The Impacts of Road Salt Application on Oxygen Demand and Organic Matter in Urban Streams
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Anthropogenic inputs of salts alongside sea level rise and saltwater intrusion have contributed to the salinization of freshwater ecosystems. Organic matter is an essential energy source for the growth and abundance of freshwater biota and is a vector for sorbing, transporting, and transforming organic and inorganic contaminants. Salinization may influence organic matter quality, nutrient cycling, and microbial communities. This study investigates how increased salinization influences organic matter and biological oxygen demand (BOD) within the water column and at the sediment/water interface of three urban streams in the Anacostia-Potomac River watershed. A standard 5-day BOD experiment at 20°C was performed under different saline conditions. The four salinity treatments were ambient (control), low (0.5 g/L), moderate (1 g/L), and high (5 g/L) by adding pure NaCl to stream water. One incubation experiment was implemented before a major snowstorm event, and another was performed immediately after the first salt pulse from road salt application. Results showed significant differences in BOD among the study sites, sampling dates, and whether there was a presence or absence of sediment; however, there were no significant differences in BOD among the salinity treatments. Additionally, salinization can alter the composition and reactivity of dissolved organic matter, as well as the microbial uptake of nutrients in urban streams. Dissolved organic carbon (DOC) increased linearly with salinity at Hickey Run with an R2 value of 0.90 whereas Paint Branch showed a significant linear decrease with an R2 value of 0.97. Salinity had different effects on DOC concentration and quality and is likely due to dispersion and flocculation. Moreover, high-frequency sensor data from USGS gages demonstrate how pH, dissolved oxygen, and specific conductivity fluctuate throughout a significant snowstorm, providing insight into stream conditions before, during, and after a major snow event. More research must be done to fully understand how salt influences organic matter, oxygen demand, and microbes.