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 ScottArkansas Water Resource Center

We want a measuring stick to tell us what phosphorus concentrations are doing?

• 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.

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

To

tal P

ho

sph

oru

s, T

P (

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.

We used two statistical methods to evaluate trends 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

The residuals represent the flow-adjusted concentrations, FACs.

Example from Illinois River

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.

Base on our analysis, the percent changes were similar for either technique…

SEN SLOPE, PERCENT CHANGE

REGRESSIO

N SLO

PE, PERCENT CH

ANG

E

-22 -20 -18 -16 -14 -12 -10 -8 -6 -4 -2

-25

-20

-15

-10

-5

0

f(x) = 0.921602188085941 x + 1.02402370426436R² = 0.891679001610852

When trends were significant, the slopes were significantly related with a slope near one.

This presentation will 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.

Phosphorus concentrations in the Illinois River have been decreasing,

both in Arkansas and Oklahoma.

TAKE HOME MESSAGE!

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.

How did the concentrations change over time across the Illinois River?

Illinois River

Flow

-Adj

uste

d Co

ncen

trati

ons

HIGHER

LOWERTime

This would be no change over time.

How did the concentrations change over time across the Illinois River?

Illinois River

Flow

-Adj

uste

d Co

ncen

trati

ons

HIGHER

LOWERTime

WWTPs are direct inputs, and if phosphorus was conservative we would expect…

How did the concentrations change over time across the Illinois River?

Illinois River

Flow

-Adj

uste

d Co

ncen

trati

ons

HIGHER

LOWERTime

Now, let’s combine WWTP changes with landscape nutrient management and we

see…

How did the concentrations change over time across the Illinois River?

Illinois River

Flow

-Adj

uste

d Co

ncen

trati

ons

HIGHER

LOWERTime

In theory, this would happen but in reality we see something quite different.

In reality, we saw that phosphorus concentrations increased (to ~2002), then

decreased through 2011.

Illinois River

Flow

-Adj

uste

d Co

ncen

trati

ons

HIGHER

LOWERTime

When we look at little closer, the decrease might be more exponential.

Illinois River

Flow

-Adj

uste

d Co

ncen

trati

ons

HIGHER

LOWERTime

Faster decrease at the beginning, and then slower at the end.

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

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

IR AR59

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

Flo

w-A

dju

ste

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on

cen

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IR Watts

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

Flo

w-A

dju

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on

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IR Tahlequah

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

Flo

w-A

dju

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Flint Creek

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.

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.

At the farm-scale, the export of poultry litter can reduce phosphorus

applied to the soil, and in runoff.

Nutrient mass balanced showed…

At the farm-scale, the export of hay in the absence of litter application can

reduce phosphorus.

2007 2008 2009 2010 2011 2012

-1,600

-1,400

-1,200

-1,000

-800

-600

-400

-200

0

200

400

N & P Loads (kg)

NP

2006 and earlier: 1400 kg P storage

Net phosphorus export ranged from 200-400 kg/yr.

Only Partial Year Data

Phosphorus concentration in the Illinois River have been decreasing…

It is likely that decreases will continue, but at a slower rate

than the past decade.

In December 2012, we measured phosphorus

concentrations ~0.05 mg/L during base flow conditions.

Questions?