Temporal changes in suspended sediment transport in an Atlantic catchment, NW Spain

Catchment scale suspended sediment (SS) transport studies in northwest Spain are of special interest as little research at this scale has been done in this region. However, the role of sediments in the transfer of nutrients and contaminants to coastal areas in this region has been highlighted. Data were collected from the Corbeira catchment during a 3-year period and the variability in SS load at different temporal scales (within-events variability, monthly/seasonal, and annual) was analyzed. The statistical relationship between discharge and suspended sediment concentration (SSC) from samples obtained every 15 days as well as during runoff events in October 2004 to September 2007 showed a marked scatter of points. Hence, the rating curve method does not seem appropriate to estimate SSC in this catchment. The results also demonstrated that at the within-events scale, most of the SS peaks preceded the discharge peaks (70% of runoff events), implying that zones nearby or well connected to the stream are the dominant sediment source areas. In some cases, rills and ephemeral gullies developed in cropland were the main source of sediment delivered to the stream. Furthermore, a reduction in SSC was observed in sequences of events, which can be mainly linked to a phenomenon of sediment exhaustion. At the seasonal scale, most of the total annual SS load was transported during the autumn months, the period in which, generally, the largest number of events occurred, while in the summer, total annual SS load was very low (<1%). At the annual scale, specific SS yield (SSY) ranged from 5.4 to 11.2 Mg km(-2) y(-1). The variability in SSY was correlated with the number and magnitude of runoff events recorded yearly, since runoff events dominated SS transport and yield. For instance, in the last hydrological year (2006/07), more than 80% of the SS load was exported in runoff events involving <10% of the time. (C) 2010 Elsevier B.V. All rights reserved.