Stream-upland connections and the effects of stream...

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Dispersion (m 2 s -1 ) 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 Exchange Coef, α (s -1 ) 0 1e-5 2e-5 3e-5 4e-5 5e-5 Storage Zone Area, A S (m 2 ) 0.00 0.04 0.08 0.12 0.16 0.20 Reach 1, 0-145 m Reach 2, 145-290 m Area Coefficient, c 2 4 6 8 10 12 14 Inflow, q LAT (m 3 s -1 m -1 ) 1.0e-6 1.5e-6 2.0e-6 2.5e-6 3.0e-6 3.5e-6 A S /A 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Discharge (L s -1 ) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0 10 20 30 40 Discharge (L s -1 ) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 L S (m) 2e+5 3e+5 4e+5 5e+5 6e+5 7e+5 8e+5 Stream-upland connections and the effects of stream discharge on transient storage processes Brian L. McGlynn 1 , Michael Gooseff 2 , Cindy Hugenschmidt, and Robert S. McGlynn 3 1. Department of Land Resources & Environmental Sciences, Montana State University, Bozeman 2. Department of Aquatic, Watershed, and Earth Resources, Utah State University 3. Institute for Hydrology, Freiburg University, Germany 4. Department of Earth Sciences, Dartmouth College Stream Tracer Solute Transport Modeling Three LiBr salt stream tracer experiments along a 290 m stream reach. Br addition rate was 105.5 meq L -1 for each experiment. Electrical conductance (EC) data was collected on a 120s interval at 145m and 290m. Grab samples for Br analysis were collected periodically throughout the experiments, based on EC. An EC-Br relationship was determined, and the Br breakthrough curves were simulated using the transient storage model OTIS: where, C is the solute concentration in the stream (meq L -1 ), C S is the storage zone solute concentration (meq L -1 ), C L is the local inflow solute concentration (set to 0), Q is the stream discharge (m 3 s -1 ), q L is the local inflow (m 3 s -1 m -1 ), D is the longitudinal dispersion (m 2 s -1 ), α is the storage zone exchange rate (s -1 ), A is the cross-sectional area of the stream (m 2 ), A S is the cross-sectional area of the storage zone (m 2 ), t is time, and x is the downstream distance (m) (Runkel, 1998). Because discharge is changing throughout the tracer experiment (decreasing baseflow), the following relationship was developed from Manning’s Equation: and, c is a coefficient representing a relationship among channel roughness, slope and wetted perimeter. Optimal values of A S , D, α, c, and q L were obtained using UCODE, a universal computer code for model optimization (Poeter and Hill, 1998) MODELLING METHODS ( ) ( ) C C q C C x C AD x A x C A Q t C L L S + + + = α 1 ( ) S S S C C A A dt dC = α 6 . 0 cQ A = [Eq. 1] [Eq. 2] [Eq. 3] INTRODUCTION PART I MODELING RESULTS Stream–catchment connections and the linkages between stream discharge and transient storage processes remain poorly understood. We seek to investiagte stream catchment connections and the impact of discharge magnitude on transient storage dynamics. Previous studies of transient storage in streams have suggested that hyporheic exchange should dominate transient storage as discharge decreases because of reduced stream cross-sectional area relative to the cross-sectional area of the hyporheic zone. However, no direct relationships have been developed between stream discharge and transient storage influences on solute transport. We tested the hypothesis that the influence of transient storage on solute transport increases with decreasing stream discharge. 1) Three separate conservative tracer stream additions with LiBr during baseflow recession (over 12 days) in a 16.9 ha headwater catchment, at Maimai New Zealand. 2) Breakthrough of bromide was measured and simulated with OTIS for 2 sub-reaches within the 580 m study reach (145 m, 290 m, 425 m, and 580 m from the injection). 3) Discharge decreased from 1.11 to 0.14 l s-1 at the injection point, and from 4.5 to 1.5 l s-1 at 580 m over the course of the three tracer tests. 4) Terrain analysis was used to quantify stream morphology and local inflow area along the stream. 5) Synoptic sampling during the two steady-state tracer was used to measure variability in later inflow quantity, δ 18 O, and silica concentrations. Utah State UNIVERSITY References: Poeter E. P., and M. C. Hill. 1998. Documentation of UCODE, a computer code for universal inverse modeling. Water Resources Investigation Report 98-4080. U.S. Geological Survey, Denver, Colorado. [http://water.usgs.gov/software/ucode.html] Runkel, R. L. 1998. One-dimensional transport with inflow and storage (OTIS): A solute transport model for streams and rivers. U.S. Geological Survey. Water Resources Investigations Report 98-4018. [http://co.water.usgs.gov/otis/] Acknowledgements: We extend our thanks to Paul Schuster for sample analysis, John Payne, Jagath Ekanayake, and Breck Bowden of LandCare Research, NZ for