The Emerging Global Threat of Salt Contamination of Water Supplies in Tidal Rivers

Abstract

Salt contamination of water supplies in tidal rivers is a global problem, but it has received little attention beyond site-specific studies. Drought, sea-level rise, navigation channel dredging, and watershed land-use change increase the risk of salinization and threaten drinking water supplies, agricultural irrigation, and infrastructure (via corrosion). The emerging issue of salt contamination of water supplies in tidal rivers and its diverse impacts highlight the critical need for interdisciplinary research that must integrate knowledge from oceanography, hydrology, and water resource management. Here we elucidate oceanic and hydrological processes regulating saltwater intrusion into estuaries and tidal rivers as well as watershed processes driving enhanced chemical weathering and export of watershed salts into rivers. By synthesizing studies around the world, we discuss how sea-level rise, prolonged drought, and increasingly extreme weather events in a changing climate are driving more frequent saltwater intrusion events that threaten water security globally. We propose a convergent research agenda toward the development of a decision support tool for salinity management. Specifically we recommend making ion-specific measurements and developing hydrological-hydrodynamic models to simulate the transport of major salt ions. These models can then be combined with artificial intelligence algorithms and enhanced monitoring to explore management strategies with stakeholders.

Keywords: Tidal rivers; climate change; freshwater salinization; saltwater intrusion; water supplies.

1

(a) Global map of population density (color) and locations of the tidal rivers with reported saltwater contamination issues (blue dots). Global maps of the projected (b) median regional relative sea-level change and (c) seasonal mean relative changes (%) in the number of dry days (i.e., days with less than 1 mm of rain) from 1995–2014 to 2100 averaged across available Coupled Model Intercomparison Project Phase 6 (CMIP6) models in the high emission SSP5-8.5 scenario. The sea-level projection is from ref and the dry days projection is from ref .

2

(a) A schematic plan view of an estuary showing different salinity (in units of g kg^–1) subregions including the tidal river where many drinking water intakes are located. (b) A schematic along-channel section view of the typical volume and salt transport regimes in an estuary. Blue lines show isohalines, and colors show salinity. The white arrows indicate volume transports, while the black arrows indicate salt transports. The dotted line shows the position of the mean sea level. Note that for corresponding pairs of arrows, incoming and outgoing salt transports are almost identical, while outgoing volume transports are substantially larger than the incoming volume transports due to the river runoff.