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How Does Flooding Affect Salts in Rivers?

Climate and human development affect salt levels during floods.

A is a map of 259 USGS sites in the continental United States. B is a line graph showing the number of stations with at least a single observation in each year in the period (1940–2020) and the cumulative percentage of observations at each year; both lines go up over time.

The spatial distribution of the 259 sites used in the study with their long-term specific conductance values (a) and the temporal coverage of the data (b).

[Reprinted under a Creative Commons Attribution 4.0 International License (CC BY 4.0) from Ombadi, M., et al. “Urbanization and Aridity Mediate Distinct Salinity Response to Floods in Rivers and Streams across the Contiguous United States.” Water Research 220, 118664 (2022). DOI:10.1016/j.watres.2022.118664.]

The Science

Salinity (the amount of salts dissolved in water) is an important water quality variable. It directly affects fish and other aquatic life and determines how river water can be used for agricultural and industrial purposes. Scientists studied how floods affect river salinity by analyzing a large dataset from 259 monitoring stations in rivers across the United States. They found that floods mostly decrease salt levels in rivers by dilution. However, salt levels can increase for roughly 6% of flood events. The changes depend strongly on salt levels in the few days prior to the flood. Climate and human development also affect how salts in different rivers change during floods.

The Impact

Future climates are expected to be warmer and drier, with more intense extreme events like floods. Growing populations will also increase the extent of urbanization. These results provide insights into how salt levels of rivers will change due to floods and other factors related to climate and human development. These results will be useful for developing new models that watershed managers can use to plan for an uncertain future.

Summary

Researchers examined how floods affect river salinity by analyzing a large dataset of streamflow and specific conductance (a measure of salt levels) for 259 United States Geological Survey (USGS) monitoring sites. Scientists used a combination of statistical methods and machine learning models to determine how river salt levels change at different sites due to floods. They found that floods mostly decrease salt levels in rivers by dilution. However, salt levels can increase for roughly 6% of flood events. The changes depend strongly on salt levels in the few days prior to the flood. Climate and the extent of human development also affect how salts in different rivers change during floods. Notably, urbanization in temperate climates can increase dilution of salts, and mining in arid climates can increase river salinity during floods.

Principal Investigator

Charuleka Varadharajan
Lawrence Berkeley National Laboratory
[email protected]

Program Manager

Jennifer Arrigo
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

This research was supported by the U.S. Department of Energy’s (DOE) Office of Science program in Biological and Environmental Research (BER).

References

Ombadi, M., et al. "Urbanization and Aridity Mediate Distinct Salinity Response to Floods in Rivers and Streams across the Contiguous United States." Water Research 220 118664  (2022). https://doi.org/10.1016/j.watres.2022.118664.