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Walt McNab, Ph.D.
September 2016
Explore portions of California Groundwater Ambient Monitoring and Assessment (GAMA) data set for Central Valley.
Demonstration of how easy it is to explore a moderately large data set and gain insights with python scripting (pandas, scikit-learn, and scipy; see links on last slide to view script).
QGIS used to view results.
Analytes:
◦ Arsenic
◦ Barium
◦ Bicarbonate alkalinity
◦ Boron
◦ Calcium
◦ Chloride
◦ Chromium
◦ Copper
◦ Magnesium
◦ Manganese
◦ Nitrate
◦ Potassium
◦ Sodium
◦ Sulfate
◦ Zinc
Central Valley alluvium boundary
• Download all as text files from GAMA website.• Use pandas to filter and create pivot tables for analytes.
Historic median concentrations scaled across 10 quantiles (yellow = lowest; red = highest) using QGIS.
Ayotte et al., 2016. Predicting Arsenic in Drinking Water Wells of the Central Valley, California, Environ. Sci. Tech., 50(14), 7555-7563.
Historic medians provide a useful comparative metric, in spotty data, for the potential for encountering concentrations at a specific value.
Median As in GAMA data set, by quantile, for water supply wells through 2016.
Historic median concentrations scaled across 10 quantiles (yellow = lowest; red = highest) using QGIS.
Historic median concentrations scaled across 10 quantiles (yellow = lowest; red = highest) using QGIS.
Historic median concentrations scaled across 10 quantiles (yellow = lowest; red = highest) using QGIS.
Historic median concentrations scaled across 10 quantiles (yellow = lowest; red = highest) using QGIS.
Historic median concentrations scaled across 10 quantiles (yellow = lowest; red = highest) using QGIS.
Historic median concentrations scaled across 10 quantiles (yellow = lowest; red = highest) using QGIS.
Historic median concentrations scaled across 10 quantiles (yellow = lowest; red = highest) using QGIS.
Historic median concentrations scaled across 10 quantiles (yellow = lowest; red = highest) using QGIS.
Historic median concentrations scaled across 10 quantiles (yellow = lowest; red = highest) using QGIS.
Historic median concentrations scaled across 10 quantiles (yellow = lowest; red = highest) using QGIS.
Historic median concentrations scaled across 10 quantiles (yellow = lowest; red = highest) using QGIS.
Historic median concentrations scaled across 10 quantiles (yellow = lowest; red = highest) using QGIS.
Historic median concentrations scaled across 10 quantiles (yellow = lowest; red = highest) using QGIS.
Historic median concentrations scaled across 10 quantiles (yellow = lowest; red = highest) using QGIS.
Identify factors in the multi-parameter data set that contribute to variance.
Plot 1st, 2nd, 3rd, etc. principal component values by location to indicate spatial distribution.
Plot loadings of principal components with respect to individual analytes.
Calculations conducted with scikit-learn package.
Valley interior
Principal Component #1
Southern end of valley
West side of valley
Principal Component #2
Principal Component #3
Loadings by Principal Component (axes, colors)
NO3 and Mn reflect 2nd
principal component (opposite effect)
Boron strongly associated with 1st principal component
Delineate multi-dimensional parameter space into clusters.
Plot locations of clusters to see if cluster characteristics exhibit spatial distributions.
Calculations conducted with scikit-learn package.
Cluster 1
Cluster 5
Cluster 7
Cluster 8
1
5
7
8
0.001
0.01
0.1
1
10
100
1000
AS
MN
SO4
CL
Sodium
MG
CA
NO3Cluster 1: (1) low Mn and As, (2) high NO3
Cluster 5: (1) high concentrations of most ions, (2) high Mn and low NO3
Cluster 8: (1) high Mn and As, (2) low NO3
Cluster 7: relatively elevated Na-Cl-SO4 compared to Ca-Mg-HCO3
Conc (mg/L)
Selected Cluster Centroids
Selected clusters appear differentiated on Piper diagram.
Note that other analytes not considered in Piper diagram (trace metals) are also used to delineate K-means clusters.
Cluster 1
Cluster 5
Cluster 7
Cluster 8
Theil-Sen slope calculated for all analytes in all wells meeting certain criteria (at least 10 sample events since 1980).
Temporal trend set is much smaller than median historic concentration data set.
Calculations conducted with scipy.
Fresno Visalia
Bakersfield
Unlike median concentrations, Theil-Sen slopes do not exhibit regional-scale spatial patterns.
Spatial patterns evident on smaller scales.
Variability at small scale likely reflect local sources (for nitrate, etc.) or local hydrologic constraints.
Warm colors indicate increasing trends while cool color denote decreases.
0.00001
0.0001
0.001
0.01
0.1
1
0.00001 0.0001 0.001 0.01 0.1 1
Mg
Co
nce
ntr
atio
n T
ren
d (
mg
L-1d
ay-1
)
Ca Concentration Trend (mg L-1 day-1)
0.00001
0.0001
0.001
0.01
0.1
1
0.00001 0.0001 0.001 0.01 0.1 1
NO
3C
on
cen
trat
ion
Tre
nd
(m
g L-1
day
-1as
NO
3)
Ca Concentration Trend (mg L-1 day-1)
Positive Temporal Trends Subset
Positive Temporal Trends Subset
Temporal trend relationships are stronger between some analytesthan others.
◦ Different source terms
◦ Evaporative effects
◦ Geochemical effects (e.g., carbonate mineral equilibration for Ca and Mg)
Good correlation.
Poor correlation.
Conclusion: separate mechanisms explain rise in nitrate and rise in salt concentrations.
Loadings by Principal Component (axes, colors) for Temporal Trends
For additional background, see Exploring a Large Groundwater Quality Data Set.
To see the python script used to conduct the analyses, see script.
For questions or comments, please visit https://numericalenvironmental.wordpress.com/contact/