DISSOLVED ORGANIC MATTER AND DISSOLVED ORGANIC MATTER AND NITROGEN REDOX CHEMISTRY IN AQUATIC NITROGEN REDOX CHEMISTRY IN AQUATIC

ALPINE ECOSYSTEMSALPINE ECOSYSTEMS

Matt Miller Matt Miller

Ph.D. StudentPh.D. StudentAdvisor: Diane McKnightAdvisor: Diane McKnight

Biogeochemical Hot Spots and Hot MomentsBiogeochemical Hot Spots and Hot Moments

Hot Spot:Hot Spot: An area exhibiting high An area exhibiting high rates of biogeochemical transformation rates of biogeochemical transformation in comparison to the surrounding in comparison to the surrounding environmentenvironment

Hot Moment:Hot Moment: Short periods Short periods of time during which reactions of time during which reactions rates are higher than those rates are higher than those during the rest of the seasonduring the rest of the season

0

10000

20000

30000

40000

50000

60000

70000

5/23 6/12 7/2 7/22 8/11 8/31 9/20 10/10 10/30

Date

Dis

char

ge (m

3 /day

)

Potential Hot Moment

McClain et al. (2003)

O

Me

MeO

MeO

Me

H

O

n

O

Me

MeO

MeO

Me

H

O

n

O

Me

MeO

MeO

Me

H

O

n

O

l ignin

MeO

O

l ignin

OH

OMeOH O

l ignin

MeO

O

l ignin

OH

OMeOH

HO

OO

Me

Slide by: Rose Cory

Fe3+

Fe2+

NO3-

NO2- + DOM

DOM-N

Humics act as electron shuttle

Ferrous Wheel Hypothesis

CO2

Acetate

Oxidized DOM

DOM reducing microorganism

Reduced DOM

e-

DOM: Electron TransferDOM: Electron Transfer

Slide by: Chris Jaros

Green Lakes ValleyGreen Lakes Valley

ALBION TOWNSITE

LAKE ALBION

GL4

GL5

NAVAJO STREAM

NIWOT RIDGE

Question 1:Question 1: Is the stream in the upper reaches of the Is the stream in the upper reaches of the catchment acting as a hotspot for C as well as N?catchment acting as a hotspot for C as well as N?

Question 2:Question 2: Do lakes in headwater ecosystems act as Do lakes in headwater ecosystems act as hotspots? If so, is the importance of lake processing a hotspots? If so, is the importance of lake processing a

function of seasonal changes in hydrology and/or biology?function of seasonal changes in hydrology and/or biology?

Research QuestionsResearch Questions

*Tracer Injection w/ LiBr*Tracer Injection w/ LiBr

*Modeled with OTIS*Modeled with OTIS

*Sampled for:*Sampled for:-DOC-DOC

-N species-N species-Li and Br-Li and Br

Stream as Biogeochemical Hot SpotStream as Biogeochemical Hot Spot

Miller et al. (2006)

Main Channel:

Storage Zone:

Advection

Dispersion

Lateral inflow

Transient storage

Transient storage

Decay

Decay

Modeling Hyporheic Exchange: OTISModeling Hyporheic Exchange: OTIS

Solute Transport Modeling ResultsSolute Transport Modeling Results

Miller et al. (2006)

Stream Decay (λ) Storage Zone Decay (λs)

NO3- -1.0 x 10-3 1.0 x 10-4

NH4+ 1.2 x 10-3 -7.9 x 10-5

DOC 1.6 x 10-2 -1.3 x 10-4

Redox Index 6.5 x 10-3 -8.4 x 10-5

λC

λsC

Reactive Transport ResultsReactive Transport Results

Hydrologic Controls on DOMHydrologic Controls on DOM

Hood et al. (2003)

Alpine: Green Lake 4 (GL4)Alpine: Green Lake 4 (GL4)

Subalpine: Lake Albion (ALB)Subalpine: Lake Albion (ALB)

GL4 (Alpine) ALB (Subalpine)

Response to Hydrologic

Change

Response to Biological

Change

Humic Redox Results

0.27

0.32

0.37

0.42

0.47

0.52

3-May 22-Jun 11-Aug 30-Sep

RI

Wetland = 0.51

Stream = 0.39 Rain Event Peak

Chl a

0.27

0.32

0.37

0.42

0.47

0.52

3-May 22-Jun 11-Aug 30-Sep

RI

Rain Event

Peak Chl a

Wetland = 0.51

Stream = 0.39

GL4 (Alpine) ALB (Subalpine)

Response to Biological

Change

Lake ModelingLake Modeling

There is clearly a large signal due to both hydrologic and There is clearly a large signal due to both hydrologic and biologic changes in the system.biologic changes in the system.

Modeling Approach: Mass Balance for a Lake with a Well Modeling Approach: Mass Balance for a Lake with a Well Mixed Epilimnion (both GL4 and ALB)Mixed Epilimnion (both GL4 and ALB)

Proposed Mass Balance CalculationsProposed Mass Balance Calculations

Conservative Transport:Conservative Transport:

Reactive Transport (1Reactive Transport (1stst order rxn. at steady-state): order rxn. at steady-state):

Variables to be modeled: DOC, NOVariables to be modeled: DOC, NO33--, NH, NH44

++, FI, PARAFAC, FI, PARAFAC

11stst Order Rxn.? Order Rxn.?k(?): DOC, chlorophyll a, temperature, pH, etc?k(?): DOC, chlorophyll a, temperature, pH, etc?