Land development and road salt usage drive long-term changes in major-ion chemistry of streamwater in six exurban and suburban watersheds, southeastern Pennsylvania, 1999–2019

In urbanized areas, the “freshwater salinization syndrome” (FSS), which pertains to long-term increases in concentrations of major ions and metals fresh surface waters, has been attributed road salt application. addition FSS, water composition changes as an influx sodium (Na + ) recharge may displace calcium (Ca 2+ ), magnesium (Mg potassium (K trace by reverse cation exchange. These changing ion fluxes can result adverse impacts on groundwater waters used for municipal supplies. Few datasets exist quantify FSS a watershed scale or link its manifestation potential controlling factors such urban development, land use/land cover (LULC), wastewater treatment plant (WWTP) discharges upstream areas. Here, we use two decades (1999–2019) monthly streamwater quality data combined with daily streamflow six exurban suburban watersheds southeastern Pennsylvania examine relations among Ca , Mg K Na chloride (Cl − sulfate (SO 4 2- alkalinity (HCO 3 factors. Flow-normalized annual baseflow (August ̶ November) Cl increased all over 20-year study, providing evidence FSS’s that sustains streamflow. Additionally, redundancy analysis using 2019 flow-normalized values identified following positive associations between solute variables: 1) impervious (ISC), 2) SO ISC total WWTP discharge volume, 3) HCO agriculture volume. From human health perspective, exceeded U.S. Environmental Protection Agency’s 20 mg L -1 threshold individuals restricted low diet. Furthermore, indices evaluate corrosivity source drinking infrastructure inform practices, Chloride Sulfate Mass Ratio Larson Ratio, two- seven-fold time. Collectively, results elucidate causal infrastructure.