Patterns of c-q hysteresis loops and within an integrative pollutograph for selected inorganic and organic solutes and E. coli in an urban salted watershed during winter-early spring periods.

Concentration – discharge (c-q) hysteresis loops are used to qualitatively understand solute transport pathways to streams. The majority of c-q studies involve non-urban areas in environmental settings such as the subtropics, mountains, and high latitude rivers. Only a few involve urban or urban salted watersheds. In this study, we explore c-q hysteresis plots and pollutographs for a variety of inorganic solutes (Cl − , Na + , K + , SiO 2 , NO 3 − ), dissolved organic carbon and an indicator of the aromatic fraction (SUVA 254 ), and a microbiological indicator ( E. coli ) in an urban salted watershed. The major hydrologic events are snow melts. The overarching hypothesis is that the hysteresis behavior can be explained by extending the pathway analysis (i.e., relative importance of storm event water, C SE ; groundwater C G ; and soil water, C SO ) from the Evans-Davis classification scheme that describes six behaviors to account for differences in source locations and the biogeochemical behavior of the solutes along these pathways. Data sets for the years 2013, 2014, and 2015 were assembled from a series of undergraduate and graduate research projects performed over this period. The results of these studies indicate that: 1) Cl − and Na + exhibit a combination of C2 (C SE > C SO > C G ) and C3 (C G > C SE > C SO ) behavior during salting season and A1 (C SO > G G > C SE ) and A2 (C SO > C SE > C G ) behavior in non-salting times; 2) SiO 2 shows A3 (C G > C SO > C SE ) behavior in all events, 3) K + changes from C2 to C1 (C SE > C G > C SO ) with concentration depletion over subsequent events; 4) NO 3 − changes from A2 to C1 or C2 with concentration depletion over subsequent events; 5) DOC and SUVA 254 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. An integrative pollutograph for a snow melt event shows, 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) NO 3 − 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 to 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. [ABSTRACT FROM AUTHOR]