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Total Phosphorus Concentration, mg/L

Some Examples of Concentration-Flow Curves, cont.

The Grand River provides another example of a stream where both point and nonpoint sources contribute to elevated phosphorus concentrations. Note that much of the total phosphorus under low flows is comprised of soluble reactive phosphorus (lower right graph). This pattern of increasing SRP concentrations under low flow suggests point source impacts low flow conditions. Under high flow conditions, the soluble reactive phosphorus remains low.

Prior to the onset of phosphorus removal at sewage treatment plants in the Lake Erie Basin the pattern of total phosphorus-flow graphs showed much higher low flow concentrations. This is illustrated for the Sandusky River below Bucyrus from earlier WQL data sets. Note the differences in the Y-axis scales for the Grand River and for the earlier data from the Sandusky River below Bucyrus.

Sandusky River, Bucyrus, Jan 1974 - May 1981

10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0

TP

1

10

100 Flow, cfs

1000

10000

1.40

1.20

1.00

TP (mg/l)

0.80

0.60

0.40

0.20

0.00

1

Soluble Reactive Phosphorus (mg/l)

0.350

0.300

0.250

0.200

0.150

0.100

0.050

0.000

Page 2.e.4

1

Grand River

10/1/1999 - 9/30/2004

TP

10

100 1000 Flow (cfs)

10000

100000

Grand River

10/1/1999 - 9/30/2004

SRP

10

100 1000 Flow (cfs)

10000

100000

Water Quality Laboratory, Heidelberg College

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