Isotope hydrology: Stable isotopes in water resources assessment Luis Araguás Workshop on Flow-path characterization, Munich, 29 June 2010 International Atomic Energy Agency Isotope Hydrology Section
Outline Stable isotopes in the context of water resources assessment and mgmt. Isotope labelling, from precipitation (input) to groundwater Validation of conceptual groundwater flow models: Information provided by tracers and isotopes of water and/or dissolved salts on origin and dynamics Case studies and examples
Some questions put forward Is there present replenishment of groundwater in this aquifer and if yes, where recharge takes place? and how much? are we using fossil groundwater? Is groundwater being recharged locally? Is there a connection between groundwater and nearby rivers/lakes? Is there a risk of contaminating these wells? Does a decrease in water level endanger water supply?
Water resources assessment and management in context Monitor and review performance Characterize hydrological settings and assess properties of aquifers and river basins Implement management practices
Water resources assessment Quantity and quality issues functioning of the aquifer/catchment Atmospheric waters Runoff Hydrological settings Recharge/discharge Interconnections Flow paths, age Vulnerability to pollution
Tools to address such questions Basic hydro(geo)logical information (water levels, hydraulic conductivity, transmissivity, water flow velocity, etc.) TRACERS OF WATER AND SOLUTES Water chemistry and physical parameters Dissolved salts and gases (CFCs, SF 6,noble gases) Artificially injected tracers (dyes, isotopes, ) Environmental isotopes Stable isotopes O-18, C-13, H-2, S-34, Cl-36, Radioactive isotopes H-3, C-14, Cl-36, Kr-81,
3D-diagrams to visualize groundwater origin, dynamics and flow patterns in Bangladesh
Approach Integration of several tools including geological and hydrological settings, hydraulics, hydrochemistry, geophysics, soil properties, climate, etc. Tracers help in identifying and delimiting homogeneous water entities, indicating their origin and history. Spatial and depth variability is analysed to define groundwater flow patterns and interactions
Water samples for isotope analyses
Sampling: confined vs unconfined aquifers Representative water samples: Importance of adequate sampling
Samples for analysis may represent a complex distribution of waters with different origins, evolution, chemistry and age
Water cycle isotope labelling: global to local scales
O-18 vs. H-2 relationship: comparison between isotope contents of precipitation and groundwater Long-term weighted O-18, H-2 in precip.
Attenuation of isotope signal of precipitation during recharge: local isotope index
Possible causes for different isotope signals between local precipitation and groundwater Recent vs. old recharged waters (paleowaters isotope shift, groundwater dating) Recharge from distant areas (altitude) Recharge from rivers (usually more negative) Recharge from lakes, reservoirs, (more enriched) Seasonal recharge (selection of rain events) Evaporation before infiltration Mixing with deep groundwater..
Isotope mapping showing different recharge zones, water bodies and interactions Morocco
O-18 vs. H-2 relationship: comparison between isotope contents of precipitation and groundwater Long-term weighted O-18, H-2 in precip.
Determination of the altitude of recharge Isotope altitude gradient (-0.18 per mil per 100 m) determined from precipitation and springs
Determination of the altitude of recharge, Canary Isl.
