1. Diane McKnight, Matt Miller, Rose Cory and Mark Williams
Coupling of carbon and nitrogen cycles through humic redox reactions in an alpine stream
Diane McKnight, Matt Miller, Rose Cory and Mark Williams
Depart. Civil, Environmental & Architectural Engineering, University of Colorado

2. NWTLTER: C & N transport and reactivity in Green Lakes Valley
Response of pristine, cold regions to climate change and N enrichment

3. Hyporheic Zone: “hotspot” of biogeochemical reactions driven by mixing across redox gradient
Stream h2o mixes with groundwater and returns to the stream

4. Redox Couples Oxidizing Conditions O2 H2O NO3- N2, NH4+ Mn(IV) Mn(II)
Fe(III) Fe(II)
Oxidized Humics Reduced Humics
SO H2S
Reducing Conditions

5. DOM reducing microorganism
CO2
Acetate
Oxidized DOM
DOM reducing microorganism
Reduced DOM
Photoreduction of Ferric to Ferrous Iron e- e-
Humics act as electron shuttle
Fe3+
Fe2+
NO2- + DOM  DOM-N
Ferrous Wheel Hypothesis
NO3-

6. Tracer experiment: Navajo Meadow Stream *formed by snowmelt
*elevation~3,750m
*formed by snowmelt
and glacial runoff
*surrounded by
alpine wetland
*~150m in length

7. Approach: Tracer injection experiment and modeling with OTIS
Main Channel:
Lateral inflow
Advection
Dispersion
Transient storage
Storage Zone:
Transient storage s

8. Humic Peaks: (quinone moieties) Protein Peak
Approach: Fluorescence index 370 nm Ex, and EEM’s (Excitation and emission over a range of wavelengths)
Excitation (nm)
Emission (nm)
Humic Peaks: (quinone moieties)
Protein Peak

9. PARAFAC
Excitation-emission matrix
(EEM)
Comp Comp Comp. 3

10. “HQ”
“Q”
Quinones found in enzymes, e.g ubiquinone, and formed by lignin oxidation.
Forms of this complex are found throughout cells
Important in electron transfer reactions, such as the oxidation of NADH
Also known as coenzyme Q
Ubiquinone

11. Quinone fluorescence
AQDS/AHDS useful as models for humic fluorescence

12. Stream Br- Addition, July 10
Background [Br-] = 0 mg/L
Reach 1
Reach 2
Reach 3

13. Storage Zone Br- Simulation
Reach 1
Reach2
Reach 3
0.1 mg/L
0.1 mg/L

14. Connectivity of wells Br, Ca, del 18O & D on July 10

15. Stream Chemistry
July 10th
July 17th
July 24th
DOC LF FI SR
SUVA

16. Stream-Well ComparisonsB A A A
A,B B
A,B A B B A A A FI
Well 1 = No and Low Br, Well 2 = High Br

17. Stream Site EEMs S1 S2 S3
July
10th
(tracer)
July 17th
July 24th

18. Well Site EEMs Characteristic Humic Peaks Protein Peaks July 10th, V13

19. PARAFAC Components Red-shifted: C2 (HQ1), C3 (HQ2)
Blue-shifted: C5 (Q)
Protein: C9 2 5

20. Ex, Em spectra for HQ1 and HQ2
Note: similar excitation spectra

21. Comparison of HQ1 and AHDS
Em and Ex spectra: Same ex. max and shape. Emission max are different, probably related to H bonding, solvent, excited state rxns

22. Comparison of Q and AQDS
Very similar ex and em max (ex 260 nm; em max at 418 nm). Similar features of spectra, Q has broader peaks as typical for humics

23. Stream-Well ComparisonsB C A A
Well 1 = No and Low Br
Well 2 = High Br
F = (Σ HQ1, HQ2) / (Q)

24. Two Components Explain Fluorescence Index
Matt’s data appears on click!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

25. DOM reducing microorganism
CO2
Acetate
Oxidized DOM
DOM reducing microorganism
Reduced DOM
Photoreduction of Ferric to Ferrous Iron e- e-
Humics act as electron shuttle
Fe3+
Fe2+
NO2- + DOM  DOM-N
Ferrous Wheel Hypothesis
NO3-

26. Ferrous Wheel: Addition of Ferric Nitrate to reduced DOM samples with high ferrous iron concentrations, causes decrease in ferrous due to nitrate reduction. NOTE: Addition of Ferric Citrate causes ferrous iron to INCREASE.

27. Hyporheic zone interactions, e. g. humic redox
Hyporheic zone interactions, e.g. humic redox!!, hotspot of C & N interactions, influencing N transport in alpine systems.
Fluorescence index = HQ1/HQ2
FI increases with microbial sources
(primary and secondary)
Nitrogen and Carbon cycling coupled
by biotic and chemical processes

28. Questions?

29. Ferrous Wheel Results: Added Ferric Nitrate to Samples with high ferrous iron concentrations.. NOTE: get different results when ferric citrate added, in that case ferrous iron INCREASES.