b'Poster Session Abstracts1Stoichiometric mismatch in macronutrient ratios between source soils and sediments at the landscape scaleMicale M1,2, Upadhayay HR1, Gelsomino A2 and Collins AL11Sustainable Agriculture Sciences, Rothamsted Research, North Wyke, Okehampton, EX20 2SB UK.2Department of Agriculture, Universit degli Studi Mediterranea di Reggio Calabria,Feo di Vito 89122 Reggio Calabria - Italy Human-induced changes in both the absolute and relative contents of carbon (C), nitrogen (N) and phosphorus (P) have direct effects on soil C-sequestration and the long-term structure and function of agroecosystems, but also affect freshwater ecosystems indirectly through alteration of the N:P, C:N and C:P ratios in fine-grained sediment. Within a catchment, the stoichiometric ratio of C:N:P, known as the Redfield ratio, differs by land use due to differences in natural and anthropogenic inputs associated with them. Moreover, the fine-grained sediment C:N:P ratio is potentially driven by soil erosion and sediment delivery, deposition and associated oxidationconditions. The objective of this study is to compare the C:N:P stoichiometry of catchment source soils and stream fine-grained sediments with respect to different land use. To do this,we obtained surface soil samples from arable fields, pasture fields, woodlands, damaged road verges and stream banks from the Cocktree sub-catchment (4.5 km2) in the upper River Taw, South-West of England. The C:N:P ratio comparison between source soils and fine-grainedsediment (time-integrated suspended and deposited) samples will help to identify keydifferences and similarities in source soil and sediment C, N and P ratios, and will offerperspectives on the role of anthropogenic pressures in generating the imbalance ofmacronutrients between catchment soils and river sediments.45'