Integrating Solute Transport, Stream Metabolism and Nutrient Retention, using the Bio-Reactive Tracer Resazurin Ricardo González-Pinzón, Roy Haggerty, Alba Argerich, Sarah Acker, David Myrold

Outline Introduction Current methods to estimate stream metabolism The resazurin-resorufin system Metabolically Active Transient Storage

Introduction Stream Response Solute Transport Stream Metabolism Nutrient Dynamics

Introduction ? ? ?

These knowledge gaps obscure the functionality of stream ecosystems and how they interact with other landscape processes. Bencala et al., 2011

Introduction Stream Metabolism & Sampling Limitations: –Benthic and hyporheic chambers, and two- station diel technique. Solute Transport vs. Nutrient Dynamics: –Weak or even contradictory correlations using the Transient Storage Model (TSM).

Introduction: Stream Metabolism Christensen 2010

Introduction: Stream Metabolism (2009)

Introduction: Stream Metabolism

Introduction: Solute transport & Nutrient Dynamics Hall et al. 2002

Introduction: Solute transport & Nutrient Dynamics

Working Hypothesis Most metabolic activity and nutrient retention are associated with key active areas within TS zones, where biogeochemical gradients stimulate metabolism by aerobic microorganisms. These zones are located in the near- subsurface of hyporheic zones and in the benthos of pools and eddies; they are referred to as the metabolically active transient storage (MATS) zones.

Drawing by Kera Tucker Rru Raz Rru Resazurin (Raz) Resorufin (Rru) Living organisms Metabolically Active Transient Storage (MATS)

quantified by Raz and Rru MATS Advection Dispersion MITSSorption MAIN CHANNEL Exchange Fast & Slow decay

Haggerty, Argerich & Martí, 2008 Transformation Rates

c (  g/mL) s ( g/g) Freundlich isotherm (shown): s = K f c 1/n K f = 5.15 ± 1.34 mL/g 1/n = 0.89 ± 0.04 r 2 = Linear isotherm: s = K d c K d = 6.63 ± 0.4 mL/g r 2 = Rru- Sorption isotherm Haggerty, Argerich & Martí, 2008

Complementary Sorption- Investigation Methodology: Batch and column experiments to quantify the sorption of Raz and Rru. To prevent Raz transformation we will use sediments sterilized by gamma-radiation.

Quantitative relationship between Δ Raz and respiration

[Raz]=10 ppm [Raz]~200 ppb Quantitative relationship between Δ Raz and respiration

Research approach: Batch experiments: aerobic bacteria and facultative anaerobic bacteria. These experiments will restrict the transformation of Raz to biological mechanisms. Column experiments with different concentrations of Raz and varying physicochemical conditions to broaden respiration rates.

Study site: H.J. Andrews Experimental Forest, Oregon Total reach length = m Two reaches BEDROCK REACH (357.5 m) ALLUVIAL REACH (310.8 m) Argerich et al., in rev. Two consecutive reaches: Upper reach (bedrock reach): streambed sediments scoured to bedrock. Lower reach (alluvial reach): deep alluvium.

22 N Reach 2 Thick alluvium with alder Reach 1 Bedrock Flow Argerich et al., in rev.

Longitudinal sampling 17 h since start of the injection bedrock reach alluvial reach Raz (μg/L) Rru (μg/L) & EC (μS/cm) Argerich et al. (in rev.) Raz sensitive to spatial heterogeneity

ALLUVIAL REACH Raz & Rru (μg/L) Time since addition started (h) BEDROCK REACH Raz (µgL -1 ) Rru (µgL -1 ) Argerich et al. (in rev.) f = 0.37 (MATS/TS) A s /A = 0.19 Mean travel time= 3.5 h MATS = m 2 Raz reaction rate = 1.88 h -1 Raz reaction rate volume-weighted = 0.13 h -1 f = 1.00 (MATS/TS) A s /A = 2.45 Mean travel time= 15.3 h MATS = m 2 Raz reaction rate = 0.12 h -1 Raz reaction rate volume-weighted = 0.29 h -1

Instantaneous respiration rates (mg O 2 m -2 min -1 ) Rru:Raz ratio y=1.29ln(x)+3.05 R 2 =0.75, P=0.01 Raz to Rru proportional to whole-reach respiration rates Argerich et al. (in rev.) Respiration: alluvial = 2 x bedrock Transient storage: alluvial = 13 x bedrock Volume-weighted Raz reaction rate: alluvial = 2.1 x bedrock

Nutrient dynamics = f(MATS)  Hydrologic processes: Discharge TS  Biotic controls: Assimilatory uptake (algal mats, microbes) Dissimilatory uptake (microbes) Consumers (macro-invertebrates, fishes)  Abiotic controls: Precipitation Sorption MATS: a linking tool between hydrologic and biologic nutrient retention

Methodology: Column experiments with sterilized and unsterilized sediments to differentiate biotic and abiotic nutrient retention. Injections of conservative (NaCl) and bio- reactive tracers (NH 4, PO 4, and Raz) monitored through time. In the field, we will measure the same injectates in surface upwelling/downwelling locations.

Applications in water resources More robust techniques are needed to develop mechanistic relationships to improve our fundamental understanding of in-stream processes and how streams interact with other ecosystems Water Resources Science Water Resources Engineering Water Resources Management Understanding TS from a metabolic perspective Support to design stream restoration projects Support to design stream preservation projects

Take-home points Raz-Rru system is a “smart tracer” for MATS –May allow us to worry less about surface vs. subsurface transient storage and more about the rates of transformation in MATS. –Transformation of Raz to Rru is proportional to aerobic respiration. –Can help us to measure metabolism at different scales. MATS model can be used to differentiate metabolic activity in reaches and separate hydrologic and biologic effects.