Multiple riparian–stream connections are predicted to change in response to salinization

Abstract

Secondary freshwater salinization, a common anthropogenic alteration, has detrimental, lethal and sub-lethal effects on aquatic biota. Ions from secondary salinization can become toxic to terrestrial and aquatic organisms when exposed to salinized runoff that causes periodic high-concentration pulses. Gradual, low-level (less than 1000 ppm salinity) increases in salt concentrations are also commonly documented in regions with urbanization, agriculture, drilling and mining. Despite widespread low-level salt increases, little is known about the biological and ecological consequences in coupled riparian–stream systems. Recent research indicates lethal and even sub-lethal levels of ions can subsidize or stress microbial decomposer and macroinvertebrate detritivores that could lead to alterations of three riparian–stream pathways: (i) salinized runoff that changes microbial decomposer and macroinvertebrate detritivore and algae performance leading to changes in composition and processing of detrital pools; (ii) riparian plant salt uptake and altered litter chemistry, and litterfall for riparian and aquatic detritivores and their subsequent enrichment, stimulating decomposition rates and production of dissolved and fine organic matter; and (iii) salt consumption in salinized soils could increase riparian detritivore growth, decomposition and dissolved organic matter production. Subsidy–stress and reciprocal flows in coupled riparian–stream connections provide frameworks to identify the extent and magnitude of changes in detrital processing from salinization. This article is part of the theme issue ‘Salt in freshwaters: causes, ecological consequences and future prospects’.