Office of Water Office of Science and Technology

Photo image area measures 2” H x 6.93” W and can be masked by a collage strip of one, two or three images.

The photo image area is located 3.19” from left and 3.81” from top of page.

Each image used in collage should be reduced or cropped to a maximum of 2” high, stroked with a 1.5 pt white frame and positioned edge-to-edge with accompanying images.

May 15, 2015

Lester L. Yuan

Office of Science and Technology, Office of Water, U.S. EPA

Nitrogen, phosphorus, and harmful algal blooms

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National Lakes Assessment

• Continental-scale spatial coverage of samples • Uniform sampling protocols applied to all lakes • 2 cycles of samples completed (2007 and 2012)

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EPA statistical analysis

• Estimate relationships between nutrient concentrations and cyanobacteria biovolume, and nutrient concentrations and microcystin.

• Preliminary results suggest TN and TP are strong predictors of cyanobacteria biovolume and microcystin.

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Relationship between cyanobacteria biovolume, TN, and TP

• Strong relationship between cyano biovolume, TN, and TP

• TN and TP account for 77% of the variability in cyano biovolume

• TN accounts for more variability than TP.

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Do relationships change for different types of lakes? A preliminary classification scheme

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Examples of relationships within different lake-groups

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Relationship between microcystin, TN, and TP

• Strong relationship with TN at national scale

6 Open circles indicate MC non-detects.

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Preliminary classification scheme

• Smaller number of classes because of smaller dataset.

– Precipitation and latitude define classes.

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Relationships within lake groups

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Filled circles: observed MC concentration Open circles: Non-detects for MC

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Management of nutrients may be site-specific

• High loading rates of inorganic N loading may indicate the need for N control. – If excess N is readily available, even N-fixing cyanobacteria will preferentially

use environmental N.

• High N-fixation rates (or low external N-loading) may indicate that P control will also reduce N concentrations.

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Questions?

Lester Yuan (yuan.lester@epa.gov)

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