The river bed: a dynamic store for viable plant propagules?

TY - JOUR

T1 - The river bed: a dynamic store for viable plant propagules?

AU - Gurnell, Angela

AU - Goodson, J

AU - Thompson, K

AU - Clifford, N J

AU - Armitage, P

PY - 2007/7

Y1 - 2007/7

N2 - This paper investigates the controlling processes, species composition and spatial characteristics of plant propagule storage on river beds, and considers their significance for the changing character of river margins. Samples of the surface layers of river bed sediments were obtained from two reaches of the River Frome, Dorset, UK and one reach of the River Tern, Shropshire, UK. Samples were taken from the same bed locations on four occasions spaced at approximately four monthly intervals. Following greenhouse germination trials, 11384 viable propagules of 105 species were identified in the 192 channel bed samples. On average, 32% of the species found in the propagule samples were not present in the channel and riparian vegetation. Most of these additional species were wetland and terrestrial rather than aquatic species. The number of species and density of propagules stored on the river bed varied through time and between reaches. These findings indicate that the channel bed is a dynamic and important store for propagules, that are available for redistribution across river banks and floodplains during high river flows. Propagules were preferentially retained within particular bed habitats. On the Tern, the most retentive habitats were close to the channel margins and adjacent to riparian vegetation and trees. On the Frome, stands of emergent vegetation along the channel margin were the most retentive habitat, and were also associated with trapping of finer sediment and organic matter. This habitat, therefore, provides an aggrading environment that could potentially offer germination sites for some of the non-aquatic propagules, allowing them to contribute to root reinforcement and flow resistance during bank toe aggradation and extension. The studies thus provide evidence for a coupling of geomorphological and ecological systems, with implications for channel management and design.

AB - This paper investigates the controlling processes, species composition and spatial characteristics of plant propagule storage on river beds, and considers their significance for the changing character of river margins. Samples of the surface layers of river bed sediments were obtained from two reaches of the River Frome, Dorset, UK and one reach of the River Tern, Shropshire, UK. Samples were taken from the same bed locations on four occasions spaced at approximately four monthly intervals. Following greenhouse germination trials, 11384 viable propagules of 105 species were identified in the 192 channel bed samples. On average, 32% of the species found in the propagule samples were not present in the channel and riparian vegetation. Most of these additional species were wetland and terrestrial rather than aquatic species. The number of species and density of propagules stored on the river bed varied through time and between reaches. These findings indicate that the channel bed is a dynamic and important store for propagules, that are available for redistribution across river banks and floodplains during high river flows. Propagules were preferentially retained within particular bed habitats. On the Tern, the most retentive habitats were close to the channel margins and adjacent to riparian vegetation and trees. On the Frome, stands of emergent vegetation along the channel margin were the most retentive habitat, and were also associated with trapping of finer sediment and organic matter. This habitat, therefore, provides an aggrading environment that could potentially offer germination sites for some of the non-aquatic propagules, allowing them to contribute to root reinforcement and flow resistance during bank toe aggradation and extension. The studies thus provide evidence for a coupling of geomorphological and ecological systems, with implications for channel management and design.

U2 - 10.1002/esp.1554

DO - 10.1002/esp.1554

M3 - Article

SN - 1096-9837

VL - 32

SP - 1257

EP - 1272

JO - EARTH SURFACE PROCESSES AND LANDFORMS

JF - EARTH SURFACE PROCESSES AND LANDFORMS

IS - 8

ER -