Tracing source waters in the Pemigewasset River Watershed, NH using water stable isotopes of oxygen-18 and deuterium
Kristin M. Brandt1* and Mark B. Green1, 2
1Center
for the Environment, Plymouth State University, Plymouth, NH 03264
Research Station, U.S. Forest Service, Durham, NH 03824 2Northern
*Contact: [email protected]
• Water stable isotope analysis of δ18O and δ2H performed on a Los
Gatos Research Liquid-Water Isotope Analyzer using 0.8µl of a
hand-injected water sample
Water isotopes &
physical properties
pH
(d)
(b)
(e)
(c)
d-excess
(f)
Temperature [°C/°C]
• Sample for isotope analysis collected along with measurements of
pH, temperature, conductivity
(a)
Conductivity [μS cm-1]
• 62 spatially representative sampling sites were located on 8 rivers
based on ease of access (e.g. bridge crossings)
δ18O Methods
Water stable isotopes are essential in acquiring a more comprehensive
understanding of hydrology because they allow for a direct
measurement of the hydrogen and oxygen molecules of water. This
project will use oxygen-18 (18O) and deuterium (2H) to trace source
waters in the Pemigewasset River Watershed in central New
Hampshire. This work will create a spatially and temporally extensive
dataset of water isotopes and physical and chemical properties of the
waters of the Pemigewasset River and its main tributaries, including
the East Branch of the Pemigewasset River, the Lost River/
Moosilauke Brook, Hubbard Brook and its tributary Paradise Brook,
the Mad River, and the Baker River and its tributary Clay Brook, a
total drainage area of 622 square miles. This research is highly
exploratory in nature and has great potential to provide some
unexpected knowledge of the hydrology in the Pemigewasset River
Watershed. With this research we expect to answer the following
questions: (1) Can we effectively use isotopes to detect groundwatersurface water interaction in the Pemigewasset River Watershed? (2) Is
groundwater distinct enough to determine contributions to stream
flow? (3) Can we use groundwater detection to explain variability of
pH? (4) Can temperature be used as accurately as isotopes to detect
groundwater contributions? Spatial water chemistry patterns from a
preliminary sampling in November 2010 provide an initial glimpse
into the hydrology of the Pemigewasset River Watershed, which will
be used to refine sampling plans for the coming year.
δ2H
Abstract
Research location
Distance Upstream from study outlet, Plymouth, NH [km]
Figure 2. Spatial representation of δ18O values in
the Pemigewasset River Watershed, NH.
—Baker River
—Clay Brook
—East Branch Pemigewasset River
—Hubbard Brook
Figure 4. Values of oxygen-18 isotopes (δ18O) (a), deuterium isotopes (δ2H) (b), deuterium excess (c), pH (d), temperature (e), and
conductivity (f) at sampling sites with relation to distance upstream from the study outlet in Plymouth, NH.
Analysis
Future work
• Headwaters have isotope values that are more negative (more
depleted of heavier isotope) suggesting more groundwater
interaction with the stream
• Isotope values have a positive linear trend (become less negative)
with decreasing distance from the outlet of the watershed
Figure 1. Pemigewasset River Watershed, NH. 62
sampling sites spatially represented along 8 rivers. A
drainage area of 1611 km2 (622 mi2).
Figure 3. Spatial representation of pH in the
Pemigewasset River Watershed, NH.
—Lost River/Moosilauke Brook
—Mad River
—Paradise Brook
—Pemigewasset River
• Continue stream sampling on a monthly basis
• Sample at least one groundwater well on a monthly basis to
determine what groundwater looks like to compare stream values
to
• Greater variability in isotopes and physical properties in smaller
watersheds
• Sample precipitation on the roof of the Plymouth State
University Boyd Science Center on a biweekly basis to determine
what precipitation looks like to compare stream values to
• These data only represent the first snapshot of water stable
isotopes and water physical properties in the Pemigewasset River
Watershed. This sampling will be replicated another 8-10 times
before a full analysis can be completed.
Acknowledgements
Thank you to Mark Green and family and Chris Nealen for help
with data collection. This research is supported by the Northern
Research Station of the U.S. Forest Service.