Tracking ‘chemical cocktails’ in the Chesapeake Bay watershed using routine monitoring and high-frequency measurements

Increasing trends in base cations, pH, and salinity of freshwaters have been documented in the streams of the United States for at least the past 50 years. This process, known as Freshwater Salinization Syndrome, can be driven by a multitude of processes, including application of road salt deicers exacerbated by human-accelerated weathering of impervious surfaces. “Chemical cocktails”, or mixtures of base cations (Ca2+, K+, Mg2+, and Na+) and metals (Cu, Mn and Sr), often are released in high concentrations immediately after seasonal road salting in temperate areas. Through a combination of regular grab sampling (2-week interval) and high-frequency USGS sensor monitoring (15-minute interval), relationships were developed among specific conductance and metal concentrations. Linear relationships (e.g. R2 = 0.61 and 0.59 for Mn and Cu, respectively) show potential as proxies for understanding the behavior of metals in chemical cocktails over long-term temporal and large spatial scales. Groupings of major and trace elements, analyzed via linear regression and principal component analysis (PCA) show co-mobilization (i.e., correlations among combinations of specific conductance, Mn, Cu, Sr, and all base cations). Co-mobilization is strongest during the height of storm events but continues for at least 24 hours after peak specific conductance, which suggests lag times in contaminant mobilization. In the future, high-resolution monitoring may provide information on pulses, lag times, and sources of chemical cocktails. While proxies from sensors may need to be calibrated on a site by site basis, they show promise as a predictor of dissolved metal concentrations and relationships among elements as chemical cocktails. With specific conductance sensors becoming less expensive over time, improved understanding of these relationships may be useful for monitoring where there is limited equipment or funding.

Impact/Purpose

Urbanization has increased the concentrations of contaminants such as heavy metals and nutrients in urban streams compared to reference conditions due to increased inputs from anthropogenic sources, accelerated weathering of the built environment, and increased runoff through urban water conveyance systems. These processes create chemical cocktails that may have novel negative and synergistic effects on human health and the environment. This presentation describes how these chemical cocktails form, examines fate and transport, and discusses the use of real-time sensor data to characterize behavior and trends of nutrients and metals in urban streams in the Chesapeake Bay watershed. We also discuss future research directions to better diagnose and manage chemical cocktails that will be more cost effective and can elucidate the complex spatial and temporal scales of chemical cocktails.

Citation

Galella, J., P. Mayer, S. Kaushal, K. Wood, J. Reimer, AND L. Reed. Tracking ‘chemical cocktails’ in the Chesapeake Bay watershed using routine monitoring and high-frequency measurements. American Geophysical Union, virtual, Virtual, December 07 - 11, 2020.