Diversity and temporal sequences of forms of DOC and NO 3 ‐discharge responses in an intermittent stream: Predictable or random succession?

Storm events have major implications for biogeochemical cycles at local and regional scales and they provide an excellent opportunity to study the hydro‐biogeochemical functioning of catchments. However, concentration‐discharge ( C ‐ Q ) responses have only been studied in detail for short periods or a few selected events. In consequence, it is difficult to quantify the diversity of C ‐ Q responses in a hydrological system and impossible to assess whether the succession of forms of C ‐ Q responses follows a predictable sequence or not. Bearing in mind these shortfalls, the variability of dissolved organic carbon (DOC) and nitrate (NO 3 ) pulses during storms is analyzed in a detailed 4‐year series from an intermittent Mediterranean stream. In this study, each DOC and NO 3 ‐ Q response is synthesized by two descriptors that summarize its trend (Δ C ; dilution/flushing/no change) and shape (Δ R ; linear/nonlinear response). We observe that C ‐ Q responses are widely distributed along the two‐dimensional Δ R versus Δ C continuum. Furthermore, the temporal succession of forms of DOC and NO 3 ‐ Q responses follow a random pattern, and only the dynamics of the Δ R (NO3) descriptor show periodicity. The long‐term data set reveals that it is impossible to predict with reasonable precision the full properties of DOC and NO 3 ‐ Q responses. Thus, a “typical” C ‐ Q response does not really exist at our study site, and this apparent diversity of responses has to be handled with a probabilistic approach that allows synthesis of the complexity of the hydro‐biogeochemical functioning of a specific catchment.