Diversity and temporal sequences of forms of DOC and NO3- discharge responses in an intermittent stream: Predictable or random succession?

Abstract

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 (NO3) pulses during storms is analyzed in a detailed 4-year series from an intermittent Mediterranean stream. In this study, each DOC and NO3-Q response is synthesized by two descriptors that summarize its trend (δC; dilution/ flushing/no change) and shape (δR; linear/nonlinear response). We observe that C-Q responses are widely distributed along the two-dimensional δR versus δC continuum. Furthermore, the temporal succession of forms of DOC and NO3-Q responses follow a random pattern, and only the dynamics of the δR (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 NO3-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 hydrobiogeochemical functioning of a specific catchment. Copyright 2008 by the American Geophysical Union.