logistical, technical, and collaborative support, and to Jamie Shanley for guidance and field equipment. We also thank Rob Runkel for valuable input on modelling methods. This work was made possible by NSF grant EAR-0196381 and the 2001 AGU Horton Research Grant awarded to BLM. RESULTS AND DISCUSSION DISCUSSION OF MODELLING RESULTS: These results support previous assertions that hyporheic exchange potential increases at lower discharge, as evidenced by 1) positive relationships between a and Q and 2) increasing CSS values for a in each sequential (lower Q) experiment. However, the uncertainty associated with A S parameterization in Reach 2, and the negative relationship between A S and Q in Reach 2, but a generally positive relationship between A S and Q in Reach 1, suggests that greater relative storage zone area at lower discharge is an equivocal conclusion. Using UCODE to obtain 95% confidence intervals for parameter estimates and CSS values allowed us to evaluate the relative confidence in the OTIS model parameterization. Our results suggest that in general, at lower discharges, there is greater information available within data sets for D, a, A (or c), and q LAT . Estimates of A S were not as robust, as evidenced by the CSS value trend and the larger 95% confidence intervals obtained. This suggests that comparisons of A S /A should be made with great caution when comparing different reaches, particularly in different streams. CONCLUSIONS The storage zone area to stream area ratio (A S /A) increased with decreasing stream discharge and average local inflows to the stream decreased as stream discharge decreased. This effect was more pronounced in the headwaters where baseflow decreased at a higher rate than in reaches closer to the catchment outlet. We also tested the linkage between local subsurface water inflow to the stream channel and local upland accumulated area. We found suggestion of a linkage between topography and incremental changes in discharge. We plan to more fully assess the significance of this relationship. We found pronounced variability in δ 18 O and of SiO2 concentrations in local inflow of water to each stream reach. Uncertainty analysis is required for quantitative assessment, however our results suggest local inflows can be highly variable. This information is masked in synoptic stream sampling results that do not include high resolution quantification of incremental changes in stream discharge. A more enhanced understanding of transient storage within particular reaches is possible with analysis of stream–upland connections and repeated solute tracer experiments at varying discharge. One test at one discharge does not provide adequate comparison to either the same reach at another discharge, or another stream system. Figure 2. Br observed (points) and simulated (black line) breakthrough curves and hydrographs at 145m and 290m from injection point. During the three experiments, discharge decreased from 1.11 to 0.14 L s -1 at the injection point, and from 2.52 to 0.72 L s -1 at 290m. Br concentration plateaus were increasing due to a decrease in discharge. Figure 3. OTIS parameter and discharge (Q) relationships for both reaches. Symbols represent best-fit parameter estimate and mean Q, bars represent parameter 95% confidence intervals and the range of Q for a particular experiment. • CSS values generally increase for each parameter at lower Q (except A S,1 and c 2 ). • CSS values are highest for q LAT , and lowest for D in all experiments. α CSS values are higher than A S CSS values for all experiments. Figure 4. OTIS parameter composite scaled sensitivities (CSS) for each experiment. CSSs represent the potential to confidently optimize a parameter from a particular data set. SITE LOCATION Figure 1. (A-B) The Maimai catchments are located in NW New Zealand, on the South Island. (C) The locations of the 4 study reaches are indicated on the topographic map of the 16.9 ha K catchment. (D) The upland area draining into each 20 meter stream cell was calculated based on topographic analysis of the catchment DEM and a 0.5 ha stream threshold. Note the variability in local inflows to the stream. 