delta O-18, delta D and H-3 measurements constrain groundwater recharge patterns in an upland fractured bedrock aquifer, Vermont, USA

Citation
Md. Abbott et al., delta O-18, delta D and H-3 measurements constrain groundwater recharge patterns in an upland fractured bedrock aquifer, Vermont, USA, J HYDROL, 228(1-2), 2000, pp. 101-112
Citations number
36
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Environment/Ecology,"Civil Engineering
Journal title
JOURNAL OF HYDROLOGY
ISSN journal
0022-1694 → ACNP
Volume
228
Issue
1-2
Year of publication
2000
Pages
101 - 112
Database
ISI
SICI code
0022-1694(20000221)228:1-2<101:DODDAH>2.0.ZU;2-A
Abstract
Stable isotope ratios, measured in groundwater samples, reflect the effects of evapotranspiration on bedrock recharge and flow patterns in a 10.5 km(2 ) upland mountainous watershed in northwestern Vermont. Precipitation and g roundwater samples (n = 619) were collected weekly over a 1.5 year period. Precipitation delta(18)O ranges yearly over similar to 25 per mil (parts pe r thousand), and decreases 2.5 parts per thousand for every 1000 m of eleva tion gain, reflecting seasonal and altitudinal temperature changes. delta D values are well correlated with delta(18)O and plot close to the Meteoric Water Line, indicating no evaporation effects. In the colder months (late N ovember to early April). groundwater delta(18)O composition varies by as mu ch as 4.3 parts per thousand in response to precipitation events, indicatin g rapid local recharge to the bedrock. In the warmer months (late April to early November), variation in groundwater delta(18)O is smaller (within 0.4 parts per thousand) at the lower elevations in the watershed, reflecting a reduction of infiltration to the bedrock. However, at higher elevations (a bove 800 m asl), groundwater delta(18)O continues to respond to precipitati on events due to the sparse vegetative cover and colder temperatures that r esult in lower evapotranspiration rates. Tritium concentrations in groundwa ter range from 6.7 to 26.7 TU, indicating that groundwater residence times may vary from less than 1 year to in excess of 30 years. (C) 2000 Elsevier Science B.V. All rights reserved.