PATTERNS OF C-Q HYSTERESIS FOR SELECTED INORGANIC AND ORGANIC SOLUTES AND E. COLI IN AN URBAN SALTED WATERSHED DURING WINTER-EARLY SPRING PERIODS

C-Q hysteresis loops are used to qualitatively understand solute transport pathways to streams. Many studies involve non-urban areas in a variety of environmental settings such as the subtropics, mountains, high latitude rivers. Here, we explore c-q hysteresis plots and pollutographs for a variety of inorganic solutes, dissolved organic carbon and an indicator of the aromatic fraction (SUVA₂₅₄), and a microbiological indicator (E. coli) in an urban salted watershed mainly during snow melts. The overarching hypothesis is that the hysteresis behavior can be explained by extending the pathway analysis from the Evans-Davis classification scheme to account for differences in source locations and the biogeochemical behavior of the solutes. Data sets are for 2013, 2014, and 2015. Results are that: 1) Cl^- and Na⁺ exhibit a combination of C2 and C3 behavior during salting season and A1 and A2 behavior in non-salting times; 2) SiO₂ shows A3 behavior in all events, 3) K⁺ changes from C2 to C1 with concentration depletion over subsequent events; 4) NO₃^- changes from A2 to C1 or C2 with concentration depletion over subsequent events; 5) DOC and SUVA₂₅₄ exhibit C2 and A1 behavior, respectively; 6) E. coli changes from C2 to A2 over subsequent storms, 7) Cl^-and Na⁺ peak before the rising limb with a slight lag in the Na⁺ peak and 8) E. coli does not exhibit first-flush behavior. In a snow melt event, 1) K⁺ and DOC peak together three times, unrelated to any additional event such as rain; 2) DOC becomes more aliphatic at its first peak, and 3) NO₃^- has a concentration decrease at the second DOC/K⁺ peak and peaks on the declining limb after the third DOC/K⁺ peak. These observations can be explained in terms of the c-q plots (e.g., importance of event water), environmental behavior (e.g., conservative solute), the nature of the urban landscape (e.g., pavement), and season (e.g., damped microbial activity). We interpret the multiple concentration peaks indicate water masses originating from different compartments in the watershed are reaching the stream at different times and with different chemistries. These results extend the work of previous studies and may serve to help develop a fingerprint of solute behavior that can be used to more fully explore early season biogeochemical dynamics in an urban, salted, snow-melt dominated watershed.