Mine filtration mainly derives from river water, not locally recharged groundwater, northern Spain, Plata (1986). O-18 Local groundwater Filtration Deuterium Saja River
Mixing processes: Recharge from Chimbo river to the Guayas alluvial aquifer (Ecuador).Payne and Schoeter (1978)
Stable isotope composition of groundwater reflects mixing of two sources Recharge derived of local precipitation Recharge derived from Chimbo river Chimbo river
Example of aquifer interconnection Shallow aquifer - recent recharge Deep aquifer paleowaters Mixing line
Water types in a coastal aquifer in Qatar Oxygen-18 Seawater Shallow aquifer Mixing lines Deep aquifer Deuterium
18 O vs. TDS (salinity) diagram 18 O( ) Retorno de aguas de riego Irrigation return Líneas de mezcla Mixing lines Agua de mar Seawater Brine Salmuera Lavado de sales (rocas evaporíticas) Salt leaching (evaporites) Salinity (g/l), Cl (mmol/l) Salinidad (g/l), cloruros (mmol/l)
Isotope effects before infiltration Snow evaporation and sublimation in cold regions leading to isotope enrichment In arid zones: evaporation before infiltration in river beds or pools
Event recharge: Ti-Tree basin, central Australia 0 Weighted-Mean Rainfall Groundwater Samples 0-50 mm/month Mean Rainfall Recharge by intermittent heavy floods -20-40 -60 LMWL: 2 H = 6.9 18 O + 4.5 100-150 mm/month 50-100 mm/month 150-200 mm/month Groundwaters: 2 H = 4.0 18 O - 27.3-80 >200 mm/month -100-14 -12-10 -8-6 -4-2 18 O (, SMOW) Credit: A. Herczeg
Alluvial aquifer in semi-arid part of India Shallow groundwater Source of recharge (?)
Recharge sources in the urban aquifer of Caracas, Venezuela (Seiler, 2000). Role of leaks from water supply lines GMWL Water treatment plants Mixing line Creeks and Rivers
Santiago de Chile: Isotopes proved to be a unique tool to identify sources of recharge, groundwater origin, water flow paths and pollutant transport patterns Credit: Iriarte, S. (2003)
Localized river bank recharge in Hungary
Complex water interactions in heavily disturbed aquifers shown by chemical and isotope parameters Isotope mapping shows different water sources as well as complex 3D profiles Lee Davisson & Criss, (1997)
Different chemical and isotope evolution patterns in two sectors of the Central Valley, California
Artificial recharge - Effectiveness of Verchum Dam, Pakistan to recharge the groundwater Isotopes show that the dam is very effective to enhance recharge to groundwater (evaporative labeling) 2 H ( ) 30 20 10 0-10 -20-30 -40 Verchum Dam D/S Well Kuch Well Precip. Index -50-7 -5-3 -1 1 3 18 O ( ) Fig.. 18 O vs 2 H of Verchum Dam and downstream Wells
Groundwater recharged under present climatic conditions vs. palaeowaters
Isotope characterization of water types Paleowaters
Isotopic contrast between paleowaters and recent recharge 18 O( ) Deep groundwater Present-day precipitation
Isotope contents in deep groundwaters Northern Africa mapping fossil gw
Stable Isotopes changes in paleo-groundwaters in Northern Africa and the Middle East
18 O vs. 14 C in the Guarani aquifer, Brazil -4.0-5.0 Recent (Holocene) recharge 18 O-H2O ( vs V-SMOW) -6.0-7.0-8.0-9.0 Pleistocene paleowaters -10.0 0 5000 10000 15000 20000 25000 30000 35000 40000 45000 14 C (years) Kimmelmann et al., 1989
Groundwater types in the Guarani aquifer Distribution of carbon-14 activities (pmc) in groundwater showing main flow patterns, recharge and discharge areas
Nitrate and 15 N in groundwater Nitrogen isotopes and groundwater dating (CFC) provided the key elements for explaining varying nitrate contents and changing redox conditions in an agricultural catchment
Denitrification in a shallow aquifer due to pyrite oxidation. DOC is also oxidized at deeper horizons
Recent analytical developments Portable Rn-222 analyzer is used to identify discharge of groundwater in rivers and lakes Deployable isotope analyzers based on laser spectroscopy allow easier and faster access to water stable isotopes data for hydrological and ecological studies.
Concluding remarks Demand for sound water resources assessments will increase due to growing pressure on limited water resources. Isotope hydrology has become a proven tool, providing unique information, and is increasingly been used to characterize aquifers and catchments. Recent analytical developments will contribute to further expand the application of isotope hydrology.
Thank you!
GLOBAL NETWORK OF ISOTOPES IN PRECIPITATION (1961-2010)
Isotope profiles, aquifer near Munich, Germany Rauert et al, 1998
Geochemical (and isotopic) evolution along flow-paths