What Does USGS Research Tell Us About Phosphorus in the Boise River?

Alexandra Etheridge

April 6, 2012

Boise River history and watershed characteristics

Why Phosphorus?

Spatial Phosphorus Loading 1996-2005

Flow-weighted Phosphorus trends 1994-2010

Boise River & Snake River-Hells Canyon TMDL

Preview

History of the Boise River

Late 1800s – early 1900s diversions for irrigation, mining

Dams – 1915 Arrowrock, 1950 Anderson Ranch, 1957 Lucky Peak, 1957 Hells Canyon Dam

Geomorphological changes

Water-quality changes, increased nutrients, sediment, bacteria – urban and agriculture

Population in Treasure Valley increased 60% from 1990 to 2010

Boise River ~1900

Boise River Today

Lucky Peak Lake

Photo by ISDA

Why Phosphorus?

• Snake River-Hells Canyon TMDL – Phosphorus target = 0.07 mg/L

– Excess nutrients excess algae hypoxia/death

• Dissolved Phosphorus is a clear driver of Snake River algae growth

• No clear relationship between nutrients and floating algae in Boise

• Most algae in Boise River is benthic (attached to surfaces, bottom)

Total Phosphorous Concentrations (1996-2005)

Target at Mouth 0.07 mg/L

Downstream

Smoothed line, Irrigation Season

Smoothed line, non-irrigation Season

Flow-weighted = Total annual

phosphorus load ÷ Total annual Q

Target at Mouth 0.07 mg/L

Flow-weighted Phosphorus at Parma 1994 - 2002

268

326

294

589

298 303 328

302

0.34

0.38

0.40

0.24

0.40

0.32 0.30

0.29

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0

100

200

300

400

500

600

700

2003 2004 2005 2006 2007 2008 2009 2010

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Flow-Weighted Total Phosphorus At Parma 2003 - 2010

USGS DATA - PROVISIONAL SUBJECT TO PEER REVIEW

Target at Mouth 97 ton/yr (based on 242 kg/d)

Target at Mouth 0.07 mg/L

Robust Data 2008-2010

Study: What does Boise Contribute to Snake?

Funded by municipalities and USGS

TP at Parma every 49 h

Weekly sampling during Irrigation season in Snake and Boise

Estimated daily loads

15-minute water-quality parameters

Surrogates

What we found:

Boise River contributes 30% of TP and 72% of OP in Snake

Boise River has higher TP in winter

Boise River more dissolved than particulate

Snake River more particulate than dissolved

Phosphorus drives algae growth in Snake

Snake River Phosphorus & Floating Chlorophyll-a (Algae)

Overall spearman’s rho = -.64

Relative Contribution to Snake Boise River contributes 11% of mean annual flow in Snake

Net uptake of OP in Snake River, Owyhee River contributes ~2 – 4 % of nutrient loads measured at Nyssa

30%

53%

17%

Total Phosphorus Boise

Snake

Other

72% 39%

-11%

Orthophosphorus

15%

77%

8%

Total Nitrogen

13%

50%

37%

Suspended Sediment 2%

86%

12%

Chlorophyll-a

All measured TP concentrations in Boise River exceeded the seasonal target of 0.07 mg/L

At Adrian - 13% exceeded target

At Nyssa – 64% exceeded target

Total Phosphorus 2008 - 2010

Most phosphorus in the Boise river is dissolved

Phosphorus increases downstream

Dissolved phosphorus delivered by the Boise River floating algae growth in the Snake River

Summary

Questions

3 Synoptic sampling events August 2012

October 2012

February 2013

Up to 40 sites 25-30 surface water

10-15 groundwater

Phosphorus mass balance model

USGS Open File Report by June 30, 2013

USGS & IDEQ Synoptic Study

Phosphorus Data Summary 1994 -2005 Explanation

75th percentile (75% of results are lower than this)

25th percentile

(75% of results are higher than this)

Upper Adjacent (Largest result between 75th & 100th percentile)

Median Lower Adjacent (Lowest result between 25th & 0 percentile)

Outlier

Total Number of Samples 55

Total Phosphorus Surrogate Model Boise River

Seasonal Average TMDL Target

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

0 10 20 30 40 50 60 70

Dis

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sp

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g/L

River Mile

Right Bank

Center of River

Left Bank

Surface WaterParma

EagleIsland

Diversion Dam

Middleton

Caldwell Near Mason Slough

Glenwood Bridge

Notus

GW source of phosphorous to lower Boise River

1

10

100

1000

10000

100

1,100

2,100

3,100

4,100

5,100

6,100

7,100

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Estimated Mean Monthly Total Phosphorus Loads in pounds per day Boise River Near Parma, Idaho WY2003 - WY2008

Estimated TP Load

95% Confidence Interval

Daily Mean Flow

USGS DATA - PROVISIONAL SUBJECT TO PEER REVIEW

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

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Estimated Mean Monthly Total Phosphorus Loads Boise River Near Parma, Idaho WY2003 - WY2008

2003

2004

2005

2006

2007

2008

Most recent biological sampling

USGS DATA - PROVISIONAL SUBJECT TO PEER REVIEW

Sediment Concentrations (1996-2005)