Matt Miller and Diane McKnight Department of Civil, Environmental, and Architectural Engineering, CU-Boulder DOM processes in the Green Lakes Valley

Sources of DOM to aquatic systems Allochthonous: FA FI Leaching Autochthonous: FA FI

Examples of biotic and abiotic processes affecting DOM *Biotic: microbial respiration, photosynthesis, excretion, herbivory, predation *Abiotic: streambed sorption, photodegradation, hyporheic zone interaction, abiotic oxidation/reduction oxidation/reduction

The Hyporheic Zone *An area where stream water mixes with groundwater and eventually returns to the stream.

Redox Couples Oxidizing Conditions Reducing Conditions O 2 H 2 O NO 3 - N 2, NH 4 + Mn(IV) Mn(II) Fe(III) Fe(II) Oxidized Humics Reduced Humics SO 4 2- H 2 S

Oxidized Humics Reduced Humics Acetate Oxidized Humics Fe(II) CO 2 Reduced HumicsFe(III) Biotic Abiotic

Fluorescence Spectroscopy *2-D: Excitation at a single wavelength, emission measured over a range of wavelengths *3-D: Excitation and emission measured over a range of wavelengths *DOC components that fluoresce *Proteins (free or attached to larger molecules) *Humic substances (quinone moieties and possibly other compounds) L.F. (microbial): FI = 1.8 S.R. (terrestrial): FI = 1.3

Questions Is there substantial hyporheic zone interaction in the upper reaches of the GLV? Is h.z. interaction affecting DOM redox chemistry? Can this interaction and the subsequent chemical effects be quantified?

Hypotheses 1.H.Z. interaction plays an important role in the hydrology of the GLV. 3.Hydrologic models can be used to simulate transport. 2. H.Z. interaction is important in determining the chemical character of in-stream DOM. 4. Rose (I mean PARAFAC) can be used to quantify DOM redox chemistry.

Niwot Ridge Continental Divide Green Lakes Valley Site Description

*elevation~3,750m *formed by snowmelt and glacial runoff *surrounded by an alpine wetland/talus *~100m in length Study Site

Methods *Tracer Injection with LiBr (July 10 th ) *All sites sampled on three dates to characterize the chemical environment (July 10 th, 17 th, 24 th ) the chemical environment (July 10 th, 17 th, 24 th ) *OTIS-P used to simulate transient storage *PARAFAC used to characterize fluorescent fraction of DOM in the fluorescent fraction of DOM in the samples samples

Excitation-emission matrix (EEM) Comp. 1 Comp. 2 Comp. 3 PARAFAC

Cory and McKnight, 2005 Compared excitation and emission spectra of model quinones with ex./em. spectra of comp. 3 “quinone-like components” (Q1, Q2, Q3) 3 “semi-quinone-like comp.” (SQ1,SQ2,SQ3) 1 hydroquinone-like component (HQ)

Redox Ratio Q ox = ∑Q1,Q2,Q3 Q red = ∑SQ1,SQ2,SQ3, HQ Q red /(Q red +Q ox )

OTIS Equations Main Channel: Storage Zone: Advection Dispersion Lateral inflow Transient storage s

Water Chemistry Results

PARAFAC RESULTS

OTIS Simulation Time (h) *Large Storage Zone *High Exchange Rate d e f Stream ChannelStorage Zone

Conservative Modelling of Chemical Constituents C-C)α(CC)(C)(AD SL A q x C xA 1 x C A Q t C LIN          C-)C(Cα sS A A dt dC S s s  *Conservative transport: S.Z. λ adjusted until h.z. simulation matched measured concentration * Set upstream [DOC] to zero (all input from s.z.) *Set s.z. [DOC] to zero (all input from upstream) 25% of DOC from H.Z. and 75% from upstream

Conservative transport-PARAFAC

Conclusions * Transient storage was simulated and indicates high rates of exchange between the main channel and a large storage zone. * Water quality measurements indicate differences in storage zone and main stream channel water quality. *Oxidized quinones are transported to h.z. where they can be used as e - acceptors *Reduced quinones transported from h.z. to main stream channel are rapidly oxidized and represent an energy source for microorganisms. *Patterns of N-speciation suggest that NO 3 - is being used as an e - in the wetland and NH 4 + is oxidized in main stream channel.

Current/Future Work Examine links between N and C cycles at watershed scale. Is there an abiotic control on NO 3 - ? Ferrous Wheel Hypothesis: Acetate CO 2 Reduced Humics Fe(III) Fe(II) NO 3 - NO 2 - DOM-N Geobacter metallireducens Oxidized Humics Davidson et al., 2003

Current/Future Work Cont. Tracer experiment and development of reactive transport model using OTIS to couple C and N transport. Use model to predict rate constants and sorption/decay coefficients for reactions being modeled.