3300 3400 3500 3600 3700 3800 3900 400 500 600 700 800 900 1000 1100 1200 00 m 100 m 200 m 10 m Contour interval Scale in meters Sampling point Tracer injection point (C) 145m 290m 0m weir Average local inflow to the stream decreased as Q decreased Because A (or c) decreased with increasing Q, A S /A decreased with increasing Q Positive trend between D and Q Positive trend between α and Q. N Maimai New Zealand 42 degrees S 172 degrees E Institut für Hydrologie Albert-Ludwigs-Universität Freiburg i. Br. PART II STEADY STATE SYNOPTIC SAMPLING FIELD/DEM ANALYSIS RESULTS/DISCUSSION Streambed slope and cumulative elevation demonstrate the variability in stream gradient for each reach. The average slope ranges from 9% to 6.5% from reach to reach, but more importantly, the range of variability for each 10 meters of stream section is 4% to 14%. Stream morphology is hypothesized to be a strong driver of stream hyporheic exchange. Local inflow of area to the stream channel was computed from the catchment digital elevation model by calculating the incremental increase in catchment area from stream cell-to-stream cell in a downstream direction. The range of local inflow is greatest in the headwaters where the catchment exhibits the greatest topographic convergence and decreases toward the catchment outlet. The pattern of local inflow area reflects the highly dissected nature of the catchment topography. The catchments at Maimai are comprised of regularly alternating spur-hollow sequences with greatest topographic convergence in the headwaters. Local inflow of water to the stream channel was computed from synoptic stream samples collected every 10-20 meters during the first two steady state Br - tracer injections. The following equation was used to calculate discharge at each synoptic sampling point. Local inflow was then calculated for each reach by subtracting the upstream discharge from the downstream discharge. Local δ 18 O and SiO 2 inflow to the stream channel Local inflow solute and δ 18 O concentrations were calculated based on synoptic stream samples and calculated local inflow of water (incremental increases in discharge). This approach allows for calculation of the mass and concentration of solutes entering the stream between each sampling point. In some instances 10 meter sampling intervals were too short for accurate calculation of local inflow concentrations because the precision of the Br - analysis and the precision of the solute and isotopic data. Uncertainty analysis such as that used in hydrograph separation studies will be necessary to quantify significance from reach to reach. Despite this caveat, the data suggests that local inflows solute and δ 18 O concentrations are highly variable from stream reach to stream reach. We suggest that combined with transient storage modeling during multiple discharge magnitudes, synoptic sampling can elucidate stream catchment connections. More specifically, this approach can provide insight into the relationship between topographic variables such as local inflow and incremental inflows of water and solutes to stream channels. (A) (B) (C) DEM-BASED LOCAL INFLOW 0 ha >1 ha 0 m 580 m (D) STUDY SITE 0% 5% 10% 15% 0 100 200 300 400 500 Distance downstream in meters (0m = streamflow initiation, 580m = weir) Streambed slope % 0 10 20 30 40 Cumulative elevation meters 0 meters 145 meters 290 meters 435 meters 580 meters Reach 1 Reach 2 Reach 3 Reach 4 8.9%mean slope 7.3%mean slope 6.5%mean slope 7.8%mean slope Distance from stream initiation m 0 100 200 300 400 500 Lateral inflow of water (liters/meter) 0.000 0.005 0.010 0.015 0.020 Stream discharge liters/second 0 1 2 3 4 Lateral Inflow (liters/meter) Stream discharge Distance from stream initiation m 0 100 200 300 400 500 Later inflow of water liters/meter 0.000 0.005 0.010 0.015 0.020 Stream discharge liters/second 0 1 2 3 4 Lateral inflow of water (liters/meter) Stream discharge liters/second Distance from stream initiation m 0 100 200 300 400 500 SiO 2 PPM 0 5 10 15 20 Lateral inflow SiO 2 Stream SiO 2 Distance from stream initiation m 0 100 200 300 400 500 SiO2 PPM 0 5 10 15 20 Later inflow SiO 2 Stream SiO 2 Distance from stream initiation m 0 100 200 300 400 500 δ 18 O -15 -10 -5 0 δ 18 Ο in lateral inflow Stream δ 18 O Distance from stream initiation m 0 100 200 300 400 500 δ 18 O -15 -10 -5 0 δ 18 O in lateral inflow Streamflow δ 18 O Distance from stream initiation m 0 100 200 300 400 500 Area entering stream from adjacent uplands ha 0.0 0.5 1.0 1.5 2.0 Local inflow of area to stream ha stream injectate injectate stream ) )( (Q - Br Br Q = downstream upstream inflow local Q Q Q = inflow local downstream downstream upstream upstream inflow local ) )( ( ) )( ( Q C Q C Q C = TRACER TEST #I TRACER TEST #II STREAM MORPHOLOGY Figure 5A-E. We synoptically sampled the stream every 10 meters from the tracer injection point to the catchment outlet during the first and second steady- state tracer tests. We surveyed the stream channel elevation at each sampling point and calculated streambed slope. In addition, we calculated the incremental increase in catchment area for each stream cell (20 meters) along the stream. (A) Streambed slope and cumulative stream elevation, (B) Local inflow of area along the stream, (C) Computed later inflow of water along the stream network, (D) δ 18 O in streamwater and local inflow, and (E) SiO 2 in streamwater and local inflow. Average residence time of water in the storage zone decreased as Q increased L s (m -1 ) = Q/(A*α) t s (h -1 ) = As/(α*A) (A) (B) (C) (C) (D) (D) (E) (E)

