Freshwater salinization is the process of changing ion concentrations (e.g., Na+, Mg2+, K+, Cl−, , ) relative to background levels due to human activities (e.g., agriculture, application of road de-icing salts, water and resource extraction, climate change, and sea-level rise; Williams 2001; Cañedo-Argüelles et al. 2016). Although considerably less studied than other environmental issues (Cañedo-Argüelles 2020), salinization is widely accepted as presenting major challenges to freshwater and coastal biodiversity (Cunillera-Montcusí et al. 2022). Existing data and research show a clear rise in freshwater salinization worldwide (Dugan et al. 2017; Cañedo-Argüelles 2020; Jeppesen et al. 2020; Kaushal et al. 2021), yet key knowledge gaps and management challenges remain due to the complexity (Kaushal et al. 2018) and prevalence of the problem (Cañedo-Argüelles 2020; Jeppesen et al. 2020). Current literature has neglected to provide unbiased geographic coverage (Cunillera-Montcusí et al. 2022), and ecosystem-level responses (e.g., functions and services) are rarely assessed (Herbert et al. 2015). Compelling calls for research agendas that address the need for salinization research at multiple scales (e.g., global, regional, local) are well timed (Cunillera-Montcusí et al. 2022). One identified research gap points to the need for networks of researchers working together at regional scales using experimental approaches to identify impacts on biodiversity, community salinity thresholds, and landscape-scale drivers. Here, we document the results of a networked Global Salt Initiative (GSI) that performed in situ experiments on lakes to look at ecosystem-level impacts: their findings suggest that North American and European water quality guidelines for salt are far too low to prevent ecosystem-level impacts. The further purpose of this Special Issue (SI) is to document the results of ecosystem-level impacts of increasing salinity on lake and coastal area biodiversity and ecosystem functioning from a variety of perspectives.

The authors thank Jim Cloern, Gesa Weyhenmeyer, Steven Perez, and the Wiley editorial team for their vital and judicious assistance. The authors thank all the reviewers who graciously gave their time, expertise, and advice in helping review and improve special issue manuscripts. This study is part of the Global Salt Initiative, a working group formed during the Global Lake Ecological Observatory Network (GLEON) meeting held in 2017. The authors acknowledge the following funding sources for supporting our research, writing, and editing: Natural Sciences and Engineering Research Council (NSERC) Discovery Grant program (DG 03834-2015 to SJM and DG 05143-2016 to AMD). MC was supported by a Ramón y Cajal contract funded by the Spanish Ministry of Science and Innovation (RYC2020-029829-I).

Peer reviewed