Open Access
Coupling hysteresis analysis with sediment and hydrological connectivity in three agricultural catchments in Navarre, Spain
(Springer Verlag, 2019) Keesstra, Saskia D.; Davis, Jason; Masselink, Rens Hein; Casalí Sarasíbar, Javier; Peeters, Edwin T.H.M.; Dijksma, Roel; Proyectos e Ingeniería Rural; Landa Ingeniaritza eta Proiektuak
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.
Open Access
Dissolved solids and suspended sediment dynamics from five small agricultural watersheds in Navarre, Spain: a 10-year study
(Elsevier, 2019) Merchán Elena, Daniel; Luquin Oroz, Eduardo Adrián; Hernández García, Iker; Campo-Bescós, Miguel; Giménez Díaz, Rafael; Casalí Sarasíbar, Javier; Valle de Lersundi, Jokin del; Ingeniaritza; Institute on Innovation and Sustainable Development in Food Chain - ISFOOD; Ingeniería; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Dissolved solids (DS) and suspended sediment (SS) loads are considered relevant environmental problems. They are related to a wide range of on-site and off-site impacts, such as soil erosion or salinization of water bodies. In this study, the dynamics of DS and SS concentrations and loads were assessed in five small watersheds covering representative agricultural land uses in Navarre (Spain). To this end, discharge, DS and SS concentration data were collected during ten hydrological years at each watershed outlet, and loads were computed from discharge and concentration values. DS concentration followed a seasonal pattern imposed by the availability of water, with higher concentrations recorded in low-flow periods and lower concentration in the high-flow period. SS concentration was extremely variable, with a range of 2–4 orders of magnitude in concentration for any specific discharge. Temporal variations (both intra- and inter-annual) in DS loads were explained by differences in runoff, whereas those of SS were not, being the SS loads associated mainly with specific high flow events. These temporal patterns were observed for both agricultural (this study) and non-agricultural (literature) watersheds. From the data in the Navarrese watersheds and those available in the literature, we inferred that agricultural land use, in general, tends to increase the concentration of both DS and SS. Regarding DS and SS yields, the effects of agricultural land use on DS yields are controlled by the changes in runoff rather than the (small) changes in DS concentration. In this sense, land uses changes expected to increase runoff (i.e., a shift from forested to arable or from rainfed to irrigated agriculture) would increase DS yields. On the other hand, agricultural land use tends to increase SS yields, although the effect is highly variable depending on site-specific factors, both natural (e.g., watershed shape) and anthropogenic (e.g., degree of soil conservation practices). In the Navarrese watersheds, DS yields ranged from 1.1 to 2.2 Mg ha−1 year−1 whereas SS yields ranged from 0.3 to 4.3 Mg ha−1 year−1. DS yields seem to dominate under non-agricultural conditions and in most agricultural land uses at the small watershed scale. On the other hand, SS yields dominate in watersheds with increased soil erosion as a consequence of arable land use over erosion-prone watersheds.

Casalí Sarasíbar, Javier

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