Evidence for hydrochory and the deposition of viable seeds within winter flow‐deposited sediments: the River Dove, Derbyshire, UK

Abstract

Previous studies of the influence of hydrochory on plant dispersal have focused on relationships with existing vegetation patterns or litter deposits. River sediment deposition studies have assessed sediment accretion rates, particle size and quality. The link between seed and sediment transport and deposition has been overlooked and never quantified.This paper presents observations of over-winter viable seed and sediment deposition on three river margin sites along the River Dove, England. At these sites, 105 paired artificial turf mats were installed on the river bank top, face and toe from October 1999 to March 2000 to collect river-deposited material. From each pair, one mat was used to determine the dry weight; median particle size; percentage sand, silt, clay and organic content of deposited sediment. The other was used in germination trials to determine the number and species of deposited viable seeds. Topographic surveys and water level measurements supported the estimation of the hydrological characteristics of each mat location.Few seeds and little sediment were found on mats not inundated by river water. For these inundated, sediment characteristics varied primarily with elevation (relative to local mean river water level during the study period), with less marked between-site contrasts. The species composition of viable seeds also varied with elevation. Detrended correspondence analysis (DCA) revealed associations between river/wetland-related seed species and the bank toe samples. Regression analysis revealed significant relationships between seed number, sediment properties and mat elevation. Redundancy analysis (RDA) revealed associations between the species and abundance of viable seeds and elevation, sediment weight and organic matter content. These analyses suggest that sediment and seed deposition by rivers are closely related processes.The implications of these results for seed remobilization and dispersal and hydrochory within riparian zones are discussed, as are the implications of changes in sediment/seed delivery mechanisms, river flow regimes, and the hydraulic properties of river margins for seeds, sediments and riparian vegetation patterns.

Control of sediment dynamics by vegetation as a key function driving biogeomorphic succession within fluvial corridors

“…The dispersal of diaspores is complex and still not well understood, but transport by water (hydrochory) has been identifi ed by many authors as overriding other dispersal processes within fl uvial corridors (Skoglund, 1990;Danvind and Nilsson, 1997;Andersson et al, 2000;Goodson et al, 2003). Sediment deposition by rivers is generally accompanied by massive deposition of seeds Gurnell et al, 2004 and our results suggest that the hydrological regime, the hydrogeomorphic exposure, and sediment erosion/deposition, which are strongly modulated by vegetation structures, are key controls on the structure of the seed bank along the River Tech.…”

Invasion legacy effects versus sediment deposition as drivers of riparian vegetation

“…It may be that different aspects of flow regime, such as the duration of flood events, are more important in determining depositional processes. Goodson et al (2002), for example, found that the duration of inundation was strongly related with riverbank sediment deposition along the River Dove, UK. The amount of sediment deposited also decreased away from the water's edge, consistent with higher bank elevations rarely being inundated with flood water for an extended duration (Goodson et al 2002).…”

“…Goodson et al (2002), for example, found that the duration of inundation was strongly related with riverbank sediment deposition along the River Dove, UK. The amount of sediment deposited also decreased away from the water's edge, consistent with higher bank elevations rarely being inundated with flood water for an extended duration (Goodson et al 2002). Catchment topography, aspects of channel morphology, and land use may also override the likely influence of flow regime on sediment inputs (Jones et al 2012).…”

“…Seedling density commonly declines with increasing sediment depth (Dittmar and Neely 1999), and sediment deposition may thus uncouple the seedbank from developing or existing vegetation. However, evidence from Goodson et al (2003) indicates that large numbers of propagules can also be deposited in association with this sediment. Seed banks are a key reserve of viable propagules that play a central role in recruitment, facilitating the storage and establishment of both native and non-native species (Gioria and Pyšek 2015).…”

Sorting of seeds by hydrochory

“…Because of the complexities involved, most previous studies of seed dispersal have been descriptive and aimed at correlating these influences with the distribution of seeds (Goodson et al, 2002(Goodson et al, , 2003, or even the species composition or distributions directly (e.g. Hupp and Osterkamp, 1985;Bendix and Hupp, 2000;Hupp, 2000).…”