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Freshwater salinization syndrome (FSS) refers to the suite of interactive effects of salt ions on degradation of physical, biological,and social systems. Best management practices (BMPs), which are methods to effectively reduce runoff and nonpoint source pollution (stormwater, nutrients, sediments), do not typically consider management of salt pollution. We investigate impacts of FSS on mobilization of salts, nutrients, and metals in urban streams and storm water BMPs by analyzing original data on concentrations and fluxes of salts, nutrients, and metals from 7 urban watersheds in the Mid-Atlantic USA and synthesizing literature data. We also explore future critical research needs through a survey of practitioners and scientists. Our original data show 1) sharp pulses in concentrations of salt ions and metals in urban streams directly following both road salt events and stream restoration construction (e.g.,similar to the way concentrations increase during other soil disturbance activities); 2) sharp declines in pH (acidification) in response to road salt applications because of mobilization of H+ from soil exchange sites by Na+; 3) sharp increases inorganic matter from microbial and algal sources (based on fluorescence spectroscopy) in response to road salt applications, likely because of lysing cells and changes insolubility; 4) substantial retention (~30–40%) of Na+ in stormwater BMP sediments and floodplains in response to salinization; 5) increased ion exchange and mobilization of diverse salt ions (Na+, Ca2+, K+, Mg2+), nutrients(N, P), and trace metals(Cu, Sr) from stormwater BMPs and restored streams in response to FSS; 6) downstream increasing loads ofCl–, SO42–, Br–, F–,andI–along flowpaths through urbanstreams and P release from urban stormwater BMPs in response to salinization; and 7)a substantial annual reduction (>50%) in Na+concentrations in an urban stream when road salt applications were dramatically reduced, which suggests potential for ecosystem recovery. We compare our original results with published metrics of contaminant retention and release across a broad range of stormwater BMPs from North America and Europe.Overall, urban streams and stormwater BMPs consistently retain Na+ and Cl–but mobilize multiple contaminants based on salt types and salinity levels. Finally, we present our top 10 research questions regarding FSS impacts on urban streams and stormwater BMPs. Reducing diverse chemical cocktails of contaminants mobilized by freshwater salinization is a priority for effectively and holistically restoring urban waters.
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This content will become publicly available on May 1, 2026
Additive effects of freshwater salinization on the predator-induced traits of larval amphibians
Freshwater salinization is occurring around the world and impacting a wide variety of freshwater species that have evolved under low-salt conditions. Salt pollution reduces the survival of many freshwater taxa, but we know less about the effects of salt on individual traits. Moreover, we know even less about how salt pollution may affect phenotypically plastic traits that have evolved in response to natural stressors. In this study, we examined wood frog tadpoles (Rana sylvatica), which are a model system for predator-induced plasticity, and determined how their growth, behavior, and morphology changed in the presence of chemical cues from dragonflies (Anax junius) under four concentrations of NaCl (16, 250, 500, and 1000 mg Cl→/L). Early in the experiment, the tadpoles reduced their feeding activity in response to predator cues but did not respond to increasing salt concentrations. Tadpole mass increased with predator cues but decreased with increased salt concentrations. As expected, the predator cues induced relatively deeper tails and tail muscles, while inducing relatively shorter bodies and narrower mouths. However, we also discovered that salt induced relatively longer tails, longer bodies, and smaller eyes. Interestingly, the predator effects did not interact with salt effects for any of the traits. These results suggest that freshwater salinization has the potential to alter the traits of other freshwater species, but the effects may simply be additive. Future studies should examine salt-induced changes in a diversity of other freshwater species and investigate whether salt-induced changes in morphology have consequences to individual performance.
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- Award ID(s):
- 2243432
- PAR ID:
- 10627120
- Publisher / Repository:
- ScienceDirect
- Date Published:
- Journal Name:
- Environmental Pollution
- Volume:
- 373
- Issue:
- C
- ISSN:
- 0269-7491
- Page Range / eLocation ID:
- 126102
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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