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Stream-upland connections and the effects of stream discharge on transient storage processesBrian L. McGlynn1, Michael Gooseff2, Cindy Hugenschmidt, and Robert S. McGlynn3

1. Department of Land Resources & Environmental Sciences, Montana State University, Bozeman 2. Department of Aquatic, Watershed, and Earth Resources, Utah State University

3. Institute for Hydrology, Freiburg University, Germany 4. Department of Earth Sciences, Dartmouth College

Stream Tracer Solute Transport ModelingThree LiBr salt stream tracer experiments along a 290 m stream reach. Br addition rate was 105.5 meq L-1 for each experiment. Electrical conductance (EC) data was collected on a 120s interval at 145m and 290m. Grab samples for Br analysis were collected periodically throughout the experiments, based on EC. An EC-Br relationship was determined, and the Br breakthrough curves were simulated using the transient storage model OTIS:

where, C is the solute concentration in the stream (meq L-1), CS is the storage zone solute concentration (meq L-1), CL is the local inflow solute concentration (set to 0), Q is the stream discharge (m3 s-1), qL is the local inflow (m3 s-1 m-1), D is the longitudinal dispersion (m2 s-1), α is the storage zone exchange rate (s-1), A is the cross-sectional area of the stream (m2), AS is the cross-sectional area of the storage zone (m2), t is time, and x is the downstream distance (m) (Runkel, 1998). Because discharge is changing throughout the tracer experiment (decreasing baseflow), the following relationship was developed from Manning’s Equation:

and, c is a coefficient representing a relationship among channel roughness, slope and wetted perimeter.

Optimal values of AS, D, α, c, and qL were obtained using UCODE, a universal computer code for model optimization (Poeter and Hill, 1998)

MODELLING METHODS

( ) ( )CCqCCxCAD

xAxC

AQ

tC

LLS −+−+

∂∂

∂∂

+∂∂

−=∂∂ α1

( )SS

S CCAA

dtdC

−= α

6.0cQA =

[Eq. 1]

[Eq. 2]

[Eq. 3]

INTRODUCTION PART I MODELING RESULTSStream–catchment connections and the linkages between stream discharge and transient storage processes remain poorly understood. We seek to investiagtestream catchment connections and the impact of discharge magnitude on transient storage dynamics. Previous studies of transient storage in streams have suggested that hyporheic exchange should dominate transient storage as discharge decreases because of reduced stream cross-sectional area relative to the cross-sectional area of the hyporheic zone. However, no direct relationships have been developed between stream discharge and transient storage influences on solute transport. We tested the hypothesis that the influence of transient storage on solute transport increases with decreasing stream discharge. 1) Three separate conservative tracer stream additions with LiBr during baseflow

recession (over 12 days) in a 16.9 ha headwater catchment, at Maimai New Zealand.

2) Breakthrough of bromide was measured and simulated with OTIS for 2 sub-reaches within the 580 m study reach (145 m, 290 m, 425 m, and 580 m from the injection).

3) Discharge decreased from 1.11 to 0.14 l s-1 at the injection point, and from 4.5 to 1.5 l s-1 at 580 m over the course of the three tracer tests.

4) Terrain analysis was used to quantify stream morphology and local inflow area along the stream.

5) Synoptic sampling during the two steady-state tracer was used to measure variability in later inflow quantity, δ18O, and silica concentrations.

