Hydraulic Geometry, Hydraulics and Sediment Properties of Forest Brooks after Extensive Erosion from Upland Peatland Drainage

Abstract

Peatland drainage can affect headwater systems, causing changes in bed substrate composition and hydraulic geome-try in small brooks. We studied hydraulic geometry and sediment properties in 14 boreal forest brook reaches (width < 2 m), characterised by well-vegetated banks, high sinuosity and low width-to-depth ratio, in north-east Finland. The aims were to obtain information from channel geometry and to study brook response to extensive sediment load from land use. The results indicate that bed sediment in brooks is almost continuously mobile, which negatively reflect to ecological status of the brooks. These headwater meandering parts have limited sediment transport capacity and require a long period to recover from artificially increased sediment input from peat drainage. However, different reaches can be prioritised for restoration according to the characteristics of silted bed sediment or sediment origins. Brook width appeared to have large natural variation, causing great local velocity variations. This needs to be taken into consideration when restoring straightened reaches in small headwater areas, e.g., width in restored reaches cannot be uniform but should include variations

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

“…However, this alone does not explain all the variations observed here, especially in tributaries. In general, local characteristics in terms of channel morphology, structure and texture, local water velocity and depth, pool and riffle sequences and also macrophytes affect sediment storage conditions (Sear, 1993;Wood and Armitage, 1999;Marttila et al, 2012). In addition, the properties of the transported organic suspended sediment and organic bed sediment (Marttila and Kløve, 2008) affect settling and re-suspension.…”

Differential responses by stream and riparian biodiversity to in‐stream restoration of forestry‐impacted streams

“…). We conducted our experiment during low‐flow conditions when bed load in boreal streams is limited (Marttila, Tammela & Kløve ) and the leaf bags were rarely covered by fine sediments even in impacted reaches (J. Turunen, pers. obs.).…”

“…The negative effects of sedimentation on leaf breakdown have been related to reduced oxygen concentration and limited access by leaf-eating macroinvertebrates (Cornut et al 2010;Danger et al 2012). We conducted our experiment during low-flow conditions when bed load in boreal streams is limited (Marttila, Tammela & Kløve 2012) and the leaf bags were rarely covered by fine sediments even in impacted reaches (J. Turunen, pers.…”

Restoration increases transient storages in boreal headwater streams

“…Values of A s / A averaged 3.05 ± 2.61 ( SD ), which is higher than reported for sandy (0.32 ± 0.22) or coarse‐bed streams (0.47 ± 0.64; see Stofleth et al, for a comparison). However, our study streams are boreal headwater streams, where the width:depth ratio is generally different from that of sand or gravel‐bed streams (Marttila et al ). Boreal, headwater streams typically have stable vertical banks that create a lower width:depth ratio and deeper water areas.…”

“…The impact of increased sediment flux on stream biota is typically related to deposits rather than suspended material. Extensive sediment load reduces natural depth variation (Marttila, Tammela, & Kløve, 2012) and can be a stressor for stream organisms (Jones et al, 2012;Louhi, Ovaska, Mäki-Petäys, Erkinaro, & Muotka, 2011). Decreased depth variation reduces availability of deep pools, and movement of sediments causes streambed instability.…”