spatial and temporal variations in nutrient concentration and speciation in silver bow creek

Chris Gammons, John Babcock, Bev Plumb, Steve Parker Montana Tech, Butte, MT

Spatial and temporal variations in nutrient concentration and speciation in Silver Bow Creek

Monitoring databases for nutrients in surface waters often look like this

Why so messy?

Outline of talk

Site description Synoptic variations Seasonal variations Diel variations Lateral (bank to bank) variations Implications for monitoring

SBC-6

Warm Springs Ponds

Pit Lake

City of

Butte

5 km

46 N116 W

46 N106 W

Butte

Missoula

Clark Fork River

detail

north

Ger

man

SBC-3SBC-1

Lower SBC

0 1 2 km

12323250

Ÿ

I-15/90

Ÿ

12323240

SBC-3SBC-1

zone of hypoxia

SBC-2

WWTPLAO

MPTPUSGS gaging stationroad

SBC-1Above WWTP

SBC-6

Warm Springs Ponds

Pit Lake

City of

Butte

5 km

46 N116 W

46 N106 W

Butte

Missoula

Clark Fork River

detail

north

Ger

man

SBC-3SBC-1

Lower SBC

0 1 2 km

12323250

Ÿ

I-15/90

Ÿ

12323240

SBC-3SBC-1

zone of hypoxia

SBC-2

WWTPLAO

MPTPUSGS gaging stationroad

WWTP discharge

SBC-6

Warm Springs Ponds

Pit Lake

City of

Butte

5 km

46 N116 W

46 N106 W

Butte

Missoula

Clark Fork River

detail

north

Ger

man

SBC-3SBC-1

Lower SBC

0 1 2 km

12323250

Ÿ

I-15/90

Ÿ

12323240

SBC-3SBC-1

zone of hypoxia

SBC-2

WWTPLAO

MPTPUSGS gaging stationroad

SBC-33 km below WWTP

SBC-6

Warm Springs Ponds

Pit Lake

City of

Butte

5 km

46 N116 W

46 N106 W

Butte

Missoula

Clark Fork River

detail

north

Ger

man

SBC-3SBC-1

Lower SBC

0 1 2 km

12323250

Ÿ

I-15/90

Ÿ

12323240

SBC-3SBC-1

zone of hypoxia

SBC-2

WWTPLAO

MPTPUSGS gaging stationroad

Warm Springs Ponds

0.01

0.1

1

10

0 1 2 3 4 5 6

km below mixing zone

pp

m a

s N

nitrate

ammonia

nitrite

Synoptic changes in nutrient concentrationSBC-3 below WWTP, August, 2006

Nitrite (NO2-) forms

as intermediate during oxidation of

NH4+ to NO3

-

Nitrosomonas

NitrificationAmmonium oxidation

Step 1: NH4+ + 1.5O2 → NO2

- + 2H+ + H2Oammonium nitrite

Step 2: NO2- + ½ O2 → NO3

-

nitrite nitrate

High nitrite usually means ammonium is being oxidized

0.01

0.1

1

10

0 2 4 6 8

C. July 22, 20080.01

0.1

1

10

0 2 4 6 8

B. June 28, 20070.01

0.1

1

10

0 2 4 6 8

conc

entra

tion,

mg/

L as N

A. Aug. 08, 2006

Distance below WWTP, km

NO3-

NO3-

NO3-

NO2-

NO2-

NO2-

NH4+

NH4+

NH4+

DINDINDIN

Decrease in NH4+ due to nitrification

Increase in NO3- due to nitrification

Decrease in DIN due to assimilation

Synoptic changes (different years)

