Mud in the city: Effects of freshwater salinization on inland urban wetland nitrogen and phosphorus availability and export

Abstract

Salinization and eutrophication are nearly ubiquitous in watersheds with human activity. Despite the known impacts of the freshwater salinization syndrome (FSS) to organisms, we demonstrate a pronounced knowledge gap on how FSS alters wetland biogeochemistry. Most experiments assessing FSS and biogeochemistry pertain to coastal saltwater intrusion. The few inland wetland studies mostly add salt as sodium chloride. Sodium chloride alone does not reflect the ionic composition of inland salinization, which derives from heterogeneous sources, producing spatially and temporally variable ionic mixtures. We develop mechanistic hypotheses for how elevated ionic strength and changing ionic composition alter urban wetland sediment biogeochemistry, with the prediction that FSS diminishes nutrient removal capacity via a suite of related direct and indirect processes. We propose that future efforts specifically investigate inland urban wetlands, a category of wetland heavily relied on for its biogeochemical processing ability that is likely to be among the most impacted by salinization.

Saturated, Suffocated, and Salty: Human Legacies Produce Hot Spots of Nitrogen in Riparian Zones

“…This detrimental water quality influence of milldams on riparian zones has not been recognized before and is a new insight. Beyond milldams, such conditions and the conceptual model of Figure 6 could also extend to other landscape elements including hydrologically disconnected wetlands and/or kettle hole sediments in agricultural or rural regions (Reverey et al., 2018) and stagnant and isolated wetlands and/or stormwater basins in urban areas (Kinsman‐Costello et al., 2022; Palta et al., 2017).…”

Documenting the impacts of increasing salinity in freshwater and coastal ecosystems: Introduction to the special issue

“…Predictive modeling characterizing stream salinization patterns are needed across the globe to use as reference and management tools. Kinsman-Costello et al (2022) provide an important review of salinization syndrome impacts on urban wetlands. They identify a knowledge gap that limits our understanding of how urban wetland salinization impacts biogeochemical processing (e.g., N & P nutrient removal) in urban wetlands, which is an ecosystem service that many urban wetlands are designed to perform.…”

“…Decades of data are needed to understand prolonged salinity trends in stream surface waters outside of seasonal hydrologic variability. Shattuck et al (2022) used long‐term data for New Hampshire streams combined with insights from high‐frequency sensors (15‐min intervals) to elucidate influences of groundwater Cl − sources and extreme flooding events. Chloride concentrations increased threefold since 1953 in an urban site, and urban streams often exceed relatively lax (230 mg L −1 ) chronic chloride guidelines in all seasons, but surprisingly an extreme flood event reset Cl − levels for up to a decade.…”

Stormwater best management practices: Experimental evaluation of chemical cocktails mobilized by freshwater salinization syndrome

“…Elevated Cu concentrations are likely due to Na + dispersion of organic matter rich colloids. Cu is dispersed from sediment particle layers into suspension when Na + concentrations are elevated (Kaushal et al, 2020;Kinsman-Costello et al, 2022). Sr 2+ also showed significant co-mobilization with CaCl, mobilizing more than double the concentration compared to the other salts studied.…”

“…Positive correlations have been found between specific conductance and mobilization of base cations and trace metals like Cu, Sr 2+ , and Mn (Amrhein et al, 1992;Löfgren 2001;Kaushal et al, 2019;Galella et al, 2021) 1 . Ion exchange is thought to be a major driver of contaminant mobilization, but redox reactions and Na + dispersion of colloids likely also play a role (Kaushal et al, 2018a;Kinsman-Costello et al, 2022). Increases in the magnitude and frequency of road salt pulses may also lead to the retention and release of multiple contaminants from urban stormwater best management practices (BMPs) which are ubiquitous in urban landscapes (Kaushal et al, 2022b).…”