoma.
TAKE HOME
MESSAGE!

10. Why did we see phosphorus decreases
across the Illinois River Watershed?
There are several things contributing to the
water-quality changes, including:
• Arkansas enacted legislation to change poultry
litter management, i.e. Titles 19, 20, 21 & 22; there
was a lot going on in Oklahoma too!
• 319 Nonpoint Source, Extension, among other
State and stakeholder programs invested millions
of dollars into these watersheds
• BMPs
• Awareness (Outreach)
• Litter Export
• Some wastewater treatment plants reduced
effluent phosphorus, influencing the Illinois River.

11. How did the concentrations change over
time across the Illinois River?
Illinois River
Flow-AdjustedConcentrations
HIGHER
LOWER
Time
This would be no change
over time.

12. How did the concentrations change over
time across the Illinois River?
Illinois River
Flow-AdjustedConcentrations
HIGHER
LOWER
Time
WWTPs are direct inputs, and if phosphorus
was conservative we would expect…

13. How did the concentrations change over
time across the Illinois River?
Illinois River
Flow-AdjustedConcentrations
HIGHER
LOWER
Time
Now, let’s combine WWTP changes with
landscape nutrient management and we
see…

14. How did the concentrations change over
time across the Illinois River?
Illinois River
Flow-AdjustedConcentrations
HIGHER
LOWER
Time
In theory, this would happen but in reality
we see something quite different.

15. In reality, we saw that phosphorus
concentrations increased (to ~2002), then
decreased through 2011.
Illinois River
Flow-AdjustedConcentrations
HIGHER
LOWER
Time

16. When we look at little closer, the decrease
might be more exponential.
Illinois River
Flow-AdjustedConcentrations
HIGHER
LOWER
Time
Faster decrease at the
beginning, and then slower at the
end.

17. The reason for this variance from the step
change and then linear decrease would be:
Illinois River
• In-stream Retention
• Lab Time from Nutrient
Management and BMPs

18. The decrease observed at the sites
varied a little bit between sites.
IR AR59

19. We see a similar decrease just
downstream at the Illinois River - Watts.
Time (1997 THROUGH 2009)
97 98 99 00 01 02 03 04 05 06 07 08 09
Flow-AdjustedConcentrations
IR Watts

20. We see a decrease further downstream
at the Illinois River - Tahlequah.
Time (1997 THROUGH 2009)
97 98 99 00 01 02 03 04 05 06 07 08 09
Flow-AdjustedConcentrations
IR Tahlequah

21. The reason for less change at Tahlequah
has to do with the dynamics at Flint Creek.
Time (1997 THROUGH 2009)
97 98 99 00 01 02 03 04 05 06 07 08 09
Flow-AdjustedConcentrations
Flint Creek

22. Why did we see phosphorus decreases
across the Illinois River Watershed?
Let’s remember several things happened, including:
• Arkansas enacted legislation to change poultry
litter management, i.e. Titles 19, 20, 21 & 22; there
was a lot going on in Oklahoma too!
• 319 Nonpoint Source, Extension, among other
State and Stakeholder Programs invested millions
of dollars into these watersheds
• BMPs
• Awareness (Outreach)
• Litter Export
• Some wastewater treatment plants reduced
effluent phosphorus, influencing the Illinois River.
The big change in late
2002-3 was likely tied
to Springdale’s WWTP.

23. Why did we see phosphorus decreases
across the Illinois River Watershed?
Let’s remember several things happened, including:
• Arkansas enacted legislation to change poultry
litter management, i.e. Titles 19, 20, 21 & 22; there
was a lot going on in Oklahoma too!
• 319 Nonpoint Source, Extension, among other
State and Stakeholder Programs invested millions
of dollars into these watersheds
• BMPs
• Awareness (Outreach)
• Litter Export
• Some wastewater treatment plants reduced
effluent phosphorus, influencing the Illinois River.
But, what about nutrient
management on the farm
and landscape.

24. At the farm-scale, the export of
poultry litter can reduce phosphorus
applied to the soil, and in runoff.

25. Nutrient mass balanced showed…

27. Phosphorus concentration in the Illinois
River have been decreasing…
Itislikelythatdecreaseswill
continue,butataslowerrate
thanthepastdecade.
InDecember2012,we
measuredphosphorus
concentrations~0.05mg/L
duringbaseflowconditions.

28. Questions?