Beyond H2O: A Chemical Survey of Surface Water
at the MacLeish Field Station, Whatley, MA
Mary Gowins ’11 (AEMES) and Jenna Zechmann ’12 (STRIDE)
Ad i
Advisors:
A
Amy Rh
Rhodes,
d
R
Robert
b tN
Newton,
t
and
dA
Andrew
d
G
Guswa
Smith College, Northampton, MA 01063
Variations in Stream Hydrology
Introduction
Every stream of the Ada and Archibald Macleish Field Station
hides a unique history leading to the observed chemistry.
Alkalinity, anions, and cations present in different concentrations
indicate process and sources. The goal of this study is to give an
overview of the water chemistry and variations therein.
Hypothesis formed will serve as a basis to future work.
 Are differences in stream hydrology affecting stream chemistry?
 Are local anthropomorphic sources affecting stream chemistry?
 Will snowmelt acidify streams at MacLeish?
 Is variation in bedrock geology contributing to stream chemistry?
 Is sulfide mineral weathering at mine sites affecting stream chemistry?
Methods
Anion and Cation Results
High Dispersion ICP (Inductively Coupled Plasma)
IC (Ion Chromatography)
Stream
Stream
Snow
Stream
Stream
Stream
Wetland
Stream
Groundwater
Cation Concentrations in MacLeish Surface Water Anion Concentrations and ANC in MacLeish Surface Water
1200
1200
ANC
1000
Field and pH Data
NO3‐2
F‐
600
400
1400
Na+
SO4‐2
1200
600
400
600
Na+
500
Na+
Ca+2
800
Mg+2
F‐
K+
1000
10
Ca+2
Cl‐
Mg+2
Mg+2
600
11
2a
K+
Linear (Ca+2)
400
11
2b
1b
8
200
6
9
100
400
1a
5
300
200
1
2
4
5
6
Site Number
8
9
10
1
11
2
4
5
6
Site Number
8
9
10
4
0
200
0
0
12
Base Cation Concentrations vs Acid Neutralizing Capacity in MacLeish Surface Water
700
NO3‐2
800
200
Dissolved Oxygen of MacLeish Surface Water
Concentration Comparison of Sites 4, 1 and 2 by Date
ANC
K+
1000
Cl‐
800
1600
Ca+2
SO4‐2
Cation Concentration (μeq/L
1
2
4
5
6
8
9
10
11
Cation Concentration (μeq/L)
Anions: F, Cl, NO3, SO4
Field: Dissolved Oxygen Meter
Field: Specific Conductance Meter
Field: Specific Conductance Meter
Autotitrator: gran titration
Autotitrator: gran titration
Anion Concentration (μeq/L)
Dissolved Oxygen
Temperature
Specific Conductance
pH
Acid Neutralizing Capacity
Cations: K, Na, Mg, Ca Base Cations (μeq/L)
Site Sample Type
Number
Solute / Parameter Method
0
100
200
300
400
Acid Neutralizing Capacity (µeq/L)
500
600
700
0
11
02/27/09; Site 4
02/27/09; Site 1
03/28/09; Site 1
02/27/09; Site 2
03/28/09; Site 2
Chloride concentrations were disproportionately high at
Site 11, which is located next to a road. Road salt (NaCl)
is the probable cause. Nitrate levels were highest at Site
5. The location makes agricultural influence unlikely.
Sulfate concentrations were variable.
Dissolved oxygen is
constant among the
stream and is lower in
the wetland.
8
6
4
2
1
2
5
6
8
9
Widespread cation variation may be source locale
dependent. Ca+2 possibilities include weathering of
calcium carbonate (CaCO3) or calcium silicate minerals.
Mg+2 concentrations also vary. The high Na+
concentration at Site 11 may be road salt driven.
Spatial Variation for Water Chemistry
Spatial Variation for Water Chemistry
0
10
Site Number
Specific Conductance of MacLeish Ca+2
Surface Water
100
Concentrations at the same site decreased as
time progressed. Noting the low concentrations
of Site 4, snowmelt becomes a probable source
of dilution. However, given Site 4’s charge
balance, sample quality of the snow is
questioned.
ANC
Base cations affecting ANC should present as a 1:1 ratio.
Ca+2 is strongly correlated, appearing to drive ANC. Other
cations still have an effect, though not as pronounced.
The outlier is Site 11 due to the high Na+ .
Summary
SO4
90
Specific Conductance
is variable, hinting at
differences in ionic
composition of the
samples.
Specific Conductance (µS)
80
70
60
50
40
30
20
10
0
1
pH of MacLeish Surface and Ground Water
14
12
10
8
6
4
2
0
4
1
2
5
6
8
9
10
2
5
6
8
9
10
Site Number
pH
Dissolved Oxygen (mg/L)
10
11
Site Number
The majority of sites fall
within close range of pH
neutrality. Site 4 exhibited a
pH close to 5.6, the expected
pH of precipitation. Site 9 may
be acidic due to characteristic
wetland nutrient
cycling
f
factors.
Wetland Chemistry may be causing consistently lower concentrations.
Site 8 concentrations may be affected due to downstream proximity.
Acknowledgements
We would like to thank Professors Amy Rhodes, Robert Newton, and Andrew Guswa,
for their invaluable advice and enlightening discussions. We also would like to
acknowledge Smith’s support of this research through the Achieving Excellence in
Mathematics, Engineering and Sciences (AEMES) program and the Student Research in
Departments (STRIDE) program.
Calcium ion concentration is highest at Site 10; note the
watershed is mainly comprised of Conway schist‐marble.
The majority of the watersheds are underlain by a
combination of Conway schist‐marble and schist‐quartzite,
resulting in lower concentrations. We hypothesize higher
concentrations near the contact of the intrusive rock may
be due to mineralization from magmatic fluids. The amount
of bedrock weathering causes a high enough concentration
to strongly influence ANC.
Note Site 6 is a stream choked with leaves,
leaves while Site 9
consists of stagnant water covering decaying leaves. Both
sites exhibit low ANC, suggesting that tannins from
decaying leaves underwater may detract from ANC. ANC
was highest at Site 10 , a well‐incised stream flowing
quickly over rocks. ANC is extremely low at Site 4, as is
expected with precipitation. Even when accounting for
bedrock ANC still varies.
Sulfate concentrations are higher to the west,
west
suggesting sulfide bearing minerals may be
contributing to the stream water. Mineralization
of pyrite (FeSO2) and galena (PbS) occurred at the
schist‐granodiorite contact, also where the mines
are located. Atmospheric sulfur could cause equal
concentrations.
‐2
Chemical analysis of the waters of the MacLeish Field Station revealed a complex history. Watersheds containing Conway schist‐marble bedrock have the highest concentrations of Ca+2 and ANC, suggesting that calcite weathering strongly affects stream water chemistry. Snow
stream water chemistry. Snow melt and runoff contain lower concentrations of ions, affectively diluting the streams. Road salt had a pronounced effect on water chemistry. Knowledge of probable correlations with ion concentrations allows streams to be treated properly as safe resources and habitats. Knowing sources of chemical phenomena will allow for accurate predictions of chemistry variation and how stream users may need to change their behaviors.