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Application and development of isotope techniques to evaluate human impacts on water balance and nutrient dynamics of large river basins (F33021)


Summary


This CRP will focus on assessing our understanding of the hydrology of large river basins by applying water isotopes and additional geochemical and isotope parameters as means to constrain water balance and nutrient dynamics in large river basins.
Environmental and anthropogenic land-use changes at basin-scales have dramatically altered the dynamics of the world’s largest rivers and have adversely impacted water quantity as well as quality. The CRP was formulated based on the conclusions and recommendations of a Consultant Meeting in November 2012 and will improve the expertise among Member States in the use of environmental isotopes. Furthermore, it will increase our understanding of the relationship between hydrological and biogeochemical processes in large river basins. The aim of the CRP is to target 50+ of the largest rivers of the world, in order to obtain an improved and quantitative understanding of how human impacts directly influence the water quality of our river and surface water systems, and to enhance and improve the IAEA Global Network of Isotopes in Rivers (GNIR).

Background situation analysis


Large rivers are a significant freshwater source of drinking, agricultural and industrial water supplies. Moreover, large rivers are economically important for fisheries, transportation and energy production. Transported nutrients as well as sediments are crucial for the fertilization of agricultural lands as well as maintaining riparian and coastal zone stability. Human impacts upon large watersheds, like intense agriculture, discharge of municipal or industrial water, impoundments, irrigation, and damming have profound effects on river biogeochemistry, as well as water balance.
As demonstrated by an IAEA pilot CRP [1], water isotopes are essential to observe environmental and anthropogenic changes, such as the sources of river water, impact of dams, and enhanced evaporation. In combination with discharge data from gauging stations isotopes provide a better understanding of hydrological processes in space and time and help to quantify basin-scale water balance. However, the impact of human activities on the biogeochemistry and sediment load of the river is not adequately covered by measuring water isotopes alone. Seasonal and multi-year longitudinal observations of other additional isotope parameters as well as geochemical tracers in rivers remain relatively scarce, despite the interpretive power of isotope information to trace sources and fate of nutrients.
For example, the chemistry and isotopes of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) provide insights into natural and man-made carbon sources, carbon cycling, and bioproductivity [e.g. 2 and 3]. Changes in the isotope composition of 13C, 15N, and 34S of POM (Particulate organic matter) indicate seasonal changes in POM sources and are a useful method to identify hotspots of biogeochemical reactions [e.g. 4]. The 18O and 15N composition of nitrate adds a perspective on the origin of nutrients and hence allows distinguishing between natural and synthetic inputs [e.g. 5]. In summary, the analyses of selected parameters in combination with water isotopes help to constrain carbon, nitrogen, and sediment dynamics within large river basins.

Nuclear Component


Measurement of stable isotopes in water (18O, 2H), tritium, selected dissolved solutes (13C of DIC; 13C of DOC; 13C, 15N, and 34S of POM; 18O and 15N of nitrate), and potentially selected radioactive isotopes of suspended matter (Sr, Nd, Pb, Li, Mg, and Ca).

Specific research objectives


1. Review and assess the use of water isotopes to evaluate the sources of water, hydrological processes and water balance of large river basins.
2. Review and assess the application of existing as well as new sampling and analytical methods of geochemical and isotope parameters in order to evaluate nutrient and sediment dynamics in large river basins.
3. Improve the understanding and assessment of human and environmental impacts on water balance, nutrient cycling and sediment transport in large river basins.
4. Improve the interpretation of the relationship between hydrological and biogeochemical processes in large river basins.

Expected research outputs

1. A better estimation and interpretation of hydrological processes, water sources and water balance for selected global rivers based on water isotopes.
2. Improved understanding of the application of environmental isotopes in order to assess natural nutrient and sediment fluxes at river basin scale as well as human impacts.
3. Technical reports describing recommended sampling and analytical methods of interpreting and integrating environmental isotopes into global river monitoring networks.
4. Isotope and geophysical and chemical data will be generated from selected monitoring stations, which will contribute to the IAEA Global Network on Isotopes in Rivers (GNIR).

Expected research outcomes


1. Improved capability and expertise among Member States in the use of environmental isotopes in order to assess hydrological and biogeochemical processes in large river basins.
2. Best-practices guidelines for sampling, analytical and evaluation methods which will facilitate comparing global and trans-boundary river data.
3. Better understanding of possible environmental and human impacts on river water quality and quantity, which provides a base for further research as well as management strategies for decision makers.

Assumptions


1. Interested participants from Member States are already engaged in the assessment of water balance and water quality of large river basins.
2. Appropriate staffing is available for field and analytical work; laboratory premises and computing facilities to conduct isotopic and chemical analysis are available or are provided in cooperation by other participating institutes.
3. National authorities/institutes will provide all necessary permissions and field collection support in a timely manner.
4. There is an on-going research or interest, and competent professionals in the area of hydrology, water biogeochemistry, isotope analysis and interpretation.

Timetable of project activities


References


[1] IAEA, Monitoring isotopes in rivers: creation of the Global Network of Isotopes in Rivers (GNIR). IAEA-TECDOC-1673, Vienna, Austria (2012).
[2] IAEA, Application of isotope techniques for assessing nutrient dynamics in river basins. IAEA-  TECDOC-1695, Vienna, Austria (2013).
[3]Clark, I., Fritz, P., Tracing the carbon cycle, In: Environmental Isotopes in Hydrogeology, CRC Press/Lewis Publishers, Boca Raton, FL (1997) 112-136.
[4]Kendall, C., Silva, S.R., Kelly, V.J., Carbon and nitrogen isotopic compositions of particulate organic matter in four large river systems across the Unites States, Hydrol. Processes 15, (2001) 1301-1346.
[5]Clark, I., Fritz, P., Nitrogen cycling in rural watersheds, In: Environmental Isotopes in Hydrogeology, CRC Press/Lewis Publishers, Boca Raton, FL (1997) 148-154.