Utah StateUNIVERSITY

References:Poeter E. P., and M. C. Hill. 1998. Documentation of UCODE, a computer code for universal inverse modeling. Water Resources Investigation Report 98-4080. U.S. Geological Survey, Denver, Colorado. [http://water.usgs.gov/software/ucode.html]Runkel, R. L. 1998. One-dimensional transport with inflow and storage (OTIS): A solute transport model for streams and rivers. U.S. Geological Survey. Water Resources Investigations Report 98-4018. [http://co.water.usgs.gov/otis/]Acknowledgements:We extend our thanks to Paul Schuster for sample analysis, John Payne, Jagath Ekanayake, and Breck Bowden of LandCare Research, NZ for logistical, technical, and collaborative support, and to Jamie Shanley for guidance and field equipment. We also thank Rob Runkel for valuable input on modelling methods. This work was made possible by NSF grant EAR-0196381 and the 2001 AGU Horton Research Grant awarded to BLM.

RESULTS AND DISCUSSION

DISCUSSION OF MODELLING RESULTS:These results support previous assertions that hyporheic exchange potential increases at lower discharge, as evidenced by 1) positive relationships between a and Q and 2) increasing CSS values for a in each sequential (lower Q) experiment. However, the uncertainty associated with AS parameterization in Reach 2, and the negative relationship between AS and Q in Reach 2, but a generally positive relationship between AS and Q in Reach 1, suggests that greater relative storage zone area at lower discharge is an equivocal conclusion.

Using UCODE to obtain 95% confidence intervals for parameter estimates and CSS values allowed us to evaluate the relative confidence in the OTIS model parameterization. Our results suggest that in general, at lower discharges, there is greater information available within data sets for D, a, A(or c), and qLAT. Estimates of AS were not as robust, as evidenced by the CSS value trend and the larger 95% confidence intervals obtained. This suggests that comparisons of AS/A should be made with great caution when comparing different reaches, particularly in different streams.

CONCLUSIONS• The storage zone area to stream area ratio (AS/A) increased with decreasing stream

discharge and average local inflows to the stream decreased as stream discharge decreased. This effect was more pronounced in the headwaters where baseflow decreased at a higher rate than in reaches closer to the catchment outlet.

• We also tested the linkage between local subsurface water inflow to the stream channel and local upland accumulated area. We found suggestion of a linkage between topography and incremental changes in discharge. We plan to more fully assess the significance of this relationship.

• We found pronounced variability in δ18O and of SiO2 concentrations in local inflow of water to each stream reach. Uncertainty analysis is required for quantitative assessment, however our results suggest local inflows can be highly variable. This information is masked in synoptic stream sampling results that do not include high resolution quantification of incremental changes in stream discharge.

A more enhanced understanding of transient storage within particular reaches is possible with analysis of stream–upland connections and repeated solute tracer experiments at varying discharge. One test at one discharge does not provide adequate comparison to either the same reach at another discharge, or another stream system.

Figure 2. Br observed (points) and simulated (black line) breakthrough curves and hydrographs at 145m and 290m from injection point. During the three experiments, discharge decreased from 1.11 to 0.14 L s-1 at the injection point, and from 2.52 to 0.72 L s-1 at 290m. Br concentration plateaus were increasing due to a decrease in discharge.

Figure 3. OTIS parameter and discharge (Q) relationships for both reaches. Symbols represent best-fit parameter estimate and mean Q, bars represent parameter 95% confidence intervals and the range of Q for a particular experiment.

• CSS values generally increase for each parameter at lower Q (except AS,1 and c2).

• CSS values are highest for qLAT, and lowest for D in all experiments.

• α CSS values are higher than ASCSS values for all experiments.

Figure 4. OTIS parameter composite scaled sensitivities (CSS) for each experiment. CSSs represent the potential to confidently optimize a parameter from a particular data set.

SITE LOCATIONFigure 1.

(A-B) The Maimai catchments are located in NW New Zealand, on the South Island.

(C) The locations of the 4 study reaches are indicated on the topographic map of the 16.9 ha K catchment.

