Hydrochemistry
Analysing and interpreting the chemistry of water can provide valuable insights into groundwater-surface water interactions. Dissolved constituents can be used as environmental tracers to track the movement of water. For example, a particular characteristic of the groundwater chemistry can be used as an indicator of groundwater discharge when measured in the surface water. Such tracers can be used to determine source areas of water and dissolved chemicals in catchments, calculate hydrologic and chemical fluxes between groundwater and surface water, calculate water ages that indicate the length of time water and dissolved chemicals have been present in the catchment (residence times), and determine average rates of chemical reactions that take place during transport (Winter et al, 1998). Geochemical mass balance models have been used to estimate mixing ratios of river water and groundwater (Cook et al, 2003). Chemicals or materials can be introduced specifically to study groundwater-surface water interactions and are referred to as artificial tracers.
Environmental tracers can occur naturally or may be released into the general landscape by human activities. Some of the commonly used environmental tracers include:
- field parameters such as electrical conductivity or pH;
- major ions such as calcium, magnesium, sodium, chloride and bicarbonate;
- stable isotopes in the water molecule of oxygen-18 (18O) and deuterium (2H);
- radioactive isotopes such as tritium (3H) and radon (222Rn); and
- industrial chemicals such as chlorofluorocarbons (CFC) and sulphur hexafluoride (SF6).
Several studies have used a combination of these tracers (eg major ions, stable and radioactive isotopes) to assess groundwater-surface water interactions (Crandall et al, 1999; McCarthy et al, 1992; Herczeg et al, 2001; Cook et al, 2003; Baskaran et al, 2004).
Advantages
- Valuable tool in developing a conceptual understanding of groundwater flow near a stream and useful in providing information on groundwater evolution, residence times or mixing ratios that would otherwise be difficult to determine. The range of hydrogeological processes that can be investigated under field conditions is probably the great strength of this method.
- Measurements of an environmental tracer along the stream can be a powerful tool to map the spatial distribution of groundwater inflows. This can be more rapid or cheaper than physically based methods such as seepage meters or hydrometric studies, particularly if field chemistry parameters such as EC or pH can be used.
- Time series monitoring of environmental tracers can provide information on the changes in seepage flux at a stream site. Such water chemistry monitoring is commonly undertaken to complement hydrographic data collection and analysis.
- Stable and radioactive isotopes can be used as a preliminary investigation tool or as an independent means of confirming the results of other methods. Deuterium, oxygen-18 and radon-222 are the most commonly used isotopes to investigate groundwater-surface water interactions.
Disadvantages
- Can be expensive due to the logistics of sampling or the cost of laboratory analysis.
- A high level of expertise may be required for their sampling and interpretation.
- Tracers such as deuterium, oxygen-18 or tritium can have long lead times between sample collection and the final analytical results. This is in contrast with parameters such as water level, temperature or electrical conductivity where real-time monitoring and data access is possible.
- Models used to quantify seepage flux from hydrochemical data can require estimates of parameters that are difficult to measure in the field.
Data Availability
Refer Water Quality Data
Case Studies
Alstonville Plateau, NSW
Border Rivers, NSW/Qld
Daly River, NT
River Murray at Hattah-Kulkyne Park, Vic
Upper Lachlan Catchment, NSW
Wollombi Catchment, NSW
Columbia River, Oregon USA
Suwannee River Basin, Florida, USA
Lot River, France
Lot River
Relevant Links
Australian Nuclear Science and Technology Organisation (ANSTO)
Australian Radiation Protection and Nuclear Safety Agency Radioanalytical Services
CSIRO Isotope Analysis Service
International Atomic Energy Agency
Joint International Isotopes in Hydrology Program (JIIHP)
Murray-Darling Basin Commission Groundwater Quality Sampling Guidelines
National Association of Testing Authorities, Australia (NATA)
National Water Quality Management Strategy (NWQMS)
SAHRA Isotopes and Hydrology
US Geological Survey Resources on Isotopes
US Geological Survey Environmental tracers of surface water-groundwater interactions
US Geological Survey Study and interpretation of the chemical characteristics of natural water
References
Baskaran S, Budd KL, Habermehl R and Carter A, 2004. Groundwater-surface water interactions in upper Lachlan valley: preliminary investigation using hydrochemical and stable isotopes. In: Conference Proceedings 9th Murray Darling Basin Groundwater Workshop Bendigo, Victoria 17-19 February 2004.
Cook PG, Favreau G, Dighton JC and Tickell S, 2003. Determining natural groundwater influx to a tropical river using radon, chlorofluorocarbons and ionic environmental tracers. Journal of Hydrology 277:74-88.
Crandall CA, Katz BG and Hirten, JJ, 1999. Hydrochemical evidence for mixing of river water and groundwater during high-flow conditions, lower Suwannee River basin, Florida, USA. Hydrogeology Journal 7, 454-467.
Herczeg A, Lamontagne S, Pritchard J, Leaney F and Dighton J, 2001. Groundwater-surface water interactions: testing conceptual models with environmental tracers. 8th Murray Darling Basin Groundwater Workshop, Victor Harbor, South Australia. P. 6B.3.
McCarthy KA, McFarland WD, Wilkinson JM and White LD, 1992. The dynamic relationship between ground water and the Columbia River: using deuterium and oxygen-18 as tracers. Journal of Hydrology 135, 1-12.
Winter, TC, Judson, WH, Franke, OL and Alley WM. 1998. Groundwater and surface water a single resource. Circular 1139, U.S. Geological Survey, Denver.