Widespread spring discharge drives major water–salt–heat fluxes in salt marshes

Abstract

The occurrence, spatial distribution, and flux significance of submarine groundwater discharge (SGD) through preferential pathways in low-permeability salt marshes remain poorly understood. Using thermal infrared imaging and in situ measurements, we mapped 983 saline springs in winter and 413 in summer across six tidal creeks on the muddy coast of Jiangsu, China. The estimated spring-derived water discharge rate ranged from 0.8 to 6.9 cm d⁻¹ in winter and 0.4 to 3.1 cm d⁻¹ in summer, accompanied by substantial salt and heat fluxes. Spring distributions exhibit strong geomorphic control, with preferred discharge zones at intermediate creek-bed elevations. Spring abundance declined by more than 50% between surveys, suggesting that focused preferential SGD pathways may respond to multiple natural and anthropogenic environmental factors. These results identify spring-type SGD as a widespread, dynamic, yet vulnerable pathway for transferring water, salt, and heat between subsurface aquifers with tidal creek networks.