CROSS-SITE COMPARISON OF VARIABILITY OF DOC AND NITRATE C–Q HYSTERESIS DURING THE AUTUMN–WINTER PERIOD IN THREE MEDITERRANEAN HEADWATER STREAMS: A SYNTHETIC APPROACH

Abstract

The forms, rotational patterns and trends of hysteretic loops of dissolved organic carbon (DOC) and nitrate (NO3) were investigated in three headwater Mediterranean streams during one autumn–winter period using two biogeochemical descriptors summarizing the changes in solute concentrations (ΔC) and the overall dynamics of each hysteretic loop (ΔR). The study had two aims: (1) to examine whether the variability of solute hysteretic loops monitored in different streams during cold seasons followed a consistent and recurring pattern, (2) to identify hydrological parameters which could potentially influence features of the DOC and NO3 hysteresis. Relationships between hysteresis features and hydrological parameters in the studied streams were explored using multivariate redundancy analysis (RDA). Both DOC and NO3 typically increased in concentration during storm events, although hysteretic loops did not obey any consistent pattern across the three streams. The rotational patterns of DOC and NO3 hysteresis ranged widely, from clockwise to counterclockwise. Storm hydrographs and also the magnitude of antecedent storm events were explanatory of the DOC and NO3 concentration changes across the study sites. However, the detailed hydrological information did not offer a satisfactory explanation of the entire DOC and NO3 concentration dynamics during the storm events.