Dissolved Organic Carbon Concentration and Fluorescence Characterization of Tempe Town Lake

By Marissa Raleigh

Tempe Town Lake Background• Man-made lake built in the Salt River channel• Held in by inflatable dams• Designed for both flood control and recreation• The largest loss is through evaporation, major input is precipitation

http://4.bp.blogspot.com/-EjQ_SIBPSxo/ULjJm43TfCI/AAAAAAAAC0g/b8LOPO88qfY/s1600/tempe+town+lake+aerial.jpg

0.5 miles

Fluorescence

DOCMethodsSampling• Twice a week• After Rain events

Measurements:• pH• Temperature• Conductivity• Dissolved Oxygen• Dissolved Organic Carbon

(DOC)• Fluorescence

An excitation-emission matrix (EEM) is produced

Fluorescence occurs when an excited electron relaxes to its ground state by emitting a photon

What is Fluorescence?

Fluorescence is a method used to look at the composition of DOC

Dissolved Organic CarbonDissolved Organic Carbon

Sample DateSep'12

Jan'13 May'13

Sep'13 Jan'14

DO

C (m

g/L)

2

3

4

5

6

7

Pre

cipi

tatio

n (in

.)

0.0

0.5

1.0

1.5

2.0

Tem

pera

ture

(deg

C)

0

20

40

60

80

100

DOC (mg/L)Precipitation (in.)Temperature (deg C)

• Overall seasonal pattern w/higher concentrations in Fall/Spring

• Concentrations increase w/rain events

Fluorescence Sum

Sample DateSep'12

Jan'13 May'13

Sep'13 Jan'14

Fluo

resc

ence

Sum

0.1

0.2

0.3

0.4

0.5

Pre

cipi

tatio

n (in

.)

0.0

0.5

1.0

1.5

2.0

Fluorescence Sum

• Measure of total fluorescence intensity

• Rain events bring in fluorescent material

• Overall pattern is different from DOC

Data

Freshness Index• Indicates the proportion of recently

produced DOC• The ‘freshness’ is generally high,

indicating much of the DOC in Tempe Town Lake is “recently produced”, most likely by algae

• Decreases after rain events suggest run-off has ‘older’ organic matter

Fluorescence Index (FI)• Higher values (>1.5) reflect

microbially-derived DOC; Lower values reflect terrestrially-derived DOC

• Tempe Town Lake is highly microbial• Rain events bring in DOM different

from what is currently in the lake

Fluorescence Index

Sample Date

Fluo

resc

ence

Inde

x

1.45

1.50

1.55

1.60

1.65

1.70

Pre

cipi

tatio

n (in

.)

0.0

0.5

1.0

1.5

2.0Freshness

Sample DateSep'12

Jan'13 May'13

Sep'13 Jan'14

Fres

hnes

s

0.80

0.82

0.84

0.86

0.88

0.90

0.92

0.94

Pre

cipi

tatio

n (in

.)

0.0

0.5

1.0

1.5

2.0

Summary

• Dissolved organic carbon concentrations [DOC] vary both seasonally and with precipitation

• Total fluorescence changes mainly with precipitation

• Precipitation brings in material that is different from what is presently in the lake at the time of sampling

• Hilairy Hartnett• Zach Smith, Maggie Bowman, and the entire CaNDy

Lab group• Funding from ASU/NASA Space Grant and NSF

CAREER #0846188

Acknowledgements

Questions???