(D) The upland area draining into each 20 meter stream cell was calculated based on topographic analysis of the catchment DEM and a 0.5 ha stream threshold. Note the variability in local inflows to the stream.3300 3400 3500 3600 3700 3800 3900

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00 m 100 m 200 m10 m Contour interval

Scale in meters

Sampling pointTracer injection point

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Average local inflow to the stream decreased

as Q decreased

Because A (or c) decreased with increasing Q, AS/A

decreased with increasing Q

Positive trend between D and Q

Positive trend between α and Q.

N

Maimai

New Zealand

42 degrees S

172 degr ees E

Institut für HydrologieAlbert-Ludwigs-Universität Freiburg i. Br.

PART II STEADY STATE SYNOPTIC SAMPLINGFIELD/DEM ANALYSIS RESULTS/DISCUSSION

Streambed slope and cumulative elevationdemonstrate the variability in stream gradient for each reach. The average slope ranges from 9% to 6.5% from reach to reach, but more importantly, the range of variability for each 10 meters of stream section is 4% to 14%. Stream morphology is hypothesized to be a strong driver of stream hyporheic exchange.

Local inflow of area to the stream channel was computed from the catchment digital elevation model by calculating the incremental increase in catchment area from stream cell-to-stream cell in a downstream direction. The range of local inflow is greatest in the headwaters where the catchment exhibits the greatest topographicconvergence and decreases toward the catchment outlet. The pattern of local inflow area reflects the highly dissected nature of the catchment topography. The catchments at Maimai are comprised of regularlyalternating spur-hollow sequences with greatest topographic convergence in the headwaters.

Local inflow of water to the stream channel was computed from synoptic stream samples collected every 10-20 meters during the first two steady state Br- tracer injections. The following equation was used to calculate discharge at each synoptic sampling point.

Local inflow was then calculated for each reach by subtracting the upstream discharge from the downstream discharge.

Local δ18O and SiO2 inflow to the stream channelLocal inflow solute and δ18O concentrations were calculated based on synoptic stream samples and calculated local inflow of water (incremental increases in discharge). This approach allows for calculation of the mass and concentration of solutes entering the stream between each sampling point.

In some instances 10 meter sampling intervals were too short for accurate calculation of local inflow concentrations because the precision of the Br-

analysis and the precision of the solute and isotopic data. Uncertainty analysis such as that used in hydrograph separation studies will be necessary to quantify significance from reach to reach. Despite this caveat, the data suggests that local inflows solute and δ18O concentrations are highly variable from stream reach to stream reach. We suggest that combined with transient storage modeling during multiple discharge magnitudes, synoptic sampling can elucidate stream catchment connections. More specifically, this approach can provide insight into the relationship between topographic variables such as local inflow and incremental inflows of water and solutes to stream channels.

(A)

(B)

(C)

DEM-BASED LOCAL INFLOW

0 ha

>1 ha

0 m

580 m (D)

STUDY SITE

0%

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ope

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s0 meters 145 meters 290 meters 435 meters 580 metersReach 1 Reach 2 Reach 3 Reach 4

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Distance from stream initiation m0 100 200 300 400 500La

tera

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ater

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ater

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eter

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Distance from stream initiation m0 100 200 300 400 500

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δ18Ο in lateral inflowStream δ18O

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Distance from stream initiation m0 100 200 300 400 500

Area

ent

erin

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tream

fro

m a

djac

ent u

plan

ds h

a

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stream

injectateinjectatestream

) )( (Q -Br

BrQ

=

downstreamupstreaminflow local QQQ −=

inflow local

downstreamdownstream

upstreamupstream

inflow local))((

))((

Q

CQCQ

C =

TRACER TEST #I TRACER TEST #II

STREAM MORPHOLOGYFigure 5A-E. We synoptically sampled the stream every 10 meters from the tracer injection point to the catchment outlet during the first and second steady-state tracer tests. We surveyed the stream channel elevation at each sampling point and calculated streambed slope. In addition, we calculated the incremental increase in catchment area for each stream cell (20 meters) along the stream. (A) Streambed slope and cumulative stream elevation, (B) Local inflow of area along the stream, (C) Computed later inflow of water along the stream network, (D) δ18O in streamwater and local inflow, and (E) SiO2 in streamwater and local inflow.

Average residence time of water in the storage zone decreased as Q increased

L s(m

-1)=

Q/(A

*α)

t s(h

-1)=

As/

(α*A

)

(A)

(B)

(C) (C)

(D) (D)

(E)(E)