Storage, properties and seasonal variations in fine‐grained bed sediment within the main channel and headwaters of the River Sanginjoki, Finland

Abstract

AbstractLowland catchments in Finland are intensively managed, promoting erosion and sedimentation that negatively affects aquatic environments. This study quantified fine‐grained bed sediment in the main channel and upstream headwaters of the River Sanginjoki (399.93 km2) catchment, Northern Finland, using remobilization sediment sampling during the ice‐free period (May 2010–December 2011). Average bed sediment storage in river was 1332 g m−2. Storage and seasonal variations were greater in small headwater areas (total bed sediment storage mean 1527 g m−2, range 122–6700 g m−2 at individual sites; storage of organic sediment: mean 414 g m−2, range 27–3159 g m−2) than in the main channel (total bed sediment storage: mean 1137 g m−2, range 61–4945 g m−2); storage of organic sediment: mean 329 g m−2, range 13–1938 g m−2). Average reach‐specific bed sediment storage increased from downstream to upstream tributaries. In main channel reaches, mean specific storage was 8.73 t km−1, and mean specific storage of organic sediment 2.45 t km−1, whereas in tributaries, it was 126.94 and 34.05 t km−1, respectively. Total fine‐grained bed sediment storage averaged 563 t in the main channel and 6831 t in the catchment. The proportion of mean organic matter at individual sites was 15–47% and organic carbon 4–455 g C m−2, with both being highest in small headwater tributaries. Main channel bed sediment storage comprised 52% of mean annual suspended sediment flux and stored organic carbon comprised 7% of mean annual total organic carbon load. This indicates the importance of small headwater brooks for temporary within‐catchment storage of bed sediment and organic carbon and the significance of fine‐grained sediment stored in channels for the suspended sediment budget of boreal lowland rivers. Copyright © 2013 John Wiley & Sons, Ltd.