Lecture 37

Lecture 37

Isotope Hydrology

Hydrogeochemical Cycle

Common Isotopes Used in Hydrologic Studies

Global Distribution

Tritium

Nitrogen

Environmental Isotope Uses

Case Studies

A depiction of the hydrogeochemical cycle.

Distribution of mean d ¹⁸O of precipitation, based on stations having at least

two years of records.

Hydrogen and oxygen isotopic content of ocean water and precipitation. Due to

kinetic isotope fractionation during evaporation of moist oceanic vapor, the hydrogen

and oxygen isotopic content of water vapor above the oceans is -86‰ and -12‰,

respectively. The isotopic content of precipitation is in isotopic equilibrium with

vapor in a cloud. Thus, the d D and d ¹⁸O values of the first rain are -14‰ and

-3‰, respectively, depleting the cloud in D and ¹⁸O as precipitation occurs. Therefore,

precipitation becomes isotopically lighter and lighter as it is continuously removed

from clouds.

Monthly weighted mean d ¹⁸O of a coastal (Hatteras) and an inland (Flagstaff)

station. The moderating effect of the ocean upon temperature is evident in the

low variability of the Hatteras d ¹⁸O data.

Approximate range (in years) of dating applications of selected environmental

tracers and event markers.

Deposition in TU-meters of tritium across the continental United States

from 1953 to 1983. U.S. Geological Survey sampling stations listed are

Albuquerque, NM (ALB), Boston, MA (BOS), Cape Hatteras, NC (CAHAT),

Chicago, IL (CHI), Lincoln, NE (LINC), Madison, WI (MAD), Menlo Park,

CA (MENPK), Ocala, FL (OCALA), Portland, OR (PORT), Salt Lake City,

UT (SLC), Saint Louis, MO (STL), Waco, TX (WACO), and

Washington, DC (WASHDC).

Monthly tritium concentration in precipitation at Ottawa, Canada, 1953 through 1985.

The nitrogen cycle.

Range of nitrogen isotope composition for different sources of dissolved nitrogen

in ground water.

Average Terrestrial Abundance of Isotopes Used in Hydrogeologic Studies

Element	Isotope	Average Terrestrial Abundance (atom %)	Comments
Hydrogen	^1H	99.985
	^2H	0.015
	^3H	<10^-14	Radioactive, t_1/2 = 12.43 years
Helium	^3He	0.00014
	^4He	99.99986
Carbon	^12C	98.90
	^13C	1.10
	^14C	<10^-10	Radioactive, t_1/2 = 5,715 years
Nitrogen	^14N	99.63
	^15N	0.37
Oxygen	^16O	99.762
	^17O	0.038
	^18O	0.200
Silicon	^28Si	92.23
	^29Si	4.67^a
	^30Si	3.10
	^32Si	<10^-12	Radioactive, t_1/2 = 172 years
Sulfur	^32S	95.02
	^33S	0.75^a
	^34S	4.21
	^35S	<10^-11	Radioactive, t_1/2 = 82 days
	^36S	0.014^a
Chloride	^35Cl	75.77
	^36Cl	<10^-12	Radioactive, t_1/2 = 300,000 years
	^37Cl	24.23
Strontium	^84Sr	0.56^a
	^86Sr	9.86
	^87Sr	7.00
	^88Sr	82.58^a
Uranium	^234U	0.0055	Radioactive, t_1/2 = 247,000 years
	^235U	0.72	Radioactive, t_1/2 = 71.3 x 106 years
	^238U	99.27	Radioactive, t_1/2 = 4.51 x 109 years

Source: IUPAC (1992).

^aThese isotopes are presently not used in ground-water studies.

Ground-Water Problems Aided by Environmental Isotopes

Stable Isotope

Radioactive Isotopes

Type of Problem

d D

d ¹³C

d ¹⁵N

d ¹⁸O

d ³⁴S

d ⁸⁷Sr

^3H

^14C

^36Cl

^39Ar

^85Kr

U-diseq

Recharge and Flow Rate

Unsaturated zone

C,a

B,b

Arid Zones

C,c

B,b

Exchange of river and lake water

with ground water

C,d

C,e

Average ground-water rate in

Systems less than 5 years old

A,f

C,f

Systems between 5 and 30 years old

A,g

B,b

Characterization of a Gound-Water Mass

Local area less than 30 years old

C,h

C,i

B,b

Regional systems

A,j

C,k

A,j

C,l

B,b

Identification of Recharge Area or Source of Water

Local area

A,m

C,n

A,m

C,o

B,b

Regional systems

A,p

B,b

Leakage between Aquifers

C,q

Investigations of Ground-Water Flow in Fractured Rocks

Carbonate karst rocks

A,r

Noncarbonates

A,s

Evaluation of Ground-Water Flow and Storage Characteristics

Local system: well-mixed reservoir or piston flow

A,t

Dispersivity investigations

Separation of Stream Discharge into Ground-Water and Surface-Water Components

A,u

Sources of Dissolved Constituents

A,v

A,w

A,v

A,aa

B,x

C,v

B,b

Geochemical Reaction Modeling

A,y

C,y

Ground-Water Dating

Less than 5 years

A,p

C,n

A,f

A,u

B,bb

5-50 years

A,g

C,i

B,b

B,bb

50-1,000 years

C,bb

1,000-40,000 years

A,z

A,cc

60,000-1,200,000 years

B,dd

C,ee

Key for Remarks

Frequency of Use in Ground-Water Studies
A Has been useful in many studies
B Has received some use; looks promising for future studies as technology improves
C Has received some use
Example Applications
a Munnich (1983) b Bentley, Phillips, and Davis (1986) c IAEA (1980) and Gvirtzman and Magaritz (1986) d Payne (1983), Stichler and Moser (1979), Carlin et al. (1975), Krabbenhoft et al. (1990), and Darling, Allen , and Armannsson (1990) e Carlin et al. (1975) f Stichler and Moser (1979) and Schotterer et al. (1979) g Rauert and Stichler (1974), Fontes (1980), Phillips et al. (1989), and Solomon and Sudicky (1991) h Payne, Quijano, and Latorre (1979) i Fontes (1980) and Pearson et al. (1991) j Airey et al. (1979), Gat (1971), and Pearson et al. (1991) k Lloyd and Howard (1979) l Fontes (1980) m Schotterer et al. (1979), and Muir and Coplen (1981) n Letolle and Olive (1983) o Fontes (1980)	p Payne (1983, Gat (1971), Pearson et al. (1991), and Darling, Allen, and Armannsson (1990) q Payne (1981) r Davis et al. (1970) and Fontes (1983) s Schotterer et al. (1979) t Martinec et al. (1974) u Sklash and Farvolden (1979 and 1982), Kennedy et al. (1986), and Stewart and McDonnell (1991) v Payne (1983), Payne, Quijano, and Latorre (1979), and Simpson and Herczeg (1991) w Heaton (1986) and Hübner (1986) x Pearson et al. (1991) and Starinsky et al. (1983) y Plummer et al. (1990) and Plummer, Prestemon, and Parkhurst (1991) z Buchardt and Fritz (1980) and Pearson et al. (1991) aa Claypool et al. (1980) bb Pearson et al. (1991) and Chapter 11 cc Fontes (1983), IAEA (1983a), and Pearons et al. (1991) dd Pearson et al. (1991), Torgersen et al. (1991), and Nolte et al. (1991) ee Pearson et al. (1991)

ENV 302 - Lectures