Applications of stable water and carbon isotopes in watershed research: Weathering, carbon cycling, and water balances
Highlights
► This review outlines stable water and carbon isotope applications in hydrological and geochemical river research. ► The main focus is on silicate and carbonate weathering, the carbon and oxygen cycle, and water balances in river basins. ► These aspects of river research are of importance to the policy issues of climate change.
Introduction
Rivers are the veins of our continents and studies of river water and sediments help to understand and quantify biogeochemical dynamics in their basins as well as the their ecological and environmental impacts. In this context, river watersheds are important because, more than ever, anthropogenic factors increasingly threaten the availability and quality of clean water supplies. Considering that more than one half of the accessible freshwater runoff globally is already appropriated for human use (e.g., Postel et al., 1996, Jackson et al., 2001), and that two-thirds of all Earth's rivers are impacted by regulations (e.g., Vitousek et al., 1997), such research is important in view of its geoscientific, ecological, and environmental context.
Initially, hydro-bio-geochemical work on rivers focused mostly on the concentrations of dissolved and particulate constituents and, when discharge rates were available, enabled calculations of fluxes and mass balances for entire catchments (e.g., Paces, 1985, Probst, 1986, Probst et al., 1992, Probst et al., 1995, Ramanathan et al., 1994, Jing, 1995, Guieu et al., 1998, Chiffoleau et al., 1999, Freyssinet and Farah, 2000, Vörösmarty et al., 2000, Anderson and Dietrich, 2001, Grosbois et al., 2001, Oliva et al., 2004, Lafrenière and Sharp, 2005, Zakharova et al., 2005).
Over the last few decades, the data on inorganic and organic constituents and ionic fluxes in river basins were complemented by isotope tracers, including stable water and carbon isotopes (Hitchon and Krouse, 1972, Négrel et al., 1993, Pawellek and Veizer, 1994, Flintrop et al., 1996, Gaillardet et al., 1997, Barth et al., 1998, Kendall and McDonnell, 1998, Amiotte-Suchet et al., 1999, Aucour et al., 1999, Barth and Veizer, 1999, Telmer and Veizer, 1999, Farah et al., 2000, Karim and Veizer, 2000, Telmer and Veizer, 2000, Kendall and Coplen, 2001, Hélie et al., 2002, Karim and Veizer, 2002, Barth et al., 2003, Darling et al., 2003, Lee and Veizer, 2003, Négrel et al., 2003, Barth and Veizer, 2004, Lambs, 2004, Brunet et al., 2005, Das et al., 2005, Diefendorf and Patterson, 2005, Lambs et al., 2005, Rodgers et al., 2005, Stephens and Rose, 2005, Barth et al., 2006, Amiotte-Suchet et al., 2007, Ferguson et al., 2007, Ferguson and Veizer, 2007, Doctor, 2008, Freitag et al., 2008, Stögbauer et al., 2008, Brunet et al., 2009, Lambs et al., 2009, Dubois et al., 2010, Ferguson et al., 2011, Karim et al., 2011). The main purpose of most of these studies was to constrain the sources and cycling of water and solutes in river systems.
In this review we will summarize three aspects of hydrological and geochemical research that are of prime importance to the policy issues of climate change and include utilization of stable isotopes:
- (i)
Silicate and carbonate weathering
- (ii)
Riverine carbon and oxygen cycles
- (iii)
Water balances at the catchment scale.
Sediment transport and turnover impacted by agriculture and urbanization, investigation of the aquatic communities, and nutrient cycling are additional important applications of stable isotopes in riverine research. However, they are not discussed here to keep the review concise.
Section snippets
Silicate and carbonate weathering
River water chemistry is to a large extent a product of chemical rock weathering, dissolution/hydrolysis, and precipitation of minerals. Chemical weathering processes involve interactions between hydrological and biogeochemical cycles that are among the major controls of terrestrial and seawater chemistry, factors that ultimately control the CO2 sequestration in terrestrial and marine environments. This occurs at various timescales and happens at three major interfaces: (1) The
The riverine carbon cycle
Since rivers are potential sites for pollutant disposal, growing environmental concern led to investigations of their ecology and biogeochemistry (e.g., Barth et al., 2009). The understanding of the riverine carbon cycle is of particular interest because it reflects the state of aquatic life and its biodiversity, both within the rivers and in their catchments. Furthermore, the quantification of carbon transport by rivers, as particulate and dissolved organic and inorganic loads, is important
Water transport and mixing
Water has two elements, oxygen and hydrogen, the stable isotope systems isotope ratios of which can be readily measured without much concern for storage and preservation, providing evaporation after sampling is avoided and samples are stored in suitable sample containers (preferably made from glass or high-density polyethylene; cf. Clark and Fritz, 1997, Mook, 2000, Spangenberg and Vennemann, 2008). Specifically, stable water isotopes can serve as a conservative tracer as long as their ratios
Conclusions and challenges for future work
Our outline of selected applications of stable isotopes in river research shows the usefulness and growing importance of this technique. In this context it is particularly worthwhile to combine isotope applications with other modern biogeochemical methods of quantification, such as element concentrations, runoff, precipitation, and flux measurements. It will become increasingly important to couple water balances with other modern biogeochemical methods including ecological indicators microbial
Acknowledgments
We thank the Natural Sciences and Engineering Research Council of Canada, the Canadian Institute for Advanced Research, the Deutsche Forschungsgemeinschaft (DFG), the German Academic Exchange Service (DAAD), as well as the Sonderfonds of the University of Erlangen for support. In addition, we greatly acknowledge Patricia Wickham for assistance and two anonymous reviewers for valuable suggestions.
References (187)
- et al.
Stable isotope composition of molecular oxygen in soil gas and groundwater: a potentially robust tracer for diffusion and oxygen consumption processes
Geochimica et Cosmochimica Acta
(1998) - et al.
Controls on carbon cycling in two contrasting temperate zone estuaries: the Tyne and Tweed, UK
Estuarine, Coastal and Shelf Science
(2008) - et al.
Modelling of atmospheric CO2 consumption by chemical weathering of rocks: application to the Garonne, Congo and Amazon basins
Chemical Geology
(1993) - et al.
δ13C pattern of dissolved inorganic carbon in a small granitic catchment: the Strengbach case study (Vosges mountains, France)
Chemical Geology
(1999) - et al.
13C composition of dissolved organic carbon in upland forested catchments of the Morvan Mountains (France): influence of coniferous and deciduous vegetation
Journal of Hydrology
(2007) - et al.
A method to induce and assess isotopic equilibrium of oxygen
International Journal of Mass Spectrometry
(2002) - et al.
Distribution and origin of major and trace elements into labile and residual phase in an acid soil profile (Vosges mountains, France)
Applied Geochemistry
(2004) - et al.
Use of 13C to trace origin and cycling of inorganic carbon in the Rhône river system
Chemical Geology
(1999) - et al.
Carbon cycle in St. Lawrence aquatic ecosystems at Cornwall (Ontario), Canada: seasonal and spatial variations
Chemical Geology
(1999) - et al.
Water mixing in a St. Lawrence river embayment to outline potential sources of pollution
Applied Geochemistry
(2004)