Freshwater ecosystems embedded in urban landscapes are distinct from those associated with rural land use and land covers. Specifically, urban aquatic systems bear a unique geochemistry characterized by high salt concentrations and alkalinity due to the Freshwater Salinization Syndrome (FSS)—a suite of anthropogenic effects due to road salt usage and human-accelerated weathering. Compared to the robust body of theory and understanding that has emerged from dedicated study of urban streams (e.g., Urban Stream Syndrome, The Urban Watershed Continuum Concept), the effects of FSS on urban wetland biogeochemistry remain understudied. We characterized the FSS in urban wetlands in North East Ohio through multiple years of monitoring under a range of hydrologic conditions using a combination of continuously logging sensors (water level, flow, conductivity) and surface water sampling to measure salt ion concentrations (chloride, sulfate, nitrate, calcium, sodium, magnesium, potassium).
Results/Conclusions
Urban wetland surface waters in northeast Ohio contain chronically elevated concentrations of salt ions, particularly chloride and sulfate, and experience acute pulses of high salinity during and after winter road salting events and in dry hot conditions due to evaporative concentration when wetland water levels decline. Specific conductivities routinely were greater than 10,000 μS/cm during winter and spring events, and reached values as high as 16,000 μS/cm. Surface waters routinely contained Cl- and SO42- concentrations greater than 100 mg/L, and sometimes Cl- concentrations exceed toxicity criteria for aquatic life. Our data suggest that trends of elevated Cl- and SO42- concentrations in urban wetlands may be more pronounced than in urban streams. The FSS in inland urban wetlands is characterized not only by elevated salt concentrations, but by extreme variability in salt concentrations over time. Among wetlands, the ionic composition of salinization also varies, depending on the specific nature of salt inputs and connectivity of each wetland. The stress of salinization likely not only impacts organisms adapted to freshwater conditions, but may diminish wetland nutrient removal capacity.