mg

/L a

s N

0.0

0.5

1.0

1.5

mg

/L a

s N

0

1

2

3

4

5

A. NO3- + NO2

-

B. NH4+ + NH3

mg

/L a

s N

0

1

2

3

4

5

Outlet to WSPOU

C. DIN

01/98 01/99 01/00 01/01 01/02 01/03 01/04 01/05

mg

/L a

s P

0.0

0.2

0.4

0.6

0.8

Inlet to WSPOU

D. total dissolved PO43-

Nitrate + Nitrite

Ammonium

DINDissolved Inorganic N

Seasonal changes in nutrient concentrations SBC at Warm Springs Ponds

■ WSPOU INLET ○ WSPOU OUTLET

mg

/L a

s N

0.0

0.5

1.0

1.5

mg

/L a

s N

0

1

2

3

4

5

A. NO3- + NO2

-

B. NH4+ + NH3

mg

/L a

s N

0

1

2

3

4

5

Outlet to WSPOU

C. DIN

01/98 01/99 01/00 01/01 01/02 01/03 01/04 01/05

mg

/L a

s P

0.0

0.2

0.4

0.6

0.8

Inlet to WSPOU

D. total dissolved PO43-

Winter months

Diel changes SBC-3 below the Butte WWTP

12:00 16:00 20:00 00:00 04:00 08:00 12:00

mg

/L N

O3

-N o

r N

H4

-N

0.0

0.5

1.0

1.5

2.0

2.5

3.0

mg

/L N

O2

-N o

r P

O4

-P

0.0

0.2

0.4

0.6

0.8

Nitrate-NNitrite-NAmmonium-NPhosphate-P

7/23/2008 7/24/2008

Nutrient isotopes: synoptic

-10

-5

0

5

10

15

20

25

30

35

-1 0 1 2 3 4 5 6 7 8

δ15N

or

δ18O

distance below WWTP, km

δ15N-NH4

δ15N-NO3

δ18O-NO3

WWTP

SBC upstream

Nutrient isotopes: diel

0

5

10

15

20

25

30

12:00 18:00 0:00 6:00 12:00 18:00

δ15N

NO3-

7/24/087/23/08

NH4+

Δ = 14.1 ‰

Δ = 20 ‰

NH4-oxidizing bacteria preferentially metabolize 14N Isotopic separation is less during day (faster rates) Isotopic trends inconsistent with denitrification

1000 ft Silver Bow Creek

Silver Bow Creek WWTP discharge

USGS gaging station

How far below the confluence of SBC and WWTP before combined flow is mixed, bank-to-bank?

Lateral variations in water chemistry

300

350

400

450

500

550

600

0 2 4 6 8 10 12 14 16 18 20 22 24

SC, m

S/cm

Feet from north bank

100

340

1840

2440

Feet below confluence

Bank-to-bank profiles in specific conductance (SC)

200

300

400

500

600

700

800

0 1000 2000 3000

SC, m

S/cm

Feet below confluence of SBC and WWTP

North bank

South bank

Mixed

1000 ft

2400 feet

Silver Bow Creek

Silver Bow Creek

WWTP discharge

USGS gaging station

How far below the confluence of SBC and WWTP before combined flow is mixed, bank-to-bank?

Implications for nitrate monitoring The sample you collect is representative only of

a given spot in a given stream reach on a given day and at a certain time of day For streams like Silver Bow Creek, consider taking 24-h

integrated samples, or sample at same time of day for long-term trend analysis

For highly polluted waters, be sure to sample for all nutrients (e.g., ammonium, nitrite)

Stable isotope signatures of nitrate are also affected by synoptic and diel variations

Be careful that you are not sampling water from a stream or river that is not completely mixed

USGS 104b Montana Water Center Students

Bev Plumb John Babcock Stacey Wilcox Erika Sholey Brian Kuhn

Acknowledgements

References Plumb, B. (2009) Geochemistry of nutrients in Silver Bow

Creek, MT. M.S. Thesis, MT Tech. Gammons, C.H., Babcock, J., Parker, S.R., Poulson,

S.R. (2011) Diel cycling and stable isotopes of dissolved oxygen, dissolved inorganic carbon, and nitrogenous species in a stream receiving treated municipal sewage. Chemical Geology, 283, 44-55.

Questions??