Fluvial transport of suspended sediment and organic carbon during flood events in a large agricultural catchment in southwest France

Abstract

Abstract:Water draining from a large agricultural catchment of 1 110 km 2 in southwest France was sampled over an 18-month period to determine the temporal variability in suspended sediment (SS) and dissolved (DOC) and particulate organic carbon (POC) transport during flood events, with quantification of fluxes and controlling factors, and to analyze the relationships between discharge and SS, DOC and POC. A total of 15 flood events were analyzed, providing extensive data on SS, POC and DOC during floods. There was high variability in SS, POC and DOC transport during different seasonal floods, with SS varying by event from 513 to 41 750 t; POC from 12 to 748 t and DOC from 9 to 218 t. Overall, 76 and 62% of total fluxes of POC and DOC occurred within 22% of the study period. POC and DOC export from the Save catchment amounted to 3090 t and 1240 t, equivalent to 1Ð8 t km 2 y 1 and 0Ð7 t km 2 y 1 , respectively. Statistical analyses showed that total precipitation, flood discharge and total water yield were the major factors controlling SS, POC and DOC transport from the catchment. The relationships between SS, POC and DOC and discharge over temporal flood events resulted in different hysteresis patterns, which were used to deduce dissolved and particulate origins. In both clockwise and anticlockwise hysteresis, POC mainly followed the same patterns as discharge and SS. The DOC-discharge relationship was mainly characterized by alternating clockwise and anticlockwise hysteresis due to dilution effects of water originating from different sources in the whole catchment.

Apportioning sources of organic matter in streambed sediments: An integrated molecular and compound-specific stable isotope approach

“…This 129 autumn to spring period was chosen as it represents the most dynamic time with respect to catchment 130 sediment mobilization (e.g. Oeurng et al, 2011). Sediment volumes of 1 liter were obtained from the 131 streambed surface (approximately <50 mm depth) using a non-magnetic towel that had been 132 thoroughly washed in the stream prior to sampling.…”

Hydrological controls on DOC : nitrate resource stoichiometry in a lowland, agricultural catchment, southern UK

“…The transfer of DOC and nitrate from terrestrial sources to the channel by hydrological mechanisms results in changing relationships between concentration and river discharge, often described by a power function (C = aQ b , where C is concentration and Q is discharge) which can exhibit marked intra-annual dynamics (Oeurng et al, 2011;Morel et al, 2009;Basu et al, 2010;Outram et al, 2014). Therefore, integrated annual measurements risk masking important seasonal patterns in terrestrial-to-aquatic transfers and export of DOC and nitrate, arising from variations in hydrological pathways throughout the year, such as the interplay between groundwater and shallower lateral flows due to wetting-up of upper soil horizons in response to autumn rain (Prior and Johnes, 2002;Sandford et al, 2013;Outram et al, 2014;Yates and Johnes, 2013).…”

A modelling approach to quantify the influence of fine sediment deposition on biogeochemical processes occurring in the hyporheic zone

“…On a spatial scale, sediment biogeochemistry in upstream and downstream sections of rivers would strongly differed as up-and downstream sediments often exhibit contrasting hydraulic conductivity and OM characteristics (Vannote et al, 1980;Buffington and Tonina, 2009). On a temporal scale, hydrological events influencing the transport and deposition of sediment and associated OM would also affect river sediment biogeochemistry (Oeurng et al, 2011a(Oeurng et al, , 2011b. Therefore, the mathematical model presented here can be very useful to evaluate biogeochemical functioning in a wide range of environmental conditions.…”