1. Source waters, flowpaths, and solute flux in mountain catchments
Mark Williams

2. Watershed Hydrology

3. Mountain-Front Recharge
SNOWMELT
Mountain-Block
Recharge (MBR) +
Stream Infiltration
Mountain-Front Recharge
(MFR)

4. Abandoned Mines: Common Feature of Rocky Mountain Landscape
Result of Mining Boom in 1880’s to 1930’s
Located in remote areas at high elevation

5. HYDROLOGIC UNKNOWNS Flowpaths Residence time Add snowmelt
Circulation depth
Reservoir sizes
Groundwater fluxes
Fractured rock environment increases difficulty of understanding mountain plumbing
Add snowmelt
runoff
Permafrost

6. APPLICATION IN GREEN LAKES VALLEY: LTER RESEARCH SITE
Sample Collection
Stream water - weekly grab samples
Snowmelt - snow lysimeter
Soil water - zero tension lysimeter
Talus water – biweekly to monthly
Sample Analysis
Delta 18O and major solutes

7. Source Waters

8. Mixing Models in Catchment Hydrology

9. MIXING MODEL: 2 COMPONENTS
One Conservative Tracer
Mass Balance Equations for Water and Tracer

10. ASSUMPTIONS FOR MIXING MODEL
Tracers are conservative (no chemical reactions);
All components have significantly different concentrations for at least one tracer;
Tracer concentrations in all components are temporally constant or their variations are known;
Tracer concentrations in all components are spatially constant or treated as different components;
Unmeasured components have same tracer concentrations or don’t contribute significantly.

11. d18O IN SNOW AND STREAMFLOW
d18O fractionation of 4%o in snowmelt;
Cannot use d18O values measured at snow lysimeter directly to the catchment.
Failed assumption

12. Fractionation in Snowpack
d18O = -20‰
Snow surface
Ground
Difference between maximum 18O values and
Minimum 18O values about 4 ‰
d18O = -22‰

13. Isotopic Fractionation
Fractionation occurs as melt from surface percolates towards bottom of snowpack
Isotopic exchange between ice and percolating liquid water
d18Osolid > d18Oliquid > d18Ovapour
Molecules of surface meltwater are not the same as the ones at the base of the snowpack

14. ACCOUNTING FOR d18O IN MELTWATER
d18O values are highly correlated with amount of melt (R2 = 0.9, n = 15, p < 0.001);
Snowmelt regime is different at a point from a real catchment;
So, we developed a Monte Carlo procedure to stretch the dates of d18O in snowmelt measured at a point to a catchment scale using the streamflow d18O values.

15. NEW WATER FROM VARIOUS MODELS
M1 - Original time-series of snowpack d18O
M2 - Date-stretched time-series of snowpack d18O
M3 - Original time-series of snowmelt lysimeter d18O
M4 - Date-stretched time-series of snowmelt lysimeter d18O

16. NEW WATER AND OLD WATER
Old Water = 64%
Not Teflon basins!

17. HYDROLOGIC FLOWPATHS

18. MIXING MODEL: 3 COMPONENTS
Simultaneous Equations
Solutions
Two Conservative Tracers
Mass Balance Equations for Water and Tracers
Q - Discharge
C - Tracer Concentration
Subscripts - # Components
Superscripts - # Tracers

19. MIXING MODEL: 3 COMPONENTS(Using Discharge Fractions)
Simultaneous Equations
Solutions
Two Conservative Tracers
Mass Balance Equations for Water and Tracers
f - Discharge Fraction
C - Tracer Concentration
Subscripts - # Components
Superscripts - # Tracers

20. MIXING DIAGRAM: PAIRED TRACERS

21. FLOWPATHS: 2-TRACER 3-COMPONENT MIXING MODEL

22. FLOWPATHS: 2-TRACER 3-COMPONENT MIXING
Did we choose the right end-members?
Did we choose the right tracers?
Is there any way to quantitatively
evaluate our results?

23. END-MEMBER MIXING ANALYSIS (EMMA) Uses more tracers than components
Decides number of end-members
Quantitatively select end-members
Quantitatively evaluate results of the
mixing model

24. MIXING MODEL: Generalization Using Matrices
Simultaneous Equations
Where
One tracer for 2 components and two tracers for 3 components
N tracers for N+1 components? -- Yes
However, solutions would be too difficult for more than 3 components
So, matrix operation is necessary
Solutions
Note:
Cx-1 is the inverse matrix of Cx
This procedure can be generalized to N tracers for N+1 components

25. This slide is from Hooper, 2001

26. EMMA PROCEDURES
Identification of Conservative Tracers - Bivariate solute-solute plots to screen data;
PCA Performance - Derive eigenvalues and eigenvectors;
Orthogonal Projection - Use eigenvectors to project chemistry of streamflow and end-members;
Screen End-Members - Calculate Euclidean distance of end-members between their original values and S-space projections;
Hydrograph Separation - Use orthogonal projections and generalized equations for mixing model to get solutions!
Validation of Mixing Model - Predict streamflow chemistry using results of hydrograph separation and original end-member concentrations.

27. STEP 1 - MIXING DIAGRAMS Look familiar?
This is the same diagram used for geometrical definition of mixing model (components changed to end-members);
Generate all plots for all pair-wise combinations of tracers;
The simple rule to identify conservative tracers is to see if streamflow samples can be bound by a polygon formed by potential end-members or scatter around a line defined by two end-members;
Be aware of outliers and curvature which may indicate chemical reactions!

