USING OF C-Q HYSTERESIS PLOTS AND INTEGRATIVE POLLUTOGRAPHS TO INFER SOLUTE BEHAVIOR AND WATERSHED PROCESSES

Here we explore c-q hysteresis plots and integrative pollutographs for a variety of inorganic solutes (Cl^-, Na⁺, K⁺, SiO₂, NO₃^-), dissolved organic carbon (DOC) and an indicator of the aromatic fraction (SUVA₂₅₄) of DOC during early season in an urban salted watershed. We define an integrative pollutograph as one in which the patterns of multiple water quality metric are plotted and compared. The major hydrologic events are snow melts. The hypothesis is that 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 to account for differences in source locations and the biogeochemical behavior of the solutes along these pathways. The results indicate: 1) Cl^- and Na⁺ exhibit a combination of (C_SE>C_SO>C_G) and (C_G>C_SE>C_SO) behaviors during salting season and (C_SO>G_G>C_SE) and (C_SO>C_SE>C_G) behaviors in non-salting times; 2) SiO₂ shows (C_G>C_SO>C_SE) behavior in all events, 3) K⁺ changes from (C_SE>C_SO>C_G) to (C_SE>C_SO>C_G) to (C_SE>C_G>C_SO) with concentration depletion over subsequent events; 4) NO₃^- changes from (C_SO>C_SE>C_G) to (C_SE>C_G>C_SO) with concentration depletion over subsequent events; 5) DOC and SUVA₂₅₄ exhibit (C_SE>C_SO>C_G) and (C_SO>G_G>C_SE) behavior, respectively; and 6) Cl^-and Na⁺ peak before the rising limb with a slight lag in the Na⁺ peak. The 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) 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 to indicate water masses originating from different compartments in the watershed. We conclude that these results support our hypothesis and hope that they stimulate further research in the use of c-q hysteresis plots and integrative pollutographs to infer watershed biogeochemical dynamics.