“FORENSIC HYDROLOGY”using tracers to investigate

hydrology and biogeochemistry

BEE 3710Spring 2011

WHAT IS AN ENVIRONMENTAL TRACER? Dissolved constituents, isotopes, particles or physical properties of water that are used to track the movement of water through watersheds

Source: USGS circular 1139http://pubs.usgs.gov/circ/circ1139/

POTENTIAL CHARACTERISTICS OF TRACERS

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)

USES OF TRACERSGeneral: 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

Image source: http://www.twp.west-bloomfield.mi.us

sedimentpollutants

nutrients

ISOTOPES Same # of protons and electrons; different #

neutrons, so different masses! Some isotopes not very dominant

ISOTOPIC COMPOSITION Represented as ‘delta’ or ‘per mil’ δ(in ‰) = (Rsample/Rstandard - 1)1000

where "R" is the ratio of the heavy to light isotope in the sample or standard

A 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

ISOTOPE FRACTIONATION 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

18O/2H FOR WATER CYCLING

(SAHRA)

18O/2H FOR WATER CYCLING

(SAHRA)

18O/2H FRACTIONATION

18O/2H: APPLICATION

(Bowen et al 2006)

DYE AS A TRACER 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

DYE QUALITIES Low toxicity High visibility Consistent absorbance spectrum

(Flury & Wai 2003)

DYE AS A TRACER

QUANTIFYING DYE INFILTRATION

(Flury & Wai 2003)

TRACERS TO STUDY STREAM- GROUNDWATER INTERACTIONS

STREAM TRACERS Types: Conservative

Don’t react biologically or strongly sorb to sediment

ie: bromide, chloride Reactive

Compounds affected by biological and physical reactions

ie: NO3-

STREAM TRACERS

CONSERVATIVE FLOW TRACERS

BROMIDE + PARTICLE TRACER Studying flood effects on stream

interactions

STUDYING FLOOD EFFECTS

USING BROMIDE TO MODEL STREAM

REACH CHARACTERISTICS FROM MODELLING BROMIDE DATA

STUDYING SUBSURFACE INTERACTIONS

STUDYING SUBSURFACE INTERACTIONS Hyporheic flow from woody debris

sediment

stream

FLOW

SUBSURFACE FLOW

15N: BIOLOGICAL/REACTIVE TRACER

(Bohlke et al 2004)

15N REACTIVITY

MODEL N CYCLING Fit model to N2/N2O data

15N RESULTS

CS-137 AS A SEDIMENT TRACER

137CS CYCLING

(Ritchie & McHenry 1990)

137CS VS. SOIL EROSION

(Ritchie & McHenry 1990)

137CS PROFILES

(Zhang & Walling 2005)

SEDIMENT FINGERPRINTING

(Walling 2006)

DNA MICROSPHERES

Polylactic acid forms the framework

Magnetic iron oxide nanoparticles to enable capture

DNA for identification (and ability to have multiple “tags”)

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

DNA MICROSPHERES

HOW THEY WOULD WORK:

1

4

Collection point

PLOT EXPERIMENT

Inlet OutletTracer 2 Tracer 1

1.05 m2.20 m2.85 m

PLOT EXPERIMENT: RESULTS

Simple modified one dimensional advection dispersion model with a dispersion coefficient of 0.005 m2/s and a loss factor of 6.6:

Tracer 1

Tracer 2

MICROSPHERE MOVIE

http://www.csrees.usda.gov/newsroom/partners/21/flow.html

BIOMARKERS FOR TRACING P 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?

BIOMARKERS FOR TRACING P

P + biomarker A + biomarker B

P + biomarker AP + biomarker B

TEMPERATURE AS A TRACER

(Fanelli& Lautz 2008)

Cs137

dye

N15bromide

18O/2H

Tracers help figure out what’s going on in a complicated world!

biomarkers CFCs/

3H