Citation:

Kaushal, S., J. Reimer, P. Mayer, R. Shatkay, C. Mass, W. Nguyen, W. Boger, A. Yaculak, T. Doody, M. Pennino, N. Bailey, J. Galella, A. Weingrad, D. Collison, K. Wood, S. Haq, T. Newcomer-Johnson, S. Duan, AND K. Belt. Freshwater salinization syndrome alters retention and release of chemical cocktails along flowpaths: From stormwater management to urban streams. Freshwater Science. The Society for Freshwater Science, Springfield, IL, 41(3):420-441, (2022). https://doi.org/10.1086/721469

Impact/Purpose:

This manuscript is submitted to Freshwater Science for an invited issue on urban streams based our presentation at the 5th Symposium on Urbanization and Stream Ecology (https://www.urbanstreamecology.org/suse5.html).  Salinization of freshwater has increased in the US and globally due to anthropogenic and geologic sources creating a phenomenon termed “freshwater salinization syndrome” and associated heavy metals and nutrients that, together are termed “chemical cocktails”.   Billions of dollars are spent on attempts to address these water quality impairments using stormwater best management practices (BMPs), stream restoration, and other forms of green infrastructure (GI).  We examine which practices are effective at addressing salinization based on our results from experimental studies, field monitoring, and high-frequency sensor data.  Overall, there may be significant capacity for green infrastructure to ameliorate the effects of salinization and chemical cocktails.  However, the emerging risks from retention and release of contaminants associated with salinization should be considered in urban stormwater management.  

Description:

Billions of dollars are spent on attempts to improve urban water quality using stormwater best management practices (BMPs), stream restoration and other forms of green infrastructure (GI). While stream restoration and stormwater BMPs can retain contaminants, there is also potential to concentrate and/or remobilize contaminants from increased ion exchange, solubility, and microbial processes associated with Freshwater Salinization Syndrome (FSS). We investigated retention and release of chemical cocktails, or novel combinations of elements, across stream restoration and stormwater BMPs in response to FSS.  Based on our analysis, we also identify emerging knowledge gaps and research frontiers.  Our work shows relationships among salt ions (chloride, sulfate, bromide, fluoride, iodide), trace metals, and organics, indicating formation of chemical cocktails in urban streams and stormwater management features.  Organic matter solubility in green infrastructure and urban waters can also be influenced to differing degrees by anions such as CO32–, SO42–, H2PO4–, F–, Cl–, Br–, NO3–, and I– and to varying degrees by cations such as NH4+, K+, Na+, Li+, Mg2+, and Ca2+.  Although formation of chemical cocktails varies across urban waters, interactive effects of multiple ions and the potential to co-manage chemical cocktails of contaminants represents a knowledge gap.  Our results from experimental salinization studies, field monitoring, and high-frequency sensor data demonstrate mobilization of metals, nutrients, and base cations from sediments of restored streams and stormwater BMPs.  FSS can alter contaminant retention functions in urban streams, wetlands, and ponds and enhance release of multiple chemical cocktails of nutrients, salt ions, and metals.  Based on interactions with stakeholder, practitioners, and researchers, we also present our top 10 research questions evaluating the effects of FSS on green infrastructure.  Overall, there may be significant capacity for green infrastructure to retain some ions and contaminants, but FSS can shift contaminant “sinks” to “sources” in green infrastructure and urban landscapes.  The emerging risks from retention and release of contaminants associated with FSS should now be considered in urban stormwater management designs and in protecting infrastructure and improving urban ecosystem restoration.   

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