BEE 3710
Spring 2011
using tracers to investigate
hydrology and biogeochemistry
Dissolved
constituents, isotopes,
particles or physical properties of
water that are used to track the
movement of water through
watersheds
Source: USGS circular 1139
http://pubs.usgs.gov/circ/circ1139/
 naturally
occurring (e.g. chloride, silica, stable
isotopes, organic compounds)
 artificial or researcher introduced (e.g. various
dyes, plastic microspheres)
 sometimes unintentionally introduced! (e.g.
tritium, chlorofluorocarbons, certain radioactive
isotopes)
 a less common isotopic form of an element
 physical property of water (e.g. temperature)
General: Used to identify flow paths, travel times,
etc.
Specific uses:
 Subsurface processes

e.g. preferential flow, groundwater movement
 Surface
processes
 Biogeochemical interactions

e.g. biological nitrogen uptake
pollutants
sediment
nutrients
Image source: http://www.twp.west-bloomfield.mi.us
 Same
# of protons and electrons; different #
neutrons, so different masses!
 Some isotopes not very dominant
 Represented
as ‘delta’ or ‘per mil’
 δ(in ‰) = (Rsample/Rstandard - 1)1000

A
where "R" is the ratio of the heavy to light
isotope in the sample or standard
positive δ value means that the sample
contains more of the heavy isotope than the
standard; a negative δ value means that the
sample contains less of the heavy isotope
than the standard
 Fractionation:
when the relative amounts of
a particular isotope change due to the mass
differences

ie: lighter H & O isotopes are preferentially
evaporated
 Equilibrium


vs Kinetic fractionation
Equilibrium: redistribution occurs, but reaction
rates same for forward/backward direction
Kinetic: reaction rates not same if products
become isolated from reactants
(SAHRA)
(SAHRA)
(Bowen et al 2006)
 Useful
in surface and groundwater studies
 In subsurface, useful for investigating
infiltration patterns, flow patterns for
contaminants
 In streams, useful for quickly evaluating
travel time & mixing
 Low
toxicity
 High visibility
 Consistent absorbance spectrum
(Flury & Wai 2003)
(Flury & Wai 2003)
 Types:
 Conservative


Don’t react biologically or strongly sorb to sediment
ie: bromide, chloride
 Reactive


Compounds affected by biological and physical reactions
ie: NO3-
 Studying
flood effects on stream interactions
 Hyporheic
flow from woody debris
stream
FLOW
sediment
SUBSURFACE FLOW
(Bohlke et al 2004)
 Fit
model to N2/N2O data
(Ritchie & McHenry 1990)
(Ritchie & McHenry 1990)
(Zhang & Walling 2005)
(Walling 2006)
DNA for identification
(and ability to have
multiple “tags”)
Magnetic iron oxide
nanoparticles to enable
capture
Polylactic acid forms
the framework
DNA: a polymer of four types of monomers (A, T, C, G)
Tracer of length m:
X1 X2 X3X4 …Xm
Xi = {A, T, C, G}
Number of potential tracers = 4m
1
4
Collection
point
1.05 m
2.20 m
2.85 m
Inlet
Tracer 2
Tracer 1
Outlet
 Simple
Tracer 1
Tracer 2
modified
one dimensional
advection
dispersion model
with a dispersion
coefficient of
0.005 m2/s and a
loss factor of 6.6:
http://www.csrees.usda.gov/newsroom/partners/21/flow.html
 Excess
phosphorus applied as fertilizer can
end up in streams and lakes in the watershed
 Phosphorus can be sorbed on sediment on on
colloidal (<0.45 um ) particles/ dissolved in
water
 If we want to know where the P is coming
from….sediment tracing works for P sorbed
on sediment, but what about dissolved P?
P + biomarker
B
P + biomarker A
+ biomarker B
P + biomarker A
(Fanelli& Lautz 2008)
18O
/2H
dye
Cs137
biomarkers
CFCs/
3H
bromide
N15
Tracers help figure out what’s going on in a complicated world!