Organic matter dynamics and stable isotope signature as tracers of the sources of suspended sediment

Abstract

Abstract. Suspended sediment (SS) and organic matter in rivers can harm brown trout Salmo trutta by affecting the health and fitness of free swimming fish and by causing siltation of the riverbed. The temporal and spatial dynamics of sediment, carbon (C), and nitrogen (N) during the brown trout spawning season in a small river of the Swiss Plateau were assessed and C isotopes as well as the C/N atomic ratio were used to distinguish autochthonous and allochthonous sources of organic matter in SS loads. The visual basic program IsoSource with 13 C tot and 15 N as input isotopes was used to quantify the temporal and spatial sources of SS. Organic matter concentrations in the infiltrated and suspended sediment were highest during low flow periods with small sediment loads and lowest during high flow periods with high sediment loads. Peak values in nitrate and dissolved organic C were measured during high flow and high rainfall, probably due to leaching from pasture and arable land. The organic matter was of allochthonous sources as indicated by the C/N atomic ratio and δ 13 C org . Organic matter in SS increased from up-to downstream due to an increase of pasture and arable land downstream of the river. The mean fraction of SS originating from upper watershed riverbed sediment decreased from up to downstream and increased during high flow at all measuring sites along the course of the river. During base flow conditions, the major sources of SS are pasture, forest and arable land. The latter increased during rainy and warmer winter periods, most likely because both triggered snow melt and thus erosion. The measured increase in DOC and nitrate concentrations during high flow support these modeling results. Enhanced soil erosion processes on pasture and arable land are expected with increasing heavy rain events and less snow during winter seasons due to climate change. Consequently, SS and organic matter in the river will increase, which will possibly affect brown trout negatively.

Object‐oriented soil erosion modelling: A possible paradigm shift from potential to actual risk assessments in agricultural environments

“…This, along with the marked hilly relief and the heavy rains characteristic for the area, makes the catchment an optimal place for studying hillslope erosion processes and river sediment load dynamics. During the biennium 2009–2010, a range of field and laboratory activities has been carried out to study the use of CSIA of fatty acids to differentiate the sediment source contribution to a lowland river (Alewell et al, ; Schindler Wildhaber, Liechti, & Alewell, ).…”

Isotope‐based Fluvial Organic Carbon (ISOFLOC) Model: Model formulation, sensitivity, and evaluation

“…While the aforementioned studies highlight the strength of using [Onstad et al, 2000;Palmer et al, 2001;Dalzell et al 2007;Sakamaki and Richardson, 2011;Schindler Wildhaber et al, 2012]. With regard to in-stream transformations, large isotope fractionations of the DIC pool during assimilation (0-20&), and low isotope fractionation during decomposition of organic carbon (0-2&) suggest d 13 C FPOC can help constrain parameters associated with APOC assimilation [Jacinthe et al, 2009;Dubois et al, 2010].…”

“…Measuring and modeling of d 13 C of carbon pools provides an extra set of source and transformation equations to water quality studies and thus carbon stable isotopes have been extensively applied in recent years, primarily within data-driven approaches. d 13 C measurements of FPOC have been used to apportion sources of carbon in aquatic systems ranging from small streams to coastal waterbodies [Fox and Papanicolaou, 2007;Fox, 2009;Kendall et al, 2010;Schindler Wildhaber et al, 2012;Sarma et al, 2012]. Source apportionment studies have placed heavy emphasis on the ability of d 13 C to differentiate soil organic carbon (SOC) sources derived from C3 and C4 plants due to their significantly different d 13 C signatures of 224 to 229& and 210 to 214&, respectively [Smith and Epstein, 1971;Onstad et al, 2000;Palmer et al, 2001;Fox and Papanicolaou, 2007;Fox, 2009;Jacinthe et al, 2009;Brunet et al, 2011].…”

Sources and export of particle-borne organic matter during a monsoon flood in a catchment of northern Laos

“…Masiello and Druffel, 2001;Hilton et al, 2010;Smith et al, 2013) stable isotope fingerprinting methods may be applied to particulate material collected from hillslopes to rivers, either independently or in combination with fallout radionuclides to document variations in sediment sources and pathways across catchments (e.g. Ritchie and McCarty, 2003;Ellis et al, 2012;Schindler Wildhaber et al, 2012;Ben Slimane et al, 2013;Koiter et al, 2013). In addition, complementary information on sediment conveyed to the river by runoff and overland flow can also be inferred from water tracers such as 18 O natural abundance (for a review see Klaus and McDonnell, 2013).…”