28. STEP 2 - PCA PERFORMANCE
For most cases, if not all, we should use correlation matrix rather than covariance matrix of conservative solutes in streamflow to derive eigenvalues and eigenvectors;
Why? This treats each variable equally important and unitless;
How? Standardize the original data set using a routine software or minus mean and then divided by standard deviation;
To make sure if you are doing right, the mean should be zero and variance should be 1 after standardized!

29. APPLICATION OF EIGENVALUES
Eigenvalues can be used to infer the number of end-members that should be used in EMMA.
How?
Sum up all eigenvalues;
Calculate percentage of each eigenvalue in the total eigenvalue;
The percentage should decrease from PCA component 1 to p (remember p is the number of solutes used in PCA);
How many eigenvalues can be added up to 90% (somewhat subjective! No objective criteria for this!)? Let this number be m, which means the number of PCA components should be retained (sometimes called # of mixing spaces);
(m +1) is equal to # of end-members we use in EMMA.

30. PCA PROJECTIONS
First 2 eigenvalues are 92% and so 3 end-members appear to be correct!

31. FLOWPATHS: EMMA

32. EMMA VALIDATION: TRACER PREDICTION

33. NITROGEN DEPOSITION

34. NIWOT RIDGE NADP SITE:
N-DEP INCREASED > 4x

35. NITROGEN IN STREAMS

36. Potential
Sources of
Nitrate and
Ammonium

37. FLOWPATHS: EMMA

40. EMMA: NITRATE SOURCES Under-predicts nitrate during snowmelt
Ionic pulse important
Overpredicts nitrate during summer
Denitrification?
8-ha Martinelli: 30% stream nitrate atmos
225-ha GL4: 20% stream nitrate atmos

41. Dual isotopic
analysis of
nitrate
d 18O (no3)
d 15N (no3)

42. Green Lakes Valley: dual isotopes

43. d 18O (no3) time series

44. Hysteresis

45. DUAL ISOTOPE: NITRATE SOURCES
8-ha Martinelli: 60% stream nitrate atmos
Twice EMMA
225-ha GL4: 20% stream nitrate atmos
Same as EMMA

47. EMMA and NITRATE ISOTOPES
First time used together
20% atmospheric nitrate in 220-ha stream
EMMA, dual isotopes similar results
60% atmospheric nitrate in 8-ha stream
EMMA underestimates: unsampled flowpath
Talus nitrate microbial, not atmospheric
Denitrification probably very important

48. 1
1,300 river miles in Colordo
100,000 AMD sites in Western US

49. END OF PIPE TREATMENT STRATEGY
Millions of dollars to install
Expensive to operate
Operate for long-term
Need low-cost alternatives

51. Watershed approach, hydrometric, isotopic, and chemical measurements
CHALK CREEK MINE: GROUNDWATER SOURCE CONTROLS DEMONSTRATION PROJECT
EPA VIII 104(b)3 Program
SUPPLEMENTAL FUNDING REQUEST
Assistance Agreement MM

53. HYDROGRAPH AND ISOTOPES

54. ISOTOPES OF INTERIOR STREAMS

55. HYDROGRAPH SEPARATION

56. ZINC and HYDROGRAPH

57. SUMMARY: Mary Murphy Mine

58. Sulfur-35 (35S) IN THE ENVIRONMENT
Radioactive isotope of sulfate
Half-life of about 87 days
Produced by spallation of argon atoms in the atmosphere by cosmic rays
18Ar
N=22
16 S
N=16
Cosmic Rays O2
SO2
35SO42-
35SO42-
SO4-2

61. Tritium/3He Dating Tritium = 3H Radioactive isotope:
Half life of about 12 years
Naturally occurs in precip at about 6-8 Tritium
Units (TU)
Nuclear bomb testing in 1960’s created “bomb
peak” (1000+ TU)
Can date waters younger than about 50 years:

62. Tr = Tg = Ta Pr = Pa = f(Hr) NOBLE GAS TRACERS IN GROUNDWATER
CNG
Precipitation
C3He
sample
noble gases
well mixed
gas
exchange
C3H
1) Measure C’s
2) Derive
Tr or Pr
3) Determine
Age
Infiltration
gas
exchange
CNG
= f (Tr , Pr)
gas exchange ceases
Tr = Tg = Ta
Pr = Pa = f(Hr)
CNG remain constant
EXCEPT He
radioactive
decay
3H He

63. LEADVILLE
EPA superfund site: $100,000,000

64. NOT YOUR ORDINARY SUPERFUND SITE
$1,000,000 + per year treatment cost
1,000,000,000 gallons of min waste underground
2,000 mines, 115 mills, and 7 smelters

65. d18O VALUES
Recharge is
primarily snowmelt

66. TRITIUM VALUES
Recharge age
ranges over
several decades

67. TEMPORAL VARIATION OF d18O AND TRITIUM
d18O doesn’t change so much over time at both sites;
Tritium significantly increased after June 2003 at INF-1, indicating that significant contribution from Elkhorn.

68. MIXING DIAGRAMS Potential end-members are clustered;
The bigger the circle, the higher the uncertainty in identifying a unique end-member;
But Elkhorn is unanimous as an end-member, which is natural groundwater well

69. Most snowmelt infiltrates into subsurface
However, recharge rate is not known
Subsurface storage is much larger than we thought and may be enough to support groundwater harvesting for Front Range
Mountain block-piedmont connection unknown