Publication:

Coupling hysteresis analysis with sediment and hydrological connectivity in three agricultural catchments in Navarre, Spain

Purpose: Rain storm events mobilise large proportions of fine sediments in catchment systems. Sediments from agriculturalcatchments are often adsorbed by nutrients, heavy metals and other (in)organic pollutants that may impact downstream envi-ronments. To mitigate erosion, sediment transport and associated pollutant transport, it is crucial to know the origin of thesediment that is found in the drainage system, and therefore, it is important to understand catchment sediment dynamicsthroughout the continuity of runoff events. Materials and methods:To assess the impact of the state of a catchment on the transport of fine suspended sediment to catchmentoutlets, an algorithm has been developed which classifies rain storm events into simple (clockwise, counter-clockwise) andcompound (figure-of-eight; complex) events. This algorithm is the first tool that uses all available discharge and suspendedsediment data and analyses these data automatically. A total of 797 runoff events from three experimental watersheds in Navarre(Spain) were analysed with the help of long-term, high-resolution discharge and sediment data that was collected between 2000 and 2014. Results and discussion: Morphological complexity and in-stream vegetation structures acted as disconnecting landscape featureswhich caused storage of sediment along the transport cascade. The occurrence of sediment storage along transport paths wastherefore responsible for clockwise hysteresis due to the availability of in-stream sediment which could cause theBfirst flush^affect. Conversely, the catchment with steeper channel gradients and a lower stream density showed much more counter-clockwise hysteresis due to better downstream and lateral surface hydrological connectivity. In this research, hydrologicalconnectivity is defined as the actual and potential transfer paths in a catchment. The classification of event SSC-Q hysteresisprovided a seasonal benchmark value to which catchment managers can compare runoff events in order to understand the originand locations of suspended sediment in the catchment. Conclusions: A new algorithm uses all available discharge and suspended sediment data to assess catchment sediment dynamics.From these analyses, the catchment connectivity can be assessed which is useful to develop catchment land management.